8. H 04 A TREATISE ON CHEMISTRY A TREATISE ON CHEMISTRI BY Sir IL E. ROSCOE F.R.S. and C. SCHORLEMMER F.R.S. VOLUME III THE CHEMISTRY OF THE HYDROCARBONS AND THEIR DERIVATIVES, OR ORGANIC CHEMISTRY PART IV " Cliymia, alias Alchemia et Spagirica, est ars corpora vel mixta, vel composita, vel aggregata etiam in principia sua resolvendi, aut ex principiis in talia combinandiy-Stahl, 1723. NEW YORK D. APPLETON AND COMPANY 1892 PREFACE TO VOL. III., PART IV. The Fourth Part of the Treatise on Organic Chemistry- now presented to the public includes a description of the Aromatic Compounds containing seven atoms of Carbon, and, like the preceding part, forms a chapter complete in itself. The first portion is concerned with the Toluene Group, then come the Benzyl, Benzoyl, and Hydrobenzyl Groups, and lastly the Xylene Group of Eight Carbon Compounds. CONTENTS. PAGE Toluene Group 3 Toluene or Methylbenzene . • . 3 Addition Products of Toluene 6 Chlorine Substitution Products of Toluene 7 Monochlorotoluenes 8 Dichlorotoluenes 9 Bromine Substitution Products of Toluene 10 Monobromotoluenes 10 Dibromotoluenes 11 Tribromotoluenes 12 Tetrabromotoluenes 12 Iodine Substitution Products of Toluene 13 Fluorine Substitution Products of Toluene 13 Nitro-Substitution Products of Toluene 13 Mononitrotoluenes 13 Dinitrotoluenes 16 Trinitrotoluenes 17 Chloronitrotoluenes 19 Bromonitrotoluenes 19 Toluenesulphonic Acids 20 Toluenemonosulphonic Acids 20 Toluenedisulphonic Acids 22 Toluenetrisulphonic Acids 22 Monohydroxytoluenes and Allied Bodies 23 The Cresols » 23 Dihydroxytoluenes and Allied Bodies 31 Homocatechol or Homopyrocatechin 31 Orcinol 37 Substitution Products of Orcinol 41 Chlorine Substitution Products 41 Bromine Substitution Products 41 Iodine Substitution Products 41 Nitro-Substitution Products 41 Cresorcinol 47 Toluquinol or Toluhydroquinone 48 Toluquinone 49 Substitution Products of Toluquinone 50 Toluquinonoxime Compounds 50 Trihydroxy toluenes 53 VIII CONTENTS. PAGE Toluene Group-continued. Amido-Derivatives of Toluene 54 Amidotoluenes or Toluidines 54 Halogen Substitution Products of the Toluidines 67 Chlorotoluidines 68 Bromotoluidines 68 lodotoluidines 68 Nitro toluidines 69 Dinitrotoluidines 71 Diamidotoluenes or Tolylenediamines 72 Diazo-Derivatives of Toluene . . 74 Hydrazine-Derivatives of Toluene 75 Azo-Derivatives of Toluene 75 Phosphorus Derivatives of Toluene 83 Arsenic Derivatives of Toluene 84 Antimony Derivatives of Toluene 86 Boron and Silicon Derivatives of Toluene 87 Mercury Derivatives of Toluene 87 Benzyl Group 89 Benzyl Alcohol 89 Benzyl Ethers 94 Ethereal Salts of Benzyl 96 Substitution Products of Benzyl Alcohol and its Derivatives ... 98 Sulphur Compounds of Benzyl 105 Selenium Compounds of Benzyl 109 Nitrogen Bases of Benzyl 110 The Benzylamines 110 Amido-Substituted Benzylamines 116 Substitution Products of the Benzylamines 118 Benzyl-Derivatives of the Acid-Amides and Allied Bodies . . . 121 Phosphorus Compounds of Benzyl 124 Arsenic Compounds of Benzyl 125 Silicon Compounds of Benzyl 127 Benzoyl Group 128 Benzaldehyde 129 Benzidene Compounds ■. . . 136 Substitution Products cf Benzidene Compounds 143 Benzoic Acid 151 Salts and Ethers of Benzoic Acid 160 Oxides of Benzoyl 166 Halogen Compounds of Benzoyl 168 Sulphur Compounds of Benzoyl 170 Nitrogen Compounds of Benzoyl 172 Hippuric Acid 181 Benzenyl Compounds 194 Benzonitril and its Derivatives 197 Benzimido-Ethers 200 Benzenylamidines 202 Benzenyloxime Compounds 207 Halogen-Substitution Products of Benzoic Acid 216 Monochlorobenzoic Acids 217 Dichlorobenzoic Acids 221 Trichlorobenzoic Acids 222 CONTENTS. IX PAGE Benzoyl Group-continued. Tetrachlorobenzoic Acid 222 Monobromobenzoic Acids 223 Dibromobenzoic Acids 224 Tribromobenzoic Acids 225 Mono-Iodobenzoic Acids 225 Monofluorbenzoic Acids 226 Nitro-Substitution Products of Benzoic Acid ...... 227 Mononitrobenzoic Acids 229 Dinitrobenzoic Acids ... 234 Trinitrobenzoic Acid 235 Chloronitrobenzoic Acids 236 Bromonitrobenzoic Acids 236 lodonitrobenzoic Acids 237 Monamidobenzoic Acids 237 Chloramidobenzoic Acids 254 Bromamidobenzoic Acids 255 lodamidobenzoic Acids 255 Nitro-Amidobenzoic Acids 255 Dinitro-Amidobenzoic Acids 257 Diamidobenzoic Acids 258 Triamidobenzoic Acid 260 .Diazo-Derivatives of Benzoic Acid 260 Hydrazinebenzoic Acids 264 Azo-Derivatives of Benzoic Acid 265 Monosulphobenzoic Acids 268 Disulphobenzoic Acids 274 Chlorosulphobenzoic Acids 274 Bromosulphobenzoic Acids 274 Nitrosulphobenzoic Acids 275 Amidosulphobenzoic Acids 275 Benzophosphinic Acid 275 Benzarsenic Acids . . .277 Hydroxybenzyl Group 279 Hydroxy benzyl Alcohols 279 Hydroxybenzaldehydes 285 Orthohydroxybenzaldebyde or Salicylaldehyde . . . . . . 285 Substitution Products of Salicylaldehyde 292 Metahydroxybenzaldehyde 293 Parahydroxybenzaldehyde 294 Hydroxy benzoic Acids 297 Orthohydroxybenzoic Acid or Salicylic Acid 297 Ethereal Salts of Salicylic Acid 306 Salicylic Ethers 306 Ethereal Salts of Salicylic Ethers 307 Substitution Products of Salicylic Acid 313 Metahydroxybenzoic Acid 320 Substitution Products of Metahydroxybenzoic Acid . ... . 323 Parahydroxybenzoic Acid 326 Substitution Products of Parahydroxybenzoic Acid 334 Substitution Products of Anisic Acid 336 Anisenyloxime Compounds 339 Dibenzanishydroxylamine 341 X CONTENTS. PAGE Hydroxybenzyl Group-continued. Benzanisbenzhydroxylamine 341 Anisdibenzhydroxylamine 341 Anisbenzanishydroxylamine 342 Dianisbenzhydroxylamine 342 Benzdianishydroxylamine 342 Dihydroxybenzyl and Dihydroxybenzoyl Compounds .... 343 Dihydroxybenzoic Acids 350 Protocatechuic Acid or Orthodihydroxy ben zoic Acid .... 350 Symmetric Metadihydroxybenzoic Acid or a-Resorcylic Acid . . . 358 Asymmetric Metadihydroxybenzoic Acid or AResorcylic Acid . . 359 Adjacent Metadihydroxy benzoic Acid or y-Resorcylic Acid . . . 360 Hydroxysalicylic Acid or Paradihydroxybenzoic Acid .... 361 Trihydroxybenzoic Acids 363 Gallic Acid . 363 Pyrogallolcarboxylic Acid 378 Phloroglucinolcarboxylic Acid . 380 Hydroxyquinolcarboxylic Acid 380 Constitution of the Trihydroxybenzoic Acids 381 Quinic Acid 381 Xylene Group 386 The Xylenes or Dimethylbenzenes 390 Substitution Products of the Xylenes 392 Halogen Substitution Products of the Xylenes 392 Nitro-Substitution Products of the Xylenes 395 Xylenesulphonic Acids 398 Hydroxy-Xylenes or Xylenols 399 Dihydroxy-Xylenes 402 Trihydroxy-Xylenes 403 The Xyloquinones 404 Amido-Derivatives of the Xylenes 405 The Amidoxylenes or Xylidines 405 Nitroxylidines 408 Diamines and Triamines of the Xylenes 409 Xylyl-Compounds 410 Xylyl Alcohols «... 411 Xylylamines 412 The Tolualdehydes 413 The Toluic Acids 414 Hydroxytolualdehydes 422 Hydroxytoluic Acids 423 Dihydroxytolualdehydes 427 Dihydroxytoluic Acids 428 Xylylene Alcohols • . . . 439 Hydroxymethylbenzoic Acids 442 Aldehydes and Aldehydo-Acids 447 The Phthalic Acids 450 Phthalic Acid 452 Addition Products of Phthalic Acid 469 Halogen Substitution Products of Phthalic Acid 471 Nitrophthalic Acids 473 Amidophthalic Acids 475 Sulphophthalic Acids 476 CONTENTS. XI PAGE Xylene Group-continued. Isophthalic Acid or Metaphthalic Acid 479 Addition Products of Isophthalic Acid 481 Substitution Products of Isophthalic Acid 481 Terephthalic Acid 483 Addition Products of Terephthalic Acid 486 Substitution Products of Terephthalic Acid 488 Hydroxymethylhydroxybenzoic Acid 490 Aldehydohydroxy benzoic Acids 491 Hydroxyphthalic Acids 492 Hydroxymethyldihydroxybenzoic Acids 497 Aldehydodihydroxybenzoic Acids 502 Dihydroxyphthalic Acids 510 Trihydroxyphthalic Acids 519 Tetrahydroxyphthalic Acids 519 ORGANIC CHEMISTRY. ORGANIC CHEMISTRY, OR THE CHEMISTRY OF THE HYDROCARBON'S AND THEIR DERIVATIVES. PART IV. TOLUENE GROUP. Toluene or Methylbenzene, C6H5.CH3. 2017 This hydrocarbon was discovered by Pelletier and Walter in the oil obtained as a by-product in the manufacture of illu- minating gas from the resin of Pinus maritima. They named it " retinaphtha " {r^tinnaphte^ and determined its composition accurately.1 Shortly afterwards, Couerbe examined the liquid obtained by compressing the resin gas, and isolated from it, among other hydrocarbons, his Heptacarbure quadrihydrique, (C= 6), which, in spite of some differences, he believed to be identical with retinaphtha.2 Deville next obtained a hydro- carbon of the same composition by distilling the resin contained in Tolu balsam.3 He named it benzoene (benzodne), because, in the first place, the balsam4 from which it had been obtained contains benzoic acid; secondly, because, according to his for- mula, the hydrocarbon may be looked upon as the type of the 1 Ann. Chim. Phys. Ixvii. 269 ; Pogg. Ann. xliv. 8. 2 Ann. Chim. Phys. Ixix. 184 ; Journ. Prakt. Chern, xviii. 165. 3 Ann. Chim. Phys. [3] iii. 168 ; Journ. Prakt. Chem. xxv. 336. 4 Tolubalsam is obtained by incisions made in the bark of the Myroxylon toluifera, as mentioned by the Spanish physician Monardes in his Historia de las cosas que se traen de miestras Indias occidentalcs, which first appeared complete in Seville in 1574, and in which he says that the balsam was collected by the Indians, in the district Tolu, in the neighbourhood of Carthagena (Fliickiger and Hanbury, Pharmacographia). 4 AROMATIC COMPOUNDS. benzoic series, and finally, because this name was similar to that of benzine (benzene), to which the substance bears the greatest resemblance. He considered, nevertheless, that benzoene was not identical, but isomeric with retinaphtha; Glenard and Boudault also considered the dracyl, which they had obtained, by the dry distillation of dragon's blood (from Calamus draco),1 to be an isomeride of the former. Hofmann and Muspratt then showed that it is identical with benzoene, for which somewhat unsuitable name Berzelius sub- stituted that of toluol,2 soon universally accepted, and still in use on the Continent, while in England it has been changed forfthe sake of consistency into toluene. A complete investigation of toluene has proved that not only as regards its empirical formula, but in all its properties, it is the next higher homologue of benzene. Deville, as well as Glenard and Boudault, had already obtained from it nitrotoluene, C7H7NO2 (nitrobenzoene, nitrodracyl), by the action of nitric acid, and Hofmann and Muspratt converted this by reduction into toluidine, C7H7NH2, which resembles aniline very closely.3 Noad found that when cymene, Clf)H14, which is a constituent of Roman cumin-oil, is oxidized with nitric acid, toluic acid, C8H8O2, the homologue of benzoic acid, is formed, and on dis- tillation with caustic baryta decomposes into carbon dioxide and toluene, a reaction, which corresponds exactly to the formation of benzene from benzoic acid.4 The relation of toluene to the benzoic series, which had already been pointed out by the French chemists, was experi- mentally proved by Cannizzaro, who found that benzyl alcohol, C7H7O, which is converted by oxidation into benzoic acid, under- goes a simultaneous oxidation and reduction when heated with concentrated alcoholic potash, benzoic acid and toluene being formed.5 Finally, Fittig and Tollens ascertained the constitution of toluene. These chemists obtained it synthetically by the action of sodium on a mixture of methyl iodide and bromobenzene,6 by which reaction they not only proved that the product is methyl- benzene, but pointed out a general and simple method by which the higher homologues can be prepared, and their constitutions determined. 1 Journ Prak',. Chern, xxxi. Ill xxxiii. 466. 2 Jahresb. xxii. 354. 3 Cham. Soc. Mem. (1845) ii. 367. 4 Ibid. iii. 421. 5 Ann. Chern. Pharm. xc. 252. 6 Ibid, cxxxi. 303. TOLUENE. 5 Mansfield, whose results were subsequently confirmed by Ritthausen, was the first to prove that light coal-tar oils contain toluene and higher homologues as well as benzene1 (Part III. p. 66). Toluene also occurs, together with xylene, in wood-tar ; Cahours detected it in crude French pyroligneous acid,2 and Volk el in the oil which comes over first in the distillation of beech-wood tar.3 It is also found, together with its homologues, in several varieties of petroleum, such as that from Burmah (Rangoon tar),4 as well as in the liquid obtained by the compression of the illuminating gas which is manufactured by heating the high boiling portions of petroleum, and has been used for lighting railway carriages.5 It is obtained on the large scale from light coal-tar oil, and is chiefly employed in the colour industry. Properties.-Toluene is a strongly refractive liquid, possessing a smell similar to that of benzene; it boils at 110'3° and does not solidify at -20°. Oxidizing agents convert it into benzoic acid. It combines with aluminium chloride forming the com- pound Al2Cl6+6 C7H8, a thickish, orange-coloured liquid, which is violently decomposed by water with separation of toluene. A similar compound is formed with aluminium bromide.6 When toluene is heated with aluminium chloride to 200°, a portion of it is converted into paradimethylbenzene, paramethyl- ethylbenzene, and metamethylethylbenzene, high boiling hydro- carbons being also formed, while benzene under the same con- ditions yields toluene, ethylbenzene and diphenyl. In order to explain this remarkable reaction, Friedel and Crafts 7 assume that the following first takes place : c6h6 + A12C16=c6h5 ai2ci5+HC1 2C6H5A12C15 4- 2HC1 = C12H10 + 2 A12C16 + 2H2. The nascent hydrogen and the hydrochloric acid convert a portion of the benzene into methyl chloride and ethyl chloride, which then form toluene and ethyl benzene (Pt. III. p. 14.) : C6H5. A12C15+CH3C1 = C6H5.CH3 + A12C16. When toluene is employed, a similar reaction takes place; methyl chloride is, however, probably formed simultaneously, according to the equation : 1 Journ. Prakt. Chern. Ixi. 74. 2 Ann. Chern. Pharm. Ixxvi. 286. 3 Ibid. Ixxxvi. 335. 4 Journ. Prakt. Chern. Ixx. 300. 5 Greville Williams, Chern. News, xlix. 197. 6 Gustavson, Ber. Deutsch. Chem. Ges. xi. 2152. 7 Compt. rend. c. 692. C6H,.CH3 + ALCL = C6H5 A12C15+CH3C1. OD D L O xj O A O O 6 AROMATIC COMPOUNDS. When one part of chromium oxychloride is dissolved in ten parts of carbon disulphide, and the solution allowed to drop into a mixture of one part of toluene and ten parts of carbon disul- phide, a chocolate-brown, crystalline precipitate of the empirical formula C7H842CrO2Cl2 is formed; this is soluble in glacial acetic acid, rapidly absorbs moisture, and is decomposed by water with formation of benzaldehyde and chromous chromate, showing that it is benzidenedichlorochromic acid : /OCrCl^OH C6H5.CH< + H2O = C6H5.CHO + 4HC1 4 2CrO2. \OCrCl2.OH Alcohol and ether exert a similar action, ethyl chloride being formed in these cases. On heating the compound to 240°-245°, the chloride, C6H5.CH (OCrOCl)2, is obtained; it has a darker colour and is more stable in moist air, but behaves towards water similarly to the acid.1 ADDITION PRODUCTS OF TOLUENE. 2oi8 Dihydrotoluene, C7H10, is obtained by heating toluene with phosphonium iodide to 350°, and is a liquid boiling at 105°-1O80.2 Tetrahydrotoluene, C7H12, occurs in the distillation products of pine resin and colophonium, which are obtained on the large scale, and employed in the manufacture of varnishes, &c. The fraction boiling below 300°, which forms the smaller portion and is known as " resin spirit " or " essence of resin," is a mixture of fatty acids, aldehydes, paraffins, olefines, aromatic hydrocarbons and their addition products,3 among which is tetrahydrotoluene. This substance is a liquid boiling at 103°-105°, and is converted by bromine into a crystalline bromide, C7HcBr6. Tetrahydro toluene combines with water to form a hydrate, C7H124 2H2O, which crystallizes in long, white crystals, and, according to Renard, is identical with Anderson's colophonin, C7H14O2, obtained by exposing resin spirit to the air for a long period ;4 while accord- 1 fitard, Ann. Chim. Phys. [5] xxii. 223. 2 Baeyer, Ann. Chem. Pharm. civ. 271. 3 Kelbe, ibid. ccx. 10 ; Kelbe and Bauer, Ber. Deutsch. Chem. Ges. xvi. 2559 ; Renard, Ann. Chim. Phys. [6], i. 223. 4 Chem. News, xx. 76. TOLUENE SUBSTITUTION PRODUCTS. 7 ing to Tichborne, colophonin hydrate, C10H22O3 + H2O, is formed, and loses water on heating.1 Hexhydrotoluenc, C7H14, is prepared by heating toluene with a large excess of concentrated hydriodic acid to 280°,2 and occurs in Baku petroleum3 and in resin spirit (Renard). It is a liquid smelling like petroleum, boiling at 97°, and having a specific gravity of '772 at 0°. A mixture of concentrated sulphuric and nitric acids does not attack It in the cold, but when hot oxidizes it completely. CHLORINE SUBSTITUTION PRODUCTS OF TOLUENE. 201g By the action of chlorine on toluene in the dark, Deville obtained Benzo^ne mono chlor C7H7C1, as a thin liquid boiling at 170°,4 whilst Cannizzaro found that the monochlorinated toluene obtained by the repeated distillation of toluene in a stream of chlorine, and boiling at 175°, is identical with benzyl chloride, as it can be readily converted into benzyl alcohol.5 The same compound was also obtained by passing chlorine into toluene, but in this process an isomeric compound was frequently formed instead of the benzyl chloride, and this proved to be as stable as chlorobenzene. These enigmatical results wrere explained by Beilstein and Geitner,6 who observed that the action of chlorine on toluene varies according to the temperature at which the chlorination is effected. Benzyl chloride alone is formed when the mixture is hot, while the stable chlorotoluene is formed when the process is conducted in the cold. As, however, heat is evolved by the action of the chlorine, the toluene, if used in large quantities and not carefully cooled, may become heated almost to the boiling point, benzyl chloride consequently being formed together with more or less chlorotoluene. The nature of this mixture can readily be exhibited by oxidizing it with chromic acid, the benzyl chloride being thus converted into benzoic acid, and the chlorotoluene into chlorodracylic acid 1 Chern. News, xx. 38. 2 Wreden and Znatowicz, Ann. Chern. Pharm. clxxxvii. 161. 3 Beilstein and Kurbatow, ibid. xiii. 1818 ; see also xiv. 1620. 4 Ann. Chim. Phys. [3], iii. 178. 5 Ann. Chern. Pharm. xcvi. 246 ; ibid. cxli. 198. 6 Ibid, cxxxix. 331. 8 AROMATIC COMPOUNDS. (parachlorobenzoic acid), the acids being readily separated by means of the very great difference in their solubilities in water. Beilstein and Geitner further found that chlorotoluene is more readily obtained by dissolving a little iodine in the toluene and then chlorinating, under which conditions no benzyl chloride is formed either in the cold or on heating. As already mentioned (Part III. p. 17) all the hydrogen atoms of the aromatic group can be thus replaced by chlorine, whilst at the boiling point, in absence of iodine, substitution can only take place in the methyl group. By working alternately according to these two methods no octochlorotoluene can be obtained, the final products being pentachlorobenzidenc chloride, C6C16.CHC12 and tetrachlorobenzal chloride, C6HC14.CC13. If these be heated with antimony pentachloride in order to effect a further chlorina- tion, they decompose with formation of hexchlorobenzene.1 Monochlorotoluenes, C6H4C1.CH3. 2020 Ortfyochlorotoluene is formed only in small quantities by the chlorination of toluene in the presence of iodine : it may, however, be readily obtained from orthotoluidine by means of the diazo-reaction.2 It is a liquid boiling at 157°, which is oxidized by potassium permanganate to orthochlorobenzoic acid, whilst chromic acid solution produces complete oxidation.3 Mctachlorotoluene is not formed by the action of chlorine on toluene ; it has been prepared from metatoluidine, as well as from paratoluidine by converting this into acetoluide, C6H4(CH3) NH(C2H3O), chlorinating and decomposing the product by heat- ing with caustic potash; the monochloroparatoluidine thus ob- tained is converted into the diazo-compound, and then decom- posed with absolute alcohol;4 chloroparatoluidine has, therefore, the following constitution •. ch3 ^nh2. 1 Beilstein and Kuhlberg, Ann. Chem. Pharm. cl. 286. 2 Ibid. clvi. 79 ; Gascorowski and Wayss, Ber. Deutsch. Chem. Ges. xviii. 1939. s Emmerling, Ber. Deutsch. Chem. Ges. viii. 880. 4 Wroblevsky, Ann. Chem. Pharm. clxviii. 199. CHLOROTOLUENES. 9 Hence we see that, on the chlorination of paratoluidine, the chlorine takes up the position adjacent to the basic group, and this also occurs in many other cases. Metachlorotoluene is a liquid which boils at 156° and is con- verted by oxidation into metachlorobenzoic acid. Parachlorotoluene is the chief product of the action of chlorine on toluene in the presence of iodine.1 It is advantageous to substitute molybdenum pentachloride for iodine, and to pass the chlorine through the mixture heated on the water-bath.2 The product thus obtained does not solidify when cooled to a low temperature, since it contains various substances, such as the ortho-compound, &c., as impurities. If the parachlorotoluene be prepared from paratoluidine, it is obtained in a pure condi- tion, and then boils at 1GO'5° and solidifies at 0° to a foliaceous mass, melting at 6'5°.3 On oxidation it is converted into para- chlorobenzoic acid. Dichlorotoluenes, C6H3C12.CH3. 2021 When toluene is treated with sufficient chlorine in presence of iodine or molybdenum pentachloride, and the pro- duct purified by fractional distillation, a liquid boiling at 196° is obtained,4 which, in spite of its constant boiling point, is not a definite compound, but a mixture of three dichlorotoluenes. If chlorine be passed into the vapour of the boiling liquid until no further action takes place, the hydrogen of the methyl group is replaced by chlorine and the corresponding dichlorobenzenyl- trichlorides formed; on heating with water to 200° these are converted into three dichlorobenzoic acids: CfiH»Cl2.CCl3 + 2H.,0 = C6H3C12.CO2H + 3HC1. O O Z O' Lt D O Li Lt The formation of three dichlorotoluenes can readily be explained ; the monochlorotoluene, which is first formed, consists chiefly of the para-compound, which can yield two isomeric dichloro- toluenes, whilst the third is formed from the orthochlorotoluene which is also present, though in smaller quantity. The mixture appears to consist chiefly of asymmetric 1 Beilstein and Geitner, loc. cit. 2 Aronheim and Dietrich, Ber. Deutsch. Chern. Ges. viii. 1402. 3 Hubner and Majert, ibid. vi. 794. 4 Beilstein and Geitner; Beilstein and Kuhlberg, Ann. Chem. Pharm. cl. 313 ; Schultz, ibid, clxxxvii. 263. Aronheim and Dietrich. 10 AROMATIC COMPOUNDS. dichlorotoluene, (CH3 : Cl: Cl=l : 3 : 4), which yields the cor- responding dichlorobenzoic acid on oxidation. Dichlor otohtcne hcxchloride, C6H3C12(CH3)C16, is obtained by the continued action of chlorine on toluene in the cold, and crystallizes from carbon disulphide in large prisms melting at 150°. When it is heated with alcoholic potash to 110°, tetra- chlorotoluene, C6HC14.CH3, is formed; this compound is a liquid boiling at 280°-290°.1 The following substitution products have been obtained by the continued action of chlorine, assisted finally by the addition of antimony chloride : Melting- point. Boiling- point. a-Trichlorotoiuene 2 C6H2CL.CHs(2 : 4 : 5) 82° 230° ^-Trichlorotoluene 3 C6H2C13.CH3(2 : 3 : 4) 41° 232° Tetrachlorotoluene 4 C6HC14.CH3 96° 276°-5 Pentaclilorotoluene 5 c6ci5.ch3 218° 301°. BROMINE SUBSTITUTION PRODUCTS OF TOLUENE. 2022 All the theoretically possible compounds of this series are known. Monobromotoluenes, C«H,Br.CH„. 7 0 4 o Orthobromotoluene is formed, together with a larger amount of parabromotoluene, by the bromination of toluene in the cold. The para-compound, which crystallizes out, is removed by pressing, and the liquid cooled in a freezing mixture, in order to remove as much of the solid as possible ; the portion which remains liquid is then dissolved in alcohol and distilled, all the remaining parabromotoluene volatilizing in the vapour.6 The para-compound may also be removed by means of sodium, which does not act upon the ortho-compound in the cold.7 In order to effect this, the liquid is dissolved in benzene and allowed to stand over sodium for eight days; it is then distilled, and the fraction boiling between 170°-190° treated three or four times in the same way.8 1 Pieper, Ann. Chern. Pharm. cxlii. 304. 2 Limpricht, ibid, cxxxix. 326 ; Schultz ; Aronheim and Dietrich ; Seelig, Ber. Deutsch. Chern. Ges. xviii. 420. 3 Seelig. 4 Limpricht; Beilstein and Kuhlberg. 8 Beilstein and Kuhlberg. 6 Hubner and Jannasch, Ann. Chem. Pharm. clxx. 117. 7 Luginin, Bull. Soc. Chim. iv. 514. 8 Heymann, ibid. xxvi. 533. BROMOTOLUENES. 11 Orthobromotoluene has also been prepared from ortho- toluidine by means of the diazo-reaction.1 It is a liquid, boiling at 182°-183° and is oxidized by dilute nitric acid to orthobromo- benzoic acid, while chromic acid causes complete combustion. Metabromotoluene has been obtained from metatoluidine and from parabromotoluidine (Wroblevsky).2 It is a liquid which boils at 184'3° (Korner) and does not solidify at - 20°. Parabromotoluene. The separation of this from orthobromo- toluene is described above. It may be more rapidly effected by agitating the rectified mixture with half its volume of fuming sulphuric acid; the parabromotoluene separates out as a crystalline mass after some time.3 It boils at 182'5°,4 and is deposited from an alcoholic solution in rhombic crystals melting at 28'5°. When given to a dog, it appears in the urine as parabromohippuric acid and parabromobenzoic acid. When it is treated with chromium oxychloride, bromobenzidenedichloro- chromyl chloride, C6H4Br.CH(OCrOCl)2 is formed as a brown precipitate which is decomposed by water with formation of parabromobenzaldehyde (^tard). Dibromotoluenes, C6H3Br2.CH3. 2023 These have been prepared from the monobromotoluidines by the replacement of the amido-group by bromine, and from the dibromotoluidines by the replacement of the amido-group by hydrogen.5 The first compound in the following list has also been obtained by the direct bromination of toluene ; the process goes on much more rapidly in the presence of iodine and in the sunlight.6 Melting- Boiling- CH3 : Br : Br 13 4 point. liquid, does not solidify at - 20° - point. 240° 12 6 V » 55 55 246° 12 5 55 55 55 55 236° 12 4 55 55 55 55 - 12 3 solid 28° - 13 5 long needles 39° 246° 1 Wroblevsky, Ann. Chem. Pharm. clxviii. 171. 2 See also Grete, ibid, clxxvii. 231. 3 Hubner and Wallach, Ann. Chem. Pharm. cliv. 293. 4 Hubner and Post, ibid, clxix. 6. 5 Wroblevsky, ibid, clxviii. 161 ; Neville and Winther, Ber. Deutsch. Chem. Ges. xiii. 962 ; xiv. 417. 6 Jannasch, Ann. Chem. Pharm. clxxvi. 286. 12 AROMATIC COMPOUNDS. On treatment with nitric acid they yield all the mononitro- compounds which are theoretically possible ; most of these com- pounds crystallize in needles. Tribromotoluenes, C6H2Br3.CH3 These are obtained in a similar manner to the preceding compounds.1 ch3 Br : Br Br : Melting- point. Boiling- point. 1 3 4 5 crystals .... 88°-89° - 1 o 3 4 crystals .... 46° - 1 2 4 6 long needles . . 66° 290° 1 2 3 5 flat needles . . 52°5 - 1 2 4 5 long needles . . 112° - 1 2 5 6 flat needles . . 58°-59° - Tetrabromotoluenes, CcHBr4.CH3.2 CH3 : Br : : Br : 3 : Br : 4 : Br : 5 thin needles . Melting- point. Ill- 111° 5 Boiling- point. 1 2 1 2 3 5 6 fine needles . 116°-117° - 1 2 3 4 6 x crystals . . . 105°-108° - Pentabromotohiene, C6Br5.CH3, is formed when toluene is allowed to drop into bromine which is free from chlorine and to which some aluminium bromide has been added, as well as by replacing the amido-group of tetrabromotoluidine by bromine (Neville and Winther). It crystallizes from benzene in long needles, melting at 282°-283°. When toluene is treated with an excess of bromine containing iodine, and the temperature finally allowed to rise to 350°-400°, hexbromobenzene and tetrabromomethane are formed, the latter being, however, for the most part converted into the former.3 1 Wroblevsky ; Neville and Winther, loc. cit. 2 Ibid. 3 Gessner, Ber. Deutsch. Chern. Ges. ix. 1508. NITROTOLUENES. 13 IODINE SUBSTITUTION PRODUCTS OF TOLUENE. Only the mono-iodotoluenes, C6H4I.CH3, which are obtained from the toluidines, are known.1 Ortho-iodotoluene liquid . . Boiling- point. 204° Melting- point. Meta-iodotoluene n • • 204° - Para-iodotoluene plates . . 211°-5 35° FLUORINE SUBSTITUTION PRODUCTS OF TOLUENE. Fhtotoluene, C6H4F.CH3, is formed when the diazo-compound obtained from paramidotoluenesulphonic acid is decomposed with strong hydrofluoric acid. It is a liquid smelling of bitter almonds, and boiling at 114°.2 NITRO-SUBSTITUTION PRODUCTS OF TOLUENE. Mononitrotoluenes, C6H4(NO.2)CH3. 2024 By dissolving toluene in fuming nitric acid and pre- cipitating with water, Deville obtained nitrotoluene (protonitro- benzoene) as a colourless liquid boiling at 225°, and possessing a smell of bitter almonds and a very sweet, somewhat biting taste. This compound was then repeatedly prepared by many chemists, who confirmed Deville's statements. These circumstances served to render the following observations of Jaworsky the more remarkable; this chemist found that when nitrotoluene is dissolved in fuming nitric acid, and water added to the solution, a precipitate is formed which separates from a hot, alcoholic solution in lustrous crystals melting at 54° 1 Beilstein and Kuhlberg, Ann. Chern. Pharm. clviii. 147 ; Kbrner, Zeitschr. Chern, clxxxviii. 327. 2 Paterno and Oliveri, Gaz. Chim. Itai. xiii. 533. 14 AROMATIC COMPOUNDS. and which, boiling without decomposition at 238°, has exactly the same composition as nitrotoluene. He obtained the same compound by continuing the distillation of the liquid nitrotoluene to 240°; the residue, which solidified on cooling, was identical with the product obtained by the other method. He concluded from these experiments that pure nitrotoluene is a solid body, the crystallizing power of which is usually destroyed by liquid impurities, these also having the power of lowering the boiling point.1 These observations were confirmed by other chemists and were even taken advantage of commercially, for well crystallized nitrotoluene was manufactured on the large scale in Paris in 1867. Alexejew confirmed Jaworsky's view by obtaining the same azotoluene from the solid as from the liquid nitro toluene.2 He also found that the solid compound is converted by reduction into a solid toluidine,3 which could not be obtained from the liquid compound. Kekule, who also investigated these facts, confirmed the above observation, and showed in addition that the solid nitro- toluene is more readily oxidized to paranitrobenzoic acid and gives a better yield than the liquid; the lower boiling portion of the latter yielded a liquid toluidine containing aniline, and he therefore considered it probable that the substance which had up to that time been looked upon as nitrotoluene was a mixture of nitrobenzene and nitrotoluene.4 Rosenstiehl, however, made the discovery that the ordinary liquid toluidine is a mixture of the solid with the isomeric pseudo- toluidine,5 and that, consequently, two nitrotoluenes are formed by the nitration of toluene.6 In order to decide the question whether toluene itself is a mixture of two isomeric hydrocarbons, he investigated the behaviour of samples of toluene from various sources towards nitric acid. He took some which had been previously exposed to a red heat, and some which he had obtained by the decomposition of xylene, CcH4(CH3)2, at a high temperature. He also investigated toluene synthetically prepared, and that obtained from Tolu balsam. In all cases he obtained the two toluidines. Finally, Berthelot reduced these by heating with hydriodic acid and obtained one and the same toluene.7 1 Zeitschr. Chern. 1865, 222. 2 Ibid. 1866, 269. 3 Bull. Soc. Chiin, vii. 376. 4 Zeitschr. Chern. 1867, 225. 6 Ibid. 1868, 557. 6 Ibid. 1869, 190. 2 Ibid. NITROTOLUENES. 15 Hence the supposition appeared not improbable that the lower boiling portion of ordinary nitrotoluene would be an isomeride of the solid compound, which yields the pseudotoluidine; Rosenstiehl, however, singularly enough, did not investigate this point, and it was reserved for Beilstein and Kuhlberg to answer the question. These chemists had already prepared the liquid /3-nitrotoluene from dinitrotoluene, by converting the latter into nitrotoluidine, C6H3(NH2)(NO2).CH3, by partial reduction with ammonium sulphide, and then replacing the amido-group by hydrogen. They then found that this nitro- toluene, which they called metanitrotoluene, but which is now known as the ortho-compound, forms the more volatile portion of crude nitrotoluene and can be separated from the solid paranitro- toluene by repeated careful fractional distillation.1 A small quantity of metanitrotoluene is formed, together with the ortho- and para-compounds, by the action of fuming nitric acid on toluene.2 The relative quantities of the two chief pro- ducts which are formed depend upon the concentration of the acid, and the temperature at which the nitration is effected. When a very concentrated acid is employed and the temperature allowed to rise, paranitrotoluene is chiefly obtained, while the yield of the ortho-compound is greatly increased by employing a weaker acid and cooling the mixture well. The nitrotoluenes are manufactured on the large scale, by mixing 10 parts of toluene with 11 parts of nitric acid of specific gravity 1'22 and 1 part of sulphuric acid of specific gravity 1'33 with continual agitation, in the apparatus used for the manufacture of nitrobenzene; the mixture is then either cooled or kept warm according to the product desired. The crude product is washed with water and caustic soda solution, freed from unattacked toluene by distillation with steam, and then distilled with super-heated steam. The distillate is then repeatedly fractionated; the larger portion of the fraction distilling above 230° solidifies on cooling, and the crystals, after purification by draining and pressing, yield pure paranitrotoluene on distillation; the fraction boiling between 222°-223° consists chiefly of orthonitrotoluene, while the inter- mediate fractions contain some of the meta-compound. Orthonitrotoluene, is obtained pure when the amido-group of the isomeric nitrotoluidines, which contain the nitroxyl in the 1 Ann. Chern. Pharm. civ. i. 2 Monnet, Reverdin and Nolting, Ber. Deutsch. Chem. Ges. xii. 445 16 AROMATIC COMPOUNDS. ortho-relation to the methyl group, is replaced by hydrogen: this is best effected by heating the compound with alcohol saturated with nitrogen trioxide. It is a liquid which boils at 223°, does not solidify at - 20°, and has a specific gravity of 1163 at 23-5°. Metanitrotoluene is prepared by the same method from the corresponding nitrotoluidine. It solidifies in a freezing mixture to crystals which melt at 16°; it boils at 230°-231°, and has a specific gravity of 1'168 at 220.1 Paranitrotoluene boils at 238°, and on the gradual evaporation of its alcoholic or ethereal solution separates in large, thick rhombic crystals melting at 54°. Dinitrotoluenes, CAL (NO,\,CHq. ' Vox O 2025 Ordinary Dinitrotoluene, (CH3 : NO2 : NO2 = 1 : 2 : 4) was obtained by Deville, and is formed by the further nitration of ortho- and para-nitrotoluene. In order to prepare it, toluene is run into fuming nitric acid, without any special cooling, until oily drops separate out; the mixture is then allowed to cool, and an equal volume of sulphuric acid gradually added, the whole being then boiled for half an hour, poured into snow, and the precipi- tate recrystallized from hot carbon disulphide.2 It crystallizes in long, monoclinic needles, which melt at 72°, are only slightly soluble in cold alcohol, and still less so in cold carbon disulphide, but dissolve readily in boiling benzene. In the manufacture of dinitrotoluene on the large scale, a liquid by-product is obtained, which was formerly considered to be an isomeric dinitrotoluene.3 According to Claus and Becker it is a mixture of ordinary dinitrotoluene, orthodinitrotoluene, and orthomononitrotoluene.4 Limpricht found that 1:2:5 dinitro- toluene is also contained in it; he did not isolate this compound but converted it into the corresponding nitrotoluidine.5 Nolting and Witt, who examined a larger quantity of the by-product, obtained from it by distillation in a rapid current of steam 40 per cent, of mononitrotoluenes, consisting of almost equal parts of the para- and meta-compounds, the ortho-compound being 1 Beilstein and Kuhlberg, Ann. Chern. Pharm. clviii. 348. 2 Ibid. clvi. 13. 3 Rosenstiehl, Ann. Chim. Phys. [4] xxvii. 407. Cunerth, Ann. Ghent. Pharm. clxxii. 222. 4 Claus and Becker, Ber. Deutsch. Chern. Ges. xvi. 159G. 6 Ibid, xviii. 1400. TRINITROTOLUENES. 17 present only in very small amount. Although metanitrotoluene is only formed to a small extent by the nitration of toluene, its presence in comparatively large quantities in the mixture can be readily understood, as it resists the further action of nitric acid much more strongly than its isomerides; it therefore accumulates in the by-product, while the more readily attacked ortho-compound almost disappears.1 Orthodinitrotoluene (1:2:6) can best be obtained pure by con- verting a-trinitrotoluene into dinitroparatoluidine, and replacing the amido-group of this by hydrogen. It crystallizes in broad, golden needles, melting at 60°-61°.2 Symmetric Dinitrotoluene (1: 3: 5) may be prepared from the dinitroparatoluidine which melts at 168°, and from the dinitro- orthotoluidine melting at 208°, by suspending these in concen- trated nitric acid and saturating the well-cooled liquid with nitrogen trioxide; the product is then brought in small portions at a time into eight or ten parts of absolute alcohol, the solution cooled as soon as the evolution of nitrogen has ceased, and the dinitrotoluene then precipitated with water. On recrystallization from hot water it is obtained in small needles, whilst it crystallizes from petroleum spirit in small prisms, which join to form chain-like masses. It melts at 92° and combines with benzene, forming a double compound, C7H6 (NO2)2 + CeH6, crystallizing in large prisms which effloresce in the air.3 7-Dinitrotoluene. Beilstein and Kuhlberg obtained this com- pound by agitating metanitrotoluene with nitric acid of specific gravity 1'54 for a long time. It crystallizes from carbon disulphide in long needles melting at 60°. Trinitrotoluenes, C.H, (NOA CH,. ' V a \ 0 o 2026 a-Trinitrotoluene (1 : 2:4: 6) is formed when toluene 4 or ordinary dinitrotoluene5 is heated for some days with a mixture of nitric and sulphuric acids. It may be more rapidly prepared by dropping toluene into a mixture of pure nitric acid and sulphuric acid containing a large quantity of sulphur trioxide and warming on the water-bath.6 It is very slightly soluble in 1 Claus and Becker, Ber. Deutsch. Chern. Ges. xviii. 1336. 2 Stadel and Becker, Liebig's Ann. ccxvii. 205 ; Stadel, ibid, ccxxv. 384. 3 Stadel, Ber. Deutsch. Chem. Ges. xiv. 901 ; Liebig's Ann. ccxvii. 189 ; Hubner, ibid, ccxxii. 74 ; Neville and Winther, Ber. Deutsch. Chem. Ges. xvi. 2985. 4 Wilbrandt, Ann. Chem. Pharm. cxxviii. 178. 5 Tiemann, Ber. Deutsch. Chem. Ges. iii. 217. 6 H. Schmitt, private communication. 18 AROMATIC COMPOUNDS. cold, more readily in hot alcohol, from which it crystallizes in large, rhombic tablets or golden needles melting at 82°. On heating with ten times its weight of fuming nitric acid to 180° it is con- verted into symmetric trinitrobenzene.1 When aniline is added to its alcoholic solution, the compound C7H6(NO2)3 + C6H7N is obtained in long, red, lustrous needles melting at 83°-840.2 ft-Trinitrotoluene. Beilstein and Kuhlberg, by boiling meta- nitrotoluene with nitric and sulphuric acids, obtained a tri- nitrotoluene, the purity of which they doubted, adding that the small quantity of substance obtained by them was probably a mixture. Hepp then proved that at least two trinitrotoluenes are formed from metanitrotoluene, and that these can be separated by repeated crystallization from alcohol or carbon disulphide. /3-Trinitrotoluene, which is only formed in small quantity, is readily soluble in carbon disulphide, slightly in cold, more readily in hot alcohol, and freely in ether and acetone. It crystallizes on the gradual evaporation of its solution in the last-named solvent in transparent, asymmetric prisms melting at 112°; whilst it separates from alcohol in dazzling white plates or flat needles. On heating with alcoholic ammonia, a dinitrotoluidine is formed which melts at 94°; it is also readily attacked by aniline and caustic soda solution. 7- Trinitrotoluene is only very slightly soluble in carbon di- sulphide and cold alcohol, and separates from hot alcohol in hard, compact, yellowish white crystals, while it crystallizes from acetone in small, hexagonal tablets, melting at 104°. Concentrated alcoholic ammonia converts it, even in the cold, into a dinitrotoluidine, melting at 192°-193°. On adding aniline to a hot, alcoholic solution of 7-trinitro- toluene, combination does not occur as in the case of the symmetric trinitrotoluene, but 7-dinitrotolylphenylamine is ob- tained, diazo-amidobenzene being probably simultaneously formed: CH3.C6H2(NO2)3+3C6H6.NH? = CH3.C6H2(NO2)2N(C6H5)H + C6H6N2.NH:C6H6 + 2H2O. This compound forms orange-coloured needles melting at 142°. 7-Trinitrotoluene is also readily attacked by caustic soda solu- tion, and it must, therefore, like /9-trinitrotoluene contain two nitroxyls in adjacent positions (Part III. p. 92). 1 Claus and Becker, Bar. Deutsch. Chem. Ges. xvi. 1596. 2 Hepp, Liebig's Ann. ccxv. 344. CHLORONITROTOLUENES. 19 CHLORONITROTOLUENES, C6H3C1(NO2)CH3. 2027 Parachlororthonitrotoluene (4 : 2) has been prepared from ordinary dinitrotoluene. It is slightly soluble in cold alcohol, readily volatilizes with steam, and crystallizes in needles melting at 38°. It is not attacked by chromic acid solution.1 Orthochloroparanitrotoluene (2:4). Wachendorff obtained this compound by heating paranitrotoluene with antimony chloride to 100°. It is very readily volatile in steam, dissolves freely in alcohol, and forms long, pointed crystals melting at 64°-65°. Potassium permanganate oxidizes it to chloronitrobenzoic acid.2 Lellmann has converted it into orthochlorotoluene and ortho- chlorobenzoic acid.3 Wachendorff found that metanitrotoluene could not be chlori- nated. Wroblevsky, by the action of nitric acid on crude liquid chlorotoluene obtained two liquid nitrochlorotoluenes;4 Engelbrecht, on the other hand, employing crystalline para- chlorotoluene, obtained two solid compounds which he was unable to separate completely.5 Parachlorometatoluene, (4 : 3) has been prepared from meta- nitroparatoluidine by means of the diazo-reaction, and is identical with one of Wroblevsky's compounds. It is a strongly refractive, golden-yellow liquid, which boils at 260°-261° and solidifies at a low temperature to yellow needles melting at 70.6 BROMONITROTOLUENES, C6H3Br(NO2).CH3.7 Br : N02 Melting-point. 2 : 5 crystals . . 76-3° 2 : 4 needles . . 74°-75° 3 : 2 liquid . . - 3 : 5 prisms8 . . 86° 5 : 2 rhombic crystals9 . . . . . 55° 4 : 2 fine needles 10 .... . . . 45°'5 4 : 3 crystals . . 31°-32° 1 Beilstein and Kuhlberg, Ann. Chem. Pharm. clviii. 336. 2 Ibid, clxxxv. 273. 3 Ber. Deutsch. Chern. Ges. xvii. 534. 4 Ann. Chern. Pharm. clxviii. 203. 8 Ber. Deutsch. Chem. Ges. vii. 797. 6 Gattermann and Kaiser, ibid, xviii. 2599. 7 Neville and Winther, ibid. xiv. 417. 8 Wroblevsky, Ann. Chem. Pharm. cxcii. 203. 9 Grete, ibid, clxxvii. 246. 10 Beilstein and Kuhlberg, Hubner and Roos, Ber. Deutsch. Chem. Ges. vi. 799. 20 AROMATIC COMPOUNDS. TOLUENESULPHONIC ACIDS. Toluenemonosulphonic Acids, C6H4(SO3H).CH3. 2028 By the action of fuming sulphuric acid on toluene, Deville obtained a monosulphonic acid (Acide sulfobenzo^nique) in small, deliquescent crystalline plates, and prepared some of its salts. Later researches have shown that in this way toluene- parasulphonic acid is formed together with a little toluene-ortho- sulphonic acid.1 If, however, concentrated sulphuric acid be allowed to run into boiling toluene, only the para-acid is formed,2 while all the three isomeric sulphonic acids, together with their chlorides, are formed by the action of chlorosulphonic acid on toluene :3 /Cl 2C6H5.CH3 + 3SO< " \OH zCH3 zCH3 zOH = C6H4< + C6H4< +SOo< + 2HC1. xSO3H \SO2C1 \QH The product is poured into ice-cold water, the chlorides separating as oily liquids. After some time the toluenepara- sulphonic chloride crystallizes out and is removed, an additional amount of this being obtained by repeatedly cooling the liquid. It is then purified by re-crystallization from pure ether and decom- posed by boiling with water. The liquid chlorides are converted into the amides by treatment with ammonia, and these are then separated by fractional distillation and converted into the acids by heating with hydrochloric acid to 140°-150°. The ammo- nium salts which are obtained by the evaporation of the solu- tions are converted into the barium salts, from which either the free acids or other salts can be prepared. The aqueous solution from which the chlorides have been separated is treated with milk of lime, the calcium salts of the acids being thus formed ; the potassium salts are prepared from these, converted into the sulphonic chlorides by the action of phosphorus pentachloride and these separated as just described. 1 Engelhardt and Latschinow, Zeitschr. Chern. 1869, 67. 2 Chrustschow, Ber. Deutsch. Chem. Ges. vii. 1167. 3 Claesson and Wallin, ibid. xii. 1848 ; Claesson, ibid. xvii. Ref. 283. TOLUENESULPHONIC ACIDS. 21 The meta- and ortho-sulphonic acids can also be obtained from the three toluidines, which are converted by fuming sulphuric acid into the following sulphonic acids : ch3 ch3 ch3 /\nh2 |/\so3h Z\ \/SO3h \/NH2 \/'so3H. nh2 The toluenesulphonic acids are then obtained from these by replacing the amido-group by hydrogen; they can also be pre- pared by the action of sulphur dioxide on the diazo-compounds of the toluidines : 1 zCH3 zch3 c6h4< + so2 + h2o = c6h4< + HC1+n2. \N = NCI " xSO2.OH. Tolueneparasulphonic acid, C6H4(CH3)SO3H + H2O, crystallizes in thick deliquescent tablets or flat prisms. Tolueneparasulphonic chloride, C6H4(CH3)SO2C1, crystallizes from ether in rhombic tablets, and is only slowly decomposed by water. Tolueneparasulphonamide, C6H4(CH3)SO2.NH2, forms small crystalline plates melting at 136°, which are slightly soluble in water, more readily in alcohol. A solution of this compound in the necessary amount of caustic potash yields on evaporation a residue from which alcohol extracts the compound C0H4(CH3) SO2.NHK+H2O, crystallizing in needles.2 Toluenemetasulphonic acid, CcH4(CH3)SO3H + H2O, forms very deliquescent, thin crystalline crusts. Toluenemetasulphonic chloride, C6H4(CH3)SO2C1, is an oily liquid. Toluenemetasulphonamide, C6H4(CH3)SO2.NH2, crystallizes in long plates melting at J07°-108°. Toluene-or thosulphonic acid, CGH4(CH3)SO3H+2H2O, forms thin deliquescent plates; the chloride is an oily liquid, and the amide crystallizes in quadratic pyramids or prisms, which are almost insoluble in cold water, and only slightly soluble in alcohol. The salts of the three acids as a rule crystallize well (Claesson and Wallin). 1 Muller, Bar. Deutsch. Chern. Ges. xii. 1348. 2 Hakansson, ibid. v. 1084 ; Claesson and Berg, ibid. xiii. 1170. 22 AROMATIC COMPOUNDS. Toluenedisulphonic Acids, C6H3(CH3)(SO3H)2. 2029 a-Tolucnedisulphonic acid (CH3: SO3H : SO3H=1 : 2; 4), is a thick liquid which can be heated above 100° without de- composition ; it may be prepared by heating toluene, or its ortho- and para-suIphonic acids with fuming sulphuric acid,1 as well as by passing toluene vapour into concentrated sulphuric acid heated to 24O0.2 Its amide, C6H3(CH3)(SO2.NH2)2 is tolerably soluble in warm water, and crystallizes in prisms melting at 185°-186°. Senhofer and Forber, by heating toluene with a mixture of sulphuric acid and phosphorus pentoxide, obtained a 7-toluene- sulphonic acid,3 which is, according to Claesson, identical with the a-acid.4 ft-Toluenedisidphonic acid is obtained in small quantities in the preparation of the a-compound, and is also formed when toluenemetasulphonic acid is treated with fuming sulphuric acid (Hakansson). Its amide melts at 224° (Claesson). y-Tolucn<disulphonic acid (1:3:5). When orthotoluidine is heated with fuming sulphuric acid or with chlorosulphonic acid, toluidinedisulphonic acid (CH3 : NH2 : SO3H : SO3H = 1 :2 : 3 : 5) is formed; this yields a crystalline diazo-compound, CH3.CGH2 (N2SO3)SO3H, which is, according to Neville and Winther, con- verted into the toluenedisulphonic acid by heating with absolute alcohol under pressure,5 while Limpricht and Hasse observed that ethoxytoluenedisulphonic acid, CH3.C6H2(OC2H5)(SO3H)Q is thus formed. In order to obtain the former, the diazo-com- pound is converted into iodotoluenedisulphonic acid, and this heated with concentrated hydriodic acid. 7-Toluenedisulphonic acid forms an amide which crystallizes in small lustrous plates melting above 24O0.6 Toluenetrisulphonic Acids, C6H2(CH3)(SO3H)3. Only one of the six tolucnetrisulphonic acids which are theo- retically possible is known; it is obtained by gradually heating 1 Hakansson, Ber. Deutsch. Chern. Ges. v. 1084 : Claesson and Bey, ibid. xiii. 1170. 2 Gnehm, ibid. x. 542 ; see also Fahlberg, ibid. xii. 1052. 8 Ann. Chern. Pharm. clxiv. 226. 4 Ber. Deutsch. Chern. Ges. xvii. Ref. 284. 5 Ibid. xv. 2993. « Ibid, xviii. 2177. THE CRESOLS. 23 potassium a-toluenedisulphonate with three molecules of chloro- sulphonic acid to 240°, until the product forms a clear solution in water. The barium salt is then prepared, and from this the potassium salt, which is converted by the action of phos- phorus pentachloride into toluenetrisulphonic chloride, CcH2 (CH3)(SO2C1)3, which crystallizes from chloroform in rhombic tablets melting at 153°. On heating with water to 130° -140° the free acid is obtained; it crystallizes with six molecules of water in long, fine needles.1 MONOHYDROXYTOLUENES AND ALLIED BODIES. CH3 The Cresols, C6H4<f \OH. 2030 In 1851 Stadeler discovered in the urine of the cow, together with phenylic acid, a very similar body which he named Tartrylic acid, and considered to be the next higher homologue of phenylic acid.2 As the question was subsequently raised whether the creosote discovered by Reichenbach in wood-tar is identical with phenol or not, Fairlie, under Williamson's directions, con- ducted an investigation on the so-called coal-tar creosote (Part III. p. 70) and found in it " hydrate of cresylf C7H8O, the homologue of phenyl hydrate; he describes this compound as a strongly refractive liquid smelling like phenol and boiling at 203°, and investigated its properties with some care.3 Duclos discovered the same compound in tar from pine-wood4 and Marasse in that from beech-wood.5 Griess obtained cresol or cresyl alcohol artificially by boiling diazotoluene nitrate with water,6 and Wurtz by fusing toluene- sulphonic acid with caustic potash.7 Engelhardt and Latschinow were the first to prove that three isomeric cresols exist; they obtained pure paracfesol, or, as they called it, a-cresol, by fusing tolueneparasulphonic acid with caustic potash, and from ordinary toluidine by Griess' reaction. By the same reactions they prepared /3-cresol from the ortho- 1 Claesson, Ber. Deutsch. Chem. Ges. xiv. 307. 2 Ann. Chem. Pharm. Ixxvii. 188. 3 Chem. Soc. Journ. vii. 232. * Ann. Chem. Pharm. cix. 135. 5 Ibid. clii. 64. 6 Jahresber. 1866, 458. 7 Ann. Chem. Pharm. cxliv. 121. 24 AROMATIC COMPOUNDS. sulphonic acid and pseudotoluidine (orthotoluidine), but they did not obtain it in a pure state. They further found that thymol, C6H3(CH3)(C3H7)OH, on heating with phosphorus pent- oxide, decomposes into propylene and 7-cresol.1 This metacresol was then obtained in larger quantities by Oppenheim and Pfaff by heating hydroxyuvitic acid with lime.2 Kekuld obtained pure orthoeresol by acting with nitrous acid on orthoibluidine and by heating carvacrol (cymophenol), an isomeride of thymol, with phosphorus pentoxide.3 The constitution of the three cresols was determined with certainty by Barth, who showed that on fusion with caustic potash, orthocresol is oxidized to salicylic acid, metacresol to hydroxybenzoic acid, and paracresol to parahydroxybenzoic acid (Part III. p. 45).4 Further investigations have shown that the cresol contained in coal-tar is a mixture of the three isomerides.5 It is obtained from the oily mother-liquor left after crystallization of the phenol by dissolving in caustic soda, removing all naphthalene by a current of steam, and then fractionally precipitating the solution with hydrochloric acid ; the cresol separates out first, the phenol, being a stronger acid, remaining in solution.6 Ac- cording to another method, the solution is neutralized with hydrochloric acid and the mixture agitated with sufficient baryta water to dissolve all the phenol.7 The cresol obtained is purified by distillation until it boils at 198° -203°. Deriva- tives of all three cresols can be prepared from it, but only the para-compound can actually be extracted in the pure condition. This is effected by treating the mixture with benzoyl chloride, paracresyl benzoate, melting at 78°, being formed; this is sepa- rated by pressing from the liquid ethers of the two other cresols, purified by re-crystallization, and decomposed by caustic soda (Engelhardt and Latschinow). Baumann has pointed out that the cresol (taurylic acid) contained in the urine of graminivora occurs as the potassium salt of paracresylsulphuric acid.8 This compound also occurs in human urine during scarlatina, ery- sipelas, &c.9 The urine of horses also contains some orthocresyl 1 Zeitschr. Chern. 1869, 618. 2 Ber. Deutsch. Chem. Ges. viii. 884. 3 Ibid. vii. 1006. 4 Ann. Chem. Pharm. cliv. 356. 8 Schotten and Tiemann, ibid. xi. 783. 6 Muller, Zeitschr. Chem. 1865, 271. 7 Ihle, Journ. Prakt. Chem. [2] xiv. 442. 8 Ber. Deutsch. Chem. Ges. ix. 1389, 1716. 9 Brieger, Hoppe-Seyler's Zeitschr. iv. 204. ORTHOCRESOL. 25 sulphuric acid.1 Para- and ortho-cresol are also formed when the liver of the horse is caused to putrefy with the addition of river-mud.2 2031 Orthocresol is best obtained by adding 12 parts of pure potassium nitrite to a solution of 15 parts of orthotoluidine and 15 parts of sulphuric acid in 500 parts of water; the liquid is heated by a current of steam, and the cresol distilled off in the steam.3 It forms colourless crystals, melts at 30° and boils at 188°. Its aqueous solution is coloured blue by ferric chloride; on fusion with caustic potash it is oxidized to salicylic acid. When administered to a dog it appears in the urine as ortho- cresylsulphuric acid and oxycresylsulphuric acid (hydrotolu- quinonesulphuric acid). By the action of potassium chlorate and hydrochloric acid it yields di- and tri-chlorotoluquinone.4 Orthocresyl oxide, (CH3.CGH4)2O. If a few grains of iodine and then some aluminium are added to boiling orthocresol, alu- minium orthocresylate, (CH3.C6H4O)GA12, is formed, and this solidifies on cooling to a black vitreous mass. When subjected to dry distillation it yields, among other products, orthocresol and orthocresyl oxide, which is a colourless liquid smelling like the geranium, and boiling at 272° - 278°.5 Dichlor orthocresol, CGH2C12(CH3).OH, is obtained by the action of chlorine on boiling orthocresol; it crystallizes from alcohol in needles with a silky lustre, melts at 55° and on oxidation under- goes partial combustion, at the same time yielding trichloro- toluquinone.6 Bromorthocresol, CGH3Br(CH3)OH, has been prepared from bromorthotoluidine, and crystallizes from alcohol in lustrous golden needles melting at 88'5°.7 a-Nitro-orthocresol, C6H3(CH3)(NO2) OH(1 : 3 : 2), is formed when a solution of 2 parts of orthocresol in 2 parts of glacial acetic acid is allowed to drop into a cold mixture of 3 parts of nitric acid, of specific gravity 1*4, and 6 parts of glacial acetic acid. It is insoluble in water and crystallizes from dilute alcohol in long, yellow prisms melting at 69'5°. Its potassium salt crystallizes in garnet-red, rhombic tablets. When the hydrochloride of the amidocresol obtained from 1 Preusse, ibid. ii. 355 ; Ber. Deutsch,. Chcm. Ges. xi. 1911. 2 Baumann and Brieger, Hoppe-Seyler's Zeitschr. iii. 149, 252. s Schotten and Tiemann, loc. cit. 4 Southworth, Ann. Chern. Pharm. clxviii. 273. 5 Gladstone and Tribe, Journ. Chern. Soc. 1886, i. 25. 6 Claus and Riemann, Ber. Deutsch. Chem. Ges. xvi. 1598. 7 Wroblevsky, Ann. Chem. Pharm. clxviii. 165. 26 AROMATIC COMPOUNDS. this compound is distilled with sodium formate, a methenyl compound is formed ; this reaction is characteristic of all the amidophenols in which the amido-group is in the ortho-relation to the hydroxyl.1 Mcthcnylamidorthocresol is formed according to the following equation : zNH2 n CH3.C6H3< 4- CHO.OH = CH3.C6H3< ^CH + 2H2O. \OH \OZ It is a crystalline mass which melts at 38°-39°, boils at 200° and has a peculiar smell, resembling that of acetamide, charac- teristic of these anhydro-bases. A liquid nitrocresol boiling at 226°-230° is formed together with the solid compound.2 ft-Nitro-orthocresol (1:5:2) is prepared from the corresponding nitro-orthotoluidine by means of the diazo-reaction or by heating it with strong caustic soda. It crystallizes in fine, light yellow needles and melts at 95°.3 On reduction it yields ft-amido- orthocresol, the hydrochloride of which crystallizes readily. ry-Nitro-orthocrcsol (1 : 4 :2) is formed together with the a-com- pound when orthocresol is nitrated at as low a temperature as possible. On distillation with steam it remains behind. It is only very slightly soluble in water, readily in alcohol and ben- zene, and crystallizes in white needles united to form bushy aggregates, or in small, hexagonal tablets, being, therefore, dimorphous like paranitrophenol. It melts at 82°-85°, and forms a potassium salt, crystallizing in small brass-yellow plates. On reduction it is converted into 7-amido-orthophcnol, crystallizing in tablets which have a silvery lustre and melt at 175°. When oxidized in an acid solution, it is converted into toluquinone. Hirsch has been unable to obtain the liquid nitro- cresol mentioned above.4 Dinitro-orthocresol, C6H2 (CH3) (NO2)2 OH (1: 3 : 5 : 2), was first obtained from orthotoluidine, nitro-orthotoluidine (NH2: NO2 = 2 : 5), and orthotoluidinesulphonic acid (NH2: SO3H = 2:3), by converting them into diazo-compounds and heating these with dilute nitric acid.5 It is also formed by the further nitration of 1 Ladenburg, Ber. Deutsch. Chern. Ges. ix. 1524 ; x. 1124. 2 Hofmann and Miller, ibid. xiv. 467. 3 Neville and Winther, ibid. xv. 2978. 4 Hirsch, ibid, xviii. 1511. B Neville and Winther, ibid. xiii. 1496 ; Nolting, and Salis, ibid. xiv. 987. METACRESOL. 27 a- and 7-nitro-orthocresol (Hirsch), and of orthocresyl ether.' It crystallizes from alcohol in long, yellow prisms, and from petroleum-spirit in broad, golden-yellow needles, which have a blue surface-lustre and melt at 86°. On the reduction of its ethyl ether the diamido-ether is obtained, and this compound forms a chrysoidine with diazo- benzene (Part III. p. 301), thus affording a further proof that the nitroxyl groups in dinitrocresol have the meta-relation to each other. 2032 Metacresol. In order to prepare this compound, 100 grammes of thymol are heated for ten or twelve hours with 35 grammes of phosphorus pentoxide, the propylene which is evolved being passed into bromine in order to obtain its bromide as a by-product. The syrupy mass is brought into 115-120 grammes of fused caustic potash, and the mixture kept in a state of fusion and well agitated for five or ten minutes. It is then dissolved in water and extracted with ether in order to remove cresyl phosphate and other substances; the residue is then decomposed with hydrochloric acid, the metacresol taken up with ether, the latter distilled off, and the product purified by distillation in a current of carbon dioxide (Schotten and Tiemann). It is a liquid which smells like phenol, boils at 201° and does not solidify in a freezing mixture; if, however, a crystal of phenol be thrown into the cooled liquid it solidifies immediately, form- ing crystals resembling those of phenol and melting at 3°-4°.2 Its aqueous solution is coloured violet to blue by ferric chloride; by the action of potassium chlorate and hydrochloric acid, it is converted into dichlorotoluquinone (Southworth). Mctacresyl oxide, (CH3.C6H4)2O, is formed, together with pro- pylene and other products by the dry distillation of aluminium thymol, (C3H7(CH3)C6H3O)6A12, and is a liquid boiling at 284°-288°.3 Bromometacresol, C6H2Br(CH3)OH (1:3:5), has been pre- pared from the corresponding bromotoluidine, and crystallizes from hot water in white needles melting at 56°-57°.4 Nitrometacresol, C6H3(CH3)(NO2)OH (1:3: 5), is prepared from symmetric dinitrotoluene ; it crystallizes from hot water in light yellow, lustrous prisms, containing one molecule of water 1 Stadel, Ann. Chern. Pharm. ccxvii. 158. 2 Stadel, Ber. Deutsch. Chern. Ges. xviii. 3443. 3 Gladstone and Tribe, Journ. Chem. Soc. 1882, i. 5. 4 Neville and Winther, Ber. Deutsch. Chem. Ges. xv. 2991. 28 AROMATIC COMPOUNDS. of crystallization. It is deposited from solution in benzene in anhydrous crystals melting at 90°-91°. On reduction it yields amidometacresol, the hydrochloride of which is readily soluble.1 Trinitrometacresol, C6H(NO2)3(CH3)OH (NO2 : NO2: NO2 = 2 : 4 : 6), was obtained by Duclos from crude cresol; Nolting and Salis have prepared it from metacresol, which is readily converted into the trinitro-compound, while its isomerides yield the dihitrocresols as final products. In order to prepare it, coal-tar cresol is dissolved in 3 parts of concentrated sulphuric acid, and allowed to stand in a warm place until cresol no longer separates out on the addition of water. Crude nitric acid is then gradually added to the aqueous solution, which is subsequently evaporated, the residue being extracted with a little water to remove picric and oxalic acids, and repeatedly re-crystallized from alcohol.2 Liebermann and van Dorp obtained it by heating nitrococ- cussic acid,3 C6(NO2)3(CH3)(CO2H)OH, and Emmerling and Oppenheim by the action of nitric acid on hydroxyuvitic acid, C6H2(CH3)(CO2H) OH.4 Trinitrometacresol is slightly soluble in cold, somewhat more readily in hot water, and crystallizes in long, yellow needles melting at 105°-106°. When its ethyl ether is heated with alcoholic ammonia, no nitrous acid is removed (Nolting and Salis), which proves that it contains no nitroxyl groups in the ortho-relation (Part III. p. 63), and, therefore, that trinitrometacresol has the following constitution : CH3 no/\,no2 H\/0H no2 2033 Paracresol is most readily obtained from paratoluidine, as orthocresol is from orthotoluidine; it crystallizes in prisms melting at 36°, and boils at 198°; its aqueous solution is coloured blue by ferric chloride. It differs from its isomerides in not yielding a chlorinated toluquinone by the action of potassium chlorate and hydrochloric acid. Paracresyl oxide (CH3.C6H4)2O, has been prepared by Gladstone and Tribe in the same manner as the ortho-compound, 1 Ber. Deutsch. Chem. Ges. xv. 2978. 2 Beilstein and Kellner, Ann. Chem. Pharm. cxxviii. 165. 3 Ibid, clxiii. 101. 4 Ber. Deutsch. Chem. Ges. ix. 1094. PARACRESOL. 29 anti is also formed by heating paracresol to 300° with zinc chloride. It crystallizes from alcohol in small lustrous plates, and from petroleum spirit in needles which have a silky lustre, and melt at 165°, but readily volatilize at 1000.1 Chloroparacresol, C6H3(CH3)C1(OH) (1: 3: 4), is formed by the action of dry chlorine on anhydrous sodium paracresate. It is a colourless liquid which boils at 195°-196°, and has a peculiar, unpleasant, persistent odour. Phosphorus pentachloride converts it into a dichlorotoluene, which yields on oxidation the ortho- dichlorobenzoic acid melting at 200°.2 Dichloroparacresol, C6H2(CH3)C12.OH, is formed by the action of chlorine on boiling paracresol; it crystallizes from alcohol in monoclinic needles, and from a hot, concentrated solution in petroleum-ether in long needles melting at 39°; on the gradual evaporation of a dilute solution, it is obtained in transparent prisms with a melting point of 42°; these, however, soon fall to pieces, and the product then melts at 39°. On oxidation the dichlorobenzoic acid melting at 156° is formed (Claus and Riemann). Bromopar acresol, C6H3(CH3)Br(OH) (1:3: 4), is obtained by the action of bromine on potassium paracresate. It is a liquid which does not solidify in a freezing mixture, boils at 213°-214°, and has a less unpleasant smell than the chlorine compound (Schall and Dralle). Bromoparacresol (1: 2 : 4) may be readily obtained by the action of bromine on a solution of paracresol in chloroform ; it crystallizes in needles, melting at 17°-<8°, and boils at 218°-220°. On fusion with caustic potash it is converted into lutorcinol, CcH3 (CH3) (OH)2.3 Dibromoparacresol, C6H2(CH3)Br2(OH), is also formed when potassium paracresate is treated with bromine. It crystallizes from alcohol in prisms which are isomorphous with dichloropara- cresol and melt at 49° (Schall and Dralle). lodoparacresol, C6H3(CH3)I(OH) (1 : 3: 4), is an oily liquid, and is obtained by the action of iodine on potassium paracresate ; on fusion with potash it yields protocatechuic acid, C6H3(OH)2 CO2H, and catechol. Di-iodopar acresol, C6H2(CH3)I2(OH), is formed in the pre- paration of the mono-compound, and crystallizes in small tablets melting at 61'5° (Schall and Dralle). 1 Buch, Ber. Deutsch. Chern. Ges. xvii. 2638. 2 Schall and Dralle, ibid. xvii. 2528. s Vogt and Henninger, ibid. xv. 1081, 30 AROMATIC COMPOUNDS. a-Nitroparacrcsol, C6H3(CH3)(NO2)OH (1:3: 4), is obtained by boiling nitracetparatoluide with caustic soda,1 and by the nitration of paracresol.2 It is slightly soluble in water, readily in alcohol, and crystallizes in flat, yellow needles, which melt at 33'5°, and are volatile in steam. a- Amidopar acresol, C6H3(CH3)(NH2)OH (1:3: 4) is formed by the reduction of the nitro-compound with tin and hydro- chloric acid; it crystallizes from ether in monoclinic prisms, and when heated with formic acid yields methenylamidoparacresol, melting at 45° (Hofmann and Miller). (3-Nitroparacresol, (CH3 : NO2: OH = 1: 2 : 4), is prepared from ordinary dinitrotoluene by reducing it with ammonium sulphide to nitrotoluidine and then replacing the amido-group by hy- droxyl. It forms long yellow crystals which melt at 78° and are readily soluble in hot water and alcohol.3 (3-Amidoparacresol, (CH3 : NH2: OH =1:2:4), is obtained by the reduction of the preceding compound, and crystallizes from hot water in small plates melting at 143°-144°.4 y-Amidoparacrcsol, (CH3:NH2:OH = 1:4:2). The hydro- chloride of this base is obtained by converting the monacetyl compound of the corresponding diamidotoluene into acetamido- cresol, C6H3(CH3)OH(NH.C2H3O) and boiling this with hydro- chloric acid. It crystallizes in small glistening plates, and on treatment with potassium bicarbonate yields the free base, which forms small lustrous plates or needles, melting at 159°-161° (Wallach). The constitution of the substituted paracresols follows from their conversion into dihydroxytoluenes. Dinitroparacresol, C6H2(CH3)(NO2)2OH(1 :3 :5 :4), has been prepared from the corresponding dinitrotoluidine and by the nitration of cresolsulphonic acid.5 It is also obtained by warming the diazo-compound prepared from paratoluidinesulphonic acid with nitric acid (Neville and Winther), and by the nitration of paracresol ethyl ether; it crystallizes from dilute alcohol in yellow needles melting at 85°. On the reduction of its ethyl compound, diamidoparacresyl ether, C6H2(CH3)(NH2)2OC2H5, is 1 Wagner, Bar. Deutsch. Chern. Ges. vii. 537; Neville and. Winther, ibid. xv. 2893. 2 Armstrong and Thorpe, Jahresb. Chem. 1876, 452 ; Hofmann and Miller, toe. cit. 3 Knecht, Ann. Chem. Pharm. ccxv. 83 ; Ber. Deutsch. Chem. Ges. xv. 298. Neville and Winther, ibid. xv. 2980. 4 Wallach, ibid. xv. 2831. 5 Armstrong and Field, Ber. Deutsch. Chem. Ges. vi. 974. DIHYDROXYTOLUENES. 31 obtained ; this compound forms a chrysoidine with diazobenzene chloride, proving that the nitroxyls of the dinitrocresol are in the meta-relation to each other. Potassium dinitropar acresate, C6H2(CH3)(NO2)2OK, crystallizes in red needles and forms the " golden yellow," which was exhibited as a new dye in the Belgian section of the Vienna Exhibition in 1873.1 It is also, together with the potassium salt of dinitro-ortho- cresol, contained in " safronsurrogate," which is used for colouring milk, butter, and cheese.2 Victoria yellow or aniline orange, which formerly came into the market as a red powder, is the salt of a third dinitrocresol, the constitution of which is unknown. It crystallizes from hot water in yellowish needles, melting at 109°-IIO0.3 Thiocresols, C6H4(CH3)SH, are obtained by the reduction of the corresponding sulphonic chlorides. Orthothiocresol4 Melting- Boiling- point. point, small, delicate plates . 15° 188° Metathiocresol5 liquid . . - 188° Parathiocresol6 large plates . . . . . 43° 189° DIHYDROXYTOLUENES AND ALLIED BODIES. Homocatechol, or Homopyrocateciiin, C6H3(CH3)(OH)2 (1:3:4). 2034 Hugo Muller obtained this compound by heating its monomethyl ether, creosol, with hydriodic acid :7 zch3 zch3 c6h<-oh +hi=c6h3<oh + ch3l \och3 \oh It is also formed by fusing creosol with caustic potash,8 by boiling the diazo-compound of a-amidocresol with water (Neville 1 Piecard, Ber. Deutsch. Chern. Ges. viii. 685. 2 Wichelhaus, ibid. vii. 770. 3 Martius and Wichelhaus, ibid. ii. 206. 4 Hiibner and Post, Ann. Chcm. Pharm. clxix. 30. 5 Ibid. 6 Marcker, ibid, cxxxvi. 79. 7 Chem. News, x. 269. 8 Tiemann an I Koppe, Ber. Deutsch. Chem. Ges. xiv. 2025. 32 AROMATIC COMPOUNDS. and Winther), and by submitting a-homoprotocatechuic acid, C6H2(CH3)(OH)2CO2H, to dry distillation.1 Homocatechol is a syrup which readily dissolves in water, alcohol, ether, and benzene, and can be distilled without decomposition. It reduces silver salts and Fehling's solution in the cold, and gives a green colouration with ferric chloride, which is converted into a reddish violet by the addition of a little ammonia or carbonate of soda. Homocatechol monomethyl ether or Creosol, C6H3(CH3)(OCH3) OH(1: 3:4), occurs in beechwood-tar-creosote and in the pro- ducts of distillation of guaiacum resin.2 In order to prepare it, the portion of creosote boiling at about 220° is dissolved in ether and treated with very concentrated alcoholic potash; potas- sium creosate, C8H9KO2 + 2H2O, separates out in needles and is then decomposed by dilute sulphuric acid. It may also be prepared by heating a-homovanillic acid, C6H3(OH)(OCH3)CH2. CO2H, with lime (Tiemann and Nagai). It is a strongly re- fractive liquid boiling at 220°, and possesses a feeble odour which resembles that of vanilla and is very pleasant when the vapour is dilute. It produces a metallic mirror when warmed with a solution of a silver salt, and its alcoholic solution is coloured emerald-green by ferric chloride. Phosphorus chloride converts it into parachlorometacresol methyl ether, C6H3C1(CH3)OCH3, (CH3: OCH3: Cl = l : 3 :4), a liquid boiling at 185°.3 - Homocatechol dimethyl ether, C6H3(CH3)(OCH3)2, also occurs in creosote, and is obtained pure by boiling potassium creosate with methyl iodide and wood-spirit. It is a liquid which boils at 214°-215° and possesses the characteristic smell of the indif- ferent oils which are obtained from crude wood-tar. It is insoluble in water and alkalis, and is not coloured by ferric chloride.4 2O35 Creosote was discovered by Reichenbach in the year 1832, both in the tar and the pyroligneous acid obtained by the distillation of beech-wood.5 He describes it as a colourless, strongly refractive liquid, which begins to boil at 203° and possesses an unpleasant penetrating odour, at the same time resembling that of smoked meat, and a burning taste. He investigated its properties very carefully, and found that it 1 Tiemann and Nagai, Ber. Deutsch. Chern. Ges. x. 210. 2 Hlasiwetz, Ann. Chcm. Pharm. cvi. 339. 3 Biechele, ibid. cli. 115. 4 Tiemann and Mendelsohn, Ber. Deutsch. Chern. Ges. viii. 1136. B Schweiger's N. Jahrb. Chcm. Phys. vi. 301, 345 ; vii. 1, 57 ; viii. 57, 399. CREOSOTE. 33 coagulates albumin, and that fresh meat which has been soaked in creosote for half an hour to an hour can be dried without undergoing putrefaction. Such meat is very tasty, and Reichenbach therefore concluded that creosote is the antiseptic principle contained in smoke. He derived its name from this power of preserving meat, its most peculiar and most striking pro- perty, one too which had been known from the earliest times ; he remarks, " The Greek word Kpeas, meat, has a genitive Kpearos, or Kpeaws, contracted to Kpew$ ; crco^co signifies to preserve, or save; the two may be etymologically united in the word creosote, which expresses meat-preserving or decay-saving." Very soon after this, Runge discovered carbolic acid, and Laurent phenyl hydrate, in coal-tar, the identity of these bodies hems' recognised somewhat later. No clear views, however, were held as to the relation existing between phenol and creosote, and a confusion arose which was maintained for many years with an obstinacy unparalleled in the annals of our science. Runge and Laurent showed that creosote, in spite of many similarities, is quite a different substance from the compound obtained by them. Phenol differs from creosote more especially in being an acid, in possessing a different boiling-point, in crystallizing when cooled, and in its different behaviour towards chlorine, bromine, and nitric acid. Runge moreover adds that it imparts to meat preserved by it an abominable taste. Reichenbach, nevertheless, considered carbolic acid to be identical with his creosote, the more so as he thought that he had also discovered it in coal-tar and bone-oil. Gmelin was also of this opinion; according to him, carbolic acid, phenyl hydrate, and creosote, are chemically identical, dif- fering only in degree of purity. Gmelin's views found universal acceptance ; crystallized carbolic acid soon came into the market under the name of creosote and displaced the genuine substance obtained from wood-tar. Gorup-Besanez, who had some of the latter body, which had been prepared by Reichenbach at Blansko, in Moravia, at his disposal, compared it with " crystallized creosote," and, like Runge and Laurent, found them to be completely different; the amount of substance in his possession, however, did not admit of a close investigation. Some years later, Batka supplied him with fresh samples of creosote from Blansko, and he found that when acted upon by nitric acid, no picric acid was formed, while potassium chlorate 34 AROMATIC COMPOUNDS. and hydrochloric acid, instead of giving chloranil, C6C14O2, gave a similar substance, which, however, contained hydrogen.1 These results, however, attracted but little attention; Gmelin, indeed, mentions them in his hand-book, but only to add that Gorup-Besanez, to prove that creosote is a distinct substance, ought to have prepared it himself instead of investigating a commercial product. Two years later, Gorup-Besanez published a more extended treatise on creosote ; his determination of its composition agreed with that of Ettling, who had analysed a specimen sent by Reichenbach to Liebig. By the action of chlorine he obtained pentachloroxylone, C13H7C15O3, and hexchloroxylone, C13H6C1cO3, substances which were very similar to the chlorinated quinones obtained by Stiideler.2 About the same period Volkel published a paper - on the distillation products of wood, in which he relates his investi- gation of the creosote obtained from the tar in a pyroligneous acid works at Solothurn. He purified it by repeated solution in caustic potash, precipitation with sulphuric acid and distillation. The liquid, after purification in this manner, boiled at 202°- 208°, and in its general properties resembled Reichenbach's compound, but had a different composition, as the following results of the analyses conducted by Ettling, Gorup-Besanez, and Volkel show : 3 Carbon . . . . Creosote from Blansko. (Mean of 8 Analyses.) . . 75-21 Creosote from Solothurn. (Mean of 3 Analyses.) 7245 Hydrogen . . , . . . 7-90 7-10 Oxygen . . . . . . 16-89 20-45 100-00 100-00 Deville had previously analysed creosote prepared by Pelletier, and obtained numbers only differing slightly from those of Volkel. Volkel considered that Gorup-Besanez had not purified his creosote sufficiently, whereupon the latter treated it repeatedly by Volk el's method, without, however, altering the results obtained by analysis to any appreciable extent.4 In the same year, Williamson published the results of an 1 Ann. Chem. Pharm. Ixxviii. 231. 2 Ibid. Ixxxvi. 233. 3 Ibid. Ixxxvi. 66, 93. 4 Ibid. xcvi. 39. HISTORY OF CREOSOTE. 35 investigation made by Fairlie towards the solution of the question whether coal-tar creosote consists chiefly of carbolic acid; he thus discovered the homologue of phenol, cresyl hydrate or cresol, which boils at 203°, or at nearly the same temperature as creosote, thus introducing a new source of confusion. The research had no direct bearing on the real issue. A new chapter in the history of creosote begins with Hlasi- wetz's investigation " On Beech-Wood Tar Creosote and the Products of Distillation of the Guaiacum Resin." He had already obtained the compound C8H10O2 from the creosote from Blansko, and now found it in the distillation products of guaiacum resin, together with its lower homologue, guaiacol, O 7 O O 7 O 7 C7H8O2, which Deville and Pelletier had already obtained from the same source; he therefore called his compound creosote- guaiacol or creosol. Hlasiwetz concluded that creosote is a kind of ether of the latter, and probably contains the radical C9Hn, thus simply explaining the fact that it contains more carbon than creosol. In the following year Duclos published a paper on cresyl alcohol, which he had not only found in coal-tar, but also in the tar from the gas-works at Giessen where only wood, and for the most part fir-wood, was used.1 In criticism of this paper, Gorup-Besanez observed that these results were in opposition to all the facts known concerning the distillation products of wood, in which no phenols had yet been found. If Duclos' results were to be accepted, it would be necessary to assume that fir-wood yields different products from beech-wood. In the meantime Gerhardt calculated the formulae of the chlorinated xylones as CaHKCL09 and CsH,Cl,Oo, according to which they appear to be homologues of the chloroquinones, thus confirming Hlasiwetz's results; Gorup-Besanez then undertook the reinvestigation of these compounds, but could not obtain any creosote from Blansko ; this source had failed. In the year 1864, Hugo Muller made an important addition to the history of creosote ; he investigated a sample which had been prepared in London from Stockholm-tar and appeared to be identical with that from Blansko. By treating it with hydriodic acid be obtained methyl iodide and homocatechol (p. 31). These different researches afforded a complete proof that wood-tar creosote has nothing in common with coal-tar creosotec 1 Ann. Chcm. Pharm. cix. 135. 36 AROMATIC COMPOUNDS. The only obstacles now remaining to a complete concordance of opinion on the subject were Reichenbach's statement, which he had never confirmed, that his creosote is contained in coal-tar, and that of Duclos that wood-tar contains phenols, which no one else had been able to detect. 2036 The creosote question seemed to have received a final answer, but it was nevertheless not yet settled. In the year 1865, A. E. Hofmann investigated several commercial products which he obtained from various firms as genuine beech-wood- tar creosote, and found that they consisted chiefly of phenol. Being unacquainted with the researches of Hlasiwetz and Muller, he called the existence of creosote in question and con- cluded that it was nothing but impure phenyl hydrate, the chlorinated xylones being mixtures of chloranil with chlorinated phenols. The name of creosote ought, therefore, to be removed from our list of chemical compounds, though this would not prevent its use as a commercial term. Gorup-Besanez replied to this by pointing out that Hofmann had only proved a fact which had long been known, that phenylic acid was often sold under the name of creosote. It was im- possible that the firms mentioned by him could have sent him genuine creosote, because this article had long disappeared from the German market.1 This incident had a fortunate conclusion both for Gorup-Besanez and for the facts. Fresenius corrected his statement, pointing out that the " Verein fur chemische Industrie " at Mayence worked up beech-wood-tar for creosote. The investigation of this showed that it differed from the Blansko samples, but was probably identical with those from Solothurn. Gorup-Besanez succeeded in extracting from it a considerable quantity of guaiacol together with a smaller amount of creosol; by the action of potassium chlorate and hydrochloric acid on the crude creosote he ob- tained tetrachloroguaiacone, C7H2C14O2, and tetrachlorocreosone, C8H4C14O2, homologues of chloranil. When he treated creosote with hydriodic acid, he obtained methyl iodide and catechol, which were undoubtedly derived from the guaiacol. He assumed that catechol is the lower homologue of guaiacol and creosol, both of which yield chlorine products homologous with chloranil. He concluded from his analysis that Rhenish creosote contains the radical C3H5.2 1 Journ. Prakt. Chern, xcvii. 63. 2 Ann. Chern. Pharm. cxliii. 129. ORCINOL. 37 Marasse opposed this view; Gorup-Besanez had thought that the fraction boiling between 199° and 208° is the allyl ether of guaiacol, the latter being derived from it by the action of caustic potash. If this were the,case, allyl alcohol or some similar com- pound must be simultaneously formed, whereas no one had hitherto observed this. Guaiacol, he continues, may be the methyl ether and not the homologue, of catechol, bearing the same relation to it as creosol to homocatechol. The difference between the composition of creosote and that of the two methyl ethers contained in it is easily accounted for on the supposition that it contains substances which boil at the same temperature as guaiacol and creosol but are richer in carbon and poorer in hydrogen. He also found that creosote contains, besides ordinary phenol, its homologues cresol and phlorol, which yield the chlorine pro- ducts now known as tetrachlorotoluquinone and tetrachloro- xyloquinone.1 The composition of creosote is very variable. Brauniger found in one sample only traces of phenol and less than 2 per cent, of cresol, and in that investigated by Gorup-Besanez only a little cresol and still less phlorol,2 while Tiemann and Mendelsohn found large quantities of the latter.3 The relative amounts of guaiacol and creosol are also subject to great variations ; thus Biechle found scarcely any creosol in a second sample of Rhenish creosote obtained by Gorup-Besanez.4 The higher boiling fractions contain, moreover, the dimethyl ethers of homocatechol, pyrogallol, dimethylpyrogallol, and propylpyrogallol, which have already been partially described. The presence of phenols in wood-tar-creosote shows that it is more closely related to the so-called coal-tar creosote than was previously supposed. The latter differs from the former by the absence of guaiacol, creosol, and the dimethyl ethers just men- tioned. These must be derived from the characteristic aromatic compounds which various chemists have discovered in wood (Vol. III. Pt. II. p. 583). ORCINOL, C6H3(CH3)(OH)2 (1:8: 5). 2037 Robiquet discovered this compound in 1829 in Vario- laria dealbata, and named it orcin, because this lichen had 1 Ann. Chem. Pharm. clii. 59 2 Ibid, clxxxv. 339. 3 Ber. Deutsch. Chem. Ges. x. 59. 4 Ann. Chem. Pharm. cli. 104. 234 38 AROMATIC COMPOUNDS. formerly been called Lichen orcina, and because the name serves as a reminder that the lichen is used for the preparation of archil (orseille).1 Orcinol was then further investigated by various other chemists,2 from whose analyses Gerhardt first calculated its correct formula,3 his result being confirmed by the researches of Stenhouse.4 Orcinol occurs in the free state in all the lichens, the various species of Rocclla, Lecanora and Variolaria, which are em- ployed for the preparation of archil and litmus, and is a decomposition product of various acids and ether-like bodies prepared from these lichens. When these compounds are heated with an alkali or submitted to dry distillation, orcinol is formed, e.g: Erythrin. Orsellinic Acid. C7H5(OH)2CO2X >C4H6(OH)2 + 2H2O = 2C7H5(OH)2CO2H C7H6(OH)2CO2z Erythrol. + C4H6(OH)4. Lecanoric Acid. Orsellinic Acid. C7H5(OH)O.CO2H I + H2O = 2C7H5(OH)2CO2H. C7H5(OH)2CO Orsellinic Acid. Orcinol. C7H6(OH)2CO2H = C7H6(OH)2 + co2. In order to prepare orcinol, 6 parts of Rocclla fuciformis are macerated for twenty minutes with 60 parts of milk of lime con- taining 1 part of lime, the mass filtered and the erythrin pre- cipitated from the filtrate by hydrochloric acid ; this is boiled for half an hour with a slight excess of milk of lime, the solu- tion filtered, treated with carbon dioxide to remove the excess of lime, and evaporated nearly to dryness. The orcinol is extracted from the residue by benzene, while erythrol is left behind. When the benzene solution is shaken with water, the orcinol is taken up by the latter and is obtained pure on evaporation.5 The crude 1 Ann. Chim. Phys. xlii. 236. 2 Dumas, Ann. Chern. Pharm. xxvii. 140 ; Liebig and Will, ibid, xxvii 147 ; Scliunk, ibid. xli. 159 ; liv. 269. 3 Compt. Rend. Chim. 1845, 287. * Phil. Trans. 1848, 63 ; 1849, 393. 3 Stenhouse. ORCINOL. 39 orcinol can also be purified by distillation,1 which is best carried on in vacuo.2, Vogt and Henninger first prepared orcinol from toluene, by chlorinating toluene in presence of iodine, and warming the chlorotoluene with two to three times its weight of sulphuric acid on the water-bath ; two sulphonic acids are thus formed, which readily admit of separation, the barium salt of the one being much more soluble than that of the other, which yields orcinol when fused with caustic potash.3 The chlorotoluene obtained by the method described is a mixture of parachlorotoluene with a little orthochlorotoluene; since, however, the side chains of orcinol are arranged symmetri- cally, an inter-molecular change must take place during its preparation just as in that of resorcinol from benzeneparadi- sulphonic acid. Neville and Winther obtained orcinol by fusing symmetric bromotoluenesulphonic acid, the toluenemetadisulphonic acid obtained from orthotoluidinedisulphonic acid, or bromometa- cresol with caustic potash; they also prepared it by heating metadibromotoluene to 280°-300° with caustic potash and a little water, and finally by replacing the amido-group of amido- metacresol by hydroxyl.4 Orcinol is also formed, together with parahydroxybenzoic acid, when aloes are fused with caustic soda.5 Properties -Orcinol is readily soluble in water, alcohol, and ether, and crystallizes with one molecule of water in six-sided monoclinic prisms, which effloresce gradually over sulphuric acid, and more rapidly when heated to 100°. It is almost completely precipi- tated in fine needles when its concentrated solution is warmed with a saturated solution of common salt (Lamparter) ; it reduces ammoniacal silver solution, has an intensely sweet but unpleasant taste, and melts in the anhydrous state at 106'5°-108° (Neville and Winther). When rapidly heated, it distils almost without decomposition between 287° and 290° (Dumas). Ferric chloride produces a violet-black colouration, and bleaching powder a dark red, soon changing to yellow. In the presence of ammonia and air it is converted into orcein, the colouring matter of archil, and becomes coloured a deep reddish violet (Robiquet). Its 1 Lampai'ter, ibid, cxxxiv. 215. 2 De Luynes, Ann. Chim. Phys. [4] vi. 184. 3 Ann. Chern. Pharm. clxv. 366 ; Bull. Soc. Chim. xxi. 373. 4 Ber. Deutsch. Chern. Ges. xv. 2976. 5 Barth and Hlasiwetz, Ann. Chern. Pharm. cxxxiv. 288. 40 AROMATIC COMPOUNDS. alkaline solution when heated with a little chloroform becomes coloured first purple-red and then bright red, and on dilution with water has an intense greenish yellow fluorescence, homo- fluorescein, C23H18O5, being formed. This reaction is so delicate that the compounds which yield orcinol can readily be detected in the lichens by its means. A few pieces are boiled with 5 per cent, caustic potash and a little chloroform added to the clear solution ; it is then warmed for ten minutes on the water-bath and diluted.1 Orcinol maybe quantitatively determined by adding standardized bromine water to the dilute solution until tribromorcinol is no longer precipitated and determining the excess of bromine by a solution of potassium iodide.2 Orcinol monomethyl ether, C6H3(CH3)(OCH3)OH, is formed, together with the dimethyl ether, when orcinol is boiled with caustic potash, methyl iodide, and wood-spirit. It is a light yellow, oily liquid which boils at 273° and is soluble in alkalis. Orcinol dimethyl ether, C6H3(CH3)(OCH3)2, is a yellowish, mobile fluid which boils at 244°, is insoluble in alkalis, and is converted by oxidation into symmetric dimethoxybenzoic acid, or dimethyl-a-resorcylic acid, C6H3(OCH3)2CO2H(5 : 3:1), thus establishing the constitution of orcinol.3 Orcinol acetate, C6H3(CH3)(OC2H3O)2, is obtained by the action of acetyl chloride on orcinol, and crystallizes from alcohol in needles melting at 250.4 Orcinol diethylcarbonate, C6H3(CH3)(O.COOC2H5)2, is obtained by the action of chlorocarbonic ether on the potassium compound of orcinol, and is a thick, oily liquid boiling at 310°-312°.6 Orcinolazobenzene, CcH5N~NC6H2(CH3)(OH)2, is formed when orcinol and diazobenzene nitrate are brought together in aqueous solution. It crystallizes from a mixture of acetic acid and acetic ether in dark red needles melting at 1830.6 1 Schwarz, Ber. Deutsch. Chem. Ges. xiii. 543. 2 Reymann, ibid. viii. 790. 3 Streng and Tiemann, ibid. xiv. 1999. 4 Luynes and Lionet, Zeitschr. Chem. 1867, 561. 6 Wallach, Liebig's Ann. ccxxvi. 86. 6 Typke, Ber. Deutsch. Chem. Ges. x. 1579. SUBSTITUTION PRODUCTS OF ORCINOL. 41 SUBSTITUTION PRODUCTS OF ORCINOL. 2038 These are obtained by the same methods as the cor- responding resorcinol compounds, which they resemble very closely. Chlorine Substitution Products. Melting- point. Trichlororcinol,1 C6C13(CH3)(OH)2, long needles 123° Pentachlororcinol,2 C6C13(CH3)(OC1)2, large prisms 120o,5 Bromine Substitution Products. Monobromorcinol,3 C6H2Br(CH3)(OH)2, crystals 135° Dibromorcinol,4 C6HBr2(CH3)(OH)2, needles 146° Tribromorcinol,5 C6Br3(CH3)(OH)2, needles 98° Pentabromorcinol,6 C6Br3(CH3)(OBr)2, triclinic crystals 126° Iodine Substitution Products. Mono-iodorcinol,7 C6H2I(CH3)(OH)2, prisms 80o-5 Tri-iodorcinol,8 C6I3(CH3)(OH)2, brown tablets - Nitro-Substitution Products. {golden 'I lustrous > 120° needles ) {dark 'j yellow b 115° needles J C deep 'I a-Dinitro-orcinol,10C6H(NO2)2CH3(OH)2,-< yellow > 1640-5 t tablets J 1 Stenhouse, Proc. Roy. Soc. 1871. 2 Stenhouse, Dittlerand Liebermann, Ann. Chern. Pharm. clxix. 265. 3 Lamparter, loc. cit. 4 Tiemann and Streng, loc. cit. 5 Stenhouse and Groves, Journ. Chern. Soc. 1880, 402. 8 Stenhouse and Rammelsberg ; Dittler and Liebermann, loc. cit. 255. 7 Stenhouse, Proc. Roy. Soc. xxii. 53. 8 Stenhouse, Journ. Chern. Soc. 1864, 327. 9 Weselsky, Ber. Deutsch. Chem. Ges. vii. 441. 10 Stenhouse and Groves, Journ. Chem. Soc. 1877, i. 548. 42 AROMATIC COMPOUNDS. Melting- point. f golden /3-Dinitro-orcinol,1 C6H(NO2)2CH3(OH)2,yellow -109°-110° (needles J f long ) Trinitro-orcinol,2 C6(NO2)3CH3(OH)2, yellow ( 163'5° (needles J 203g Archil. This name was formerly employed to designate both the colouring matter which is extracted from the lichens just mentioned, and the lichens themselves. Theophrastos and Dioscorides mention a plant $v/co<? OaKdaa-Lov or ttovtcov, called by Pliny Fucus marinus, which is not a sea-weed, as the name might be taken to imply, but a lichen which grows on the rocks of certain islands, especially Crete, and is capable of dyeing wool a beautiful violet or purple colour. Archil came into the European market as early as the four- teenth century; the following account of it is given by Beck- mann :3 Among the oldest and principal Florentine families is that known under the name of Oricellarii or Rucellarii, Ruscellai or Rucellai, several of whom have distinguished themselves as statesmen and men of letters. This family are descended from a German nobleman named Ferro or Frederigo, who lived in the beginning of the twelfth century. One of his descendants in the year 1300 carried on a great trade in the Levant, by which he acquired considerable riches, and returning at length to Florence with his fortune, first made known in Europe the art of dyeing with archil. It is said that a little before his return from the Levant, happening to make water on a rock covered with this lichen, he observed that the plant, which was then called respio or respo, and in Spain orciglia, acquired by the urine a purple, or, as others say, a red colour. He therefore tried several experiments, and when he had brought to perfection the art of dyeing wool with this plant, he made it known at Florence, where he alone practised it for a considerable time to the great benefit of the state. From this useful invention the family received the name Oricellarii, from which at last was formed Rucellai. 1 Leeds, Ber. Deutsch. Chern. Ges. xiv. 483. 2 Stenhouse, Proc. Roy. Soc. xix. 41 ; Merz and Zeller, Ber. Deutsch. Chern. Ges. xii. 2038. 3 Beckmann's History of Inventions, vol. i. p. 37. ARCHIL. 43 As several documents, still preserved among the Florentine archives, confirm the above account of the origin of this family name, from the discovery of dyeing with oricello,1 we may, in my opinion, consider it as certain that the Europeans, and first the Florentines, were made acquainted with this dye-stuff and its use in the beginning of the fourteenth century. At that time the Italians brought from the East the seeds of many arts and sciences, which, afterwards sown and nurtured in Europe, produced the richest harvests ; and nothing is more certain than that the art of dyeing was brought to us from the East by the Italians. I do not believe that the merit of having discovered this dye by the above-mentioned accident is due to that Floren- tine ; but I am of opinion that he learned the art in the Levant, and on his return taught it to his countrymen, which was doing them no small service. The archil lichens, the most valuable of which are Uocella tinc- toria and A. fuciformis, occur in several varieties and in con- siderable quantity on the coasts of warm and tropical countries, such as the islands of the Mediterranean, the Canary and Cape Verde Islands, Madagascar, Zanzibar, Angola, Ceylon, Java, Peru, Chili, &c. The old method for the preparation of archil consisted in treating the lichens with stale urine and lime in large casks provided with moveable lids, a considerable quantity of alum and white arsenic being added to prevent the fermentation from passing to a further stage. The mixture is well agitated for a month and then stored in casks in which it is allowed to stand for a long time before use, the colour being found to improve on keeping. A more modern process consists in treating the finely-chopped lichens with dilute ammonia, and keeping the mixture at the temperature of the air or at a slightly higher one until a dark violet paste has been formed; this is diluted with ammonia and filtered through a press; the solution thus obtained is known as blue archil. Red archil is obtained from this by gentle heating, the ammonia being thus removed. Stenhouse proposed first to extract the lichens with milk of lime, precipitate the solution with hydrochloric acid and work up the erythrin, &c., thus obtained as by-products, the 1 These documents from the Florentine records may be found in Dominici Marine Manni de Florentinis Inventis Commentarium. Ferrariae 1731. Beck- mann quotes the passage in question. 44 AROMATIC COMPOUNDS. colouring matter being thus left in a much purer condition. Marnas of Lyons found that the best results were obtained by extracting with dilute ammonia and warming the compounds precipitated from the solution with ammonia in a current of air to 70° for about three weeks. On addition of calcium chloride a precipitate, known as French purple (pourpre fran^aise), is thrown down, and the material thus obtained yields much finer and clearer shades than archil. Since the discovery of the aniline dyes, archil has lost much of its commercial importance ; it is now only used in combina- tion with other colouring matters in order to obtain certain shades of brown, and for the production of a cheap blue for wool dyeing; the material is first grounded with indigo and then dyed with archil, the result being a dye which is similar to that of genuine indigo-blue. Cudbear or Pcrsio. The inhabitants of Sweden, Scotland, Ireland, Wales, &c., have for centuries been in the habit of using various kinds of lichen, especially Lecanora tinctoria, for wool-dyeing, the colour being produced by treatment of the lichen with urine. During last century a patent was taken out by Dr. Cuthbert Gordon for the preparation of cudbear,1 by drying and powdering the pasty mass obtained by the action of ammonia or urine on the lichens. Cudbear is prepared in the Auvergne from Variolaria orcina by a similar method. Orcein. Robiquet has given this name to the colouring matter of archil, which is formed, as he discovered, by the action of hydrogen and ammonia on orcinol.2 Gerhardt calculated its formula from the analyses of Dumas and Kane,3 and gave the following equation for its formation: C7H8O2 + NH3 + 30 = C7H7NO3 + 2H2O. Kane prepared orcein from commercial archil; he describes it as a carmine-red powder, containing carbon and nitrogen in a constant ratio, while the amount of oxygen is variable, being larger as the archil becomes older; hence he assumed that it consists of two similar colouring-matters, a-orcein and /3-orcein. Liebermann, who obtained the colouring matter by the action of gaseous ammonia and air on pure orcinol, found that two 1 Bancroft, Philosophy of Permanent Colours, 1813, i. 300. 2 Ann. Chim. Phys, Iviii. 320. 8 Ann. Chern. Pharm. xxxix. 25. CUDBEAR AND LITMUS. 45 compounds are thus formed according to the following equations: 2C7H8Oq + NH3 + 30 = C14HnNO3+3H2O C14H13NO4 + NH3 + 0 = C14H12N2O3 + 2H2O. The latter is therefore formed in larger quantity when the action of the ammonia is allowed to continue for some time; it is less soluble in aqueous ammonia and alcohol than the former compound. Both occur as amorphous masses having a beetle- green lustre, and forming splendid purple solutions with alkalis; but the solution of the second compound has a bluer shade than that of the first.1 2040 Litmus (toitrnesolso Lackmus^was discovered by the Dutch.2 It is prepared from various species of Rocella, Variolaria and Lecanora, by allowing them to ferment in contact with ammonia and carbonate of potash, as in the manufacture of archil. When the mass has become violet, stale urine, lime and potashes are added, and the mass again allowed to ferment until it has as- sumed a blue colour ; it is then mixed with gypsum or chalk, and a little indigo,3 and made up into small tablets. Kane was the first more accurately to investigate litmus, and he obtained several colouring matters and other substances from it.4 WTartha, who also investigated the colouring matter of litmus, found indigo in it; this, however, had probably been purposely added as just described, although it may possibly have been derived from the urine, which is known to contain appreciable quantities of a substance which yields indigo on decomposition. On extracting litmus with cold alcohol, Wartha obtained a red colouring matter which is indifferent towards acids, and yields litmus blue and another substance when treated with water. On evaporating the solution and treating the residue with absolute alcohol and a little acetic acid, a scarlet colouring matter is removed, and this is changed to a purple by ammonia, while the pure litmus blue remains behind as a brown powder which forms a reddish brown aqueous solution turned blue by the slightest trace of an alkali.5 According to De Luynes, the pure colouring matter is obtained by digesting 1 part of orcinol with 5 parts of ammonia and 25 1 Ber. Deutsch. Chern. Ges. viii. 1649. 2 The origin of this name is unknown ; it may perhaps be derived from Lacca musci, a lake prepared from moss. 3 Gottlieb, Chern. Tech. p. 531. 4 Loc. cit. 5 Bet. Deutsch. Chern. Ges. ix. 217. 46 AROMATIC COMPOUNDS. parts of crystallized carbonate of soda for four or five days at 60°-80°, and precipitating the solution with hydrochloric acid. It is only slightly soluble in water, and the wine-red colour of this solution is changed to bluish violet by alkalis, and to a reddish brown by acids. It yields a red solution with alcohol, and a yellow one with ether. De Luynes considers that the colouring matter is a weak acid which forms blue salts, the potassium salt existing in litmus.1 Litmus is not only employed in the laboratory in the form of litmus paper and tincture, but is also used for colouring wine and vinegar. The colouring matter can readily be recognized by its absorption spectrum; ether extracts it from an acid solution yielding a yellow liquid which absorbs the left end of the spec- trum up to E1 D. A drop of ammonia colours the solution blue, an absorption band being formed which begins at d, where it is very intense, gradually diminishing to E. On shaking with water the colouring matter is taken up, and the blue solution gives an absorption band at D ; the addition of acid now changes the colour to brick-red, and the solution gives an absorption spectrum similar to that of wine.2 Ribbon Litmus (^TourncsoUappen,tournesol en drapcaux, Bezdta, Lackmus in Fleckchen) is obtained in southern France from the expressed sap of Croton tindorium ; linen rags are soaked in the sap, dried in the sun, and then exposed on heaps of horse-dung covered with chopped straw, the ammonia evolved being sufficient to change the colour of the rags, which are fre- quently turned, to blue. They are then again dipped in the sap, to which urine has been added, the colour thus produced becoming dark green or purple-red on drying, and they are then brought into the market. It was formerly believed that the Dutch employed them for the manufacture of litmus, but this is not the case; they are actually used to colour the exterior of cheeses red. The colouring matter contained in these ribbons has not been accurately investigated; acids change it to red, but the blue colour is not restored by alkalis. 1 Jahresber. 1864, 551. 2 Vogel, Spcctralanalyse, p. 269. CRESORCINOL. 47 CRESORCINOL, C6H3(CH3)(OH)2(1:2 :4). 2041 This dihydroxytoluene, which was called lutorcin by Vogt and Henninger, may be prepared from /3- and y-amido- paracresol by the diazo-reaction1 and by fusing bromoparacresol with caustic potash.2 It is readily soluble in water, alcohol, ether and benzene, and crystallizes in monosymmetric prisms which form characteristic spherical aggregates and melt at 104° -105°. Ferric chloride produces an unstable, greenish blue colouration, and an alkaline solution becomes coloured red in the air. Like resorcinol it re- duces silver solution in the cold, is not precipitated by lead acetate, and gives a precipitate with bromine water which soon becomes crystalline. On heating with phthalic anhydride and dissolving the mass in dilute caustic soda, a solution is formed possessing as fine a green fluorescence as does that obtained by a similar process from resorcinol. It differs however from the latter in yielding no colouring matter when heated with sul- phuric acid and nitrobenzene. In presence of ammonia and moist air it is converted into yellow cresorcein, which dissolves in dilute caustic soda, forming a blue solution turned red by acetic acid. Isorcinol. Senhofer obtained this compound by the fusion of y-toluenedisulphonic acid,3 and Hakansson prepared a-isorcinol in a similar manner from a-toluenedisulphonic acid.4 Claesson subsequently showed that these two sulphonic acids are identical, and that, therefore, only one isorcinol can exist. It crystallizes in needles melting at 87°-88°, but it resembles cresorcinol so closely that Neville and Winther look upon the two as identical, an opinion which is supported by the fact that the toluenedisulphonic acid has the side chains in the same relation as cresorcinol. 1 Knecht, Ber. Deutsch. Chem. Ges. xv. 298 and 1069 ; Ann. Chern. Pharm. ccxv. 83 ; Wallach, ibid. xv. 2831 ; Neville and Winther, ibid. xv. 2980. 2 Vogt and Henninger, ibid. xv. 1081. 3 Ann. Chem. Pharm. clxiv. 131. 4 Ber. Deutsch. Chem. Ges. v. 1084. 48 AROMATIC COMPOUNDS. TOLUQUINOL, OR TOLUHYDROQUINONE. C6H3(CH3)(OH)2(1:2:5). 2042 This compound may be obtained from orthotoluidine just as is quinol from aniline,1 and may also be prepared from /?-amido-orthocresol by means of the diazo-reaction.2 It is readily soluble in water, alcohol and ether, and crystallizes from hot benzene or toluene in pointed, rhombic plates which have a nacreous lustre and melt at 124°. Caustic soda produces a bluish green colouration which rapidly changes to dark brown; bleaching powder solution gives the same reaction, but when very dilute produces a brownish red colour. Oxidizing agents readily convert it into toluquinone. Toluquinol monomethyl ether, C6H3(CH3)(OCH3)OH, is formed, together with the compound described below, by heating tolu- quinol with caustic soda, methyl iodide and wood-spirit to 190°. It has a faint smell of creosote, crystallizes in plates melting at 72°, boils at 240°-245°, and yields toluquinone on oxidation. Toluquinol dimethyl ether, C6H3(CH3)(OCH3)2, can easily be separated from the monomethyl ether, since it is insoluble in alkalis and non-volatile in steam. It is a liquid which has a pleasant smell like fennel and boils at 214°-218°. When oxidized by chromic acid in acetic acid solution, it is converted into a compound, C16HlcO4, which is precipitated by water in brick-red needles and crystallizes from its deep yellow alcoholic solution, in hair-like needles, which appear almost black when seen in masses and become silver-grey on drying. They melt at 153° and sublime when more strongly heated. Ammonium sul- phide reduces it to the compound C18H18O4, crystallizing from alcohol in small prisms, melting at 173°, which are readily re-oxidized. Diacetotoluqitinol, C6H3(CH3)(OCO.CH3)2, is formed by the action of acetyl chloride on toluquinol; it crystallizes from alcohol in large tablets melting at 72° (Nietzki). 1 Nietzki, Bcr. Deutsch. Chern. Ges. x. 834, 1935 ; Ann. Chern. Pharm. ccxv. 158. 2 Neville and Winther, Bcr. Deutsch. Chem. Ges. xv. 2979. TOLUQUINOL AND TOLUQUINONE. 49 TOLUQUINONE, C6H3(CH3)O2. 2043 This compound is formed when paradiamidotoluene,1 crude cresol2 or amidorthocresol3 is oxidized with manganese dioxide and dilute sulphuric acid, or when orthotoluidine hydro- chloride is heated with ferric chloride.4 It crystallizes in small golden-yellow plates which readily volatilize, have a penetrating smell resembling that of benzoquinone, and melt at 69°. It dissolves slightly in cold, more readily in hot water, forming a golden-yellow solution which is coloured brownish red by alkalis. Sulphurous acid reduces it to toluquinol. Dianilidotoluquinone, C6H(CH3)O2(NH.C6H5)2, is obtained by the action of aniline on tolu quinone in alcoholic solution; it crystallizes from hot glacial acetic acid in brown, matted needles, which melt at 232° -233° and form a blood-red solution in sulphuric acid. When boiled with alcohol and sulphuric acid, anilidohydroxytoluquinonc, C6H(CH3)O2(NH.C6H5)OH, is formed; it crystallizes from alcohol or acetic acid in deep blue needles and forms salts with bases. Dianilidotoluquinone anilide, C6H(CH3)O(NC6H5)(NH.C6Hd2, is formed when aniline and toluquinone are brought together in solution in a mixture of alcohol and acetic acid. It crystallizes in broad dark-brown plates which have a blue surface lustre, melt at 167° and combine with acids to form salts, which are only slightly soluble in water but crystallize well from alcohol. On heating with alcoholic sulphuric acid, anilido-ethoxytolu- quinone anilide, C6H(CH3)O(NC6H5)(NH.C6H5)OO2H5,is formed ; this compound crystallizes from alcohol in silky, red needles melting at 115°-116°, is a tolerably strong base and forms blue salts. It dissolves in concentrated sulphuric acid with a green colour. On treatment with alcoholic potash it yields anilido- hydroxytoluquinone anilide, C6H(CH3)O(NC6H5)(NHC6H5)OH, crystallizing from hot, dilute acetic acid in brownish needles, which form a deep green solution in sulphuric acid. It forms insoluble or difficultly soluble salts with the metals. Dihydroxytoluqidnone, C6H(CH3)O2(OH)2, is obtained from 1 Nietzki, loc. cit. 2 Carstanjen, Journ. Prakt. Chern. [2] xxiii. 425. 3 Nolting and. Kohn, Ber. Deutsch. Chern. Ges. xvii. 370, 4 Ladenburg, ibid. x. 1125, 50 AROMATIC COMPOUNDS. the preceding compound by the action of very dilute caustic potash solution. It is readily soluble in most solvents and crystallizes from them badly; it readily sublimes, however, in brownish yellow, lustrous plates, melting at 177°. Its salts form insoluble or only slightly soluble precipitates which are not characteristic.1 Toluquinhydrone, C6H3(CH3)O24C6H3(CH3)(OII)2, is obtained by mixing aqueous solutions of the two constituents, and crys- tallizes in fine, almost black needles which melt at 52° and are tolerably soluble in water forming a brownish yellow solution (Nietzki). SUBSTITUTION PRODUCTS OF TOLUQUINONE. The chlorine substitution products are obtained by treating orthocresol or metacresol, and therefore also crude cresol, with potassium chlorate and hydrochloric acid.2 Trichloroquinone is likewise formed by this method from orthotoluidineparasulphonic acid.3 Sulphurous acid converts them into the corresponding derivatives of toluquinol. Dichlorotoluquinone, C7H4C12O2, yellow transparent tablets. Trichlorotoluquinone, C7H3C13O2, yellow plates. m . i i , 1 • tt m rv f golden, lustrous, scaly 1 etrachlorotoluqumone, Uy-tLgOqOg) । crystals Tribromotoluquinone,4 C7H3Br3O2, yellow plates. TOLUQUINONOXIME COMPOUNDS. 2044 a-Toluqitinonoxime, C6H3(CH3)O(NOH). This compound, which is generally known as nitroso-orthocresol, is formed in an analogous manner to quinonoxime (Part III. p. 171) by the action of nitrosyl sulphate on an aqueous solution of orthocresol,5 or by adding hydroxylamine hydrochloride to a dilute solution of toluquinone.6 It is only slightly soluble in cold, more readily in hot 1 Hagen and Zincke, Ber. Deutsch. Chem. Ges. xvi. 1558. 2 Southworth, Ann. Chem. Pharm. clxviii. 274 ; Bergmann, ibid. clii. 248 ; Brauninger, ibid, clxxxv. 352 ; Knapp and Schulte, ibid. ccx. 176. 8 Hayduck, ibid, clxxii. 209. 4 Canzoneri and Spica, Ber. Deutsch. Chem. Ges. xvi. 793. 8 Nolting and Kohn, ibid. xvii. 370. 6 Goldschmidt and Schmidt, ibid. xvii. 2063. TOLUQUINONOXIME COMPOUNDS. 51 water, from which it crystallizes in long, white needles, melting at 134°-135°. It forms a reddish brown solution in dilute alkalis, and is thrown down by acids as a white, flocculent precipitate. Potassium a-toluquinonoximate, C6H3(CH3)O(NOK), is ob- tained by the addition of an ethereal solution of toluquinone- oxime to a solution of potassium ethylate, as a yellowish green precipitate, which crystallizes from acetone in brown needles. Sodium a-toluquinonoximate, C6H3(CH3)O(NONa) + 3H2O, is a dark green precipitate which crystallizes from acetone in short, brown needles, and forms a reddish brown solution in water; it detonates when heated. Toluquinonoxime gives Liebermann's reaction with phenol and sulphuric acid; potassium ferricyanide oxidizes it to /3-nitro-orthocresol, and nitric acid to dinitro-orthocresol, while it is converted into 5-amido-orthocresol by reduction. a-Toluquinone chlorimide, C6H3(CH3)O(NC1), is formed in an analogous manner to quinone chlorimide when a concentrated solution of bleaching powder is added to a dilute hydrochloric acid solution of 7-amido-orthocresol; the liquid first becomes coloured cherry-red, changing to golden-yellow, the chlorimide then separating out. It crystallizes from benzene in yellow needles, which melt at 87°-88° and detonate at higher temperatures. When boiled with water it volatilizes, a portion being simul- taneously decomposed into a-toluquinone and brown, amorphous bodies; it also gives Liebermann's reaction.1 ft-Toluquinonoxime, or Nitrosometacresol, C6H3(CH3)O(NOH), has been prepared by boiling nitrosodimethylmetatoluidine; it is slightly soluble in hot water, from which it crystallizes in small, colourless needles, while it is deposited from solution in ether or acetic acid in thick needles or prisms, decomposing at 140°-150°. ft-Toluquinonoxime acetate, C6H3(CH3)O(NO.C2H3O), is ob- tained by the action of acetic anhydride on the compound just described; it crystallizes from alcohol in prisms melting at 92°. /3-Toluquinonoxime gives Liebermann's reaction in a most characteristic manner; nitric acid oxidizes it to trinitrometa- cresol.2 1 Hirsch, Ber. Deutsch. Chem. Ges. xviii. 1514. 2 Wursterand Riedel, ibid. xii. 1799. 52 AROMATIC COMPOUNDS. The following formulae explain the isomerism of the two toluquinonoximes: a CO H^^C-CH3 II II HC CH II NOH. 0 CO HC CH II II HC C-CH3 II NOH. Paracresol does not form a nitroso-compound or quinonoxime, since the methyl group is situated in the para-position. Hydroxytoluquinonoximc, C6H2(CH3)(OH)O(NOH). This compound, which is also called nitroso-orcinol, is obtained by evaporating a solution of 12 grammes of orcinol and 4 grammes of caustic soda to a syrup, and gradually adding 12 grammes of amyl nitrite to the cold mass with constant stirring; the mixture is then gently heated on the water-bath until a small portion dissolved in water gives a red precipitate with sulphuric acid. The fused mass is then dissolved in water and precipitated with dilute sulphuric acid. Nitroso-orcinol crystallizes from alcohol in small dark red prisms, which become coloured black at 110° without melting.1 It has the following constitution : CO HC^^CH II II OH-C C-CH3 NOH. Azo-orcin, C14HnNO3. Weselsky obtained this compound by the action of his reagent on an ethereal solution of orcinol;2 it is also formed when orcinol is heated on the water-bath with nitroso- orcinol and sulphuric acid (Brunner and Kramer). It crystal- lizes in small, brownish red prisms which dissolve in alkalis forming a deep purple-coloured solution with a splendid orange- 1 Brunner and Kramer, Bor. Deutsch. Chan. Ges. xvii. 1879. 2 Ibid. vii. 439. METHYLPYROGALLOL. 53 red fluorescence; acids precipitate it from this as a scarlet powder. Its formation is quite analogous to that of azoresorcin, C12H9NO4 (Part III. p. 176), but it is not homologous with this substance. The homologous compound is, however, first formed and is converted into azo-orcin with loss of water; the latter compound may probably possess the following constitution: OOO CH3.C6H3< >NC6H2(CH3)< >C6H2(CH3)N< >c6h3ch3. // - // Liebermann obtained a similar colouring matter by gradually adding 40 grammes of his reagent to a solution of 10 grammes of orcinol in 10 grammes of sulphuric acid.1 Another colouring matter is simultaneously formed but can easily be separated, as it forms a sodium salt which is insoluble in alcohol, while that of the former forms a purple-red solution with a cinnabar-red fluorescence. The colurring matter, C22H21NO6, separated from this solution by the addition of an acid, is an amorphous mass with a beetle-green fluorescence, the aqueous alkaline solution of which has a brownish red fluorescence. The formation of this compound corresponds exactly to that of Liebermann's phenol colouring-matter, and its constitution is therefore the following: OH HO\ zOC6H3-CH3 ch3/c6hqn< ho/ j \O.C6H3-ch3 OH. \ The second colouring matter, C22H21NO7, is an oxidation product of the former, which it resembles very closely; its violet alkaline solution, however, does not fluoresce (Brunner and Kramer). TRIHYDROXYTOLUENES, C6H2(CH3)(OH)3. 2045 Mcthylpyrogallol, or Methylpyrogallic acid, is the only known compound of this group. Its dimethyl ether occurs, together with the same ethers of pyrogallol and propylpyrogallol 1 Ber. Deutsch. Chem. Ges. vii. 1110. 54 AROMATIC COMPOUNDS. in the fraction of beech-wood-tar creosote which dissolves in alkalis and boils at between 255° and 270°. In order to separate them, the mixture is heated with benzoyl chloride, the benzoic ethers separated by fractional crystallization and then decomposed by alcoholic potash. Methylpyrogallol dimethyl ether, C6H2(CH3)(OCH3)2OH, is a crystalline substance, melts at 36°, and boils at 265°. On heating with concentrated hydrochloric acid, methylpyrogallol is obtained; this closely resembles pyrogallol, and on heating sublimes in needles, which melt at 129°. Its aqueous solution is coloured brown by ferrous sulphate, and its alkaline solution rapidly turns brown in the air,1 AMIDO-DERIVATIVES OF TOLUENE. Amidotoluenes, or Toluidines, CgH4(CH3)NH2. 2046 The history of these compounds goes hand in hand with that of the nitrotoluenes. Hofmann and Muspratt reduced crude nitrotoluene by repeated treatment with alcoholic am- monium sulphide and obtained the product free from unaltered nitrotoluene by washing well with water, treating with hydro- chloric acid and distilling the liquid, after the removal of all alcohol by evaporation, with caustic soda; they thus obtained an oily liquid which solidified after some time to a crystalline mass, and to this new organic base they gave the name toluidine. The .aqueous distillate obtained in the preparation contained some ammonia and a not inconsiderable amount of base in solution ; the whole distillate was therefore treated with an excess of ammonium oxalate, evaporated to dryness on the water-bath and the residue extracted with boiling absolute alcohol, ammonium oxalate being in this way left undissolved. On cooling, toluidine oxalate separated out in white crystals, which were washed, dissolved in hot water, and decomposed with concentrated caustic potash solution. The oil which separated out solidified on cooling to a radiating crystalline mass of pure toluidine, the properties of which were then accurately investigated. After the discovery of the aniline dyes, aniline and toluidine, 1 Hofmann, Bar. Deutsch. Chem. Ges. xii. 1371. TOLUIDINES. 55 or rather a mixture of the two called aniline oil, was manu- factured on the large scale; and Rosenstiehl found in this mixture a liquid base, isomeric with the ordinary toluidine, to which he gave the name of pseudotoluidine. We have already pointed out that the three nitrotoluenes are formed in varying quantities by the nitration of toluene. If concentrated acid be employed without cooling, paranitrotoluene is chiefly formed, and this yields on reduction the solid paratoluidine obtained by Hofmann and Muspratt. If, however, a weaker acid be employed, and the temperature be kept low, more of the ortho-compound is formed, and it is from this that the pseudotoluidine is derived; a small quantity of metanitrotoluene being, however, invariably produced. The toluidines are manufactured on a large scale; the para- compound is that which is most readily obtained in the pure state, as the purification of paranitrotoluene offers no difficulties, whilst it is very difficult, working on the large scale, to obtain an orthonitrotoluene free from paranitrotoluene, so that ordinary commercial orthotoluidine always contains some of the para-compound together with metatoluidine and generally a little aniline. The amount of paratoluidine in such a mixture can readily be determined by means of the different solubilities of the oxalates in ether; at 15° Acid paratoluidine oxalate requires 6660 parts of ether. Acid orthotoluidine oxalate „ 200 „ for solution. A small quantity, about 0'2 grins., of the mixture is dissolved in 80 grms. of ether and titrated with a solution of 1 062 grms. of oxalic acid in 250 c.c. of ether until no further precipitate is formed. Each cubic centimetre of the solution employed corresponds to 0'005 grms. of paratoluidine.1 The end of the reaction can easily be recognised by the acid reaction of the solution towards litmus-paper as soon as the orthotoluidine oxalate commences to be formed. The deter- mination is rendered still more accurate by adding an excess of oxalic acid solution to the solution of the bases, filtering from the precipitate, evaporating the ether, dissolving the residue in a little water and determining the excess of oxalic acid by decinormal caustic soda solution.2 1 Rosenstiehl, Ann. Chim. Phys. (1872), xxvi. 249. 2 Lorenz, Ann. Chern. Pharm. clxxii. 190. 56 AROMATIC COMPOUNDS. In order to separate larger quantities of the base, an amount of oxalic or sulphuric acid equivalent to the paratoluidine present is added, and the whole distilled with steam; ortho- toluidine alone passes over, and the para-compound as the stronger base remains behind in combination with the acid (Rosenstiehl). Ihle dissolves the bases in ether, precipitates with an ethereal solution of oxalic acid and from time to time treats a small portion of the solution with acetyl chloride. The product is re-crystallized from hot water and its melting-point observed. Since acetparatoluide melts at 145°, and acetorthotoluide at 107°, the point at which all the paratoluidine is removed can readily be recognised.1 Binschedler gives the following process for the treatment of a mixture of 30 per cent, of paratoluidine and 70 per cent, of ortho- toluidine which comes into the market under the name of " aniline lourde sp^ciale ": 10 kilos, of the mixture of bases are gradually added to a solution of 2'5 kilos, of oxalic acid in 25 litres of boiling water to which 6 litres of hydrochloric acid of specific gravity IT 5 have been added, the mixture being then heated to the boiling point, and constantly stirred until it has cooled down again to 60°. The crystalline precipitate which consists of pure paratoluidine oxalate, is rapidly filtered off, pressed, and washed with a little water; 2 kilos, of oxalic acid are now added to the filtrate, a mixture of the oxalates being thus precipitated. When oxalic acid produces no further precipitate in the mother-liquor, it is distilled with caustic soda, orthotoluidine being obtained which contains a very small quantity of paratoluidine and only traces of aniline.2 Another method of separation, which has been patented by Leo Levy, depends upon the behaviour of the hydrochlorides of the bases towards sodium phosphate. Aniline hydrochloride gives the following reaction : Na2HPO4 + 2C6H5NH3C1 = 2NaCl + (C6H5.NH3)2HPO4. Paratoluidine hydrochloride behaves in a similar manner, while the orthotoluidine salt yields 80 per cent, of the free base and 20 per cent, of the acid phosphate: 1) C7H7.NH2HC1 + Na2HPO4 = C7H7.NH2 + NaH2PO4 + NaCl. 2) C7H7.NH2HC1 + NaH2PO4 = (C7H7.NH3)H2PO4 + NaCl. 1 Journ. Prakt. Chern. [2] xiv. 449. 2 Ber. Deutsch. Chern Ges. vi. 448. ORTHOTOLUIDINE. 57 The mixed hydrochlorides are therefore treated with a solution of sodium phosphate; the crystalline mass which is formed iszthen dissolved by warming, and the orthotoluidine removed from the surface. On cooling, the phosphates of aniline and paratoluidine separate out completely, while the phosphate of orthotoluidine remains in solution. The sodium phosphate can be recovered after separation of the bases; sodium arsenate may also be employed.1 Another process for the separation of orthotoluidine from aniline oil by means of the nitrate has been described by L. Schad.2 2047 Orthotoluidine, discovered by Rosenstiehl,3 is formed by the reduction of orthonitrotoluene and by the distillation of paramidotoluic acid with lime.4 It is a colourless liquid re- sembling aniline very closely; it soon becomes brown in the air or on exposure to light, boils at 198'5°, has a specific gravity of 1'003 at 20'2°, and does not solidify at - 20°. A solution of this base in monohydrated sulphuric acid gives a blue colouration with a solution of chromium trioxide in sulphuric acid of the same strength; the colour changes to a stable reddish violet on dilution. Nitric acid added to the sulphuric acid solution gives an orange to brown colouration, passing into yellow on the addi- tion of water. If the base be dissolved in ether and an equal volume of water added, the lower layer of the solution gives a yellow to brown colouration with dilute sulphuric acid. If the ethereal layer be now removed and shaken with dilute sulphuric acid, it becomes coloured a stable reddish violet (Lorenz). Orthotoluidine further differs from its isomerides in giving a green colouration with ferric chloride and a little paradiamido- benzene. This reaction is so delicate that a solution containing 1 in 10,000 gives a tolerably deep colouration, and a solution only one-tenth as strong as this assumes a distinct shade of green.5 All commercial aniline gives this reaction, as also does that obtained by the distillation of indigo with caustic potash, which was con- sidered to be chemically pure until Rosenstiehl proved that it contained orthotoluidine. The salts of orthotoluidine have been investigated by Beilstein and Kuhlberg. 1 Ber. Deutsch. Chem. Ges. xvi. 980. 2 Ibid. vi. 1361. 3 Zeitschr. Chem. [2] iv. 557. 4 Beilstein and. Kuhlberg, Ann. Chem. Pharm. clvi. 75. 5 Monnet, Reverdin and Nolting, Ber. Deutsch. Chem. Ges. xi. 2278. See also Reinhardt and Stadel, ibid. xv. 29. 58 AROMATIC COMPOUNDS Orthotoluidine hydrochloride, C7H9NC1H-|-H2O, forms white crystalline crusts, 37'4 parts of which dissolve in 100 parts of water at 15'5°; it is still more readily soluble in alcohol. Orthotoluidine hydrobromide, C7H9N.BrH, crystallizes very easily in large rhombic prisms ; the hydriodide resembles it, but is partially decomposed by water.1 Orthotoluidine sulphate, (C7H9N)2H2SO4, forms small crystals which become coloured violet to green in the air; 100 parts of water at 22° dissolve 7'5 parts. It is only slightly soluble in alcohol. Orthotoluidine ni ratc, C7H9N.HNO3, crystallizes in small plates ; 100 parts of water at 19'2° dissolve 10'01 parts. Orthotohiidine oxalate crystallizes in small colourless plates; 100 parts of water at 21° dissolve 2'38 parts. Methylorthotoluidine, C6H4(CH3)N(CH3)H, is formed when 750 grms. of orthotoluidine are heated for a day to 200°-220° with 400 grms. of methyl alcohol and 700 grms. of hydrochloric acid. The product is distilled in steam, and every 100 grms. of distillate dissolved in 120 grms. of hydrochloric acid and 300 grms. of water, the solution being then treated with a con- centrated solution of 40 grms. of sodium nitrite, the mixture being cooled and well agitated. The methylorthotolylnitros- amine, C6H4(CH3)N(CH3)NO, formed, which is very similar to methylnitroso-aniline, is extracted with ether, reduced with tin and hydrochloric acid, decomposed with caustic soda, and distilled with steam. Methylorthotoluidine is a colourless liquid which rapidly becomes coloured violet-brown in the air, and boils at 207°- 2O80.2 Dimethylorthotoluidine, C0H4(CH3)N(CH3)2. Thomsen ob- tained this compound by the distillation of trimethyltolyl- ammonium hydroxide ; it is also formed, together with other products, when trimethylphenylammonium iodide is heated to 220°-230°.3 It can readily be prepared pure by heating 750 grms. of orthotoluidine for two days with 670 grms. of methyl alcohol and 700 grms. of hydrochloric acid, the product being repeatedly rectified (Monnet, Reverdin and Nolting). It is a colourless liquid which has a characteristic aromatic odour and boils at 183°. 1 Stadel, Ber. Deutsch. Chem. Ges. xvi. 28. 2 Monnet, Reverdin and Nolting, Ber. Deutsch. Chem. Ges. xi. 2278. See also Reinhardt and Stadel, ibid. xv. 29. 3 Hofmann, ibid. x. 1585. DERIVATIVES OF ORTHOTOLUIDINE. 59 Trimethylortlwtolyla^^ iodide, C6H4(CH3)N(CH3)3I, is formed by the continued action of methyl iodide on ortho- toluidine.1 and crystallizes in large needles which assume a faint purple tint in the air. Boiling-point. Ethylorthotoluidine, C7H9N(C2H5)H, liquid 213°-214° Diethylorthotoluidine,2 C7H9N(C2H5)2 „ 208°-209°. Phenylorthotolylanvine, C6H5.NH(C7H7), is formed, together with diphenylamine and di-orthotolylamine, when orthotoluidine is heated with aniline hydrochloride to 280°.3 It is a crystalline substance which melts at 41°, boils at 297°-299°, and gives a violet-blue colouration with nitric acid. Di-orthotolylamine, (C7H7)2NH, is a liquid boiling at 304°- 308°. Acetorthotoluide, C7H7.N(C2H3O)H, forms long needles, melts at 107° and boils at 296°; 100 parts of water at 19° dissolve 0'86 parts (Beilstein and Kuhlberg). Orthotolyl carbamide, (C7H7)NH.CO.NH2, is formed by the action of potassium cyanate on orthotoluidine hydrochloride ; it is insoluble in cold water, moderately soluble in hot water, and readily in alcohol, crystallizing in tablets which melt at 185°.4 Di-orthotolyl carbamide, (C7H7)2NCO.NH2, is formed by the action of carbonyl chloride on orthotoluidine, by heating the latter with urea,5 or by heating its hydrochloride with cyanamide to 100°.6 It is insoluble in water, but slightly soluble in alcohol, crystallizing in fine needles which melt at 243°. Orthotolyl carbamide, or Orthotolyl isocyanate, CON.C6H4.CH3. When orthotoluidine is acted upon by chlorocarbonic ether, orthotolyl urethane, NH(C7H7)CO.OC2H5, is formed in crystals melting at 46°,7 and on heating with phosphorus pentoxide is converted into the isocyanate, which is a liquid boiling at 186° and possessing a penetrating odour (Girard). Water decom- poses it with formation of ditolyl carbamide. Orthotolyl thiocarbamide, (C7H7)HN (CS)NH2, is obtained by the action of ammonia on orthotolyl mustard oil; it melts at 155° and is readily soluble in boiling water.8 1 Thomsen, Bet. Deutsch. Chem. Ges. x. 1586. 2 Stadel and Reinhardt, loc. cit. ; Norton, Ann. Chern. Journ. vii. 118. 3 Girard and Willm, Bull. Soc. Chim. xxv. 248. 4 Cosack, Ber. Deutsch. Chem. Ges. xiii. 1089. 5 Girard, ibid. vi. 444. 6 Berger, ibid. xii. 1859. 7 Lachmann, ibid. xii. 1349 ; Neville and Winther, ibid. xii. 2324. 8 Staats, ibid. xiii. 135. 60 AROMATIC COMPOUNDS. Di-orthotolyl thiocarbamide, (C7H7.NH)2CS, is obtained by the action of carbon disulphide on an alcoholic solution of orthotolu- idine.1 It crystallizes from hot alcohol in needles melting at 158°. Orthotolyl thiocarbamide, or Orthotolyl mustard oil, CSN.C6H4. CH3, is formed when the compound just described is boiled with fuming hydrochloric acid. It is a strongly refractive liquid, boiling at 239° and possessing a pungent odour (Girard). It combines with aniline forming phenylorthotolyl thiocarbamide, (C6H5)NH(CS)NH(C7H7), which has also been prepared from orthotoluidine and phenyl mustard oil (Staats); it forms long needles melting at 139°, and is decomposed by hydrochloric acid into aniline and tolyl mustard oil. 2048 Metatoluidine was obtained by Beilstein and Kuhlberg by the reduction of metanitrotoluene,2 which is best effected by means of stannous chloride and hydrochloric acid (Cosack). According to Widmann, it is also formed when metanitrobenzyl- ene chloride, C6H4(NO2)CHC12, obtained by the action of phos- phorus chloride on metanitrobenzaldehyde, is reduced with zinc dust and hydrochloric acid.3 It is a colourless oily liquid which has a specific gravity of 0'998 at 25°, and becomes converted into a brown resinous mass when exposed to the air (Lorenz); it boils at 197° and does not solidify even at -13°. If it be dissolved in monohydrated sulphuric acid and treated with a sulphuric acid solution of chromium trioxide, a yellowish brown liquid is obtained which becomes brown on gentle heating, and is coloured greenish yellow by the addition of a little water, a larger quantity rendering it colour- less. Nitric acid added to the original solution produces a reddish colouration which rapidly becomes a deep blood-red, and then a dark dirty-red, and is converted into orange by the addition of water. When a solution of the base in equal volumes of ether and water is treated with bleaching powder solution, the aqueous layer is coloured brownish yellow and becomes turbid, while the ether exhibits a reddish fluorescence; if the ether be poured off and shaken up with water and a drop of dilute sulphuric acid, the water becomes coloured a faint violet. The salts of metatoluidine have been investigated by Lorenz.4 1 Girard, Ber. Deutsch. Chern. Ges. iv. 985 ; Berger, ibid. xii. 1854. 2 Ann. Chem. Pharm. clvi. 83. 3 Ber. Deutsch. Chem. Ges. xiii. 676 ; xiv. 2583. See also ibid. xiv. 1403. 4 Ann. Chem. Pharm. clxxii. 177. METATOLUIDINE. 61 Metatoluidine hydrochloride, C7H9N.C1H, crystallizes from a very concentrated aqueous solution in thin tablets, and from alcohol in thin, pale red crusts. Metatoluidine sulphate, (C7H9N)2SO4H2, crystallizes in long, transparent, light red, radiating needles, which are insoluble in ether, slightly soluble in alcohol, and more readily in water, 100 parts of which at 14° dissolve 6'25 parts. Metatoluidine nitrate, C7H9N.NO3H, crystallizes in large, pale red, rhombic plates, 16'42 parts of which dissolve in 100 parts of water at 15'5°; it is still more soluble in alcohol, but only slightly soluble in ether. Acid metatoluidine oxalate, C7H9N.C2O4H2, forms warty masses consisting of fine silky needles, which are only slightly soluble in ether, alcohol and water; 100 parts of the latter at 13° dissolve 2'65 parts. When its solution is warmed with meta- toluidine, the salt, (C7H9N)3(C2O4H2)2, separates out in a mass of rhombic plates which are still less soluble than the mono- acid salt. If an excess of metatoluidine be added in warm alcoholic solution to oxalic acid, small rhombic plates separate out on cooling in such quantity that the liquid solidifies to a jelly. These crystals appear to be the hydrated normal salt; after washing with alcohol and drying, they possess the appear- ance of cholesterin; they are scarcely wetted by water and when heated with it for a long time decompose into the acid salt and the free base. Methylmetatoluidine, C6H4(CH3)N(CH3)H, is formed, together with dimethyhnetatoluidine, by the action of methyl iodide on the primary base. The product is extracted with ether and freed from unattacked metatoluidine by the addition of sulphuric acid, an alkali is then added, the ether distilled off and the residual oil dried and heated with acetic anhydride. On distillation, acetic acid and acetic anhydride first come over, followed by dimethyltoluidine and finally by methylacetoluide, boiling above 250°. This is purified by repeated distillation and decomposed by heating with dilute sulphuric acid, pure methylmetatoluidine being thus obtained ; it is a colourless liquid which boils at 206°-207°, and possesses a characteristic aromatic odour. Dimethylmetatoluidine, C6H4(CH3)N(CH3)2, boils at 215° (Wurster and Riedel), and has a characteristic odour differing from that of its isomerides, but resembling that of dimethyl- aniline.1 1 Nolting, Ber. Deutsch. Chem. Ges. xi. 2278, 62 AROMATIC COMPOUNDS. Nitrosodimcthylmctatoluidine, C6H3NO(CH3)N(CH3)2, is formed on the addition of sodium nitrite to a cooled solution of di- methylmetatoluidine in hydrochloric acid. The hydrochloride thus prepared crystallizes from a hot, acidified solution in light yellow to greenish yellow needles which are only slightly soluble in cold water. Sodium carbonate liberates the free base, which crystallizes from ether in small, green plates or long needles, melting at 92°. It is precipitated by petroleum ether from a solution in chloroform in moss-green needles, and separates from benzene in large, dark green crystals containing benzene of crystallization, which they lose in the air together with their colour and lustre. All its solutions are coloured deep green. It crystallizes from water in small, lustrous green plates. Like nitrosodimethylaniline, it forms deep steel-blue coloured compounds with aniline, orthotoluidine, &c., and does not give Liebermann's reaction in the cold. Boiling dilute caustic soda converts it into nitrosocresol; potassium permanganate oxidizes it to nitrodimcthylmetatoluidine, C6H3NO2(CH3)N(CH3)2, which crystallizes in long yellow needles, melting at 84°. It is re- duced by tin and hydrochloric acid to dimcthyldiamidotcluene C6H3(CH3)(NH2)N(CH3)2. _ Since the two isomerides of dimethyltoluidine give no nitroso-compounds, the presence of metatoluidine can readily be detected in orthotoluidine, and its amount approximately determined; to effect this the hydrochlorides are prepared, the greater part of the orthotoluidine salt removed by crystallization, the mother-liquor evaporated to dryness, and the residue heated with methyl alcohol; the almost insoluble nitrosodimethylmeta- toluidine is then prepared directly from the mixture of dimethyl- toluidines thus obtained. The two bases can also be separated by fractional distillation, since the ortho-compound boils at 183° and the meta-compound at 215°.1 Metaditolylaminc, (C6H4.CH3)2NH, is formed when meta- toluidine is heated with its hydrochloride. It is a thick, oily, light yellow liquid which becomes coloured brown in the air and boils at 319°-320°.2 Acctmetatoluide, C6H4(CH3)N(C2H3O)H, crystallizes on the gradual evaporation of its aqueous solution in long needles united to form bushy aggregates; it melts at 65'5°, and boils at 1 Wurst er and Riedel, Ber. Deutsch. Chern. Ges. xii. 1796. 2 Cosack, ibid. xiii. 1088. PARATOLUIDINE. 63 303c. 100 parts of water at 13° dissolve 0'44 parts (Beilstein and Kuhlberg). Metatolyl carbamide, (C6H4.CH3)HN.CO.NI12, lias been pre- pared ffom metatoluidine and potassium cyanate ; it crystallizes from water in small plates, and from alcohol in tablets or needles, melting at 142°. Dimetatolyl carbamide, CO(NH.C7H7)2. When metatoluidine is acted upon by chlorocarbonic ether, metatolyl urethane, (C7H7)HN'.CO.OC2H5, is formed; this is a liquid which on distillation in the moist state yields alcohol, carbon dioxide, and dimetatolyl carbamide. The latter crystallizes from hot alcohol in long needles melting at 217° (Cosack).1 Metatolyl thiocarbamide, (C7II7)HN.CS.NH2, is obtained by the action of ammonia on metatolyl thiocarbimide. It is readily soluble in alcohol, slightly in cold, and more freely in hot water, and crystallizes in prisms which form star-shaped aggregates, and melt at 1O30.2 Dimetatolyl thiocarbamide, CS(NH.C7H7)2, is formed when an alcoholic solution of metatoluidine is heated for a long time with carbon disulphide. It crystallizes in concentrically arranged needles, melting at 122°, which are scarcely soluble in boiling water but dissolve readily in alcohol. Mctatolyl thiocarbamide,orMctatolylmustard oil;CSN(C6H4.CH3), is formed when the compound just described is heated with concentrated hydrochloric acid. It is a colourless liquid which boils at 244° and possesses the characteristic smell of the mustard oils in the highest degree ( Weith and Landolt.) 2049 Paratoluidine is formed by the reduction of paranitro- toluene and by heating methylaniline hydrochloride for a day to 350°; methylaniline hydriodide, on the other hand, gives a liquid toluidine,3 which is probably the ortho-compound. It may also be obtained by heating paracresol with the compound of zinc chloride and ammonia to 3OO0.4 It is slightly soluble in water, readily in alcohol and ether, and crystallizes from hot, dilute alcohol in large, colourless plates which melt at 45° and have a peculiar aromatic odour resembling that of aniline. According to Hofmann and Muspratt it boils at 198°, while Stadeler found its boiling-point to be 204°-206°.5 When it is dissolved in monohydrated sulphuric acid and treated 1 Ber. Deutsch. Chem. Ges. ; see also xii. 1450. 2 Weith and Landolt, ibid. viii. 715. 3 Hofmann, ibid. v. 720. 4 Buch, ibid. xiv. 2345 ; xvii. 2637. 5 Jahresber. 1865, 409. 64 AROMATIC COMPOUNDS. with a solution of chromium trioxide in acid of the same strength, it is only coloured yellow. A drop of nitric acid added to the original solution produces a blue colouration, which soon passes through violet and red to brown (Lorenz); in presence of aniline or orthotoluidine no blue colouration is produced, but the liquid becomes coloured blood-red. Bleaching powder solution gives no colouration with solutions of pure paratoluidine; in order therefore to detect the presence of aniline in paratoluidine, the mixture is dissolved in ether, and shaken up with an equal volume of water, a solution of bleaching powder then being added drop by drop. If aniline be present, the ether assumes a blue colour when the solution is agitated (Rosenstiehl). The salts of paratoluidine have been investigated by Hofmann and Muspratt and by Beilstein and Kuhlberg.1 Paratoluidine hydrochloride, C7H9N,HC1, crystallizes in white crusts, which become coloured in the air. 100 parts of water at 11° dissolve 22'9 parts, while 100 parts of 89 per cent, alcohol dissolve 25 parts at 17°. Paratohbidinc hydrobromide, C7H9N, HBr, crystallizes in white plates; the hydriodide is very similar (Reinhardt and Stiidel). Paratoluidine sulphate, (C7H9N)2H2SO4, forms lustrous, scaly crystals, 5'06 parts of which dissolve in 100 parts of water at 22°; they are still less soluble in alcohol. Paratohbidinc nitrate, C7H9N, HN03, crystallizes, when its solu- tion is rapidly cooled, in large rhombic tablets; when allowed to deposit more gradually, it forms long, transparent needles. 100 parts of w*ater at 23'5° dissolve 17'7 parts; it is still more readily soluble in alcohol. Acid paratoluidine oxalate, C7H9N, C2O4H2, crystallizes in rhombic needles or prisms, 0'87 parts of which dissolve in 100 parts of watei' at 14°; alcohol takes up even less. Paratohbidinc phenate, C7H9N, C6H6O, crystallizes from petro- leum ether in long needlesmelting at 31T0.2 Methylparatoluidine, C6H4(CH3)N(CH3)H, is obtained by passing methyl chloride into heated paratoluidine. The pro- duct is extracted with ether, the paratoluidine hydrochloride formed being left undissolved. Any unaltered paratoluidine is precipitated by dilute sulphuric acid, and the ether evaporated, a mixture of methyltoluidine and dimethyltoluidine being thus obtained. The former is converted by the action of acetic 1 Ann. Chem. Pharrn. clvi. 73. 2 G. Dyson, Journ. Chem. Soc. 1883, i. 468. METHYLTOLUIDINES. 65 anhydride into acetmethylparatoluide, C6H4(CH3)N(C2H3O)CH3, which crystallizes from a mixture of ether and alcohol in large plates melting at 83°. Pure methylparatoluidine is then ob- tained by boiling this compound with hydrochloric acid and decomposing the hydrochloride with caustic soda.1 It can be even more simply separated by means of its nitrosamine, in the same way as its isomeride in the ortho-series. (Monnet, Reverdin and Nolting.) It is a liquid which boils at 208° and possesses an aromatic odour. N itrosomethylparatohtidine, C6H4(CH3)N(CH3)NO, crystallizes from a mixture of ether and alcohol in large, well-formed prisms, melting at 54°. Dimethylparatoluidine, C6H4(CH3)N(CH3)2. By the action of methyl iodide on paratoluidine, Thomsen obtained trimethyl- paratolylammonium iodide, C7H7N(CH3)3I, which forms white crystals, and converted it by means of moist silver oxide into the hydroxide, which yielded the base on distillation;2 it is a liquid, which has a characteristic aromatic odour and boils at 208°. Boiling-point. Ethylparatoluidine, C7H7N(C2H5)H, liquid 217° Di-ethylparatoluidine,3 C7H7N(C2H5)2 „ 229° Phenylparatoluidine, or Phenylparatolylamine, C7H7N(C6H5)H, was obtained by Hofmann by the dry distillation of toluidine- blue or tritolylrosaniline,4 while de Laire, Girard, and Chapoteau prepared it by heating aniline with toluidine hydrochloride or toluidine with aniline hydrochloride. In both cases the product is a mixture of diphenylamine, phenyltoluidine, and ditolylamine, which cannot be readily separated by fractional distillation.5 It is also formed when equal molecules of phenol and para- toluidine, or paracresol and aniline, are heated with an excess of zinc chloride for twenty hours to 260°-300°.6 Phenylparatolui- dine crystallizes readily from alcohol in long, silky needles, melts at 87° and boils at 334'5°. Its salts, like those of diphenyl- amine, are decomposed by water, and it gives a fine blue colour- ation with concentrated nitric acid. When fused with mercuric chloride or hexchlorethane, a splendid violet colouring matter is formed. 1 Thomsen, Ber. Deutsch. Chem. Ges. x. 1582. 2 See also Hiibner, Tolle and Athenstadt, Ann. Chem. Pharm. ccxxiv. 336. 3 Morley and Abel, ibid. 93, 313. 4 Ibid, cxxxii. 291. s Buch, Ber. Deutsch. Chem. Ges. xvii. 2634. 6 Morley and Abel, Ann. Chem. Pharm. cxl. 347. 66 AROMATIC COMPOUNDS. Diparatolylamine, (C6H4.CH3)2NH, is obtained by heating paratoluidine with its hydrochloride to 210°-240°. It forms long needles melting at 79°,1 boils at 355°-360°, and is coloured yellow by nitric acid. Its salts are decomposed by water. Diparatolylnitrosamine, (C6H4.CH3)2N(NO), is deposited from petroleum-ether in golden-yellow, hollow, rhombic crystals, melting at 100°-101°. When it is gradually added to well-cooled fuming nitric acid, hcxnitrodiparatolylaminc, (C6H(NO2)3CH3)2NH, is formed; this crystallizes in small yellow pyramids which melt at 258°, and are slightly soluble in the usual solvents.2 - Acetparatoluide, CGH4(CH3)N(C2H3O)H, was first observed by Riche and Berard in the preparation of aniline oil by means of iron and acetic acid, and then prepared by repeated distillation of paratoluidine with acetic acid.3 Arndt and Stadeler obtained it in the same way from crude aniline, and separated it from the acetanilide formed by dissolving the mixture in acetic acid and precipitating the less soluble acet- toluide with water.4 Acetparatoluide is dimorphous; on the gradual evaporation of its alcoholic solution it separates in monoclinic crystals; when a hot solution is allowed to cool, however, it crystallizes in rhombic needles.5 It melts at 147°6, and boils at 307°.7 1,000 parts of water dissolve 0'56 parts at 65°, and 0'886 parts at 22°. Paratolyl carbamide, (C7H7)NH.CO.NH2. Sell prepared this compound by the action of potassium cyanate on toluidine sulphate,8 and Steiner obtained it, together with ditolylguanidine, by treating fulminate of mercury with paratoluidine.9 It is readily soluble in hot water, and crystallizes in thick needles melting at 172°.10 Diparatolyl carbamide, (C7H7NH)2CO, is formed on the distillation of the compound just described (Sell), or when it is heated to 150°-170° with paratoluidine.11 It is also obtained when carbonyl chloride is passed into a solution of paratoluidine in chloroform.12 It is insoluble in water, and crystallizes from 1 Ber. Deutsch. Chern. Ges. vi. 446. 2 Cosack, ibid. xiii. 1092 ; Lehne, ibid. xiii. 1544. . 3 Ann. Chern. Pharm. cxxix. 77. 4 Chern. Centralbl. 1864, 707. 5 Panebianco, Jahresber. 1878, 678. 6 Hubner, and Wallach, Ann. Chern. Pharm. cliv. 302. 7 Beilstein and Kuhlberg, ibid. clvi. 74. 8 Beilstein and Kuhlberg, ibid, cxxvi. 157. 9 Ber. Deutsch. Chern. Ges. viii. 519. 10 Cosack, ibid. xii. 1450. 11 Weith, ibid. ix. 821. 12 Michler, ibid. ix. 710 PARATOLYL URETHANE. 67 hot alcohol in flat needles, which resemble those of benzoic acid and melt at 256.° \ Paratolyl urethane, or Pthyltolyl carbamate, (C7H7)NH(CO) (OC.2H5), is obtained by the action of chlorocarbonic ether on paratoluidine in ethereal solution. It is insoluble in water and crystallizes from alcohol in long prisms, melting at 52°. Paratolyl carbimide, CO.N.C7H7, is obtained by the distillation of the carbamic ether with phosphorus pentoxide, as a strongly refractive liquid boiling at 185°; its vapour possesses a penetrating odour and causes a flow of tears.1 Paratolyl thiocarbamide, (C7H7)NH(CS)NH, is formed when paratoluidine hydrochloride is heated with ammonium thio- cyanate,2 and by the combination of paratolyl mustard oil with ammonia.3 It is slightly soluble in cold water and crystallizes from hot alcohol in small tablets or thick needles melting at 182°. Diparatolyl thiocarbamide, (C7H7.NH)2CS, crystallizes from hot water in large, pointed prisms, melting at 1760.4 Paratolyl thiocarbimide, or Paratolyl mustard oil, CS.N.C7H7. Hofmann obtained this compound by heating the substance just described with phosphorus pentoxide.5 In order to prepare it, paratolyl thiocarbamide is heated to 160° with 30 per cent, sulphuric acid.6 It crystallizes from ether in long, white needles, melts at 26°, and boils at 237°. While both its isomerides possess the characteristic pungent odour of the mustard oils, the smell of paratolyl thiocarbimide resembles that of oil of aniseed. Like other thiocarbimides it combines with ammonia, the amines, and the aromatic amido-bases to form compound thio-ureas. HALOGEN SUBSTITUTION PRODUCTS OF THE TOLUIDINES. 2050 A very large number of these has been prepared, but only the mono-substitution products will be here described. 1 Hofmann, Ber. Deutsch. Chem. Ges. iii. 656. 2 Clermont and Wehrlin, Bull. Soc. Chim. xxvi. 126. 3 Staats, Ber. Deutsch. Chem, Ges. xiii. 136. 4 Sell, loc. cit. ; Maly, Jahresber. 1869, 637. 5 Ber. Deutsch. Chem. Ges. i. 173. 6 Liebermann and Natanson, Liebig's Ann. ccvii. 160. 68 AROMATIC COMPOUNDS. Chlorotoluidines, CoH3C1(CH3)NH2. Melting- Boiling- CI13 : : NH2 : : Cl point. point. 1 2 4 small plates1 . . . . . 29-5° 241° 1 3 4 thin plates2 . . . . . 30° 230° 1 4 3 liquid3 . . . - 222° 1 4 2 crystals4 .... . . . 26° 237°-238-5° Bromotoluidines, C6H3Br(CH3)NH2. CH3 : : NH2 : Br 1 2 3 liquid5 - 1 2 4 plates6 . . 32° 253°-257° 1 2 5 rhombohedra7 . . . . . 58° 240° 1 3 4 prisms8 . . 32° -- 1 8 5 9 „ • • • • • . . 36° 255°-260° 1 3 6 10 » . . 78-5° 240° 1 4 2 11 5? . . 26° - 1 4 3 12 ,, • • • • • . . 8° 240° Neville and Winther have also prepared dibromotoluidines together with higher substitution-products, by methods which give a knowledge of their constitutions.13 o o CH3 : NH2 : I 12 4 needles14 . . . . 49° - 13 4 small plates15 . . . . . 189° - Iodotoluidines, CcH3I(CH3)NH2. 1 Beilstein and Kuhlberg, Ann. Chem. Pharm. clvi. 81; clviii. 337. 2 Gattermann and Kaiser, Per. Deutsch. Chem. Ges. xviii. 2599. 3 Wroblevsky, Ann. Chem. Pharm. clxviii. 153 ; Ber. Deutsch. Chem. Ges. vii. 1062. 4 Lellmann, ibid. xvii. 534. 6 Neville and Winther, ibid. xiii. 1945. 6 Kbrner, Zeitschr. Chem. 1869, 636 : Hubner and Wallach, Ann. Chem. Pharm. eliv. 298 ; Heynemann, ibid, clviii. 340 ; Hubner and Roos, Ber. Deutsch. Chem. Ges. vi. 799. 7 Wroblevsky ; Grete, Ann. Chem. Pharm. clxxvii 249. 8 Neville and Winther, Ber. Deutsch. Chem. Ges. xiii. 972. 9 Wroblevsky, Ann. Chem. Pharm. cxcii. 192, 203 ; Neville and Winther. 10 Wroblevsky ; Neville and Winther. 11 Neville and Winther, Ber. Deutsch. Chem. Ges. xiv. 418. 12 Wroblevsky, Ann. Chem. Pharm. clxviii. 153. 13 Ber. Deutsch. Chem. Ges. xiv. 419. 14 Heynemann, loc. cit. 15 Glassner, ibid. viii. 561. NITROTOLUIDINES. 69 NITROTOLUIDINES, C6H3(CH3)NH2(NO2). 2051 The numbers subjoined refer to the positions of the side-chains in the order given in the formula. a-Orthonitro-orthotoluidine (1:2:6) is formed by the partial reduction of the orthodinitrotoluene melting at 60° - 61°. It is slightly soluble in water, more readily in alcohol, and crystallizes in long, light yellow needles melting at 90° - 91°; it may be converted into orthonitrotoluene by the elimination of the amido-group.1 13-Orthonitro-orthotohtidine, (1:2:3) is obtained as a by- product in the preparation of the compound next described, and crystallizes from dilute alcohol in orange-yellow prisms, united in bushy aggregates, which melt at 97°. It is converted into metanitrotoluene when heated with a solution of nitrogen trioxide.2 Metanitro-orthotoluidine (1:2:5) is obtained by the nitration of acetorthotoluide and decomposition of the products with the calculated quantity of alcoholic potash. It is readily soluble in alcohol, but only very slightly in boiling water, from which it crystallizes in small, citron-yellow needles, melting at 127° -128°. On heating with an alcoholic solution of nitrogen trioxide, metanitrotoluene is obtained, while when the amido-group is replaced by bromine, orthobromometanitrotoluene is formed, and can be converted into orthobromotoluene by means of the diazo-reaction. Paranitro-orthotohtidine (1:2:4). When the phthalyl- toluide obtained by heating orthotoluidine with phthalic anhydride is nitrated, two mononitro-compounds are formed, one of which occurs only in small quantities and on decomposi- tion with ammonia yields the orthonitro-orthotoluidine just described, while the other gives paranitro-orthotoluidine, which melts at 109°, and may be converted into paranitrotoluene by means of the diazo-reaction (Stadel). It is also formed when orthotoluidine is dissolved in 10 parts of sulphuric acid and the well-cooled solution treated with the calculated quantity of nitric acid, mixed with twice its weight of sulphuric acid. The 1 Cunerth, Ann. Chem. Pharm. clxxii. 223 ; Bernthsen, Ber. Deutsch. Chern. Ges. xv. 3016 ; Stade], Ann. Chem. Pharm. ccxxv. 384. 2 Lellmann and Wiirthner, ibid, ccxxviii. 239. 3 Beilstein and Kuhlberg, ibid, clviii. 345. 70 AROMATIC COMPOUNDS. corresponding nitracet-toluide is obtained in a similar manner by dissolving acetorthotoluide in 20 parts of sulphuric acid ; if, however, only 4 parts be taken, the acetyl-compound of meta- nitro-orthotoluidine is also formed.1 a-Orthonitrometatoluidine (1 : 3 : 2) is prepared by the nitra- tion of acetmetatoluide and decomposition of the product with alcoholic potash. It crystallizes in fine, saffron-yellow needles melting at 132°-134°. On heating with an alcoholic solution of nitrogen trioxide, it is converted into orthonitrotoluene (Beilstein and Kuhlberg). ^-Orthonitrometatoluidine (1:5:2) was obtained by Limpricht from the corresponding dinitrotoluene (p. 71). It is slightly, soluble in cold, more readily in hot water, and readily in alcohol; crystallizes in reddish yellow needles, and may be converted into orthonitrotoluene by means of the diazo-reaction.2 Orthonitroparatoluidine (1 :4 : 2) was obtained by the partial reduction of ordinary dinitrotoluene.3 This compound alone is formed when the reduction is effected with ammonium sulphide in the cold; if, however, the mixture be warmed, paranitro- orthotoluidine is also formed.4 Orthonitroparatoluidine is best prepared by dissolving 100 grams, of paratoluidine in 2,000 grams, of concentrated sulphuric acid, and gradually adding a mixture of 75 grams, of concentrated nitric acid with 300 grams, of sulphuric acid to the solution cooled below 0°. After standing for some time, the liquid is poured into ice-water.5 It crystal- lizes from hot water in broad, yellow, monoclinic needles (Panebianco), melting at 77'5°, and may be converted into orthonitrotoluene by means of the diazo-reaction. Mctanitroparatoluidine (1: 4 :3) was obtained by Beilstein and Kuhlberg from acetnitroparatoluide; the latter is best prepared by dissolving acetparatoluide in 4 parts of sulphuric acid, and adding the calculated amount of nitric acid mixed with 2 parts of sulphuric acid to the well-cooled solution. If the amount of sulphuric acid be increased, the acetyl-compound of orthonitroparatoluidine is also formed, while metanitroparatolui- dine can be obtained by the direct nitration of paratoluidine if less sulphuric acid be used (Nolting and Collin). 1 Nolting and Collin, Bcr. Deutsch. Chem. Ges. xvii. 261. 2 Ibid, xviii. 1401. 3 Beilstein and Kuhlberg, Ann. Chem. Pharm. civ. 14. 4 Limpricht, Ber. Deutsch. Chem. Ges. xviii. 1400 ; Graeff, Ann. Chem. Pharm. ccxxix. 340. 6 Nolting and Collin, loc. cit. DINITROTOLUIDINES. 71 It is readily soluble in alcohol, but only slightly in boiling water, and crystallizes in red needles or prisms, melting at II60.1 On heating with a solution of ethyl nitrite, metanitro- toluene is formed. Metanitroparamethyltoluidine, C6H3(NO2)(CH3)NH(CH3), is obtained by heating nitro toluidine with methyl iodide and wood-spirit; it crystallizes from alcohol in red needles, and from benzene in tablets melting at 84° - 85°. Metanitropara-ethyltoluidine, C6H3(N O2)(CH3)NH(C2H5), forms large, red needles melting at 58°-59° (Gattermann). DINITROTOLUIDINES, C6H2(CH3)(NO2)2NH2. 2052. a-Dinitro-orthotoluidine (1: 3 :5 :2) is formed when dinitro-orthocresyl ethyl ether is heated with alcoholic ammonia. It is scarcely soluble in boiling alcohol, slightly in toluene, and crystallizes in prisms or tablets which exhibit a blue iridescence and melt at 208°.2 (DDinitrotoluidine is obtained by heating /3-trmitrotoluene with alcoholic ammonia; it crystallizes from glacial acetic acid in short, golden-yellow needles, melting at 94°. y-Dinitrotolibidine is formed, even in the cold, by the action of alcoholic ammonia on7-trinitrotoluene; it is almost insoluble in the ordinary solvents with the exception of hot acetone and glacial acetic acid, and forms small, hard, golden-yellow crystals melting at 192°-193°. Adjacent Dinitroparatoluidine (1 : 3 : 5 :4) is formed when acetparatoluide is brought into concentrated nitric acid and the product treated with alcoholic potash;3 it may also be obtained by the action of alcoholic potash on dinitroparacresyl ethyl ether.4 It is slightly soluble in alcohol, and crystallizes from carbon disulphide in yellow needles, melting at 1680.5 Chromic acid oxidizes it to chrysanisic acid, C6H2(CO2H)(NO2)2NH2. Symmetric Dinitroparatoluidine (1 :2 : 6 : 4) is obtained by the reduction of a-trinitrotoluene with ammonium sulphide; it 1 Gattermann, Ber. Deutsch. Chcm. Ges. xviii. 1482 2 Stadel, ibid. xiv. 900. 3 Beilstein and Kuhlberg, Ann. Chem. Pharm. clviii. 341; Kelbe, Ber. Deutsch. Chern Ges. viii. 877. 4 Stadel, loc. cit. 5 Hubner, Ann. Chem. Pharm. ccxxii. 74. 72 AROMATIC COMPOUNDS. crystallizes from acetic acid in yellow, hair-like needles, melting at 166'5°-168°. It does not yield chrysanisic acid on oxidation, but a brown powder which is probably an azo-compound.1 Thiotoluidine, (CH3.C6H3.NH2)2S, is formed when paratolu- idine is heated with sulphur and litharge to 140°. It crystallizes from alcohol in lustrous, odourless plates melting at 103°, and is a di-acid base. Its salts crystallize well, but are decomposed by a large quantity of water. When the solution is heated with ferric chloride or any other oxidizing agent, it first becomes yellow, passing into brownish red, and then to dull red, a dark flocculent precipitate being finally formed.2 DIAMIDOTOLUENES, or TOLYLENEDIAMINES, C6H3(CH3)(NH2)2. 2053 a-Diamidotoluene, or ordinary Metatoluylenediamine (1:2:4) was discovered by Hofmann in the high boiling portions of crude aniline oil,3 and was then obtained by him as a product of the reduction of ordinary dinitrotoluene with iron and acetic acid. It is best prepared by the reduction of dinitrotoluene with tin and hydrochloric acid.4 It crystallizes from hot water in long needles, melts at 99°, and boils at about 280°. Its aqueous solution becomes dark-coloured in the air. a-Diamidotoluene monohydrochloride, C7H1ON2.HC1, is obtained by dissolving the base in the calculated amount of hydrochloric acid, and is left as a radiating crystalline mass when the solution is evaporated.5 a-Diamidotoluene dihydrochloride, C7H1ON2(C1H)2, crystallizes from warm hydrochloric acid in needles. a-Diamidotoluene sulphate, C7H10N2.SO4H2 + 2H2O, crystal- lizes from water in long prisms, with a vitreous lustre, and is precipitated in crystals by the addition of alcohol to its aqueous solution. Diamidotoluene, or Orthotoluylenediamine (1:3:4) is formed by the reduction of metanitroparatoluidine with tin and hydro- 1 Beilstein, Ber. Deutsch. Chem. Ges. xiii. 243. 2 Merz and Weith, ibid. iv. 393. 3 Jahresb. Chem. 1861, 512 ; Hell and Schoop, Ber. Deutsch. Chem. Ges. xii 723. 4 Beilstein, Ann. Chem. Pharm. exxx. 242. 5 Bernthsen, Ber. Deutsch. Chem. Ges. xi. 1759. DIAMIDOTOLUENES. 73 chloric acid. It forms brilliant white scales, which are tolerably stable when dry; its aqueous solution, on the contrary, rapidly becomes coloured black in the air. It melts at 88'5°, and boils at 265°. When a crystal is thrown into water it takes up a rapid rotatory motion in dissolving, as do the other diamines (Pt. III. p. 238). fl-Diamidotoluene hydrochloride, C7H1ON2(C1H)2, crystallizes in long, very soluble needles. fl-Diamidotohuene sulphate, 2(C7H10N2.SO4H2) 4- 3H2O, is more readily soluble in water than the a-compound, and is precipitated by alcohol in brilliant white scales, with a nacreous lustre.1 Methyl - fl - diamidotoluene, oi' Metamidoparamethyltoluidine, C6H3(CH3) (NH2) NH (CH3), is prepared in a similar manner to the following compound, and crystallizes in four-sided tablets, melting at 43°-44°. Ethyl-fl-diamidotoluene, C6H3(CH3)(NH2)NH(C2H5), is ob- tained by the reduction of metanitropara-ethyltoluidine, and crystallizes from sulphuretted hydrogen water in large, colourless tablets, which melt at 54°-55°, and soon become dark-coloured in the air. The peculiar rotatory motion assumed by the diamines when dissolving in water was first observed with this compound. A crystal which is not too heavy acquires such a rapid motion that it appears to have a completely closed path. A trace of fat on the water causes cessation of the motion (Gattermann). y-Diamidotoluene, or Paratohtylenediamine (1: 3: 5) was ob- tained by Beilstein and Kuhlberg from metanitro-orthotoluidine; it is also formed when ortho-amido-azotoluene or metamido- azotoluene is reduced with tin and hydrochloric acid.2 It is readily soluble in water, crystallizes from hot benzene in aggre- gates of tablets, melts at 64°, and boils at 273°-274°. On oxidation with manganese dioxide and sulphuric acid, it yields toluquinone. y-Diamidotobuene hydrochloride, C7H1ON2(HC1)2, crystallizes from hot hydrochloric acid in small plates with a nacreous lustre. y-Diamidotoluene sulphate, C7H10N2.SO4H2, is slightly soluble in cold, more readily in hot water, and is precipitated from this solution by alcohol as a white powder. 1 Beilstein and Kuhlberg, Ann. Chern. Pharm. clviii. 351. 2 Nietzki, Ber. Deutsch. Chern. Ges. x. 832, 1158. 74 AROMATIC COMPOUNDS. As already mentioned, solutions of its salts to which a little orthotoluidine has been added are coloured a deep green by ferric chloride. Nietzki at first attributed the colouration to paratoluylene-diamine alone, but he afterwards found that the colour was only produced in samples prepared from ortho-amido- azotoluene, which had not been completely freed from ortho- toluidine ; the pure compound only gives the reaction after the addition of the latter base. 3-Diamidotoluene (1 : 2 :3) is formed by the reduction of orthonitro-orthotoluidine. It forms red crystals, which are readily taken up by the usual solvents, smell like acetamide, melt at 61°-62° and boil at 255°.1 DIAZO-DERIVATIVES OF TOLUENE. 2054. Only the derivatives of paratoluidine have hitherto been prepared pure ; they are obtained by the methods used in the preparation of the corresponding benzene derivatives.2 The diazo-compounds of the two other toluidines have only been obtained as intermediate products in the preparation of derivatives; many examples of this kind have already been given. Diazotoluene nitrate, CH3.C0H4N~NO.NO2, crystallizes in white needles. Diazotoluene sulphate, CH3.C6H4N=N.O.SO2.OH, forms lus- trous needles or prisms. Diazo-amidotohtene, CH3.C6H4N=zN.NH.CcH4.CH3, is pre- pared by passing nitrogen trioxide into a solution of paratolu- idine in a mixture of alcohol and ether.3 It crystallizes in yellow or reddish yellow needles or prisms, and gives a platini- chloride (C14H16N3)2PtCl6, which forms yellow tablets. Diazobenzene-amidotoluene, CfiH,No.NH.Cz.H..CH„ was ob- 7 v D 4 0 4 O' tained by Griess as a product of the action of diazobenzene nitrate on paratoluidine,4 as well as of that of diazotoluene nitrate on aniline.5 It crystallizes in narrow, yellow plates. The formation of the same compound by two different reactions 1 Lellmann and. Wiirthner, Ann. Chem. Pharm. ccxxviii. 243. 2 Griess, Jahresb. Chem. 1866, 458. 3 Griess, Ann. Chem. Pharm. cxxi. 277 4 Ibid, cxxxvii. 60. 5 Ber. Deutsch. Chem. Ges. vii. 1619. AZOTOLUENES. 75 which should yield isomeric substances, is analogous to the case of diazobromobenzene-amidobenzene, which has been already discussed. HYDRAZINE-DERIVATIVES OF TOLUENE. 2055 Paratolylhydrazine, CH3.C6H4.NHzz:NH2, is prepared from paratoluidine just as is phenylhydrazine from aniline. It crystallizes from ethereal solution in rhombic tablets, melts at 61°, boils with slight decomposition between 240°-244°, and is slightly soluble in water, but readily in alcohol.1 Diparatolylhydrazine, (CH3.C6H4)2N-NH.„ is formed by the action of zinc-dust and acetic acid on diparatolylnitrosamine; it crystallizes from benzene in colourless plates melting at 171°- 172°, and is a weak monacid base. Mercuric oxide converts it into diparatolylamine without the formation of a tetrazone-com- pound (Pt. III. p. 29).2 AZO-DERIVATIVES OF TOLUENE. 2056 Azotoluenes, CH„.C,.H.NzzNCfiH,.CHo, are formed by reduction of the nitrotoluenes or oxidation of the toluidines, and are converted into hydrazotoluenes, C7H7.NH - NH.C7H7, by further reduction. Ortho-azotoluene is obtained by the action of zinc-dust and alcoholic potash, or sodium amalgam and alcohol on orthonitro- toluene,3 as well as by the oxidation of orthotoluidine with potassium permanganate, ammonia and oxalic acid being simul- taneously formed.4 It is volatile with steam and crystallizes from ether in red prisms melting at 55°. It is reduced to orthohydro- azotohcene by the further action of sodium amalgam ; this forms colourless crystals melting at 165°, which decompose at a higher temperature into orthotoluidine and ortho-azotoluene, and are readily oxidized to the latter in the air. 1 E. Fischer, Ber. Deutsch. Chem. Ges. ix. 890. 2 Lehne, ibid. xiii. 1546. 3 Petriew, Beilstein's Org. Chem. 976 ; Ber. Deutsch. Chem. Ges. vi. 557. 4 Hoogewerff and van Dorp, ibid. xi. 1203. 76 AROMATIC COMPOUNDS. Meta-azotoluene is most readily formed by treating metanitro- toluene with zinc-dust and alcoholic potash.1 It crystallizes from weak alcohol in orange-coloured rhombic prisms melting at 55°. When it is heated with alcoholic ammonium sulphide, the liquid met ahy dr azotoluene is formed and rapidly re-oxidizes in the air. Para-azotoluene may be best obtained by dissolving 1 part of paranitrotoluene in 10 parts of alcohol and gradually adding 22 parts of 4 per cent, sodium amalgam together with a sufficient quantity of acetic acid 2 The oxidation of paratoluidine with potassium permanganate affords a very poor yield of the azo- compound, but better results may be obtained by oxidizing the sulphate of the base with potassium ferricyanide (Barsilowsky). It is also formed by the action of chromic acid on a solution of paratoluidine in glacial acetic acid,3 and by that of bleaching powder on the base dissolved in chloroform.4 It is slightly soluble in alcohol, readily in ether and petroleum- spirit, crystallizing from the latter in orange-yellow needles which melt at 144°. When it is heated to 100° with alcoholic ammonia • in a closed vessel, parahydrazotoluene is formed and crystallizes in large needles or tablets which melt at 124° and decompose into paratoluidine and parazotoluene when more strongly heated. It rapidly becomes oxidized to the latter when its alcoholic solution is exposed to the air (Melms). Barsilowsky, by the oxidation of paratoluidine with potassium ferricyanide, obtained parazotoluene and an isomeric substance,5 which Perkin also obtained by the action of potassium dichromate on a solution of toluidine sulphate.6 It forms red, hexagonal crystals and is a weak base; Perkin was only able to prepare its platinichloride, from the composition of which he concluded that the compound was a triparatolylenediamine, C21H21N3, while Barsilowsky found that it is reduced by alcoholic ammonium sulphide to a compound isomeric with hydrazotoluene, which crystallizes in small colourless plates and readily oxidizes in the air. It is a weak base tmd forms a very characteristic oxalate, (CuH1(5N2)2C2H2O4 + H2O, which separates from dilute alcohol in star-like aggregates, which are very similar to the seed feathers of the dandelion. 1 Barsilowsky, Ann. Chern. Pharm. ccvii. 114. 2 Helms, Bcr. Deutsch. Chern. Ges. iii. 549. 3 Perkin, Journ. Chcm. Soc. 1880, i. 553. 4 Schmitt, Journ. Prakt. Chern. [2] xviii. 198. 6 Ann. Chem. Pharm. ccvii. 102. 6 Journ. Chem. Soc. 1880, i. 546. AMIDO-AZOTOLUENES. 77 Klinger and Pitschke have now found that the red substance is an amido-azo-compound of the formula C28H28N4.1 It is decomposed into paratoluidine and paraleucotohcidine, C21H25N3, by energetic reduction with tin and hydrochloric acid. This compound crystallizes in small colourless plates, and is readily oxidized io pararosotoluidine, C21H23N3, which forms small lustrous red plates, and dissolves in water with an intense violet-red colour. The red substance has, therefore, the following con- stitution, C21H17(NH2)2N ~ N.C6H5.CH3. These compounds will be more fully described in the sequel. Ortlio-azoxytolueneQJA^N , is formed when orthonitrotoluene is heated with a solution of sodium in methyl alcohol, and crystallizes from warm petroleum-ether in yellow, monoclinic needles melting at 59°-60°. It is not converted into the isomeric hydroxyazotoluene, C7II7.N2.C7H6.OH, on heating with concentrated sulphuric acid, but a large quantity of ortho- toluidine is formed, the oxygen thus liberated producing the oxidation of a portion of the ortho-azoxytoluene to a mixture of amorphous acids. Klinger and Pitschke consider that the conversion of azoxy- benzene into hydroxyazobenzene (Pt. III. p. 297) is brought about in a similar manner, and may be looked upon as " hy- droxylation by direct oxidation." 2 Amido - azotoluenes, CH3.C6H.N = N.C6H3(CH3)NH2, are formed by the action of nitrous acid on orthotoluidine and metatoluidine, while paratoluidine, as already mentioned, is thus converted into diazo-amidotoluene. Compounds belonging to this group are also formed by the action of a diazoparatoluene salt on orthotoluidine or metatoluidine, as well as on aniline, etc.3 Amidortho-azotohiene is obtained by passing nitrogen trioxide into orthotoluidine floating on a saturated solution of common salt. The product is allowed to stand for some time, washed with water to remove any orthocresol which has been formed, treated with dilute caustic soda and finally boiled with dilute hydrochloric acid, the hydrochloride thus obtained being then decomposed by ammonia. Amidortho-azotoluene is slightly soluble in water, readily in alcohol, and crystallizes in lustrous, golden plates or tablets, 1 Ber. Deutsch. Chern. Ges. xvii. 2439. " Ibid, xviii. 2551. 3 Nietzki, ibid. x. 662, 832, 1156. 78 AROMATIC COMPOUNDS. melting at 100°. The hydrochloride, C14H15N3.C1H, is only slightly soluble in water, and crystallizes in long, thin tablets with a silver lustre. This compound is decomposed into orthotoluidine and para- tolylenediamine by the action of hydrochloric acid and tin or zinc dust, and has therefore the-"following constitution: / >N=N</ >NH2. ch3 -ch3 Amidometa-azotolucne, crystallizes from alcohol in broad, golden-yellow needles melting at 80°. The hydrochloride forms ]ong, dark blue needles, which are only slightly soluble in hot alcohol, and, like all the other salts of this class, is decomposed by water. On reduction with tin and hydrochloric acid, para- tolylenediamine is formed. Ortho-amidopara-azotoluene forms yellow tablets melting at 127° -128°; its hydrochloride crystallizes in cinnabar-red needles, which appeal' of a steel-blue colour when seen by reflected light. Metamidoparazotoluene crystallizes from alcohol in large, yellow, plates, melting at 127°; the hydrochloride forms small, steel-blue needles. Para-amidopara-azotoluene. In order to prepare this compound, the isomeric diazo-amidoparatoluene is heated for twelve hours to 65° with five times its weight of paratoluidine and one equiva- lent of paratoluidine hydrochloride. It crystallizes from alcohol or acetic ether, in orange-red lustrous needles melting at 1185°. Its hydrochloride crystallizes in light yellow needles and forms a green solution in water. It is converted into paratoluidine and orthotolylenediamine by reduction.1 On treatment with fuming sulphuric acid, a mixture of di- sulphonic acids is formed, which comes into the market as " Acid yellow R," since it dyes a redder shade than the colouring matter obtained from amido-azobenzene (Part III. p. 307), which is therefore called " Acid yellow G." a-Azoxy toluidine, C14H12N2(NH2)2O, is formed by the action of sodium amalgam on a solution of orthonitroparatoluidine in absolute alcohol, and crystallizes from hot water in small, yellow needles melting at 148°. It is a diacid base, and on further reduction yields the following compounds : 1 Nolting and Witt, Ber. Deutsch. Chem. Ges. xvii. 77. AZOXYTOLUIDINES. 79 a-Azotoluidine, or Symmetric a-diamido-azotoluene, C14H12N2 (NH2)2, crystallizes from hot water in red needles which are readily soluble in alcohol and melt at 159°. a-Hydrazotoluidine, C14H12(N2H2)(NH2)2, is almost insoluble in cold water and alcohol, but is slightly soluble in hot alcohol; it forms small, colourless, rhombic tablets which melt at 180°. It is tolerably stable in contact with cold water and alcohol, but rapidly oxidizes when heated with them in the air.1 (3-Azoxy toluidine, C14H12K2(NH2)2O, is obtained from para- nitro-orthotoluidine and crystallizes in long, yellow to yellowish red, silky needles melting at 168°; its salts crystallize well. When heated with concentrated sulphuric acid, it is' converted into the isomeric hydroxyazo-compound, just as is the case with azoxybenzene (Part III. p. 296): /N.C7H6.NH2 NC7H5(OH)NHq 0<l =11 \n.c7hg.nh2 nc7h6.nh2. This compound crystallizes from alcohol in small, dark red needles, which melt at 212° with decomposition. Its hydro- chloride and sulphate are only slightly soluble in water. On treatment with stannous chloride and hydrochloric acid, it is resolved into ordinary diamidotoluene and diamidocresol, C6H2(CH3)(NH2)2OH, the hydrochloride of which crystallizes in white needles which become coloured blue in the air; the free base immediately becomes resinous. A-Azotoluidine, or Symmetric jB-diamido-azotohiene, C14H12N2 (NH2)2, crystallizes from hot water in small, yellow needles, and is deposited on the gradual evaporation of its alcoholic solution in long, red needles, which melt at 197°, and are slightly soluble in water, readily in alcohol. The sulphate is only slightly soluble in water, the hydrochloride being somewhat more readily dissolved. ^-Hydrazotohtidine, C14H12(N2H2)(NH,)2, forms yellow needles which rapidly oxidize when exposed to the air in a moist state. It decomposes without melting when heated, and burns with a brilliant flame. It is almost insoluble in absolute alcohol, but dissolves readily in dilute alcohol and water.2 1 Buckney, ibid. xi. 1451. 2 Limpricht, Ber. Deutsch. Chem. Ges. xviii. 1403; Graff, Ann. Ghem. Pharm. ccxxix. 340. 80 AROMATIC COMPOUNDS. The constitutions of the two azotoluidines are expressed by the following formulae : a. fl. nh2__ _nh2 nh2_ _nh2 / >N-n/ \ CH3/ \n=n/ >CH3. ~ch3 ch3 Metanitroparatoluidine is immediately converted by sodium amalgam into the corresponding diamidotoluene, while metanitro- ortho- and a-orthonitrometa-toluidine yield resinous products on oxidation (Limpricht). Asymmetric diamido-azotoluenc, C7H7N~NC7H5(NH2)2, cor- responds to chrysoidine (Part III. p. 301) and is formed by the action of diazotoluene nitrate on a-diamidotoluene. It crystal- lizes from alcohol in orange-yellow needles melting at 183°. Its hydrochloride, (C14H16N4)C1H, forms red needles.1 2057 Tolusafranine, C21H20N4. The history of this dye, which is simply known as " safranine " in commerce, has already been briefly indicated. Phenosafranine chloride, the lower homologue of tolusafranine, has been proved 2 to have the following con- stitution : N oOo™' N-Cl I NH2. This formula explains all the facts which have been already given (Part III. p. 369) concerning this substance, and also its formation from one molecule of paradiamidobenzene and two molecules of aniline. Hofmann and Gey ger were the first to subject the com- mercial product to a searching examination; they ascertained 1 Hofmann, Ann. Chern. Pharm. x. 218. 2 Witt, Ber. Deutsch. Chern. Ges. xix. 3121. Nietzki, ibid. 3163. TOLUSAFRANINE. 81 that it is a hydrochloride of the formula C21H21N4C1, which is not attacked by alkalis, but is readily decomposed by moist silver oxide, and that it is not a derivative of aniline, as had been up to that time assumed, but of orthotoluidine, from which it can be obtained by the action of nitrous acid and oxidation of the products with arsenic or chromic acids.1 Witt then found that it is formed by heating amido-ortho-azotoluene with orthotoluidine hydrochloride,2 and by the oxidation of a mixture of orthotoluidine and paratoluylenediamine.3 In order to prepare it, a solution of equal molecules of orthotoluidine and hydrochloric acid is treated with the calculated quantity of sodium nitrate, to obtain amido-ortho-azotoluene ; the product, after the addition of some orthotoluidine hydrochloride, is allowed to stand and is then reduced with zinc-dust and hydrochloric acid, a mixture of 7-diamidotoluene and orthotoluidine being formed, which is then neutralized and oxidized with potassium clichromate; if the solution were kept acid, toluquinone would be formed.4 The safranine is then precipitated with common salt, filtered off, pressed, dried and brought into the market.5 Tolusafranine hydrochloride, C21H21N4C1, is tolerably soluble in water and alcohol, forming red solutions which possess a characteristic fluorescence; the salt is precipitated from its aqueous solution by the addition of hydrochloric acid in red crystals, which are best obtained by crystallizing the commercial product from boiling, dilute alcohol. The free base, obtained from this compound by means of silver oxide, probably has the formula C21H21N4OH, and forms reddish brown crystals which take a faint green metallic lustre on drying, but have not yet been obtained free from silver chloride; they are soluble in water and alcohol, but not in ether. Tolusafranine nitrate, C21H21N4.NO3, crystallizes in reddish brown needles which are only very slightly soluble in cold water. Tolusafranine picrate, C21H20N4.C6H3(NO2)3O, is obtained by the addition of picric acid to a solution of one of the salts of the base, and forms brownish red needles, insoluble in water, alcohol and ether. 1 Ber. Deutsch. Chem. Ges. v. 526. 2 Ibid. x. 874. 3 Ibid. xii. 939 ; Bindschedler, Hid. xiii. 207. 4 Nolting, Schultz, Steinkohlentheer, 1049. 5 Ibid. 527. 82 AROMATIC COMPOUNDS. Tolusafranine shows all the characteristic reactions of the safranines (Part III. p. 323). It is employed as a substitute for saffron for dyeing silk and cotton mordanted with tannin. 2058 Toluylene-blue, G15H18N4.HC1 + H2O, is formed when 36 grms. of nitrosodimethylaniline hydrochloride, and 24 grms. of metatoluylenediamine, each dissolved in 500 c.cm. of water at 30°, are mixed.; evolution of heat takes place and a deep green colouration is produced. If the solution be now allowed to stand, flat, lustrous brown prisms separate out, but gradually fall into a fine crystalline powder. These readily form blue solutions in water, alcohol and acetic acid ; traces of free mineral acids change the colour into reddish brown, the original shade being restored by alkalis. The base is precipitated by alkalis from its solution as a resinous mass which takes a cupreous lustre in the air. Toluylene-blue is converted by tin and hydrochloric acid into the leuco-compound, C15H2ON4HC1, which is a deliquescent crystalline substance and is very readily re-oxidized. Toluylene-red, C15H16N4, is formed, together with the leuco- compound, when toluylene-blue is boiled with water for 15-20 minutes. Stannous chloride precipitates the colouring matter as a double tin salt in crystals, which are then decomposed by an alkali. Toluylene-red crystallizes in orange-red needles containing four molecules of water, which they lose at 150°-160°. The anhydrous base is blood-red and only slightly soluble in alcohol; it forms rose-red normal salts, which are stable and readily soluble in water, while its acid salts are coloured blue and are decomposed by water. Tohcylene-violet, C14H14N4, h formed by warming toluylene- blue with metatoluylenediamine dissolved in dilute acetic acid for twelve hours to 35°-40°, the leuco-base of the blue compound being simultaneously formed : 3C15H18N4 + 2C7H10N2 = C14H14N4+3C15H20N4. Toluylene-violet forms red crystals with a green reflection and is even less soluble than toluylene-red ; its solution is flesh- coloured and shows a remarkable orange-yellow fluorescence. Its slightly soluble normal salts are coloured violet and crystal- lize well, while the acid salts have a grass-green colour. TOLUYLENE COLOURS. 83 Witt o-ives the following constitutional formulae for these O 0 compounds:1 Toluylene-blue. zN(CH3)2 c6h4< II ZCH C6H3<NH2 \nh; Toluylene-red. zn(uh3)2 C6H4< \N c C6H3-NH \nh2 Toluylene-violet. /NH2 C6H3-CHs 0 c6hZnh \nh2 PHOSPHORUS DERIVATIVES OF TOLUENE. 2059 Paratolylphosphorus dichloride, CH3.COII4PC12, is obtained by the continued heating of 15 parts of toluene with 200 parts of phosphorus trichloride and 3 parts of aluminium chloride, or by heating mercury paratolyl with phosphorus trichloride to 180°-190°.2 It is a crystalline mass, which fumes slightly in the air, melts at 25°, and boils at 245°. Paratolylphosphorus tetrachloride, CH3.C6H4PC14, is formed by the combination of the compound just described with chlorine, and crystallizes from benzene in pointed prisms melting at 42°. When heated in a sealed tube to 200°, it decomposes with formation of the dichloride and parachlorobenzyl chloride : 2CH3.C6H4PC14 = CH3.C6H4PC12+CH2C1.C6H4C1+PC13+HC1. It rapidly deliquesces in the air, forming paratolylphosphorus oxychloride, CH3.C6H4POC12, which is, however, best obtained in a similar manner to phenylphosphorus oxychloride, by the action of sulphur dioxide on the tetrachloride. It is a thick liquid, boiling at 284°-285°. Paratolyl phosphenylous acid, CH3.CcH4PO2H2, is formed by the action of water on the dichloride. It is slightly soluble in water and crystallizes from alcohol in tablets melting at 104°-105°. Paratolylphosphenilic acid, CH3.C6H4PO(OII)2, is obtained by decomposing the tetrachloride or the oxychloride with water. It is readily soluble in alcohol and crystallizes from water in matted, woolly needles which melt at 181°. It is decomposed by ignition 1 Ber. Deutsch. Chern. Ges xii. 931. 2 Michaelis and Paneck, Liebig's Ann. ccxiL 203. 84 AROMATIC COMPOUNDS. with lime, with formation of toluene and calcium phosphate. Potassium permanganate oxidizes it to parabenzophosphcnilic acid, CO2H.C6H4PO(OH)2, which will be described under benzoic acid. Paratolylphosphine, CH3.C6H4.PH2, is obtained by heating tolylphosphenylous acid in an atmosphere of carbon dioxide. It is a liquid which possesses a most intense smell, inhalation of its vapour producing headache and bleeding of the nose. It boils at 178° and solidifies at a lower temperature to a crystalline mass which melts at 4°. It is rapidly oxidized to to'ylphosphenylous acid in the air. It combines with hydriodic acid to form paratolylphosphonium iodide, CH3.CcH4.PH3I, crystallizing in broad, lustrous needles which deliquesce in the air and sublime in cubes when heated to 340° in a current of. carbon dioxide. Dimethylparatolyl phosphine, CH3.C6H4.P(CH3)2, is obtained by the action of zinc methyl on the dichloride, and is a liquid which has an unpleasant smell, boils at 210°, dissolves in acids and is not oxidized by exposure to the air. Mercuric oxide con- verts it into dimethyltolylphosphine oxide, CH3.CGII4.P(CH3)2O) which is a thick liquid. The phosphine combines with methyl iodide to form CH3.CGH4P(CH3)I, crystallizing in needles which melt at 225° and yield a strongly alkaline, deliquescent hydroxide.1 The corresponding chloride is a very hygroscopic crystalline body.2 Orthotolylphosphorus dichloride, CH3.C6H4PC12, is obtained by heating orthomercury tolyl with phosphorus trichloride. It is a liquid which boils at 244° and does not solidify even at -20°. It combines with chlorine forming the tetrachloride as a solid yellow mass. It is decomposed by water with formation of orthotolylphosphenylous acid, which is a liquid but forms crystal- line salts, while the orthotolylphosphenilic acid obtained from the tetrachloride consists of small crystalline grains which melt at 141° (Michaelis and Paneck). ARSENIC DERIVATIVES OF TOLUENE. 2060 Arscnparatolyl chloride, CH3.C6H4AsC12, is obtained by heating mercury paratolyl with arsenic trichloride.3 It crystal- lizes in tablets, melts at 31°, and boils in an atmosphere of carbon dioxide at 267° without decomposition. It combines with chlorine 1 Czimatis, Ber. Deutsch. Chem. Ges. xv. 2014. 2 Ibid. 2018. 3 Michaelis and La Coste, Ann. Chem. Pharm. cci. 246. ARSENIC DERIVATIVES OF TOLUENE. 85 forming the tetrachloride, a yellow crystalline mass, which is semi-fluid at the ordinary temperature but solidifies completely on cooling. It is converted by water into tolylarsenic acid, CH3.C6H4AsO(OH)2, which crystallizes in long, thin needles. When the dichloride is boiled with caustic soda solution, arsen- tolyl oxide, CH3.C6H4AsO, is formed as a powder melting at 156°. Arsendi paratolyl chloride, (CH3.C6H4)2AsC1, is formed when mercury tolyl is boiled for a long time with three or four times its amount of arsentolyl chloride.1 It is an oily, yellow liquid which is converted by boiling alcoholic potash into arsenditolyl oxide ((CH3.C6H4)2As)2O, which crystallizes from ethei' in silky needles melting at 98°. The monochloride combines with chlorine to form arsendiparatolyl trichloride, (CH3.C6H4)2AsC13, a yellow powder which is immediately converted by water into dipara- tolylarsenic acid, (C7H7)2AsO(OH), a white crystalline mass which is slightly soluble in water, readily in alcohol, from which it crystallizes in granules melting at 1G7°. It is oxidized by an alkaline solution of potassium permanganate to dibenzo- arsenic acid, (CO2H.C6H4)2AsO2H. Triparatolylarsine, (CH3.C6H4)3As, is formed by heating arsenparatolyl oxide to 360°: 3CH3.CfiH4AsO = (CHo.C6H4),As+As20o. O 4 \ 6 0 4/6 1 Z 6 It separates from ethereal solution in large crystals which melt at 145° and only volatilize at temperatures above 360°. When chlorine is passed into its chloroform solution, arsentri- tolyl dichloride, (CH3.C6H4)2AsC12, is formed as a white crystal- line mass which is dissolved almost without decomposition by boiling water. Tritolylarsine is oxidized by alkaline potassium permanganate solution to tribenzo-arsenic acid, (CO2H.C6H4)3As(OH)2, which will be described under benzoic acid. Arsenorthotolyl chloride, C6H3.C6H4AsC12, has been obtained from mercury orthotolyl and arsenic trichloride, and is a faintly smelling liquid which boils at 264°-265° in an atmosphere of carbon dioxide without undergoing decomposition. It combines with chlorine to form the tetrachloride, which is a thick honey- yellow liquid. When the dichloride is boiled with soda solution, arsenorthotolyl oxide, CH3C6H4AsO, is formed as a powder which 1 La Coste, ibid. ccviii. 18. 86 AROMATIC COMPOUNDS. is readily .soluble in hot water, slightly in alkalis, and melts at 145°-146°. Orthotolylarsenic acid, CH3.C6H4As.O(OH)2, is obtained by the action of water on the tetrachloride, and crystallizes from hot water in fine needles, which melt at 159°-160° and are con- verted by prolonged heating into the crystalline anhydride, arscnorthotolyl dioxide, CH3.C6H4AsO2 (La Coste and Michaelis). ANTIMONY DERIVATIVES OF TOLUENE. 2061 These compounds are obtained by the action of sodium on a mixture of antimony trichloride with bromotoluene dissolved in benzene.1 Paratolylstibine, Sb(C6H4.CH3)3, is readily soluble in benzene, slightly in alcohol, and crystallizes in large, transparent, lustrous tablets melting at 127'5°. It forms compounds with the elements of the chlorine group, which crystallize from benzene in lustrous prisms. Melting-point. Paratolylstibine chloride, Sb(C7H7)3Cl2 . . 156'5° Paratolylstibine bromide, Sb(C7H7)3Br2 . . 233'5° Paratolylstibine iodide, Sb(C7H7)3I2 . . 182'5° Paratolylstibine oxide, Sb(C7H7)3O, is obtained by treating the bromide with alcoholic potash and washing the residue with water; it is slightly soluble in benzene, from which it crystallizes in small needles melting at 223'5°. If it be dissolved in hot glacial acetic acid and treated with sufficient water to produce turbidity, fine, transparent crystals of paratolylstibine hydroxide, Sb(C7H7)3(OH)2, are deposited on cooling; this compound melts at 169'5°. Metatolylstibine, Sb(C6H4.CH3)3, forms large tablets melting at 64'5°; the bromide, which melts at 113° and crystallizes well, is much more readily soluble in ether than its isomerides. Orthotolylstibine is a thick liquid, and forms a crystalline bromide.2 3 Michaelis and Genzken, Ber. Deutsch. Chem. Ges. xvii. 924. 2 Ibid. MERCURY DERIVATIVES OF TOLUENE. 87 BORON AND SILICON DERIVATIVES OF TOLUENE. 2062 Paratolylboron chloride, CH3.C6H4BC12, is obtained by the action of boron chloride on mercury paratolyl, and is a colourless crystalline mass, which melts at 27°. Water converts it into tolylboric acid, CH3.C6H4B(OH)2, a violent reaction taking place; this compound crystallizes from hot water in fine needles melting at 240°.1 Paratolylsilicon chloride, C H3.C6H4SiCl3, is obtained by heating mercury tolyl with silicon tetrachloride to 300°-320°. It is a strongly refractive liquid which boils at 218°-220°, fumes in the air and is converted by dilute ammonia into paratolyl silicic acid, CH3.C6H4SiO(OH), which separates from ether as an oil which gradually changes into a thick, elastic mass. It commences to lose water at 100° and is completely converted at 200° into paratolylsilicon oxide, which is a solid mass.2 Silicon paratolyl, Si(C6H4.CH3)4, is readily obtained by the action of sodium on a mixture of silicon chloride and parabromo- toluene. It separates from benzene in transparent crystals melting at 228°, and boils above 3G0° without decomposition.3 Dichlorosilicon orthoditobuide, SiCl2(NH.C7H7)2, is formed by the action of silicon tetrachloride on orthotoluidine. It forms a colourless, amorphous mass which readily absorbs moisture with formation of silica and toluidine hydrochloride. Hydrochloric acid gas decomposes it into toluidine hydrochloride and silicon tetrachloride.4 MERCURY DERIVATIVES OF TOLUENE. 2063 Dreher and Otto obtained mercury paratolyl by the action of sodium amalgam on the bromotoluene obtained by the direct bromination of toluene.5 Ladenburg then showed that the ortho-compound is also formed in this way and can readily be 1 Michaelis and Becker, ibid. xv. 185. 2 Ladenburg, Ann. Chem. Pharm. clxxiii. 162. 3 Polis, Ber. Deutsch. Chem. Ges. xviii. 1542. 4 Harden, Journ. Chem. Soc. 1887, 44. 8 Ann. Chem. Pharm. cliv. 171 88 AROMATIC COMPOUNDS. separated from the para-compound by re-crystallization from benzene.1 In order to prepare it, bromotoluene to which a little acetic ether and petroleum have been added, is boiled with 1 ;5 per cent, sodium amalgam for a long time in an apparatus connected with an inverted condenser, and the products separated by re-crystallization from hot benzene.2 Mercury orthotolyl, (CH3C6H4)2Hg, is more readily soluble in benzene than the para-compound and crystallizes in large triclinic tablets melting at 107°. Mercury paratolyl forms matted needles which melt at 238° and can be distilled without decomposition, if the heating be very carefully performed. It is only slightly soluble in cold water. Its derivatives resemble those of mercury phenyl. 1 Ann. Chcm. Pharm. clxxiii. 162. 2 Ibid. cci. 246 BENZYL GROUP. 2064 The compounds obtained by the replacement of one atom of hydrogen in the methyl group of toluene by other elements or radicals are looked upon as derivatives of a mono- valent radical phenylmethyl or benzyl, C6H5.CH2. BENZYL ALCOHOL, C6H5.CH2.OH. Liebig and Wohler, in 1832, observed that when oil of bitter almonds, C7H6O, is treated with alcoholic potash in absence of air, benzoic acid, C7H6O2, is formed, together with an oily substance, which is different from the original oil; they make the following remarks : " Although we have not investigated this new product more carefully, there can be no doubt, provided that the alcohol takes no essential part in the reaction, that it is formed either by separation of oxygen from the oil of bitter almonds or by some reaction involving the sharing of the elements of water. In the former case its composition will be expressed by the formula C14H12O, in the latter by C14H14O2"1 (C = 6, 0 = 8). Cannizzaro then found that this substance is " the alcohol corresponding to benzoic acid," and that although its composition does not correspond with that of the ordinary alcohols, it behaves towards reagents as an alcohol, the aldehyde of which would be oil of bitter almonds. He obtained the latter compound by oxidizing the alcohol with ordinary nitric acid, while chromic acid gave benzoic acid. He further showed that the action of hydrochloric acid produced an ethereal chlorine compound, C7H7C1, which is derived from the alcohol of benzoic acid and is reconverted into the alcohol by treatment with caustic potash; when heated with alcoholic ammonia it yielded a base which differed essentially 1 Ann. Chcm. Pharm. iii. 254, 261. 90 AROMATIC COMPOUNDS. from toluidine. He also prepared the acetate, which is decom- posed by warming with caustic potash into acetic acid and the alcohol of benzoic acid, and says : " This kind of alcohol appears to be the type of a whole class of new alcohols, the more complete investigation of which is now in progress."1 In the course of this investigation he found that concentrated alcoholic potash produced a decomposition in which benzoic acid and toluene were formed from the alcohol, so that the latter stands in the same relation to toluene as wood-spirit to marsh gas:2 C7H8O + KOH = C7H5KO2 + 2H2 C7H8O + H2 = C7H8 + H2O. He also succeeded in converting toluene into the alcohol; by the action of chlorine on the boiling hydrocarbon he obtained chlorobenzyl, which was identical with that obtained by the action of hydrochloric acid on the alcohol. On heating with potassium acetate, both compounds gave benzyl acetate, which yielded the alcohol on saponification with caustic potash.3 This compound had previously been in the hands of several chemists, who had not, however, recognised its nature. Fremy isolated from Peru balsam a compound which he named cinnamem, from which he obtained cinnamic acid and peruvin, C9H12O, by heating with caustic potash.4 The latter compound, according to Plantamour, who prepared it the same way and also observed the formation of cinnamic acid, is ethyl cinnamate; he was led to this conclusion by the fact that when he heated it with caustic potash and evaporated the whole to dryness, he obtained potassium cinnamate and a combustible vapour which he took for ethyl alcohol. He remarks that the origin of this substance, which was only recognised in this indirect and remarkable manner, still requires explanation.5 Scharling first accurately determined the composition of cinnamem and looked upon it as a compound ether. The peruvin, C7H8O, obtained from it he considered as an alcohol, probably identical with Cannizzaro's compound. When he brought it into contact with platinum black, the smell of oil of bitter almonds was produced.6 Strecker then expressed his conviction that cinnamem is the cinnamic ether of benzyl alcohol,7 and was confirmed by Kraut, 1 Ann. Chem. Pharm. Ixxxviii. 129. 2 Ibid. xc. 252. 3 Ibid xcvi. 246. 4 Ibid. xxx. 324. 5 Ibid. xxx. 341. 6 xcvii. 168. 7 Lehrb. Org. Chem. 1856, 456. BENZYL COMPOUNDS. 91 according to whom Fremy's peruvin was a mixture of this alcohol and toluene, Plantamour's compound being, however, the pure alcohol. The acid taken for cinnamic acid was obviously benzoic acid and the combustible vapour consisted of toluene.1 The liquid portion of Peru balsam2 consists chiefly of the benzoate and cinnamate of benzyl, but also contains some free benzyl alcohol.3 Both ethereal salts occur in Tolu balsam,4 and the latter in liquid styrax.5 Benzyl alcohol also seems to be contained in the oil of the cherry-laurel, which consists chiefly of benzaldehyde and its cyanhydrin (Tilden).6 The action of alcoholic potash on oil of bitter almonds, which was observed by Cannizzaro, is characteristic of the aromatic aldehydes, oxidation and reduction taking place simultaneously: C6H5.CHO + KOH = C6H5.CO.OK + H2 C6H,.CHO + H2 = C6H5.CH2.OH. Benzyl alcohol is also formed by the action of sodium amalgam and water on benzaldehyde7 and on benzoic acid,8 while the fatty acids are not changed by nascent hydrogen. Benzoyl chloride, C6H5.COC1, is also reduced to benzyl alcohol by the action of sodium amalgam and hydrochloric acid,9 while a better yield may be obtained by adding sodium amalgam to an ethereal solution of benzamide, C6H5.CONH2, which contains water and has been rendered faintly acid with hydrochloric acid.10 1 Ann. Chem. Pharm. cvii. 208. 2 Peru balsam, like Tolu balsam, was first described by the Spanish physician Monardes (p. 3) ; the latter is derived from Myroxylon toluifera, the former from Myroxylon pareirae, a native of Central America in the district of Costa del Balsamo. Peru balsam contains the same substances as that from Tolu, together with several of a different nature, this being due to the difference in the methods of extraction employed in the two cases. While the latter is obtained by the simple process of making incisions, it is necessary to remove the bark before extracting the Peru balsam. In order to accomplish this, it is first loosened by blows of a hammer or the back of an axe, and is then superficially charred by burning torches or bundles of twigs, the effect of this treatment being either to detach it or to render its removal a matter of no difficulty. The stem is next wrapped round with rags, which become saturated with the balsam, and are then removed and heated with water ; the balsam is thus separated from the cloth and sinks to the bottom of the vessel (Fliickiger and Hanbury, Pharmacographia, 2 Ed. p. 205). 3 Kraut, Ann. Chem. Pharm. clii. 131. 4 Ber. Deutsch. Chem. G^. ix. 830. 5 Laubenheimer, Ann. Chem. Pharm. clxiv. 289. 6 Pharm. Journ. Trans. [3] v. 761. 7 Friedel, Ann. Chem. Pharm. cxxiv. 324. 8 Herrmann, ibid, cxxxii. 75. 9 Lippmann, ibid, cxxxvii. 252. 10 Guareschi, Gazz. Ghim. Itai. iv. 465 ; Ber. Deutsch. Chem. Ges. vii. 1462. 92 AROMATIC COMPOUNDS. It is best obtained from benzyl chloride, which can readily be prepared from toluene, by boiling it for two hours with water and lead hydroxide,1 or by simply boiling it for two days with 25-30 parts of water, 76 per cent, of the theoretical yield being thus obtained.2 According to Mennier, it may be advantageously prepared by boiling equal parts of benzyl chloride and potassium carbonate with 10 parts of water for several hours.3 Cannizzaro's process does not serve for the preparation of the alcohol from benzaldehyde, as the action of the alcoholic potash is only gradual, even on long continued heating, and a consi- derable loss is experienced through the formation of resinous products. If, however, 10 parts of the aldehyde be shaken up with a solution of 9 parts of caustic potash in 6 parts of water until a permanent emulsion is obtained, and sufficient water to form a clear solution be then added to the semi-solid mass of crystals formed on standing by the separation of potas- sium benzoate, the benzyl alcohol can readily be extracted from the liquid with ether. The ether is then distilled off and the residue purified by rectification without being dried. In this way 92 per cent, of the theoretical yield can be obtained, while the application of alcoholic potash only gives a yield of 43 per cent. Since only one half of the benzaldehyde is converted into the alcohol, benzyl chloride is a more economical source ; it is, however, more difficult to obtain in a state of purity than benzaldehyde and therefore does not yield a pure product so readily. As mentioned above, it is impossible to dry the alcohol before distillation; it combines with calcium chloride slowly in the cold, more rapidly on heating, and is attacked by solid caustic potash.4 If two molecules of benzaldehyde be added to a solution of one atom of sodium in 12 parts of methyl alcohol and the mixture heated in an apparatus connected with inverted condenser, a white substance soon separates out, which seems to be a compound of methyl benzoate and sodium methylate, since it is formed when these are heated together. If the heating be continued for about two days and the mass neutralized with glacial acetic acid, and then heated with water, an oil separates out which can 1 Grimaux and Lauth, Ann. Chern. Pharm. cxliii. 80. 2 Niederist, ibid, cxcvi. 353. 3 Bull. Soc. Chim. xxxviii. 159. 4 R. Meyer, Ber. Deutsch. Chcm. Ge\ xix. 2394. BENZYL ALCOHOL. 93 be separated into two portions by distillation. About two-thirds of the whole boil between 198°-210°, and consist of a mix- ture of equal molecules of methyl benzoate, boiling at 199°, and benzyl alcohol, boiling at 206°. These cannot be separated, but if the benzoate be saponified, pure benzyl alcohol can readily be obtained. The smaller portion of the product, about 20-30 per cent, on the benzaldehyde employed, boils at 320°-324°, and consists of benzyl benzoate. This is polymeric with the aldehyde and is formed directly from it: c6h5.cho c6h5.ch9X U U V *> it \ _ - /° c6h5-cho c6h5.co z The chief reaction, however, consists in the conversion of the benzaldehyde in the presence of sodium methylate into methyl benzoate and benzyl alcohol: 2C6H-.CHO + ch3.oh = C6H5.CO.OCH3 + CcH5.CH2.OH. The two latter appear to be then partially converted into benzyl benzoate and methyl alcohol.1 If this reaction be employed for the preparation of benzyl alcohol, the original product is simply saponified. In order to prepare it from Peru balsam, the latter is thoroughly agitated with 2 volumes of caustic potash of sp. gr. 1'2, the emulsion exhausted with ether, the extract separated and eva- porated, and the residual oil heated with 4 volumes of caustic potash of sp. gr. 1'3 until a homogeneous liquid is obtained. The pulpy mass of crystals formed on cooling is pressed in linen, and the liquid diluted with water and distilled until the dis- tillate ceases to appear milky. The alcohol is then separated from the aqueous distillate and the portion which remains dis- solved in the latter extracted by ether.2 Properties.-Benzyl alcohol is a liquid which possesses a faint aromatic odour, boils at 206°, and has a sp. gr. of 1'063 at 0°. It is not insoluble in water, as was at one time thought, for 100 parts of water at 17° dissolve 4 parts (R. Meyer). When heated with hydriodic acid and a little phosphorus to 170°- 180°, it is almost completely reduced to toluene, only a small 1 L. Claisen, private communication. 2 Kaehler, Ber. Deutsch. Chem. Ges. ii. 512. 94 AROMATIC COMPOUNDS. amount of higher boiling substances being formed.1 Its other characteristic properties which were ascertained by Cannizzaro have been already mentioned. BENZYL ETHERS. 2065 Benzyl methyl ether, C6H5.CII2.O.CH3, was obtained by Sintenis by heating benzyl chloride with methyl alcohol and caustic potash.2 It is a pleasant smelling liquid, which boils at 167°-168° and is decomposed by chlorine in the cold with formation of benzaldehyde and methyl chloride : C6H5.CH2.O.CH3 + Cl2 = C6H6.COH + CH3C1 + HCL Benzyl ethyl ether, C6H5.CH2.O.C2H5, is formed when benzyl chloride is boiled with alcoholic potash, and is a mobile liquid, possessing a pleasant odour and boiling at 182°-184°.3 Chlorine acts upon it in the cold just as on the methyl ether; at the boiling point, however, benzoyl chloride is formed : CJL.CEUO.CJD + 2CL = C6H5.COC1 + CJLC1 + 2HC1. \J U H h o h \) O HU In the presence of iodine, ethyl iodide and parachlorobenz- aldehyde, C6H4C1.COH, are obtained (Sintenis). Bromine produces a similar decomposition, benzaldehyde, ethyl bromide and hydrobromic acid being first formed ; the latter then decomposes another portion of the ether into benzyl bromide and ethyl bromide, and the benzaldehyde is converted into benzoyl bromide by the excess of bromine.4 Dibenzyl ether or Benzyl oxide, (C6H5.CH2)2O. Cannizzaro obtained this compound by heating benzyl alcohol to 120°-125° with boron trioxide and treating the product with water and potassium carbonate. When the dried oil is distilled, unaltered benzyl alcohol comes over first, and then the ether, a resinous hydrocarbon remaining behind in the retort. Dibenzyl ether is a colourless, oily liquid, which boils at 310°-315° and has a faint indigo-blue fluorescence. It decomposes into toluene and 1 Gra.be, Ber. Deutsch. Chern. Ges. viii. 1054. 2 Ann. Chern. Pharm. clxi. 334. 3 Cannizzaro, Jahresb. 1856, 582. 4 Paterno, Gaz. Chim. Itai. i. 586. BENZYL ETHERS. 95 benzaldehyde when heated to a few degrees above 315° in a sealed tube ; a very small quantity of the resinous hydrocarbon is also formed in this way. Dibenzyl ether is also formed in small quantity, together with various hydrocarbons, when benzyl chloride is heated with water to 190°.1 C. W. Lowe prepared dibenzyl ether in the following way:- Sodium was added to benzyl alcohol diluted with ether. Towards the end of the reaction heat was applied in order to convert all the alcohol into sodium benzylate. The product was mixed with benzyl chloride and gently heated, when a rather violent reaction set in. Dibenzyl ether is a perfectly colourless liquid, having a slight but persistent odour of hawthorn blossom. Its sp. gr. at 16° is 1'0359. It boils at 295°-298°, at the same time being partially resolved into toluene and benzaldehyde. This decomposition goes on more rapidly at 315C as Cannizzaro found, a very small quantity of a resinous body being formed at the same time. Benzyl phenyl ether, C6H5.CH2.O.C6H5, is obtained by heating benzyl chloride with potassium phenate and alcohol to 1OO0.2 It forms scaly crystals with a nacreous lustre, melts at 38°-39° and boils at 286°-287° (Sintenis). On heating with con- centrated hydrochloric acid to 100°, it decomposes into benzyl chloride and phenol; hydrobromic acid produces a similar decomposition. Chlorine attacks it in the cold with formation of benzyl chloride and substitution products of phenol, the action of bromine being quite analogous. In the presence of mercuric oxide, on the other hand, substitution products of the ether are formed (Sintenis). Melting- Boiling- point. point. Benzyl chloro- ] C6H5.CH2 ) phenyl ether j C6H4C1 f 0 long needles 70°-71° Benzyl bromo- ) C6H5.CH2 1 phenyl ether J C6H4Br J 0 long needles 59°-59'5° - Benzyl ortho- i CfiH5.CH2 ) cresyl ether3 J CH3.C6H4 J 0 liquid - 285°-290° Benzyl para- 1 C6H5.CH2 > q hexagonal | 41° cresyl ether J CH3.C6H4 ) prisms Ethers of benzyl with the dihydroxybenzenes are formed when 1 Limpricht, Ann. Chem. Pharm. cxxxix. 307. 2 Lauth and Gnmaux, ibid, cxliii. 81. 3 Stadel, Bcr. Deutsch. Chem. Ges. xiv. 898. 96 AROMATIC COMPOUNDS. the latter are heated with benzyl bromide and alcoholic potash.1 Melting- point. Bi • 1 n u (OH ) large lustrous 1 , enzylqumol, C„H,1 0 J scales } 122 Dibenzylquinol, C6H4(O.CH2.C6H5)2, lustrous tablets 130° Dibenzylresor- ) ~ j r x f small lustrous 1 cinol, J O6H4(O.CH2.C6H5)2) | tablets y 76 Dihenzylcate- J yellow needles 61" ■ ETHEREAL SALTS OF BENZYL. 2066 Benzyl chloride, C6H5.CH2C1. Cannizzaro obtained this compound by the action of hydrochloric acid on benzyl alcohol and it is also formed by that of chlorine on boiling toluene.2 It is prepared on the large scale by the latter method, the toluene being contained in large glass balloons heated by a bath of calcium chloride, and the chlorine passed through in such a manner that it chiefly comes in contact with the vapour of the toluene. This is effected by only allowing the leaden conducting tube, which terminates in a short piece of glass tubing, to dip a small distance below the surface of the boiling liquid. The vapours of toluene are condensed by a cooling arrangement and the hydrochloric acid evolved is led into water. The product is washed with water containing a little caustic soda, and the benzyl chloride freed from unaltered toluene and higher substitution products by distillation. It is a colourless liquid, the vapour of which has a penetrating aromatic smell, rapidly produces a flow of tears and attacks the mucous membrane most violently. It boils at 176° and has a sp. gr. of IT07 at 14°. As it undergoes double decom- position very readily, it is employed for the preparation of the other benzyl compounds, and it is also used to a considerable extent in the synthesis of the higher members of the aromatic series. It is also technically employed in the manufacture of benzaldehyde and in the colour industry. 1 Schiff and Pellizzari, Ann. Chem. Pharm. ccxxi. 365. 2 Beilstein and Geitner, ibid, cxxxix. 337. BENZYL IODIDE. 97 Benzyl bromide, C6H5.CH2Br, is formed by the action of hydrobromic acid on benzyl alcohol, and by that of bromine on boiling toluene.1 It is a liquid which first smells like cress and then like mustard oil; its vapour, like that of the chloride, pro- duces a flow of tears. It boils at 198°-199°, and has a sp. gr. of 1'438 at 22°. Benzyl iodide, C6H5.CH2I, was obtained by Cannizzaro in the impure state by the action of iodine and phosphorus on benzyl alcohol. Lieben prepared the pure compound by allowing benzyl chloride to stand in the dark for three weeks with five times its weight of hydriodic acid.2 It is also formed by the action of potassium iodide on benzyl chloride,3 and is a colourless, crystal- line body, the vapour of which produces a most copious flow of tears; it is only slightly soluble in alcohol, but readily in ether and carbon disulphide. It fuses at 24° to a liquid which has a sp. gr. of 1'7335, and on further heating becomes coloured red, decomposing at about 240°, at which temperature it com- mences to boil, into iodine, hydriodic acid, and a hydrocarbon which smells like toluene. Benzyl nitrate, C6H5.CH2.NO3. appears to be formed by the action of silver nitrate on benzyl chloride: the product of the reaction decomposes on distillation with an energetic evolution of red fumes, the distillate consisting of benzaldehyde and benzoic acid.4 The same products are obtained by treating benzyl iodide with silver nitrite.5 2067 Benzyl acetate, C6H5.CH2 C2H3O2. Cannizzaro obtained this compound by distilling benzyl alcohol with acetic and sulphuric acids, as well as by heating benzyl chloride with potassium acetate, and alcohol. It is a liquid which possesses an aromatic odour, boils at 206°, and has a sp. gr. of 1'057 at 16'5°.6 It is converted into the benzyl ether of hydrocinnamic acid or benzylacetic acid by the action of sodium: 4C6H5.CH2.O.CO.CH3+2Na = 2C6H5.CH2.O.CO.CH2.CH2.O6H5 + 2NaO.CO.CH3 + H2. Boiling-point. Benzyl propionate, C7H7.O.C3H5O 219°-220°. Benzyl butyrate, C7H7.OC4H7O 238°-240°. 1 Kekule, Ann. Chem. Pharm. cxxxvii. 139; Cannizzaro, ibid. cxli. 198; Beilstein, ibid, cxliii. 369 ; Lauth and Grimaux, ibid. cxlv. 113. 2 Zeitschr. Chem. [2] vi. 736. 3 V. Meyer, Ber. Deutsch. Chem. Ges. x. 311. 4 Brunner, Ber. Deutsch. Chem. Ges. ix. 1744. 8 van Renesse, ibid. ix. 1454. 6 Conrad and Hodgkinson, Liebig's Ann. cxciii. 298. VOL. III.-PART IV. 98 AROMATIC COMPOUNDS. Those ethers are acted upon by sodium in the same way as the acetate (Conrad and Hodgkinson). The compounds thus formed will be subsequently described. Benzyl oxalate, (CcH5.CH2)2C2O4, is formed by the action of benzyl chloride on silver oxalate,1 and by heating benzyl alcohol with oxalic acid.2 It crystallizes from hot alcohol in lustrous white, scaly crystals, melting at 80'5°. Isonitrosobenzyl ether, C6H5.CH2.O.N=:CH.CO.CH3, is prepared by heating benzyl chloride with a solution of sodium and isonitroso-acetone (Part I. p. 572, and Part III. p. 170, note} in absolute alcohol. It crystallizes from petroleum ether in colourless tablets, which have a pleasant smell of flowers and melt at 45°-4G0.3 Acetoxime benzyl ether, C6H5.CH2.ON~C(CH3)2, is obtained in a similar manner from acetoxime, and is a pleasant smelling liquid which decomposes into acetone and benzylhydroxylamine when boiled with concentrated hydrochloric acid : C6H5CH2.O.N=C(CH3)2+H2O^ I CO(CH3)2. The compound actually obtained in this way is benzylhydroxy- ammonium chloride, which crystallizes in silvery scales, and is converted into benzyl iodide by heating with hydriodic acid :4 CcH3. CH2.O.NH3C1 + 3HI=C6H5.CH2I + NH.C1 + H.,0 +L. VO £ O' V O 4 'k * & * 4 SUBSTITUTION PRODUCTS OF BENZYL ALCOHOL AND ITS DERIVATIVES. 2068 Substitution-products are not formed by the direct action of chlorine, bromine, or nitric acid on benzyl alcohol, since all these reagents produce oxidation. Its ethers, how- ever, can undergo direct substitution, and if an atom of hydrogen in one of them be replaced, para-compounds are formed, from which the corresponding alcohols may readily 1 Beilstein and Kuhlberg, Liebig's Ann. cxlvii. 341. 2 Dumas and Demar^ay, Compt. Rend. Ixxxiii. 688. 3 Meyer and Ceresole, Ber. Deutsch. Chern. Ges. xv. 3071. 4 Janny, ibid. xvi. 170. SUBSTITUTION PRODUCTS OF BENZYL ALCOHOL. 99 be obtained. Thus, parachlorobenzyl alcohol, C6H4C1.CH2.OH, is prepared by boiling its chloride or bromide with water : C6H4Cl.CH2Br+H20 = C6H4C1.CH2OH + HBr. The haloid,ethers can also be converted into the acetate by boil- ing with alcohol and potassium acetate, and this saponified by heating with ammonia: CfiH.Cl.CH2.O.C2H3O + NH3 = C6H.C1.CH2.OH+C2H3O.NH2. 4 A o 0 0 4 4 40 4 The higher chlorinated benzyl chlorides have been converted into their alcohols by means of this reaction. Paranitrobenzyl alcohol can readily be prepared by nitrating benzyl acetate or oxalate and heating the product with am- monia. Chlorine substitution-products of benzyl chloride can be obtained, as already mentioned, by treating it with chlorine in the cold or in presence of iodine, as well as by allowing chlorine to act upon the vapour of boiling, chlorinated toluene. Accord- ing to Beilstein and Kuhlberg, the latter is the better method, and is now generally adopted. The bromine substitution-products are prepared in a similar manner; the use of this method has shown that substitution does not readily take place in the methyl group when bromine is allowed to act on boiling orthobromotoluene. Paranitrotoluene is converted by bromine at high temperatures into paranitrobenzyl bromide; paranitrobenzyl chloride and metanitrobenzyl bromide can also be readily obtained, but not the ortho-compound. If orthonitrotoluene be heated with bromine, no orthonitrobenzyl bromide is found, but the product, according to Wachendorff, consists of dibromorthonitrotoluene, C6H2Br2(NO2)CH3, which is not attacked by potassium acetate or silver acetate even at 1600.1 It possesses the exceptional property of dissolving in aqueous alkalis and being reprecipitated by mineral acids, and Greiff was therefore induced to examine it more carefully. He found that it is not dibromonitrotoluene, but the isomeric dibromortho-amidobenzoic acid, C6H2Br2(NH2)CO2H. Since the isomerides of orthonitrotoluene behave quite differently towards bromine, it follows that the ortho-position facilitates a mutual exchange between the oxygen of the nitroxyl and the 1 Ann. Chern. Pharm. clxxxv. 259. 100 AROMATIC COMPOUNDS. hydrogen of the methyl. How this intermolecular change takes place has not yet been explained, but it seems probable that orthonitrobenzyl bromide is first formed and is then con- verted by the nitroxyl group into ortho-amidobenzoic acid, just as benzyl chloride is oxidized to benzoic acid by nitric acid. 2069 Parachlorobenzyl alcohol, CfiH4Cl.CH2.OH, is formed by boiling the corresponding bromide or chloride with water,1 or by heating parachlorobenzyl acetate to 100° with aqueous ammonia.2 It is readily soluble in alcohol, scarcely in cold, but somewhat more readily in warm water, from which it crystallizes in long needles melting at 70'5° (Jackson and Field). Oxidizing agents convert it into parachlorobenzoic acid. Melting-point. Dichlorobenzyl alcohol,3 C6H3C12.CH2OH, needles 77° Trichlorobenzyl alcohol,4 C6H2C13.CH2OH, crystals - Tetrachlorobenzyl alcohol,5 C6HC14.CH2OH, „ - Pentachlorobenzyl alcohol,6 C6C15.CH2. OH, short needles 193° Parachlorobenzyl ethyl ether, C6H4C1.CH2.O.C2H5, is formed by heating parachlorobenzyl chloride7 or parachlorobenzyl acetate8 with alcoholic potash; it is a liquid which boils at 218°,9 and is split up by chlorine in the cold into ethyl chloride and parachlorobenzaldehyde. Phenylchlorocarbylethyl ether, or Benzylethoxyl chloride, C6H5. CHC1.O.C2H5, is prepared by boiling benzylidene chloride, C6H5.CHC12, for a long time with alcoholic ammonia. It is a liquid which boils at 210°-212° and is converted into ethyl metanitrobenzoate, C6H4(NO2)CO.OC2H6, by nitric acid.10 Parachlorobenzyl chloride, C6H4C1.CH2C1, is obtained together with a little of the ortho-compound, by the chlorination of benzyl chloride in presence of iodine, and by the action of chlorine on boiling monochlorotoluene, as a liquid which boils at 213°-214°.u It is prepared pure from parachlorotoluene;12 it crystallizes from alcohol in lustrous needles or prisms which 1 Jackson and Field, Ber. Deutsch. Chem. Ges. xi. 905 ; Amer. Chern. Journ. ii. 88. 2 Beilstein and Kuhlberg, Ann. Chem. Pharm. cxlvii. 344. 3 Ibid. 350. * Ibid. clii. 241. 6 Ibid. 245. 6 Ibid. 246 7 Naquet, ibid. Suppl. [2] 250. 8 Neuhof, ibid, cxlvii. 345 9 Sintenis, ibid. clxi. 335. 10 Hubner and Bente, Ber. Deutsch. Chem. Ges. vi. 805. 11 Neuhof, Ann. Chem. Pharm. cxlvi. 320. 12 Jackson and Field, Ber. Deutsch. Chem. Ges. xi. 904. PARABROMOBENZYL ALCOHOL. 101 melt at 29°, readily sublime, and possess an aromatic vapour which attacks the mucous membrane very violently. Dichloro- Melting- | point. Boiling- point. benzyl- chloride,1 Trichloro- C6H3C12.CH2C1, liquid . . - 241° benzyl- chloride,2 Tetrachloro- ' -C6H,C13.CH2C1, „ . . - 273° benzyl- chloride,3 Pentachloro-' CfiHCl..CH2Cl, „ . . 4 0 4 4 ' " 1 - 296° benzyl- chloride,4 C6C15.CH2C1, fine needles 103° 325°-327° Parachlorobenzyl bromide, C6H4Cl.CH2Br, resembles the chloride very closely ; it melts at 48'5°.5 Parachlorobenzyl acetate, C6H4C1.CH2 O.C2H3O, is obtained by boiling the chloride with potassium acetate and absolute alcohol; it is a liquid which boils at 240° and has an aromatic odour.6 Parabromobenzyl alcohol, C6H4Br.CH2.OH, is formed when the bromide is boiled with water for several days; it crystallizes from a hot solution in flat, elastic, pearly needles which have an aromatic odour, melt at 69°, and only volatilize slowly with steam.7 Parabromobenzyl bromide, C6H4Br.CH2Br. This compound is prepared by passing bromine vapour into a boiling mixture of parabromotoluene and orthobromotoluene, which is obtained by the direct bromination of toluene. After the calculated quantity has been added, the liquid is allowed to cool, a portion of the bromide crystallizing out in large, rhombic prisms. The mother- liquor is then distilled with steam in which the ortho- is more readily volatile than the para-compound. The latter can also readily be obtained in long, thick, transparent prisms by allowing bromine to act upon the mixture of bromotoluenes in the sun- light.8 Parabromobenzyl bromide crystallizes from alcohol in needles which melt at 61° and are volatile with steam ; its vapour 1 Beilstein and Kuhlberg, Ann. Chem. Pharm. cxlvi. 146, 326. 3 Ibid. cl. 290. 3 Ibid. 299. 4 Ibid. 302. 8 Field and Jackson, toe. cit. 6 Neuhof, Ann. Chem. Pharm. cxlvii. 345. 7 Jackson and Lowry, Ber. Deutsch. Chem. Ges. x. 1209. 8 Schramm, ibid. xvii. 2922 ; xviii. 350. 102 AROMATIC COMPOUNDS. has a pleasant, aromatic odour, but attacks the eyes, nose, and throat very violently.1 Parabromobcnzyl acetate, C6H4Br.CH2.O.C2H3O, is a liquid which has a pleasant smell resembling that of acetic ether, and decomposes on distillation.2 Mctabromobenzyl bromide, CcH4Br.CH2Br, is obtained in a similar manner to the para-compound ; the yield is, however, very poor. It crystallizes in plates or needles which melt at 41°, and its vapour attacks the mucous membrane violently, but has a somewhat different smell from that of the para-compound. It only volatilizes slowly in a current of steam, but with remark- able rapidity in ether and tolerably readily in alcohol. It is not attacked by chromic acid solution, but the corresponding alcohol, which has not been further investigated, is oxidized by it to metabromobenzoic acid.3 Orthobromobenzyl alcohol, C6H4Br.CH2.OH, crystallizes from hot water in flat needles, which melt at 80°, and readily volatilize with steam.4 Orthobromobenzyl bromide, CGH4Br.CH2Br, is only formed with difficulty, and has not been obtained pure, since it decomposes on distillation. It is an oily liquid, which does not solidify at -15°, volatilizes with steam, possesses an aromatic odour, and rapidly attacks the mucous membrane ; a drop placed on the tongue causes severe pain.5 Sodium acts upon its ethereal solution with formation of various products, among them being anthracene : ZCH\ Qh4< I ^c0h4. Para-iodobenzyl alcohol, C6H4I.CH2.OH, crystallizes from carbon disulphide in scales and from boiling water in long needles, which have an aromatic odour and melt at 71'7°.6 Para-iodobenzyl bromide, CcH4I.CH2Br, is formed by the action of bromine vapour on heated para-iodotoluene, and crystallizes from alcohol in flat, white needles, which melt at 78'7°, possess an aromatic odour, and attack the mucous membrane less violently than the bromobenzyl bromides. Boiling water con- verts it into the alcohol.7 1 Schramm, Bor. Deutsch. Chern,. Ges. viii. 1672 ; ix. 931. 2 Jackson and Lowry, ibid. x. 1209. 3 Jackson and White, Amer. Chem. Journ. ii. 315. 4 Jackson, ibid. viii. 932. 5 Jackson, Ber. Deutsch. Chern. Ges. ix. 932. 6 Jackson and Mabery, ibid. xi. 56 ; Amer. Chem. Journ. ii. 251. 7 Jackson and Mabery, loc. cit. PARANITROBENZYL ALCOHOL. 103 2070 Paranitrobenzyl alcohol, C6H4(NO2)CH2.OH, is prepared by heating its acetate or oxalate with ammonia to 1OO0,1 and by the action of caustic soda on paranitrobenzaldehyde.2 It crystal- lizes from boiling water in fine, lustrous, colourless needles, which become coloured in the air and melt at 93°. On oxidation it yields paranitrobenzoic acid. Paranitrobenzyl chloride, C6H4(NO2).CH2C1, is obtained, to- gether with the ortho- and meta-compounds, by the action of concentrated nitric acid on benzyl chloride,3 the chloride being gradually added to the acid which has been previously cooled to -15°.4 It is also formed by treating paranitrotoluene with chlorine at 135°-190°.5 It crystallizes from boiling alcohol in fine, white needles, or small, nacreous plates, which melt at 76°. An alkaline solution of pyrogallol reduces it to paranitro- toluene.6 Paranitrobenzyl bromide, C6H4(NO2)CH2Br, is formed when paranitrotoluene is heated to 120°-130° with bromine; the reaction takes place at 70°-80° in the presence of ferrous bromide, which acts as a bromine carrier.7 On the gradual evaporation of its solution in a mixture of ether and alcohol, it crystallizes in thin tablets, which melt at 99°-100°. It destroys the skin, producing a burning pain, and the vapour given off by its hot alcoholic solution attacks the mucous membrane most violently (Waehendorff). Paranitrobenzyl iodide, C6H4(NO2)CH2I, is obtained by heat- ing the chloride with potassium iodide and alcohol; it crystallizes in four-sided tablets, melting at 127°, and its vapour produces a flow of tears.8 Paranitrobenzyl nitrate, C6H4(NO2)CH2NO3. Beilstein and Kuhlberg prepared this compound by the action of concentrated nitric acid on the alcohol, and believed that it was dinitrobenzyl alcohol. Stiidel found, however, that it loses nitric acid when heated with water to 100°, and that it yields paranitrobenzoic acid on oxidation,9 and Orth prepared it by heating the chloride 1 Beilstein and Kuhlberg, Ann. Chern. Pharm. cxlvii. 343. 2 Basler, Ber. Deutsch. Ghent. Ges. xvi. 2715. 3 Beilstein and Geitner, Ann. Chcm. Pharm. cxxxix. 327; Grimaux, ibid. cxlv. 146 ; Abelli, Gaz. Chim. Itai. xiii. 97. 4 Strakosch, Ber. Deutsch. Chcm. Ges. vi. 1056. 5 Waehendorff, Ann. Chern. Pharm. clxxxv. 271. 6 Pellizzari, Ber. Deutsch. Chcm. Ges. xviii. Ref. 150. 7 S^heufeln. Ann. Chern. Pharm. ccxxxi. 177. 8 Kumpf, ibid. xvii. 1074. 9 Ibid. xiv. 903. 104 AROMATIC COMPOUNDS. ■with alcohol and silver nitrate.1 It crystallizes from hot water in fine, white needles, and from alcohol in long, flat needles, melting at 71°. Paranitrobenzyl acetate, C6H4(NO2)CH2.C2H3O2, is obtained by dissolving benzyl acetate in well-cooled concentrated nitric acid (Beilstein and Kuhlberg) or by heating the chloride with potassium acetate and alcohol (Grimaux). It crystallizes from hot alcohol in long, pale yellow needles, melting at 78°. Paranitrobenzyl oxalate, (C6H4(NO2)OH2)2C2O4, was obtained by Beilstein and Kuhlberg by dissolving benzyl oxalate in concentrated nitric acid; on heating with aqueous ammonia it is converted into the alcohol. 2071 Metanitrobenzyl alcohol, C6H4(NO2)CH2. OH, was prepared by Grimaux, together with metanitrobenzoic acid, by the action of alcoholic potash on metanitrobenzaldehyde as a thick, oily liquid, which decomposes on heating, but boils at 178°-180° under a pressure of 3 mm.2 Mctanitrobenzyl chloride, C6H4(NO2)CH2C1, is formed by the action of phosphorus pentachloride on the alcohol; it crystallizes from hot petroleum ether in long, light yellow needles, which melt at 45°-47°, and produces painful irritation and burning on the skin.3 Orthonitrobenzyl alcohol, CGH4(NO2)CH2.OH. When ortho- nitrotoluene is given to a dog, it appears in the urine as ortho- nitrobenzoic acid, and as the urea salt of uronitrotoluic acid, 2C13H15NO9.CO(NH2)2 + 5H2O, crystallizing in long needles, which are very readily soluble in water, slightly in cold alcohol, and insoluble in ether. On boiling this with baryta water and decomposing the barium salt formed with sulphuric acid, uro- nitrotoluic acid, C13H15NO9, is obtained as a crystalline mass resembling asbestos, which is extremely soluble in water and alcohol and has a strongly acid reaction. On boiling with dilute sulphuric acid it decomposes into a syrupy acid and orthonitro- benzyl alcohol;4 this compound can also be prepared by the action of caustic soda on orthonitrobenzaldehyde.5 It is slightly soluble in water, readily in alcohol and ether, and crystallizes in long, fine needles, which melt at 74°, and can be sublimed, but detonate when rapidly heated. 1 Kumpf, xv. 1136. 2 Zeitschr. Chem. 1867, 562. 3 Gabriel and Borgmann, Ber. Deutsch. Chem. Ges. xvi. 2064. 4 Jaffe, Hoppe-Sey lev's Zeitschr. ii. 47. 5 Friedlander and Henriques, Ber. Deutsch. Chem. Ges. xiv. 2801. SULPHUR COMPOUNDS OF BENZYL. 105 Orthonitrobenzyl chloride, C6H4(NO2)CH2C1, is formed, as already mentioned, together with its isomerides, by the nitration of benzyl chloride, and was first isolated from the product by Kumpf.1 It is also obtained by the action of phosphorus penta- chloride on the alcohol.2 It crystallizes from petroleum ether in large rhombohedra melting at 48°-49°. Orthonitrobenzyl iodide, CcH4(NO2)CH2I, is prepared by heat- ing the chloride with potassium iodide and alcohol; it forms rhombohedral plates melting at 75°, and its vapour causes a flow of tears. Octhamidobenzyl alcohol, C6H4(NH2)CH2.OH, is obtained by the action of hydrochloric acid and zinc-dust on orthonitrobenzyl alcohol in alcoholic solution. It crystallizes from benzene in white needles, which melt at 82°, become coloured brown in the light or in the air, and have a faint smell resembling that of aniline. It combines with acids forming soluble, crystallizable salts.3 SULPHUR COMPOUNDS OF BENZYL. 2072 Benzyl hydrosulphide, or Benzyl mercaptan, CcH5.CH2.SH. Miircker obtained this compound by heating benzyl chloride or benzyl bromide with an alcoholic solution of potassium hydro- sulphide.4 Otto prepared it by the action of benzyl chloride on potassium thiosulphate,5 and Bottinger by fusing thiobenzalde- hyde, C6H5.CSH, with caustic potash, benzyl disulphide and a little benzoic acid being simultaneously formed.6 It is a colourless, powerfully refractive liquid which has an unpleasant smell of leeks, boils at 195°, and has a sp. gr. of 1'058 at 20°; its vapour produces a flow of tears. It gradually oxidizes in the air, more rapidly in the presence of ammonia to benzyl disulphide; an ethereal solution of bromine produces the same effect. Mercury benzyl mercaptide, (C6H5.CH.2S).,Hg, is formed by heating the hydrosulphide with mercuric oxide ; it crystallizes from alcohol in long, silky needles. Mercuric chloride, in 1 Friedlander and Henriques, xvii. 1073. 2 Gabriel and Borgmann, Ber. Deutsch. Chem. Ges. xvi. 2064. 3 Friedlander and Henriques, ibid. xv. 2109. 4 Ann. Chem. Pharm. cxxxvi. 75. 5 Zeitschr. Chem. [2] vi. 23. 6 Ber. Deutsch. Chem. Ges. xii. 1055. 106 AROMATIC COMPOUNDS. alcoholic solution, gives with the mercaptan a white precipitate of C6H5.CH2.S.HgCl. Lead benzyl mercaptide, (C6H5.CH2S)2Pb, is obtained in small yellow plates by mixing hot, alcoholic solutions of lead acetate and benzyl mercaptan. Parachlorobenzyl hydrosulphide, C6II4C1.CH2.SH, is formed when parachlorobenzyl chloride is boiled with an alcoholic solu- tion of potassium hydrosulphide. According to Beilstein, it is obtained in lustrous crystals, melting at 84°-85°,1 while accord- ing to Jackson and White, it is an oily liquid which possesses a most repulsive and penetrating odour, and solidifies on cooling in crystals which melt at 19°-2O0.2 Paranitrobenzyl hydrosulphide, C6H4(NO2)CH2.SH, crystallizes from alcohol in small, colourless, lustrous plates, melting at 14O0.3 Benzyl ethyl sulphide, C6H5.CH2.S.C2H5, is prepared by the action of ethyl iodide on a solution of sodium in benzyl hydro- sulphide, and is a transparent liquid, which boils at 214°-216°,4 and possesses a penetrating odour resembling that of ordinary mercaptan. Orthobenzyl thioformate, (C6H5.CH2.S)3CH, is formed when an aqueous solution of sodium benzyl mercaptide is heated with chloroform; it separates from hot alcohol in colourless crystals, melting at 98°. When heated with fuming nitric acid to 250°, it is decomposed into benzyl mercaptan and formic acid.5 Benzyl sulphide, (C6H5.CH2)2S. Marcker obtained this com- pound by heating benzyl chloride with an alcoholic solution of potassium sulphide. It crystallizes from hot alcohol in large, dazzling white plates, and from ether or chloroform in large, thick, rhombic tablets,6 melting at 49°. On distillation it yields stilbene, C14H12, and sulphuretted hydrogen; dibenzyl, C14H14, tolallyl sulphide, C14H10S, and thio- nessal, C28H20S, are simultaneously formed. Methyl iodide and benzyl sulphide react even in the cold, more rapidly on warming, with formation of benzyldimethyl- sulphine iodide, CGH5.CH2(CH3)2SI, and trimethylsulphine iodide, 1 Beilstein, Ann. Chern. Pharm. cxvi. 347 ; cxlvii. 346. 2 Amer. Chern. Journ. ii. 167. 3 Strakosch, Bor. Deutsch. Chem. Ges. v. 598. 4 Marcker, Ann. Chem. Pharm. cxl. 88. 5 Dennstedt, Ber. Deutsch. Chem. Ges. xi. 2265. 6 Forst, Ann. Chem. Pharm. clxxviii. 671. SULPHUR COMPOUNDS OF BENZYL. 107 (CH3)3SL The first stage of the reaction is represented by the following equation : 2CH3I + (C6H5.CH2)2S = (CH3)2S + 2C6H5.CH2I. The methyl sulphide then combines with the iodides forming the compounds mentioned. If the product be extracted with water, shaken up with silver chloride and the filtrate then fractionally precipitated with platinum chloride, benzyl dimethyl- sulphine platinichloride, (C6H5.CH2(CH3)2S)aPtCl6, separates out first; it crystallizes from water in long, orange-red needles.1 Cahours,2 who has also investigated the action of methyl iodide on benzyl sulphide, gives the following equation : 3CH3I + (C6H5.CH2)2S = (CH3)3SI + 2C6H5.CH2I. Benzyl bromide and methyl sulphide, on the other hand, react in the following way : C6H5.CH2Br+2(CH3)2S = (CH3)3S Br + C6H5.CH2.S.CH3. If methyl alcohol be also present, benzyl methyl ether is formed instead of benzyl methyl sulphide : C6H5.CH2Br + (CH3)2S + 2CH3.OH = (CH3)3SBr + C6H5.CH2.O.CH3+H2O. Benzyl oxysulphide, (C6H5.CH2)2SO, is formed by the action of concentrated nitric acid on the sulphide; it crystallizes from alcohol in small plates which have a satin lustre, melt at 133°,3 and are converted into sulphuric acid and benzoic acid by the further action of nitric acid (Miircker). Benzyl disulphide, (CGH5.CH2)2S2, is best obtained by the action of bromine in ethereal solution on benzyl mercaptan, and is also formed when benzyl chloride is treated in alcoholic solution with potassium disulphide; it crystallizes from alcohol in small, lustrous plates, melting at 66°-67°. Nascent hydrogen reconverts it into benzyl mercaptan (Miircker). It is decomposed on heating, yielding the same products as benzyl sulphide. Benzyl dioxy sulphide, or Dibenzyl sulphone, (C6H5.CH2)2SO2, is formed in small quantity in the preparation of potassium benzyl 1 Scholler, Ber. Deutsch. Chern. Ges. vii. 1274. 2 Compt. Rend. Ixxx. 1319. 3 Otto and Liiders, Ber. Deutsch. Chern. Ges. xiii. 1284. 108 AROMATIC COMPOUNDS. sulphonate.1 It may readily be obtained, however, by oxidizing benzyl oxysulphide with potassium permanganate and glacial acetic acid (Otto and Liiders); it is insoluble in water, and crystallizes from hot alcohol in flat needles, which melt at 150°. 2073 Benzylsulphonic acid, C(.H5.CH2.SO2.OH. Bolder pre- pared this compound by boiling benzyl chloride for several hours with a concentrated solution of normal potassium sulphite, the potassium salt obtained being converted into the lead salt, and this decomposed with sulphuretted hydrogen.2 It is a deliquescent crystalline mass, and is also formed by the oxidation of benzyl disulphide with nitric acid.3 When it is fused with caustic potash, it yields benzoic acid (Vogt), together with some benzene and a larger quantity of toluene.4 Potassium benzylsulphonate, C6H5.CH2.SO3K 4- H2O, crystal- lizes from hot water in well-developed rhombic prisms. Barium benzylsulphonate, (C6H5.CH2.SO3)2Ba + 2H2O, is obtained by the addition of barium chloride to the solution of the potassium salt; it forms plates, which are only slightly soluble in water. Lead benzylsulphonate, (CGH5.CH2.SO3).,Pb. If the barium salt be decomposed with dilute sulphuric acid, and the hot filtrate saturated with lead hydroxide, the basic salt C0H5.CH2. SO3.PbOH, is obtained as a lustrous, crystalline precipitate, which is converted into the normal salt by carbon dioxide; this crystallizes from hot water in lustrous plates. Potassium chlorobenzylsulphonatc, C6H4C1.CH2.SO3K + H2O, is prepared from chlorobenzyl chloride and potassium sulphite, and crystallizes in needles; barium chloride added to the potassium salt yields barium chlorobenzylsulphonatc, (C6H4CI. CH2.SO3)2Ba + H2O, which forms colourless lustrous crystals. When the potassium salt is fused with caustic potash, sali- cylic acid and parahydroxybenzoic acid are formed (Vogt and Henninger). Benzylsulphonic chloride, Cf)H5.CH2.SO2Cl. Barbaglia endea- voured to prepare this compound by the distillation of potassium benzylsulphonate with phosphorus pentachloride, but only ob- tained benzyl chloride, together with phosphorus oxychloride and some thionyl chloride.5 In order to prepare it, the potas- sium salt is treated with an equal weight of phosphorus chloride 1 Vogt and Henninger, Ann. Chem. Pharm. clxv. 375. 2 Ibid. cliv. 50. 8 Barbaglia, Ber. Deutsch. Chem. Ges. n. 687. 4 Otto, ibid. xiii. 1288. 5 Ibid. v. 270. SELENIUM COMPOUNDS OF BENZYL. 109 and the mixture gently warmed until the reaction is complete. The product is then washed with water and the residue crystal- lized from ether. Benzenesulphonic chloride forms colourless prisms, which melt at 92° and are decomposed when more strongly heated into benzyl chloride and sulphur dioxide ; it is con- verted by ammonia into benzylszdphonamide, C6H5.CH2.SO,.NH2, which crystallizes from water in prisms melting at 1050.1 Niirobenzylsulphonic acid, C6H4(NO2)CH2.SO3H, is formed by the action of fuming nitric acid on barium benzyl sulphate. A mixture is thus obtained which contains, together with the para-compound, a little of the orthonitro-acid and the dinitro- acid, which cannot be completely separated. On boiling with a mixture of nitric and sulphuric acids, dinitrobenzylsulphonic acid, C6H3(NO2)2CII2.SO3H, is obtained; it forms salts, which crystallize well. On reduction it is converted into diamido- benzylsulphonic acid, C6H3(NII2)2CH2.SO3H, which crystallizes from hot water in silky needles.2 SELENIUM COMPOUNDS OF BENZYL. 2074 Benzyl selenide, (C6TL.CH2)2Se, is prepared by treating phosphorus pentaselenide with alcoholic soda solution in absence of air, and heating the sodium selenide thus formed with benzyl chloride to the boiling point of the latter. When the solution cools, benzyl selenide separates out first and then some benzyl diselenide, which is separated by recrystallization from hot alcohol. Benzyl selenide crystallizes in long, white needles or transparent prisms, which have a faint aromatic odour and melt at 45'5°. Like methyl selenide, it combines with acids forming unstable salts. Benzyl diselenide, (C6H5.CH2)2Se2, is obtained by boiling crude sodium selenide, prepared by igniting sodium selenite with char- coal, with alcohol and benzyl chloride. It crystallizes from hot alcohol in straw-yellow, fatty scales, which melt at 90° and become coloured red in the sunlight. Nitric acid oxidizes it to benzylselenic acid, C6H5.CH2 SeO2H, crystallizing from hot water in needles which when impure possess a most unpleasant smell, which is not nearly so strong in the pure compound. It is a strong acid. 1 v. Pechmann, Ber. Deutsch. Chem. Ges. vi. 534. 2 Mohr, Ann. Chem. Pharm. ccxxi. 215. 110 AROMATIC COMPOUNDS. When benzyldiselenide is digested for some days with methyl iodide, a black mass is obtained which is a mixture of benzyl iodide, trimethylselenine iodide and benzyldimethylselenine tri- iodide : (C6H5.CH2), Se2+5CH3I = C6H-.CH2I + (CH3)3SeI + C6H5.CH2(CH3)2SeI3. The latter crystallizes from hot alcohol in black, heavy needles which have a metallic lustre, melt at 65° and possess a repulsive odour. They commence to sublime below 100°, and their vapour attacks the eyes violently. If the alcoholic solution be treated with silver nitrate, the excess of silver removed by hydrochloric acid and the filtrate then treated with platinum chloride, a precipitate of (CcH5.CH2.(CH3)2Se)2 PtCl6 is obtained consisting of microscopic, yellow, quadratic plates.1 NITROGEN BASES OF BENZYL. The Benzylamines. 2075 Cannizzaro states in his first paper on the alcohol of benzoic acid, that when the ethereal chloride prepared from it by the action of hydrochloric acid is treated with alcoholic ammonia, a base which differs from toluidine is formed (p. 89). Three years later he found that this is tribenzylamine, (C7H7)3N.2 In the year 1862, Mendius made the important discovery that the nitrils of the fatty acids combine with hydrogen to form amines, and that those of the aromatic series behave in a similar manner, inasmuch as benzonitril, C7H5N, yields a powerful base, C7H9N, which, however, is not identical with toluidine, " as might have been expected from the hitherto accepted views as to the re- lations of the bases homologous with aniline to the corresponding members of the benzoic acid series," but differs both from it and the isomeric methylaniline in its properties. It also appeared to him improbable that it was identical with the lutidine con- tained in coal-tar oil; he, therefore, decided, in the absence of a careful comparison between the two substances, "to introduce 1 Loring Jackson, Ann. Chcm. Pharm. clxxix. 8. 2 Jahra>b. 1856, 582. NITROGEN BASES OF BENZYL. 111 the base prepared from benzonitril into scientific literature as a new compound and to denote it by a new name."1 Two years later, Cannizzaro published a paper on " The Amines of Benzyl Alcohol " in which he says " Toluidine, C7H9N, is generally looked upon as the primary benzylamine. I have obtained results which do not agree with this supposition." He found that the primary benzylamine, which he had prepared from benzyl cyanate (benzyl isocyanurate), is a strong base resembling ethylamine and amyla- mine in its properties. He also obtained it, together with dibenzyl- amine and tribenzylamine, by heating benzyl chloride with alcoholic ammonia,2 and described the separation of these bases and the properties of benzylamine.3 In order to prepare the latter, a mixture of benzyl chloride and alcoholic ammonia is allowed to stand for some days ; a portion of the tribenzylamine separates out in crystals, and a further quantity is left behind when the alcohol is removed from the filtrate by distillation and the residue treated with hot water. The solution is then evaporated to dryness, and the most soluble portion of the residue, consisting chiefly of benzylamine hydrochloride is separated by fractional crystallization. This is then decomposed by caustic potash and the base allowed to remain in contact with some solid potash in order to dry it, and at the same time avoid exposure to carbon dioxide. It is then purified as much as possible by fractional distillation and treated with dry carbon dioxide; a solid compound is formed which is washed with anhydrous ether to remove the last adhering traces of dibenzylamine. The residue is then converted into the crystal- lized hydrochloride and the pure base finally liberated by caustic potash. According to Limpricht, the base is prepared by heating benzyl chloride with a solution of ammonia in commercial absolute alcohol for twenty-four hours in a steam bath and re- moving free ammonia and the largest portion of the alcohol by distillation. The residue is treated with water to precipitate the mixed bases, which are then dissolved in alcohol and treated with hydrochloric acid, the acid solution being allowed to cool gradually. Tribenzylamine hydrochloride separates out in prisms or needles, and a mixture of this salt with plates of dibenzyl- amine hydrochloride is obtained by the concentration of the mother-liquor; the residual liquid after repeated evaporation 1 Ann. Chcm. Pharm. cxxi. 144. 2 Ibid, cxxxiv. 128. 3 Ibid. Suppl. iv. 24. 112 AROMATIC COMPOUNDS. to a syrup, solution in hot water and reconcentration, yields benzylamine hydrochloride. The water employed for the precipitation of the bases contains some benzylamine, which may be extracted by saturating the liquid with hydrochloric acid, evaporating to dryness and extracting with hot absolute alcohol, which leaves ammonium chloride undissolved. The hydrochlorides of di- and tri-benzylamine are purified by re-crystallization from water or alcohol. The primary base is always present in the smallest quantity, while the relative amounts of the other two are very variable; sometimes a large quantity of tribenzylamine is formed with only traces of dibenzylamine, while in other cases the relation is the inverse of this.1 2076 Benzylamine, C6H5.CH2.NH2. Mendius obtained this compound by treating benzonitril in alcoholic solution with zinc and hydrochloric acid, freeing the solution from alcohol and unattacked nitril by distillation, saturating the residue with caustic potash and extracting the benzylamine with ether. The ethereal solution is then treated with hydrochloric acid, the benzylamine hydrochloride, which is obtained on evaporating the solution, re-crystallized from absolute alcohol and the pure base then set free by caustic potash. Hofmann obtained benzylamine by the action of zinc and hydrochloric acid on thiobenzamide, C6H5.CS.NH2,2 which is formed by the direct combination of sulphuretted hydrogen with benzonitril: C6H5.CS.NH2 + 4H = c6h5.ch2.nh2 + h2s. Both these methods are tedious, and, like the preparation from benzyl chloride and ammonia, only give a small yield. Benzyl- amine can, however, be readily prepared in large quantities by heating benzyl chloride with an equivalent amount of silver cyanate, until the violent reaction has ceased; a mixture of benzyl isocyanate and benzyl isocyanurate is formed and after distillation is re-distilled over caustic potash. The product thus obtained contains some di- and tri-benzylamine, since the mix- ture of isocyanates always contains some benzyl chloride. These can be removed by converting the whole into the hydrochlorides or by extracting the benzylamine by shaking out with water. 1 Ann. Chem. Pharm. cxliv. 304. 2 Bar. Deutsch. Chem. Ges. i. 102. BENZYLAMINE. 113 It is then converted into the hydrochloride which is decomposed by caustic potash, and the base dried over solid potash and redistilled.1 It can also be readily obtained by decomposing benzylacet- amide, CcH5.CH2.NH.(C2H3O), which is prepared by the action of benzyl chloride on acetamide, with alcoholic potash.2 Another simple method of preparation has been found by Hofmann. On heating benzyl chloride with potassium cyanide, phenylacetonitril, C6H5.CH2.CN, is obtained ; when water is added to a solution of this compound in concentrated sulphuric acid, phenylacetamide, C6H5.CH2.CO.NH2 is precipitated. This is then treated with a molecule of bromine, a 5 per cent, solution of four molecules of caustic potash added with continual agita- tion and the liquid heated by a current of steam : a mixture of benzylamine and brominated benzylamine distils over, which is converted into pure benzylamine when allowed to stand for some time over sodium amalgam, all the bromine being replaced by hydrogen.3 Hofmann has shown that the amides of other monobasic acids can readily be converted by this reaction into amines containing one atom of carbon less in the molecule. He has carefully investigated the course of the reaction in the case of acetamide, and finds that acetbromamide, CH3.CO.NHBr, is first formed, and that this loses hydrobromic acid with formation of methyl isocyanate, which assumes the elements of water and splits up into carbon dioxide and methylamine. Benzaldehyde, which is now a cheap commercial product, can also be readily converted into benzylamine. It combines with hydrocyanic acid to form phenylhydroxyacetonitril, C6H5.CH (OH2)CN, which is converted by treatment with alcoholic ammonia into phenylamido-acetonitril, C6H5.CH(NH2)CN. On boiling this with dilute sulphuric acid, phenylamido- acetic acid is formed and decomposes into benzylamine and carbon dioxide on distillation. These products of decom- position recombine to some extent forming benzylammonium benzylcarbamate (p. 114), which is, however, readily decomposed by alkalis. Pure benzylamine hydrochloride may also be obtained by treating the distillate with hydrochloric acid.4 Properties.-Benzylamine is a colourless liquid which has a 1 Strakosch, Ber. Deutsch, Chern. Ges. v. 692. 2 Rudolph, ibid. xii. 1297. 3 Ibid, xviii. 2734. 4 Friedlander and Tiemann, ibid. xiv. 1969. 114 AROMATIC COMPOUNDS. characteristic, faint, aromatic odour, does not become coloured in the light, boils at 185° and has a sp. gr. of 0'990 at 14°. It is soluble in water in every proportion, but is insoluble in strong alkalis, and is therefore precipitated by caustic potash from its aqueous solution. It has a strong alkaline reaction, fumes with hydrochloric acid and rapidly absorbs carbon dioxide, so that a drop exposed to the air is soon converted into small, silky needles of the carbonate. It combines with benzyl chloride to form dibenzylamine hydro- chloride. Benzylamine hydrochloride, C7H7NH3C1, forms quadratic tablets, very soluble in water and alcohol; its platinichloride is a granular, crystalline precipitate. Benzylamine nitrite, C7H7NH3.NO2, is obtained by shaking the hydrochloride with silver nitrite and ether. It is extracted from the silver chloride, which is simultaneously formed, by cold absolute alcohol, and is deposited on the evaporation of this solution in well-formed crystals, which decompose with evolution of nitrogen when gently warmed.1 Benzylammonium benzylcarbamate is formed by the com- bination of benzylamine with carbon dioxide : /ONH3(CH2.C6H5) CO. + 2NH2.CH2.C6H5 = co< Zj it it V U \ \NH(CH2.C6H5). It is readily soluble in water, volatilizes when the solution is boiled, and crystallizes from alcohol in small, lustrous plates which melt at 99°. 2077 Bibenzylamine, (C6H5.CH2)2NH, is a thick liquid, which has a sp. gr. of 1'033 at 14° and is insoluble in water, but readily soluble in alcohol. When a small quantity is rapidly heated it distils unaltered at above 300°, but on gradual distilla- tion it is decomposed with formation of ammonia, toluene, dibenzyl, C14H14, stilbene, C14H12, lophine, C21H16N2, and other bodies.2 When heated to 260° in a stream of hydrochloric acid, it gradually and incompletely decomposes into benzyl chloride and benzylamine hydrochloride, while at 100° it combines with benzyl chloride forming tribenzylamine. On treatment with 1 Curtius, Bcr. Deutsch. Chern. Ges. xvii. 958 2 Brunner, Ann. Chern. Pharm. cli. 131. DIBENZYLAMINE. 115 bromine and a large quantity of water, it decomposes into benzylamine and benzaldehyde: (C6H..CH2)2NH + H2O+Br2= C6H5.COH+C6H5.CH2.NH2+2HBr. Iodine has a similar action but requires a temperature of 140° (Limpricht). Dibenzylamine hydrochloride, (C7H7)2NH2C1, is readily soluble in hot water and alcohol, but much less freely in the cold, and crystallizes in large, flat, prisms, or, when its alcoholic solution is rapidly cooled, in thin plates. The hydrobromide and hydriodide are very similar. Dibenzylamine nitrate, (C7H7)2NH2.NO3, is less soluble than the other salts and crystallizes in flat needles or prisms. Tribenzylamine, (C6H5.CH2)3N, is also formed, together with other bodies, when benzaldehyde is gradually heated to 180° with ammonium formate. Formamide is the first product and decomposes into carbonic oxide and ammonia, which then act upon the benzaldehyde: 3C6H5.COH + 3CO+NH3 = (C6H5.CH2)3N + 3CO2. This is the most convenient method for the preparation of tribenzylamine, 100 grms. of benzaldehyde yielding 40 grms. of the pure product.1 It is slightly soluble in cold alcohol and crystallizes from a hot solution in needles, plates, or monoclinic tablets (Panebianco) melting at 91°. Small quantities can be distilled without decomposition, but larger quantities split up, yielding the same products as the secondary base. It also resembles the latter in its behaviour towards bromine and iodine, benzaldehyde and dibenzylamine being formed. When its hydrochloride is heated to 250° in a stream of hydrochloric acid, it decomposes into benzyl chloride and dibenzylamine hydrochloride, while Lauth obtained benzyl chloride and ammonium chloride by treating the free base in a similar manner at 180°2. It does not combine with benzyl chloride, and hence no tetrabenzylammonium chloride is formed in its preparation from benzyl chloride and ammonia; it com- bines with ethyl iodide, however, on heating to form a crystal- lized compound, which does not yield a hydroxide on treatment w'ith silver oxide, but decomposes into its constituents.3 It 1 Leuckart, Ber. Deutsch. Chern. Ges. xviii. 2341. 2 Ibid. vi. 678. 3 Vasca-Lanza, ibid. vii. 82. 116 AROMATIC COMPOUNDS. also forms a crystallized compound when heated with methyl sulphate to IOO0.1 The salts of tribenzylamine have been crystallographically investigated by Panebianco.2 Tribenzylamine hydrochloride, (C7H7)3NHC1, is slightly soluble in cold alcohol and water, and crystallizes from its hot solution in quadratic prisms. It decomposes above 270°, a large quantity of toluene being formed (Rohde). The platinichloride crystal- lizes in orange-coloured, monoclinic needles. Tribenzylamine nitrate, (C7H7)3NHNO3, forms rhombic crystals which are insoluble in water and slightly soluble in alcohol. Tribenzylamine sulphate, (C7H7)3NH)2SO4, forms monoclinic crystals, is insoluble in water, slightly soluble in alcohol, and combines with aluminium sulphate forming tribenzylammonium alum, (C21H22N)2A12(SO4)4 + 24H2O, which is deposited in regular crystals and is soluble in water but not in alcohol. Nitrosodibenzylamine, (C7H7)2N(NO). Rohde obtained this compound, together with benzaldehyde, by distilling a con- centrated alcoholic solution of tribenzylamine with nitric acid: ZCH2.C6H5 /CH2.C6H5 n^-ch2.c6h5 + no2.oh=n^no + coh.c6h5+h9o. \ch2.c6h6 ■ \ch2.c„h5 It is readily soluble in alcohol and ether, and crystallizes in quadratic tablets, melting at 52°; it does not combine with acids, and is converted into dibenzylamine by the action of nascent hydrogen or hydrochloric acid. AMIDO-SUBSTITUTED BENZYLAMINES. 2078 Diethylbenzylamine, C6H5.CH2.N(C2H5)2, is obtained by- heating benzylamine with ethyl iodide, or benzyl chloride with diethylamine. It is a transparent, oily liquid, which boils at 211°-212°, and combines with ethyl iodide on heating with formation of triethylbenzylammonium iodide, N(C6H5.CH2) (C2H5)3I, which can also be prepared from benzyl iodide and 1 Claesson and Lundvall, Ber. Deutsch. Chem. Ges. xiii. 1703. 2 Jahrcsb. 1878, 476. ETHYLBENZYLAMINE. 117 triethylamine, and forms large, colourless crystals, which are readily soluble in water; on dry distillation it is decomposed into triethylamine and benzyl iodide, while it is not attacked when heated with concentrated hydriodic acid.1 When iodine is added to it in alcoholic solution, the periodide, N(C6H5.CH2) (C2H5)3I3, separates out in black-blue monoclinic prisms, which have a metallic lustre. Ethyldibenzylamine, (C6H5.CH2)2NC2H5, was obtained by Limpricht from ethyl iodide and dibenzylamine; it is an oily liquid. Diethyldibenzylammonium, iodide, (O6H5.CH2)2(C2H5)2NI, is formed by the combination of diethylbenzylamine with benzyl iodide. It crystallizes from hot water in needles possessing a diamond lustre ; when it is distilled with hydriodic acid, benzyl iodide is liberated (V. Meyer). Benzylphenylamine, or Benzylaniline, C6H5.CH2.N(C6H5)H, is formed when benzyl chloride is heated with aniline to 160°. The free base crystallizes from hot alcohol in four-sided prisms, melting at 32°.2 It may also be obtained by the action of hydrochloric acid and zinc-dust on thiobenzanilide,3 C6H5.CS.N (C6H5)H. Benzylphenyldimethylammonium chloride, (C6H5.CH2)C6H5 (CH3)2NC1, is readily formed by the direct combination of benzyl chloride with dimethylaniline. It crystallizes from water or alcohol in tablets, which melt at 110°, and is split up into its constituents by distillation. It is not decomposed by boiling with water and silver oxide, but its decomposition may be effected by employing silver sulphate. If the sulphuric acid be removed by baryta water from the solution thus formed, and the filtrate concentrated, the hydroxide is obtained as a strongly alkaline, syrupy mass, which is converted into the carbonate in the air. On distillation it decomposes smoothly into dimethyl- aniline and benzyl alcohol,4 while tetra-ethylammonium hydroxide under similar conditions yields triethylamine, ethylene and water. Benzyldiphenylamine, C6H5.CH2.N(C6H5)2, is formed when diphenylbenzothiamide, C6H5.CS.N(C6H5)2, is treated with hydrochloric acid and zinc-dust. It crystallizes from hot alcohol 1 Ladenburg and Struve, Ber. Deutsch. Chern. Ges. x. 43 ; Ladenburg, ibid. x. 561, 1153, 1634 ; V. Meyer, ibid. x. 309, 964, 1291. 2 Fleischer, Ann. Chern. Pharm. cxxxviii, 22. 3 Bernthsen and Trompetter, Ber. Deutsch. Chem. Ges. xi. 1760. 4 Michler and Gradmann, ibid. x. 2079. 118 AROMATIC COMPOUNDS. in long white needles which melt at 87°, and does not combine with acids (Bernthsen and Trompetter). Dibenzyltolylamine, (C6H5.CH2)2NC6H4.CH3. This base, which is also known as dibenzyltoluidine, was prepared by Cannizzaro by heating paratoluidine with alcohol and benzyl chloride. It crystallizes from hot alcohol in very fine needles, melting at 54'5°-55°, and is a weak base; it differs from the isomeric tribenzylamine in forming salts which are decomposed by water.1 SUBSTITUTION PRODUCTS OF THE BENZYLAMINES. 207g These are formed by the action of ammonia on the corresponding haloid ethers. Halogen substitution products. These compounds are strong bases and form crystalline salts; the primary compounds absorb carbon dioxide from the air. Melting-point. "X- }C.H4C1.CH2,NH2, liquid . . "am7ne> } ((WLCH^NH, aystab . . 29' Paratrichloro- } 1T ^TT x XT ( rhombic > ^o.-o 1 i • 4 r I \ loD benzylamine, J v b 4 2/3 » prisms ) p^zx4(c«H'Br^^^prisms • • 7s^79^ Para-iodo- ) C6H4LCH2.NH2, liquid . . benzylamine, J 6 4 2 2' 1 Paradi-iodo | (C6HJ.CH2)QNH, needles . . 76° benzylamine,7 J K 6 4 "2 Paratn-iodo- | (CfiH.I.CH2)3N, needles . . 114 50 benzylamine,8 p « 4 2/3 Orthobromo- } C6H4Br.CH2.NH2, liquid . . benzylamine,9 J 0 4 2 2 1 1 Ann. Chern. Pharm. Suppl. iv. 80. 2 Berlin, Ann. Chern. Pharm. Suppl. cli. 137 ; Jackson and Field, Amer. Chern. Journ. ii. 95. 3 Ibid. 4 Ibid. 5 Jackson and Lowry, Per. Deutsch. Chern. Ges. x. 1211. 6 Jackson and Mabery, Amer. Chern. Journ. ii. 257. 7 Ber. Deutsch. Chern. Ges. xi. 58. 8 Ibid. 9 Jackson and White, Amer. Chern. Journ. ii. 317. NITROBENZYLAMINES. 119 Melting-point. Orthodibromo- ) tt \ vu rhombic 1 , i • i r (CRJ±Anr.UJxJ9lN.tl ■< A i r ab benzylamine,1 J ' ° 4 2/2 crystals J ten"n"0'} (CABr.CH^N, crystals. . 1215"-122' Paranitrobenzylamines have been prepared by Strakosch by heating paranitrobenzyl chloride with aqueous ammonia to 100°. The primary base could not be isolated ; the secondary base combines with acids, while the tertiary does not, thus rendering the separation of these two a matter of no difficulty.3 Paradinitrobenzylamine, (C6H4(NO2)CH2)2NH, crystallizes from hot alcohol in large, yellowish, lustrous plates, melting at 93°; its hydrochloride forms lustrous, yellow prisms, which are only slightly soluble in water and alcohol, while its platini- chloride, which crystallizes in yellow needles, is almost insoluble. Paratrinitrobenzylamine, (C6H4(NO2)CH2)3N, is slightly soluble in hot alcohol, readily in glacial acetic acid and nitro- benzene, and crystallizes in lustrous, white needles, which melt at 163°, and possess a pleasant odour. Paranitrobenzylphenylamine, C6H4(NO2)CH2.N(C6H5)H, is formed by heating paranitrobenzyl chloride with aniline; it crystallizes from hot alcohol in pointed, lustrous, yellow needles. Its hydrochloride crystallizes from hot hydrochloric acid in small lustrous plates which are decomposed by water with separation of the base (Strakosch). Metanitrobenzylamines. Aqueous ammonia converts meta- nitrobenzyl chloride into the secondary and tertiary amines, while in the presence of alcohol only the former, together with a small quantity of the primary base, is formed.4 Metanitrobenzylamine, C6H4(NO2)CH2.NH2, is a yellow, oily liquid, which becomes solid in the air from absorption of carbon dioxide. Its oxalate crystallizes in needles, which are only slightly soluble in water. Metadinitrobenzylamine crystallizes from alcohol in small yellow, rhombic plates, melting at 87°. Its hydrochloride and platinichloride are only slightly soluble in water. Metatrinitrobenzylamine is slightly soluble in alcohol, more readily in benzene, and forms monoclinic prisms, melting at 162°. It does not combine with hydrochloric acid. Metanitrobenzylphenylamine is formed by the action of aniline 1 Jackson and White, Amer. Chern. Journ. ii. 317. 2 Ibid. 3 Ber. Deutsch. Chern. Ges. vi. 1056. 4 Borgmann, Chem. Centralb. 1885, 456. 120 AROMATIC COMPOUNDS. on metanitrobenzyl chloride. The hydrochloride, which is thus obtained, forms small white, lustrous plates. It is decomposed by water with formation of the base, which crystallizes in long, orange-red needles, melting at 86°. Amidobenzylamines are obtained by the reduction of the nitro-compounds with tin and hydrochloric acid. Paradiamidobenzylamine, (C6H4(NH2)CH2)2NH, is readily soluble in hot water and alcohol; it crystallizes in needles with a satin lustre, or in plates which melt at 106°, and volatilize without decomposition when more strongly heated. The hydrochloride, (C6H4(NH3C1)CH2)2NH2C1, is readily soluble in water, slightly in hydrochloric acid, and crystallizes in small white, lustrous plates; the platinichloride, C14H18N3Cl.PtCl6, forms large pointed reddish-yellow needles which are readily soluble in water. Paratriamidobcnzylamine, (C6H4(NH2)CH2)3N, is insoluble in water, and crystallizes from hot alcohol in octahedra, possessing a diamond lustre and melting at 136°. Its hydrochloride crystallizes in yellow needles, and is so readily soluble in water, alcohol, and hydrochloric acid, that it cannot be obtained pure. In the preparation of the base, the action of the tin and hydrochloric acid must not be allowed to continue too long, as under these circumstances it is split up into paradiamido- benzylamine and paratoluidine : /CH2.C6H..NH2 ch2.c6h4.nh, N^-CH,.C6H4.NH2+2H = HN< +CH3.C6H4.NH2. \ch:.c6h..nh2 xCH2.C6H,.NH2 2 U 2 2 0 4 2 Paramiddbenzylphenylamine, C6H4(NH2)CH2.N(O6H5)H, can- not be obtained by the action of tin and hydrochloric acid on the nitro-compound, since a more deeply seated decomposition takes place; the reduction may, however, be effected by employing ammonium sulphide. The base is soluble in water and alcohol, and crystallizes in silky scales, which melt at 88° and become coloured red in the light. Metadiamidobenzylamine forms prismatic needles, melting at 86°; its hydrochloride, (C6H4(NH3C1)CH2)2NH2C1, crystallizes from concentrated hydrochloric acid in long, pinkish needles, and forms a readily soluble platinichloride. Metatriamidobenzylamine forms needles melting at 142°; its platinichloride is only slightly soluble. Metamidobenzylphenylamine melts at 67°. BENZYLACETAMIDE. 121 BENZYL-DERIVATIVES OF THE ACID-AMIDES AND ALLIED BODIES. 2080 Benzylacetamide, C6H5.CH2.N(C2H3O)H, was prepared by Strakosch by heating benzylamine with glacial acetic acid for several hours;1 it is more readily formed by the action of benzyl chloride on acetamide,2 and is very soluble in alcohol and ether, slightly in petroleum naphtha, from which it crystallizes in small plates, which have a pleasant smell of flowers and melt at 57°. It boils at 300° and is not attacked by acids or aqueous alkalis; alcoholic potash, however, converts it into acetic acid and benzylamine. Bibenzyloxamide, (C6H5.CH2.NH2)2C2O2, is obtained by boiling benzylamine with ethyl oxalate; it is insoluble in water, slightly soluble in hot alcohol, from which it crystallizes in scales, which possess a satin lustre and melt at 216°. Cyanobenzylamine, C18H16N4, is obtained by passing cyanogen into a cold solution of benzylamine: CpH-.CHn.NHo C=N C6H,.CH2.NH.C=NH O D Z Li " XJ t) Lt + I = I c6h5.ch2.nh2 c=n c6h5.ch2.nh.c=nh. It forms lustrous crystals, which are soluble in alcohol and melt at 140°. If hydrochloric acid be added to the alcoholic solution, the salt, C18H16N4(C1H)2, is obtained in white, silky needles. When it is allowed to stand in contact with hydro- chloric acid for some time, it is converted into dibenzyloxamide (Strakosch). Benzylcyanamide,, C6H5.CH2.NH(CN), is formed when cyan- ogen chloride is passed into an ethereal solution of benzyl- amine, and crystallizes in tablets melting at 33°. It changes spontaneously into benzy ley anuramide or benzylmelamine, (C6H5. CH2.NH)3C3N3, which has a much higher melting-point and crystallizes from alcohol in plates; the change takes place more readily at 100°. When an alcoholic solution of benzylcyanamide is boiled with benzylamine hydrochloride, dibenzyl guanidine (C6H5.CH2.NH)2 C.NH, is formed; this compound crystallizes from alcohol in 1 Ber. Deutsch. Chem. Ges. n. 697. 2 Rudolph, ibid. xii. 1297. 122 AROMATIC COMPOUNDS. plates or tablets, melting at 100°. The hydrochloride, (C7H7. NH)2C.NH.C1H, is slightly soluble in water, more readily in alcohol (Strakosch). Dibenzylcyanamide, (C6H5.CH2)2N.CN, was obtained by Lim- pricht from dibenzylamine and cyanogen chloride; it crystallizes from alcohol in plates, melting at 53°-54°. Benzyl isocyanate, or Benzyl carbimide, C6H5.CH2N : CO, was prepared by Letts in the impure state and in small quantity, by distilling benzyl chloride with silver cyanate j1 the isocyanurate is always formed at the same time. It is a liquid which gives all the characteristic reactions of the isocyanates and possesses an extremely penetrating odour, its vapour attacking the eyes violently. Benzyl isocyanurate, (C6H5.CH2)3N3(CO)3, crystallizes from hot alcohol in silky needles, melting at 157°. It boils above 320°, and when fused with caustic potash yields benzylamine. Cannizzaro seems to have obtained the same substance in small quantity and together with other products by the action of cyanuric chloride on benzyl alcohol.2 Benzyl isothiocyanate, or Benzyl mustard oil, C6H5.CH2.N:CS. Hofmann obtained this compound by dissolving benzylamine in carbon disulphide, and distilling the white, crystalline compound formed with an alcoholic solution of mercuric chloride3 It is a liquid which boils at about 243° and possesses the smell of water-cress (Nasturtium officinale} in such a remarkable degree that Hofmann was induced to search for it in the oil of this plant; it is not, however, present, the odoriferous constituent in water-cress being phenylpropionitril, C6H5.C2H4.CN,4 while benzonitril, C6H5CN, is that of the nasturtium (Tropaeohcm majusif Benzyl thiocyanate, C6H5.CH2.S.CN, is formed by heating benzyl chloride with an alcoholic solution of potassium thio- cyanate. It is insoluble in water, and crystallizes from alcohol in long, transparent prisms, which have a sharp, burning taste, and a penetrating smell resembling that of cress. According to Henry,6 it melts at 3G°-38° and boils with partial decomposition at 256°, while Barbaglia found its melting-point to be 41° and its boiling-point 230°-235°.7 1 Bar. Deutsch. Chem. Ges. v. 90 ; see also Strakosch, ibid, v, 692 ; Ladenburg, ibid. x. 46. 2 Ber. Deutsch. Chem. Ges. iii. 517. 8 Ibid. i. 201. 4 Ibid. vii. 520. 5 Ibid. vii. 518. 6 Ibid. ii. 638. 7 Ibid. v. 688. BENZYL UREAS. 123 Concentrated nitric acid converts it into paranitrobenzyl thio- cyanate, C6H4(NO2)CH2.S.CN, which can also be obtained by the action of paranitrobenzyl chloride on potassium thiocyanate. It crystallizes from alcoholic solution in small, brittle crystals. Various halogen substitution-products of this compound are also known.1 Benzyl selenocyanate, C6H5.CH2.Se.CN, crystallizes from alcohol in white needles or prisms, which have an extremely repulsive smell and melt at 71'5°.2 Benzyl carbamate, or Benzyl urethane, C6H5.CH2.O.CO.NH2, was obtained by Cannizzaro, together with a little benzyl isocyanurate and dibenzyl urea, by the action of cyanogen chloride and cyanuric chloride on benzyl alcohol.3 It is also formed when urea nitrate is heated to 130°-140°4 with benzyl alcohol; it crystallizes from hot water in large plates, which melt at 86° and decompose into benzyl alcohol and cyanuric acid at 220°. Benzyl urea, (C6H5.CH2)NII.CO.NH2, is formed, together with symmetric dibenzyl urea, by the action of benzyl chloride on an alcoholic solution of potassium cyanate,5 as well as by that of alcoholic ammonia on benzyl isocyanate (Letts). It is also obtained when a solution of benzylamine hydrochloride is boiled with potassium cyanate.6 It is tolerably soluble in hot, readily in boiling alcohol, and crystallizes in long, white needles, melting at 147°-1475O. Symmetric dibenzyl urea, CO(NH.CH2.C6H5)2, is formed when the compound just described is heated to 200° (Cannizzaro), as well as when benzyl isocyanate is heated with water in a sealed tube to 100°, and also when benzyl alcohol is heated to 100° with urea nitrate (Letts), benzylaldehyde being simultaneously formed (Campisi and Amato). It is insoluble in water and crystallizes from alcohol in needles melting at 167°. It does not combine with hydrochloric acid or nitric acid, but gives a plantinichloride. Asymmetric dibenzyl urea, (C6H5.CH2)2N.CO.NH2, has been obtained by Paterno and Spica from dibenzylamine hydrochloride and potassium cyanate; it is slightly soluble in cold, readily in hot water, and crystallizes in thick prisms, melting at 124°-125°. 1 Jackson, Field, Mabery, Lowry, loc. cit. 2 Jackson, Ann. Chern. Pharm. clxxix. 15. 3 Ber. Deutsch. Chern. Ges. iii. 517 ; iv. 412. 4 Campisi and Amato, ibid. iv. 412. 5 Paternd and Spica, ibid. ix. 81. 6 Ibid. 124 AROMATIC COMPOUNDS. Benzyl thiocarbamide, C6H5.CH2.NH.CS.NH2,has been prepared in an analogous manner from benzylamine hydrochloride and potassium thiocyanate; it is very soluble in water and melts at 101°. Symmetric dibenzyl thiocarbamide, (C6H5.CH2.NH)2CS, is formed when an alcoholic solution of benzylamine is heated with carbon disulphide until the evolution of sulphuretted hydrogen ceases. It crystallizes in large, four-sided, lustrous tablets, melt- ing at 114°; it is converted into dibenzyl urea when its alcoholic solution is treated with mercuric oxide (Strakosch). Asymmetric dibenzyl thiocarbamide, (CcH5.CH2N)2CS.NH.„ is prepared from dibenzylamine hydrochloride and potassium thiocyanate ; it is slightly soluble in water, readily in alcohol, and crystallizes in long needles melting at 15G°-157° (Paterno and Spica). PHOSPHORUS COMPOUNDS OF BENZYL. 2o8i Primary and secondary benzylphosphine are formed when benzyl chloride is heated with phosphonium iodide and zinc oxide. The product of the reaction is distilled with water, an oily liquid coming over, which possesses a very characteristic, persistent odour, and is a mixture of toluene and benzylphos- phine. The residue contains dibenzylphosphine and other substances, which, however, remain in solution, while the dibenzylphosphine crystallizes out on standing, more rapidly in the presence of caustic potash ; it is then removed from the liquid and recrystallized from boiling alcohol.1 Benzylphosphinc, C6H5.CH2.PH2, is a strongly refractive liquid, boiling at 180°; it is oxidized on exposure to the air with such rapidity that its temperature rises to above 100°, thick, white needles being deposited. Benzylphosphonium iodide, C6H5.CH2.PH3I, is obtained by the addition of fuming hydriodic acid to benzylphosphine, as a white precipitate which crystallizes from the hot acid in long, white needles. When these are washed with ether and dried in a stream of hydrogen, they are converted into large, well-formed tablets. Water decomposes the compound into its constituents. 1 Hofmann, Ber. Deutsch. Chern. Ges. v. 100. ARSENIC COMPOUNDS OF BENZYL. 125 Dibenzylphosphine, (C6H5CH2)2PH, crystallizes in needles which form star-like aggregates, are colourless and tasteless, do not combine with acids, and melt at 205°. While dimethyl- phosphine and ethylphosphine are spontaneously inflammable in the air, dibenzylphosphine is not acted upon by oxygen, even at a higher temperature. Triphenylbenzylphosphonium chloride, P(C6H5)3(CH2.C6H5)C1, is readily formed by the combination of benzylchloride with triphenylphosphine. It is readily soluble in alcohol and water, and separates from the latter in rhombic crystals which contain one molecule of water and are efflorescent. Other salts, which are characterized by their power of crystallization, have been prepared from this compound by double decomposition; they are decomposed by boiling caustic soda, with formation of triphenyl- phosphine oxide and toluene :1 P(C6H5)3(C6H5.CH2)C1 + NaOH = PO(C6H5)3+C6H5.CH3+NaCl. ARSENIC COMPOUNDS OF BENZYL. 2082 When benzyl chloride, diluted with absolute ether, is treated with arsenic trichloride and sodium, a reaction commences after some time, which in the course of a few days may raise the temperature to the boiling-point of ether, the following com- pounds being formed : Dibenzylarsine trichloride. 2C7H7C1 + AsC13 + 2Na = (C7H7)2AsC13 + 2NaCl. Tribenzylarsine dichloride. 3C7H7C1 + AsC13 + 4Na= (C7H7)3AsC12 + 4NaCl. If the sodium chloride be now removed, the ether distilled off and the residue treated with ordinary ether containing water, the chlorides are converted into oxychlorides, which separate out as a powder, while resinous by-products containing arsenic go into solution. The powder is washed with ether and then treated with boiling dilute caustic soda solution; dibenzylarsenic acid goes into solution, while the residue consists of tribenzylarsine oxide, which is very slightly soluble in the cold solution, and is, therefore, removed by cooling and filtering. 1 Michaelis and V. Soden, Ann. Chern. Pharm. ccxxix. 319. 126 AROMATIC COMPOUNDS. Dibenzylarsenic acid, (C6H5.CH2)2AsO.OH, is precipitated from its alkaline solution by acids ; it is only very slightly soluble in cold, more readily in boiling water, and crystallizes from hot dilute alcohol in fine, white plates, melting at 210'5°. It dissolves in hot dilute hydrochloric acid and the solution on cooling deposits the compound (C7H7)2As(OH)2C1, in fine needles, which melt at 128° and are reconverted into the acid by water. It forms similar compounds with hydrobromic, hydriodic and nitric acids. It is decomposed on heating with concentrated hydro- chloric acid: 2(C7H7)2AsO2H + 2HC1 = 2C7H7C1 + 2C7H8 + As2O3 + H2O. It behaves in this reaction similarly to cacodylic or di- methylarsenic acid. Its alkaline salts are soluble in water and alcohol; those of the calcium group separate from alcohol in crystals; the silver salt is a white precipitate, insoluble in water. Tribenzylarsine oxide, (C0H5.CH2)3AsO, crystallizes from dilute alcohol in lustrous needles, melting at 219'5°. On heating with hydrochloric acid it is converted into the oxychloride, (C7H7)3 As(OH)Cl, which melts at 162°-163° and is reconverted into the oxide by alkalis. Tribenzylarsine, (CcH5CH2)3As. When a little acetic ether is added to the mixture employed in the preparation of the compounds just described, the reaction becomes so violent that it has to be moderated by cooling : 3C7H7C1 + AsC13 + 6Na = (C7H7)3As + 6NaCl. If the treatment described above be then proceeded with, the oxychlorides are obtained as before, but the solution contains tribenzylarsine and no resinous by-products; it crystallizes from alcohol in large colourless needles, melting at 104°. On heating with ethyl iodide, tribenzylarsonium iodide, (C6H5.CH2)3C2H5AsI, is formed, and crystallizes in small white plates, which are slightly soluble in water, readily in alcohol.1 Tribenzylarsine is isomeric with tritolylarsine, (C6H4.CH3)3As, which, like triphenylarsine, forms no compounds with the alcoholic iodides. 1 Michaelis and Paetow, Ber. Deutsch. Chern. Ges. xviii. 41. SILICON TETRABENZYL. 127 SILICON COMPOUNDS OF BENZYL. 2083 Silicon tetrabenzyl, or Silicotetrabenzylmethane, Si(CH2. cch5)4, is formed by the action of sodium on a mixture of benzylchloride and silicon chloride, to which a little acetic ether has been added, and which has been diluted with ether. It separates from warm ether in crystals melting at 127'S0.1 1 Polis, Ber. Deutsch. Chern. Ges. xviii. 1543. 128 AROMATIC COMPOUNDS. THE BENZOYL GROUP. 2084 It has been already mentioned in the introductory sketch of the development of organic chemistry (Part I. p. 11), that Wohler and Liebig showed in their classical research, Investiga- tions on the Radical of Benzoic Acid, that oil of bitter almonds, benzoic acid, and a number of substances prepared from these, all contain a "compound basis " of the formula C7H5O, to which they gave the name of benzoyl (the latter portion of the word being derived from vXg, matter).1 They communicated their results to Berzelius, who makes the following remarks in his reply: " The results which you have obtained by the investigation of oil of bitter almonds, are certainly the most important which have hitherto been attained in the field of vegetable chemistry, and promise to throw an unexpected light upon that department of science. The fact that a substance which is composed of carbon, hydrogen and oxygen, combines with other substances, but especially with those which form salts and bases, in precisely the same manner as do simple substances, proves that there are ternary compound atoms (of the first order), and the radical of benzoic acid is the first well-established instance of a ternary substance which possesses the properties of an element. " The facts brought forward by you give rise to such wide considerations that they may be looked upon as marking the commencement of a new era in vegetable chemistry. From this standpoint I should propose to name the first discovered radical composed of more than two elements, proin (from the word 7rpw\,, commencement of the day, in the sense, dvo TrpwL ew? ea-Trepos, Acts xxviii. 23), or orthrin (from opc^po1?, dawn.)" In view, however, of the circumstance that the long familiar name benzoic acid would have also been altered, and that it is customary to respect terms in general use, provided only that 1 Ann. Chem. Pharm. iii. 249. BENZALDEHYDE. 129 they do not admit of a double interpretation, it seemed to him most suitable to accept the name benzoyl.1 In the next year, nevertheless, he opposed the idea of the existence of oxygenated radicals and looked upon oil of bitter almonds as an oxide of picramyl, C7H6 (irtKpos, bitter, and dpAjy^akp. almond), a name which was never generally adopted. BENZALDEHYDE, C6H5.CHO. 2085 The poisonous qualities of bitter almonds were known to the ancients, and they were employed in medicine in the middle ages: Valerius Cordus, who has been already mentioned under the history of ether, described them as constituents of lozenges. At the commencement of this century, Bohm, an apothecary's assistant in Berlin, discovered that the aqueous distillate of bitter almonds contains prussic acid,2 and this dis- covery led to the assumption that the latter is poisonous, a property which its discoverer, Scheele, had, somewhat strangely, overlooked. Schaub, Schrader, Ittner and other chemists3 confirmed the dangerous nature of this substance, and Schrader,4 and Matres,5 an apothecary in Montauban, observed that a liquid oil is also obtained by the distillation of bitter almonds with water. This oil was more closely examined by Vogel and Robiquet, the former6 of whom found that the most remarkable and striking property of oil of bitter almonds is that it is converted into a crystalline body by exposure to the air or by treat- ment with pure oxygen or oxymuriatic acid (chlorine), while Robiquet showed that the leaves of the cherry-laurel yield an oil which resembles oil of bitter almonds in every respect, and that the substance obtained from it by oxidation has acid pro- perties.7 Stange, an apothecary of Basel, who also obtained this solid substance from the cherry-laurel, recognized it as benzoic acid,8 an 1 Ann. Chern. Pharm. iii. 282. 2 Scherer's Journ. x. 126 ; Gilbert, Ann. Phys. xiii. 503. 3 Ittner, Beitrage zur Geschichte der Blausdure, Freiburg and Constanz, 1809 ; Preyer, Die Blausawre, Bonn, 1870, 154. 4 Schrader, Berlin. Jahrb. Pharm. ii. 43. 5 Journ. Pharm. v. 289. 6 Schweigger, Journ. Chern. Phys. xx. 59 ; xxxii. 119. 7 Ann. Chim. Phys. xv. 29 ; xxi. 250. 8 Buchner's Report. Pharm. xiv. 329, 361 ; xvi. 80. 130 AROMATIC COMPOUNDS. observation which was confirmed by Wohler and Liebig. These chemists determined its composition, and that of the oil of bitter almonds, and ascertained the relations of the two com- pounds. To oil of bitter almonds they gave the name of benzoyl hydride, which was later changed to benzoic aldehyde and benzaldehyde. Shortly before this, Robiquet and Boutron-Charlard had found that when bitter almonds are freed from fatty matters by pressure, an odourless residue is left which yields the characteristic smell of oil of bitter almonds on the addition of water. The oil in question, or its elements, had there- fore been left behind in the pressed mass and had not been removed by the process. They, therefore, concluded that oil of bitter almonds is a compound of water with a peculiar principle, which they endeavoured to isolate. The use of water being impossible, they extracted the pressed almonds with boiling alcohol, and obtained, together with resin and a liquid sugar, a crystalline compound containing nitrogen, to which they gave the name of amygdalin. This compound, to which the taste of bitter almonds is due, gave no smell of bitter almonds when treated with water, nor did either of the two other compounds, nor the residue, nor even of a mixture of them all. The prussic acid and oil of bitter almonds had vanished from their hands.1 They found further, that sweet almonds contain no amygdalin and that the latter yields benzoic acid when oxidized by nitric acid, while Peligot observed the formation of oil of bitter almonds as an intermediate product in this reaction. Wohler and Liebig, who also accurately determined the composition of amygdalin, succeeded in finding the solution of the problem. They showed that both sweet and bitter almonds contain a peculiar nitrogenous substance, emulsin, which con- verts amygdalin in presence of water into benzaldehyde, prussic acid, and grape sugar • C20H27NOu + 2H2O = C7H6O - CNH + 2C6H12O6. The action of the ferment is destroyed by boiling water and by heating with alcohol, so that when dried and powdered bitter almonds are shaken up with boiling water and distilled, none of the liquid oil is obtained, and the same result occurs when, as in 1 Ann. Chim. Phys. xliv. 352. OCCURRENCE OF BENZALDEHYDE. 131 Robiquet and Boutron-Charlard's process, they are treated with boiling alcohol.1 Amygdalin, which is the first example of a glucoside, a large number of which bodies is now known, occurs in many plants, chiefly the Amygdalacece, Drupacece and Pomacece, which all yield benzaldehyde and prussic acid when distilled with water. The kernel of the peach also yields an oil resembling oil of bitter almonds in every respect,2 while that obtained from the leaves, flowers, seeds and bark of the cherry, contains both oil of bitter almonds and another oil which has a penetrating, repul- sive odour.3 This subject will be further discussed under Amygdalin. According to Winkler, the fresh leaves of the cherry-laurel {Prunus laurocerasus), the cherry (Prunus padus) and the peach, contain a small quantity of free oil of bitter almonds varying in amount with the water present,4 which can be extracted by ether. Ittner looked upon oil of bitter almonds as a compound of hydrocyanic acid and an ethereal oil, but Vogel opposed this view, for he had found that it could be easily freed from hydro- cyanic acid by treatment with caustic potash or baryta water, or by distillation with mercuric oxide.5 Since, however, the oil containing hydrocyanic acid is readily converted into the polymeric benzoin, C14H12O2, by caustic potash, Wohler and Liebig proposed to remove the acid by shaking up with milk of lime and ferrous sulphate, calcium ferrocyanide being formed ; a loss of about 10 per cent, is experienced in the process. According to Bertagnini it is better to shake the oil with three or four volumes of acid sodium sulphite, remove the crystals which separate out and wash with alcohol.6 AU the hydrocyanic acid is not removed by this process, and the double sulphite is therefore recrystal- lized from hot alcohol before being distilled with caustic soda.7 The oil containing hydrocyanic acid is not simply a mixture of benzaldehyde and hydrocyanic acid, but contains phenylhydroxy- acetonitril, C6H5.CH(OH)CN, which, like other cyanhydrins or nitrils of hydroxyacids, readily decomposes into its constituents. Winkler had noticed some time previously that crude oil of bitter almonds is converted by hydrochloric acid into mandelic acid 1 Ann. Chern. Pharm. xxii. 1 ; Robiquet and Boutron, ibid. xxv. 175 ; Liebig, ibid. xxv. 190. 2 Righini, ibid. x. 359 ; Geissler, ibid, xxxvi. 331. 3 Winkler, Repert. Pharm. Ixvii. 1, 56. 4 Jahresb. Chern, iv. 519. 5 Loe. cit. ; Ittner, ibid. xxiv. 395. 6 Ann. Chern. Pharm. Ixxxv. 183. 7 Muller and Limpricht, ibid. cxi. 136. 132 AROMATIC COMPOUNDS. orphenylhydroxyacetic acid, CcH5.CH(OH)CO2H, the formation of which, however, cannot be taken as a proof of the presence of the nitril, for this acid is also formed when a mixture of hydrochloric acid, hydrocyanic acid and benzaldehyde, is heated to boiling. Fileti, however, supplied the proof by showing that phenyl- ethylamine, C6H5.CH2.CH2.NH2, is formed by the action of zinc and hydrochloric acid on an alcoholic solution of crude oil of bittei' almonds or of the cherry-laurel, while a mixture of benz- aldehyde and hydrocyanic acid subjected to the same treatment yielded methylamine.1 2086 Oil of bitter almonds is prepared on the large scale.by distilling the pressed residue of bitter almonds with water. In order to get all the amygdalin into solution and obtain the best yield of oil, Pettenhofer brings 12 parts of the roughly powdered mass into 100-120 parts of boiling water, keeps it at the boiling-point for 15-30 minutes, and after cooling adds 1 part of the powder stirred up with 6-7 parts of water, and then rapidly distils.2 The aqueous distillate contains some oil in solution, which is removed by a subsequent distillation. Pettenhofer obtains a yield of 0'9 per cent, of oil of bitter almonds on the pressed residue, while on the large scale the yield is in this way 0'74-1'67 per cent, or 0'42-0'95 parts in 100 of bitter almonds. The great variation in these numbers is partly accounted for by the varying amounts of amygdalin present, but is also due to the admixture of sweet almonds.3 Some manufacturers free the oil from hydrocyanic acid; the purified oil, however, oxidizes much more readily than when in the crude state, so that others add hydrocyanic acid and warm gently4 in order to make it keep better, the nitril, which will be described under Phenylhydroxyacetic acid, being formed. Oil of bitter almonds is chiefly employed in perfumery, and as a flavouring, for which, however, it must be used with care. Extracts of bitter almonds and of cherry-laurel are used in medicine. Benzaldehyde can be obtained in many other ways, some of which have been already mentioned under the benzyl com- pounds. Dumas and Peligot obtained it by oxidation of cinnamic acid, CJT5.CH=CH.CO2H;5 Muller prepared it in a similar 1 Gaz. Chim. Itoi. viii. 446. 2 Ann. Chem. Pharm. cxxii. 77. 3 Fliickiger and Hanbury, Pharmacographia, 2nd ed. 250. 4 Dusart, Bull. Soc. Chim. [2] viii. 459. 5 Ann. Chem. Pharm. xiv. 385. PREPARATION OF BENZALDEHYDE. 133 manner from oil of cinnamon, which contains cinnyl alde- hyde,1 and Toei from styrone or cinnyl alcohol, C6H5.CHrx CH.CH2.OH.2 Various other allied aromatic compounds yield benzaldehyde on oxidation. Cannizzaro showed that it is the first product of the oxidation of benzyl alcohol (p. 91), while Guckelberger and Keller found it among the products which are formed by the action of potassium permanganate and sulphuric acid on the albuminoids.3 It is readily obtained from benzoic acid by reduction carried on in aqueous solution by means of sodium amalgam,4 or by heating with stannous oxide.5 Baeyer obtained it by passing the vapour of benzoic acid or of phthalic acid, C6H4(CO2H)2, over heated zinc-dust6 and Chiozza by the action of copper hydride on benzoyl chloride.7 Piria found that it is formed by distilling a mixture of calcium benzoate and formate.8 When the vapour of benzene or toluene, mixed with air, is brought into contact with a glowing spiral of platinum or palla- dium, benzoic acid is formed together with some benzaldehyde, which is formed in larger quantity from xylene (dimethylbenzene) or cymene (methylpropylbenzene.)9 Toluene, as already men- tioned (p. 6), forms a compound with chromium oxychloride, which is decomposed by water with formation of benzaldehyde. This is also formed when benzyl chloride is boiled with dilute nitric acid or water and lead nitrate,10 as well as by heating benzidene chloride, C6H5.CHC12, with silver oxide, mercuric oxide,11 or alcoholic potash,12 or with water to 140°-16O0.13 When this compound is heated with two molecules of sulphuric acid to 30°, hydrochloric acid is evolved and a syrupy liquid formed, which is decomposed by water into sulphuric acid and benz- aldehyde.14 On the small scale benzaldehyde is best prepared by gradually heating benzidene chloride to 130° with the necessary amount of anhydrous oxalic acid : C6H5.CHC12 + C2H,O4 = C6H,.CHO + CO + CO2 + 2HC1. VU & it A ** & 1 Journ. Prakt. Chern. xviii. 385. 2 Ann. Cham. Pharm. Ixx. 5. 3 Ibid. Ixiv. 60 ; Ixxii. 86. 4 Kolbe, ibid, cxviii. 122. 5 Dusart, Compt. Rend. Iv. 448. 6 Ann. Chern. Pharm. cxl. 296. 7 Ibid. Ixxxv. 232. 8 Ibid. c. 105. 9 Coquillon, Compt. Rend. Ixxvii. 444 ; Ixxx. 1089. 10 Grimaux and Lauth, Bull. Soc. Chim. [2] vii. 106. 11 Gerhardt, Traite Chim. iv. 721. 12 Cahours, Ann. Chern. Pharm. Suppl. ii. 253. 13 Limpricht, ibid, cxxxix. 319. 14 Oppenheim, Ber. Deutsch. Chern. Ges. ii. 213. 134 AROMATIC COMPOUNDS. The residue is distilled under diminished pressure, and the aldehyde purified by a single rectification.1 2087 Benzaldehyde is manufactured by boiling 2 parts of benzyl chloride with 3 parts of lead nitrate, or better, copper nitrate, and 10 parts of water for several hours in an apparatus connected with an inverted condenser, the operation being conducted in a current of carbon dioxide; half the liquid is then distilled off, and the oil separated from the water. It is obtained from benzidene chloride by heating it under pressure in an iron vessel with caustic soda. According to Espenschied it is possible to heat without pressure in an apparatus connected with an inverted condenser if milk of lime be used, or if whitening, or some other finely-divided insoluble substance, be added and the whole stirred into an emulsion, which boils at a higher temperature and thus facilitates the decomposition of the chloride. Jacobsen recommends a process in which benzidene chloride is heated with glacial acetic acid and zinc chloride, benzaldehyde and acetyl chloride being formed ; the necessary amount of water is then allowed to flow in, and the acetic acid which is formed, recovered.2 The benzaldehyde thus obtained, which always contains chlorine compounds, is used in the colour industry. The pure compound may be obtained from it by preparing the double sulphite, which has already been mentioned, and decomposing this with caustic soda solution. Properties.-Benzaldehyde is a colourless, strongly refractive liquid which has a well known characteristic smell and a burn- ing aromatic taste. It dissolves in more than 300 parts of water;3 boils at 179°, and has a specific gravity of 1'0636 at 0° and of 1'0504 at 15°. In the pure state it rapidly oxidizes in the air and is also oxidized by boiling with chromic acid solution, manganese dioxide and sulphuric acid, or freshly precipitated ferric oxide.4 It is, however, only slowly attacked by strong, boiling nitric acid ; the red, fuming acid only yields benzoic acid, but when mixed with sulphuric acid gives substitution products.5 It differs from the aldehydes of the fatty series in not reducing an alkaline copper solution.6 1 Anschiitz, Liebig's Ann. ccxxvi. 18. 2 Bcr. Deutsch. Chern. Ges. xiii. 2013 ; xiv. 1425. 3 Fliickiger, Jahresb. Chem. 1875, 182. 4 Grager, Ann. Chem. Pharm. cxi. 124. 5 Lippmann and Hawliczek, Bcr. Deutsch. Chem. Ges. ix. 1463. 6 Tollens, ibid. xiv. 1950. BENZALDEHYDE. 135 It is converted into benzyl alcohol by treatment with sodium amalgam and water ; hydrobenzoin is simultaneously formed, together with the isomeric isohydrobenzoin C14H12(OH)2, which compounds, together with benzoin, CcH5.CH(OH)CO.C6H5, obtained by heating benzaldehyde with alcoholic potassium cyanide solution, will be subsequently described. Benzaldehyde is not poisonous; when taken internally it appears in the urine as hippuric acid;1 it is not decomposed when heated to dull redness, but is decomposed, chiefly into benzene and carbon monoxide, when passed through a tube filled with pumice stone and heated to bright redness.2 Benzaldehyde readily combines with other carbon compounds with elimination of water and is therefore largely employed, both on the small and large scale, for the synthesis of con- densation products, which will be subsequently described. Only a few of the most important reactions will be mentioned here. (1.) When benzaldehyde is heated with sodium acetate and acetic anhydride, cinnamic acid, C6H5.CH-CH.CO2H, is formed. The homologues of this acid are prepared in an analogous manner from the other fatty acids. (2.) Aromatic ketones are easily obtained by the con- densation of a fatty ketone with benzaldehyde; thus ordinary acetone yields methylcinnyl ketone, CH3.CO.CHzzCH.C6H5, which is converted by the further action of benzaldehyde into dicinnyl ketone or cinnamone, CO(CH=z:CH.C6Hr))2. (3.) When benzaldehyde is heated with aniline and zinc chloride, diamidotriphenylmethane, C6H5.CH(C6H4.NH2)2, is obtained ; if dimethylaniline be employed, the base, C0H5.CH (C6H4.N.(CH3)2)2, is formed, and this yields on oxidation the colouring matter known as benzaldehyde-green or malachite- green. (4.) Benzaldehyde combines with the nitroparaffins to form aromatic nitro-olefines, such as phenylnitro-ethylene, C6H5. CH-CHNO2, etc. 1 Frerichs and Wohler, Ann. Chem. Pharm. Ixv. 337. 2 Barreswill and Boudault, ibid. lii. 360. 136 AROMATIC COMPOUNDS. BENZIDENE COMPOUNDS. 2088 Benzaldehyde, like other aldehydes, behaves as the oxide of a dyad radical, which is called benzylene, benzylidene or benzidene. As in all analogous cases, the corresponding alcohol cannot be prepared, but ethers, ethereal salts, and other derivatives are known. Bcnzidene diethyl ether, C6H5.CH(OC2H5)2, was obtained by Wicke by the action of benzidene chloride on sodium ethylate. It is a liquid which possesses a pleasant smell resembling that of the geranium, and boils at 222°. Wicke has also prepared various other ethers.1 Benzidene dichloride, C6H6.CHC12. Cahours prepared this compound by the action of phosphorus pentachloride on oil of bitter almonds2 and named it chlorobenzol, a name which was subsequently changed into chloride of oil of bitter almonds and finally into benzal chloride (benzaldehyde chloride), which is still employed. It is also obtained by treating benzaldehyde with carbonyl chloride or succinyl chloride : 3 /CC12X ZCOX c6h5.cho+c2h4< >=C6H6.CHC12+C2H 4Z >0. \co z " ZCOZ It is, however, most readily prepared by passing chlorine into boiling toluene until it has gained 75 per cent, in weight and then purifying the product by fractional distillation.4 It is a colourless liquid which boils at 206°-207° and has a specific gravity of 1'295 at 16°.5 In the cold it has only a feeble smell, but when heated it gives off a penetrating vapour which produces a flow of tears. It is manufactured and employed for the preparation of benzaldehyde. Benzidene dibromide, C6H5.CHBr2, is formed by the action of phosphorus pentabromide on benzaldehyde; it is a powerfully 1 Wicke, Ann. Chem. Pham,. cii. 363. 2 Ann. Chim. Phys. [3] xxiii 329. 3 Rembold, Ann. Chem. Pham, cxxxviii. 189. 4 Beilstein and Kuhlberg, ibid, cxlvi. 322. 5 Hiibner and Bente, Bcr. Deutsch. Chem. Ges. vi. 804. BENZIDENE COMPOUNDS. 137 refractive liquid, which can only be distilled without decomposi- tion under considerably reduced pressure.1 Benzidene di-iodide, CGH5.CHI2. Geuther and Cartmell, by the action of hydriodic acid gas on benzaldehyde, obtained a peculiar compound, which they named benzaldehyde oxyiodide, C21H18I4O; it forms colourless, rhombic tablets, which melt at 28° and rapidly become coloured dark in the light. It smells exactly like cress, and can be volatilized with steam, yielding a vapour which attacks the eyes and nose most violently, the pain caused being greater and more enduring than that pro- duced by acrolein. When it is heated with silver nitrate solution, a smell of benzaldehyde is produced.2 The constitution of this body, the formula of which can be expressed as C6H5.CHO + 2C6H5.CHI2, is unknown. Benzidene diacetate, C6H5.CH(C2H3O2)2. Wicke obtained this compound by the action of silver acetate on benzidene chloride;3 it is also formed when benzaldehyde is heated with acetic anhydride,4 and crystallizes from ether in small, monoclinic tablets or in twins, which have the swallow-tail form of crystals of gypsum. It melts at 45°- 46°,5 and boils at 220°.6 Wicke has also prepared some other ethereal salts of benzidene. Potassium benzidene sulphite, C6H5.CH(OH)SO3K. This compound, which was earlier called the bisulphite of benz- aldehyde-potash, was obtained by Bertagnini in crystals by agitating benzaldehyde with a concentrated solution of acid potassium sulphite.7 It crystallizes from hot, dilute alcohol in long plates, which are slightly soluble in cold alcohol, readily in water, but are almost insoluble in a concentrated solution of acid potassium sulphite. It is decomposed by simply boiling with water, more readily by acids or alkalis, with separation of benz- aldehyde, which can thus be obtained pure (p. 134). Sodium benzidene siblphite, C6H5.CH(OH)SO3Na-j-H.,O, forms small crystals, and behaves like the potassium salt. Ammoniibtn benzidene sulphite, C6H5.CH(OH)SO3NH4 + H90. Bertagnini, on shaking benzaldehyde with a concentrated solu- tion of acid ammonium sulphite, observed an evolution of heat and obtained a clear solution from which no crystals separated out. 1 Michaelson and Lippmann, Ber. Deutsch. Chem. Ges. Suppl. iv. 113. 2 Ann. Chem. Pharm. cxii. 20. 3 Ibid. cii. 368. 4 Geuther, ibid. cvi. 251 ; Hubner, Zeitschr. Chem. 1867, 277. s Perkin, ibid. 1868, 172. 6 Neuhof, Ann. Chem. Pharm. cxlvi. 323. 7 Ibid. Ixxxv. 183. 138 AROMATIC COMPOUNDS. Otto, however, obtained the compound in crystals by mixing alcoholic solutions of sulphur dioxide and hydrobenzamide; a precipitate is formed consisting of microscopic needles which are slightly soluble in alcohol, readily in water, and separate from the latter in transparent crystals containing three molecules of water.1 Benzaldehyde does not form an analogous compound with acid aniline sulphite, but a very stable substance of the empirical formula, 2C7H6O + 2C6H7N + SO2, is produced, and crystallizes from water in long, flat needles.2 Benzidene sulphide, C0H5.CHS. Cahours prepared this com- pound by heating benzidene chloride with an alcoholic solution of potassium hydrosulphide and named it sulphobenzene.3 It was then further investigated by Fleischer4 and Bbttinger.5 It crystallizes from hot alcohol in nacreous plates and from ether in transparent, four-sided prisms, melting at 70°-71°. On heating with caustic potash it yields benzyl hydrosulphide, benzyl disulphide and some benzoic acid,' and on dry distillation gives stilbene, C14H19, tolallyl sulphide, C14H10S, and thionessal, c28h20s. Parabenzidene sulphide, (C6H5.CHS)n. By the action of am- monium sulphide on an alcoholic solution of benzaldehyde, Laurent obtained a compound of this composition, which he called sulphobenzoyl hydride (hydrure de sulfobenzdile\ and de- scribed as a powder consisting of microscopic granules, which became soft at 90°-95°, and, after careful fusion, solidified to a transparent mass. It is odourless, but imparts to the hands a very repulsive, adhering alliaceous odour.6 On dry distillation it yields the same products as benzidene sulphide. The compound which Klinger obtained by passing sulphuretted hydrogen into a solution of benzaldehyde in absolute alcohol and named a-benzothio-aldehyde, is probably identical with this body. It is amorphous, softens at 80°-85°, and is converted by acid chlorides into ft-benzothio-aldehyde, which is slightly soluble in alcohol, readily in hot glacial acetic acid, and crystallizes in lustrous white needles, melting at 225°-2260.7 This compound is most readily obtained by dissolving 1 Neuhof, Ann. Chern. Pharm. cxii. 308. 2 Schiff, ibid. cxl. 130 ; ccx. 128. 3 Ann. Chim. Phys. [3] xxiii. 333 ; Ann. Chern. Pharm. Ixx. 40. 4 Ibid. cxl. 234. 5 Ber. Deutsch. Chern. Ges. xii. 1053. 6 Ann. Chim. Phys. [3] i. 292 ; Ann. Chern. Pharm. xxxviii. 320 ; see also Rochleder, ibid, xxxvii. 346. 7 Ber. Deutsch. Chern. Ges. ix. 1893. BENZALDOXIME. 139 amorphous benzothio-aldehyde in hot benzene and adding a small quantity of iodine also dissolved in benzene ; lustrous needles of the formula CGH5.CHS + CGHG soon separate out, which lose benzene and become opaque at 125°-130°.1 a-Benzothio-aldehyde is also formed, together with ammonia, when an alkaline solution of benzothiamide, C6H5.CS.NH2, is treated with sodium amalgam.2 Both thio-aldehydes, when heated with copper dust, yield stilbene, C14H10, as the chief product, and the amorphous com- pound on fusion with caustic potash yields the same products as benzidene sulphide (Bbttinger). Klinger was unable to convert the latter, which he considered to be y-benzothio-aldehyde, into the ^-compound by the action of acetyl chloride or iodine ; the ^-compound is probably a polymeric modification, and is best called parabenzidene sulphide. 2089 Benzidenoxime, or Benzaldoxime, CGH5.CH.NOH, is formed when benzaldehyde and sufficient alcohol to form a clear solution are added to an aqueous solution of hydroxylamine hydrochloride containing an excess of sodium carbonate : C6H5.CHO + H2N.OH = CcH5.CH-N.OH + H2O. After twenty-four hours the mixture is extracted with ether and the residue, after the evaporation of the ether, rectified. Benzaldoxime is an oily liquid, which boils above 220° with partial decomposition, and is decomposed by hydrochloric acid into the substances from which it is formed. On treatment with alcoholic caustic soda it gives the compound C6H5.CH.NONa, which crystallizes from water in small, lustrous plates. By the action of methyl iodide on this, the methyl ether, C6H5.CH, NOCH3, is obtained as a light, oily liquid, which has a very pleasant, fruity odour, and boils at 190°-192°; other ethers have been prepared in a similar manner.3 Hydrobenzamide, or Tribenzidenediamine, N2(CH.C6H5)3. Acet- aldehyde combines directly with ammonia to form aldehyde ammonia, CH3.CH(OH)NH2, but benzaldehyde behaves in a completely different manner; three molecules of the latter lose all their oxygen, which combines with the hydrogen of two molecules of ammonia, the place of this being taken by the benzidene groups. 1 Ber. Deutsch. Chem. Ges. x. 1877. 2 Bernthsen, ibid. x. 36. 3 Petraczek, ibid. xv. 2783 ; xvi. 823. 140 AROMATIC COMPOUNDS. Hydrobenzamide is slowly formed when benzaldehyde is allowed to stand in contact with aqueous ammonia;1 more rapidly when the two are heated together.2 Benzaldehyde absorbs dry ammonia, and if the product of this absorption be allowed to stand in a vacuum, water is lost and hydrobenzamide remains ;3 it is also formed when benzidene- dichloride is allowed to stand for some months with aqueous ammonia.4 It is readily soluble in alcohol and ether, and crystallizes in lustrous, rhombic pyramids, melting at 110°; very fine crystals may be obtained by pouring an excess of aqueous ammonia on to a mixture of equal volumes of benzaldehyde and ether, and allowing the whole to stand.5 It is tasteless, but its alcoholic solution has, according to Laurent, a faint taste of burnt almonds. On boiling with alcohol it slowly decomposes into ammonia and benzaldehyde ; acids rapidly produce this decom- position. On oxidation with aqueous chromic acid, a large quantity of benzoic acid is formed (Fownes). When it is boiled with caustic potash or heated to 120°-130°, it is converted into the isomeric amarine, which will be sub- sequently described; the relation between the two compounds is shown by the following formulae : Hydrobenzamide. C6H5.CH=Nx >CH.C6H5. cgh5.ch=nz Amarine. c6h5.c.nh II >cn.c6h5. c6h5.c.nh Thiobenzaldine, (C6H5.CH)3S2NH. Laurent obtained this compound, the analogue of thialdine (Pt. II. p. 75), by allowing a mixture of crude oil of bitter almonds, ammonium sulphide and ether, to stand for several weeks. It crystallizes in nacreous plates or monoclinic prisms which melt at 125°, and impart an unpleasant smell to the skin. When it is boiled with alcohol, sulphuretted hydrogen is given off, while alcoholic potash decomposes it with evolution of ammonia.6 Benzidene-aniline, C6H5.CH=zN.C6H5. Gerhardt and Laurent obtained this compound by heating benzaldehyde with aniline, 1 Laurent (1836), Ann. Chim. Phys. Ixii. 23 ; Ixvi. 18 ; Ann. Chem. Pharm. xxi. 130. 2 Rochleder, ibid. xli. 89. 3 Herzfeld, Ber. Deutsch. Chem. Ges. x. 1271. 4 Engelhardt, Ann. Chem. Pharm. ex. 77. 6 Eckmann, ibid. cxii. 175. 8 Ann. Chem. Pharm. xxxviii. 323. CONDENSATION PRODUCTS OF BENZALDEHYDE. 141 and named it benzoylanilide.1 The same compound is formed, as shown by Schiff, when benzaldehyde is heated with thio- carbanilide :2 3CS(NHC6H5)2+6C6H5.CHO = 6C6H5.CH - N. C6H5+CS2+2CO2+H2S + 2H2O. It is very soluble in alcohol and ether, separating from the latter in warty crystals, and crystallizing from carbon disulphide in yellow needles, which melt at 42°,3 and are volatile with steam. It does not combine with acids, and is partially decomposed on heating into benzaldehyde and aniline. 2090 Benzidene-aniline cyanhydrate, C6H5.CHzzzN.CeH5.CNH. Cech obtained this compound by the action of potassium cyanide on an alcoholic solution of benzaldehyde and aniline or aniline hydrochloride; it is also formed when hydrocyanic acid is passed into fused benzidene-aniline, and is decomposed into its com- ponents by heat. It crystallizes from carbon disulphide in silky needles, which melt at 82°, sublime readily, and are volatile with steam. Benzidcnephenylhydrazine, C6H5.CH-N.NH.CcH5, is formed by a violent reaction when benzaldehyde and phenylhydrazine are brought together. It crystallizes from dilute alcohol in monoclinic prisms, which melt at 152'5° and can be volatilized without decomposition. Benzidenediphenylhy dr azine, C6H5.CH - NC.(C6H5)2, forms small yellow crystals, melting at 122°.4 Phenylbenzaldehydine, or Benzidene-orthodiamidobenzene, (C6H5. CH~N)9CgH4, is formed when a dilute aqueous solution of orthodiamidobenzene hydrochloride is shaken up with benz- aldehyde, the hydrochloride thus obtained being purified by re-crystallization, and the base precipitated with caustic potash. Phenylbenzaldehydine is insoluble in water and crystallizes from alcohol in six-sided prisms, melting at 133°-134°. Phenylbenzaldehydine hydrochloride, C2OH16N2.HC1, crystallizes in colourless prisms which are only slightly soluble in water, and lose hydrochloric acid when their solution is boiled. When the base is heated with ethyl iodide to 100°-120°, the compound C20H16N2.C2H5I is formed; it crystallizes from hot water in colourless, thick prisms, melting at 211°-213°.5 1 Jahresb. Chern. 1850, 488. 2 Ann. Chern. Pharm. cxlviii. 336. 3 Cech, Ber. Deutsch. Chem. Ges. xi. 246. 4 E. Fischer, Ann. Chem. Pharm. cxc. 134, 179. 5 Engelbrecht and Ladenburg, Ber. Deutsch. Chem. Ges. xi. 1653. 142 AROMATIC COMPOUNDS. Benzideneparadiamidobenzene, (C6H5.CH~N)2C6H4, is formed by the action of paradiamidobenzene on benzaldehyde; it crystallizes from alcohol in plates which have a silver lustre, and melt at 140°; it is decomposed by acids into its components, since only the ortho-diamines form stable basic aldehydines1 (Part III. p. 62). Bcnzidcnedi'incthylparadiamidobenzene, C0H5.CH zzz N.C6H4.N (CH3)2, is readily formed by heating benzaldehyde with di- methylparadiamidobenzene, and crystallizes from hot alcohol in lustrous plates or needles, melting at 93°. It is a feeble, di-acid base.2 Dibenzidcnc-ortbiodiamidotoluene, or Tolubenzaldehydine, (C6H5. CH"N)2C6H3.CH3, has been obtained by Ladenburg from orthodiamidotoluene; it crystallizes in lustrous, monoclinic prisms, melting at 195'5°; on oxidation with potassium perman- ganate, it yields dibenzidcncdiamidobenzoic acid, (C6H5.CH=N)2. C6H3CO2H. The hydrochloride, C21H18N2.C1H, crystallizes from hot dilute hydrochloric acid in long needles. When it is heated with ethyl iodide, it is converted into the iodide, C21H18N2.C2H5I, which crystallizes in thick prisms, and, on treatment with silver oxide, yields the corresponding hydroxide, which remains behind after evaporation of the solution as a strongly alkaline, oily liquid.3 Dibenzidenemctadiamidotohiene crystallizes from a mixture of ether and alcohol in small lustrous tablets, melting at 122°-128°. It does not combine with acids, but when heated to 140°-150° for a considerable time, it is converted into a base, which Schiff considers to be amarine.4 Bcnzidenephenyldiamine, C6H5.CH(NH2)NH(C6H5). When benzonitril, C6H5.CN, is heated with aniline hydrochloride to 220°-240°, phenylbenzenylamidine 5 is formed, and this is con- verted into the diamine by the action of zinc and dilute acetic acid : zNH2 C6H5.C< + 2H = C6H5.CH< \nh.c6h5 xNH.C6H5. It is very soluble in all solvents, with the exception of water and separates from dilute alcohol in indistinct crystals, melting at 1 Ladenburg, Ber. Deutsch. Chem. Ges. xi. 599. 2 Calm, ibid. xvii. 2938. 3 Ibid. x. 1126 ; xi. 591, 1648. 4 Ann. Chem. Pharm. cxl. 98. 5 Bernthsen, Liebig's Ann. clxxxiv. 348. BENZIDENE UREIDES. 143 114'5°-115°. At a higher temperature it distils without decom- position, and on heating with chloroform and alcoholic potash yields the smell of the carbamines. Benzidenephenylamine hydrochloride, C13H14N2.C1H, crystallizes from water in thick prisms, melting at 223°-224'5°.1 Benzidene-acetamide, C6H5.CH(NH.C2H3O)2, is formed by heating benzaldehyde with acetamide, and crystallizes from hot water in fine silky needles.2 Benzidene urethane, C6H5.CH(NH.CO.OC2H5)2, is formed when hydrochloric acid is added to a mixture of benzaldehyde and ethyl carbamate. It separates from alcohol as a silky crystalline mass, which melts at 171°, and can be sublimed.3 Benzidene ureides are formed by heating benzaldehyde with urea, and are split up again into these substances by boiling with water.4 znh.co.nh2 Benzidenedi-ure'ide, C6H5.CHA , fine needles. \nh.co.nh2 zNH.CO.NH2 C6H5.CHA , white powder. Benzidenetri-ure'ide, -C0.NH9 C6H5.CH< \nh.co.nh2. zNH.CO.NH2 c6h5.ch< \n-co.nh2 Benzidenetetra-ureide, CAL.CH , white powder. \n-CO.NH, c6h5.ch< xNH.CO.NH2. SUBSTITUTION PRODUCTS OF BENZIDENE COMPOUNDS. 2091 Orthochlorobenzaldehyde, C6H4C1.CHO. By the action of phosphorus pentachloride on salicylaldehyde, C6H4(OH)CHO, orthochlorobenzidene chloride, C6H4C1.CHC12, is obtained as an 1 Bernthsen and Seymanski, Bar. Deutsch. Chern. Ges. xiii. 917. 2 Roth, Ann. Chern. Pharm. cliv. 72. 3 Bischoff, Ber. Deutsch. Chem. Ges. vii. 634, 1082. 4 Schiff, Ann. Chem. Pharm. cxl. 115 ; cxlviii. 330 ; cli. 892. 144 AROMATIC COMPOUNDS. oily liquid, which boils at 227°-230°, and possesses a penetrating smell and a sharp burning taste. When this compound is heated with water to 170°, the aldehyde is formed ; it is a liquid which boils at 210°, has a sharp smell and taste, and readily oxidizes in the air to orthochlorobenzoic acid. It combines with acid sodium sulphite.1 Metachlorobenzaldehyde is formed when benzaldehyde is chlorinated in presence of a dehydrating agent, such as sul- phuric acid, zinc chloride, aluminium chloride, etc., and is a liquid boiling at 210°-213°.2 It may also be obtained by heating a hydrochloric acid solution of metamidobenzaldehyde and cuprous chloride to the boiling-point and then gradually adding a solution of sodium nitrite.3 Parachlorobcnzaldehydc is obtained by boiling parachlorobenzyl bromide with water and lead nitrate in an atmosphere of carbon dioxide. It crystallizes in white tablets, melting at 47'5°, which are slightly soluble in cold, more readily in hot water, and readily in alcohol ; it smells like benzaldehyde, readily oxidizes in the air and unites with acid sodium sulphite to form a compound which is only slightly soluble.4 The product of the action of chlorine on benzidene chloride in presence of iodine is a mixture of ortho- and para-chloro- benzidene chlorides, which boils at 230°-237°,5 and was formerly thought to be the pure para-compound.6 When it is heated with anhydrous oxalic acid, boiled with lead nitrate, or heated to 170° with water, a mixture of the aldehydes is obtained, boiling at 210c-214°; in the cold it smells like benzaldehyde, but when heated has a very sharp, penetrating odour and causes a flow of tears. The same mixture is formed, together with ethyl iodide, when benzyl ethyl ether is treated with chlorine in presence of iodine :7 C6H6.CH2.O.C2H5 + IC13=C6H4C1.CHO + C2H5I + 2HC1. Didhlorobenzaldehyde, C6H3C12.CHO(C1: Cl = 3 : 4). Beilstein and Kuhlberg, by the action of chlorine on boiling dichloro- 1 Henry, Ber. Deutsch. Chem. Ges. ii. 135. 2 Muller, ibid, xviii. Ref. viii. 680. 3 Ibid, xviii. Ref. 395. 4 Jackson and White, ibid. xi. 1042. 5 Anschutz, Ann. Chem. Pharm. ccxxvi. 19. 6 Beilstein and Kuhlberg, ibid, cxlvi. 327. 7 Sintenis, Ber. Deutsch. Chem. Ges. iv. 699. CHLORINE DERIVATIONS OF BENZALDEHYDE. 145 toluene, obtained a dichlorobenzidene chloride, CgHgCl^CHCl^1 which boils at 257°, and is converted into the aldehyde by heating with water to 200°. It is soluble in boiling water, more readily in alcohol, and crystallizes in fine needles, which melt at 68°, volatilize in steam, and combine with acid sodium sulphite.2 A compound, which is probably identical with this, is ob- tained by the further chlorination of metachlorobenzaldehyde in presence of a dehydrating agent, and is described as a liquid, boiling at 240°-2430.3 a-Trichlorobenzaldehyde, C6H2C13.CHO. The further chlori- nation of a-trichlorotoluene yields a-trichlorobenzidcne chloride, C6H2C13.CHC12, which boils at 280°-281°, and solidifies be- low 0° in fine needles.4 The aldehyde obtained by heating it with water to 260° is insoluble in water, crystallizes in very fine needles, which melt at 112°-113°, and is volatile with steam.5 [3-Trichlorobenzaldehyde. The ^-trichlorobenzidene chloride obtained from /3-trichlorotoluene, melts at 84°, boils at 280°, and yields the /3-trichlorobenzaldehyde which melts at 90° (Seelig). Tetrachlorobenzidene chloride, COHC14.CIIC12, has been prepared from tetrachlorotoluene ; it is a liquid, which boils at 305°-306°, and is decomposed by water at 250°. The aldehyde thus formed has not been further investigated.6 Pentachlorobenzidene chloride, C6C15.CHC12. is formed by the continued action of chlorine on benzidene chloride in presence of iodine and finally of antimony chloride. It crystallizes from alcohol in long flat plates, melts at 109°, boils at 334°, and is not attacked by water even at 300°.7 Orthobromobenzaldehyde, C6H4Br.CHO, has been prepared by boiling orthobromobenzyl bromide with water and lead nitrate ; it is a heavy, oily liquid, which oxidizes very rapidly in the air.8 Metdbromobenzaldehyde, C6H4Br.CHO, is a liquid which does not solidify in a freezing mixture (Jackson and White), boils at 233°-236°, and may be prepared by the bromination of benzaldehyde in presence of a dehydrating agent (Muller). Parabromobenzaldehyde, C6H4Br.CHO, crystallizes in long white needles, melting at 57°. 1 Ann. Chern. Pharm. cl. 291. 3 Ibid. clii. 228. 3 Ber. Deutsch. Chern. Ges. Ref. xviii. 25. 4 Ann. Chern. Pharm. cl. 299 ; Seelig, Ber. Deutsch. Chern. Ges. xviii. 420. 5 Ibid.; Ann. Chern. Pharm. clii. 238. 6 Ibid. cl. 303. 7 Hid. cl. 306. 8 Jackson and White, Amer. Chern. Journ. iii. 32. 146 AROMATIC COMPOUNDS. Para-iodobcnzaldeltyde, C6H4I.CHO, also forms needles, melting at 73° (Jackson and White). 2092 Orthonitrobenzaldehyde, CcH4(NO2'CHO, is formed in small quantity, together with the meta-compound, by the action of a mixture of nitric and sulphuric acids on benzaldehyde.1 It may, however, be more readily prepared from orthonitrocinnamic acid, C6H4(NO2)CHzz:CH.CO2H. When the ethyl ether of this acid is dissolved in concentrated nitric acid and treated with sodium nitrite, the temperature of the mixture not being allowed to rise more than a few degrees, a compound is formed which contains a nitric acid residue in the side chain. The mixture is poured, after having stood for some hours, into water, and the oil which separates out distilled in steam, sodium carbonate being added from time to time; the distillate consists of water and pure orthonitrobenzaldehyde.2 It can be still more conveniently prepared by oxidizing orthonitrocinnamic acid with potassium permanganate in alkaline solution (Friedlander and Henriques). The solution must be cooled with ice and shaken up with benzene at short intervals in order to remove the aldehyde from the further action of the oxidizing agent. The benzene solution is then evaporated, the aldehyde remaining behind.3 It is readily soluble in alcohol, slightly in water, and crystal- lizes in long, light yellow needles, melting at 46°, which smell like benzaldehyde in the cold, but give off a penetrating vapour when heated. It forms a readily soluble compound with acid sodium sulphite, which crystallizes in small, lustrous plates ; concentrated caustic soda solution decomposes it completely into orthonitrobenzyl alcohol and orthonitrobenzoic acid. When a little water and caustic soda are added to its solution in acetone, indigotin, C16H10N2O2, the colouring matter of indigo, separates out after a short time.4 Orthonitrobenzaldoximc, CcH4(NO2)CH.NOH. Gabriel and Meyer, by the action of hydrochloric acid and amyl nitrite on amidorthonitrophenylacetic acid, obtained a diazo-compound : NH2.C6H3(NO2)CH2.CO2H + 2NO2H + HC1 = C1N = NCcH3(NO2)CH2NO + CO2 + 3H2O. 1 Rudolph, Ber. Deutsch. Chem. Ges. xiii. 310. 2 Friedlander and Henriques, ibid. xiv. 2801. 3 Einhorn, tbid. xvii. 119. 4 Baeyerand Drewsen, ibid. xv. 2857. METANITROBENZ A LDEHYDE. 147 On heating with alcohol, this is converted into nitroso- methylnitrobenzene, C6H4(NO2)CH2NO, this being decomposed by oxidation with formation of nitrogen monoxide and orthonitro- benzaldehyde, which was first prepared pure by this method.1 This substance was subsequently recognised as orthonitrobenzal- doxime and prepared from the aldehyde and hydroxylamine.2 It crystallizes from hot water in hair-like needles, which melt at 95°, have a sweet taste, and form a yellow solution in alkalis. Its methyl ether, C6H4(NO2)CH.NOCH3, is formed by heating it to 100° with caustic potash, methyl alcohol and methyl iodide ; it is only slightly soluble in water, readily in alcohol, and crystallizes in silky needles, melting at 58°. Metanitrobcnzaldehydc, C6H4(NO2)CHO, was first obtained by Bertagnini by the action of a mixture of nitric and sulphuric acids on benzaldehyde.3 In order to prepare it, 1 part of the latter is dissolved in a mixture of 5 volumes of fuming nitric acid with 10 volumes of sulphuric acid, the temperature being kept below 15°. The nitro-compound is precipitated by water, washed and re-crystallized from dilute alcohol.4 It forms lustrous white needles, melting at 58°,5 smells like benzaldehyde when cold, but gives off a penetrating vapour when heated, and combines with the acid sulphites of the alkalis (Bertagnini), as well as with acid aniline sulphite 6 to form crystalline compounds. Metanitrobenzidene chloride, C6H4(NO2)CHC12, is obtained by the action of phosphorus pentachloride on the aldehyde; it crystallizes from alcohol in needles or small thin plates, melting at 6 5°.7 Metanitrobenzidene bromide, C6H4(NO2)CHBr2, is formed by heating the aldehyde with bromine to 140°, and crystallizes in microscopic tablets, melting at 101°-102°.s Metanitrobenzaldoxime, C6H4(NO2)CH.NOH, was first obtained from metanitro-amidophenylacetic acid and was called nitroso- methylmetanitrobenzene? It is readily formed by the combination of hydroxylamine 1 Ber. Deutsch. Chem. Ges. xiv. 832, 2332. 2 Gabriel, ibid. xv. 3057. 3 Ann. Chem. Pharm. Ixxix. 260. 4 Widmann, Ber. Deutsch. Chem. Ges. xtH. 678 ; see also Friedlander and Henriques, ibid. xiv. 2801. 5 Lippmann and Hawliczek, ibid. ix. 1463. 6 Schiff, Ann. Chem. Pharm. cxcv. 301. 7 Widmann, Ber. Deutsch. Chem. Ges. xiii. 676. 8 Wachendorff, Ann. Chem. Pharm. clxxxv. 266. 9 Gabriel, Ber. Deutsch. Chem. Ges. xv. 834. 148 AROMATIC COMPOUNDS. with metanitrobenzaldehyde,1 and crystallizes from water in long, flat needles, melting at 118°-119°. Its methyl ether also forms flat needles and melts at 63°-63'5°. Trinitrohydrobenzamide, N2(CH.C6H4.NO2)3, is formed by the action of ammonia on metanitrobenzaldehyde; it is insoluble in water and ether, and only slightly soluble in boiling alcohol, from which it separates out in flocks consisting of very thin needles. When it is heated to 125° or boiled with dilute caustic potash solution, it is converted into the isomeric trinitro-amarine, which forms warty crystals and has a feeble alkaline reaction. Its salts are difficultly soluble and have a very bitter taste (Bertagnini). Paranitrobenzaldehyde, C6H4(NO2)CHO, is prepared by boiling 10 parts of paranitrobenzyl chloride with 60 parts of water, 14 parts of lead nitrate, and 10 parts of nitric acid of sp. gr. 13, for several hours. If the solution be more dilute, nitrobenzyl alcohol is formed instead of the aldehyde. The product is shaken out with ether and the aldehyde separated by means of acid sodium sulphite.2 Paranitrobenzaldehyde may also be readily obtained by the oxidation of paranitrocinnamic acid.3 It crystallizes from hot water in thin prisms, often an inch in length, which melt at 106°, have a characteristic smell, and do not volatilize readily in steam. Its compound with acid sodium sulphite is readily soluble in water and crystallizes in small iridescent plates. It is not attacked to an appreciable extent by boiling nitric acid, which must not, however, be too concentrated, but is quantitatively converted into parahydroxybenzoic acid by chromic acid.4 When it is heated with aniline hydrochloride and zinc chloride, /paranitrodiamidotriphenylmethane, CH(C6H4.NH2)9 C6H4.NO2, is formed, which on reduction yields paraleucaniline, CH(C6H4.NH2)3. It is oxidized by mercuric oxide to pararosani- line, C(OH)(C6H4.NH2)3 (Fischer and Greiff). Paranitrobenzidene chloride, C6H4(N O2)CHC19, is formed by the action of phosphorus pentachloride on paranitrobenzalde- hyde ; it crystallizes from alcohol in short, well-formed prisms, melting at 46°.5 Paranitrobenzidene bromide, C6H4(NO2)CHBr2, is formed by 1 Gabriel, Bar. Deutsch. Chem. Ges. xv. 3061. 2 0. Fischer and Greiff, ibid. xiii. 669. 3 Baeyer, ibid. xiv. 2317 ; Friedlander, ibid. xiv. 2577 ; Basler, ibid. xvi. 2714. 4 0. Fischer, ibid. xiv. 2525. 6 Zimmermann and Muller, ibid, xviii. 996. ORTHAMIDOBENZALDEHYDE. 149 heating paranitrotoluene with bromine to 140°, and crystallizes from alcohol in needles or small rectangular plates, melting at 82°-82,50.1 Both compounds are converted into pararosaniline when heated with aniline.2 Paranitrobenzaldoxime, C6H4(NO2)CH~N.OH, crystallizes from hot water in lon^ needles, melting at 128'5°.3 2093 Orthamidobenzaldehyde, C6H4(NH2)CHO, was first ob- tained by Gabriel in small quantities by oxidizing orthamido- benzaldoxime with an acid solution of ferric chloride.4 Fried- lander and Henriques found that orthonitrobenzaldehyde is converted by the action of tin and acetic acid into anthranil,5 C7H5NO, a compound which stands to anthranilic acid or orthamidobenzoic acid in the same relation as lactimide to a-amidopropionic acid (Part II. p. 142). This is converted into orthamidobenzaldehyde by heating with ferrous sulphate and ammonia : 6 /NH zNH2 C6H4( I + 2H = C6H4( \co \CHO. The latter can also be obtained directly in the same way from orthonitrobenzaldehyde.7 It is very soluble in alcohol, less readily in water, forming a yellow solution, and crystallizes in lustrous plates, which are volatile with steam, their vapour possessing a penetrating smell resembling that of an indigo vat. It melts at 39°-40°, and solidifies on cooling in a crystalline mass; at a higher temperature a portion distils without de- composition, while the remainder is converted into a dark yellow, resinous mass. It can be heated with caustic soda solution or ammonia without undergoing any change ; dilute mineral acids, however, readily convert it into an amorphous condensation product. When it is heated with acetic anhydride, acetylorthamidobenzaldehyde, C6H4(NH.C2H3O)CHO, is formed; it crystallizes from hot water in long white needles, melting at 70°- 71°. Orthamidobenzaldoxime, C6H4(NH2)CHz=N.OH, is formed by 1 Wachendorff, Ann. Chern. Pharm. clxxxv. 268. 2 Zimmermann and Muller, Ber. Deutsch. Chern. Ges. xvii. 2936. 3 Gabriel and Herzberg, ibid. xvi. 2000. 4 Ber. Deutsch. Chern. Ges. xv. 2004. 5 Ibid. xv. 2105. 6 Friedlander, ibid. xv. 2572. 7 Friedlander and Gbhring, ibid. xvii. 456. 150 AROMATIC COMPOUNDS. the reduction of the corresponding nitro-compound with am- monium sulphide, and crystallizes from hot water in long, flat, lustrous needles, melting at 132°-1330.1 Metamidobenzaldchyde, C6H4(NH2)CHO, is obtained by re- ducing metanitrobenzaldehyde with ammonia and ferrous sulphate, and distilling the product with steam; it is a yellow, oily liquid, which solidifies at low temperatures and yields amorphous condensation products with even greater readiness than the ortho-compound (Friedlander and Gdhring). Metamidohcnzaldoxime, C6H4(NH2)CH~N.OH, is formed when a solution of metanitrobenzaldoxime in caustic soda is added to a hot solution of ferrous sulphate saturated with ammonia, the blue-black ferrous hydroxide being converted into brown ferric hydroxide. The filtrate is rendered faintly acid with hydrochloric acid, treated with ammonia and then extracted with ether; the residue left on evaporation of the ethereal extract consists of metamidobenzaldoxime, which crystallizes from hot benzene in fine, snow-white needles, melt- ing at 88°. Oxidation with an acid solution of ferric chloride yields an amorphous, yellow oxidation product of metamido- benzaldehyde.2 Paramidobcnzaldehyde, C6H4(NH2)CHO, has been obtained as a decomposition product of its aldoxime ; it crystallizes from water in small, indented plates, which melt at 69'5°-71'5°, but soon change into a modification insoluble in water and melting at a higher temperature. When heated with acetic anhydride and sodium acetate, it is converted into acedylparamidobenzalde- hyde, C6H4(NH.C2H3O)CHO, which crystallizes from hot water in long, lustrous needles, melting at 155» Par amidobenz aldoxime, C6H4(NH2)CH~N.OH, is formed by the action of ammonium sulphide on paranitrobenzaldoxime, and crystallizes from hot water in yellow tablets, melting at 124°. It dissolves in an excess of hydrochloric acid, forming a solution which soon deposits dark red needles with a blue re- flection, while hydroxylamine remains in solution. Caustic soda decomposes the red compound, paramidobenzaldehyde or its con- densation products being set free.3 Dimethylparamidobenzaldchydc, CcH4.N(CH3)2CHO. When zinc chloride is allowed to act on a mixture of chloral hydrate 1 Gabriel and Mayer, Ber. Deutsch. Chern. Ges. xiv. 2338. 2 Gabriel, ibid. xvi. 1997. 3 Gabriel and Herzberg, ibid. xvi. 2000, BENZOIC ACID. 151 and dimethylaniline, dimethylamidophenylhydroxytrichlorethane is formed, and is decomposed by caustic potash with formation of dimethylparamidobenzaldehyde and chloroform or decomposition products of these : /CH(OH)CC13 .CHO C6H4<f = C6H4< +chci3. \N(CH3)2 XN(CH3)2 The new compound crystallizes in small plates, which melt at 73°, readily dissolve in alcohol and hot water, and are volatile with steam.1 BENZOIC ACID, C6H5.COOH. 2094 The products formed by the dry distillation of gum ben- zoin 2 are mentioned in writings which date back as far as the sixteenth century. Hieronymus Rosello, who, under the name of Alexius Pedemontanus, published a work, De Secretis, in the year 1557, mentions in it the butter of benzoin, and Libavius in his Alchymia, written in 1595, says that when laser3 vel benzoin is distilled, water comes over first, followed by a thick oil, " ultima exit instar mannae, gummi." Blaise de Vigenere, whose Traits de feu et du sei, appeared after his death in 1608, says that with a strong fire " infinies petites aiguilles et fila- ments" appear, which must be soon removed because they would otherwise melt like marrow (moelle). About the same period, Turquet de May erne in his Pliar macopoea teaches how to obtain flowers of benzoin from the residue by subliming it in an 1 Rocssneck, Ber. Deutsch. Chern. Ges. xviii. 1516 ; xix. 365. 2 This resin is obtained by means of incisions in the bark of Styrax Benzoin, a tree indigenous to Java and Sumatra. It is sent into the European market from the latter island, and this was formerly the only source from which it could be obtained. A highly valued variety is now sent from Siam, but nothing further is known as to its origin. It was formerly counted as one of the costly spices. It is first mentioned by Ibn Batuta, who travelled in the East about the years 1325 -1349, and describes it under the name of Luban Jawi (incense of Java). The latter word was then the name of Sumatra, and the Arabs designated by it the whole archipelago, as well as the products obtained from it. The Arabic name gradually became corrupted into banjawi, benjui, benzui, benzoe, benzoin, and in English also benjamin or gum benjamin, which is now the name in general commercial use (Fliickiger and Hanbury, Pharmacogra/phia, 2nd ed. p. 403). 3 Laser is the name of a Persian and Indian product on which a tax was imposed at the Roman customs-house in Alexandria during the second century of our era. Some suppose that it was asa foetida, while benzoe was also called asa dulcis. 152 AROMATIC COMPOUNDS. earthen vessel to which a cap of paper has been adapted, or by heating it mixed with sand in a retort, and since that time flores benzoes have been an ordinary pharmaceutical prepara- tion. A solution of the resin in alcohol was also in use; mixed with lead acetate it was employed as a choice cosmetic under the names of magistcrium benzoes or lac Virginis. Ehrenfried Hagendorn, a physician of Gorlitz, in 1671 found in this a salt which was identical with flowers of benzoin, both in smell and taste. Lemery in 1675 also remarked on the acid nature of this substance, saying, " les flours de benjoin ont uno aridity fort agrdablef a fact which was further proved by the researches of Scheele, who showed, in 1775, that the flowers of benzoin could be more economically obtained by digesting the resin with slaked lime and water for some hours, boiling and adding hydrochloric acid to the filtrate; finally, Lichtenstein in 1782 conclusively proved that they are an acid. The correct composition of benzoic acid was determined in 1832 by Liebig and Wohler,1 who showed that it is a compound of the radical benzoyl, C7H6O (p. 89). Mitscherlich, on the other hand, showed in 1834 that it is decomposed into carbon dioxide and benzol on heating with milk of lime, and looked upon it as a carbonic acid derivative of benzol; Liebig opposed this view, as he considered the benzol to be merely a product of the destruction of the benzoic acid ; the latter compound can, however, as was shown somewhat later, be readily prepared synthetically from carbon dioxide and benzol, and we can therefore look upon it as carbonic acid, CO(OH)2, in which one hydroxyl has been replaced by phenyl, or as a compound of phenyl with carboxyl. The latter supposition corresponds to that of Berzelius, according to which, benzoic acid is oxalic acid copulated with phenyl, oxalic acid being dicarboxyl. Many varieties of benzoin contain cinnamic acid 2 in addition to benzoic acid and frequently only the former.3 Both these acids occur, either free or in the form of ethereal salts, together with other aromatic compounds, in Tolu balsam (p. 1), Peru balsam (concerning which Lehmann had already stated in his Dissertation de balsamo peruviano (1709), that on decomposition it yields flowers resembling flowers of benzoin), Mecca balsam (BalsamodendronOpobalsamum et gileadcnsis}, myrrh (B. Myrrhaf 1 Ann. Ghent. Pharm. iii. 249. 2 Kolbe and Lautemann, ibid. cxix. 136 ; Fliickiger, Pharmacographia. 3 Aschoff,. Jahresb. 1861, 400. OCCURRENCE OF BENZOIC ACID. 153 liquid sty rax, acaroid resin (Xanthorrheo hast Uis), dragon's blood and other resins. Benzoic acid has also been found in the per- fume known as hilan-hilan or ilang-ilang, which is prepared from the flowers of Unona odoratissima} as well as in plums (Prunus domestica chlorocarpap and the cranberry.3 It also occurs in vanilla, the fruit of the clove-tree, the seeds of the spindle-tree {Euonymus europaeus) and the root of the sweet flag (Acorus calamus), &c. The coumarin which occurs in Holcus odoratus, Anthoxanthicm odoratum (sweet-scented vernal grass), and woodruff was at one time mistaken for benzoic acid. In the year 1776, Rouelle stated that the urine of the cow and the camel contains a salt similar to flowers of benzoin, and Scheele, in 1785, obtained a substance, the properties of which agreed with those of benzoic acid, by extracting with alcohol the solid residue left on the evaporation of urine and treating the "soapy extract" with nitric acid. Fourcroy and Vauque- lin found, in 1797, that the urine of graminivora contains benzoic acid, but Liebig, in 1829, showed that this substance is a new nitrogenous acid, which he named hippuric acid, and which splits up when the urine is allowed to stand, yielding benzoic acid. According to some observers, however, benzoic acid frequently occurs along with hippuric acid in the urine, and it has also been found in a gland in the beaver,4 and in the kidneys of the ox.5 It is probable that in all these cases the acid is formed by the decomposition of hippuric acid. It has also been observed as a decomposition product of various alkaloids, such as atropine, cotoine, &c., and is formed in small quantity by the oxidation of albuminoids. It may be obtained in large quantities by the oxidation of those aromatic compounds which possess a side chain containing carbon (Part III. p. 12). It also occurs in coal-tar.6 The various synthetical methods by which it has been pro- duced have already been given (Part III. p. 30). 2°95 It was formerly prepared exclusively from gum benzoin, and the acid used in medicine is still obtained from it by sublima- tion ; it always contains a small amount of an ethereal oil, which 1 Gal, Ber. Deutsch. Chern. Ges. vi. 824. 2 Ducheek, Gmelin's Org. Chern, n. 332. 3 Loew, Journ. Prakt. Chern. [2] xix. 312. 4 Wohler, Ann. Chern. Pharm. Ixvii. 360. 5 Seligsohn, Chern. Centralbl. 1861, 241. 6 Schulze, Ber. Deutsch. Chern. Ges. xviii. 615. 154 AROMATIC COMPOUNDS. gives it its peculiar smell.1 In order to obtain it in this way, the coarsely powdered resin is heated to about 170° in a flat iron vessel; this is covered with filter-paper and fitted with a conical cap of strong paper, in which the acid collects.2 Accord- ing to Wohler, the gum benzoin is dissolved in an equal volume of absolute alcohol and fuming hydrochloric acid added to the hot solution until the resin commences to separate out; it is then distilled, water being added at intervals, and the distillate, which contains ethyl benzoate, warmed with caustic potash and then heated to boiling and saturated with hydrochloric acid. Benzoic acid separates out on cooling and is found to possess precisely the same smell as the sublimed acid.3 In order to extract the acid from the resin by Scheele's method, it is well mixed with an equal weight of slaked lime, repeatedly boiled out with water, the filtrate evaporated to one-sixth of its original bulk, treated with bleaching-powder solution, and then boiled with hydrochloric acid until all the chlorine has been removed. The acid separates out on cooling and is re-crystallized from hot water.4 It is prepared from the urine of cows or horses by allowing it to stand for several days, clarifying with milk of lime, evaporating the liquid to one-fourth of its bulk and precipitating the benzoic acid with hydrochloric acid. Since the evaporation produces a very unpleasant smell, it is better to precipitate the excess of lime by carbonic acid and add ferric chloride, to precipitate ferric benzoate, which is then decomposed by hydrochloric acid. The acid thus obtained is purified by being redissolved in milk of lime with the addition of a little bleaching-powder solution, separated by hydrochloric acid and re-crystallized from hot water. The final product (acidum lenzoicum ex urina) still smells of urine, and is not employed for pharmaceutical purposes. The smell may, however, be disguised by the addition of some of the sublimed acid. About two kilos, of acid are obtained from 1,000 kilos, of urine.5 P. and E. Depouilly have proposed to obtain benzoic acid from phthalic acid,6 which is obtained by the oxidation of 1 Jacobsen found in it methyl benzoate, benzyl benzoate, vanillin, guiacol, catechol and other aromatic compounds {Per. Deutsch. Chcm. Ges. xvii. Ref. 354). 2 Mohr, Ann. Chem. Pharm. xxix. 117 ; Lowe, Journ. Prakt. Chem. cviii. 257. 3 Ann. Chem. Pharm. xlix. 245. 4 Stenhouse. 5 Hofmann, Ber. Entw. Chem. Ind. ii. 431. 6 Jahresb. Chem. 1865, 328. PREPARATION OF BENZOIC ACID. 155 naphthalene and is now manufactured on the large scale. When its calcium salt is heated to 330°-350° with slaked lime in absence of air, calcium benzoate and calcium carbonate are formed : 2C6H4(CO2)2Ca + Ca(OH)2 = (C6H5.CO2)2Ca + 2CO3Ca. According to the method of Laurent and Castelhaz,1 acid ammonium phthalate is converted into phthalimide by heating, and this is then distilled with lime, benzonitril being formed : C=NH / \o + Ca(OH)2 = C6H5CN + CaCO3 + H2O. \ / CO The benzonjtril is then converted into benzoic acid by boiling with caustic soda solution. Benzoic acid is now generally prepared from toluene ; this may be simply oxidized by boiling with dilute nitric acid, but it is more advantageous to first convert it into benzyl chloride,2 and then boil 100 parts of this with 300 parts of nitric acid of sp. gr. 1'313 and 200 parts of water for about ten hours in an apparatus connected with an inverted condenser, until the smell of benzyl chloride and benzaldehyde has disappeared, and the liquid solidifies on cooling to a crystalline mass, no oily drops being formed.3 This method, according to A. von Rad, is not adapted for the preparation of the acid on the large scale; it can, however, be readily obtained by heating benzotrichloride or benzenyl chloride with water under pressure :4 C6H5.CC13 + 2H.,0 = C6H5.CO9H + 3HC1. Since it is difficult to prepare pure benzenyl chloride, the acid obtained always contains chlorine substitution products, which adhere to it very obstinately. Espenschied proposes to boil benzenyl chloride with milk of lime or caustic soda and whitening, and then to proceed as in the preparation of benzaldehyde from benzal chloride (p. 136). 1 Jahresb. Chem. 1868, 459. 2 Grimaux and Lauth, Bull. Soc. Chim. vii. 100. 3 Lunge and Petri, Ber. Deutsch. Chem, Ges. x. 1275. 4 Dingier's Polyt. Journ. ccxxxi. 538. 156 AROMATIC COMPOUNDS. Jacobsen obtains benzoic acid, together with acetyl chloride, by heating benzenyl chloride with glacial acetic acid and some zinc chloride: CJL.CCL + 2CH3.CO.OH = CJL.CO.OH + 2CH3.COC1 + HC1. v O o o v u o In order to avoid the evolution of hydrochloric acid, which carries off acetyl chloride with it, half of the acetic acid is replaced by zinc acetate. Benzoic acid can also be prepared without the formation of acetyl chloride, by heating benzenyl chloride with a little acetic acid and zinc acetate, and gradually adding the amount of water necessary for the formation of the acid.1 Since benzaldehyde is now manufactured, it can readily be employed as a source of benzoic acid. 2096 Properties.-It crystallizes in lustrous, flat, monoclinic plates oi' needles ; by the gradual evaporation of its solution it is obtained in larger tablets, which however are always thin, while when Guichard allowed a mixture of benzoin resin and carbon disulphide to stand for a long time, tolerably large crystals were formed, which had exactly the appearance of crystals of gypsum.2 Benzoic acid has a sharp acid taste and produces a peculiar irritation in the throat; it melts at 121'4°, and boils at 249° (Kopp), but volatilizes at 100°, and sublimes rapidly at 140°. It also volatilizes with steam, one gramme passing over with two litres of water (Nolting). Its vapour has an aromatic, pene- trating odour, produces coughing and attacks the eyes violently, more mildly when it is mixed with steam. The specific gravity of its vapour is, according to Mitscherlich, 4'27; according to C. and V. Meyer, who determined it in diphenylamine vapour, it is 4'24,3 the calculated number being 4'229. 1,000 parts of water dissolve :4 at 0 10 20 30 40 50 60 70 80 90 100° 170 2-10 2'90 410 5-55 7'75 11 55 1775 2715 4075 5875 parts of the acid. 100 parts of absolute ether at 15° dissolve 3135 parts; 100 parts of 40 per cent, alcohol, 41'62 parts; and 100 parts of 1 Ber. Deutsch. Chem. Ges. xiii. 2013. 2 Ibid. vi. 453 3 Ibid. xi. 2258. 4 Bourgoin, Ann. Chim. Phys. [5] xv. 168. SALYLIC ACID. 157 absolute alcohol, 4G'G8 parts of benzoic acid;1 boiling alcohol dissolves about twice this quantity. It also readily dissolves in chloroform, carbon disulphide, volatile and fatty oils and con- centrated sulphuric acid. It is characteristic of benzoic acid that certain impurities, even when they are present in extremely small quantities, alter its physical properties to a very considerable extent; so largely in fact, that the impure acid has been mistaken for an isomeride. Thus, E. Kopp, by the oxidation of gum benzoin with dilute nitric acid, obtained the amorphous parabenzoic acid as a white powder, which melts at 113°; it is converted into ordinary benzoic acid by distillation.2 Another so-called isomeric acid was named salylic acid by Lautemann and Kolbe, because they had obtained it from salicylic acid, C6H4(OH)COOH.3 The latter was converted into a chlorine compound by phosphorus pentachloride and this was decomposed by water into hydro- chloric acid and chlorosalylic acid or orthochlorobenzoic acid, C6H4C1.CO.,H. Salylic acid was obtained from this by the action of water and sodium amalgam. This compound crystal- lizes from hot water in indistinct needles or small plates, which, on drying, form an odourless sandy powder, while the soft, light plates of benzoic acid have a faint but distinct aromatic odour. When its aqueous solution is boiled, however, the characteristic smell becomes perceptible. It melts at a lower temperature than benzoic acid, from which it also differs in fusing when heated with a quantity of water insufficient to dissolve it, and in the fact that its hot, saturated solution becomes milky on cooling and then again clear, crystalline flocks being deposited. Its salts also differ from the benzoates in crystalline form and in solubility. Kekule confirmed these results,4 and Griess obtained a substance which he found to be identical with salylic acid, by decomposing azo-amidobenzoic acid suspended in boiling alcohol with nitrogen trioxide.5 Kolbe and Lautemann put forward the suggestion that the isomerism of these acids was due to a difference be- tween their radicals,6 but Cannizzaro showed that on distillation with caustic baryta they both yield the same substance, viz., benzene.7 The two acids were then assumed to be physical isomerides, 1 Bourgoin ; Bull. Soc. Chim. xxix. 242. 2 Compt. Bend. Chim. 1849, 154. 3 Ann. Chern. Pharm. cxv. 187. 4 Ibid, cxvii. 158. 8 Ibid, cxvii. 34. 6 Ibid. cxv. 169. 7 Ibid. Suppl. i. 247. 158 AROMATIC COMPOUNDS. until Reichenbach and Beilstein showed that salylic acid is nothing but a more or less impure benzoic acid.1 If the acid ob- tained from salicylic acid be subjected to distillation with steam, a perfectly pure benzoic acid passes over which possesses the correct melting-point and all the characteristic properties. Kolbe has confirmed this result, and finds that his salylic acid contains a small quantity of a yellow, resinous substance, which is not volatile in steam. When some of this is added to a hot, satu- rated solution of pure benzoic acid, the liquid on cooling deposits crystals of salylic acid. The admixed substance can be destroyed by the addition of potassium permanganate to the hot solution.2 The salylic acid obtained from azo-amidobenzoic acid con- tains a little nitrobenzoic acid, as does the benzoic acid which is prepared by the oxidation of toluene with dilute nitric acid.3 When this acid is distilled, a trace of the nitro-compound vola- tilizes with it and prevents it from crystallizing well, while when a little of the nitro-compound is added to a hot saturated solution of pure benzoic acid, it becomes milky on cooling and deposits flocks, which are much more soluble than the pure acid and melt at a lower temperature. Pure benzoic acid cannot be prepared from this either by sublimation or re-crystallization, but the impurity can readily be removed by dissolving in concentrated ammonia, saturating with sulphuretted hydrogen, heating to boil- ing, and then evaporating off the ammonium sulphide on the water-bath. Hydrochloric acid now precipitates pure benzoic acid, while amidobenzoic acid remains in solution (Reichenbach and Beilstein). An admixture of cinnamic acid, which melts at 133'3°, also lowers the melting-point of benzoic acid considerably,4 so that a mixture of equal parts of the two acids melts at 84'3°, an excess of either acid raising the melting-point.5 Benzoic acid is employed in the manufacture of colouring matters and in medicine. It has antiseptic properties, but exerts a more feeble action than salicylic acid.6 The observation that cranberries withstand fermentation and putrefaction better than most other fruits, gave the clue to the discovery of benzoic acid in them. 1 Ann. Chem. Pharm. cxxxi. 309. 2 Journ. Prakt. Chem. [2] xii. 151. 8 Fittig, Ann. Chem. Pharm. cxx. 214. 4 Kolbe and Lautermann, Ann. Chem. Pharm. cxix. 136. 5 Kaehler, Ber. Deutsch. Chem. Ges. ii. 515. 6 Kolbe and v. Meyer, Journ. Prakt. Chem. [2] xxii. 133, 178. DECOMPOSITIONS OF BENZOIC ACID. 159 2097 When benzoic acid is distilled with slaked lime or caustic baryta, it is decomposed into benzene and carbon dioxide (Mitscherlich). It also undergoes this decomposition when heated with caustic soda,1 and when its vapour is passed over heated pumice stone2 or iron.3 Some diphenyl is always formed in this way, and at a very high temperature the acid is decomposed with separation of graphite and formation of carbonic oxide, carbon dioxide, hydrogen and diphenyl, C12H10.4 When its vapour is passed over heated zinc-dust, it is reduced to benz- aldehyde.5 Sodium amalgam reduces its boiling solution with formation of benzaldehyde, benzyl alcohol, a crystalline com- pound, C14H14O2, and benzoleic acid, C7H10O2,° which is further described below. On heating with concentrated hydriodic acid to 275°-280°, it is first reduced to toluene, but heptane and hexane are formed on further heating the latter being derived from the benzene, which is formed by the decomposition of the acid.7 It is not attacked by chromic acid solution ; ozone converts it in alkaline solution into carbon dioxide and water.8 It is con- verted in the animal organism into hippuric acid and appears in this form in the urine ;9 a portion is simultaneously oxidized to succinic acid, which is also formed when an aqueous solution of benzoic acid is treated with lead dioxide and sulphuric acid.10 On oxidation with manganese dioxide and sulphuric acid, Carius obtained carbon dioxide, formic acid, and some phthalic acid,11 while Oudemans also detected a small quantity of the isomeric terephthalic acid.12 When the solution of its calcium salt is electrolyzed, the acid is not decomposed in a similar manner to the fatty acids, but the nascent oxygen exerts an oxidizing action, with formation of carbon dioxide, carbonic oxide, and some acetylene.13 Benzoleic acid, or Hydrobenzoic acid, C7H10O2, is formed when sodium amalgam is allowed to act on a boiling solution of benzoic 1 Barth and Schreder, Ber. Deutsch. Chem. Ces. xii. 2555. 2 Barreswill and Boudault, Journ. Pharm. Chim. n. 265. 3 F. d'Arcet, Journ. Prakt. Chem. xiii. 427. 4 Schulz, Ann. Chem. Pharm. clxxiv. 202. 5 Baeyer, ibid. cxl. 295. 6 Kolbe, ibid, cxviii. 122 ; Herrmann, ibid, cxxxii. 75. 7 Berthelot, Jahresb. Chem. 1867, 364. 8 Gorup-Besanez, Ann. Chem. Pharm. cxxv. 207. 9 Wohler, Berzelius' Lehrb. Ed. 4, iv. 376 ; see also hippuric acid. 10 Meissner and Shepard, Jahresb. Chem. 1866, 397. 11 Ann. Chem. Pharm. cxlviii. 72. 12 Zeitschr. Chem. 1869, 84. 13 Berthelot, Bull. Soc. Chim. [2] ix. 103 ; Bourgoin, ibid. 431. 160 AROMATIC COMPOUNDS. acid, hydrochloric acid being added at intervals benzyl alcohol and a crystalline substance, C14H14O2,1 are simultaneously formed. Otto obtained the same acid from hydrobenzuric acid,2 and, together with other compounds, by the action of sodium amalgam on benzoyl glycollic acid (p. 165).3 It is an oily liquid, which has a repulsive odour resembling that of valerianic acid, and is rapidly altered in the air. When hydrochloric acid is passed into its alcoholic solution, the ethyl ether is formed and resembles ethyl valerate, but has a sharper smell; in the air the smell becomes exceedingly disagreeable, and, since it clings persistently to the clothes, increases the difficulty of the investigation of the compound and the free acid. SALTS AND ETHERS OF BENZOIC ACID. 2098 Benzoic acid decomposes carbonates in aqueous solution, but when a current of carbon dioxide is passed into an alcoholic solution of potassium benzoate, potassium carbonate separates out. Most of the benzoates are soluble in water and alcohol; some, such as the sodium and barium salts, are withdrawn from their solutions by animal charcoal, and calcium benzoate is decomposed by it, so that free benzoic acid can be extracted by ether.4 Potassium benzoate, C7H5KO2 + 3H2O, crystallizes with diffi- culty in small plates which effloresce in the air and are very soluble in water and alcohol. Sodium, benzoate, C7H5NaO2 + H2O, crystallizes in needles, which also effloresce in the air and are very soluble in alcohol. It is used in medicine. Ammonium, benzoate, C7H5(NH4)O2, separates from a solution containing an excess of ammonia in deliquescent rhombic crystals; it is also employed medicinally. Large crystals of the less soluble acid salt, C7H5(NH4)O2 + C7H6O2, are obtained by the gradual evaporation of its aqueous solution (Berzelius). Calcium benzoate, (C7H5O2)2Ca + 2H2O, crystallizes from hot water in long lustrous needles which form fascicular aggregates ; they dissolve in 29 parts of cold water and effloresce in the air. 1 Herrmann, Ann. Chem. Pharm. cxxxii. 75, 2 Ibid, cxxxiv. 115. 3 Ibid. cxlv. 350. 4 L. Liebermann, Ber. Wien. Akad. 1877, 331. ETHYL BENZOATE. 161 Barium benzoate, (C7H5O2)2Ba 4- 3H2O, is only slightly soluble in water, and crystallizes in needles or hard, lustrous tablets. Lead benzoate, (C7H5O2)2Pb 4- H2O, is obtained by the addi- tion of lead acetate to a solution of the potassium salt; it is a crystalline, difficultly soluble precipitate. Copper benzoate, (C7H5O2)2Cu 4- 2H2O, crystallizes in light blue plates united in spherical masses or in needles. Silver benzoate, C7H5AgO2, is a curdy precipitate, which is soluble in alcohol and crystallizes from hot water in flat needles. Mercuric benzoate, (C7H5O2)2Hg 4- H2O, crystallizes from hot water in needles which are almost insoluble in cold water. Ferric benzoate, (C7H5O2)6Fe2. Berzelius obtained this salt in yellow needles by dissolving ferric hydroxide in aqueous benzoic acid; it is decomposed by water and alcohol with formation of an insoluble basic salt. Sestini was unable to prepare this compound.1 When a soluble benzoate is added to neutral ferric chloride, a reddish yellow precipitate is thrown down, which is decomposed by washing with water into a soluble acid salt and an insoluble basic salt. If the iron solution has been previously treated with sufficient ammonia to produce a dark red coloura- tion, soluble benzoates give a voluminous, hydrated, flesh-coloured precipitate of (C7H5O2)3Fe2(OH)3, which is not altered by cold water. These reactions are employed for the separation of iron from manganese and for the detection of benzoic acid and its separa- tion from other acids. Methyl benzoate, C6H5.CO.OCH3, is best prepared by passing hydrochloric acid into a solution of benzoic acid in methyl alcohol, distilling, and then precipitating the ether with water.2 It is a liquid which possesses an aromatic odour and boils at 199°. Bthyl benzoate was prepared by Scheele as long ago as 1785, by the distillation of a mixture of alcohol, benzoic acid and hydro- chloric acid. It is not formed when an alcoholic solution of the acid is allowed to stand in the cold, but the ether is gradually formed if a little hydrochloric acid be added, or if the liquid be heated to 100°. In order to prepare it, the method adopted for the preparation of the methyl ether may be followed, or the alcoholic solution of the acid may be heated with sulphuric or 1 Zeitschr. Chern, iv. 668. 2 Carius, Ann. Chem. Pharm. ex. 210. 162 AROMATIC COMPOUNDS. hydrochloric acid. It is a liquid which has a pleasant aromatic smell, and boils at 213°. Ethyl benzoate is also readily formed by the action of benzoyl chloride on alcohol (Wohler and Liebig), which is more readily attacked by it than water. The presence of alcohol even in very dilute aqueous solution can therefore be detected by warming it with a little benzoyl chloride and removing the excess of this by caustic soda; even when only 0 1 per cent, of alcohol is present, the characteristic smell of ethyl benzoate can be distinctly recognized (Berthelot; see Part I. p. 318). Boiling-point. Isopropyl benzoate,1 C6H5.CO.OCH(CH3)2 . 218° Propyl benzoate,2 C6H5.CO.OC3H7 . . . 229'5° Butyl benzoate,3 C6H5.CO.OC4H9 . . . 247'3° Amyl benzoate,4 C6H5.CO.OC5Hn . . . 260'7° Octyl benzoate,5 CGH5.CO.OC8H17 . . . 306° Allyl benzoate,6 C6HvCO.OC3H5 . . . 228° v ' O 3 0 3 Benzyl benzoate, C6H5.CO.OCH2.C6H5. Cannizzaro obtained this compound by the distillation of benzyl alcohol with benzoyl chloride or benzoic anhydride.7 It boils at 323°-324°, has the sp. gr. of 1'1227 at 19°, and solidifies in a freezing mixture to lustrous, compact crystals, melting at 21 °.8 As already mentioned, it is also formed by the action of sodium methylate on benz- aldehyde (p. 93) and is a constituent of Peru balsam9 and of Tolu balsam,10 but has not yet been obtained from them in the pure state. If the ether be submitted to distillation while it still contains water, it is decomposed with formation of benzoic acid, benzyl alcohol and toluene. Ethylene benzoate, (C6H5.CO2)2C2H4. Wurtz prepared this compound by the action of silver benzoate on ethylene bromide ;11 it crystallizes from ether in lustrous, rhombic prisms,12 melting at 67°. 1 Silva, Ann. Chem. Pharm. cliv. 255. 2 Linnemann, ibid. clxi. 28. 3 Ibid. clxi. 92. 4 Rieckher, ibid. Ixiv. 336. 5 Zincke, ibid. clii. 7. 6 Hofmann and Cahours, ibid. c. 358 ; cii. 297. 7 Ibid. xc. 254. 8 L Claisen, private communication. 9 Kraut, Ann. Chem. Pharm. clii. 129 ; Ber. Deutsch. Chem. Ges. ii. 18. 10 Busse, ibid. ix. 830. 11 Jahresb. Chem. 1859, 676. 12 Bodewig, ibid. 1879, 676. PHENYL BENZOATE. 163 The following propylene ethers have been prepared in a similar manner : Melting-point. Propylene benzoate:1 C6H5.CO.OCH2 , viscous fluid - CgH5.CO.OCH.CH3 Trimethylene benzoate:2 CgH-.CO.OCHA^TT i+1 kqo C6H5.CO.OCH2/CH2' scaly crystals • • • • 53 Dimethylmethylene benzoate:3 \CH3' monoc^nlc pyramids . 69-71° The last of these yields acetone on saponification. Benzidcne benzoate, (C6H5.CO.O)2CH.C6H5, is formed by the action of benzidene chloride on silver benzoate, and crystallizes in transparent prisms, melting at 50°.4 The benzoic ethers of glycerol, erythrol, mannitol, the glucoses, etc., have also been prepared.5 2099 Phenyl benzoate, C6H5.CO.OC6H5. Ettling and Sten- house observed a compound among the distillation products of copper benzoate which they named benzoic oxide, C7H5O,6 while Gerhardt considered it to be the radical benzoyl.7 List and Limpricht then found that it has the formula C13H10O2, and is decomposed by alcoholic potash into benzoic and carbolic acids, so that it is a compound of benzoic acid and phenyl oxide.8 They further showed that it is identical with the benzophenide, which Laurent and Gerhardt obtained by the action of benzoyl chloride on phenol.9 Phenyl benzoate is readily formed when benzoyl chloride is heated with phenol until hydrochloric acid ceases to be evolved, and also when phenol is heated with benzamide.10 It is readily soluble in alcohol and ether, and crystallizes from a mixture of these in lustrous, monoclinic prisms,11 which melt at 71° and sublime at a higher temperature. Its smell resembles that of 1 Friedel and Crafts, Zeitschr. Chem. 1871, 489 ; Mayer, Ann. Chern. Pharm. cxxxiii. 255. 2 Reboul, Ann. Chim. Phys. [5] xiv. 500. 3 Oppenheim, Ann. Chem. Pharm. Suppl. vi. 360 ; Friedel and Ladenburg, ibid. cxlv. 195. 4 Engelhardt, Jahresber. Chem. 1857, 471 ; Wicke, Ann. Chem. Pharm. cii. 356. 5 Berthelot, ibid. Ixxxviii. 311 ; xcii. 302 ; Jahresber. 1855, 677 ; 1856, 660 ; 1860, 509. 6 Ann. Chem. Pharm. liii. 77, 94. 7 Ibid. Ixxxvii. 162. 8 Ibid. xc. 190. 9 Ibid. Ixxv. 75 ; Ixxxvii. 161. 10 Guareschi, ibid. clxxi. 141. 11 Bodewig, Jahresber. 1879, 675. 164 AROMATIC COMPOUNDS. the geranium. Chlorine and bromine effect substitution in the phenyl and not in the benzoyl group. Trinitrophenyl benzoate, C6H5.CO.OC6H2(NO2)3, Gerhardt and Laurent prepared this compound by heating picric acid with benzoyl chloride. It is insoluble in water, slightly soluble in cold, more readily in hot alcohol, and crystallizes in lustrous, golden-yellow, rhombic plates, which detonate when heated.1 Cresyl benzoate, C6H5.CO.OC6H4.CH3. The three isomeric ethers have been prepared by Engelhardt and Latschinow.2 Melting- Boiling- Orthocresyl benzoate, oily liquid . . point. point. Metacresyl benzoate, crystals . . . . 38° 290°-300° Paracresyl benzoate, six-sided tablets . 70° - Phenylene benzoate, (C6H5.CO.O)2C6H4, is also known in three isomeric forms, which are obtained from the dihydroxybenzenes. Melting-point. Dibenzoylcatechol, rhombic crystals3 ... - Dibenzoylresorcinol, scales4 117° Dibenzoylquinol, silky needles 5 199° Tribenzoylphloroglucinol, (C6H5.CO.O)3C6H3, forms small, lus- trous scales, which are almost insoluble in alcohol.6 The benzoic ether of pyrogallol, according to Malin, does not crystallize, but its dimethyl ether, and two homologues of the latter which occur in the higher boiling portions of beech-wood-tar oil, give very characteristic ethereal salts of benzoyl.7 Since these three ethereal salts, which are very similar in their properties, can be separated by means of their different solubilities, they will be mentioned here : Melting-point. Benzoylpyrogallol dimethyl ether: CJLW.OCJL(OQHA, 118° v O v O X Z Benzoylmethylpyrogallol dimethyl ether: C6H6.CO.OC6H2(CH3)(OCH3)2 .... 118°-119° Benzoylpropylpyrogallol dimethyl ether : C6H5.CO.OC6H2(C3H7)(OCH3)2 ... 91° 1 Ann. Chem. Pharm. Ixxv. 77. 2 Zeitschr. Chcm. 1869, 615 ; see also Kekule, Bcr. Deutsch. Chcm. Ges. vii. 1007 ; Guareschi, Ann. Chem. Pharm. clxxi. 142. 3 Nachbauer, ibid. cvii. 243. 4 Malin, ibid, cxxxviii. 76 ; Dbbner, Bcr. Deutsch. Chem. Ges. xi. 2269. 5 Dobner and Wolff, ibid. xii. 661. 6 Hlasiwetz and Pfaundler, Ann. Chem. Pharm. cxix. 199. 7 Hofmann, Ber. Deutsch. Chem. Ges. xii. 1373. BENZOYL-LACTIC ACID. 165 Quinonoxime benzoate, C6H4O(NO.CO.C6H5), is formed when benzoyl chloride is added to sodium quinonoximate (Part III. p. 172), which is covered with pure ether or chloroform. It crystallizes in yellowish needles, which melt with decomposition at 168°-175°, and give Liebermann's reaction with phenol and sulphuric acid.1 2100 Benzoyl-glycoIlic acid, C6H5.CO.OCH.2.CO,H, has hitherto only been prepared from hippuric acid or benzoylamido-acetic acid, by treating it with nitrous acid,2 or by passing chlorine into its dilute alkaline solution.3 It crystallizes from hot water in thin tablets or large prisms, and decomposes on boiling with water, or more rapidly with dilute mineral acids, into benzoic and glycollic acids. Otto, by the action of sodium amalgam on its aqueous solution, obtained benzoleic acid (p. 159) and two other isomeric acids which have not yet been thoroughly investigated. Ethyl benzoyl-glycollate, C6H5.CO.OCH.2.CO2C2II5. Andrejew obtained this substance by heating ethyl chloracetate with sodium benzoate; it is a liquid which boils at 277°-279°, and decomposes into alcohol, benzoic acid and glycollic acid, when boiled with alcoholic potash.4 Benzoyl-lactic acid, CH3(CH.O.CO.C6H5)CO.,H, is formed when lactic acid is heated to 180° with benzoic acid,5 as well as by the action of benzoyl chloride on lactic acid or calcium lac- tate.6 It separates from a hot, aqueous solution in tablets or needles, melting at 112°. On boiling with water or a dilute acid it is decomposed into lactic and benzoic acids. Ethyl benzoyl-lactate, C10H9O4.C2H5, is formed by the action of benzoyl chloride on ethyl lactate, and by heating silver benzoyl- lactate with ethyl iodide. It is a liquid which boils at 288°, and is decomposed into lactic acid and ethyl benzoate by heating with water to 150°. Benzoyl compounds of tartaric and racemic acids have also been prepared.7 1 Walker, Ber. Deutsch. Chcm. Ges. xvii. 399. Strecker, Ann. Chcm. Pharm. Ixviii. 54 ; Strecker and Sokolow, ibid. Ixxx. 17. 3 Gossmann, ibid. xeix. 181. 4 Ibid, cxxxiii. 284. 5 Strecker and Sokolow, loc. cit. ; Strecker, ibid. xci. 359. 6 Wislicenus, ibid, cxxxiii. 264. 7 Dessaignes, Jahresber. 1857, 307 ; Perkin, Ann. Chcm. Pharm. Suppl. v. 274 ; Anschutz and Pictet, Ber. Deutsch. Chcm. Ges. xiii. 1178. 166 AROMATIC COMPOUNDS. OXIDES OF BENZOYL. 2ioi Benzoyl oxide, or Benzoic anhydride, (C6H5.CO)2O, was discovered by Gerhardt in 1853. He first prepared it by heating benzoyl chloride with sodium benzoate, and named it anhydrous benzoic acid or benzoyl benzoate ;1 he subsequently found that it can be more simply obtained by the action of phosphorus oxy- chloride on an excess of sodium benzoate, a portion of this being simultaneously converted into benzoyl chloride.2 Phos- phorus pentachloride 3 or chloride of sulphur4 may be employed instead of phosphorus oxychloride. It is also formed in small quantity when benzoic acid is heated with phosphorus pent- oxide,5 and in larger amount by heating benzoyl chloride to 140°-150° with barium oxide,6 or to 160°-220° with benzoic acid.7 Gerhardt had already found that it may easily be ob- tained by the action of benzoyl chloride on potassium oxalate : KoC2O. + 2C6H5.COC1 = (C6H5.CO)2O + 2KC1 + CO + CO2, m 4 U X O / it L Anhydrous oxalic acid may be advantageously employed instead of the potassium salt; the reaction takes place at 50°-60° ac- companied by a regular evolution of gas, and 80 per cent, of the theoretical yield is obtained, together with some unattacked chloride and benzoic acid.8 Finally, it can also be obtained by heating benzenyl trichloride with silver oxide, or with concen- trated sulphuric acid containing 4'6 per cent, of water :9 C6H5.COx 2C6H5.CC13 + 3Ho0 >0 + 6HC1. c6h6.co/ Anhydrous oxalic acid may be substituted for the sulphuric acid :10 2C6H5.CC13 + 3C2O4H2 = (C6H5.CO)2O + 3HC1 + 3CO + 3CO2. 1 Ann. Chern. Pharm. Ixxxii. 127. 2 Ibid. Ixxxvii. 73. 3 Wunder, Journ. Prakt. Chem. Ixi. 280. 4 Heintz, Pogg. Ann. xcviii. 458. 6 Etard and Gal, Bull. Soc. Chim. xxv. 342. 6 Gal, Ann. Chem. Pharm. cxxviii. 127. 7 Anschiitz, Ber. Deutsch. Chem. Ges. x. 1882. 8 Ibid. 9 Janssen, ibid. xii. 1495, Patent 30 Oct. 1878 (No. 6689). 10 Anschutz, ibid, ccxxvi. 20. BENZOIC ANHYDRIDE. 167 Benzoic anhydride crystallizes in rhombic prisms (Bodewig), melting at 42e; it boils at 360° (Anschutz), and is tolerably soluble in alcohol and ether. It is scarcely attacked by cold water, but when heated with water it gradually forms benzoic acid, and with alcohol, ethyl benzoate. When heated in a stream of hydrochloric acid, it decomposes into benzoyl chloride and benzoic acid.1 Chlorine and bromine exert a similar action, substitution products being simultaneously formed. Benzoyl acetyl oxide, CH3.CO.O.CO.CcH5. Gerhardt prepared this compound by the action of acetyl chloride on sodium benzoate, and named it anhydrous benzoic acetic acid.2 It is a heavy, oily liquid, which has a pleasant smell like that of Spanish wine, is gradually attacked by water, more rapidly by alkalis, and is completely decomposed by distillation into benzoic anhydride and acetic anhydride.3 It is also formed when ben- zoic acid is heated to 220° with acetic anhydride.4 According to Loir, an anhydride is obtained by the action of benzoyl chloride on sodium acetate, which differs from that prepared by Gerhardt's method in yielding acetyl chloride when heated with hydro- chloric acid to 130°, while Gerhardt's compound is first attacked at 160°, with formation of benzoyl chloride.5 This, however, is inaccurate, and Greene has shown that the compound, in what- ever way it is prepared, behaves in exactly the same manner towards hydrochloric acid, the same products-acetyl chloride and acetic acid, benzoyl chloride and benzoic acid-being formed as in the case of the anhydrides themselves.6 A number of other mixed anhydrides are now known, which, like the foregoing, decompose on distillation into benzoic an- hydride and another simple anhydride,7 and must therefore be looked upon rather as mixtures than definite compounds. Benzoyl dioxide, ox Benzoyl peroxide, (C6H5.CO)2O2, was prepared by Brodie by the action of benzoyl chloride on barium dioxide ; it separates from ether or carbon disulphide in rhombic crystals, which melt at 103-50, detonate when more strongly heated, and when boiled with caustic potash are converted into benzoic acid with evolution of oxygen.8 1 Mosling, Ann. Chern. Pharm. cxviii. 303. 2 Ibid. Ixxxvii. 81. 3 Anschutz, ibid, ccxxvi. 12. 4 Ibid. 5 Ann. Chim. Phys. [5] xviii. 132. 6 Bull. Soc. Chim. xxxiii. 424. 7 Gerhardt, Ann. Chern. Pharm. Ixxxii. 127 ; Ixxxvii. 163 ; Chiozza, ibid. Ixxxiv. 106 ; Ixxxvi. 259 ; Chiozza and Malerba, ibid. xci. 102. 8 Ann. Chern. Pharm. cviii. 80 ; Lippmann, Monatsh. Chern, v. 560. 168 AROMATIC COMPOUNDS. HALOGEN COMPOUNDS OF BENZOYL. 2102 Benzoyl chloride, C6H5.COC1, was discovered in 1832 by Wohler and Liebig; they obtained it by the action of dry chlorine on pure oil of bitter almonds, and describe it as a trans- parent liquid the vapour of which violently attacks the eyes, and has a peculiar, very penetrating odour resembling the sharp smell of horse-radish.1 Cahours then prepared it by the action of phosphorus pentachloride on benzoic acid,2 Gerhardt by that of phosphorus oxychloride on sodium benzoate,3 and Bechamp by heating benzoic acid with phosphorus trichloride.4 Friedel sub- sequently observed its formation when hydrochloric acid is passed over a mixture of benzoic acid and phosphorus pentoxide heated to 200°,5 this being an important general method for the forma- tion of acid chlorides. Harnitz-Harnitzky stated that it might also be obtained by exposing a mixture of carbonyl chloride and benzene vapour to the action of sunlight,6 but Berthelot was unable to confirm this statement,7 although it is undoubtedly formed in this way when aluminium chloride is present, (p. 30).8 It also may be obtained by heating benzenyl trichloride with anhydrous oxalic acid: CcH5.CC13 + C,O.H2 = CJL.COC1 + 2HC1+CO2+CO. Benzoic anhydride is also formed in this reaction. In order to prepare the chloride, a mixture of two molecules of phosphorus trichloride with three molecules of benzoic acid is heated until hydrochloric acid ceases to be evolved, water is then added and the oily liquid which separates purified by distillation; accord- ing to another method, benzoic acid is heated with one molecule of phosphorus pentachloride, and the mixture distilled, the dis- tillate consisting at first of phosphorus oxychloride mixed with a little benzoyl chloride, followed by pure benzoyl chloride. The phosphorus oxychloride is then employed for a further prepara- tion by being heated with sodium benzoate, an excess of which 1 Monatsh. Chem. iii. 262. 2 Ibid. lx. 251. 3 Ibid. Ixxxvii. 63. 4 Journ. Prakt. Chem. Ixviii. 489. 5 Bull. Soc. Chim. ii. 80. 6 Ann. Chem. Pharm. cxxxii. 72. 7 Bull. Soc. Chim. xiii. 9, 392. 8 Ador, Crafts and Friedel, Ber. Deutsch. Chem. Ges. x. 1854. BENZOYL CHLORIDE. 169 must be avoided, as, otherwise, some benzoic anhydride would be formed. The crude chloride, prepared by either of these methods, is freed from adhering chlorides of phosphorus by treatment with cold water, and is then purified by distillation. Properties. - It is a strongly refractive liquid, which fumes in the air, has a sp. gr. of 1'2324 at 0° and solidifies when cooled in crystals melting at --1°. It boils at 198°; its vapour attacks the lungs and mucous membrane very violently. It is gradually decomposed by cold, more rapidly by hot water, with formation of benzoic and hydrochloric acids; it is rapidly converted into ethyl benzoate by alcohol, and the other alcohols produce a similar reaction. Since it undergoes double decomposition so readily, it is largely employed for the preparation of other benzoyl derivatives; many examples of this have been already given and others will be met with in the sequel. It is also employed to a considerable extent in the same way as acetyl chloride, for determining the number of hydroxyl groups con- tained in carbon compounds. Gerhardt and Laurent found that the compound C6H5.CHO 4- C6H5.COC1 is formed by the action of chlorine on benzaldehyde ; this substance is insoluble in cold alcohol, crystallizes in lustrous plates, is decomposed by distillation into its components, and by boiling with water into hydrochloric acid and benzaldehydo- benzoic acid;1 the latter compound corresponds to the ethidene- chloracetin (Part II. p. 72) obtained in a similar manner from acetaldehyde, and is, therefore, benzidene benzochlorohydrin : /Cl c6h6.ch< x0C0.C6H5. O D Benzoyl bromide, C6H5.COBr. Wohler and Liebig, by the action of bromine on oil of bitter almonds, obtained a crystalline compound which they looked upon as benzoyl bromide. This substance was subsequently shown by Claisen to be benzidene- benzobromohydrin ; this chemist then prepared benzoyl bromide by heating three molecules of benzoic acid with two molecules of phosphorus tribromide; it is a transparent, colourless liquid, has an odour resembling that of the chloride, but fumes more strongly in the air, is more readily attacked by water and boils at 218°- 219°.2 It combines with benzaldehyde to form the com- 1 Jahresber. Chem. 1850, 489. 2 Bar. Deutsch. Chem. Ges. xiv. 2473. 170 AROMATIC COMPOUNDS. pound just mentioned, benzidene benzobromohydrin or bromo- benzylbenzoate, ^Hg.CHBr.O.CO.CgHg, which crystallizes from boiling petroleum ether in short prisms or thick tablets, which melt at 69°-70° and are decomposed by distillation into their components. Paterno obtained the same compound, together with ethyl bromide, benzyl bromide and benzaldehyde, by the action of bromine on ethyl benzoate, but considered it to be benzoyl bromide.1 Benzoyl iodide, C6H5.COI. Wohler and Liebig obtained this compound by heating the chloride with potassium iodide as a colourless, foliated, crystalline mass, which readily melts, a little iodine being set free, has a penetrating odour and is decom- posed by water and alcohol. It has not been analyzed. Benzoyl fluoride, C0H5.COF. Borodin prepared this compound by the distillation of the chloride with acid potassium fluoride, F2HK, in a platinum retort. It is a heavy, oily and colourless liquid, which boils at 161'5°, has a still more powerful odour than the chloride, and is decomposed by water into benzoic and hydrofluoric acids.2 SULPHUR COMPOUNDS OF BENZOYL. 2103 Thiobenzoic acid, C6H5.CO.SH. Cloez obtained salts of this acid by the action of benzoyl chloride on potassium sulphide and double decomposition of the potassium thiobenzoate thus formed with other metallic salts.3 The compound which he separated from the potassium salt and looked upon as thio- benzoic acid proved to be benzoyl disulphide. The free acid is obtained by decomposing the potassium salt with dilute hydro- chloric acid; a yellow liquid, smelling of sulphur compounds, separates out and soon solidifies to a crystalline mass, melting at 24°, which decomposes on distillation but is volatile with steam. It is readily oxidized to benzoyl disulphide, this action taking place even when its alcoholic solution is evaporated in the air.4 Potassium thiobenzoate, C6H5.CO.SK, crystallizes from alcohol in yellowish tablets or prisms, and is very readily soluble in water. The silver salt is a yellowish white, and the lead salt a 1 Gaz. Chim. Itai. i. 586. 3 Ami Chcm. Pharm. cxxvi. 60. 3 Ibid. cxv. 27. 4 Engelhardt, Latschinow and Malyschew, Zeitschr. Chcm. 1868, 353. THIOBENZOIC ACID. 171 white precipitate; both of these readily blacken and decompose. Copper sulphate gives a greenish yellow precipitate which after some time becomes red and then contains benzoyl disulphide : ferric chloride yields a violet-brown precipitate which becomes yellow on warming. Ethyl thiobenzoate, C6H5.CO.SC2H5, is formed by the action of benzoyl chloride on lead mercaptide, Pb(SC2H5)2,1 and of ethyl iodide on silver thiobenzoate. It is a yellow, repulsive smell- ing liquid, which boils at 242°-243° and is decomposed by saponification with caustic potash into benzoic acid and ethyl hydrosulphide, while potassium hydrosulphide yields the latter compound and thiobenzoic acid. It is oxidized by potassium permanganate and dilute sulphuric acid to benzoic acid and ethylsulphonic acid.2 Phenyl thiobenzoate, C6H5.CO.SC6H5, is obtained by heating benzoyl chloride with phenyl hydrosulphide.3 It crystallizes from alcohol or benzene in lon<r lustrous needles, meltinaf at 56°. Benzyl thiobenzoate, C6H5.CO.S.CH2.C6H5, is readily soluble in alcohol and benzene, and forms lustrous, asymmetric crystals, melting at 39'5°. Its behaviour towards reagents resembles that of the ethyl ether.4 Benzoyl sulphide, or Thiobenzoic anhydride, (C6H5.CO)2S, was obtained by Wohler and Liebig in an impure condition by the distillation of benzoyl chloride with lead sulphide. It is pre- pared by treating potassium thiobenzoate with benzoyl chloride (Engelhardt, Latschinow and Malyschew). It crystallizes from ether in large prisms, which melt at 48° and decompose on distillation. When heated with ammonia it yields benzamide and thiobenzoic acid ; the latter is also formed by the action of potassium hydrosulphide, while benzoic acid is obtained in addition when caustic potash is employed. Benzoyl disulphide, (C6H5.CO)2S2, is formed by the oxidation of thiobenzoic acid and by heating benzoic anhydride in a stream of dry sulphuretted hydrogen.5 It is prepared by adding a solution of iodine in potassium iodide to an aqueous solution of potassium thiobenzoate. It is only slightly soluble in alcohol and ether, and crystallizes from hot carbon disulphide in large 1 Tiitschew, Jahresber. Chern. 1863, 483. 2 Beckmann, Journ. Prakt. Chern. [2] xvii. 463. s Schiller and Otto, Ber. Deutsch. Chem. Ges. ix. 1635. 4 Liiders and Otto, ibid. xiii. 1285. 5 Mosling, Ann. Chem. Pharm. cxviii. 304. 172 AROMATIC COMPOUNDS. prisms or six-sided tablets which melt at 128°, and become coloured violet-red at a slightly higher temperature. Dithiobenzoic acid, C6H5.CS.SH, is formed in small quantity when benzoyl chloride is heated with lead sulphide. It is more easily obtained by treating benzenyl trichloride with a very dilute alcoholic solution of potassium sulphide:1 CJL.CCL + 2K2S = CJL.CS.SK + 3KC1. V D O Zt V U Acetate of lead first precipitates lead sulphide from the solution obtained, and then the lead salt of the acid, which is finally decomposed by hydrochloric acid. It is a dark violet-red, heavy, oily liquid, which gives a carmine-coloured solution in ether, and rapidly forms a resinous mass when exposed to the air. Lead dithiobenzoate, (C6TT5.CS2)2Pb, is a vermilion-coloured precipitate, which crystallizes from boiling xylene in fine, red needles. Benzoyl thiocyanate, C6H5.CO.S.CN, is obtained by the action of benzoyl chloride on lead thiocyanate in the cold. It is a yellow liquid which has a penetrating odour resembling that of bitter almonds, and can only be distilled without decomposition in a vacuum.2 It combines with ammonia, forming benzoyl thiocarbamide, (C6H5.CO)HN.CS.NH2, and is, therefore, probably benzoyl mustard oil, CcH5.CO.N.CS. NITROGEN COMPOUNDS OF BENZOYL. 2104 Benzamide, C6H5.CO.NH2. Wohler and Liebig obtained this compound by the action of benzoyl chloride on ammonia, and Fehling subsequently prepared it by boiling hippuric acid with water and lead dioxide.3 Dumas found that it is also formed when ethyl benzoate is brought into contact with aqueous ammonia, the reaction taking place more rapidly when the mixture is heated to 100.°4 It is also formed by a similar reaction from benzoic anhydride.5 1 Engelhardt and Latschinow, Zeitschr. Chcm. 1868, 456 ; see also Fleischer, Ann. Chcm. Pharm. cxl. 240. 2 Miquel, Ann. Chim. Phys. [5] xi. 300. 3 Fehling, Ann. Chcm. Pharm. xxv. 48 ; Schwarz, ibid. Ixxv. 195. 4 Compt. Pend. xxv. 734. 5 Scheitz, Marsh and Geuther, Zeitschr. Chcm. 1868, 302. BENZAMIDE. 173 In order to prepare it, benzoyl chloride is triturated with solid ammonium chloride, the product washed with cold water, and crystallized from hot water or alcohol;1 or equal molecules of benzoic acid and ammonium thiocyanate may be heated to 150° -170°, carbonyl sulphide, ammonia, sulphuretted hydrogen and carbon dioxide being evolved, while benzamide remains behind and only requires to be freed from benzoic acid by washing with ammonia.2 It is slightly soluble in cold, more readily in hot water, especially when it contains ammonia, and dissolves readily in both alcohol and ether. When its aqueous solution is rapidly cooled, it separates out in small plates, while on more gradual cooling it is deposited in fine needles, which gradually change into larger crystals. The latter are also obtained by allowing a mixture of ethyl benzoate and ammonia to stand, or by gradually cooling the fused compound ; they consist of well-formed, mono- clinic tablets,3 melting at 128°.4 It boils at 286°-290°, a small portion being decomposed into water and benzonitril, C6H5.CN. The latter compound may be readily prepared from it by simply heating with a dehydrating agent; Wohler and Liebig had observed that when heated with caustic baryta, an oily, aromatic liquid having a sweet taste, was formed, and that it might also be obtained by passing the vapour of the compound through a red-hot tube. This substance was afterwards recognized as the benzonitril discovered by Fehling in the year 1844.5 Benzamide is not decomposed by heating with dilute alkalis; when it is boiled with strong caustic potash or hydrochloric acid it decomposes into ammonia and benzoic acid, and on boiling with phenol, ammonia and phenyl benzoate are formed.6 When heated with ethyl nitrite to 120°, the following reaction takes place;7 c6h5.co.nh2+no.oc2h5=c6h5.co.oc2h5+h2o+n2. If its solution in aqueous ether be treated with sodium amalgam and kept neutral by the addition of hydrochloric acid, benzyl alcohol is formed.8 1 Gerhardt, Chim. Org. iii. 268. 2 Kekule, Ber. Deutsch. Chem. Ges. vi. 113. 3 Klein, Ann. Chem. Pharm. clxvi. 184. 4 Schiff and Tassinari, Ber. Deutsch. Chem. Ges. x. 1785. 5 Wohler, Ann. Chem. Pharm. cxcii. 362, 6 Guareschi, ibid, clxxi. 141. 7 Meyer and Stuber, ibid. clxv. 186. 8 Guareschi, Ber. Deutsch. Chem. Ges. vii. 1462. 174 AROMATIC COMPOUNDS. It is converted into aniline by the action of bromine in alkaline solution, just as acetamide in similar circumstances yields methylamine (p. 113). Benzamide hydrochloride, C6H5.CO.NH2.C1H, is formed by dissolving benzamide in hot concentrated hydrochloric acid,1 or by passing hydrochloric acid into a mixture of equal mole- cules of benzonitril and water.2 It crystallizes in long prisms, which rapidly lose acid in the air. Mercuric benzamide, (C6H5.CO.NH)2Hg, is prepared by dis- solving mercuric oxide in a hot, aqueous solution of benzamide;3 on cooling the liquid, a semi-solid crystalline mass is formed, which is obtained by re-crystallization from alcohol in plates melting at 222°-224°.4 2105 Benzoyl derivatives of amines and amido-bases are formed by the action of benzoyl chloride on the latter: Dimethylbenzamide :5 Melting- point. Boiling- point. C6H5.CO.N(CH3)2, large crystals . 41°-42° 255°-257° Diethylbenzamide :6 C6H5.CO.N(C2H5)2, liquid . . . 280°-282° Ethylenebenzamide:7 (C6H5.CO.NH)2C2H4, needles . . 249° - Benzanilide, or Benzoylaniline, C6H5.N(CO.C6H5)H. Gerhardt obtained this compound by the action of benzoyl chloride on aniline,8 and Leuckart found that it is also formed when phenyl isocyanate is treated with benzene in presence of aluminium chloride.9 It is insoluble in water and crystallizes from alcohol in nacreous plates, which melt at 1GO°-161°,10 and volatilize without decomposition at a higher temperature. It is not attacked by boiling aqueous acids or alkalis, but yields aniline and benzoic acid when it is fused with caustic potash. Concen- 1 Dessaignes, Ann. Chern. Pharm. Ixxxii. 234. 2 Pinner and Klein, Ber. Deutsch. Chem. Ges. x. 1896 ; xi. 10. 3 Dessaignes, loc. cit. 4 Oppenheim, Ber. Deutsch. Chem. Ges. vi. 1392, 5 Hallmann, ibid. ix. 846. 6 Ibid. 1 Hofmann, ibid. v. 246 ; Kraut and Schwartz, Ann. Chem. Pharm. ccxxiii. 43. 8 Ibid. lx. 311 ; Ixxxvii. 164. 9 Ber. Deutsch. Chem. Ges. xviii. 873. 10 Wallach and Hofmann, Ann. Chem. Pharm. clxxxiv. 80. BENZANILIDE. 175 trated nitric acid converts it into the three isomeric benzoyl- nitranilines, C6H4(NO2)N(CO.C6H5)H : Melting-point. Ortho,1 long, light yellow needles . . 94°-95° Meta,2 plates 155'5° Para,3 small prisms 199° The two latter are converted by reduction into the corre- sponding benzoyldiamidobenzenes, C6H4(NH2)N(CO.C6H5)H, while the ortho-compound forms phenylenebenzamidine, C6H5.Cy \C6H4, a substance which will be subsequently N Z described. Melting point. Benzoylmethylaniline :5 C6H5N(CO.C6H5)CH3, small monoclinic crystals 59° Benzoyldiphenylamine:6 (C6H5)2N(CO.C6H5), rhombic needles . . . 176°-177° Benzovlorthotoluide:7 (C6H4.CH3)N(CO.C6H5)H, needles .... 142°-143° Benzoylparatoluide :8 (C6H4.CH3)N(CO.C6H5)H, long needles . . 155° 2106 Methylenedibenzamidc, CH2(NH.CO.CcH5)2. By heating hippuric acid, C9H9NO3 (p. 181), with lead peroxide and dilute sulphuric or nitric acid, Schwarz obtained a crystalline substance, which he extracted from the product by alcohol. This dissolves in concentrated sulphuric or nitric acid without change, and is only attacked by oxidizing agents with difficulty and he therefore called it hipparaffin (par it os, parum affinis). Its analysis led to the formula C16H16N2O2.9 Maier, who also prepared it, assigned to it the composition C8H7NO, and found that another crystal- line substance, hipparin, C8H9NO2, is obtained in its prepa,ra- tion.10 Schwarz subsequently resumed his investigation, and showed that the latter compound is ethyl hippurate ; by heating 1 Mears, Ber. Deutsch. Chem. Ges. ix. 774 ; Schwarz, ibid. x. 1709. 2 Bell, ibid. vii. 498 ; Hiitmer, ibid. x. 1716. 3 Stover, ibid. vii. 463 and 1314. 4 C. A. Bell, ibid. vii. 497 and 1504 ; Sennewald, ibid. ix. 775 ; Stover, loo. cit. 5 Hepp, ibid. x. 237. 6 Hofmann, Ann. Chem. Pharm. cxxxii. 166 ; Bernthsen, ibid, cxcii. 13. 7 Bruckner, ibid. ccv. 230. 8 Kelbe, Ber. Deutsch. Chem. Ges. viii. 875. 9 Ann. Chem. Pharm. Ixxv. 201. 10 Ibid, cxxvii. 162. 176 AROMATIC COMPOUNDS. hipparaffin with water to 170°-180°, he obtained benzamide and a substance which gave the reactions of an aldehyde, and which he identified, in spite of some differences in its properties, with the ethylenedibenzimide which he had obtained by the action of phosphorus pentoxide on a mixture of aldehyde and benzamide.1 Kraut and Schwarz, however, found that it is actually identical with methylenedibenzamide,2 which had been obtained by Hepp and Spiess by the action of concentrated sulphuric acid on a mixture of methylal, CH2(OCH3)2, and benzonitril.3 It is insoluble in cold, slightly soluble in hot water, and crystallizes from alcohol in bushy aggregates of needles, melting at 223°. It is decomposed on boiling with 32 per cent, sulphuric acid, with formation of ammonia, benzoic acid and formaldehyde. Ethidenedibenzamide, CH3.CH(NH.COC6H5)2. Limpricht obtained this compound by the action of benzoyl chloride on aldehyde-ammonia,4 and Nencki by that of benzamide on alde- hyde containing a few drops of hydrochloric acid.5 It is prepared by adding first paraldehyde and then benzonitril to well-cooled sulphuric acid, and diluting with water after some hours (Hepp and Spiess). It crystallizes from alcohol in long, white needles, which melt at 204° and sublime without decomposition. It is decomposed by fuming nitric acid into aldehyde and benzamide. Dibenzamide, N(CO.C6H5)2H, was prepared by Baumert and Landolt, together with benzamide, by the action of benzoyl chloride on potassium amide.6 Barth and Senhofer found that it is readily formed when benzonitril is treated with a mixture of sulphuric acid and phosphorus pentoxide; the solution is allowed to stand for some hours and then diluted with water, which slowly precipitates the compound in crystals : 7 2C.H5.CN + 2H9O = (C6H5.CO)2NH + NH3. It is also formed when lophine, which is obtained by the dry distillation of hydrobenzamide, is treated with a solution of chromium trioxide in acetic acid, it being thus smoothly converted into benzamide and dibenzamide : 8 C2,H16N2+20 + H2O = C7H5O.NH9 + (C7H5O)2NH. 1 Wien. Akad. Ber. Ixxvii. 762. 2 Ann. Chem. Pharm. ccxxiii. 40. 3 Ber. Deutsch. Chem. Ges. ix. 1424. 4 Ann. Chem. Pharm. xeix. 119. 5 Ber. Deutsch. Chem. Ges. vii. 159. 6 Ann. Chem. Pharm. exi. 5. 7 Ber. Detdsch. Chem. Ges. ix. 975, 1073. 8 E. Fischer and Proschke, ibid. xiii. 708. THIOBENZAMIDE. 177 It separates from dilute alcohol in long, thin needles, which melt at 148°, and decompose at a higher temperature, giving off an odour of benzaldehyde. It is almost insoluble in cold and scarcely soluble in hot water, but dissolves readily in ether, chloroform and benzene, from the last two of which it separates in rhombic crystals. On boiling with caustic potash it decom- poses into benzoic acid and ammonia. It dissolves readily in dilute caustic soda, the solution when concentrated depositing small glittering needles of the com- pound (C7H5O)2NNa; it also occurs in short, distorted prisms containing half a molecule of water, which is lost at 120°. The solution gives a precipitate with silver nitrate, consisting of (C7H5O)2NAg, and is also precipitated by other metallic salts. Schafer, by heating benzamide in a stream of hydrochloric acid, obtained a compound which he considered to be dibenz- amide hydrate (C7H5O)2NH + 2H2O; it crystallizes in small plates, which melt at 99°, and do not lose water at a higher temperature, but decompose into benzoic acid and benz- amide.1 This substance is evidently acid ammonium benzoate, C7H5(NHJO2 + C7HgO22 Dibenzanilide, (CcH5.CO)?NC6H5. Gerhardt and Chiozza ob- tained this compound by the action of benzoyl chloride on benz- anilide. It crystallizes from alcohol in fine, lustrous needles, which melt at 137° and sublime when more strongly heated.3 By heating benzoic acid with phenyl mustard oil, Losanitsch obtained a crystalline, foliaceous mass of a dibenzanilide, melt- ing at 155°.4 Steiner, on the other hand, who prepared it by Gerhardt's method and also by heating tribenzhydroxylamine, N(OC7H5O)(C7H5O)2, found the melting-point of both prepara- tions to be 1610.5 Thiobenzamide, C6H5.CS.NH2, was prepared by Cahours by passing sulphuretted hydrogen into an alcoholic, ammoniacal solution of benzonitril: C6H5.CN + SH, = C6H5.CS.NH2. It crystallizes from hot water in long, yellow needles, melting at 117°; when heated with water and mercuric oxide, it is recon- verted into benzonitril, while it is reduced to benzylamine by 1 Ann. Chern. Pharm. clxix. 111. 2 Beilstein, Org. Chern. 1101. 3 Ann. Chem. Pharm. Ixxxvii. 302. 4 Ber. Deutsch. Chem. Ges. vi. 176. B Ann. Chem. Pharm. clxxviii. 235. 178 AROMATIC COMPOUNDS. zinc and hydrochloric acid.1 Iodine acts upon its alcoholic solution in the following manner : 2C7H7SN + 2I2 = C14H10SN2 + 4HI + S. The compound obtained in this way crystallizes from hot alcohol in lustrous, snow-white needles, which melt at 90° and distil without decomposition at a higher temperature. It is a very stable compound, and is not altered by being heated to 150° with hydrochloric acid, sulphuric acid or tolerably concentrated nitric acid. On boiling with caustic potash it is gradually con- verted into benzoic acid, ammonia being evolved. Zinc and hydrochloric acid reduce it in alcoholic solution to the base, C14H14N2,2 which is isomeric with ethenyldiphenylamidine (Part III. p. 217) ; benzene and benzonitril are simultaneously formed.3 It crystallizes in small plates, melting at 71°, is a monacid base and forms an alkaline solution in alcohol. Thiobenzanilide, or Phenylthiobenzamide, C6H5.CS.N(C6H5)II, is formed when benzanilide is heated with phosphorus penta- sulphide,4 and crystallizes from alcohol in thin, yellow tablets or prisms, melting at 97'5°-98'5°. Diphenylthiobcnzamide, C6H5.CS.N(C6H5)2, is formed when asymmetric diphenylbenzenylamidine is heated to 130°-140° with carbon disulphide : C6H5.C(NH)N(C6H5)2 + CS2 = C6H5.CS.N(C6H5)2 + CNSH. It crystallizes from solution in benzene or alcohol in dark yellow, asymmetric prisms, melting at 150°-151°.5 2107 Benzoyl urea, C6H5.CO.NH.CO.NH2. Zinin obtained this compound by heating urea to 150°-155° with benzoyl chloride; 6 the anhydride may be substituted for the chloride in this reaction.7 The monobenzoyl urea crystallizes from alcohol in long, thin plates, which melt atabout 200°and decompose into benz- amide and cyanuric acid when carefully heated beyond this point. Symmetric ethylbenzoyl urea,8 CO j COC H ' neec^es- Asymmetric ethyl- ) oc ( NH2 rhombohedra benzoyl urea,9 J ] N(C2H5)CO.C6H5' rhombonedra- 1 Hofmann, Bar. Deutsch. Chcm. Ges. i. 102. 2 Ibid. ii. 644. 3 Wanstrat, ibid. vi. 335. 4 Bernthsen, ibid. xi. 503. 5 Bernthsen, Ann. Chern. Pharm. cxcii. 37. 6 Ibid. xcii. 404. 7 Geuther, Sclieitz and Marsh, Zeitschr. Chern. 1868, 305. 8 Leuckart, Journ. Prakt. Chern. [2] xxi. 33 ; Miquel, Ann. Chim. Phys. [5] xi. 318. 9 Lossner, Journ. Prakt. Chem. [2] x. 251. DIBENZOYL UREA. 179 Dibenzoyl urea, CO(NH.CO.C6H5)2, is formed, together with hydrochloric acid, carbon dioxide, ammonium chloride, benzoic acid and benzonitril, when benzamide is heated to 160°-170° with carbonyl chloride,1 and also from guanidine and benzoic anhydride at 100°:2 nh2 nh.co.c6h5 I - /CO.C6H5 I C=NH. + O< =NH3+CO I " xco.c6H5 I nh2 nh.co.c6h5. It crystallizes from alcohol in needles melting at 210°, and is decomposed by boiling with strong acids into carbon dioxide, ammonia and benzoic acid, while dilute caustic potash solution converts it into benzamide and carbon dioxide. Benzoyl thio-urea, C6H5.CO.NH.CS.NH2, is formed when thio- urea is heated with benzoyl chloride 3 and by the action of dilute ammonia on benzoyl thiocyanate.4 It crystallizes from dilute alcohol in small prisms which have a very bitter taste and melt at 171°. Miquel has prepared the following compounds by the action of benzoyl thiocyanate on amines and amido-bases : Melting-point. Ethylbenzoyl thio-urea : J NH.CO.C6H5 p . n<?.0 CS ( NH CH6 ' nne Prisms- • • • 134 Phenylbenzoyl thio-urea: J NH.CO.CJEL . ,, 11QO 14 0° ^(NHCR6 5, *on» neec"es- • • • 148-149 Benzylbenzoyl thio-urea : ™ J NH.CO.CLH, n . ..,0 vu I CH C II ' small prisms. • • Paratolylbenzoyl thio-urea: ™ J NH.CO.C6H5 . GSlNHC6H4CH3'lon8Pn^ • ■ ' 160 Benzoylphenylhydrazine, C6H5.NH -NH(CO.C6H5). In order to obtain this compound, two molecules of phenylhydrazine are dissolved in five times their amount of ether, the solution cooled 1 Schmidt, Journ. Prakt. Chern. [2] v. 58. 2 Creath, Ber. Deutsch. Chem. Ges. vii. 1739. 3 Pike, ibid. vi. 755. 4 Miquel, Ann. Chim. Phys. [5] xi. 313. 180 AROMATIC COMPOUNDS. and then treated with a molecule of benzoyl chloride. The mixture is filtered, the hydrochloride of phenylhydrazine removed by boiling with water, and the residual benzoylphenylhydrazine crystallized from boiling alcohol. It forms fine prisms, melting at 168°, dissolves readily in warm, dilute caustic potash, and is precipitated from this solution by acids. Yellow mercuric oxide converts it in alcoholic solution into benzoylazobenzene, C6H5.Nzz:N.CO.C6H5, a dark red, oily liquid, which is reconverted into the original compound by reduction.1 Mcthylbenzoylphenylhydrazine, C6H5N (CH3).N Hf CO.C6H5). This compound is prepared by adding sodium and then methyl iodide to a solution of benzoylhydrazine in wood-spirit; the mixture becomes warm, and after standing for several hours is heated to 100° for a short time in order to complete the reaction. Methylbenzoylphenylhydrazine crystallizes from hot alcohol in fine, white needles, melting at 153°. When its solution in hydrochloric acid is treated with a trace of nitrous acid, an intense red colouration is produced, which becomes dark brown with large quantities. When methylbenzoylphenylhydrazine is heated with concentrated hydrochloric acid, it is decomposed into benzoic acid and methylphenylhydrazine; the latter compound may be detected by conversion into its characteristic tetrazone, which melts at 137°, and not, as was formerly stated, at 133° (Part III. p. 270).2 Dibenzoylphenylhydrazine, C6H5N(CO.C6H5)N(CO.C6H5)H, is obtained by the action of benzoyl chloride on benzoylphenyl- hydrazine or on potassium phenylhydrazinesulphonate. It crystal- lizes from hot alcohol in fine prisms, which melt at 177°-178°, and dissolve slowly in aqueous alkalis. If the alkaline solution be treated with the calculated quantity of sodium and heated, the sodium dissolves and on cooling, a salt, C20H15N2O2Na, separates out in lustrous plates, which are readily soluble in water. Methyldibcnzoylphenylhydrazinc, C(.H5N(CO.C6H5) N(CO.CcH5) CH3, is formed when the solution of the sodium salt is heated with methyl iodide. It forms well-developed, soft, white crystals which melt at 145°, and are insoluble in water or alkalis, but dissolve readily in hot alcohol. On distillation with caustic potash it is decomposed into benzoic acid and hydrazophcnyl- methyl, C6H5.NH - NH(CH3). This substance is a colourless oil which rapidly oxidizes in the air, but forms stable salts. When 1 E. Fischer, Ann. Chern. Pharm. cxc. 125. 2 Tafel, Ber. Deutsch. Chern. Ges. xviii. 1739. HIPPURIC ACID. 181 mercuric oxide is added to its ethereal solution, it is converted into azophenylmethyl, CJI5N-NCH3, a yellow oil, which pos- sesses a characteristic smell, volatilizes with ether vapour, more rapidly with steam, and distils at about 150° with considerable decomposition (Tafel). Benzoyldiphenylhydrazinc^Q^EL^^ - NH(CO.C6H5), was ob- tained by Fischer from benzoyl chloride and diphenylhydrazine; it is slightly soluble in alcohol and ether, and crystallizes from hot acetone in fine needles, melting at 1920.1 HIPPURIC ACID, C9H9NO3. 2ioS Rouelle, in the year 1776, as has been already mentioned under benzoic acid, found a salt in the urine of the cow and the camel, which is analogous to flowers of benzoin, and Fourcroy and Vauquelin observed a peculiai' acid, which they took to be benzoic acid, in the urine of graminivora. Liebig, however, showed in 1829, that this acid contains nitrogen and differs completely from benzoic acid in its properties ; he says, ' Since I have more especially investigated the acid obtained from the urine of the horse, I will designate it, for want of a more suit- able term, as " hippuric acid " (ittttos, horse, ovpov, urine). On heating it decomposes with formation of various products, among them being benzoic acid, the experience of Fourcroy and Vauquelin, " that benzoic acid can be obtained from horse's urine, but is not contained in it as such " being thus confirmed.'2 Liebig first obtained for it the formula C10H10NO3, which he subsequently corrected,3 his later analyses being confirmed by those of Dumas and Peligot.4 Pelouze then found that on boiling hippuric acid with manganese dioxide and very dilute sulphuric acid, benzoic acid, ammonia and carbon dioxide are formed,5 while Fehling obtained benzamide and carbon dioxide by boiling it with water and lead dioxide.6 Dessaignes then made the important observation that it is decomposed into benzoic acid and glycocoll (amido-acetic acid) when treated with boiling alkalis or acids,7 and he, with the majority of chemists, 1 Ann. Chem. Pharm. cxc. 78. 3 Pogg. Ann. xvii. 389. 3 Ibid, xxxii. 573. 4 Ann. Chem. Pharm. xiv. 69. 6 Ibid. xxvi. 60. 6 Ibid, xxviii. 40. 7 Journ. Prakt. Chem. xxxvii. 244. 182 AROMATIC COMPOUNDS. assumed that hippuric acid is a copulated compound of benzoic acid and glycocoll, although, as was pointed out by Berzelius, this assumption does not in the least account for the action of lead dioxide. An important advance towards the determination of the consti- tution of hippuric acid was made by Strecker,1 who found that it is converted by the action of nitrous acid into benzoylglycoIlic acid (p. 165), which was more closely investigated by him in conjunc- tion with Sokolow. This compound assumes the elements of water and splits up into benzoic acid and glycollic acid, and must, therefore, be considered as a copulated compound of these, its amido-derivative being hippuric acid.2 Dessaignes now endeavoured to prepare hippuric acid arti- ficially by heating glycocoll with benzoyl chloride, but without success; he attributed his failure to the evolution of hydrochloric acid and therefore substituted the zinc salt of glycocoll, zinc amido-acetate, and found that hippuric acid is slowly formed when benzoyl chloride is allowed to act upon this in the cold, more rapidly at 120°.3 He also obtained it subsequently by heat- ing benzoic acid with glycocoll to 160°,4 and Jazukowitzsch pre- pared it by heating chloracetic acid with benzamide;5 the yield was, however, small, owing to the formation of free hydrochloric acid. These syntheses finally proved that hippuric acid is benzoylamido-acetic acid : CH2.NH2 CH2.NH.CO.CfiH5 XX X v O + HO.CO.C6H5 = I +H.0. COOH CO.OH CH2C1 CH2.NH,CO.C6H5 | " + NH2CO.C6H5= I " + HC1. CO.OH CO.OH It is also formed, together with other products which will be subsequently mentioned, from benzoyl chloride and silver amido- acetate,6 and very readily when glycocoll is heated with benzoic anhydride 7 or when benzoyl chloride is added to a concentrated aqueous solution of the former.8 Liebig detected it in human urine, about 1 grm. being excreted 1 Ann. Chern. Pharm. Ixviii. 54. 2 Ibid. Ixxx. 17. 3 Ibid. Ixxxvii. 325. 4 Jahresber. Chern. 1857, 367. 5 Zeitschr. Chern. 1867, 466. 6 Journ. Prakt. Chem. [2] xxiv. 239 ; xxvi. 145. 7 Curtins, Ber. Deutsch. Chem. Ges. xvii. 1662. 8 Baum, Zeitschr. Physiolog. Chem. ix. 465. HIPPURIC ACID. 183 per diem.1 According to Weismann it is formed more freely during a vegetable than an animal diet,2 and according to Ducheck it is not invariably present.3 Pettenkofer found 1'3 per cent, of it in the urine of a girl suffering from St. Vitus's dance, whose diet consisted exclusively of apples and bread; the amount decreased as soon as meat was again taken.4 Lehmann observed its occurrence during diabetes, even before Liebig had detected its presence in normal human urine,5 and since that time it has frequently been observed in large quantities in diabetic urine. It also occurs largely in the acid urine of persons suffering from fevers of every kind.6 Liebig,7 and Dumas 8 assumed that fresh horses' urine contains hippuric acid which is converted into benzoic acid on standing. The former subsequently stated that horses and bullocks excrete hippuric acid when they are allowed to remain idle for some time, and benzoic acid when they are working to the full extent of their powers,9 and Erdmann and Marchand found10 that the urine of carriage horses usually contains the former and that of plough horses the latter. Lehmann, however, who investigated the urine of a large number of horses, both sound and diseased, well and badly fed, found only hippuric acid without exception, provided that the urine had not been allowed to stand too long in the air. After standing for a considerable time, and especially after the formation of ammonia, only benzoic acid is present, being formed by a special ferment. When such urine was added to a sample of the fresh material, containing hippuric acid alone, the latter decomposed on evaporation and only benzoic acid could then be detected.11 Roussin found a large quantity of urea but no hippuric acid in the urine of Arab stallions, which did not work but were kept for breeding ; that of others, which were used by the Spahis for riding, contained little urea, but 0'5-1 per cent, of hippuric acid ; in one sample of urine which was passed after a long journey the amount rose to 1'4 per cent., and 0'78 per cent, was found in that of omnibus horses.12 Stiideler found about 1'5 per cent, of hippuric acid in cows' 1 Baum, Zeitschr. Physiolog. Chern, cvi. 164. 2 Jahresber. Chern. 1858, 572. 3 Gmelin, Org. Chern, v. 332. 4 Ann. Chem. Pharm. lii. 86. 8 Journ. Prakt. Chem. vi. 113. 6 Gmelin's Org. Chem. v. 334. 7 Ann. Chem. Pharm. xxx. 280. 8 Ann. Chim. Phys. Ivii. 331. 9 Ann. Chem. Pharm. xli. 272 ; Organ. Chem. in Anwendung auf Phys, und Pathol. Ixxxiv. 10 Journ. Prakt. Chem. xxvi. 491. 11 Gmelin, Organ. Chem. v. 332. 13 Compt. rend. xlii. 583. 184 AROMATIC COMPOUNDS. urine,1 and, according to Hallwachs, a cow passes more than 50 grms. of the acid during twenty-four hours.2 Kraut observed that cows which are allowed to graze give more hippuric acid than those which are stall fed,3 while only traces are formed when they are fed on spent grain from a distillery.4 In the urine of cows fed on oat-straw and wheat-straw, with the addition of some beans, 2'1-27 per cent, was found, while that of cattle fed on bean-straw and clover contained only 0'4 per cent., and when ordinary meadow hay was given, 14 per cent.5 The urine of sucking calves contains uric acid but no hippuric acid (Wohler). The latter occurs in the urine of sheep, goats, hares, rabbits, and elephants (Schwarz). Schwarz found it in very considerable quantity in the urine of a camel, the sample being very concentrated, as only four ounces were passed during the day, and Lehmann detected it in the urine of the tortoise (Testudo graeco). Pettenkofer observed its occurrence in the scurf which is formed on the skin during the rare disease known as ichthiosis,6 and J. Davy found it in butterflies, moths, and their chrysalides and excrements.7 The urine of dogs also contains a small quantity of the acid even during an exclusively meat diet or after long fasting,8 while it has never been found in the urine of pigs.9 2109 Ure was the first to make the important observation that the urine of a patient who has taken benzoic acid contains a large amount of hippuric acid.10 Wohler had previously suggested that benzoic acid is changed to hippuric acid in the organism, for he had found in the urine of a dog to which half a drachm of benzoic acid had been given an acid which he mistook for benzoic acid, but which he subsequently found to be identical with the hippuric acid discovered by Liebig.11 Under his direc- tions Keller conducted a research on the subject, taking 2 grains of benzoic acid in the evening and repeating the dose three times daily during the following days. His urine, which now possessed a strongly acid reaction, contained a considerable amount of hippuric acid, and, as Wohler says, " since benzoic acid seems 1 Ann. Chern. Pharm. Ixxvii. 17. 2 Ibid. cv. 209 3 Chern. Centralbl. 1858, 831. 4 Schwarz, Ann. Chern. Pharm. liv. 31. 8 Henneberg, Stohmann and Rautenberg, ibid, cxxiv. 201. 6 Ibid. xc. 378 7 New Edinb. Phil. Journ. xlv. 17. 8 Salkowski, Ber. Deutsch. Chern. Ges. xi. 500. 9 Boussingault, Ann. Chim. Phys. [3] xv. 97 ; von Bibra, Ann. Chcm. Pharm. liii. 98. 10 Repert. Pharm. xxvii. 642. 11 Berzelius, Lehrb. Chern. 1831, iv. 376. HIPPURIC ACID. 185 not to affect the health, large quantities of hippuric acid might readily be prepared in this manner, the only requisite being a man who would continue the manufacture for weeks.1 These observations were confirmed by Garrod,2 Schwarz and others; Marchand found 39 2 grains of hippuric acid in his urine after eating' 30 grains of benzoic acid.3 Many other compounds, which are converted into benzoic acid by oxidation, are changed into hippuric acid by their passage through the organism; such are benzaldehyde,4 cinnamic acid,5 C6H5.CH=CH.CO2H, hydrocinnamic acid or phenylpro- pionic acid,6 C6H5.C2H4.CO2H, phenylglycoIlic acid,7 C6H5.CH (OH)CO2H, quinic acid,8 C6H7(OH)4CO2H, and even toluene.9 The substitution products of benzoic acid appear in the urine as the corresponding derivatives of hippuric acid; thus phenylacetic acid, C6H5.CH2.CO2H, gives phenylaceturic acid10; salicylic acid, C6H4(OH)CO2H, is converted into salicyluric acid,11 and toluic acid, C6H4(CH3)CO2H, into toluyluric acid;12 phthalic acid, however, remains unchanged.13 It follows from this, that the monobasic aromatic acids, and hydroxy-acids, combine with glycocoll with elimination of water in their passage through the organism. After Liebig had discovered hippuric acid, he raised the ques- tion whether it must be considered as a compound of benzoic acid with an unknown compound body, or as a peculiar acid by the decomposition of which benzoic acid is formed, just as oxalic and formic acids are formed when sugar or starch is treated with nitric acid. He decided for the latter view, and says: " The first view is rendered improbable by the fact that I have been unable to prepare even the slightest trace of benzoic acid from horses' fodder, which is the source of their urine, even if this acid be contained in Anthoxanthum odoratum and Holcus odoratus. as found by Vogel, its identity being rendered doubtful by its 1 Ann. Chern. Pharm. xliii. 108. 2 Phil. Mag. xx. 501. 3 Journ. Prakt. Chem. xxxv. 309. 4 Frerichs and Wohler, Ann. Chem. Pharm. Ixviii. 336. 5 Erdmann and Marchand, Journ. Prakt. Chem. xxvi. 491. 6 E. and H. Salkowski, Ber. Deutsch. Chem. Ges. xii. 653. 7 Grabe and Schultzen, Ann. Chem. Pharm. cxlii. 349. 8 Lautemann, ibid. cxxv. 12. 9 Nauyen and Schultzen, Zeitschr. Chem. 1868, 29. 10 E. and H. Salkowski, loc. cit. 11 Bertagnini, Ann. Chem. Pharm. xcvii. 249. 12 Kraut, ibid, xcviii. 360. 13 Grabe and Schultzen, loc. cit. 186 AROMATIC COMPOUNDS. different crystalline form." These fragrant grasses were after- wards found to contain not benzoic acid but coumarin, C9H6O2, which is the anhydride of orthohydroxyphenylacrylic acid, C6H4(OH)C2H2.CO2H. After it had been proved that benzoic acid and allied sub- stances are converted into hippuric acid in the organism, it seemed probable that that occurring in the urine of graminivora would be derived from benzoic acid or other benzoyl compounds occurring in the fodder. Hallwachs, therefore, investigated the chief grasses and plants in question, but was unable to detect the slightest trace of benzoic acid or any other compound which could yield hippuric acid; he also showed that coumarin and chlorophyll, which might be looked upon as allies of the benzoyl series, pass through the organism unchanged.1 O. Loew found, however, that quinic acid, which occurs in many plants, is also present in hay, and considered it to be the source of the hippuric acid.2 Although the latter acid can be obtained from quinic acid, it passes through the organism almost unchanged, only a very small portion being converted into hippuric acid.3 The amount of hippuric acid in the urine is naturally greater when such fruits as plums and cranberries, which contain benzoic acid, have been eaten;4 but Ducheck found a much larger quantity than would correspond to the amount of benzoic acid contained in the plums. As already mentioned, hippuric acid occurs largely in the urine of diabetic patients who subsist on a meat diet, and in that of others who have passed several days without taking food, as well as in small quantity in the urine of dogs after a meat diet or long fasting. It follows from these facts with tolerable certainty that the hippuric acid, or rather the aromatic group contained in it, is derived from the albuminoids, which are known to yield benz- aldehyde and benzoic acid on oxidation, while phenylpropionic acid is formed from them by the pancreatic fermentation (E. and H. Salkowski). E. Salkowski has adduced a further proof for this in the fact that phenylaceturic acid, (CGH5.CH2.CO)NH.CH2.CO2H, which is the homologue of hippuric acid, occurs in horses' urine and 1 Ann. Chem. Pharm. cv. 207. 2 Journ. Prakt. Chern. [2] xix. 309. 3 Stadelmann, Jahresber. Chem. 1879. 982. 4 Ducheck, Gmelin's Org. Chem. v. 332 ; Thudichum, Jahresber. Chem. 1863, 656. PREPARATION OF HIPPURIC ACID. 187 can readily be split up into glycocoll and phenylacetic acid, C6H5.CH.2.CO2H. The latter acid is also formed, together with phenylpropionic acid, by the putrefraction of albumen.1 The source of the hippuric acid is therefore identical with that of the uric acid, which is especially formed in the organism of the carnivora. 2iio The acid is best prepared from the urine of cows or oxen, which often contains such a large quantity that it is preci- pitated by the addition of hydrochloric acid. If this be not the case, the urine is boiled up with milk of lime, filtered, and the filtrate neutralized with hydrochloric acid, evaporated, and then treated with an excess of hydrochloric acid.2 Putz proposes to precipitate the neutral solution with ferric chloride and decom- pose the washed precipitate with hydrochloric acid.3 The acid obtained by these methods is always discoloured, but the im- purity may be removed by dissolving it in warm chlorine water,4 or treating its aqueous solution with bleaching powder.5 It is more convenient to effect the purification by allowing 3 parts of the acid to stand in contact with 1 part of nitric acid, of sp. gr. 1'3, and filtering off the mother-liquor after twenty- four hours.6 It can also be dissolved in hot, dilute caustic soda solution and treated with potassium permanganate until yellow crystals separate out on the addition of hydrochloric acid.7 These are boiled with water and animal charcoal and then finally re-crystallized from hot water. Hippuric acid is also readily obtained when finely powdered, dry amido-acetic acid is gradually added to an excess of heated benzoic anhydride, and the mixture heated on an oil-bath until it becomes coloured red. It is then allowed to cool, dissolved in water and neutralized with caustic soda, the solution being subsequently acidified with hydrochloric acid and allowed to stand for several days. The precipitated hippuric acid is boiled with water and animal charcoal, the filtrate concentrated on the water-bath and then allowed to cool slowly. The large crystals which are formed are then washed with petroleum spirit to remove any adhering benzoic acid.8 1 Ber. Deutsch. Chem. Ges. xvii. 3010. 2 Gregory, Ann. Chem. Pharm. Ixiii. 125. 3 Jahresber. Chem. 1877, 795. 4 Dauber, Ann. Chem. Pharm. Ixxiv. 202. 5 Conrad, Journ. Prakt. Chem. [2] xv. 244. 6 Hutstein, Jahrcsb. 1854, 453. 7 Gossmann, Ann. Chem. Pharm. xcix. 374 ; Conrad, loc. cit. 8 Curtius, Ber. Deutsch. Chem. Ges. xvii. 1662. 188 AROMATIC COMPOUNDS. Properties.-It forms long, lustrous, rhombic prisms or needles (Fig. 1), which are sometimes opaque, and which dissolve in GOO parts of water at 0°; it is only slightly soluble in cold alcohol and ether, but dissolves readily in warm water and alcohol. It is in- soluble in petroleum spirit, and can be separated from benzoic acid by means of this property. It reddens litmus, but has not a sour taste, melts at 187'5° (Conrad) and decomposes at tem- peratures above 240°, with formation of hydrocyanic acid, benzoic acid, benzonitril, and a black, resinous substance.1 When it is heated with caustic potash to 260°, ammonia and benzonitril are given off, while calcium carbonate, calcium benzoate and carbon remain behind. Caustic baryta effects a similar decomposition, Fig. 1. barium cyanate being formed in addition, while when an excess of baryta is employed, benzene, ammonia and methylamine are given off and barium carbonate and benzoate formed, but no cyanide.2 It has been already mentioned that on heating with strong acids or alkalis it decomposes into benzoic acid and glycocoll; these products are also formed when it is heated to 120° with a concentrated solution of zinc chloride ; when, how- ever, it is distilled with anhydrous zinc chloride, benzonitril and carbon dioxide are formed.3 On oxidation with lead dioxide and sulphuric acid or with 1 Limpricht and Uslar, Ann. Chern. Pharm. Ixxxviii. 133. 2 Kraut, Jahresber, 1863, 348 ; Conrad, loc. cit. 3 Gossmann, Ann. Chern. Pharm. c. 69. THE HIPPURATES. 189 nitric acid, it is converted into hipparaffin or methylenedibenz- amide (p. 175): CH2.NH(C0.C6H5) 2 | " +4O = CH2(NH.CO.C6H5)2+3CO2 + 2H2O. co2h The substitution products of hippuric acid will be described among the corresponding derivatives of benzoic acid. 2i11 The. Hippurates. Hippuric acid decomposes carbonates and dissolves zinc with evolution of hydrogen. Its salts are for the most part soluble in water and crystallize well; they have been investigated by Schwarz.1 Potassium, hippurate, C9H8KNO3 + H2O, forms vermicular crusts consisting of pointed rhombic prisms; on heating it forms a vapour which possesses a smell resembling that of Satureja hortensis. It combines with hippuric acid forming the acid salt, C9H8KNO3 + C9H9NO3 + H2O, which crystallizes in quadratic tablets possessing a satin lustre. Sodium hippurate, 4C9H8NaNO3 + H2O, is a crystalline mass which readily dissolves in water and hot alcohol. Acid ammonvum, hippurate, C9H8(NH4)NO3+C9H9NO3+H2O, crystallizes in small, quadratic prisms ; the normal salt has not been prepared. Calciu/m hippurate, (C9H8NO3)2Ca 4- 3H2O, forms rhombic prisms,2 which are soluble in 18 parts of cold and 6 parts of boiling water (Liebig). Strontium, hippurate, (C9H8NO3)2Sr + 5H2O, crystallizes in fascicular aggregates, composed of four-sided prisms; it is only slightly soluble in cold water and alcohol, but dissolves readily in them when hot. Barium hippurate, (C9H8NO3)2Ba + H2O, crystallizes in crusts made up of quadratic prisms. Schwarz, in endeavouring to separate a mixture of hippuric and benzoic acids by means of their barium salts, obtained, first, barium benzoate, then barium hippurate, and, finally, from the mother-liquor, the double salt, C7H5O2.Ba.C9H8NO3+5H2O, in characteristic warty masses.3 Magnesium hippurate, (C9H8NO3)2Mg + 5H2O, forms warty crystals. Zinc hippurate, (C9H8NO3)2Zn + 5H2O, crystallizes in small 1 Ann. Chern. Pharm. liv. 33. 2 Schabus, Jahresber. Chern. 1850, 411. 3 Ann. Chern. Pharm. Ixxv. 192. 190 AROMATIC COMPOUNDS. plates, which after dehydration dissolve in 53'2 parts of water at 17'5°, and in 4 parts at 1000.1 Lead hippurate, (C9H8NO3)2Pb + 2H2O, is a curdy precipitate crystallizing from a large quantity of hot water in fine, silky needles, which often suddenly take up a molecule of water and change into lustrous, four- sided tablets. Copper hippurate, (C9H8NO3)2Cu + 3H2O, is slightly soluble in cold water, more readily in hot alcohol, and crystallizes in small, pointed, rhombic prisms of a blue colour. Silver hippurate, 2C9H8AgN03 + Hl>0, is a curdy precipitate, which crystallizes from hot water in aggregates of lustrous needles. When ferric chloride is added to a solution of a normal hippurate, a cream-coloured precipitate of ferric hippurate is thrown down, which contains more or less basic salt according to the greater or less dilution of the solution ; this fact was dis- covered by Putz, who employed the compound for the prepara- tion of hippuric acid from urine. It is almost insoluble in pure water, but dissolves in presence of free hippuric acid, an excess of ferric chloride and in alcohol. Wreden has proposed to employ this reaction for the determination of hippuric acid in urine. Henneberg, Stohmann, and Rautenberg, found that it is most convenient for this purpose to make use of a solution of ferric nitrate which has been standardized with pure hippuric acid. The urine is acidified with nitric acid, heated to boiling to remove carbon dioxide, neutralized with calcium carbonate, treated with an excess of lead nitrate, and then diluted to a known volume and filtered. An aliquot portion of the filtrate is heated and titrated with the ferric nitrate solution until a drop of the clear liquid gives a blue colouration with potassium ferrocyanide, the distinction between this and the white of the lead ferrocyanide which is formed at first, being very sharp.2 Methyl hippurate, C9H8(CH3)NO3, is obtained by the action of hydrochloric acid on a hot solution of hippuric acid in methyl alcohol.3 It is slightly soluble in cold, more readily in hot water and in alcohol, and crystallizes in long, white prisms, which melt at 80'5°, and decompose at 250° with formation of ammonia and benzonitril. Ethyl hippurate, C9H8(C2H5)NO3, is formed in a similar 1 Lowe, Jahrcsber. 1855, 536. 2 Ann. Chern. Pharm. cxxiv. 182. 3 Jaqucmin and Schlagdenhauffen, Compt. Rend. xlv. 1011 ; Conrad, Journ. Prakt. Chem. [2] xv. 247. THE HIPPURATES. 191 manner to the methyl ether,1 and also by allowing a saturated, warm alcoholic solution of hippuric acid to stand for a month in a warm place.2 It may also be readily prepared by heating ethyl amido-acetate with benzoic anhydride to 100°.3 It crystallizes from hot water in long, white, silky needles, which melt at 60'5°, have no odour, but a sharp taste resembling that of oil of turpentine, and de- compose on heating. On distillation with steam, it decomposes into alcohol and the free acid. The following ethers have also been prepared :4 Melting- point. Butyl hippurate, C9H8(C4H9)NO3, prisms 40°-41° Isobutyl hippurate, C9H8(C4H9)NO3 small, rhombic prisms 45°-46° Amyl hippurate, C9H8(C5HU)NO3, small needles . . 27°-28° When hippuric acid is distilled with phosphorus pentachloride, hydrochloric acid is evolved and the distillate consists, first, of phosphorus oxychloride, then of benzoyl chloride and finally of the compound C9H6C1NO, which crystallizes from ether in flat, four-sided, monoclinic prisms, melting at 40°-50°. It boils at 220°, is not attacked by alcoholic potash, and on fusion with potash yields benzoic acid and ammonia.5 The formation of this substance may be explained by the following equations : CH^NH.CO.CJL CH2.NH.CO.C6H5 | ' +2PC15= | " ' + 2POC13 + HC1. CO.OH CC13 ch9.nh.co.c6h5 chx I =11 >N.CO.CcH5 + 2HC1. CC13 CCr Hippuramide, (CcH5.CO)NH.C2H2O.NH2, is formed by the action of aqueous ammonia on the ethyl ether; it separates from hot water in short, thick crystals, melting at 183° (Jaque- min and Schlagdenhauffen ; Conrad). Hippuramido-acetic acid, C11H12N2O4, is formed, together with hippuric acid, by the action of benzoyl chloride on silver 1 Stenhouse, Ann. Chern. Pharm. xxi 148 ; Conrad, loc. cit. 2 Liebig, Ann. Chem. Pharm. Ixv. 351. 3 Curtius, Ber. Deutsch. Chem. Ges. xvii. 1662. 4 Campani and Bizzarri, Bull. Soc. Chim. xxxv. 427 ; Campani, Ber Deutsch. Chem. Ges. xi. 1247. 5 Schwanert, Ann. Chem. Pharm. cxii 59. 192 AROMATIC COMPOUNDS. amido-acetate, and is probably derived from the hippuric acid which is first formed : ch2.nh.co.c6h6 ch2.nh.co.c6h, I " +NH2.CH2.CO.OH = I CO.OH CO.NH.CH,.CO.OH + h2o It crystallizes from hot water in rhombic tablets or needles, melting at 206'5°. On boiling with hydrochloric acid, it decom- poses into amido-acetic acid and benzoic acid; on heating with dilute acids, on the other hand, both hippuric acid and amido- acetic acid are formed. Its salts crystallize well; the ethyl ether, which melts at 117°, combines with ammonia forming hippurglycollamidc, which crystallizes in large, transparent plates, melting at 202°. An acid, C10H12N3O4, is also formed by the reaction just men- tioned, and crystallizes from hot water in microscopic needles which melt at 240°, and are decomposed by hot hydrochloric acid into amido-acetic acid, benzoic acid, and a non-crystallizable, nitrogenous compound.1 Hydrobenzuric acid, C18H24N2O6, is obtained by the action of sodium amalgam on a concentrated solution of hippuric acid in caustic soda solution; it forms a mass resembling turpentine, and becomes crystalline after standing for months. When it is treated with an excess of sodium amalgam and water, it decom- poses into hydrobenzyhcric acid, C16H21NO4, and amido-acetic acid. The former is an oily liquid, which gradually solidifies; on boiling with alkalis it decomposes into hydrobenzoic acid, benzyl alcohol and amido-acetic acid. Its alkaline solution oxidizes in the air with formation of hydroxybenzyluric acid, C1gII2]NO5, which is a crystalline mass melting at 60°-70°.2 2ii2 Ornithuric acid, C19H20N2O4. Shepard found that ben- zoic acid is not converted into hippuric acid in the organism of birds, but into another nitrogenous compound, which was more closely examined by Jaffe.3 He obtained it from the excre- ments of hens which were fed with benzoic acid; it is very slightly soluble in water and crystallizes from hot alcohol in minute needles, melting at 182°. Its solution reddens litmus. The following salts are characteristic : 1 Curtins, Journ. Prakt. Chcm. [2] xxvi. 145. 2 Otto, Ann. Chern. Pharm. cxxxiv. 303. 3 Jaffe, Bar. Deutsch. Chcm. Ges. x. 1925 ; xi. 406. ORNITHINE. 193 Calcium ornithibrate, (C19H19N2O4)2Ca, is obtained by adding the ammonium salt to a solution of calcium chloride and heatino; the mixture ; it is a crystalline precipitate, which is only very slightly soluble in water. Barium ornithurate, (C19H19N2O4)2Ba, is exceptionally soluble in water and alcohol, and is deposited from its alcoholic solution in opaque, crystalline flocks, which after drying form a snow- white powder. On boiling the acid with hydrochloric acid, it decomposes almost immediately into benzoic acid and benzoylornithine, Ci2Hi6N2O3, which is almost insoluble in alcohol and crystallizes from water in very brittle needles, melting at 225° -230°. It forms readily soluble salts with the mineral acids. If the boiling with hydrochloric acid be continued for some time, the acid decomposes into benzoic acid and ornithine, C5H12N2O2, which is very deliquescent, has a strongly alkaline reaction and a somewhat caustic taste. It combines with acids to form salts which crystallize well. Ornithine has the composition of a diamidovalerianic acid, and the constitution of these compounds can therefore be expressed by the following formulae : Ornithine. nh2 c4h7.co2h nh2 Benzoylornithine. nh2 c4h7.co2h nh.co.c6h6 Ornithuric acid. NH.CO.C6H5 c4h7.co2h nh.co.c6h5. Free ornithine, which has an alkaline reaction, will, of course, have the following formula: nh2 c4h7.co nh3.o 194 AROMATIC COMPOUNDS. BENZENYL COMPOUNDS. 2ii3 These compounds are closely allied to the benzoyl deriva- tives. Phosphorus chloride converts benzoic acid, C6H5.CO.OH, first into benzoyl chloride, C6H5.COC1, and then by further action into benzenyl chloride, C6H5.CC13. The latter is also formed by the continued action of chlorine on boiling toluene; on heating with caustic potash it is reconverted into benzoic acid, which therefore bears the same relation to it as formic acid to chloroform. The action of the potash is probably to form benzenyl alcohol or orthobenzoic acid in the first instance: C0H5.CC13 + 3K0H=C6H5.C (0H)3+3 KC1. This is, however, as unstable as orthoformic acid and immedi- ately decomposes into water and benzoic acid ; ethers are, how- ever, known, such as ethyl orthobenzoate, C6H5.C(OC2H5)3, obtained by the action of sodium ethylate on benzenyl tri- chloride. Benzoic acid itself may, therefore, be looked upon as a benzenyl compound, and this view was actually taken by Berzelius (Part I., p. 12). A large number of compounds which are formed by the action of hydroxylamine on benzoyl chloride may also be in- cluded among the benzenyl derivatives. The simplest of these is benzyhydroxamic acid: N.OH c6h5.c^ \OH. Benzonitril, CcH-.CN, and its compounds with alcohols, such as benzimido-ethyl ether : NII C6H5.C^ xoc2h5. also belong to this class. The latter compound is converted by ammonia into benzenylamidine or benzimido-amide : NII C6H5.C^ \nh2. BENZENYL TRICHLORIDE. 195 Benzenyl amidines which contain the radical phenyl, &c., are obtained by heating benzonitril with the hydrochlorides of amido-bases ; thus aniline yields phenylbenzenylamidine : NH C6H5.CZ \N(C6H5)H. Another series of amidines (Part III., p. 216) consists of the anhydro-bases, which are formed from the orthoamido-compounds by the elimination of water; benzoylorthodiamidobenzene in this way yields phenylenebenzenylamidine : /N. c0h4< >c.c6h5. \NHZ Benzenyl trichloride or Benzo-trichloride, C6H5.CC13. Liebig and Wohler found during their researches on the radical of benzoic acid, that benzoyl chloride is converted by phosphorus pentachloride into a strongly-smelling, oily substance, which they did not investigate more closely.1 It was made the subject of research by Schischkow and Rosing2 and also by Limpricht,3 who found that it is also formed when benzidene dichloride, C6H5.CHC12, is treated with chlorine, and named it benzoic trichloride. Benzenyl trichloride is most readily obtained by passing chlorine into boiling toluene until no further increase in weight takes place.4 The product is then washed with caustic soda solution, dried over ignited potassium carbonate and recti- fied ; it is employed in the colour industry and is manufactured on the large scale, being purified by distillation in a vacuum. Benzenyl trichloride, which is also known as phenylchloroform, is a powerfully refractive liquid, which has a characteristic penetrating odour, boils at 213°-214°, and has a sp. gr. of 1'380 at 14°. On heating with water to 150°, it is converted into benzoic acid, while benzoic anhydride is formed when it is heated with sulphuric acid which contains 4'6 per cent, of water (p. 166). It is decomposed by fuming nitric acid with formation of metanitrobenzoic acid (Beilstein and Kuhlberg). 1 Ann. Chern. Pharm. iii. 265. 2 Jahresber. Chem. 1858, 279. 3 Ann. Chem. Pharm. cxxxiv. 55 ; cxxxv. 80 ; cxxxix. 323. 4 Beilstein and Kuhlberg, ibid, cxlvi. 330. 196 AROMATIC COMPOUNDS. Bcnzenyl tribromide,, C6H5.CBr3, is formed by the action of bromine on boiling toluene, and is a colourless liquid which has an exceedingly violent action on the eyes and mucous mem- brane. It cannot be distilled, since it decomposes at about 150°; on heating with water it is readily converted into benzoic acid, while it is only very slowly attacked by boiling alcohol.1 Bcnzenyl ethyl ether, C6H5.C(OC2H5)3. This compound, which is also called ethyl orthobenzoate, was obtained by Limpricht, who heated the chloride to 100° with a solution of sodium in absolute alcohol. It is a transparent, colourless liquid, which smells like ethyl benzoate and boils at 220° - 225°. Benzenyl triacetate, C6H5.C(OC2H3O)3, is formed by the action of silver acetate on the chloride, and is a liquid which decom- poses on distillation into acetic anhydride and benzoic an- hydride. If it be allowed to stand in the air or over sulphuric acid in a vacuum, white needles separate out, which melt at 70°, and have the composition of acetobenzoic anhydride (Limpricht). Monochlorobcnzenyl trichloride, C6H4C1.CC13. The ortho- compound has been obtained by the action of phosphorus penta- chloride on salicylic acid, C6H4(OH)CO2H; it is crystalline, melts at 30° and boils at 26 O0.2 The meta-compound has been prepared in a similar manner from metasulphobenzoic acid, C6H4(SO3H)CO2H, and boils at 235°;3 the para-compound is formed by the chlorination of benzenyl trichloride in presence of iodine; it boils at 245° and yields parachlorobenzoic acid when heated with water to 200° (Beilstein and Kuhlberg). Dichlorobenzenyl trichloride, C6H3C12.CC13, has been prepared by the action of chlorine on a boiling mixture of the dichloro- toluenes obtained by chlorinating toluene. The product boils at 273°-280° and yields three dichlorobenzoic acids on heating with water.4 Trichlorobenzenyl trichloride, C6H2C13.CC13, is formed by pass- ing chlorine into boiling trichlorotoluene ; it crystallizes from alcohol in very fine needles, melts at 82° and boils at 307°-308°. Tctrachlorobenzenyl trichloride, C6HC14.CC13, forms fine, short needles, melts at 104° and boils at 316°.5 1 Ince, Abst. Proc. Chcm. Soc. 1885-6, 131. 2 Kolbe and Lautemann, Anti. Chcm. Pharm. cxv. 195. 3 Carins and Kammerer, ibid, cxxxviii. 58. 4 Schulz, ibid, clxxxvii. 260 ; Aronheim and Dietrich, Ber. Deutsch. Chcm. Ges. viii. 1401. 5 Beilstein and Kuhlberg, Ann. Chcm. Pharm. cl. 286. BENZONITRIL. 197 BENZONITRIL AND ITS DERIVATIVES. 2114 Benzonitril, C6H5.CN. This substance was prepared by Liebig and Wohler by heating benzamide with baryta,1 but was not investigated by them, and its identity with the benzonitril discovered by Fehling was established at a much later period. The latter chemist obtained it by the dry distillation of ammo- nium benzoate,2 from which it is formed by loss of water. It can be prepared by a similar reaction from benzamide, C6H5.CO.NH2, by heating it with phosphorus pentoxide,3 phos- phorus pentachloride,4 phosphorus pentasulphide,5 benzoyl chlo- ride,6 potassium benzoate,7 or caustic lime.8 Among many other methods of preparation, some of which have been already mentioned (Part III., p. 31), the following are the most important. It can readily be obtained by distilling two molecules of benzoic acid with one molecule of potassium thiocyanate : C6H5.CO2H + HSCN = C6H5.CN + CO2 + H2S. One half of the benzoic acid is converted into the potassium salt, from which it can readily be recovered.9 Lead thiocyanate may be substituted for the potassium salt:10 2C6H5.CO2H + Pb(SCN)2 = 2C6H5.CN + PbS + H2S + 2COr Benzonitril is synthetically prepared by the distillation of sodium benzenesulphonate with potassium cyanide,11 as well as by heating iodobenzene to 350° with silver cyanide,12 or by the action of cyanogen chloride on benzene in presence of aluminium chloride.13 It is obtained from aniline by converting the latter into diazobenzene chloride and heating this with a solution of 1 Wohler, Ann. Chern. Pharm. cxcii. 362. 2 Ibid. xlix. 91. 3 Hofmann and Buckton, ibid. c. 155. 4 Gerhardt, Chim Org. iv. 762 ; Henke, Ann. Chern. Pharm. cvi. 276. 8 Henry, Ber. Deutsch. Chern. Ges. ii. 307. 6 Sokol ow, Gerhardt's Org. Chim. i. 386. 7 Kekule, Ber. Deutsch. Chern. Ges. vi. 113. 8 Anschutz and Schulz, Ann. Chem. Pharm. cxcvi. 48. 9 Letts, Ber. Deutsch. Chem. Ges. v. 673. 10 Kriiss, ibid. xvii. 1766 11 Merz, Zeitschr. Chem. 1868, 33 ; Ber. Deutsch. Chem. Ges. iii. 710. 12 Merz and Weith, ibid. x. 746. 13 Friedel and Crafts, Bull. Soc. Chim. xxix. 2. 198 AROMATIC COMPOUNDS. the double cyanide of potassium and copper.1 It can easily be prepared in the pure state by distilling benzamide with phos- phorus pentoxide and rectifying the product over the latter. A good yield is obtained by Letts's process, according to which the mixture of benzoic acid and potassium thiocyanate is heated in an apparatus connected with an inverted condenser until a white, solid mass has been formed. The product is then dis- tilled, the distillate freed from benzoic acid by means of ammonia, and the benzonitril finally distilled in steam ; he thus obtains 80 per cent, of the theoretical yield. Merz, by the distillation of 500 grms. of sodium benzenesulphonate with 330 grms. of potassium cyanide, obtained in one case 130 and in another 140 grms. of the crude 80 per cent, nitril, while Henry, employing his own method, obtained half the theoretical yield. Properties.-Benzonitril is a mobile liquid, which smells like oil of bitter almonds, has a sp. gr. of 1'023 at 0°, boils at 191° and solidifies in a mixture of ether and solid carbon dioxide to a crystal- line mass, melting at -17°.2 It is miscible with alcohol and ether, and dissolves in about 100 parts of water (Fehling). On boiling with caustic potash it is converted into benzoic acid, and it is re- duced in alcoholic solution by zinc and hydrochloric acid to benzyl- amine (Mendius); fuming sulphuric acid in the cold polymerizes it to cyanphenin, but on heating, forms metasulphobenzoic and benzenedisulphonic acids (Hofmann and Buckton). When it is mixed with benzene and concentrated sulphuric acid, dibenz- imido-oxide, C14H12N2O, is obtained ; it crystallizes in thick vitre- ous prisms and has basic properties.3 On heating it with dilute hydrochloric acid, dibenzamide is formed.4 Both substances are obtained when well-cooled, fuming sulphuric acid is allowed to drop into benzonitril, and the mixture treated with water after standing for some time.5 Their formation is explained by the following equations: c6h5.cn • C6H5.COX + H2O = )NH c6h5.cn c6h5.c^nh. c6h5.cox c6h5cox >nh+h2o = )nh+nh3. C6H6.CdNH C6H5COZ 1 Sandmeyer, Ber. Deutsch. Chem. Ges. xvii. 2653. 2 Hofmann, Jahresber. 1862, 335. 3 Klein and Pinner, Ber. Deutsch. Chem. Ges. xi. 764. 4 Pinner, ibid. xvii. 2006. 6 Gumpert, Joum. Prakt. Chem. [2] xxx. 87 ; Pinner, ibid. xxx. 125. BENZONITRIL. 199 When benzonitril is shaken up with a warm mixture of caustic potash solution and hydrogen peroxide, it is rapidly converted into benzamide, pure oxygen being evolved :1 C6H5.CN + 2H2O2=C6H5.CO.NH2 + H2O + O2. If benzonitril be taken internally, it appears in the urine in the form of oxybenzonitrilsulphuric acid, C6H4(O.SO3H)CN, which readily decomposes into sulphuric acid and the nitrils of salicylic acid and parahydroxybenzoic acid ; the meta-compound, however, is not formed.2 Benzonitril combines with hydrobromic acid to form the crystalline compound, C6H5.CN + 2HBr, which is converted by water into benzamide :3 C6H5.CBr2.NH2 + H2O = C6H5.CO.NH2 + 2HBr. According to Henry, a similar compound is formed with hydriodic,4 but not with hydrochloric acid; when, however, a current of the latter gas is passed into an ethereal solution of platinum chloride and benzonitril, long needles separate out, which decompose in dry air into their three components.5 When benzonitril is heated with bromine, the monobromide, (C7H5NBr)2, is formed; it crystallizes from ether in small needles, which partially sublime when heated and are partially decomposed into bromine, benzonitril and cyanphenin ; while on heating with lime, some carbon dioxide and ammonia are evolved in addition to the compounds mentioned. A dibromide also appears to exist, but it is very unstable.6 It combines with some metallic chlorides to form the following solid compounds, C7H5N,AuC13, (C7H5N)2PtCl4, (C7H5N)2SnCl4 and (C7H5N)2TiCl4, the last of which forms bright crystals which may be sublimed.7 2115 Cyanphenin, C21H15N3. This compound, which corre- sponds to cyanethin (Part I., p. 562), was obtained by Cloez by heating benzoyl chloride with potassium cyanate,8 and Engler prepared it, as already mentioned, from benzonitril 1 Radziszewski, Ber. Deutsch. Chem. Ges. xviii. 355. 2 Baumann, ibid. xvii. Ref. 256. 3 Engler, Ann. Chem. Pharm. exlix. 307. 4 Bull. Soc. Chim. vii. 85. 5 Klein and Pinner, Ber. Deutsch. Chem. Ges. x. 1891. 6 Engler, Ann. Chem. Pharm. cxxxiii. 144. 7 Henke, ibid. cvi. 284. 8 Ibid. cxv. 27. 200 AROMATIC COMPOUNDS. bromide. Hofmann found that it is formed when benzonitril is heated with sodium,1 and Klein and Pinner when it is treated with fuming sulphuric acid.2 It is also obtained in tolerable quantity, according to Henry, together with benzonitril, by the action of phosphorus pentasulphide on benzamide, and, together with an oily base, C16H18N2, the hydrochloride of which, ClcH19 N2C1, crystallizes in six-sided tablets, when benzonitril is heated with zinc ethyl.3 Cyanphenin is a hard, crystalline substance, which melts at 231°, sublimes in needles, and boils above 350°. It is insoluble in water, slightly soluble in alcohol and ether, more readily in carbon disulphide and ethyl iodide. It is not attacked when heated with aqueous or alcoholic potash, but is converted into benzoic acid by heating to 220° 4 with fuming hydriodic acid, or to 250° with concentrated hydrochloric acid (Frankland and Evans). BENZIMIDO-ETHERS. 2116 The, Benzimido-ethcrs include the compounds which are formed by the action of hydrochloric acid on a mixture of benzonitril with an alcohol. Of these compounds the isobutyl ether has been more fully described;5 its formation is preceded by that of a compound which forms large, lustrous crystals, which fume in moist air and decompose into hydrochloric acid, ammonium chloride and isobutyl benzoate : zNH3C1 c6h5.c/oc4h9+h2o=HC1+NH4C1+C6H5.CO.OC4H9. \ci If, however, the compound be freed from benzonitril and isobutyl alcohol by washing with ether and allowed to stand over caustic soda, a molecule of hydrochloric acid is given off and the hydrochloride of benzimido-isobutyl ether remains 1 Ber. Deutsch. Chern. Ges. i. 198. 2 Ibid. xi. 764 ; Pinner, Journ. Prakt. Chem. [2] xxx. 125. 3 Frankland and Evans, Journ. Chem. Soc. 1880, i. 563. 4 Engler, Ann. Chem. Pharm. cxlix. 310. 8 Pinner and Klein, Ber. Deutsch. Chem. Ges. x. 1889 ; xi. 4. BENZIMIDO-ETHERS. 201 behind ; it decomposes on heating into benzamide and isobutyl chloride: .NH2C1 c6h5.c< = c6h5.co.nh2+c4h9ci. \oc4h9 It is decomposed by a solution of ammonia in absolute alcohol, with formation of the free isobutyl ether, ammonium chloride and benzenylamidine hydrochloride. Benzimido-isobutyl ether, C6H5.C(NH)OC4H9, is a thick, oily liquid, which partially decomposes on distillation; it readily recombines with hydrochloric acid; cold, concentrated sulphuric acid converts the hydrochloride into the acid sulphate, C6H5C (OC4H9)NH2.SO4H, which crystallizes in long, pliant needles. Benzimido-acetic ether, C6H5.C(NH)OC2H3O, is formed by boiling the isobutyl ether with acetic anhydride; it is insoluble in water and acids, dissolves in alcohol and crystallizes in needles, melting at 116°. Benzimido-ethyl ether, C6H5.C(NH)OC2H5. The hydrochloride of this compound forms large, lustrous, transparent prisms, which decompose at 118°-120° with formation of benzamide. In other respects the compound resembles its isobutyl analogue.1 Benzimido-thio-ethyl ether, C6H5.C(NH)SC2H5. The hydro- chloride of this compound is formed when hydrochloric acid is passed into a mixture of ethyl mercaptan and benzonitril: ^NH2C1 C6H5.CN4 hs.c9h5+hci = c6h,.c< \sc2h5. It crystallizes in thick prisms, which melt at 188° and are readily soluble in water and alcohol. The hydriodide is obtained by heating thiobenzamide to 100° with ethyl iodide : znh2 .nh2i c6h5.c< +ic2h6=c6h5.c^ \sc2h5. It forms long, monosymmetric prisms, melting at 142.° Alkalis separate the ether from these salts as a strongly-smelling, oily liquid, which is soluble in water and readily decomposes into benzonitril and mercaptan.2 1 Pinner, Ber. Deutsch. Chern. Ces. xvi. 1654. 2 Bernthsen, Ann. Chern Pharm. cxcvii. 348. 202 AROMATIC COMPOUNDS. Benzimido-thiobenzyl ether, C6H5.C(NH)S.CH2.C6H5. The hydrochloride is obtained by the action of benzyl chloride on thiobenzamide, or of hydrochloric acid on a mixture of benzyl hydrosulphide and benzonitril. It is soluble in water and alcohol, and crystallizes in white tablets melting at 181°. The free base is very unstable (Bernthsen). BENZENYLAMIDINES. 2117 Benzenylamidine or Benzimido-amide, C6H5.C(NII)NII2, is formed, as already mentioned, by the action of alcoholic ammonia on the hydrochloride of benzimido-isobutyl ether: .NH2C1 /zNH9C1 c6h5.c< + nh3=c6h5.c< " +ho.c4h9. xOC4H9 \NH2 Free benzimido-isobutyl ether is simultaneously formed, but the quantity of this product diminishes when the temperature at which the reaction is carried out is raised.1 The product is evaporated in a vacuum, the residue washed with ether and crystallized from alcohol, yielding benzenylamidine hydrochloride in flat needles, which are decomposed by caustic potash but not by ammonia; by shaking out with ether and evaporating, the free base is obtained as a crystalline mass, which is slightly soluble in water, readily in alcohol and has an alkaline taste and reaction. It decomposes spontaneously after some time with evolution of ammonia, which is also given off on heating, benzonitril and cyanphenin being formed. If it be heated to 100° with ethyl iodide, the product decomposed with caustic soda and extracted with ether, ethyl- benzenylamidine, C6H5C(NC2H5)NH2, is obtained as a strongly alkaline, thick, oily liquid. Dibenzenyltriamine, C14H13N3, is formed, together with acet- amide, when benzenylamidine is boiled with acetic anhydride : NK ^NH C6H5.C< 2C6H5.C\ = 1 >NH + NH3. \nh2 c6h5.c< w 1 Pinnei' and Klein, Ber. Deutsch, Chem. Ges. x, 1889. PHENYLBENZENYLAMIDINE. 203 It crystallizes in long, flat needles, which melt at 108°-109° and are not decomposed even at 2400.1 Phenylbenzenylamidine, C6H5.C(NH)N(C6H5)H, is obtained, together with diphenylbenzenylamidine, by heating benzonitril to 220°-240° with aniline hydrochloride : NII c6h5.cn + N(C6H5)H2 = c6h5.c^ \N(C6H5)H. The product is extracted with cold water and the solution precipitated with ammonia ; the base thus obtained is very readily soluble in alcohol, and crystallizes badly in small crusts or warts composed of plates, which melt at 111°-112°, and, on further heating, partially sublime and are partially decomposed into aniline and benzonitril. Phenylbenzenylamidine hydrochloride is a syrup, miscible with water and alcohol in all proportions.2 It is converted by the action of sodium amalgam on its alcoholic solution into benzidenephenyldiamine, C6H5.CH(NH2)N(C6H5)H.3 When phenylbenzenylamidine is heated with carbon disul- phide, its thiocyanate is obtained together with thiobenzanilide ; an intermediate product is probably first formed and then decomposed at the higher temperature: 4 /NH\ C6H5.C^-S-^CS = C6H5.CS.N(C6H5)H 4- NCSH. \N(C6H5)H Symmetric diphenylbenzenylamidine, C6H5.C(NC6H5)N(CcH5)H. This compound was first prepared by Gerhardt, who obtained it by warming benzanilide with phosphorus pentachloride and then heating the product with aniline.5 The compound CJL.CCL.NtCJIJH is first formed, and is converted, with loss of hydrochloric acid, into benzanilidimidoMoride, which acts upon the aniline in the following manner : ,nc6h5 ^nc6h5 C6H,.Cf +N(C6H5)H9 = C6H5.C< + HC1, \C1 ~ ' \n(C6H5)H 1 Ber. Deutsch. Chem. Ges. xi. 4. 2 Bernthsen, Ann. Chem. Pharm. clxxxiv. 348. 3 Bernthsen and Szymanski, Ber. Deutsch. Chem. Ges. xiii. 917. 4 Bernthsen, Ann. Chem. Pharm. cxcii. 31. 5 Ann. Chem. Pharm. cviii. 217. 204 AROMATIC COMPOUNDS. Benzanilidimidochloride crystallizes from petroleum ether in large, transparent, lustrous plates, melts at 39°-40°, and boils without decomposition at about 310°; water decomposes it rapidly, benzanilide being reproduced.1 Diphenylbenzenylamidine is also formed by the action of aniline on benzenyl trichloride,2 and by heating benzanilide with aniline hydrochloride and phosphorus trichloride.3 It is slightly soluble in water, readily in alcohol, and crystallizes in needles, melting at 144° (Wallach and Hoffmann). On heating with hydrochloric acid to 150°, it decomposes into benzoic acid and aniline, while, on heating with sulphuric acid, thiobenzanilide and phenyl mustard oil are formed (Bemthsen). Its hydro- chloride, C19H16N2.C1H, is only very slightly soluble in cold water and crystallizes from alcohol in needles. Asymmetric diphenylbenzenylamidine, C6H5C(NH)N(C6H5)2, is prepared by heating benzonitril with diphenylamine hydro- chloride to 180°-190°. It is exceptionally soluble in alcohol and tolerably in ether, from which it crystallizes in thin, yellowish, alkaline, rhombic tablets, melting at 112°. It decomposes on boiling into diphenylamine and benzonitril; when it is heated with carbon disulphide, its thiocyanate is formed together with diphenylthiobenzanilide, C6H5.CS.N(C6H5)2. Its hydrochloride crystallizes in needles or monoclinic prisms, which are readily soluble in water (Bernthsen). Diphenylparamidobcnzenylamidinc or Carbotriphenyltriamine, C19H17N3, was first prepared by Hofmann by heating aniline with tetrachloromethane ;4 it is more readily formed, however, from tetrabromomethane.5 Weith obtained it by heating para- nitrobenzoic acid with aniline and phosphorus trichloride, and reducing the diphenylparanitrobenzenylamidine thus formed with tin and hydrochloric acid,6 while Mich]er and Walder prepared it by the action of aniline on trichloromethylsulphonyl chloride, CC13.SO2C1.7 It is insoluble in water, slightly soluble in ether, and crystallizes in long tablets, melting at 198°. On distillation it decomposes into hydrocyanic acid, benzonitril, ammonia, aniline, and diphenylamine, while on heating with 1 Wallach and Hoffmann, Ann. Chern. Pharm. clxxxiv. 79. 2 Limpricht, ibid, cxxxv. 82 ; Dobner, Ber. Deutsch. Chern. Ges. xv. 233. 3 Hofmann, Zeitschr. Chem. 1866, 165 4 Hofmann, Jahresber. Chem. 1858. 351. 5 Bolas and Groves, Ann. Chem. Pharm. clx. 173. 6 Ber. Deutsch. Chem. Ges. xii. 101. 7 Ibid. xiv. 2174. PHENYLENEBENZENYLAMIDINE. 205 hydrochloric acid to 160°, aniline and paramidobenzoic acid are formed: ^NC6H5 H2N.C6H4.C< -F 2H9O = H2N.C6H4.CO2H + \n(C6H5)H 2N(C6H5)H2. Phenylcnebenzenylamidine, C13H10N2, was termed anhydro- benzodiamidobenzene by Hubner, and is obtained by heating benzoylorthodiamidobenzene : /NH2 /NHx c6h / co.c2h5 = c6h4( >c.c6h5 + h20. \NHZ \ N It may also be easily prepared by reducing benzoylorthonitro- anilide with tin and hydrochloric acid, the rise of temperature caused by the reaction being sufficient to bring about the forma- tion of the anhydro-base. It is slightly soluble in water, readily in alcohol, and crystallizes from glacial acetic acid in lustrous tablets, melting at about 280°; the hydrochloride, C13H1ON2.C1H, forms long needles, which are readily soluble in water. The base is not attacked by benzoyl chloride even at 260°; on heating with iodine and alcohol, however, the periodide, C13H10N2.IH.I2, is formed, and crystallizes in small plates which resemble iodine, but have a green surface lustre and are con- verted by boiling with water into the hydriodide, C13H10N9.IH + h2o, crystallizing in long, light yellow needles. Dimethylphcnylenebenzenylamide ammonium iodide, C13H10N2 (CH3)9I. When the anhydro-base is heated with methyl iodide to 180°, the periodide, C13H10N2(CH3)2I3, is formed; this sub- stance crystallizes in long, brownish red needles, and is con- verted into the mono-iodide by boiling in alcoholic solution with freshly precipitated lead hydroxide. This compound crystallizes from hot water in long needles; caustic potash precipitates from its solution the hydroxide, C13H10N2(CH3)2OH, in white flocks, which melt at 152° and are insoluble in water, but dissolve readily in hot alcohol. Its solution has a bitter taste, and its salts crystallize well; it has the following constitution : OH CH3X I /CH3 >N< c6h4< >.c6h5. 206 AROMATIC COMPOUNDS. riienylenenitrobenzcnylamidine, C13H9(NO2)N2, is obtained by dissolving the anhydro-base in fuming nitric acid ; it crystallizes from alcohol in yellowish, microscopic needles, melting at 196°. It is reduced by tin and hydrochloric acid to amidobenzenyl- phenylene-amidine, C13H9(NH2)N2, which crystallizes from alcohol in small needles, melting at 240°. The hydrochloride, C13H9 (NH2)N2(C1H)2, forms small plates, which are very soluble in water; the sulphate, C13H9(NH2)N2.SO4II2 + 2H9O, is only slightly soluble in hot water, and crystallizes in broad needles. A large number of other similar anhydro-bases is also known.1 The following compounds belong to the same class. Benzenylamidophenate, C13H9NO. Ladenburg prepared this compound by heating ortho-amidophenol with benzoyl chloride, and by the distillation of the former with phthalic anhydride : zcox h9nx ,nx C6Hz >0+ " >c6h4 = c6h5.c< >C6H4+CO2+H„O. zcoz hoz zoz It crystallizes from dilute alcohol in lustrous plates, melts at 103°, and boils at 314°-317°; it combines with acids to form unstable salts; the platinichloride, (C13H10NO)2PtCl6, crystal- lizes from alcohol which contains hydrochloric acid in yellow prisms. On heating the base with concentrated hydrochloric acid to 150°, it decomposes into benzoic acid and orthamido- phenol.2 Benzenylamidothiophenate, C13H9NS, is formed by boiling benzanilide with sulphur :3 C6H5.CO.NH(C6H5) + s = c6h5.c< >c6h4 + h2o. ZSZ It is also obtained by the action of benzoyl chloride on ortho- amidothiophenol, as well as by heating the latter with benz- aldehyde, or benzonitril.4 It is formed in smaller quantity, together with other products, when phenyl mustard oil is heated with benzoyl chloride.5 It crystallizes from alcohol in needles, which, especially when heated, smell like tea-roses and geraniums, melt at 115°, and boil at about 360°. Like the preceding compound, it is a base and forms a platinichloride 1 Hiibner, Ann. Chern. Pharm. ccviii. 278 ; ccix. 339 ; ccx. 328. 2 Ber. Deutsch. Chem. Ges. ix. 1526. 3 Hofmann, ibid. xii. 2359. 4 Ibid. xiii. 1223. 5 Ibid. xiii. 17. BENZHYDROXAMIC ACID. 207 which crystallizes in long needles. It is not attacked when heated with concentrated hydrochloric acid to 200°; on fusion with caustic potash it is resolved into amidothiophenol and benzoic acid. BENZENYLOXIME COMPOUNDS. 2i18 The three hydrogen atoms of hydroxylamine can, as was pointed out by Lossen, be successively replaced by benzoyl: Benzhydroxylamine, NOH2(CO.C6H5), Dibenzhydroxylamine, NOH(CO.C6H5)2, Tribenzhydroxylamine, NO(CO.C6H5)3. The last of these compounds is an indifferent substance; the two others are acids, and have therefore been called by Lossen benzhydroxamic acid and dibenzhydroxamic acid.1 Certain cases of physical isomerism and of metamerism are characteristic of them and their derivatives. Lossen showed somewhat later that these peculiarities as well as numerous decompositions of the compounds in question can readily be explained if benzhydrox- amic acid be looked upon as an oximido-compound of benzenyl;2 its formation is then expressed by the following equations: N.OH C6H5.COC1 + h2n.oh = C6H5.C< + H,O. O J Z O 3 \ \ci /N.OH /N.OH C6H5.C< + H2O = C6H5.C\ + HCL \ci XOH It is, however, also possible that the hydroxylamine forms an additive compound with the benzoyl chloride, and that hydro- chloric acid is then given off: 3 /OH ZOH C6H5.C^-NH.OH = C6H5.C< 4- HC1. NCI ^N.OH 1 Ann. Chem. Pharm. clxi. 347. 2 Ber. Deutsch. Chem. Ges. xvi. 873. 3 Ibid, xviii. 1189. 208 AROMATIC COMPOUNDS. The other compounds are then formed by the replacement of the hydrogen of the hydroxyls. Hydroxylamine hydrochloride is dissolved in 8-10 parts of water, together with an equivalent amount of sodium car- bonate, and 3 parts of benzoyl chloride gradually added, the whole being then well shaken up and cooled; the dibenz- hydroxamic acid separates out togethei' with a portion of the benzhydroxamic acid, which is removed by recrystallization from hot alcohol. The benzhydroxamic acid remaining in the solution is precipitated by barium chloride, and then liberated from the well-washed precipitate by dilute sulphuric acid. A further quantity of it can be obtained, since dibenzhydroxamic acid splits up into benzoic acid and benzhydroxamic acid when heated with baryta water. Benzhydroxamic acid ox Bcnzenyloximic acid, C6H5.C(OH)NOH, crystallizes in rhombic plates or tablets, and dissolves in 445 parts of water at 6°, much more readily in tolerably warm water, very readily in alcohol and slightly in ether. It has an acid reaction, melts at 124°-125°, and undergoes a sudden, violent decomposition at a higher temperature. When heated with dilute hydrochloric acid, it decomposes into hydroxylamine and benzoic acid. It is monobasic, but forms acid salts with the alkali metals. Acid potassium benzhydroxamatc, C6H5.C(OH)NOK-f-C6H3.C (OH)NOH, is tolerably soluble in cold water, scarcely in alcohol, and crystallizes in small rhombic plates or flat, pointed prisms, which deflagrate sometimes with the production of flame, when heated. The normal salt is readily soluble in alcohol; on evaporation of the solution, however, the acid salt and potassium carbonate separate out. Acid sodium benzhydroxamatc, C6H5.C(OH)NONa + C6H5.C (OH)NOH + 3H2O, is somewhat more readily soluble in water, slightly in alcohol, and crystallizes in long, thin plates, or large elongated tablets, which rapidly deliquesce in the air. Acid barium hydroxamate, (C7H6NO2)2Ba + C7H7NO2, forms small prisms scarcely soluble in water and alcohol. Normal barium hydroxamate, (C7H6NO2)2Ba, is obtained by the addition of barium chloride to a solution of the acid potassium salt which has been treated with ammonia; it forms microscopic needles. The calcium salt is a precipitate resembling alumina; the benzhydroxamates of most of the other metals are also insoluble. The behaviour of the acid and its acid salts towards ferric DIBENZHYDROXAMIC ACID. 209 chloride is very characteristic ; a dark red precipitate is formed which dissolves in an excess of the precipitant with a deep cherry-red colour, which is not altered by the addition of dilute hydrochloric or sulphuric acid, but is destroyed by concentrated hydrochloric acid ; the addition of water causes the reappearance of the colour. If the original solution contains hydrochloric acid, ferric chloride only produces a colouration. When the barium salt is distilled with a little water aniline is formed:1 2(C6H5C(OH)NO)2Ba + H2O = 2C6H5.NH2 + CO2 + BaCO3. Ethyl benzhydr oxamate, C6H5.C(OH)OC2H5, is obtained by the action of ethyl iodide and caustic potash on a solution of the acid in alcohol,2 as well as by that of benzoyl chloride on ethyl hydroxylamine, H2N(OC2H5).3 It is very slightly soluble in water, readily in alcohol, and crystallizes in thick tablets, which melt at 64°-65° and are resolved at 190° into alcohol, aldehyde, benzamide and phenyl isocyanate. It is readily soluble in alkalis, being re-precipitated from solution by acids and even by carbon dioxide; on heating with concentrated hydrochloric acid, it decomposes into benzoic acid and ethyl hydroxylamine. If equal molecules of the ether and caustic potash be dissolved in alcohol and treated with silver nitrate, a white precipitate of C6H5.C(OAg)NOC2H5, is obtained, which blackens only on heating, while silver benzhydroxamate blackens and decomposes immediately on precipitation. Benzoyl ethylbenzhydroxamate, or Benzethylbenzhydroxylamine, C6H5.C(O.CO.C6H5)NOC2H5, is obtained by the action of benzoyl chloride on an alkaline solution of the ether; it is readily soluble in alcohol and ether and forms transparent rhombic crystals, melting at 48°-49°.4 2119 Dibenzhydroxamic acid, or Benzoylbenzoximic acid, C6H5.C (OH)NO.CO.C6H5, which is produced by the action of benzoyl chloride on benzhydroxamic acid, crystallizes from hot alcohol in needles, and on the spontaneous evaporation of the solution in large, lustrous, rhombic prisms; it has an acid reaction, melts at 153°,5 and decomposes violently at a higher temperature with formation of carbon dioxide, benzoic acid, benzanilide and phenyl isocyanate.6 On heating with hydrochloric acid it splits up into 1 Ann. Chem. Pharm. clxxv. 323. 2 Waldstein, ibid, clxxxi. 384. 3 Giirke, ibid. ccv. 278. 4 Pieper, ibid, ccxvii. 8. 5 Steiner, ibid, clxxviii. 226. 6 Pieschel, ibid, clxxv. 305. 210 AROMATIC COMPOUNDS. benzoic acid and hydroxylamine, while alkalis decompose it into benzhydroxamic acid and benzoic acid, so that the former acid can be prepared from it by means of baryta water. Its alkali salts on the other hand are decomposed by water even in the cold, more rapidly on heating, with formation of benzoic acid, carbon dioxide and diphenyl urea : NO.CO.C6H5 2C6H5.C\ + H2O = 2CGH5.CO.OK + \OK ZN(C6H5)H co< + co2. \n(C6H5)H As already mentioned, benzhydroxamic acid can be directly converted into aniline, "while dibenzhydroxamic acid yields derivatives of this-phenyl isocyanate, benzanilide and diphenyl urea-from which aniline can easily be obtained. Since the homologues of benzoic acid also yield oximes, a general method is established by which the carboxyl of a monobasic aromatic acid can be replaced by an amido-group (Lossen). Inversely, the amido-group of amido-compounds can be re- placed by carboxyl, and aniline thus converted into benzoic acid (Part III. p. 31). Potassium dibenzhydroxamate, C6H5.C(OK)NO.CO.CeH5, is precipitated in thin plates when alcoholic solutions of the acid and caustic potash are mixed. If silver nitrate be added to its freshly prepared aqueous solution, a white precipitate of the silver salt is obtained; if this be dried, covered with ether and treated with ethyl iodide, the ethyl ether is obtained in two isomeric forms, one of which is an oily substance,1 while the other is dimorphous. a-Ethyl dibenzhydroxamate, C6H5.C(OC2H5)NO.CO.C6H5, is the chief product of the reaction; it is readily soluble in ether and alcohol, and crystallizes in four- or eight-sided rhombic prisms, melting at 58.° (3-Ethyl dibenzhy dr oxamate, which is only formed in very small quantity, is more readily soluble than the a-compound and forms triclinic crystals, melting at 63°. These modifications cannot be directly converted into each 1 Eiseler, Ann. Chern. Pharm, clxxv. 326 ; Giirke, ibid. ccv. 279. TRIBENZHYDROXYLAMINE. 211 other; on heating they decompose into benzonitril, aldehyde and benzoic acid: C6H5.C(OC2H5)NO.CO.C6H5 = c6h5.cn + c2h4o+ C6H5CO.OH. Concentrated hydrochloric acid decomposes them into benzoic acid, ethyl benzoate and hydroxylamine, while on heating with caustic potash, benzoic acid and two isomeric ethylhydroxamic acids are formed. The oily ether is also readily soluble in alcohol and ether, and behaves chemically like the two others ; it is only formed in small quantity and has not been closely investigated. a-Ethylbenzhydroxamic acid, C6H5.C(OC2H5)NOH, is readily soluble in alcohol and ether; it crystallizes from a mixture of ether and benzene in monoclinic tablets or prisms,melting at 53'5°. The ethyl ether, C6H5.C(OC2H5)NOC2H5, is formed by the action of ethyl iodide on a solution of the acid in alcoholic potash.1 It is a powerfully refractive liquid which has a pleasant aromatic odour, and boils at 244° with slight decom- position ; its vapour has a sp. gr. of 6'56 (Giirke). On heating with alcohol and hydrochloric acid, it forms ethyl benzoate and ethyl hydroxylamine. ^-Ethylhydroxamic acid is isomorphous with the a-compound, but it melts at 67'5°-68°, is more soluble in petroleum spirit, less so in caustic potash, and is more readily extracted from this by ether. Its ethyl ether is so similar to that of the a-compound that it is doubtful whether they are distinct substances. Both acids are formed simultaneously by the action of hydroxylamine on benzimido-ethyl ether.2 It is almost completely converted into ethyl ^-dibenzhydroxa- mate by the action of benzoyl chloride.3 2120 Tribeitzhydroxylamine, or Dibenzobenzoximate, C6H5.C (O.CO.C6H5)NO.CO.C6H5, is obtained in three modifications by treating dry hydroxylamine hydrochloride with a solution of benzoyl chloride in toluene, or by heating potassium dibenz- hydroxamate with benzoyl chloride.4 It is, however, best 1 Lossen and Zanni, Ann. Chem. Pharm. clxxxii. 220. 2 Lossen, Ber. Deutsch. Chem. Ges. xvii. 1587. 3 Giirke, Ann. Chem. Pharm. ccv. 281. 4 Lossen, Ann. Chem. Pharm. clxi. 360 ; clxxv. 282 ; clxxxvi. 34 ; Steiner, ibid, clxxviii. 225. 212 AROMATIC COMPOUNDS. prepared by acting upon silver dibenzhydroxamate with a solution of benzoyl chloride in petroleum ether, and allowing the whole to stand until the silver chloride has separated as a dense precipitate (Lossen). a-Tribenzhydroxylamine is slightly soluble in cold, more readily in hot alcohol and ether, and forms monoclinic crystals, elongated in the direction of the ortho-diagonal,1 which melt at 100°. It is completely split up into benzoic acid and dibenz- hydroxamic acid by heating for an hour with hydrochloric acid of sp. gr. 1'05. (3-Tribcnzliydroxylamine is insoluble in ether, slightly soluble in cold, more readily in hot alcohol, and forms small, lustrous, monoclinic crystals, melting at 141°-142° (Klein and Trech- mann). It is decomposed by concentrated hydrochloric acid at 150° into benzoic acid, dibenzhydroxamic acid and hydroxyl- amine. 7- Tribenzhydroxylamine is only formed in small quantity; it crystallizes in short, monoclinic prisms, melting at 112°, and is to a large extent converted into the /3-compound by dilute hydrochloric acid. All the three modifications are resolved on dry distillation into benzoic anhydride and phenyl isocyanate : JNO.COC6H6 c6h5.c^ ■ = C6H5NCO+(CO.C6H5)2O. xO.CO.C6H5 They are decomposed by alcoholic potash into dibenzhydrox- amic acid and benzoic acid. The chemical behaviour of these substances is therefore iden- tical, and they present an instance of trimorphism, for although they all crystallize in forms belonging to the monoclinic system, these forms are distinct ones and cannot be derived from one another. Benzenylamidoxime, or Bcnzhy dr oxamide, C6H5.C(NOH)NH2, is formed when a solution of hydroxylamine and benzonitril in dilute alcohol is heated to 80° for about eighteen hours:2 _N.OH c6h5.c=n+hqn.oh=c6H5.cr \nh2. 1 Klein and Trechmann, Ann. Chem. Pharm. clxxxvi. 104. 2 Kruger and Tiemann, Ber. Deutsch. Chem. Ges. xvii. 126, 1687 ; xviii. 727, 1053. BENZHYDROXAMIDE. 213 It is also formed by the action of hydroxylamine on benz- amidine, C6H5.C(NH)NH2, and was described by Pinner as benzoxamidine.1 It is readily soluble in alcohol and ether, and crystallizes from hot water in long, flat, acute prisms, melting at 79°-80°. It is precipitated by petroleum spirit from its solution in benzene in needles. Its solution is coloured deep red by ferric chloride; it forms salts both with acids and bases. Benzamide and nitrous oxide are formed by the action of sodium nitrite on its hydro- chloride, while when heated to 200° with hydrochloric acid, it decomposes into ammonium chloride and benzoic acid. Benzenylamidoxime is poisonous; thus, 0'5 grm. proved fatal to a dog, 0T grm. to a rabbit, and 0'03 grm. to a frog, o7 o 7 c> o Its alkyl ethers are formed by heating the sodium salt with the corresponding iodide. Ethyl ether of benzenylamidoxime, C6H5.C(NOC2H5)NH2, is almost insoluble in water, but readily soluble in alcohol and ether, and crystallizes in rhombic plates, which melt at 67°, and dissolve in acids but not in alkalis. Its hydrochloride crystal- lizes well. Benzenylethoxime chloride, C6H5.C(NOC2H5)C1, is formed when sodium nitrite is added to a well-cooled solution of the ether: C6H5.C(NOC2H5)NHo + HC1 + NaNO2 = C6H5.C(NOC2H5)OH + NaCl + H2O + N2. C6H5.C(NOC2H5)OH + HC1 = C6H6(NOC2H5)C1 + H2O. According to Lossen, a diazo-compound is probably formed at first, and then decomposes in the following manner : 2 /NOC2H5 z.NOC2H5 C6TI5.Cx + HC1 = C6H5.C < + N2 -p H2O. XN=NOH XC1 The chloride is also readily produced by the action of phosphorus pentachloride on ethyl benzhydroxamate, C6H5.C(NOC2H5)OH.3 It is an oily, aromatic liquid, which boils at 239°, is not decom- posed by water or alcohol, and is not even attacked when heated for a short time with acids and alkalis. When heated with alcoholic ammonia to 160°-180°, however, the amidoxime ethyl ether is re-formed, and it is converted by the action of a 1 Kruger and Tiemann, Ber Deutsch. Chem. Ges. xviii. 184. 2 Ber. Deutsch. Chem. Ges. xviii. 1193. 3 Ibid. 214 AROMATIC COMPOUNDS. solution of sodium in absolute alcohol into ethyl ethylbenz- hydroxamate. Benzoylbenzenylamidoxime, C6H5.C(NO.CO.C6H5)NH2, is formed by the action of benzoyl chloride on benzenylamidoxime. It crystallizes in fine, white needles, which melt at 140°, and are soluble in alcohol, ether, and acids, but not in alkalis. 2i2i Dibenzenylazoxime, (C7H5)2N2O, is obtained by heating the compound just described beyond its melting-point, or by treating it with dehydrating agents, such as benzoic anhydride or benzoyl chloride: NO.CO.C6H5 no. c6h5.c^ = c6h5.c( >c.c6h5+h2o. \nh2 \-N-^ It is scarcely soluble in water, but readily in alcohol, and crystallizes in long, fine needles, which, after drying, resemble asbestos and melt at 108°, but sublime at a much lower temperature. Ethenylbenzenylazoxime is formed by the action of acetic anhy- dride on benzenylamidoxime, and is very similar to the preceding compound, crystallizing in needles which readily sublime, have a characteristic odour and melt at 41°. It is isomeric with benz- cnylethenylazoxime, which is obtained by the action of benzoyl chloride on ethenylamidoxime, CH3.C(NOH)NH2, and forms aromatic needles, which melt at 57° and sublime very easily.1 The isomerism of these two compounds is shown by the follow- ing for mu he: Ethenylbenzenylazoxime. c6h5.c^ JC.ch3 Benzenylethenylazoxime. ^N0\ ch3.c< >c.c6h5. Acetylbenzenylamidoxime, C6H5.C(NO.CO.CH3)NH2, is formed by the action of acetyl chloride on an ethereal solution of benz- enylamidoxime. It crystallizes from alcohol in small plates or flat prisms, which melt at 96°, and are easily converted into ethenylbenzenylazoxime, the change being brought about even by boiling with water.2 Ethyl benzenylamidoximccarboxylatc, CcH5.C(NH2)NO.CO.OC2H5, 1 Nordmann, Ber. Deutsch. Chcm. Ges. xv. 2754. 2 Schultz, ibid, xviii. 1080. BENZENYLAZOXIME CARBINOL. 215 is obtained by adding ethyl chlorocarbonate to a solution of benzenylamidoxime in chloroform. It crystallizes in long, lustrous needles, which melt at 127° and are decomposed at a higher temperature, or on heating with water, into the following compound, alcohol being removed : Benzenylazoxime carbinol, C8H6N2O2, is most simply prepared by heating benzenylamidoxime with ethyl chlorocarbonate. It crystallizes from hot water in long needles, melting at 197°. It readily dissolves in alkalis; its aqueous solution has an acid reaction and decomposes the carbonates of the alkaline earth metals. Silver nitrate precipitates the white crystalline silvei- salt from a solution neutralized with ammonia, and copper sul- phate, the green copper salt, (C8H5N2O2)2Cu. According to the method by which it is prepared, benzenyl- azoxime carbinol should have the first of the following formulas; its whole behaviour, however, corresponds with the second, and an intramolecular change must therefore be assumed: ' ^N0\ c6h5.c< >co ZNHZ c6h5.cz >c.oh. Z-N-z ■ Carbonyldibenzenylamidoxime, (C6H5.C(NH2)NO)2CO, is formed when benzenylamidoxime is brought into contact with carbonyl chloride dissolved in benzene. It is almost insoluble in the latter and is precipitated by water from its alcoholic solution in small plates, melting at 128°-129°. On heating with caustic soda solution, the preceding compound is formed.1 Benzenylazoxime propenylcarboxylic acid, CnH10N2O3, is ob- tained by heating benzenylamidoxime with succinic andydride: .N.OH CH2-CO\ c6h5.c^ + I >0 = W2 CH-COZ .N-°\ c6h5.cz >c-ch-ch2-co.oh + h2o. N = z It crystallizes from hot water in small, lustrous, white, rhombic plates or prisms, melting at 120°. The anhydrides of other dibasic acids give similar compounds.2 1 Falck, Ber. Deutsch,. Chern. Ges. xviii. 2467. 3 Schultz, ibid, xviii. 2458. 216 AROMATIC COMPOUNDS. Metanitrobenzenylamidoxime, C6H4(NO2)C(NH2)NOH. Meta- mtrobenzonitril readily combines with hydroxylamine to form this compound. It crystallizes in orange-coloured prisms, melt- ing at 174°. A series of compounds has been prepared from it, corresponding to those described above.1 Mrtamidobenzenylawddoxime, C6H4(NH2)C(NH2)NOH, is formed by the reduction of the preceding compound, and separates from ether as a yellow oil which gradually solidifies. Its hydrochloride, C6H4(NH3C1)C(NH3C1)NOH, crystallizes from hot water in prisms. Metahydroxybenzenylamidoxi^ C6H4(OH)C(NH2)NOH, has been prepared from the amido-compound by the diazo-reaction, and crystallizes from dilute alcohol in light yellow needles, melt- ing at 1630.2 HALOGEN-SUBSTITUTION PRODUCTS OF BENZOIC ACID. 2122 When an atom of hydrogen in benzoic acid is replaced by an element of the chlorine group, a meta-compound is formed, and not, as in the case of toluene and the benzyl compounds, a para-compound, accompanied by a small amount of an ortho- compound. Substituted benzoic acids are obtained by the oxidation of the corresponding alcohols and aldehydes, as well as of the substitu- tion products of toluene and such other compounds as are them- selves readily oxidized to benzoic acid. They may also be obtained from the amidobenzoic acids by means of the diazo-reaction. The old method, proposed by Griess, consisted in heating a diazo-amidobenzoic acid with hydrochloric, hydrobromic, or hydrofluoric acid : N.NH.C6H4.C0oH 11 + HC1 = nh2.c6h4.co2h + C6H4CLCO2H + n2. nc6h4.co2h He subsequently found that the sulphates of the diazobenzoic acids are more suitable for the purpose ; one part is boiled with 3 to 5 parts of the hydracid, the substituted benzoic acid 1 Schopff, Ber. Deutsch. Chem. Ges. xviii. 1063. 2 Ibid, xviii. 2472. ORTHOCHLOROBENZOIC ACID. 217 separating out on cooling as a mass of crystals. Hydriodic acid acts in this way even in the cold:1 NC6H4.CO2H II + HI = c6hj.co2h + so.h9 + n2. nso4h A reaction which possesses considerable theoretical interest has been employed for the preparation of these compounds by v. Richter. When paranitrochlorobenzene or paranitrobromobenzene is heated with alcohol and potassium cyanide, the nitroxyl group is replaced by hydrogen, and the cyanogen group takes the meta-position, the nitnl of metachloro- or metabromobenzoic acid being formed, while metanitrochlorobenzene is converted into orthochlorobenzoyl chloride. Orthonitrochlorobenzene and orthonitrobromobenzene, on the other hand, are not attacked by potassium cyanide.2 The halogen-substitution products are readily converted into benzoic acid by the action of sodium amalgam and water. Monochlorobenzoic Acids, C6H4C1.CO2H. 2122 Orthochlorobenzoic acid was obtained by Chiozzain 1852, by heating salicylic acid (orthohydroxybenzoic acid) with phos- phorus pentachloride, and decomposing the fraction of the dis- tillate boiling between 200°-250° with water.3 It was believed to be identical with the chlorobenzoic acid which is formed by the direct chlorination of benzoic acid, until Limpricht and Uslar, as well as Kolbe and Lautemann, showed that the latter compound is a distinct substance, and gave it a distinctive name, chloro- salylic acid.4 Kekule obtained the same acid in a similar manner from wintergreen oil, which consists chiefly of methyl salicylate.5 Its formation will be discussed under salicylic acid. In order to prepare it, an intimate mixture of one molecule of sodium salicylate with two molecules of phosphorus pentachloride is distilled, the portion boiling above 240° separated, and de- composed by boiling caustic soda solution, the acid being then precipitated by hydrochloric acid (Kolbe and Lautemann). The precipitate is dissolved in the smallest possible quantity of 1 Ber. Deutsch. Chem. Ges. xviii.'96O. 2 Ibid. iv. 459. 3 Ann. Chem. Pharm. Ixxxiii. 317. 4 Ibid. cxv. 183. 5 Ibid, cxvii. 145. 218 AROMATIC COMPOUNDS. boiling water and treated with a slight excess of weak milk of lime; calcium salicylate is thus formed and separates completely when the solution is well stirred and heated on the water-bath for some hours. The filtrate is precipitated with hydrochloric acid, and the orthochlorobenzoic acid purified by re-crystallization from boiling water.1 The mixture of acids can also be separated by distillation with steam, with which salicylic acid alone vola- tilizes.2 Pure salicylic acid may be substituted for the sodium salicylate.3 According to. Glutz, it is better to employ wintergreen oil, to which the phosphorus pentachloride must be gradually added, the mixture heated for a considerable time until hydrochloric acid ceases to be evolved, and then distilled and treated as above.4 Orthochlorobenzoic acid is also formed when orthochloro- toluene is boiled with a dilute solution of potassium perman- ganate.5 It dissolves in 881 parts of water at 0°, is readily soluble in hot water and alcohol, and crystallizes in long, silky needles, which melt at 137°, and sublime in lustrous crystals. It melts when heated with a little water, in the same manner as benzoic acid. When heated to 200° with caustic potash, it yields 10 per cent, of salicylic acid and 20 per cent, of meta- hydroxybenzoic acid, equal quantities being formed when caustic soda is employed (Ost). Calcium orthochlorobenzoate, (C7H4ClO2)2Ca + 2H2O, crystallizes in prisms, which are very slightly soluble in alcohol, but very readily in water. The solution of the acid in ammonia is there- fore not precipitated by calcium chloride, and it may thus be distinguished from its isom erides. Orthochlorobenzoyl chloride, C6H4C1.COC1, is obtained in the pure state by the action of phosphorus chloride on the acid. It is a heavy, powerfully refractive liquid which fumes in the air and boils at 235°-238° (Emmerling). Orthochlorobenzonitril, C6H4C1.CN, is formed by the action of phosphorus pentachloride on salicylamide, C6H4(OH)CO.NH2. It crystallizes from hot watei' or ether in white needles, which smell like benzonitril and melt at 42°--43°. It sublimes readily, 1 Beilstein and Reichenbach, Ann. Chem. Pharm. cxxxii. 311. 2 Hubner and Upmann, Zeitschr. Chem. 1870, 293. 3 Hubner and Biedermann, Ann. Chem. Pharm. cxlii. 263 ; Wilkens and Rack, ibid. ccxxii. 192. 4 Glutz, ibid, cxliii. 194 ; Ost, Jowrn. Prakt. Chem. [2] xi. 386. 5 Emmerling, Ber. Deutsch. Chem. Ges. viii. 880. METACHLOROBENZOIC ACID. 219 boils at 232°, and is converted into orthochlorobenzoic acid when heated to 150° with dilute hydrochloric acid.1 2124 Metachlordbenzoic acid. Herzog, in 1840, found that the action of chlorine upon benzoic acid produces, among other pro- ducts, a chlorinated acid resembling benzoic acid, but he did not analyze the substance.2 Scharling subsequently obtained an acid by the distillation of urine with hydrochloric acid, which had the composition of chlorobenzoic acid, and which he named chloro- michmic acid (opA/xp.a, urine),3 but, as Gmelin pointed out, it was not to be distinguished from chlorobenzoic acid.4 Stenhouse prepared the latter by treating benzoic or cinnamic acid with chlorine, bleaching powder or potassium chlorate and hydro- chloric acid, but was unable to free it from higher chlorine substitution products.5 Field, however, found that it can be obtained pure by boiling benzoic acid with potassium chlorate and hydrochloric acid, and this was confirmed by Otto.6 As already mentioned, this acid was believed to be identical with the chlorobenzoic acid prepared from salicylic acid, until Lim- pricht and Uslar showed that the acid obtained in this way is different from that obtained by treating sulphobenzoic acid with phosphorus pentachloride, and decomposing the resulting chloro- benzoyl chloride with water.7 The chlorobenzoic acids formed by these different reactions were made the subject of a close investigation by Beilstein and Schlun, which resulted in their proving the existence of three isomerides, the third of which had been obtained by Beilstein and Wilbrand from nitrodracylic acid (Part III. p. 34).8 Metachlorobenzoic acid was also obtained by Saint-Evre9 by the action of chlorine on a solution of benzoic acid in caustic potash, and was named cliloronicednic acid, C6H5C1O2. It is also formed when benzoic acid is heated with antimony chloride and the product treated with water,10 as well as by the oxidation of metachlorotoluene with chromic acid.11 In order to prepare it, potassium chlorate is gradually added to benzoic acid suspended in hydrochloric acid; the reaction, 1 Henry, Ber. Deutsch. Chern. Ges. vi. 492. 2 Brandes, Arch. Pharm. xxiii. 15. 3 Ann. Chem. Pharm. xli. 48 ; xlii. 265. 4 Handb. Org. Chem. iii. 92. 5 Phil. Mag. xxvii. 129 ; Ann. Chem. Pharm. Ixv. 55. 6 Ibid, cxxii. 142. 7 Ibid. cii. 259. 8 Ibid, cxxxiii. 293. 9 Ibid. Ixx. 257. 10 Gerhardt, Traite Chim. Org. iii. 214. 11 Wroblewsky, Ann. Chem. Pharm. clxviii. 200. 220 AROMATIC COMPOUNDS. which proceeds quietly, must be occasionally aided by gentle warming. When 26 parts of chlorate have been added to 10 parts of the acid and about 90 parts of hydrochloric acid, the mixture is heated to boiling, and the acid which separates on cooling converted into the barium salt, which is then purified by re-crystallization. According to Hubner and Weiss, it can readily be obtained and in a very pure condition by heating 7 grms. of benzoic acid to 150° with 4 grms. of manganese dioxide which has been washed with hydrochloric acid, and 40 grms. of fuming hydrochloric acid, and re-crystalling the product two or three times.1 Properties.-It dissolves at 0° in 2840 parts of water (Kolbe and Lautemann), more readily in hot water and alcohol, and crystallizes in concentrically grouped needles, which melt at 153° and readily sublime. On fusion with caustic potash it yields only metahydroxybenzoic acid 2; it does not melt under water. Calcium metachlorobenzoate, (C7H4C102)2Ca + 3H2O, forms scaly crystals, which dissolve in 82'6 parts of water at 12°. Metachlorobenzoyl chloride, C0H4C1.COC1, is a strongly refrac- tive liquid, boiling at 2250.3 Metachlorohippuric acid, C6H4C1.CO.NHCH2.CO2H, is formed together with dichlorohippuric acid by the action of potassium chlorate and hydrochloric acid on hippuric acid,4 and is found in the urine after metachlorobenzoic acid has been administered.5 It is a tough, amorphous mass, which is scarcely soluble in cold, more readily in boiling water; it forms crystalline salts. It decomposes into amido-acetic acid and metachlorobenzoic acid when boiled with concentrated hydrochloric acid. Dichlorohippuric acid, C6H3C12.CO.NH.CH2.CO2H, is less soluble in hot water than the preceding compound, and is con- verted by long contact with water into a granular crystalline mass; on boiling with hydrochloric acid it decomposes into a-dichlorobenzoic acid and amido-acetic acid. Mctachlorobenzonitril, CGH4C1.CN, was prepared by Lim- pricht and Uslar by the distillation of metasulphobenzamide, C6H4(CO.NH2)SO2.1NH2, and metasulphamidobenzoic acid, C6H4(CO2H)SO2.NH2, with phosphorus chloride. It crystallizes 1 Ber. Deutsch. Chem. Ges. vi. 175. 2 Dembey, Ann. Chem. Pharm. cxlviii. 221. 8 Limprieht and Uslar, ibid. cii. 262 ; Graebe ; ibid, cxxxviii. 197. 4 Otto, ibid, exxii. 129. 5 Ibid, exlii. 346. PARACHLOROBENZOIC ACID. 221 from alcohol in prisms, which smell like benzaldehyde, melt at 40°, and readily volatilize with steam.1 Parachlorobenzoic acid, or Chlorodracylic acid, was first obtained by Beilstein and Wilbrand from paramidobenzoic acid by the diazo-reaction.2 Beilstein and Geitner then prepared it by the oxidation of parachlorotoluene with chromic acid solution,3 while Emmerling found that it is better to employ crude chlorotoluene and a dilute solution of potassium permanganate for this pur- pose, the orthochlorobenzoic acid formed being easily removed by boiling water.4 Muller found that it is also formed when chlorobenzene is oxidized with manganese dioxide and sulphuric acid,5 a formation corresponding to that of benzoic acid from benzene. Parachlorobenzoic acid dissolves in 5288 parts of water at 10°, crystallizes from alcohol in long, lustrous needles, melts at 236° and sublimes in plates at a higher temperature. Calcium parachlorobcnzoate, (C7H4C102)2Ca + 3H2O, crystal- lizes in small plates or needles, and is even less soluble in water than the corresponding salt of the meta-acid. Parachlorobcnzoyl chloride, C6H4C1.COC1, is a heavy liquid, which fumes in the air, is strongly refractive, and boils at 220°-222° (Emmerling). Dichlorobenzoic Acids, C6H3C12.CO2H. 2125 a-Dichlorobenzoic acid, (3: 4). Otto first prepared this compound by boiling dichlorohippuric acid with hydrochloric acid ;6 it is also obtained by the oxidation of dichlorotoluene and dichlorobenzyl chloride,7 as well as when parachlorobenzoic acid is heated to 200° with antimony pentachloride.8 It is formed, together with the following compound, by heating benzoic acid with bleaching powder solution,9 or by the action of potassium chlorate and hydrochloric acid,10 metachloro- benzoic acid being, of course, the first product. It is slightly soluble in cold, more readily in hot water, and crystallizes in fine, lustrous needles, melting at 201°-202°. 1 Ann. Chem. Pharm. cvi. 32. 2 Ibid, cxxviii. 270. 3 Ibid, cxxxix. 336. 4 Ber. Deutsch. Chem. Ges. viii. 880. 5 Zeitschr. Chem. 1869, 137. 6 Ann. Chem. Pharm. cxxii. 147. 7 Beilstein and Kuhlberg, ibid. clii. 225 ; Lellmann and Klotz, ibid, ccxxxi. 308. 8 Beilstein, ibid, clxxix. 284. 9 Claus and Thiel, Ber. Deutsch. Chem. Ges. viii. 948. 10 Claus and Pfeifer, ibid. v. 658 ; vi. 721. 222 AROMATIC COMPOUNDS. ^-Dichlorobenzoic acid, (3 :6), is formed by heating ortho- chlorobenzoic acid with hydrochloric acid and potassium chlorate or potassium dichromate,1 and by replacing the amido-group of a-chloramidobenzoic acid by chlorine.2 It crystallizes in needles, which melt at 153'5° (Lellmann and Klotz) and dissolve in about 1200 parts of cold water. y-Dichlorobenzoic acid, (2 : 6), is obtained, together with the preceding compounds, when dichlorobenzyl chloride is heated with water to 200°; it crystallizes from alcohol in small needles, melting at 126'5°.3 Z-Dichlorobenzoic acid, (2 : 4), is formed by the oxidation of the corresponding dichlorotoluene with nitric acid, and crystallizes in long, pliable needles, melting at 158°. e-Dichlorobenzoic acid, (3 : 5), has also been prepared from symmetric dichlorotoluene, and forms long needles, melting at 182° (Lellmann and Klotz). Trichlorobenzoic Acids, C6H2C13.CO2H. 2126 a-Trichlorobcnzoic acid, (2:4: 6), is obtained by the oxidation of a-trichlorotoluene,4 and by heating a-trichloro- benzyl chloride5 to 260° with water; it crystallizes in needles which melt at 163°. ft-TriMorobenzoic acid has been obtained from the corre- sponding aldehyde by oxidation with potassium permanganate ; it melts at 129°.6 Trichlorobcnzoic acid, (3:4: 5), is formed when chrysanisic acid, C6H2(NO2)2(NH2)CO2H, is heated with fuming nitric acid. It forms fine needles, melting at 203°.7 Tetrachloeo benzoic Acid, C6HC14.CO2H. Beilstein and Kuhlberg prepared this compound by heating tetrachlorobenzyl chloride with water to 280°; it melts at 187°. 1 Beilstein, Ann. Chern. Pharm. clxxix. 285. 2 Rack and Wilkens, ibid, ccxxii. 201. 3 Schultz, ibid, clxxxvii. 269. 4 Jannasch, ibid, cxlii. 301 6 Beilstein and Kuhlberg, Ber. Deutsch. Chern. Ges. xviii. 420. 6 Seelig, ibid, xviii. 420. 7 Salkowski, Ann. Chern. Pharm. clxiii. 28. THE MONOBROMOBENZOIC ACIDS. 223 Monobromobenzoic Acids, C6H4Br.CO2H. 2127 Orthobromobcnzoic acid was first prepared by Griess from anthranilic acid or ortho-amidobenzoic acid by the diazo- reaction, but was not further investigated by him.1 It was, how- ever, examined by v. Richter, who found it to bo identical with that which he had obtained from metabromonitrobenzene by means of the reaction already mentioned (p. 217).2 Zincke obtained it by boiling orthobromotoluene with dilute nitric acid;3 it is, however, better to employ a dilute solution of potassium permanganate.4 It is more readily soluble in cold water than its isomerides, and is still more soluble in hot water, from which it crystallizes in long needles, which melt at 150° and sublime in small plates. Barium orthobromobenzoate, (C7H4BrO2)2Ba, is very readily soluble in water, and crystallizes from alcohol in long needles containing two molecules of alcohol. Metabromobenzoic acid. Peligot obtained this substance in the year 1838 by the action of bromine on silver benzoate,5 and Herzog, in 1842, by acting upon benzoic acid with bromine in the sunlight.6 The compound thus prepared, however, was not pure. Reinecke then found that the pure compound can readily be obtained by heating benzoic acid to 100° with bromine and water;7 it may also be prepared in this manner from benzamide, the reaction taking place at 120°,8 and bromanil being formed at the same time: C6H5.CO.NH2+Br2+H20 = C6H4Br.CO2H + NH4Br. According to Hubner and Angerstein, it can also be prepared by Peligot's method, if dry silver benzoate be submitted to the action of bromine vapour in the sunlight.9 Griess also obtained it from metamidobenzoic acid10 and Sandmeyer from meta- bromaniline, which he diazotized and brought into a solution of potassium cuprous bromide heated to 90°; thenitril, which was 1 Ann. Chern. Pharm. cxxxv. 121. 2 Bcr. Deutsch. Chern. Ges. iv. 464 ; v. 428. 3 Ibid. vii. 1502. 4 Rhalis, Ann. Chem. Pharm. cxcviii. 102. 6 Ibid, xxviii. 246. 6 Brandes, Arch. Pharm. xxiii. 16. 7 Zeitschr. Chem. 1865, 116; 1869, 100. 8 Friedberg, Ann. Chem. Pharm. clviii. 26. 9 Ibid, clviii. 2. 10 Ibid, cxvii. 25. 224 AROMATIC COMPOUNDS. thus formed, was then decomposed by boiling soda-solution;1 Wroblewsky prepared it by the oxidation of metabromotoluene.2 Metabromobenzoic acid is very slightly soluble in water, readily in alcohol, crystallizes in needles, melts at 155°, sublimes at a higher temperature and boils above 280°. On fusion with caustic potash, metahydroxybenzoic acid is formed together with a little salicylic acid, and, probably, some parahydroxy benzoid acid. Barium metdbromdbenzoatc, (C7H4BrO2)2Ba + 4H2O, is very slightly soluble in water and crystallizes in small, flat needles. Parabromobenzoic acid was first obtained by Griess from par- amidobenzoic acid.3 It is formed by the oxidation of parabromo- toluene,4 parabromo-ethylbenzene,5 etc., with dilute nitric acid or chromic acid, and may also be obtained from parabromaniline by means of Weith's reaction (Part III. p. 31).6 It is almost insoluble in cold water, and only slightly soluble in boiling water, from which it crystallizes in small plates. It is readily soluble in alcohol and ether, and separates from them in small needles, melting at 251°. Barium parabromobenzoate, (C7H4BrO2)2Ba, crystallizes in nacreous plates, which are readily soluble in water. Dibromobenzoic Acids, C6H3Br2CO2H. Br. : Br. Melting-point. a) 3:4 small needles,7 . . . . , . 229-230° /?) 2 : 3 small needles,8 . . . . . . 147° 7) 3 : 5 flat needles,9 . . . . . . 213°-214° 8) 2 : 5 flat needles,10 . . . . . 153° e) 2 : 4 needles or tablets,11 . , . . 168°-170° 1 Ber. Deutsch. Chern. Ges. xviii. 1495. 2 Ann. Chem. Pharm. clxviii. 156. 3 Ibid, cxxxv. 121. 4 Hubner, Ohly and Philipp, ibid, exliii. 247. 5 Fittig and Kbnig, ibid, cxliv. 283. 6 Weith and Landolt, Ber. Deutsch. Chem. Ges. viii. 717. 7 Burghardt and Beutnagel, Ann. Chem. Pharm. ccxxii. 184. 8 Beutnagel, ibid, ccxxii. 105. 9 Beilstein and Geitner, ibid, cxxxix. 4 ; Neville and Winther, Ber. Deutsch. Chem. Ges. xiii. 970. 10 Holzapfel, Ann. Chem. Pharm. ccxxii. 107. 11 Neville and Winther, loc. cit. iodobenzoic acids. 225 Tribromobenzoic Acids, C6H2Br3.CO2H. Melting-point. a) silky needles 1 234°-235' /3) small needles2 195° 7) needles3 186'5° 8) needles4 178° Pentabromobenzoic acid, C6Br5.CO2H. When metabromo- benzoic acid is heated to 150° with bromine and water, a-tribromobenzoic acid is formed, and on further heating with bromine at 200° is converted into pentabromobenzoic acid. It crystallizes from alcohol in thin plates or long, broad needles which become brown and melt at 234°-235° (Reinecke). Mono-iodobenzoic Acids, C6H4I.CO2H. 2128 Ortho-iodobenzoic acid was obtained by Griess and Richter from anthranilic acid, and by the latter also from meta-iodo- nitrobenzene. Kekule prepared it by the oxidation of ortho- iodotoluene with dilute nitric acid. It is slightly soluble in water, readily in alcohol, and crystallizes in long, white needles, which melt at 157° and readily sublime. On fusion with potash, salicylic acid is formed. Meta-iodobenzoic acid has been prepared by Griess, Lunge, and Hubner, and by Grothe from metamidobenzoic acid. It is also formed when benzoic acid is heated with potassium iodate and dilute sulphuric acid, and by the action of iodine and iodic acid on sodium benzoate. It forms small plates or needles, melting at 186°-187°; on heating with caustic potash solution it is con- verted into metahydroxybenzoic acid, and with ammonia into metamidobenzoic acid. Para-iodobenzoic acid was obtained by Griess5 from par- amidobenzoic acid, and by Korner6 by the oxidation of para- iodotoluene. It crystallizes in small plates melting at 256°.7 1 Reinecke, Zeitschr. Chem. 1869, 110. 2 Smith, Ber. Deutsch. Chem. Ges. x. 1706. 3 Volbrecht, ibid. x. 1708. 4 Lawrie, ibid. x. 1705. 5 Ber. Deutsch. Chem. Ges. iv. 522. 6 Zeitschr. Chem. 1868, 327. 7 Schmidt and Schultz, Ann. Chem. Pharm. ccvii. 333. 226 AROMATIC COMPOUNDS. According to Beran it cannot be obtained perfectly pure by recrystallization, but must be sublimed, plates which melt at 265°-266°1 being obtained in this way. Monofluorbenzoic Acids, C6H4F.CO2H. 2129 These compounds are obtained by passing nitrogen trioxide into solutions of the amidobenzoic acids in alcohol, a diazo-amidobenzoic acid being formed, which is decomposed into fluorbenzoic acid and amidobenzoic acid hydrofluoride on warming with fuming hydrofluoric acid :2 N.CcH4.CO2H 11 + hf=c6h4f.co9h+nh2.c6h4.co9h+n2. n.nh.c6h4.co9h They can be still more simply obtained from the diazobenzoic acid sulphates (p. 260). As much as 5 grms. of these compounds may be administered daily to a dog without injuring it; they appear in the urine as the fluorhippuric acids,3 C9H8FNO3, which crystallize in needles or prisms. Orthoflicorbcnzoic acid crystallizes in fine needles, is readily soluble in alcohol, more readily in water, and melts at 117°- 118°. Orthofluorhippuric acid melts at 121'5°. Metafluorbenzoic acid crystallizes from hot water in broad, lustrous plates or needles, which resemble those of benzoic acid and melt at 123°-124°. Metafluorhippuric acid melts at 152°-153°. Parafluorbenzoic acid resembles the meta-compound, and melts at 180°'-181°. This substance was first prepared by Schmitt and v. Gehren from ordinary amidobenzoic acid, and was there- fore looked upon as metafluorbenzoic acid. The amido-acid employed probably contained the para-compound as an im- purity. The fluorbenzoic acid crystallizes, according to their account, in pointed rhombic prisms, which have a characteristic sweet taste, and melt at 182°. On distillation with lime it yields phenol, which was mistaken by Schmitt and v. Gehren for fluor- 1 Ber. Deutsch.Chern. Ges. xviii. 137. 2 Schmitt and v. Gehren, Journ. Prakt. Chem. [2] i. 394 ; Paterno and Oliveri, Gaz. Chim. 1882, 95. 3 Coppola, ibid. xiii. 521. THE NITROBENZOIC ACIDS. 227 benzene ; a high boiling compound is also formed, which probably consists chiefly of diphenyl oxide :1 (CeH4F.CO2)2Ca 4- 2Ca(OH)2 = 2C6H5.OH + CaF2 + 2CaCO3. Parafluorhippuric acid melts at 161'5°. Difluorbenzoic acid, C6H3F2.CO2H, is formed, together with chromic fluoride, when benzoic acid is treated with chromium hexfluoride. It is scarcely soluble in cold, only slightly in boil- ing water, but more readily in hot benzene, and sublimes less readily than benzoic acid, in flat, white needles, melting at 232°. Calcium difluorbenzoate, (C6H3F2.CO2)2Ca + 3H.,O, crystallizes from hot water in fascicular aggregates of white, lustrous needles, which dissolve in 200 parts of water at 15°.2 NITRO-SUBSTITUTION PRODUCTS OF BENZOIC ACID. 2130 In the year 1839, Plantamour obtained an acid very rich in oxygen by the action of nitric acid on cinnamic acid, benzalde- hyde being also formed. He gave no name to the new substance, since he wished to ascertain by investigation whether it could be classed along with any known acid. Analysis led to the formula C13H10O9, and this formula was confirmed by the composition of the silver salt.3 In the next year, Mulder found that nitrobenzinic acid is formed by the action of nitric acid on benzoic acid, cinnamic acid and oil of cinnamon. He determined the correct com- position of the compound and formulated it as C14H8O4 + N2O3 + H2O, according to which it is a compound of nitrous acid with an organic substance containing two atoms of hydrogen less, and one atom of oxygen more than benzoic acid. He also found it to be identical with the acid discovered by Plantamour, who had overlooked the presence of nitrogen.4 The same acid was prepared by Blyth and Hofmann by the distillation of styrolene (phenylethylene) with strong nitric acid.5 1 Paterno and Oliveri, Gaz. Chim. xiii. 533. 2 Jackson and Hartshorn, Ber. Deutsch. Chem. Ges. xviii. 1993. 3 Ann. Chem. Pharm. xxx. 348. 4 Ibid, xxxiv. 297. 3 Ibid. liii. 304. 228 AROMATIC COMPOUNDS. Abel detected it among the products of the action of nitric acid on cumene (isopropylbenzene),1 and Blumenau obtained it in the same way from dragon's blood.2 The acid formed by the nitration of benzoic acid was then investigated by Zinin,3 Gerland,4 Voit5 and Ernst,6 the three last-mentioned giving directions for its preparation. Glenard and Boudault had, in 1843, obtained nitrodracylic acid, C8H6(NO2)O2, by the action of fuming nitric acid on the dracyl (toluene) obtained from dragon's blood, and Gerhardt considered it to be nitrobenzoic acid.7 Wilbrand and Beilstein showed, however, that it is not identical, but isomeric with the latter, and that another acid is formed in small quantity, which appears to be ordinary nitrobenzoic acid.8 It was ob- tained about the same time by Fischer, who named it para- nitrobenzoic acid,9 while that derived from benzoic acid was known as orthonitrobenzoic acid until it was recognized as oelonging to the meta-series (Part III., p. 41). The third isomeride, now known as orthonitrobenzoic acid, was first prepared by Radziswesky from phenylacetic acid, but was believed to be ordinary nitrobenzoic acid.10 Beilstein and Kuhlberg then prepared the ortho-acid from cinnamic acid (phenylacrylic acid),11 and considered it as identical with Radziswesky's compound, this being confirmed by Pirogow.12 Griess was the first to recognize the fact that not only metanitrobenzoic acid, but also its two isomerides are formed by the nitration of benzoic acid; from 4,000 grms. of benzoic acid he obtained, in addition to the chief product, 347 grms. of orthonitrobenzoic acid and 35 grms. of paranitrobenzoic acid,13 while according to Widnmann, the ortho-acid formed amounts to 25 per cent, of the weight of benzoic acid employed.14 The older investigators had all the three nitrobenzoic acids under their obser- vation, but their purest compounds were probably specimens in which one or other of the isomerides simply predominated. This is shown by the following facts; toluene, cumene, styrolene, oil of cinnamon and cinnamic acid are oxidized by dilute nitric acid 1 Ann. Chern. Pharm. Ixiii. 308. 2 Ibid. Ixvii. 313. 3 Journ. Prakt. Cbm. xxxvi. 93. 4 Ann. Chern. Pharm. Ixxxvi. 143 ; xci. 185. 5 Ibid. xcix. 100. 6 Zeitschr. Chern. 1860, 477. 7 Ann. Chern. Pharm. xlviii. 343. 8 Ibid, cxxvi. 255 ; cxxviii. 257. 9 Fischer, ibid, cxxvii. 137. 10 Ber. Deutsch. Chern. Ges. iii. 648. 11 Ann. Chern. Pharm. clxiii. 121. 12 Ibid, clxiii. 140. 13 Ibid, clxvi. 129 ; Ber. Deutsch. Chern. Ges. x. 1868. 34 Ann. Chern. Pharm. cxcliii. 223. ORTHONITROBENZOIC ACID. 229 to benzoic acid, which is converted by the concentrated acid into the nitrobenzoic acids. Toluene is converted by strong nitric acid into the three isomeric nitrotoluenes, the chief product being the para-compound, the meta-compound being only formed in small quantity (p. 15), while on the nitration of benzoic acid, the meta-acid forms the chief product, and the para- compound only occurs in small quantity. Concentrated nitric acid converts cinnamic acid, and probably styrolene and cumene, into para- and ortho-nitro-compounds, the meta-compound being possibly formed in small quantity. All these nitro- derivatives of the hydrocarbons, as well as the nitro-cinnamic acids, yield the corresponding nitrobenzoic acids on oxidation. Which of these predominated, therefore, in the mixtures in question, depended, in the first instance, upon the concentration of the nitric acid employed. The nitrobenzoic acid obtained from cinnamic acid and styrolene was probably a mixture of the para- and ortho-acids, and this would also be the composition of that obtained from dragon's blood and cumene by the aid of fuming nitric acid. These mixtures may, however, have also contained dinitrobenzoic acids and styphnic acid, both of which are formed by the action of nitric acid on benzoic acid. Mononitrobenzoic Acids, CeH4(NO2)CO2H. 2131 Orthonitrobenzoic acid. In order to prepare this com- pound, the mixture obtained by the nitration of benzoic acid is converted into the barium salts, from which the barium ortho- nitrobenzoate can readily be obtained in crystals, which are then decomposed by dilute sulphuric acid.1 Orthonitrobenzoic acid can also be readily obtained by boiling orthonitrotoluene for a long time with a solution of potassium permanganate.2 Crude nitrotoluene may also be employed since the larger portion of the slightly soluble paranitrobenzoic acid can easily be separated. The barium salts are prepared from the mother-liquors of this and separated as described below.3 Orthonitrobenzoic acid dissolves in 100 parts of water at 16'5°; it is more readily soluble in hot water and crystallizes from it in large colourless needles. It is obtained in asymmetric tablets 1 Widnmann, Ann. Chern. Pharm. cxciii. 202. 2 Widnmann, Ber. Deutsch. Chem. Ges. viii. 392 3 Monnet, Reverdin and Nolting, ibid. xii. 443. 230 AROMATIC COMPOUNDS. or prisms by the spontaneous evaporation of its alcoholic solution. It melts at 147°, and has an intensely sweet taste, which also characterizes its salts. Barium orthonitrobenzoate, (C6H4.NO2.CO2)2Ba + 3H2O, crys- tallizes on the spontaneous evaporation of its solution in water, in which it is more readily soluble than the acid, in large, yellow, asymmetric tablets, which lose their water over sulphuric acid. Bthyl orthonitrobcnzoatc, C6H4(NO2)CO2.C2H5, forms asym- metric crystals, melting at 30°. Orthonitrobcnzoyl chloride, C6H4(NO2)COC1, is a faint yellow liquid, which solidifies at a low temperature to a crystalline mass, and decomposes on heating. When heated with silver cyanide, the nitril of nitrophenylglyoxylic acid is formed, and this is converted by reduction into isatin, an oxidation product of indigo.1 Orthonitrobenzonitril, C6H4(NO2)CN. By the action of am- monia on orthonitrobenzoyl chloride, orthonitrobenzamide, C6H4(NO2)CO.NH.„ is formed, and crystallizes in long needles, melting at 174°; it is converted into the nitril on heating with phosphorus pentoxide.2 The latter may also be obtained syn- thetically from orthonitraniline by diazotizing it with hydro- chloric acid and sodium nitrite, and bringing the compound thus obtained into an almost boiling solution of copper sulphate and potassium cyanide :3 2C6H4(NO2)N2C1 + Cu2(CN)2 = 2C6H4(NO2)CN + N2+ Cu2Cl2. It crystallizes in needles which are readily soluble in alcohol and hot water, melt at 109°, and sublime when more strongly heated. 2132 Metanitrobenzoic acid is best obtained by bringing an in- timate mixture of one part of previously fused and finely powdered benzoic acid with two parts of nitre into three or four parts of sulphuric acid, the mixture being well stirred, and then heating until the nitrobenzoic acids have separated out as an oily layer.4 In a well-conducted operation these contain little or no unaltered benzoic acid. Should this be present in large quantity, it is 1 Claissen and Shadwell, Ber. Deutsch. Chern. Ges. xii. 350. 2 Barthlein, ibid. x. 1713. 3 Sandmeyer, ibid, xviii. 1492. 4 Ernst, loc. eit. ; Leo Liebermann, Ber. Deutsch. Ghent. Ges. x. 862 ; Widn- mann, Ann. Chern. Pharm. cxciii. 216. METANITROBENZOIC ACID. 231 removed by distillation with water, and the product then heated to boiling with 20 parts of water and neutralized with barium hydroxide. Barium metanitrobenzoate crystallizes out on cool- ing. The mother liquor is evaporated and the residue repeatedly extracted with small quantities of cold water, the salt of the ortho-acid being obtained on the evaporation of the solution. A further crop of crystals of the meta-compound are obtained by dissolving the residue in 20 parts of boiling water and cooling the solution, the barium salts of paranitrobenzoic acid, benzoic acid and styphnic acid remaining in solution. Metanitrobenzoic acid dissolves at 16'5° in 425, and at 100° in 10 parts of water; on cooling it separates from the solution in small plates ; it crystallizes from dilute alcohol in monoclinic tablets, melting at 140°-141°; when gradually cooled the melting-point falls to 135°-136°, but rises again after some time, or when the remelted acid is allowed to cool rapidly (Widnmann). It possesses the characteristic property of melting under hot water; it commences to sublime at temperatures above 100°, and its vapour provokes coughing. Sodium metanitrobenzoate, C6H4(NO2)CO2Na 4- 3H2O, crystal- lizes in coarse, colourless or yellowish tablets, and may te employed for the purification of the crude acid.1 Barium metanitrobenzoate, (C6H4.NO2.CO2)2Ba + 4H2O, crys- tallizes in thin prisms, and is less soluble than the free acid. Ethyl metanitrobenzoate, C6H4(NO2)CO2.C2H5, has been pre- pared by the action of hydrochloric acid on an alcoholic solution of the acid, by that of alcohol on its chloride, and by the nitra- tion of ethyl benzoate. It is also formed when ethyl nitrate and benzoic acid in ethereal solution are treated with sulphuric acid.2 It crystallizes in monoclinic prisms, which melt at 41° and have an aromatic smell, boils at 298°, and decomposes into ethylene bromide and metanitrobenzoic acid when heated to 170°-200° with bromine.3 Metanitrobenzoyl chloride, C6H4(NO2)COC1, crystallizes in pyramids with a diamond lustre or in long, fine prisms, which melt at 33°-34°4 and smell like benzoyl chloride. Metanitrobenzamide, C6H4(NO2)CO.NH2, forms yellow, mono- clinic needles, and melts at 140°-142°. 1 Hiibner, Ann. Chern. Pharm. ccxxii. 72. 2 Fittica, Journ. Prakt. Chem. [2] xvii. 221. 3 Naumann, Ann. Chem. Pharm. cxxxiii. 202. 4 Claissen and Thompson, Ber. Deutsch. Chem. Ges. xii, 1943. 232 AROMATIC COMPOUNDS. Mctanitrohippuric acid, C6H4(NO2)CO.NH.CH2.CO2H. Ber- tagnini obtained this compound in the year 1851 by taking 6 grms. of nitrobenzoic acid daily and isolating the nitrohippuric acid from his very acid urine. He also prepared it by adding sulphuric acid to a solution of hippuric acid in cold, fuming nitric acid. It crystallizes from alcohol in silky needles, melting at 162°. It is decomposed by boiling fuming hydrochloric acid into glycocoll and nitrobenzoic acid.1 Mctanitrobcnzonitril, C6H4(NO2)CN, is formed by the action of phosphorus pentoxide or phosphorus chloride on the amide, as well as by the nitration of benzonitril and, synthetically, from metanitraniline in a similar manner to the ortho-compound. It crystallizes in needles, melting at 117°-118°.2 2133 Paranitrobenzoic acid is prepared by the oxidation of paranitrotoluene with strong nitric acid (Beilstein and Wilbrand; Fischer), with potassium dichromate and dilute sulphuric acid 3 or with potassium permanganate.4 It dissolves in 1200 parts of water at 17°, and in 140 parts at 100° without melting, is more readily soluble in alcohol and crystallizes in yellowish white, lustrous plates, which melt at 238° and sublime in needles. Barium paranitrobenzoate, (C6H4.NO2.CO2)2Ba + 5H2O, crys- tallizes in yellow, transparent, monoclinic prisms, which dissolve in 250 parts of cold and 8 parts of boiling water. It forms an anhydrous double salt with barium benzoate, (C6H5.CO2)2Ba 4- (C6H4.NO2.CO2)2Ba, which crystallizes in large, colourless or brownish, lenticular aggregates. The calcium salt and calcium metanitrobenzoate both form double salts with calcium benzoate.5 JEthyl paranitrobenzoate, C6H4(NO2)CO2.C2H5, forms assymetric plates, which melt at 57°, and are converted by heating with ammonia into paranitrobenzamide, C6H4(NO2)CO.NH2, which crystallizes in needles melting at 197°-198°. Paranitrobenzoyl chloride, C6H4(NO2)COC1, boils at 202°- 205° under a pressure of 105 mm., and crystallizes from petro- leum spirit in fine needles, melting at 75°.6 1 Ann. Chem. Pharm. Ixxviii. 100 ; Schwanert, ibid. cxii. 69 ; Conrad. Journ. Prakt. Chem. [2] xv. 254. 2 Beilstein, Ann. Chem. Pharm. cxlvi. 336 ; Engler, ibid, cxlix. 297 ; Schoppf, Ber. Deutsch. Chem. Ges. xviii. 1063. 3 Beilstein and Geitner, Ann. Chem. Pharm. cxxxix. 335 ; Korner, Zeitschr. Chem. 1869, 635 ; Rosenstiehl, ibid. 1869, 701. 4 Michael and Norton, Ber. Deutsch. Chem. Ges. x. 580. 5 Salkowsky, ibid. ix. 24 ; x. 1257. 6 Gevekoht, Ann. Chem. Pharm. ccxxi. 335. PARANITROHIPPURIC ACID. 233 Paranitrobenzonitril, C6H4(NO2)CN, is obtained by heating the amide with phosphorus pentoxide,1 as well as by diazotizing paranitraniline and pouring the solution into a well agitated solution of potassium cuprous cyanide in potassium cyanide, heated to 9O0.2 It crystallizes from alcohol in plates, and sublimes on heating in long, feathery crystals, melting at 147°. Paranitrohippurie acid, C6H4(NO2)CO.NH.CH2.CO2H, is formed, together with paranitrobenzoic acid, by the passage of paranitrotoluene through the system in the dog, and is found in the urine combined with urea. It crystallizes from hot water in orange-red prisms, melting at 129°.3 So-called, isomerides of the three nitrobenzoic acids. It was early stated by Mills that four mononitrobenzoic acids exist, and Fittica thought that he had prepared five new isomerides, differing from the three already mentioned in their melting points, three of them being also distinguished by their citron- yellow colour. He obtained these substances " by peculiar methods, which chiefly consisted in avoiding with the greatest care all trustworthy modes of purification," 4 but the researches of others have shown that his compounds do not exist.5 The melting points and physical properties of the nitrobenzoic acids, like those of benzoic acid itself, are greatly altered by very small quantities of admixed impurities; when benzoic acid is nitrated, small amounts of the dinitrobenzoic acids are always formed in addition to the three mononitrobenzoic acids, and the product also contains benzoic acid and styphnic acid (trini- troresorcinol), the latter of which gives it its yellow colour. Bodewig found that three of Fittica's new acids are simply impure forms of metanitrobenzoic acid, which he obtained from them by crystallization; the two others gave no measurable crystals ; he also observed that this acid, besides its stable form, exists in two unstable modifications, which also crystallize in the monoclinic system, but differ from the stable form in their crystallographic constants. Their crystals soon become opaque, from the formation of the stable form, a change which takes place in one of the unstable modifications even when its crystals are allowed to remain in the mother liquor. He further 1 Fricke, Ber. Deutsch. Chern. Ges. vii. 1322. 2 Sandmeyer, ibid, xviii. 1492. 3 Jaffe, ibid. vii. 1673. 4 Kekule, Lehrb. Org. Chem. iii. 554. 5 Erlenmeyer and Widnmann, Ber. Deutsch. Chem. Ges. viii. 392 ; Griess, ibid. viii. 526 ; Ladenburg, ibid. viii. 535 and 853 ; Salkowsky, ibid. viii. 636 : Liebermann, ibid. x. 1036 ; Claus, ibid. xiii. 891 ; Fittica, ibid. xiii. 1537. 234 AROMATIC COMPOUNDS. proved their identity by converting them into the ethyl ether.1 Fittica's acids, therefore, have no more real existence than salylic acid (p. 158). Dinitrobenzoic Acids, C6H3(NO2)3CO2H. 2134 The appended numbers indicate the position of the nitro xy Is when that of the carboxyls is 1. a-Dinitrobenzoic acid, (2 : 5), was obtained by Griess, together with the two following and styphnic acid, by heating one part of orthonitrobenzoic acid with ten parts of a mixture of equal amounts of fuming sulphuric and nitric acids.2 It is slightly soluble in cold water, and on evaporation separates out in prisms; it is deposited from the hot saturated solution as a yellowish oil, which solidifies in needles, melting at 177°. It is reduced to a-diamidobenzoic acid by tin and hydrochloric acid. Baritam a-dinitrobenzoate, (CeH3(NO2)2CO2)2Ba + 4H2O, forms long, six-sided plates, which are slightly soluble in cold, more readily in hot water. ft-Dinitrobenzoic acid, (2 : 4), is also formed by the oxidation of ordinary dinitrotoluene with fuming nitric acid,3 and by the nitration of paranitrobenzoic acid.4 It melts in hot water and crystallizes from it in long, lustrous, brittle needles, or on spon- taneous evaporation in large, rhombic tablets or prisms, which melt at 179° and have a bitter taste. Tin and hydrochloric acid convert it into metadiamidobenzene, carbon dioxide being eliminated. Barium ft-dinitrobenzoate, (C6H3(NO2)2CO2)2Ba + 3H2O, is tolerably soluble in cold water and crystallizes in white, rhombic, or six-sided tablets. y-Dinitrobenzoic acid, (2 : 6), is very freely soluble in boiling water, crystallizes in fine, matted, white needles, melts at 202°, and, like its isomerides, has a very bitter taste. It decomposes on distillation into carbon dioxide and metadinitrobenzene, and on reduction yields metadiamidobenzene. Barium y-dinitrobenzoate, (C6H3(NO2)2CO2\Ba + 2H2O, is very readily soluble in water and crystallizes in needles. 1 Bar. Deutsch. Chem. Ges. xii. 1983 ; Zeitschr. Kryst. iv. 58. 2 Ber. Deutsch. Chem. Ges. vii. 1223. 3 Tiemann and Judson, ibid. iii. 223 ; Wurster, ibid. vii. 148. 4 Claus and Halberstadt, ibid. xiii. 815 ; Stromeyer, Ann. Chem. Pharm. ccxxii. 79. THE DINITROBENZOIC ACIDS. 235 Z-Dinitrobenzoic acid, (3 : 5), or Ordinary dinitrobenzoic acid, was first prepared by Cahours :1 it is obtained by heating ben- zoic acid 2 or metanitrobenzoic acid 3 with a mixture of nitric and sulphuric acids, or by oxidizing symmetric dinitrotoluene with chromic acid 4 or nitric acid (Hubner). In order to prepare it, 20 grms. of benzoic acid are dissolved in 180 grms. of concentrated sulphuric acid, one-third of the volume of fuming nitric acid added, and the whole heated nearly to boiling for four hours and then poured into two volumes of cold water ; a yield of 30 grms is obtained.5 It crystallizes from hot water in thin, quadratic tablets, and from alcohol in prisms, which melt at 204°-205°, and sublime in needles. On reduction it yields S-diamidobenzoic acid. Its salts detonate violently when heated. Barium Z-dinitrobenzoate, (CGH3(NO2)2CO2)2Ba + H2O, forms small crystals, readily soluble in hot water (Hubner). e-Dinitrobenzoic acid, (3 : 4), is formed at the same time as the /3-acid by the action of a mixture of nitric and sulphuric acids on paranitrobenzoic acid. It has an intensely bitter taste, is only slightly soluble in cold water, fuses under hot water and crystallizes from it in stellate groups, melting at 161°. These crystals sublime at a higher temperature, and detonate violently when heated on platinum foil.6 Barium e-dinitrobenzoate, (C6H3(NO2)2CO2)2Ba + 4H2O, forms a white, radiating crystalline mass. Trinitrobenzoic Acid, C6H2(NO2)3CO2H. 2135 This compound is obtained by heating trinitrotoluene to 100° with fuming nitric acid for a week. It crystallizes from hot water in rhombic prisms, melts at 190° and sublimes at a higher temperature.7 1 Ann. Chern. Pharm. Ixix. 241. 2 Michler, ibid, clxxv. 152. 3 Muretow, Zeitschr. Chern. 1870, 641. 4 Stadel, Ber. Deutsch. Chem. Ges. xiv. 902. 5 Hubner, Ann. Chem. Pharm. ccxxii. 72. 6 Claus and Halberstadt, Ann. Chem. Pharm. xiii. 815. 7 Tiemann and Judson, ibid. iii. 224. 236 AROMATIC COMPOUNDS. Chloronitrobenzoic Acids, C6H3C1(NO2)CO2H. Cl: N02 Melting-point. a) 2:5 silky needles or rhombic tablets1 . . 164°-165° /3) 3:6 prisms2 137°-138° 7) 3:2 long, thin needles or six-sided tablets 3 235° 8) 3:5 small needles4 147° e) 4:3 small needles5 179°-180° 2:4 readily soluble crystals 6 136°-137° The first three of these acids have been obtained by the nitration'of ortho- and meta-chlorobenzoic acid. The fourth acid is prepared from the corresponding amidonitrobenzoic acid and the fifth by the nitration of parachlorobenzoic acid; this compound and the last have also been obtained by the oxida- tion of the corresponding chloronitrotoluenes. Since the £-acid melts at the same temperature as the /3-acid, they were considered to be identical, but this is not the case, as the £-acid is derived from paranitrotoluene, and can be converted into orthochlorobenzoic acid. Bromonitrobenzoic Acids, C6H3Br(NO2)CO2H. a) Br: N02 Melting-point. 177°-178° 2:5 long needles 7 ft 3 6 monoclinic prisms 8 140°-140° 7) 3 : 2 monoclinic crystals 9 250° $ 4:3 small plates or needles10 199° <0 3:5 long needles or thin, six-sided tablets11 161° 2:4 long needles 12 163°-164° 1 Kekule, Ann. Chern. Pharm. cxvii. 135; Hiibner, Zeitschr. Chern. 1886, 614 ; Hubner and Biedermann, Ann. Chem. Pharm. cxlvii. 263 ; Wilkens and Rack, ibid, ecxxii. 192. 2 Ulrich, ibid, ccxxii. 95. 3 Tbid. 4 Grube, Ber. Deutsch.. Chem. Ges. x. 1703. 5 Hiibner and Biedermann ; Raveill, Ann. Chem. Pharm. ccxxii. 182. 6 Wachendorff, ibid, clxxxv. 275. 7 Burghard, Ber. Deutsch. Chem. Ges. viii. 560 ; Rahlis, Ann. Chem. Pharm. cxcviii. 109; Seheufelen, ibid, ccxxxi. 181. 8 Hiibner, Ohly and Philipp, ibid, cxliii. 233 ; Hubner and Meeker, Zeitschr. Chem. 1867, 565 ; Hubner and Petermann, Ann. Chem. Pharm. exlix. 132 ; ccxxii 101. 9 Ibid. 10 Ibid. ; Raveill, Ber. Deutsch. Chem. Ges. x. 1707 ; Ann. Chem. Pharm. ccxxii. 177 ; Seheufelen. 11 Hesemann and Kohler, ibid, ccxxii. 166. 12 Seheufelen. ORTHO-AMIDOBENZOIC ACID. 237 The first is formed by the nitration of orthobromobenzoic acid, as well as by the oxidation of the corresponding bromo- nitrotoluene, and yields 3-dibromobenzoic acid when the nitroxyl is replaced by bromine. The following two have been prepared from metabromobenzoic acid and are converted into anthranilic acid by reduction (Part III., p. 50). The 3-acid is obtained from parabromobenzoic acid and from metanitrobromo- toluene, the e-acid from the corresponding amidonitrobenzoic acid, and the £-acid by the oxidation of the corresponding bromonitrotoluene. Iodonitrobenzoic Acids, C6H3I(NO2)CO2H. I:NO2 Melting-point a) 3:2 slightly soluble crystals1 235° ft 3:6 readily soluble, melts under water 2 . . . 179° 7) 3:4 readily soluble, does not melt under water3 192° 4 : 3 readily soluble in alcohol, very slightly in water4 210° The first three are formed by the nitration of meta-iodobenzoic acid, and the last one from para-iodobenzoic acid. MONAMIDOBENZOIC ACIDS, C6H4(NH2)CO2H. 2136 Ortho-amidobenzoic acid. Fritzsche, in his research on aniline, mentioned that the product of the first action of potash on indigo is a characteristic acid, which he subsequently obtained pure by employing indigo-blue in the place of crude indigo. He determined its composition, and his results were confirmed by the remarkable decomposition which occurred on heating. "Anthranilic acid decomposes when it is heated to a tempera- ture just exceeding its melting-point into carbon dioxide, which is given off as a gas, and aniline." 5 Liebig looked upon this research as of exceptional interest, and its confirmation appeared to him to be so important and 1 Cunze and Hiibner, ibid. cxxxv. 106 ; Grothe, Journ. Prakt. Chem. [2] xviii. 324. 2 Ibid. 3 Ibid. 4 Glassner, Ber. Deutsch. Chem. Ges. viii. 562. 5 Journ. Prakt. Chem. xxiii. 67 ; Ann. Chem. Pharm. xxxix. 76. 238 AROMATIC COMPOUNDS. necessary, that lie instituted further investigations, which cor- roborated the results obtained by Fritsche.1 At the same time he discovered an excellent method for the preparation of anthranilic acid, which will be described below. Gerland subsequently showed that the acid in question is isomeric with benzamic acid (metamidobenzoic acid).2 Hubner and Petermann succeeded in preparing anthranilic acid syn- thetically from benzoic acid ; by the nitration of metabromo- benzoic acid, they obtained two isomeric nitrobromobenzoic acids, C6H3Br(NO2)CO2H, both of which yielded anthranilic acid on reduction (Part III., p. 50). It may be more simply obtained by the reduction of ortbonitrobcnzoic acid with tin and hydrochloric acid;3 the tin is precipitated with sulphuretted hydrogen and the filtrate evaporated to dryness, the residue treated with an excess of ammonia and the solution then acidified with acetic acid. The greater portion of the anthra- nilic acid crystallizes out; the remainder is then obtained as the copper salt by the method described below. Sandmeyer observed that almost half of the nitrobenzoic acid is converted into salicylic acid on reduction with tin and hydrochloric acid.4 In order to prepare it from indigo, the crude material is finely powdered and boiled for ten hours with ten times its amount of strong caustic potash solution, a small quantity of manganese dioxide being occasionally added, and the original volume of the solution maintained throughout the operation by the repeated addition of small quantities of water. The solution is then neutralized with sulphuric acid, freed from most of the potassium sulphate by crystallization and evaporated to dryness. Potassium anthranilate is extracted from the residue by alcohol and is then converted into the copper salt, which is obtained as a light green precipitate by distilling off the alcohol, acidifying with acetic acid and adding copper acetate or sulphate; the free acid is obtained from this by the action of sulphuretted hydrogen.5 Bbttingei' found that the only definite compound formed in this reaction, in addition to 28 per cent, of anthranilic acid, is formic acid:6 C16H10N2O2 + 20 + 4H2O = 2C7H7NO2 + 2CH2O2. 1 Ann. Chern. Pharm,. xxxix. 91. 2 Ibid. Ixxxvi. 143. 3 Beilstein and Kuhlberg, Ann. Chem. Pharm. clxiii. 138. 4 Ber. Deutsch. Chem. Ges. xviii. 1494. 6 Hiibner and Petermann, Ann. Chem. Pharm. cxlix. 142. 6 Ber. Deutsch. Chem. Ges. x. 269. PROPERTIES OF ORTHO-AMIDOBENZOIC ACID. 239 Ortho-amidobenzoic acid dissolves in about 250 parts of cold, more readily in hot water, and readily in alcohol. The solution has a sweet taste, but is acid to litmus paper, and shows a blue fluorescence when the acid is pure. It crystallizes in small plates, or on the gradual evaporation of its solution, in rhombic needles, melts at 145°, and sublimes when carefully heated, but decomposes into carbon dioxide and aniline when distilled, more completely when mixed with powdered glass (Liebig). On treatment with sodium amalgam, benzoic acid and ammonia are formed (Hubner and Petermann) : C6H4(NH2)CO2H + 2H=C6H5.CO2H + NH, Most of its,metallic salts crystallize well. Ortho-amidobenzoic acid hydrochloride, C7H7NO2.HC1, is readily soluble in water and alcohol, slightly in ether, and crystallizes in needles or four-sided prisms, melting at 191°; its solution is not precipitated by platinum chloride. Formortho-amidobenzoic acid, 2CcH4(NH.CHO)CO9H + H.,O, is obtained by heating ortho-amidobenzoic acid with formic acid, and crystallizes from chloroform in fine, matted needles, which, after drying, form a light, very readily electrified mass, and melt at 168°. When it is heated with phosphorus pentoxide, phenyl carbamine is formed.1 Acetortho-amidobenzoic acid, C6H4(NH.C2H3O)CO2H, is formed by the oxidation of acetorthotoluide with potassium perman- ganate,2 and by heating a mixture of equal molecules of anthranilic acid and acetic anhydride.3 It is slightly soluble in cold, readily in hot water, and crystallizes from acetic acid in flat, rhombic needles, which melt at 179°-180°. Diacetortho-amidobenzoic acid, C6H4N(C2H3O)2CO2H, is ob- tained by boiling anthranilic acid with an excess of acetic anhydride, and forms crystals, melting at 220° (Bedson and King). Benzortho-amidobenzoic acid, C6H4(NH.CO.C6H5)CO2H, is formed by the action of benzoyl chloride on anthranilic acid and by the oxidation of benzoylorthotoluide. It crystallizes from alcohol in long needles, melting at 182°.4 1 v. Meyer and Bellmann, Journ. Prakt. Chem. [2] xxxiii. 24. 2 Bedson and King, Ber. Deutsch. Chem. Ges. xiv. 263. 3 Jackson, ibid. xiv. 886. 4 Bruckner, Ann. Chem. Pharm. ccv. 134. 240 AROMATIC COMPOUNDS. Ortho-amidobenzamidc, CGH4(NH2)CO.NH2, is formed when anthranilcarboxylic acid is dissolved in aqueous ammonia: /CO /CO.NH2 c8h/ I +nh3=c0h/ +co2. \ n.co2h xh. It crystallizes from hot water in nacreous plates, and from chloroform in large, white plates, melts at 108°, and boils with slight decomposition at about 300°. It is converted into ortho- amidobenzoic acid by acids and alkalis.1 Ortho-amidobcnzonitril, C6H4(NH2)CN, is obtained by the action of tin and hydrochloric acid on orthonitrobenzonitril; it crystallizes in yellowish needles, melts at 103°, and forms readily soluble salts.2 2137 Anthranil, C7H5NO, is formed by the action of tin on a solution of orthonitrobenzaldehyde in glacial acetic acid, and is a colourless, oily liquid, which has a characteristic, penetrating smell, is volatile with steam, and commences to boil at 210°-215=, the greater portion of it being decomposed. It rapidly becomes brown and resinous when exposed to the air or to light. It is a very feeble base, and combines with mercuric chloride to form the compound C7H5NO + HgCl2, which crystallizes in fine needles and is readily soluble in alcohol and hot water, but on heating with a solution of potassium chloride, is resolved into its constituents.3 Anthranil is converted into anthranilic acid by the action of alkalis: /CO /CO.OH c6h4< I +h2o=c6h4< \NH XNH2. When heated with ammonia and ferrous sulphate it is con- verted into orthonitrobenzaldehyde, while anthranilcarboxylic acid is formed when it is heated with ethyl chlorocarbonate : ZCO /CO C6H4< I +COC1(OC2H5) = C6H4< I +c2h6ci. XNH \N.CO.OH This compound crystallizes from hot water in fine needles, which decompose into carbon dioxide and anthranil at 230°. It 1 Kolbe, Journ. Prakt. Chem. [2] xxx. 475. 2 Barthlein, Bar. Deutsch. Chem. Ges. x. 1713. 3 Friedlander and Henriques, ibid. xv, 2105. BENZO YLANTHR ANIL. 241 dissolves in dilute caustic soda, forming a solution which possesses a splendid blue fluorescence; this, however, soon disappears, anthranilic acid being formed. Anthranilcarboxylic acid is also obtained by the oxidation of isatin, and will be more fully described along with this substance. Benzoylantliranil is readily obtained by the action of benzoyl chloride on anthranil: ZCO /CO C6H4; | +COC1.C6H5 = C6H4< | + HC1. \NH \N.CO.C6H5 It crystallizes from a mixture of benzene and ligroin in long needles, which melt at 122°-123°, and dissolve when heated with dilute alkalis, benzortho-amidobenzoic acid beinoj formed.1 Dicyanamidobenzoyl, C9H5N3O, is the name given by Griess to a compound which he obtained by passing cyanogen into a cold aqueous solution of anthranilic acid : zNH2 /NH'-C-CN c6h4< " +c2N2=c6H4( II +h2o. 'CO.OH \CO - N It is slightly soluble in water, readily in hot alcohol, and crystallizes in small, yellowish prisms; although it does not contain a carboxyl group, it has an acid reaction and is a monobasic acid.2 Carboxamidocyanamidobenzoyl, C9H7N3O2, is formed when the preceding compound is heated with strong ammonia in a sealed tube: nh-c-cn nh - c - co.nh2. c6H4< 11 +h2o = c6h4/ || \CO-N XCO -N It crystallizes from hot water in fine needles and from alcohol in plates, has an acid reaction and forms salts with bases, the hydrogen of the imido-group being probably replaced by the metal. Carboxylcyanamidobenzoyl, 2C9H6N2O3+H2O, is obtained by heating dicyanamidobenzoyl with baryta water: /NH-C-CN NH-C-CO.OH C6H4( II + 2H2O = C6H4< || + NH, \CO-N XCO - N 1 Friedlander and Wleiigel, Ber. Deutsch. Chem. Ges. xvi. 2227. 2 Ibid. xi. 1986 and 2180. 242 AROMATIC COMPOUNDS. It crystallizes in small, white plates, which are slightly soluble in cold water and alcohol; it is a dibasic acid. When it is boiled with water or acids, or simply heated, carbon dioxide is evolved and carbimidamidobenzoyl, C8H6N2O2, formed. This compound crystallizes from hot water in needles melting at 214°. It possesses basic properties and has the following constitution: /NH-CH C6H4( || XCO-N. Griess has also prepared various other derivatives of dicyan- amidobenzoyl.1 Ethoxy cyanamidobenzoyl, C10H10N2O2, is formed when an alcoholic solution of anthranilic acid is saturated with cyanogen, allowed to stand for some time and then evaporated : /NH2 c6h4< + c2n2 + ho.c2h5= \CO.OH /NH-C-OC2H6 C6hZ II +h2o + hcn. \CO -N It crystallizes from hot alcohol in needles, melts at 173°, and can be distilled in small quantities without undergoing decomposition.2 2138 Ur amidobenzoyl, C8H6N2O2, is prepared by fusing anthranilic acid with urea or by boiling the preceding com- pound with hydrochloric acid : /NH-C-OC2H5 /NH-CO c6h4< II " +h„0=c6h4< I +HO.C2H5. \co-N ■ \co-NH It is slightly soluble in water and alcohol, crystallizes in lustrous plates melting above 350°, dissolves in caustic potash solution and is reprecipitated by carbon dioxide. Fuming nitric acid converts it into nitro-ur amidobenzoy I, C8H5(NO2)N2O2, which crystallizes in honey-yellow prisms, and is converted by reduction into the slightly soluble amido-uramidobenzoyl, C8H5(NH2)N2O2, 1 Ber. Deutsch. Chern. Ges. xviii. 2417. 2 Griess, ibid. ii. 415. BENZOYLGUANIDINE. 243 which forms yellow needles and yields salts, which are also only slightly soluble and crystallize well (Griess). Ortho-uramidobenzoic acid, C8H8N2O3. This compound, which is the acid corresponding to the anhydride just described, is formed by the action of potassium cyanate on ortho-amidobenzoic acid hydrochloride:1 ZNHO zNH.CO.NH2 C6H4< " +CONH=C6H4< xCO2H \CO2H. It crystallizes in needles, and on treatment with nitric acid only yields one dinitro-compound, which will be subsequently mentioned. Orthobenzoglycocy amidine, or Benzoyl guanidine, C8H7N3O, is obtained by heating ethoxycyanamidobenzoyl with alcoholic ammonia : NH-C-OC2H5 c6h4( II " +nh3= XCO -N NH- C=NH C6H4< I +HO.C2H5. \co-NH It may also be obtained by allowing a solution containing cyanamide and anthranilic acid to stand :2 c6h4.nh2 c6h4 -nh 1 + CN.NH2= I >c - NH + H.,0. CO.OH CO NH It crystallizes in nacreous plates, which are only slightly soluble in water and alcohol. Benzoyl guanidine nitrate, C8H8N3O.NO3, is a very characteristic salt; it crystallizes in small plates, which are almost insoluble in water and alcohol. 2139 a-Metkylorthobenzoglycocyamidine, or a-Orthobenzocreatin- ine, C8H6(CH3)N3O, is formed when a strongly alkaline solution of the preceding compound is treated with methyl iodide and allowed to stand for some days. It is almost insoluble in cold, slightly soluble in hot water, more readily in boiling alcohol, and 1 Griess, Journ. Prakt. Chern. [2] v. 371. 3 Griess, Ber. Deutsch. Chem. Ges. xiii. 977. 244 AROMATIC COMPOUNDS. crystallizes in lustrous needles, which have a slightly bitter taste and a neutral reaction. The hydrochloride, C9H9N3O.C1H, crystallizes in narrow plates, which readily dissolve in water without decomposition. ^-Orthobenzocreatininc is obtained by heating ethoxycyan- amidobenzoyl with aqueous methylamine. It resembles the a-compound in forming lustrous needles, which have a very faintly bitter taste, but differs from it in being soluble in baryta water and caustic potash solution, and in forming salts which are decomposed by water. The constitution of these compounds is shown by the following formulas: c6h4-n.ch3 | >C=NH CO NH 0 C6H- nh I >C=NH. CO NCH3 Oxalanthranilic acid, or Orthobenzamoxalic acid, C9H7NO5+H2O. Friedlander and Ostermaier first obtained this compound by the oxidation of carbostyril, C9H7NO, with potassium permanganate, and named it carbostyrilic acid. They then found that on heating with dilute hydrochloric acid or caustic soda solution it decomposes into anthranilic acid and oxalio acid.1 Kretschy recognized it by this property as identical with the cynuric acid which is formed by the oxidation of cynurenic acid, C9H6NO (CO2H), a substance occurring in the urine of the dog. He also prepared it by gradually heating oxalic acid to 150° with anthranilic acid:2 ZNH2 /NH.CO.OH c6h.< + ho.co.co.oh=c6h.< +h2o. \CO.OH \cO.OH It has also been obtained by the oxidation of other substances, which, like those just mentioned, are derivatives of quinoline, a compound which has the following constitution : HC N Z\ZX HC C CH HC C CH ^Z\Z CH CH 1 Griess, Bar. Deutsch. Chem. Ges. xv. 332. 2 Monatsheft Chem. V. 16. DINITRODIPHENYLAMINE-ORTHOCARBOXYLIC ACID. 245 Oxalanthramlic acid is slightly soluble in cold water, readily in alcohol and ether, and crystallizes from the latter in hard needles united to form druses. It is a powerful dibasic acid. Normal calcium benzamoxalate, 2C'9H5NO5Ca + 5H2O, is the most characteristic salt of this acid. It separates out in glittering prisms when calcium chloride is added to a solution of the ammonium salt. 2140 Dinitrodiphcnylamine-orthocarboxylic acid, C6H4(NH. CeH3(NO2)2)CO2H, is formed when anthranilic acid is heated with chlorodinitrobenzene, (Cl: NO2: NO2 = 1: 2 :4), and an excess of ammonia : ZNH2 C6H4< + C6H3C1(NO2)2+2NH3= \CO.OH NH- C6H3(NO2)2 c6h4< +nh4ci. \co.onh4 The ammonium salt produced mthis way forms lustrous, ruby- red plates ; the free acid is obtained by the addition of strong hydrochloric acid to this salt, and is almost insoluble in water, only very slightly soluble in cold alcohol and glacial acetic acid, crystallizing from a hot mixture of these in small, orange-yellow, matted needles, which fuse at 262°-264° to a brownish red liquid, which appears almost black when seen in thick layers; when it is carefully heated a portion distils without decomposi- tion, but it detonates when rapidly heated on platinum foil. Its alkaline salts are slightly soluble in cold, more readily in hot water, and crystallize in reddish yellow to ruby-red plates, which detonate on heating. All the other salts are almost insoluble. The barium salt is a dark cinnabar-red precipitate. This compound does not yield the corresponding amido-acid on reduction with tin and hydrochloric acid, but this is converted into diamidohydro-acridine ketone with elimination of water; this substance, which will be subsequently described, has the follow- ing constitution: CH NH CNH2 ^\/\/^ HC C C CH I II I! | HC C C CNH2 ^/\/\^ CH CO CH 246 AROMATIC COMPOUNDS. Other amido-acids, in which the carboxyl does not stand in the ortho-position to the amido-group, also yield dinitro- diphenylaminecarboxylic acids with chlorodinitrobenzene, but these are converted by reduction into the corresponding diamido- acids. This reaction, therefore, may be employed as a ready method for ascertaining whether or not an aromatic amido-acid belongs to the ortho-series. The compound to be tested is heated to boiling with chlorodinitrobenzene, alcohol and some ammonia for some time. If an ortho-compound be present, the product yields on reduction a base insoluble in alkalis ; in other cases an acid is obtained.1 2141 Metamidobenzoic acid. Zinin obtained this compound in 1845 by the action of ammonium sulphide on nitrobenzinic acid (metanitrobenzoic acid) and named it benzamic acid? Chancel, in 1849, converted nitrobenzamide into amidobenzamide by the same method, but he looked upon the substance obtained as aniline urea and named it carbanilamide. By boiling it with caustic potash solution he obtained carbanilidic acid, which Gerland subsequently proved to be identical with benzamic acid.3 Voit, who investigated its salts, remarked that the latter name is unsuitable, since only the radicals of dibasic acids form amic- acids, and he therefore proposed the name amidobenzoic acid.4 In order to prepare it, a solution of metanitrobenzoic acid in strong ammonia is saturated with sulphuretted hydrogen in absence of air, concentrated and treated with acetic acid. Meta- nitrobenzoic acid may also be reduced with tin and hydrochloric acid and the double tin salt of the amido-acid decomposed with sulphuretted hydrogen. The amidobenzoic acid is then pre- cipitated from the filtrate, previously neutralized with ammonia, by acetic acid. It is slightly soluble in cold, more readily in hot water and alcohol, and crystallizes in warty masses of needles, which melt at 174° and partially volatilize at a higher temperature without decomposition ; when it is heated with spongy platinum (Chancel) or baryta, it decomposes into carbon dioxide and aniline. Its solu- tion has an acid reaction but a sweet taste, and decomposes in the air with separation of a brown powder, its alkaline solution 1 Jourdan, Ber. Deutsch. Chem. Ges. xviii. 1444. 2 Journ. Prakt. Chem. xxxvi. 93. 3 Ann. Chem. Pharm. Ixxxvi. 142. 4 Ibid. xeix. 100. METAMIDOBENZOIC ACID. 247 behaving in a similar manner. Its metallic salts crystallize well. Metamidobenzoic acid hydrochloride, C7H7NO2.C1H, crystallizes in prisms, which are readily soluble in water, slightly in hydro- chloric acid; the platinichloride forms golden-yellow needles, and the double tin salt, C7H7NO2.ClH + SnCl2, crystallizes in plates (Beilstein and Wilbrand). Its other compounds with acids also crystallize well. Metamidobenzamide, CGH4(NH2)CO.NH2, is obtained, accord- ing to Chancel, when ammonium sulphide is added to a boiling aqueous solution of metanitrobenzamide. It is readily soluble in water, and forms large, yellow crystals, melting at 750.1 Like amidobenzoic acid it is a monacid base. Metamidobenzonitril, CGH4(NH2)CN, is formed when meta- nitrobenzonitril is reduced with zinc and hydrochloric acid 2 or tin and acetic acid,3 as well as by heating meta-uramidobenzoic acid with phosphoric acid : 4 /CO-Ox /CN c,h4< >nh3 = c,,h/ +co2+h2o. NNH.CCX NII, It crystallizes from dilute alcohol in long, white needles, melts at 53°-54°, boils at 288°-290°, and is decomposed by powerful reducing agents into ammonia and benzonitril, the latter being partially converted into benzylamine. When it is treated with alcoholic potash and chloroform, the carbamine, C6H4(NC)CN, is formed; it has an overpowering odour and has not been further investigated. Metamidobenzonitril is a monacid base and forms salts which crystallize well. Methylmetamidobenzoic acid, or Metabenzosarcosine, CGH4(NH. CH3)CO2H, was obtained by Griess as a decomposition product of a-benzocreatine ; it is slightly soluble in cold, more readily in hot water, and crystallizes in small plates. Dimethylmetamidobenzoic acid, CGH4.N(CH3)2CO2H. The methyl ether of this acid is formed by a molecular change from the following compound, and is a liquid which has a faint aromatic odour, and boils at 270°. The acid is obtained from it by decomposition with alcoholic potash, and is also only slightly 1 Beilstein and Reichenbach, Ann. Chern. Pharm. cxxxii. 142. 2 Hofmann, Ber. Deutsch. Chcm. Ges. i. 196. 3 Fricke, ibid. vii. 1321. 4 Griess, ibid. viii. 861. 248 AROMATIC COMPOUNDS. soluble in hot water; it crystallizes in dull needles, melting at 151°. Trimethylamidobcnzoic acid, ox Metabenzobetaine, C7H4N(CH3)3 O? + H2O. The iodide of this compound is formed when a solu- tion of amidobenzoic acid in methyl alcohol is allowed to stand in contact with an excess of caustic potash and methyl iodide ; it forms short prisms of the formula C7H5O2N(CH3)3I + H2O. The free base, which is obtained by the action of lead hydroxide, crystallizes in deliquescent needles, which lose one molecule of water at 105°, and have a neutral reaction and bitter taste. The anhydrous compound is converted on fusion into the methyl ether of the preceding compound.1 /VV /C6H4N(CH3)2 C0< >N(CH3)3 = co< \ 0 z xOCH3 zN(C2H3O)H Acetmetamidobenzoic acid, C6H4\ , is metameric xCO2H with hippuric acid and is formed when metamidobenzoic acid is heated to 160° with glacial acetic acid. It crystallizes in fine, white needles, is almost insoluble in cold water, has a bitter taste, at the same time resembling that of saltpetre, and melts at 245°; it sublimes, however, at a lower temperature.2 2142 Amidobenzoic acid percyanide, (C6H4(NH2)CO2H)2C2N2, is the name given by Griess to a compound to which he had previously assigned the formula C6H4(NH2)CO2HC2N2, and which is obtained by passing cyanogen into an aqueous solution of metamidobenzoic acid. It is a yellow, crystalline substance, which is insoluble in water, scarcely soluble in alcohol and ether, and has acid properties. On distillation it decomposes into water, carbon dioxide, ammonia, ammonium cyanide and met- amidobenzonitril. When heated to 130° with alcohol, it decom- poses into metamidobenzoic acid and metabenzamoxalic acid. C6H4.NH.C(NH)C(NH)NH.C6H4 I I +3H2O = co2h co9h c6h4.nh9 " C6H4.NH.CO.CO.OH I + I + 2NH3. co2h co2h 1 Griess, Bar. Deutsch. Chem. Ges. vi. 586. 2 Forster, Ann. Chem. Pharm. cxvii. 165 ; Kaiser, Bcr. Deutsch. Chem. Ges. :viii. 2946. CYANOCARBOXAMIDOBENZOIC ACID. 249 Metabenzamoxalic acid, or Oxalamidobenzoic acid, is also formed by heating metamidobenzoic acid with oxalic acid, and crystal- lizes from hot water in narrow white plates.1 Cyanocarbimidobenzoic acid, 3C9H7N3O2 4- H.,O, is formed together with the percyanide according to the equation : NH, CN NH C=NH C„H / + | = C6H / | xCO2H CN \CO2H CN It is only very slightly soluble in cold water, readily in hot alcohol, and crystallizes in elliptical plates, which have an acid reaction and combine with bases and acids. Cyanocarboxamidobenzoic acid, C9H6NO3, is obtained by the action of nitrous acid on a cold solution of the preceding com- pound in hydrochloric acid : NH C=zNH c6h4< I + hno2 = \C09H CN nh-co C6H4< I +n2 + h2o. xCO2H CN It crystallizes in lustrous, white plates, which have a sweet taste, and are almost insoluble in cold water, but are decomposed by boiling water with formation of carbon dioxide, hydrocyanic acid and carboxamidobenzoic acid. When it is dissolved in ammonia, uramidobenzoic acid is formed : ZNH CO ZNH CO Cen/ | +NH3=C6H4< | + HCN. \CO2H CN \co2h nh2 Methylamine, ethylamine, &c., act in a similar manner, and a large number of substituted uramidobenzoic acids can, therefore, be prepared in this way.2 If cyanogen be passed into an alcoholic solution of metamido- benzoic acid, the percyanide, which has been already mentioned, 1 Griess, Ber. Deutsch. Chem. Ges. i. 191 ; xi. 1985 ; xvi. 336; xviii. 2412 ; Schiff, ibid. xix. 252. 2 Griess, ibid, xviii. 2415. 250 AROMATIC COMPOUNDS. is deposited, and the two following compounds crystallize out on allowing the mother liquor to stand : Carbimidamidobenzoic acid. /CO2H c6h4< /NH2 \nhx 2C6H4< + C2N2 = )C=NH + HCN. \co2h ,nhz c6h4< xCO2H Ethoxycarbimidamidobenzoic acid. /NH2 C6H4< + C2N2 4 HO.C2H5 = \co2h AH C=NH C6H4< I + HCN. \co2h oc2h5 Carbimidamidobenzoic acid, or Guanidodibenzoic acid, C1KH1Q N3O4, is obtained from the crude product by extraction with boiling water; it separates out on cooling in needles, which are purified by being dissolved in hydrochloric acid, the solution neutralized with ammonia and then precipitated by acetic acid. The precipitate is at first amorphous, but soon changes into needles. It forms salts with both acids and bases.1 Ethoxycarbimidamidobenzoic acid, 2C10H12N2O3 + 3HQO, is slightly soluble in water, more readily in alcohol, and crystallizes in needles.2 Meta-uramidobenzoic acid, C8H8N2O3 + H2O, is formed when the preceding compound is boiled with hydrochloric acid : NH C~NH ZNH CO c6h4< I + h2o = c6h4< I +ho.c.,h5. xco2h och3 \co2h nh2 Menschutkin obtained it from potassium cyanate and met- amidobenzoic acid hydrochloride, and named it oxybenzuramic acid? Griess then showed that it is also formed by bringing metamidobenzoic acid into fused urea.4 It is slightly soluble in water, more readily in alcohol, and crystallizes in needles or 1 Griess, Zeitschr. Chem. 1867, 534. 2 Journ. Prakt. Chem. [2] iv. 296. 3 Ann. Chem. Pharm. cliii. 84. 4 Ber. Deutsch. Chem. Ges. ii. 47. METABENZOGLYCOCYAMINE. 251 fine prisms. Its salts have been investigated by Menschutkin. On treatment with concentrated nitric acid it yields three di- nitro-compounds (p. 255). Meta-urethanebcnzoic acid, C10HnNO4, is formed by the action of nitrous acid on ethoxycarbimidamidobenzoic acid1 and by treating metamidobenzoic acid with ethyl chlorocarbonate; /NH2 COCI /NH CO C6H4< + I = C6H4< I +HC1. XCO2H oc2h, xco2h oc2h5 Zj «J Lt Lt V It crystallizes in plates, which are slightly soluble in water, dissolve in alcohol in every proportion, and melt at 189°. Carboxamidobenzoic acid, or Metacarbamidobenzoic acid, C15Hi2 N2O5, is obtained by heating uramidobenzoic acid to 200°, or by repeatedly evaporating the solution of its barium salt:2 ZNH, /NH.C6H4.CO2H 2CO< " = CO< " + CO(NH2)2. \nh.c6h4.co2h \NH.C6H4.CO2H It is also formed when meta-urethanebenzoic acid is heated above its melting-point,3 and crystallizes in microscopic needles, which are insoluble in water, alcohol and ether. 2143 Metabenzoglycocyamine, or Metaguanidobenzoic acid, C8H9 N3O2 + H2O, was first obtained by Griess by boiling amido- benzoic acid percyanide with caustic potash solution; it is also formed by the action of ammonia on ethoxycarbimidamido- benzoic acid, as well as, similarly to glycocyamine (Part II. p. 97), by allowing an alcoholic and ammoniacal solution of cyanamide and metamidobenzoic acid to stand :4 c6h4.nh2 c^n c6h4.nh-c=nh I +1 =1 I co2h nh2 co2h nh2 It is slightly soluble in alcohol, and crystallizes from hot water in thin, four-sided tablets which dissolve in caustic potash, but are reprecipitated by carbon dioxide. It forms salts with the 1 Griess, Ber. Deutsch. Chem. Ges. ix. 796. 2 Griess, Zeitschr. Chem. 1868, 650 ; Ann. Chem. Pharm. clxxii. 170. 3 Wachendorff, Ber. Deutsch. Chem. Ges. xi. 701. 4 Griess, ibid. vii. 575 ; viii. 323. 252 AROMATIC COMPOUNDS. mineral acids, but does not combine with acetic acid. On boil- ing with baryta water, uramidobenzoic acid is first formed : zNH.C(NH)NH2 znh.co.nh2 c6h4< +h20=c6h4< +nh3. \co2h \co2h On continued boiling, metamidobenzoic acid and urea or de- composition products of these are produced. a-Metabenzocreatine, 2C8H8(CH3)N3O2-}-3H2O, is formed by the action of methyl iodide and caustic potash on a solution of the preceding compound. It is slightly soluble in water and alcohol, crystallizes in pointed plates, and decomposes into urea and benzosarcosine when boiled with baryta water. [3-Mctabcnzocreatinc is prepared from ethoxycarbimidamido- benzoic acid and methylamine, and crystallizes from hot water in small plates. On heating with baryta water it yields meta- amidobenzoic acid, methylamine, and carbon dioxide (Griess). The metabenzocreatines, like benzoglycocyamine, exist in the free state as salts, and have the following constitution: C6H4.N (CH3) c=nh co o-nh3 0 C6H4.NH.C-NH I b * CO-0-N(CH3)H2 If these compounds be compared with those of the ortho-series, it is found that the latter contain a molecule of water less or are anhydro-compounds, this class of bodies being very readily formed by and characteristic of the ortho-series. Phenylvietabenzoglycocyamine, C8H8(O6H5)N3O2 + H2O,is formed when cyanocarbimidamidobenzoic acid is heated with aniline: ZNH C=NH c6h4( I +h2n.c6h5= ^co2h cn ZNH C=NH C6H4< | +HCN. \co2h. n.c6h5h It is insoluble in alcohol, but slightly soluble in hot water, readily in hydrochloric acid and caustic potash, and crystallizes in needles or plates, which have a bitter taste followed by a sweet after-taste. PARAMIDOBENZOIC ACID. 253 Amidophenylmetabenzoglycocyamine, C8H8(CGH4.NH2)N3O2, is prepared in a similar manner from paradiamidobenzene; it crystallizes in small prisms, and is a diacid base.1 2144 Paramidobenzoic acid is obtained by the reduction of paranitrobenzoic acid with ammonium sulphide,2 or better with tin and hydrochloric acid.3 It is tolerably soluble in water, very readily in alcohol, and crystallizes in long needles forming fascicular aggregates; it melts at 186°-187°, and decomposes at a higher temperature into carbon dioxide and aniline, a decomposition which may also be effected by heating it to 160° -180° with hydrochloric acid. It is characteristic of paramidobenzoic acid that lead acetate gives with its aqueous solution a crystalline precipitate of the double salt, C7H4(NH2)O9PbC9H3O2.4 Paramidobenzoic acid hydrochloride, C7H7NO2.HC1, crystallizes in small plates or prisms. Paramidobenzamide, CGH4(NH2)CO.NH2, is formed by the reduction of paranitrobenzamide with ammonium sulphide, and forms large, light yellow crystals, which melt at 178°-179°, and are much less soluble in water than those of the meta-compound.5 Paramidobenzonitril, CGH4(NH2)CN, may be prepared from paranitrobenzonitril,6 and by the distillation of para-uramido- benzoic acid with phosphorus pentoxide.7 It is readily soluble in alcohol and boiling water, and crystallizes in needles, melting at 100° (Fricke). It forms crystalline salts with acids. Dimethylparamidobenzoic acid, C6H4N(CH3)2CO2H, is obtained by heating the amido-acid with caustic potash, methyl iodide and wood spirit. It crystallizes in short, broad needles, melt- ing at 235°, and combines with acids and bases, but is insoluble in acetic acid.8 Acetparamidobenzoic acid, CGH4(NH.C2H3O)CO2H. Hofmann obtained this compound by the oxidation of acetparatoluide with potassium permanganate. It is slightly soluble in water, readily in alcohol, and crystallizes in needles, which melt with decomposition at 25O0.9 On boiling with hydrochloric acid it is converted into paramidobenzoic acid.10 1 Griess, Ber. Deutsch. Chern. Ges. xvi. 336. 2 Fischer, Ann. Chern. Pharm. cxxvii. 142. 3 Beilstein and Wilbrand, ibid, cxxviii. 264. 4 Ladenburg, Ber. Deutsch. Chern. Ges. vi. 130. 5 Beilstein and Reichenbach. Ann. Chern. Pharm. cxxxii. 144. 6 Engler, ibid, cxlix. 302; Fricke, Ber. Deutsch. Chem. Ges. vii. 1322. 7 Griess, ibid. viii. 861. 8 Michler, ibid. ix. 401. 9 Ibid. ix. 401. 10 Kaiser, ibid, xviii. 2942. 254 AROMATIC COMPOUNDS. Para-uramidobenzoic acid, C8H8N2O3, is formed at the same time as paracarbamidobenzoic acid by fusing paramidobenzoic acid with urea, or potassium cyanate with paramidobenzoic acid hydrochloride. It forms elongated plates, is scarcely soluble in cold, only very slightly in boiling water, more readily in hot alcohol. Concentrated nitric acid only forms one dinitro-com- pound. Paracarbamidobenzoic acid, C1BH12N2O6, is obtained by heating the preceding compound, and forms small needles which are insoluble in the ordinary solvents. CHLORAMIDOBENZOIC ACIDS, C6H3C1(NH2)CO2H. Cl: NH2 Melting-point. a) 2:5 small, readily soluble needles,1 . . 212° /3) 3:6 long, almost insoluble needles,2 , . . 148° 3) 3:5 needles,3 . . 216° e) 4:3 small needles,4 . . 212° 2145 The chloramidobenzoic acids corresponding to 7- and £- chloronitrobenzoic acids are unknown. Two others have, how- ever, been prepared, one of which has been obtained from chlorisatin, and should be identical with the /3-acid, but melts at 204°;5 it will subsequently be mentioned. The second has been prepared by Griess together with the e-acid by decomposing metadiazobenzoic acid imide, C6H4N3.CO2H, with hydrochloric acid; it crystallizes in small prisms and has the constitution C1:NH2 = 2:3.6 1 Hiibner and Biedermann, Ann. Chern. Pharm. cxlvii. 258 ; Rack and Wilken, ibid, ccxxii. 198. 2 Cunze and Hiibner, ibid, cxxxv. Ill ; Hiibner and Weiss, Bar. Deutsch. Chem. Ges. vi. 175. 3 Grube, ibid. x. 1703. 4 Hubner and Biedermann; Raveill, Ann. Chem. Pharm. ccxxii. 177. 5 Dorsch, Journ. Prakt. Chem. [2] xxxiii. 50. 6 Griess, Ber. Deutsch. Chem. Ges. xix. 313. NITRO-AMIDOBENZOIC ACIDS. 255 BROMAMIDOBENZOIC ACIDS, C6H3Br(NH2)CO2H. a) Br : NH2 Melting-point. . . 180° 2:5 broad needles1 ft 3:6 long, slightly soluble needles 2 . . 208° 7) 3:2 needles3 . . 172° 4:3 light yellow needles4 . • . . . . 225° e) 3:5 colourless, tough needles5 . . . . 215° IODAMIDOBENZOIC ACIDS, C6H3I(NH2)CO2H. Melting-point. a) 3:2 brown needles 137° /3) 3:6 needles melting with decomposition 209° These have been prepared from the iodonitrobenzoic acids and are converted by reduction into orthamidobenzoic acid. NITRO-AMIDOBENZOIC ACIDS, C6H3NO2(NH^CO2H. 2146 Seven of the ten acids possessing this composition which are possible according to theory are known, and their constitution is shown on the next page. The first three have been obtained from meta-uramidobenzoic acid, which, as already mentioned, yields three dinitro-compounds. These cannot be directly separ- ated, but on boiling with dilute ammonia are converted into the mononitro-uramidobenzoic acids, which can be separated by means of their barium salts : C8H6(NO2)2N2O3+H2O = C8H7(NO2)N2O3+no2.oh. They are re-converted by concentrated nitric acid into the 1 Burghard, Ber. Deutsch. Chern. Ges. viii. 560. 2 Hubner and Meeker, Zeitschr. Chem. 1867, 564 ; Hubner, Ohly and Philipp, Ann. Chem. Pharm. exliii. 241 ; Hubner and Petermann, ibid, exlix. 133. 3 Ibid. 4 Burghard ; Raveill. 5 Hesemann and Kohler, Ann. Chem. Pharm. ccxxii. 169. 256 AROMATIC COMPOUNDS. dinitro-compounds, which on boiling with water yield the nitro- amidobenzoic acids:1 znh.co.nh2 znh2 C6H2(NO2)2< =c6h3(N02)< " +N2o + co2. xCO2H xCO2H co2h YJnh, CO2H ^Jnh2 no2 co2h hY02 co2h nh2 co2h f>H2 NOj^ co2h 4\nh2 X/NO2 CO2H NO2^NH2 a-Nitro-amidobenzoic acid is slightly soluble in water, readily in alcohol, and crystallizes in yellow needles or prisms.2 Nitrous acid converts it into orthonitrobenzoic acid, and on reduction with tin and hydrochloric acid it yields a-diamidobenzoic acid. ^-Nitro-amidobenzoic acid forms lustrous, yellowish red needles or plates, which are readily soluble in alcohol and slightly in water, and when gently heated sublime in rhombic plates with- out melting. Heated in a capillary tube it melts at 298° with complete decomposition.3 It is converted by nitrous acid into paranitrobenzoic acid, and by tin and hydrochloric acid into /3-diamidobenzoic acid. y-Nitro-amidobcnzoic acid crystallizes in thick, golden yellow needles or prisms, which melt at 156°-157°,4 and dissolve readily in alcohol and hot water. Nitrous acid converts it into orthonitrobenzoic acid, and reducing agents into y-diamido- benzoic acid. Z-Nitro-amidobcnzoic acid was obtained by Griess from dinitro- para-uramidobenzoic acid,5 and by Salkowski by heating nitro- anisic acid, C6H3NO2(OCH3)CO2H, with ammonia to 140°- 17O0.6 It crystallizes in small, yellow needles, which are scarcely soluble in water, only slightly in boiling alcohol, and melt at 1 Griess, Ber. Deutsch. Chem. Ges. ii. 434 ; v. 192; xi. 1733. 2 Journ. Prakt. Chem. [2] v. 235. 3 Kaiser, Ber. Deutsch. Chem. Ges. xviii. 2947. 4 Ibid, xviii. 2951. 5 Loe. cit. 6 Ann. Chem. Pharm. clxxiii. 52. DINITRO-AMIDOBENZOIC ACIDS. 257 284°. It is converted by the diazo-reaction into metanitrobenzoic acid, and by reduction into ^-diamidobenzoic acid. c-Nitro-amidobenzoic acid was prepared by Griess from dinitro- ortho-uramidobenzoic acid, and by Hubner from the nitrosalicylic acid which melts at 228° by heating the ethyl ether with alcoholic ammonia; e-nitro-amiddbenzamide, C6H3NO2(NH2)CO. NH2, is thus obtained, and crystallizes in small, yellow needles, melting at 140°; it is converted into the acid by boiling with baryta water.1 Rhalis obtained it, together with paranitraniline, by heating the nitrobromobenzoic acid which melts at 179°- 180° with ammonia.2 It crystallizes from hot water in long, lustrous, yellow needles, melting at 270°. Ethyl nitrite con- verts it into metanitrobenzoic acid, and on reduction it yields a-diamidobenzoic acid. ^-Nitro-amidobenzoic acid. Hubner obtained the amide of this acid from the nitrosalicylic acid which melts at 144°; it crystallizes in yellow plates, melting at 109°, and on boiling with baryta water yields the acid, which is readily soluble in alcohol and crystallizes from hot water in long, yellow, silky needles, melting at 204°. Nitrous acid converts it into metanitrobenzoic acid. rj-Nitro-amidobenzoic acid is formed by the reduction of S-dinitrobenzoic acid with ammonium sulphide,3 and crystallizes from water in long,golden yellow needles, or small, compact prisms, melting at 208°. It is converted into metanitrobenzoic acid by ethyl nitrite, while metachlorobenzoic acid may be obtained from it by replacing the amido-group by chlorine and the nitroxyl by hydrogen; its constitution is thus established. DINITRO-AMIDOBENZOIC ACIDS, C6H2(NO2)2(NH2)CO2H. 2147 Dinitro-orthamidobenzoic acid or Dinitro-anthranilic acid (NO2: NO2 = 3 : 5) is prepared by the action of ammonia on the ether of dinitrosalicylic acid. It is slightly soluble in alcohol, and crystallizes from it in lustrous, golden scales, melting at 25 6°.4 1 Ann. Chem. Pharm. xix. 21. 2 Ibid, cxcviii. 112. 3 Bocker, Grube and Rollwage, Ber. Deutsch. Chem. Ges. x. 1703 ; Ann. Chem. Pharm. ccxxii. 81. 4 Salkowski, Ann. Chem. Pharm. clxxiii. 40. 258 AROMATIC COMPOUNDS. Dinitroparamidobenzoic acid, (NO2: NO2 = 2 : G). Cahours, in 1849, found that an acid soluble in ammonia is formed by the action of fuming nitric acid on nitranisic acid, in addition to dinitro-anisol and trinitro-anisol (Part III., p. 125). This sub- stance being of a splendid golden yellow colour, he named it chrysanisic acid, C7H5N3O7, looking upon it as a homologue of picric acid.1 After trinitrocresol had been prepared, Kolbe suggested that it is identical with chrysanisic acid,2 but Beilstein and Kellner showed that this is not the case, since the latter has the formula C7H5N3O6, and differs from the isomeric trinitro- toluene, which was prepared and described by Wilbrand.3 The actual constitution of chrysanisic acid was determined by Salkowski, who found that it is not contained in the product of the action of nitric acid on nitranisic acid, but is formed by the action of ammonia on dinitro-anisic acid:4 CcH2(OCH3)(NO2)2CO2H + NH3 = C6H2(NH2)(NO2)2CO2H + ho.ch3. It may also be obtained by the oxidation of dinitropara- toluidine,5 and crystallizes from hot water, in which it is only very slightly soluble, in fine needles, and from alcohol in lustrous, golden, rhombic plates, melting at 259°. On heating to 200°- 210° with fuming hydrochloric acid, /3-trichlorobenzoic acid is formed, and with nitric acid it yields picric acid, while the dinitro-anisic acid from which it is prepared is converted into /3-dinitrophenol when heated with water to 170°.6 DIAMIDOBENZOIC ACIDS, CcH3(NH2)2CO2H. 2148 The formation of these has been already mentioned under the dinitro- and nitro-amido-benzoic acids. The numbers signify the position of the amido groups. a-Diamidobenzoic acid (2 : 5) is slightly soluble in alcohol and hot water, and crystallizes in very small prisms, which decompose on heating with formation of paradiamidobenzene. 1 Ann. Chim. Phys. [3] xxvii. 454. 2 Lehrb. Org. Chem. ii. 145. 3 Ann. Chem. Pharm. cxxviii. 164. 4 Ibid, clxiii. 1. 6 Friederici, Bar. Detdsch. Chem. Ges. xi. 1975. 6 Salkowski and Rudolph, ibid. x. 1254. DIAMIDOBENZOIC ACIDS. 259 ft-Diamidobenzoic acid (3:4) crystallizes from hot water in small plates, which melt at 211°, and decompose at a higher temperature, more easily when mixed with powdered glass or lime, into carbon dioxide and orthodiamidobenzene. y-Diamidobenzoic acid (2:3) forms long, yellowish white needles, and also yields orthodiamidobenzene on heating. b-Diamidobenzoic acid (3 : 5) is slightly soluble in water, more readily in alcohol, and crystallizes in long needles which melt at 228° when gradually heated, but at 236° when rapidly heated,1 and are carbonized at a higher temperature with evolution of ammonia. On heating with caustic baryta, it decomposes into carbon dioxide and metadiamidobenzene. It decomposes car- bonates and forms salts which crystallize well. Its dilute aqueous solution is coloured deep yellow by nitrous acid (p. 263). Barium diamidobenzoatc, 2(C6H3(NH2)2CO2)2Ba t- 3H2O, cry- stallizes in yellowish prisms, which are readily soluble in water. Like its isomerides, it also combines with acids. b-Diamidobenzoic acid hydrochloride, C6H3(CO2H)(NH2)2 (C1H)2, is readily soluble in water, but only slightly in hydro- chloric acid, and crystallizes in needles. 8-Diamidobenzoic acid sulphate, (C6H3(CO2H)(NH2)2)SO4H2, forms white needles or prisms, which are slightly soluble in water and still less so in alcohol.2 Hexmethyl-b-diamidobenzoic acid, or, as Griess called it, six- fold methylated diamidobenzoic acid, is not an acid in its properties but a strongly alkaline ammonium hydroxide and, at the same time, a salt. The iodide is formed by the action of methyl iodide and caustic potash on a solution of 8-diamido- benzoic acid in methyl alcohol. It crystallizes in six-sided tablets or plates, and when treated in concentrated aqueous solution with silver oxide yields the free base : N(CH3)3 zN(CH3)3I / \ C6H<CO.OH + Ag2O = C6H3^CO.O + 2AgI. \N(CH3)3I \N(CH3)3OI1 It is obtained on evaporation as a crystalline mass, which consists of small plates, is very hygroscopic and behaves like 1 Hubner, Ann. Chern. Pharm. ccxxii. 85. 2 Griess, ibid. cliv. 328. 260 AROMATIC COMPOUNDS. caustic potash. The carbonate crystallizes from alcohol in small plates, is readily soluble in water and has an alkaline reaction.1 TRI-AMIDOBENZOIC ACID, C6H2(NH2)3CO2H. Salkowski obtained this compound by the reduction of chrysanisic acid with tin and hydrochloric acid. It crystal- lizes from boiling water in fine, lustrous needles, and decom- poses on heating into carbon dioxide and triamidobenzene. Its solution has an acid reaction, and it is at once a monobasic acid and a diacid base. DIAZO-DERIVATIVES OF BENZOIC ACID. 2149 The amidobenzoic acids behave in some respects like amido-acetic acid and its homologues, and in others like aniline, since they can be easily converted into diazobenzoic acids. For this purpose, a magma of amidobenzoic acid and nitric acid is well cooled by ice and saturated with nitrogen trioxide, the nitrate formed being then precipitated with alcohol and ether. Other salts are obtained in a similar manner. The sulphates are best prepared by dissolving the nitrate in a cold mixture of equal parts of water and sulphuric acid, and precipitat- ing in crystals by the addition of strong alcohol and then ether.2 The diazobenzoic acids, which, like the diazophenols, only exist as anhydrides, are obtained from these salts by the action of caustic potash. They also form double salts, which Griess looks upon as basic salts : Diazobenzoic acid. ZN -N CW I \co-o Diazobenzoic acid nitrate. ZN-N.NO3 c6h4< \CO.OH. Diazobenzoic acid seminitrate. /Nz=N.O.CO.C6H. c6hZ I XCO.OH N=N.N03. 1 Griess, Ber. Deutsch. Chem. Ges. vii. 39; Bruhl, ibid. viii. 485. 2 Griess, ibid, xviii. 960. DIAZO-DERIVATIVES. 261 The substituted amidobenzoic acids, as well as their amides, nitrils, &c., also form diazo-compounds. Orthodiazobenzoic acid nitrate, NO3.N2.C6H4.CO2H, is readily soluble in water, and crystallizes in rhombic or six-sided tablets, or prisms, which Explode violently on heating. When it is re- peatedly dissolved in water and precipitated with alcohol and ether, or when an alcoholic solution of anthranilic acid is treated with nitrogen trioxide, orthodiazobenzoic acid seminitrate, NO3.N2. C6H4.CO2.N2.C6H4.CO2H, is formed; it crystallizes in long, white needles, and detonates violently when heated.1 Metadiazobenzoic acid nitrate crystallizes in prisms, which are slightly soluble in cold water.2 On adding an alkali to its solution, xN -N a precipitate of metadiazobenzoic acid, CGH4/ | , is thrown \CO-O down. This forms a yellow mass which is very unstable. Metadiazobenzoic acid sulphate, HSO4.N2.CGH4.CO2H, forms long, narrow plates, which are readily soluble in water. When it is repeatedly precipitated from aqueous solution by the addition of alcohol and ether, it becomes converted into the basic salt, to which Griess has given the formula 5C7H4N2O2, 2SO4H2.3 According to Beilstein it is probably 2(C7H5N2O2)2 SO4 + C7H5N2O2(OH).4 It crystallizes in small needles. When the normal sulphate is heated, it decomposes with a violent evolution of gas and formation of free sulphuric acid, sulphoxybenzoic acid, and a very stable compound, C14H10SO8,5 which probably has the following constitution: SO2(C6H3(OH) CO2H)2. Metadiazobenzoic acid platinichloride, (C7H5N2O2)2PtCl6, is obtained by the addition of platinum chloride to a solution of the nitrate; it crystallizes in yellow prisms. Metadiazobenzoic acid perbromide, Br2N-BrN.CGH4.CO2H, is precipitated as an oil by the addition of a solution of bromine in hydrobromic acid to a solution of the nitrate; it soon solidifies to a mass of yellow prisms, and is converted by ammonia into diazobenzoic acid imide. , Metadiazobenzamide nitrate, NO3.N2.CGH4.CO.NH2, crystallizes in white, explosive needles. 1 Griess, Ann. Chem. Pharm. cxvii. 39, cxxxv. 121 ; Bor. Deutsch. Chem. Ges. ix. 1653. 2 Griess, Ann. Chem. Pharm. cxx. 126. 3 Ber. Deutsch. Chem. Ges. ix. 1655. 4 Handb. Org. Ghem. 1139. 6 Jahresb. Chem. 1864, 351. 262 AROMATIC COMPOUNDS. Metadiazobenzonitril nitrate, NO3.N2.C6H4.CN, forms explosive needles or prisms which are only slightly soluble in cold water.1 Paradiazobenzoic acid nitrate also crystallizes in white, explosive prisms.2 /N2\ hitrodiazobenzoic acid, C6H3(NO2)< bO, is formed when \coz 8-nitro-amidobenzoic acid is brought into absolute alcohol nearly saturated with nitrogen trioxide; it forms light yellow, explosive plates.3 Diazobenzcne-amidobenzoic acid, C6H5.N~N.NH.C6H4.CO2H, is obtained by mixing aqueous solutions of diazobenzene nitrate and metamidobenzoic acid.4 According to Griess, this compound is identical with that obtained by the action of aniline on metadiazobenzoic acid, and which was therefore considered to have the constitution C(.H5.NH.N=zN.C6H4.CO2H. Griess, however, expresses the constitution of both compounds by the same formula, C6H6.NH=NH=NH.C6H4.CO2H (Part III., p. 269).5 By either process, a yellow, crystalline substance is obtained, which separates from ether in small plates, and is decomposed by hydrochloric acid with formation of metamidobenzoic acid, metachlorobenzoic acid, metahydroxybenzoic acid, aniline, phenol and nitrogen. The acid forms a yellow solution in alkalis; on the addition of barium chloride to its ammoniacal solution, which must not be too dilute, the barium salt separates out in small, light yellow crystals. Mctadiazo-amidobenzoic acid,QO N.C6H4.CO2H, is formed by the action of metamidobenzoic acid on metadiazo- benzoic acid,6 and therefore as an intermediate product when nitrogen trioxide is passed into an alcoholic solution of metamido- benzoic acid.7 It forms orange-yellow, crystalline granules, which are almost insoluble in water, alcohol, ether, &c., and detonate at 180°. It is soluble in alkalis, and is reprecipitated by acids, even acetic acid. On boiling with hydrochloric acid, it decomposes with evolution of nitrogen into metamidobenzoic acid and metachlorobenzoic acid. It is a tolerably strong dibasic acid and decomposes carbonates. 1 Griess, Bar. Deutsch. Chem. Ges. ii. 370. 2 Jahresb. Chem. 1864, 353. 3 Salkowski, Ann. Chem. Pharm. clxxiii. 63. 4 Griess, ibid. cxxxvii. 63. 8 Ber. Deutsch. Chem. Ges. vii. 1619. 6 Jahresb. Chem. 1864, 353. ' Ann. Chem. Pharm. cxvii. 1. DIAMIDOBENZOIC ACIDS. 263 Paradiazo-amidobenzoic acid was obtained by Beilstein and Wilbrand by treating a saturated alcoholic solution of paramido- benzoic acid with a solution of nitrogen trioxide in alcohol. It is an orange-yellow, crystalline powder, which is only slightly soluble in boiling alcohol.1 Isomeric compounds are formed from metadiazobenzoic acid and paramidobenzoic acid, and from paradiazobenzoic acid and metamidobenzoic acid (Griess). 2150 The Action of Nitrous Acid on the Diamidobenzoic Acids. When sodium nitrite is added to a neutral solution of a-diamido- benzoic acid, which contains the amido-group in the para-position, paramidodiazobenzoic acid is formed : /NH2 /nh2 C6H3-NH2 + NO2H = C6H3-N-N + 2H2O. \CO.OH \ \ CO-O It is insoluble in ether, slightly soluble in hot alcohol, readily in hot water, and crystallizes in fine needles or four-sided plates, which are brass coloured, have a very bitter taste, and detonate on heating. It does not combine with bases, but forms crystal- line salts with acids; it also combines with amido-bases and phenols to form azo-compounds.2 Nitrous acid acts upon the two orthodiamidobenzoic acids (ft and 7) in the following manner : /NH2 /NH\ C6H,$-NH2 + NO2H = C6H <-N = N + 2H2O. \COOH \CO.OH The diazoAniidobenzoic acids obtained in this manner crystal- lize in needles and are powerful acids, the barium salts of which are only slightly soluble in cold water.3 Metadiamidobenzoic acid corresponds exactly with metadi- amidobenzene in its behaviour towards nitrous acid. In a very dilute solution a yellow colouration is produced, and this reaction is so delicate that one part of nitrous acid can be detected in five million parts of water. In concentrated 1 Ann. Chern. Pharm. cxxviii. 269. 2 Griess, Ber. Deutsch. Chem. Ges. v. 200, xvii. 603. 3 Griess, ibid. ii. 436. 264 AROMATIC COMPOUNDS. solutions a reddish-brown precipitate of triamido-azobenzoic acid is formed: /NH2 zNH2 /NH2 2CoH3-NH2 +NO2H=C6H„^-N=N-C6H2<-NH9 +2H2O. \CO.OH \CO.OH \CO.OH This substance is soluble in alkalis, and is reprecipitated by acids.1 znh.nh2 HYDRAZINEBENZOIC ACIDS, C6H4Z \CO.OH. 2151 These compounds are obtained from the amidobenzoic acids by the methods which are employed in the preparation of phenylhydrazine from aniline (Part III., p. 275). Orthohydrazinebenzoic acid is slightly soluble in alcohol and ether, and crystallizes from hot water in fine needles. It reduces Fehling's solution and salts of silver and mercury in the cold, and combines with bases and acids. When it is gently heated with concentrated hydrochloric acid or heated rapidly to 220°-230° in a stream of carbon dioxide, the anhydride is formed. ZNH\ Orthobenzoylhydrazide, C6H4/ /NH, forms crystals which XX) z are slightly soluble in alcohol, ether, and hot water, have an acid reaction, and are readily dissolved by alkalis. It does not com- bine with acids, and does not reduce salts of mercury or Fehling's solution, but causes a precipitation of silver from an ammoniacal solution.2 Metahydrazinebenzoic acid is insoluble in ether, slightly soluble in alcohol and hot water, and crystallizes in small, yellowish plates, which melt with decomposition at 186°. It has an acid reaction, combines with acids and bases, and reduces Fehling's solution. Nitrous acid converts it into the imide of metadiazo- benzoic acid: zCO2H zCO2H c6h4< " + no9h=c6h4< + h9o. \NH-NH2 " \N-N 1 Voit, Ann. Chern. Pharm. xcix. 100 ; Griess, ibid. cliv. 334; Ber. Deutsch, Chern. Ges. xvii. 606. 2 Fischer, Ber. Deutsch. Chern. Ges. xiii. 679. AZO-DERIVATIVES OF BENZOIC ACID. 265 This is a monobasic acid, which is scarcely soluble in cold, slightly in hot water, and readily in alcohol; it crystallizes in thin plates, melting at 160°. Metahydrazinebenzoic acid is decom- posed in presence of diazobenzene nitrate with formation of diazobenzoic acid imide, metamidobenzoic acid, diazobenzene- imide and aniline.1 AZO-DERIVATIVES OF BENZOIC ACID. 2152 These are formed, like other azo-compounds, by the reduction of the corresponding nitro-derivatives, the following substances being obtained: Azoxybenzoic acids. /N.C6H4.CO2H O< I xN.C6H4.CO2H Azobenzoic acids. N.C6H4.CO2H n.c6h4.co2h Hydrazobenzoic acids. HN.C6H4.CO2H hn.c6h4.co2h. Ortho-azoxybcnzoic acid. Griess prepared this body by heating equal parts of orthonitrobenzoic acid and caustic potash with alcohol.2 It may also be obtained, together with orthonitro- toluene, by boiling orthonitrobenzyl alcohol with caustic potash.3 It is only slightly soluble in water, and crystallizes from hot alcohol in small, white, rhombic prisms, which decompose on fusion. The barium salt is readily soluble in water and forms pointed crystals. Ortho-azobenzoic acid is formed by the action of sodium amalgam on a solution of sodium orthonitrobenzoate. It is almost insoluble in water and crystallizes from hot alcohol in fine, dark-yellow needles, which melt at 237° with partial decomposition. Its yellow barium salt crystallizes with seven molecules of water in prisms, or with nine molecules in needles.4 Orthohydrazobenzoic acid is obtained by treating a concentrated alkaline solution of azoxybenzoic acid with sodium amalgam.5 It crystallizes from alcohol in colourless, elliptical plates or 1 Griess, Ann. Chem. Pharm. ix. 1657 ; Fischer, ibid. xvi. 1335. 2 Ibid. vii. 1611. 3 Jaffe, Hoppe-Seyler's Zeitschr. ii. 57. 4 Griess, Ber. Deutsch. Chem. Ges. x. 1869. 5 Griess, ibid. vii. 1612. 266 AROMATIC COMPOUNDS. microscopic prisms, and is readily oxidized to the preceding compound. Metazoxybenzoic acid is insoluble in water, slightly soluble in alcohol and ether, and forms microscopic needles or plates. Its barium salt is an almost insoluble precipitate.1 Mctazobcnzoic acid was first prepared by Neubauer by the oxidation of metamidobenzoic acid with potassium perman- ganate, but was not further investigated.2 Beilstein and Wil- brand then found that an acid is formed by the action of zinc on an alkaline solution of metanitrobenzoic acid, which, according to its composition, lies between nitro- and amido-benzoic acids.3 Strecker, who prepared it by means of sodium amalgam, named it azobenzoic acid.4 It is also formed by the action of zinc on ammonium metanitrobenzoate.5 Acids separate it from its salts as a light-yellow, viscid precipitate, which becomes granular when heated with alcohol, and is only slightly soluble in water, alcohol, and ether. Its almost insoluble barium salt crystallizes in microscopic, rhombic plates containing five mole- cules of water. On distillation with lime, azophenylene, C12H8N2, is formed, while its copper salt yields azobenzene on dry distillation.6 Mctahydrazobenzoic acid was obtained by Strecker by adding ferrous sulphate and then hydrochloric acid to an alkaline solution of the azo-acid. It is also formed by the continued action of sodium amalgam and other reducing agents. It is amorphous, insoluble in water, and only slightly soluble in alcohol. It is readily oxidized in alkaline solution to the preceding compound and, like hydrazobenzene, undergoes an intermolecular change (Part III., p. 295), when it is boiled with concentrated hydrochloric acid, diamidodiphenic acid, C12H6(NH2)2(CO2H)2, being formed.7 Parazobenzoic acid is almost insoluble in alcohol, water and ether, and forms a yellow or reddish precipitate, which becomes granular on boiling and melts at about 24O0.8 The barium salt is a flesh-coloured precipitate; azophenylene is formed when the calcium salt is distilled (Claus). Parahydrazobenzoic acid is insoluble in water and crystallizes 1 Griess, Jahrcsber. 1864, 352. 2 Ann. Chern. Pharm. cvi. 70. 3 Ibid, cxxviii. 267. 4 Ibid, cxxix. 129. 5 Sokolow, Journ. Prakt. Chem. xciii. 425 ; Liebert, ibid, xciii. 429. 6 Claus, Ber. Deutsch. Chem. Ges. viii. 41. 7 Griess, ibid. vii. 1609 ; Schultz, Ann. Chem. Pharm. cxcvi. 18. 8 Reichenbach and Beilstein, Ann. Chem. Pharm. cxxix. 144 ; Bilfinger, ibid. cxxxv. 154. DIAZOXYBENZOIC ACID. 267 from alcohol in needles; its alkaline solution absorbs oxygen with formation of the azo-acid. Ah Diazoxybenzoic acid, 0^ | >C6H3.CO2H. When 3-dinitro- \n^ oenzoic acid is dissolved in caustic soda and treated with sodium amalgam, the liquid becomes coloured black but remains perfectly clear, appearing brown when diluted. Acids added to this solu- tion precipitate diazoxybenzoic acid as an amorphous, black powder, which is insoluble in water, alcohol, ether, &c., and detonates feebly on heating. The alkali salts form black solu- tions in water ; the salts of other metals are black precipitates. The barium salt, when dried at 70°, becomes so strongly electrified that the particles continue in motion for hours; it loses this property at a higher temperature. Tin and hydrochloric acid reduce the acid to S-diamidobenzoic acid. Isodiazoxybenzoic acid is obtained from /3-dinitrobenzoic acid and resembles the preceding compound, but is not attacked by tin and hydrochloric acid.1 Azonitromethanebenzoic acid, NO2.CH2NrzNC6H4.CO2H, is formed when an aqueous solution of pure metadiazobenzoic acid nitrate is mixed with a dilute solution of nitromethane in caustic potash, and the whole treated with an excess of hydrochloric acid after standing for some time. It is readily soluble in hot alcohol and ether, slightly in boiling water, and crystallizes in stellate groups of yellowish-red plates, which are almost tasteless and detonate on heating. Silver nitrate added to its ammoniacal solution produces a deep red precipitate.2 N.C6H4.CO2H Azo-aceto-acetic benzoic acid, 11 , is obtained N.CH(CO.CH3)CO2H by the action of metadiazobenzoic acid sulphate on aceto-acetic ether, the method described for the preparation of the preceding compound being followed. It is thrown down by hydrochloric acid as a light yellow precipitate consisting of microscopic spheres, and is insoluble in boiling water, crystallizing from hot alcohol in narrow plates or small needles, which have a bitter taste. On careful heating it fuses to an oil, which solidifies on cooling to a waxy mass, but at a higher temperature it detonates 1 Meyer and Michler, Ann. Chem. Pharm. clxxv. 152 ; Per. DcuBch. Chem. Ges. vi. 746, vii. 422. 2 Griess, ibid, xviii. 961. 268 AROMATIC COMPOUNDS. feebly, a large quantity of carbon separating out. Its silver salt is a light yellow, amorphous precipitate. NC6H4.CO2H Azomalonic-benzoic acid, 11 . Griess obtained this NCH(CO2H)2 compound in a similar manner from malonic ether. Hydrochloric acid separates it from the product as an amorphous, fiery yellowish red precipitate, which crystallizes from hot alcohol in microscopic plates. On heating it froths up and chars. zSO3H MONOSULPHOBENZOIC ACIDS, C6H,< \COOH. 2I53 Orthosulphobenzoic acid is formed, together with ortho- sulphamidobenzoic acid, when orthotoluenesulphamide is oxidized with potassium permanganate. On the addition of hydrochloric acid to the filtrate, the anhydride of the sulphamide separates out, while acid potassium orthosulphobenzoate remains in solu- tion and is deposited in large monoclinic tablets.1 It may also be obtained by heating the diazo-compound of anthranilic acid with an alcoholic solution of sulphur dioxide.2 It crystallizes from water in large, monoclinic tablets, which do not deliquesce in the air and melt at 240° with decomposition. On fusion with caustic potash salicylic acid is formed.3 Acid barium orthosulphobenzoate, (C7H5SO3)2Ba + 2H2O, crystallizes in needles, and is less soluble in water than the normal salt. Orthosulphamidobenzoic acid is not known in the free state, as when it is liberated from its salts by the addition of an acid it is immediately converted into the anhydride : zSO2.NH2 CcH4 = c6hZ >nh + h2o. ^CO.OH 00 This body is slightly soluble in cold, more readily in hot water and alcohol, and forms crystals which melt at 220° and are 1 Remsen, Ann. Chern. Pharm. clxxviii. 293 ; Fahlberg and Remsen, Bar. Deutsch. Chern. Ges. xii. 471. 2 Wiesinger, ibid. xii. 1349. 3 Bottinger, ibid. viii. 374. SACCHARIN. 269 sweeter than sugar. The salts, which are readily soluble in water, have also a sweet taste. When the anhydride, which is called benzoylsulphimide, is heated to 150° with hydrochloric acid, it is converted into orthosulphobenzoic acid. It is not attacked by phosphorus pentachloride. According to Fahlberg and List1 it is a powerful antiseptic, and, since a very dilute solution of it is as sweet as a concen- trated solution of cane sugar, they believe that it may find an extended application. It could thus be used as a sweetening agent in the diet of patients suffering from diabetes and in many other cases as a cheap substitute for sugar. They propose for it the unsuitable name of saccharin, which has also been given (Part II., p. 547) to the lactone of saccharic acid. 2154 Metasulphobenzoic acid. In 1834 Mitscherlich found that benzoic acid combines with anhydrous sulphuric acid, SO3, to form an acid which can be heated to above 150°, and boiled with water without decomposition. Its barium salt can also be boiled with caustic potash without losing sulphuric acid. He says, " I propose to name it provisionally benzoylsulphuric acid, since the complexity of its composition necessitates a name which gives a clue to its constitution without indicating it fully."2 Fehling, who investigated its salts more closely, observed that when heated with an excess of caustic potash until complete decomposition has taken place, it yields a residue containing both sulphite and sulphate of potassium, a behaviour which is characteristic of the salts of hyposulphuric acid. " This acid, therefore, contains hyposulphuric and not sulphuric acid," and he therefore called it benzoylhyposulphuric acid.3 It was then investigated with great care by Limpricht and v. Uslar, who recognised it as a sulphonic acid.4 It is also formed by the action of sulphuric acid on benzonitril5 and benzoyl chloride,6 as well as by heating the latter with silver sulphate;7 and by treating metadiazo-amidobenzoic acid with an alcoholic solution of sulphur dioxide.8 1 Journ. Soc. Chem. Ind. iv. 608 ; Ber. Deutsch. Chem. Ges. xix. Eef. 374. 2 Ann. Chem. Pharm. xii. 314. 3 Ibid, xxvii. 322. 4 Ibid. cii. 239 ; cvi. 27. 5 Buckton and Hofmann, ibid. c. 155. 6 Oppenheim, Ber. Deutsch. Chem. Ges. iii. 735. 7 Carins and Kammerer, Ann. Chem. Pharm. cxxxi. 155 ; Ador and Oppenheim, Ber. Deutsch. Chem. Ges. iii. 738 ; Kammerer, ibid. iv. 219. 8 Vollbreeht and Wiesinger, ibid. x. 715. 270 AROMATIC COMPOUNDS. In order to prepare metasulphobenzoic acid, the vapour of sulphur trioxide is passed over benzoic acid, which has been previously fused and powdered, until a transparent mass is formed; or two parts of benzoic acid are heated with one part of fuming sulphuric acid for some time. The product then contains some parasulphobenzoic acid in addition to metasulpho - benzoic acid and free sulphuric acid.1 It is diluted with water, neutralized with barium carbonate and filtered, the filtrate being then heated and treated with hydrochloric acid. The acid salt of the para-acid crystallizes out first on cooling, and then that of the meta-acid, which is purified by recrystallization. The product of the reaction may also be saturated with milk of lime, the filtrate treated with potassium carbonate, and the potassium salt which is thus obtained, recrystallized.2 Metasulphobenzoic acid is a colourless, crystalline mass, which deliquesces in moist air, but solidifies again in dry air. It is not altered by boiling nitric acid. On fusion with potash, metahydroxybenzoic acid is formed (Barth), while with sodium formate it yields isophthalic acid (v. Meyer). The Mctasulphobcnzoatcs. Metasulphobenzoic acid is a power- ful dibasic acid, which decomposes even barium chloride and barium nitrate. Its normal salts are usually readily soluble, while the acid salts dissolve much less easily. Normal potassium metasulphobenzoate, C7H4SO5K2, forms de- liquescent crystals ; the acid salt, C7H5SO5K, crystallizes in long needles, which contain two and half or five molecules of water and are readily soluble in water and alcohol.3 Normal barium metasulphobenzoate, C7H4SO5Ba + 3H2O, is very soluble, and can with difficulty be obtained in well- developed crystals; it is usually deposited in crusts. The acid salt, (C7H5SO5)2Ba + 3H2O, dissolves in 20 parts of cold water, readily in hot water and alcohol, and crystallizes in monoclinic prisms. Normal lead mctasidphobenzoatc, C7H4SO5Pb + 2H2O, is much more readily soluble in hot water than in cold, and forms fine, radiating crystals, resembling those of wavellite. Silver metasulphobenzoate, C7H4SO6Ag2 + H2O, crystallizes in yellow prisms which readily dissolve. Normal ethyl metasulphobenzoate, C7H4SO6(C2H5)2, is prepared from the chloride of the acid and absolute alcohol, and forms a 1 Ann. Chon. Pharm. clxxviii. 275. 2 Barth, ibid, cxlviii. 33. 3 Otto, ibid, cxxii. 155. MONOSULPHOBENZOIC ACIDS. 271 thick liquid which has a faint ethereal odour, and decomposes on heating. It is soluble in water, and its solution decomposes when heated into alcohol and the acid. Acid ethyl metasulphdbenzoate or Ethyl metasulphobenzoic acid, C7H5SO5.C2H5. The ammonium salt of this acid, C7H4SO5 (NH4).C2H5, is obtained by passing ammonia into an alcoholic solution of the normal ether or by the action of alcoholic ammonia on the chloride. It crystallizes in large, four-sided, transparent tablets. If the ammonia be precipitated with platinum chloride, and the excess of platinum removed by sulphuretted hydrogen, a solution of the free acid is obtained; its salts crystallize well and are readily soluble. Its constitution is probably represented by the former of the two following formulae : zso3h c6h4< \co2.c2h5 zSO3.C2H5 c6h4< xCO2H Mctasulphobenzoyl chloride, C7H4SO3C12, is obtained by heating the dry acid with phosphorus pentachloride; the phosphorus oxychloride is then distilled off and the residue washed with water. It is a thick, oily liquid, which has a faint but unpleasant odour, and decomposes on distillation into sulphur dioxide and metachlorobenzoyl chloride. The latter is also formed when the compound is heated to 140°-150° with phosphorus pentachloride. When it is allowed to stand for some time in contact with water or when the acid is acted upon by one molecule of phosphorus pentachloride, the monochloride is formed : zSO2.OH XCOC1 /SO9C1 or C6H4< XCO.OH This separates from ether in warty masses, and is decomposed by boiling water, &c., with formation of metasulphobenzoic acid. Metasulphobenzamide, C7H4SO3(NH2)2, is formed by the action of concentrated aqueous ammonia on the chloride. It is almost insoluble in cold water and crystallizes from hot water or ordinary alcohol in needles containing a molecule of water, while it separates from absolute alcohol in small, vitreous, anhydrous crystals. 272 AROMATIC COMPOUNDS. When it is heated with phosphorus pentachloride the following reaction takes place: zSO2NH2 /SO9.NH2 C6H4< + PCI, = C6H4< " + POC13 + HC1. xCO.NH2 ' \CC1=NH The imido-chloride which is thus formed has not been obtained pure;1 it decomposes on distillation with formation of meta- chlorobenzonitril, while ammonia or water converts it into sulphamidobenzonitril, CN.C6H4.SO2.NH2, which separates from alcohol in crystals, melting at 152°-153°. Metasulphamidobenzoic acid, C7H7NSO4, is formed when the nitril or amide is heated with caustic potash solution: zSO2.NH2 zSO2.NH2 C6H4< " + koh = c6h4< + nh3. \co.nh2 \co.ok It is slightly soluble in cold water, and crystallizes from a hot solution in scales resembling those of potassium chlorate, and melting above 200°. It is a monobasic acid, and forms crystallizable salts. Ethyl metasulphamidobenzoate, C7H6(C2H5)NSO4, is obtained by heating the silver salt with ethyl iodide, or by passing hydro- chloric acid into an alcoholic solution of the acid. It is also formed when ammonia is passed into a solution of sulphobenzoyl chloride in a mixture of alcohol and ether. It crystallizes from alcohol in monoclinic prisms.2 xSH Metathiohydrobenzoic acid, C6H4<^ , is prepared by the xCO2H action of tin and hydrochloric acid on metasulphobenzoyl chloride. It is tolerably soluble in water, more readily in alcohol, and sublimes, when heated in a current of carbon dioxide, in flat needles, melting at 146°-147°. It oxidizes when exposed to the air in a moist state, or more rapidly when acted upon by bromine water, to metadithiobcnzoic acid, S2(C6H4.CO2H)2, which is scarcely soluble in water, and only slightly in alcohol, crystallizing from the latter in short needles which melt at 24G°-2470.3 1 Huth and Wallach, Ber. Deutsch. Chem. Ges. ix. 427. 2 Hart, Amer. Chem. Journ. i. 342. 3 Frehrichs, Ber. Deutsch. Chem. Ges. vii. 792. PARASULPHOBENZOIC ACID. 273 2155 Parasulphobcnzoic acid is obtained by the oxidation of paratoluenesulphonic acid; it is not necessary to employ pure material for its preparation, and the mixture of the three isomeric acids which is obtained by dissolving toluene in sulphuric acid may be conveniently made use of. The para-compound is the chief constituent of the mixture, and, together with the meta- acid, is readily oxidized, while the ortho-acid remains unaltered (Remsen). One hundred grammes of toluene are dissolved in the smallest possible quantity of fuming sulphuric acid, the solution made up to five litres with water, and heated until it becomes colourless. Hydrochloric acid and barium chloride are then added to the filtrate and the precipitated acid barium salt purified by re- crystallization ; 200 grammes of it are obtained in this way.1 It is also formed by the action of alcoholic sulphurous acid on paradiazobenzoic acid (Vollbrecht and Wiesinger). Parasulphobenzoic acid is readily soluble in water, and crystallizes in needles, which are not deliquescent and melt with decomposition at about 200°. On fusion with caustic potash, parahydroxybenzoic acid is formed, while with potas- sium formate it yields terephthalic acid. The potassium salt forms transparent needles which easily dissolve. Normal barium parasulphobenzoate, C7H4SO5Ba + 2H2O, crystallizes in small, tolerably soluble needles. The acid salt, (C7H5SO5)2Ba+ 3H2O, is slightly soluble in hot water, and forms long, flat, lustrous needles. zso2.nh2 Parasulphamidobenzoic acid, C6H5^ , is formed by \CO.OH the oxidation of paratoluenesulphamide with chromic acid solution. It is almost insoluble in cold, slightly soluble in hot water, and readily in alcohol, crystallizing in long, flat, lustrous prisms. 1 Hart, loc. cit. 274 AROMATIC COMPOUNDS. zSO3H DISULPHOBENZOIC ACIDS, C6H3^-CO,H. \so3h 2156 a-Disulphobenzoic acid (2 : 4) is obtained by the oxida- tion of a-toluenedisulphonic acid.1 It is readily soluble in water, insoluble in alcohol, and is deposited from solution in concentrated hydrochloric acid in large crystals, melting above 285°. On heating to 250° with caustic potash, the asymmetric dihydroxybenzoic acid melting at 204° is formed ; at a higher temperature resorcinol is obtained. ft-Disulphobcnzoic acid (3 : 5) is formed when benzoic acid is heated to 250° with fuming sulphuric acid and phosphorus pentoxide. It is a white, hygroscopic, crystalline mass, which on fusion with potash yields the asymmetric dihydroxybenzoic acid, which melts at 232°-233°, while resorcinol is formed when it is heated to 350° with caustic soda.2 Both compounds are strong tribasic acids. zSO3H CHLOROSULPHOBENZOIC ACIDS, CcH3C1( ZCO2H 2157 Four of these compounds are known. The first is obtained by the oxidation of orthochlorotoluenesulphuric acid,3 the second by the action of sulphur trioxide on metachlorobenzoic acid,4 and the last two, one of which only has been examined, from parachlorobenzoic acid.5 zSO3H BROMOSULPHOBENZOIC ACIDS, C6H3BrZ ZCO2H One of these derivatives has been prepared by the oxidation of orthobromotoluene,6 a second from metabromobenzoic acid and sulphur trioxide,7 and two others by the oxidation of the isomeric parabromotoluenesulphonic acids,8 one of them having been also obtained from parabromobenzoic acid.9 1 Blomstrand, Ber. Deutsch. Chern. Ges. v. 1084 ; Fahlberg, Amer. Chern. Journ. ii. 181. 2 Barth and Senhofer, Ann. Chern. Pharm. clix. 271. 3 Hubner and Majert, Ber. Deutsch. Chern. Ges. vi. 792. 4 Otto, Ann. Chern. Pharm. cxxiii. 216. 5 Bottinger and Collen, ibid. cxci. 29. 6 Hubner and Retschy, ibid, clxix. 45. 7 Hubner and Upmann, Zeitsch. Chern. 1870, 295 ; Hubner and Lennep, ibid. 1871, 67. 8 Hubner and Post, Ann. Chcm. Pharm. clxix. 6. 9 Bottinger, ibid. cxci. 13. NITROSULPHOBENZOIC ACIDS. 275 zSO3H NITROSULPHOBENZOIC ACIDS, C6H3(NO2)< ' . \CO.?H 2158 Mulder, as early as the year 1840, prepared a nitro- sulphobenzoic acid by the action of fuming sulphuric acid on metanitrobenzoic acid, but did not investigate it. Limpricht and v. Uslar then obtained one by the nitration of meta- sulphobenzoic acid.1 Remsen prepared another from parasulph- amidobenzoic acid 2 in the same way, and Hart obtained the same compound by nitrating parasulphobenzoic acid. He also prepared another isomeride from orthosulphobenzoic acid and two additional ones by the oxidation of the corresponding nitro- toluenesulphonic acids. AMIDOSULPHOBENZOIC ACIDS. Two of these compounds have been obtained by the action of sulphuric acid on metamidobenzoic acid.3 One of these and three others are formed when the corresponding nitrosulpho- benzoic acids are reduced.4 /PO(OH)2 BENZOPHOSPHINIC ACID, C6H/ XCO.OH 215g This body may be readily obtained by dissolving 10 grams, of paratolylphosphinic acid in a litre of water, adding an excess of caustic potash, heating to 50°, and then running in a solution of 18'4 grams, of potassium permanganate. The latter is completely reduced after about a week, and the solution is then filtered, acidified with acetic acid and evaporated. The potassium acetate is extracted from the residue by alcohol, and the residual acid potassium benzophosphinite dissolved in hot, concentrated hydrochloric acid, the benzophosphinic acid being 1 Bottinger, Ann. Chern. Pharm. cvi. 27. 2 Ibid, clxxviii. 288 ; Hart, Amer. Chern. Journ. i. 342. 3 Griess, Journ. Prakt. Chern. [2] v. 244. 4 Limpricht and v. Uslar ; Hart. 276 AROMATIC COMPOUNDS. deposited from this solution on cooling in transparent, lustrous, striated tablets, which are readily soluble in water, and crystal- lize from it in matted needles with a satin lustre. It melts above 300°, and decomposes when more strongly heated, one portion becoming carbonized while the remainder decomposes into benzoic and metaphosphoric acids. It is not attacked by bromine and water at 130°, while tolylphosphinic acid is decomposed by these at the ordinary temperature into phosphoric acid and bromotoluene. It is a tribasic acid, but readily forms acid salts. Acid potassium benzophosphinate, C6H4(PO3H2)CO.,K + H.,O, crystallizes in fine needles, which are readily soluble in water, slightly in alcohol. When hydrochloric acid is added to its solution,the double salt, C6H4(PO3H2)CO2K+C6H4(PO3H2)CO2H, separates out; it crystallizes from hot water in small prisms. It may also be obtained as a precipitate resembling cream of tartar, by adding the free acid to a tolerably concentrated solution of a potassium salt. Silver benzoplwsphinate, C6H4(PO3Ag2)CO2Ag, is obtained as an amorphous precipitate by adding silver nitrate to a solution of the acid neutralized with ammonia. On heating with methyl iodide, the methyl ether is formed as a thick liquid, which decomposes on boiling. Benzophosphine chloride, C6H4(POC12)COC1, is formed by the action of phosphorus chloride on the acid ; it is a crystalline mass, melts at 83°, boils at 315°, and is attacked by cold water, but is readily decomposed by boiling water.1 Trimcthylphosphobcnzobetaine, C6H4(CO.O)P(CH3)3 + 3H9O. The chloride of this compound is formed by the oxidation of trimethylparatolylphosphonium chloride with potassium per- manganate : zCH3 ,CO.OH C6H4< + 30 = C6Hx + H90. \P(CH3)3C1 \P(CH3)3C1 It crystallizes in short, lustrous prisms, which are readily soluble in water, less so in alcohol. The base, which is liberated by alkalis, crystallizes from hot alcohol in rhombohedra, which deliquesce in the air. When the chloride is heated with an excess of caustic potash solution it decomposes with formation of benzoic acid and trimethylphosphine oxide. 1 Michaelis and Panek, Ber. Deutsch. Chern, Ges. xiv. 405. BENZARSENIC ACIDS. 277 Bimethylphosphinc-oxide benzoic acid, CGH4.PO(CH3)2.CO2H, is formed by the oxidation of dimethyltolylphosphine oxide, and crystallizes in prisms which have a feebly acid taste, melt at 243°, sublime almost without decomposition, and are not easily attacked by caustic potash solution.1 BENZARSENIC ACIDS. 2160 Benzarsenic acid, CGH4(AsO3H2)CO2H, is obtained by oxidizing paratolylarsenic acid in alkaline solution. It is only slightly soluble in water, and crystallizes in large, transparent tablets or nacreous plates. On heating the anhydride, arseno- benzoic acid, C6H4(AsO2)CO2H, is formed; this compound, which corresponds to paranitrobenzoic acid, is a yellowish powder, soluble in hot alcohol. Acid potassium benzarsenate, CGH4(AsO3H2)CO2K + C6H4 (AsO3H2)CO2H, crystallizes from hot water in transparent, triclinic tablets. AsOtpHjO Acid calcium benzarsenate, CGH4/ bCa-|-II2O> \CO OZ forms nacreous plates, slightly soluble in water. Silver benzarsenate, CGH4(AsO3Ag2)CO2Ag, is an amorphous precipitate, which yields the crystalline methyl ether on heating with methyl iodide. Benzarsene chloride, CgH4(AsC12)CO2H, is obtained by the action of phosphorus trichloride on the acid : CGH4(AsO3H2)CO2H + 2PC13 = C6H4(AsC12)COC1 + POC13 + P(OH)3. The product of the reaction is carefully treated with water, and yields the chloride, crystallizing in needles, which melt at 157°-158°, and are decomposed by boiling water. Benzarsene iodide, CGH4(AsI2)CO2H, is formed by the action of hydriodic acid and phosphorus on the acid, and crystallizes from chloroform in yellow needles, melting at 153°. Benzarsenious acid, C6H4As(OH)2CO2H, is prepared by dis- solving the iodide in carbonate of soda and precipitating with hydrochloric acid; it is thrown down in crystals, and crystallizes 1 Michaelis and Czimatis, Ber. Deutsch. Chem. Ges. xv. 2018. 278 AROMATIC COMPOUNDS. from hot water in fine needles, which are converted into the anhydride, C6H4(AsO)CO2H, at 160°. Calcium bcnzarscnite, (C6H4(AsO2H2)CO2)2Ca, crystallizes in nacreous plates, which lose a molecule of water on heating. Silver nitrate added to its solution produces a white precipitate of silver benzarsenite, C6H4(AsO)CO2Ag. Pibenzarsenic acid, (C6H4.CO2H)2AsO.OH, is formed by the oxidation of paraditolylarsenic acid with potassium permanganate and forms fine, lustrous plates, which are scarcely soluble in water, and only slightly in alcohol and hydrochloric acid. Its salts do not crystallize well. Dibenzarsene iodide, (C6H4.CO2H)2AsI, is obtained by heating the acid with hydriodic acid and amorphous phosphorus. It is a crystalline mass which dissolves in alcohol and ether, and melts above 280°. Dibenzarsenious acid, (C6H4.CO2H)2AsOH, is prepared by de- composing the iodide with sodium carbonate ; on the addition of hydrochloric acid, it is obtained as a crystalline precipitate, which is slightly soluble in water, more readily in alcohol. Calcium dibenzarsenite, HOAs(C6H4.CO2)2Ca + 2H2O, is pre- cipitated by alcohol from its aqueous solution as a white powder. Tribcnzarsenic acid, (HO)2As(C6H4.CO2H)3, is formed when tritolylarsine is oxidized ; it is tolerably soluble in water and separates from alcohol in crusts, from ether in granular crystals. Potassium tribenzarsenate, AsO(C6H4.CO2K)3, separates from alcohol in crystalline crusts, which are readily soluble in water. Tribenzarsenious acid, or Arsenctribenzoic acid, As(C6H4.CO2H)3, is obtained by the reduction of tribenzarsenic acid with hydriodic acid and phosphorus ; it crystallizes from ether, in small, colourless needles. Sodium arsene^&ew2:oaZe,As(C6H4.CO2Na)3 + 2H2O, crystallizes from hot water in short, fine needles. The silver salt is a yellowish precipitate.1 1 La Coste, Ann. Chcm. Pharm. ccviii. 1. HYDROXYBENZYL GROUP. 279 HYDROXYBENZYL GROUP. .OH Hydroxybenzyl Alcohols, C6H4<; \ch2.oh. 2161 Orthohydroxybenzyl alcohol. Piria, in 1845, found that salicin, which is contained in willow bark, is split up by the action of dilute acids or of emulsin (p. 130) into grape sugar and a new compound which he therefore named saligenin;1 c13h18o7 + h2o=C6H12O6+C7H8O2. 1O XO 4 4 U 14 v I O This substance, which was subsequently also called salicyl alcohol, because it was found to stand to salicylic acid in the same relation as benzyl alcohol to benzoic acid, was obtained by Beilstein and Reineke by the action of sodium amalgam and water on salicyl aldehyde,2 and Greene found that it is also formed when phenol is heated with methylene chloride and caustic soda solution :3 ZOH C6H5.ONa + CH2C12 +NaOH=C6HZ + 2NaCl. \ch2.oh The decomposition of salicin by dilute acids cannot be employed for its preparation, since a portion of the alcohol is converted into saliretin (p. 280), and the following method, devised by Piria, is therefore made use of. Fifty parts of salicin are brought into 200 parts of water, and 3 parts of emulsin added, this substance being obtained by macerating pressed almonds with 3 parts of water for two hours, and precipitating the solution with alcohol. After twelve hours the greater portion of the saligenin has crystallized out, and the remainder is extracted from the 1 Ann. Chem. Pharm. Ivi. 37. 2 Beilstein and Reineke, ibid, cxxviii. 179. 3 Amer. Chem. Journ. ii. 19. 280 AROMATIC COMPOUNDS. solution with ether. The crude product is then re-crystallized from hot benzene.1 Orthohydroxybenzyl alcohol dissolves in 15 parts of water at 22°, and in almost all proportions in boiling water, readily in alcohol and ether. It crystallizes in small rhombohedra, or tablets, which melt at 82° and sublime at 100°. It forms a bluish red solution in sulphuric acid, and its aqueous solution is coloured deep blue by ferric chloride. Saliretin, C14H14O3 = C6H4(OH)CH2O.C6H4.CH2OH. Bracon- not found that concentrated sulphuric acid converts salicin into a resinous substance, and Piria, who observed that dilute acids have the same effect, gave the product its name, which is intended to suggest both its nature and source.2 Saliretin is formed from salicin by elimination of the elements of water; in order to prepare it, salicin is heated to 80° with 10 parts of fuming hydrochloric acid, the product precipitated by water, dissolved in dilute alcohol and again precipitated by a solution of salt.3 It is a yellowish powder, which dissolves in alkalis and does not yield either salicylaldehyde or salicylic acid on oxidation. Concentrated nitric acid converts it into picric acid. The saliretin obtained by the action of concentrated sulphuric acid has the formula C28H26O5,4 while a compound, C56H50O9, is formed by heating saligenin with acetic anhydride (Beilstein and Seelheim). Salireton, C14H12O3, is formed in small quantity, together with other resinous products, when saligenin is heated with glycerol. It crystallizes from hot water in plates or needles, which melt at 121 '5°, are coloured red by strong sulphuric acid, and are not affected by ferric chloride.5 Orthohydroxybenzyl methyl ether, or Orthomethoxybenzyl alcohol, C6H4(OCH3)CH2OH, is formed when saligenin is heated with methyl iodide, caustic potash and wood spirit; it is a liquid, which boils at 247'5° and solidifies in a mixture of ether and solid carbonic acid to a glassy mass.6 Orthohydroxybenzyl ethyl ether, C6H4(OC2H5)CH2.OH, is a pleasant smelling liquid, which boils at 265° and solidifies at 0° 1 Beilstein and Seelheim, Amer. Chem. Journ. cxvii. 84. 2 Ann. Chem. Pharm. xxx. 179. 3 Kraut, ibid. clvi. 124. 4 Gerhardt, Ann. Chim. Phys. [3] vii. 215. 6 Giacosa, Journ. Prakt. Chem. [2] xxi. 221. 6 Cannizzaro and Korner, Ber. Deutsch. Chem Ges. v. 436. SALICIN. 281 to a crystalline mass. It gives no colouration with ferric chloride, and is oxidized by dilute nitric acid to ethoxybenzoic acid or ethyl salicylic acid, CeH/OCoH^CO.OH.1 Caffeol, C8H10O2. When coffee beans are roasted, the follow- ing substances are given off from 100 parts : 0'05 of caffeol, 0'18 of caffeine, 0'48 of fatty acids, chiefly palmitic and acetic, carbon dioxide and small quantities of pyrrol, methylamine and quinol, derived probably from the quinic acid which is contained in the beans. Caffeol is a liquid which boils at 195°-197°, and possesses the fine aroma of coffee in a very marked degree. Its alcoholic solution gives with ferric chloride a red colouration which is not destroyed by sodium carbonate. It only dissolves with difficulty in concentrated caustic potash solution, and on fusion with caustic potash yields salicylic acid; it is probably therefore a methyl ether of saligenin, and has the constitution C6H4(OH)CH.2.OCH3.2 The fact that it gives a red colouration with ferric chloride, which shows it to be a phenol, is in accordance with this sup- position. Rotsch has also found that hydroxybenzyl methyl ether, already mentioned, which is isomeric with caffeol, smells strongly of burnt coffee, but loses the smell completely on purification. This behaviour may be explained by the formation of small quantities of caffeol as a by-product, to which the crude product owes its smell. 2162 Salicin, or Orthohydroxylenzyl glucoside, C6II4(CH2.OH) OC6HuO5. After several chemists had unsuccessfully endeavoured to obtain the bitter principle of willow-bark, which was recom- mended in cases of intermittent fever as a substitute for quinine, in the pure state, Leroux succeeded in purifying it to such an extent that it could be readily crystallized.3 It was at first thought to be an alkaloid, although this was afterwards shown not to be the case, and the difficulty experienced in obtaining compounds of it with other substances prevented chemists from examining it more closely until Piria subjected it to a careful investigation, which resulted in a complete explanation of its nature.4 It occurs in the bark, leaves, and female flowers of many trees which do not all belong to the willow tribe, and to the extent of 4 per cent, in Salix helix, pentandra, and prcecox-, it 1 Rotsch, Monatsch. Chem. i. 621. 2 Bernheimer, ibid. i. 456. 3 Ann. Chim. Phys, xliii. 440. 4 Ann. Chem. Pharm. xxx. 151 and 189 ; Ivi. 49 ; Liebig, ibid. xxx. 185. 282 AROMATIC COMPOUNDS. has also been found in the bark and leaves of the poplar,1 in the flower buds of Spiraea Ulmaria (p. 28G) and in castoreum2 (Wohler). In order to prepare it, 3 parts of willow-bark are extracted three times with boiling water, the extract evaporated down to 9 parts, digested for twenty-four hours with 1 part of litharge, filtered and evaporated to a syrup. The salicin separates out and is purified by re-crystallization.3 It forms needles, plates, or rhombic prisms, which dissolve in 30 parts of water at the ordinary temperature, and freely in hot water and alcohol, but are insoluble in ether; it has a very bitter taste, and forms a purple-red solution in sulphuric acid. Dilute nitric acid oxidizes it to helicin, C6II4(CHO)OC6H11O5 (p. 288), which may be re- converted into salicin by sodium amalgam and water. As helicin can be artificially prepared by the action of acetochloro- hydrose on salicyl aldehyde, it is also possible, as Michael has shown, to prepare salicin artificially; this is the first instance of the synthesis of a glucoside occurring in nature.4 Salicin melts at 201°, and solidifies on cooling to a crystalline mass; when it is heated, however, for some time to 230°- 240°, it partially decomposes into saliretin and glucosane5 (Part II. p. 540). Its aqueous solution rotates the plane of polarization to the left.6 When taken internally a portion of it appears in the urine as saligenin, salicylaldehyde and salicylic acid, the remainder being excreted unchanged;7 its occurrence in castoreum is thus explained. It is used in medicine in cases of intermittent fever, acute rheumatism, &c., and is also employed for adulterating quinine. Populin, or Benzoylsalicin, C13H17(C6H5.CO)O7 + 2H.2O, was discovered by Braconnot in the bark and leaves of the aspen poplar, Populus trcmula* and carefully investigated by Piria.9 Piccard also observed it, along with salicin and other substances, in the buds of Populus pyramidalis, nigra et balsaniifera™ and Schiff obtained it artificially by fusing salicin with benzoic anhydride.11 1 Braconnot, Ann. Chim. Phys. xliv. 296 ; Tischhausen, Ann. Chern. Pharm vii. 280. 2 Ibid. Ixvii. 360. 3 Dnflos, ibid. viii. 200. 4 Amer. Chem. Journ. v. 171. 5 Schiff, Ber. Deutsch. Chem. Ges. xiv. 304. 6 Hesse, Ann. Chem. Pharm. clxxvi. 116. 7 Laveran and Millon, ibid. lii. 435; Eanke, Jahresb. Chem. 1852, 711. 8 Ann. Chim. Phys. xliv. 296. 9 Ann. Chem. Pharm. Ixxxi. 245 ; xcvi. 375. 10 Ber. Deutsch. Chem. Ges. vi. 890. 11 Ann. Chem. Pharm. cliv. 5. BENZOYLSALICIN. 283 It crystallizes in extremely thin needles, which dissolve in 2,420 parts of water at 15° and in 42 parts at 100°; it loses its water of crystallization at 100° and melts at 180°. Its taste resembles that of liquorice ; it is coloured amaranthine red by sulphuric acid. Boiling baryta water decomposes it into salicin and benzoic acid; emulsin has no action upon it, but on boiling with a dilute acid it yields saliretin, benzoic acid and dextrose,1 while salicin, benzamide, and ethyl benzoate are obtained by heating it with alcoholic ammonia. Nitric acid oxidizes it to benzoyl-helicin, which is the corresponding aldehyde. It has, therefore, the following constitution : ZCH,.OH c6h4< xOC6H10(CO.C6H5)O5 2163 Metahydroxybenzyl alcohol is obtained by the action of sodium amalgam on an aqueous solution of metahydroxybenzoic acid which is kept acid by the repeated addition of small quantities of hydrochloric acid. It is readily soluble in alcohol and hot water, crystallizes in tough needles, melts at 63°, and boils with partial decomposition at about 300°; its aqueous solution is coloured violet-blue by ferric chloride. Hydrochloric acid converts it into a viscid resin, and on fusion with caustic potash it is oxidized to metahydroxybenzoic acid. Mctahydroxybenzyl acetate, C6H4(OH)CH2.O.C2H3O, is formed by the action of a mixture of acetic and sulphuric acids on the alcohol, and forms crystals which melt at 55° and are only very slightly soluble in water; the solution is coloured violet-blue by ferric chloride. It boils with decom- position at 295°-302°. Metahydroxybenzyl diacetate, or Mcta-acetobenzyl acetate, C6II4 (OC2H3O)CH2.OC2H3O, is formed by heating the alcohol to 160° with acetic anhydride, and is a liquid which boils at 290°, and does not give a colouration with ferric chloride.2 Parahydroxybenzyl alcohol is obtained by the action of sodium amalgam on a solution of parabenzaldehyde in dilute alcohol acidified with sulphuric acid. It is readily soluble in water, alcohol and ether, and crystallizes in needles, melting at 110°. It forms a splendid reddish violet solution in concentrated sulphuric acid.3 1 Schmidt, Ann. Chern. Pharm. xix. 92. 2 Velden, Joum. Prakt. Chern. [2] xv. 165. 3 Biedermann, Ber. Deutsch. Chem. Ges. xix. 2373. 284 AROMATIC COMPOUNDS. Parahydroxybenzyl methyl ether, or Anise alcohol, CcH4(OCH3) CH2.OH, is formed by the action of alcoholic potash on anis- aldehyde (paramethoxybenzaldehyde).1 It is also formed when parahydroxybenzyl alcohol is heated with methyl iodide and caustic potash, and crystallizes in hard, lustrous needles, which have a faint spirituous odour and a burning taste; it melts at 25°, and boils at 258'80.2 Paramethoxybenzyl chloride, C6H4(OCH3)CH2C1, is prepared by saturating the alcohol with hydrochloric acid ; it is a liquid with a fruity odour and burning taste. On treatment with sodium methylate it yields the dimethyl ether C6H4(OCH3)CH2.OCH3, a liquid boiling at 225'5°.3 Parahydroxybenzyl acetate, C6H4(OH)CH2.O.C2H3O, is formed in a similar manner to the meta-compound, and crystallizes in yellowish needles melting at 84°. Para-acetobenzyl acetate, C6H4(OC2H3O)CH2.OC2H3O, also forms yellow needles, melting at 75° (Biedermann). Paramethoxybenzylamine, C6H4(OCH3)CH2.NH2, is obtained by the action of ammonia on the chloride, and crystallizes from hot water in small needles which have a strongly alkaline reaction and melt above 100°. The secondary base, (C8H9O)2NH, is formed simultaneously; it is less soluble in water, and crystal- lizes in plates melting at 32°-33°.4 Parahydroxybenzyl thiocarbimide, C6H4(OH)CH2N - CS, has been already mentioned as sinalbin mustard oil (Part II. p. 392). It is a product of the decomposition of sinalbin, C30H44N2S2O16, which crystallizes in small, lustrous needles and is readily soluble in water, slightly in alcohol; it is converted by myrosin in presence of water into sinalbin mustard oil, acid sinapin sulphate, and grape sugar: WW,, - c8h,nos + C10H23NO5,H2SO4 + C6H12O„. Sinalbin mustard oil is a non-volatile, oily liquid, which has a very sharp taste and blisters the skin. When the sulphur is removed it is converted into parahydroxyphenylacetonitril, CcH4(OH)CH2.CN, which was considered to be the ortho- compound by Laubenheimer, and Will.5 1 Bertagnini and Cannizzaro, Ann. Chem. Pharm. xcviii. 189. 2 Cannizzaro and Korner, Per. Deutsch. Chem. Ges. v. 436. s Cannizzaro, Ann. Chem. Pharm. cxxxvii. 246. 4 Ibid. cxvii. 240. 5 Ann. Chem. Pharm. cxcix. 150. SALICYLALDEHYDE. 285 /OH HYDROXYBENZALDEHYDES, C6H4<f \CHO. Orthohydroxybenzaldehyde, or Salicylaldehyde. 2164 The volatile oil of the flowers of Spircca Ulmaria was first examined by Pagenstecher, an apothecary of Berne, who discovered in it an acid, the aqueous solution of which is coloured violet by ferric chloride,1 and which was called " spiroyhuasser- stoffsaure" C12H6O(C = 6,0 = 8) by Lowig, to whom Pagenstecher intrusted its further investigation.2 He and Weidmann sub- sequently found that when the ethereal solution is shaken with caustic potash, this is coloured yellow, and on evaporation of the ether an indifferent oil remains behind, which possesses the smell of the flowers in a very marked degree, while if the alkaline solution be distilled with phosphoric acid, an acid oil passes over first, followed by an acid crystallizing in long needles. They now called the former of these spirccic acid, or spiroyl hydride, C13H10O4.3 About the same time, Piria, working in Dumas' laboratory, found that salicin on oxidation with potassium dichromate and dilute sulphuric acid yields a volatile, oily, aromatic liquid, which he called salicyl hydride, C7H6O2. This is isomeric with benzoic acid, and is to be looked upon as a hydracid, which, on heating with caustic potash, yields salicylic acid, C7H6O3, just as benzoyl hydride under similar circumstances yields benzoic acid. The radicals benzoyl, C7H5O, and salicyl, C7H5O2, are different oxidation products of the hydrocarbon, C7H5.4 Dumas, to whom Pagenstecher showed his preparations from Spiraea, noticed the great similarity of the oil to salicyl hydride and suggested that spiraeic acid is identical with the latter;5 this had already been proved by Ettling, who named the compound salicylous or spiroylous acid.6 The compound was mistaken for an acid because it is at once an aldehyde and a phenol, and therefore forms salts. Salicylaldehyde also occurs in the juice of various plants 1 Buchner's Report. Pharm. xlix. 337 ; li. 364. 2 Pogg. Ann. xxxvi. 383. 3 Ibid. xlvi. 57. -♦ Ann. Chern. Pharm. xxix. 300, xxx. 151. 5 Ibid. xxix. 306. 6 Ibid. xxix. 309; xxxv. 241. 286 AROMATIC COMPOUNDS. belonging to the genus Spiraea,1 in the stein and root of Crepis foetida? and in the larvae of Chrysomela populi, which live on willows and poplars, and possess small openings along the body from which salicyl aldehyde may be pressed out in oily drops.3 Enz also obtained it by distilling the beetle with water.4 In order to prepare it, a mixture of 3 parts of salicin and 3 parts of potassium dichromate is treated with 24 parts of water, to which 4'5 parts of sulphuric acid diluted with 12 parts of water are added. When the reaction is complete, the mixture is distilled until the distillate passes over clear, and the oily portion then separated from the water; some of the aldehyde remains dissolved in the water and is extracted by ether.5 If the distillation be continued too long, furfurol passes over, and all preparations made from the aldehyde then become intensely red-coloured on standing.6 The flower-buds of Spircea Ulmaria omy give a very small yield of salicyl aldehyde on distillation with water, but a larger quantity is obtained when sulphuric acid and potassium di- chromate are added, thus showing that the buds contain salicin.7 Salicyl aldehyde is obtained synthetically, along with the isomeric parahydroxybenzaldehyde, by the action of chloroform on a solution of phenol in caustic soda (Part III. p. 32). They are separated by distillation in steam, with which the latter is not volatile.8 Properties.-Salicylaldehyde is a liquid with a pleasant aromatic smell and a burning spice-like taste; it boils at 196'5°, solidifies at 20° to large crystals, and has a specific gravity of 1'1731 at 13'5°. Its aqueous solution, even when very dilute, is coloured violet by ferric chloride, and yellow by alkalis; it does not reduce Fehling's solution,9 and forms difficultly soluble com- pounds with the acid sulphites of the alkali metals,10 this property being made use of in its purification (Reimer and Tiemann). It produces a fine reddish violet colouration in a solution of rosaniline which has been decolourized by sulphurous acid.11 The aldehydes of the fatty acids, benzaldehyde, &c., also give this reaction (Part II. p. 495). 1 Wicke, Ann. Chem. Pharm. Ixxxiii. 175. 2 Ibid. xci. 374. 3 Jahresber. Chem. 1850, 583. 4 Ibid. 1859, 312. 6 Schiff, Ann. Chem. Pharm. cl. 193. 6 Ibid. ccx. 115. 7 Buchner, ibid. Ixxxviii. 284. 8 Reimer and Tiemann, Bcr. Deutsch. Chem. Ges. ix. 824. 9 Tollens, ibid. xiv. 1959. 10 Bertagnini, Ann. Chem.. Pharm. Ixxxv. 93. 11 Schmidt, Ber. Deutsch. Chem. Ges. xiv. 1848. SALICYLALDEHYDE COMPOUNDS. 287 Asa phenol it forms salts, ethers, and ethereal salts. Potassium salicylaldehyde, CGH4(OK)CHO + H2O, is obtained by adding caustic potash to a solution of the aldehyde in dilute alcohol; it crystallizes in light yellow, nacreous, quadratic tablets, which are readily soluble in water. The compound CGH4(OK) CHO 4- CGH4(OH)CHO is obtained in fine, fascicular groups of needles by adding the aldehyde to an alcoholic solution of the potassium salt. Barium salicylcddehyde, (C6H4(CHO)O)2Ba+ 2H2O, crystallizes in yellow needles, which are slightly soluble in cold water. Copper salicylaldehyde, (CGH4(CHO)O)2Cu, is a very character- istic salt; when an aqueous solution of copper acetate is added to a dilute alcoholic solution of the aldehyde, the liquid becomes coloured emerald green, and after a few minutes deposits spark- ling crystals; the liquid then presents a most beautiful appearance when placed in the sunlight. The crystals become brownish- green on drying, and are only slightly soluble in water and alcohol (Ettling). Lead salicylaldehyde, CGH4(CHO)OPb.OH, is formed when basic lead acetate is added to an alcoholic solution of the alde- hyde ; it is a yellow precipitate which dissolves on heating, and separates out on cooling in heavy, light-yellow granules. Methyl salicylaldehyde, CGH4(OCH3)CHO, is obtained by heating the sodium salt with methyl alcohol and methyl iodide.1 It is an oily liquid which possesses a faint odour, boils at 238°, and, when perfectly free from salicylaldehyde, solidifies after some time to tough prisms melting at 35°. It forms a compound with acid ammonium sulphite, which crystallizes in lustrous prisms and is readily soluble in water and alcohol. The potassium sulphite compound also crystallizes well, but is only slightly soluble in cold alcohol. Bthyl salicylaldehyde, CGH4(OC2H5)CHO, was obtained by Perkin in a similar manner, as a strongly refractive liquid boiling at 247°-249°. It is also formed when a mixture of calcium formate and calcium ethyl salicylate is distilled, while, when calcium salicylate is substituted for the ethyl compound, only phenol is formed.2 Benzyl salicylaldchyde, CGH4(OCH2.CGH5)CHO, crystallizes from boiling alcohol in flat, rhombic prisms, which melt at 46°, 1 Perkin, Journ. Chern. Soc. xx. 418 ; Voswinkel, Ber. Deutsch. Chem. Ges. xv. 2024. 2 Gottig, ibid. x. 8. 288 AROMATIC COMPOUNDS. and have a faint odour resembling that of cloves. It boils above 360°, and forms an irritating vapour.1 Acetyl salicylaldehyde, C6H4(OC2H3O)CHO, is formed when the sodium salt is suspended in ether and treated with acetic anhydride. It is extremely soluble in alcohol, crystallizes in fine, silky needles, melts at 37°, and then solidifies to a mass possessing a satin lustre. Its boiling-point lies at about 253°; it combines with the acid sulphites of the alkali metals.2 Benzoyl salicylaldehyde, C6H4(O.CO.C6H5)CHO, was obtained by Perkin by the action of benzoyl chloride on the sodium compound. It is a thick oily liquid, which boils above 360°, and forms the usual compounds with the acid sulphites of the alkali metals.3 2165 Helicin, 4C6H/OC6HnO5)CHO + 3H2O, is formed by the action of dilute nitric acid on salicin.4 In order to prepare it, salicin is treated in flat basins or plates with eight times its weight of nitric acid of sp. gr. 1'15, containing lower oxides of nitrogen, which may be introduced by the addition of a few drops of the red, fuming acid. The helicin is filtered off after some hours and washed two or three times with cold water.5 It is readily soluble in hot water and alcohol, but not in ether, and crystallizes in small, very fine needles, which have a faint, bitter taste, lose their water of crystallization at 100° and melt at 175°. It is not coloured by ferric chloride; if a blood- red colouration be produced, it contains nitrosalicylic acid. It is resolved into dextrose and salicylaldehyde by the action of acids, alkalis and emulsin. It can be synthetically prepared by acting upon potassium salicylaldehyde with an alcoholic solution of acetochlorohydrose :6 .CHO C«H4<\ + C6H7C1(C2H3O)4O5 + 4C2H5.OH = /CHO C6H,< + 4C2H5OC2H3O + KC1. V \ 4 O Lt o \OC6HnO5 It is reduced to salicin by the action of sodium amalgam and water.7 It forms a compound with acid sodium sulphite, 1 Perkin, Journ. Chem. Soc. xxi. 122. 2 Ibid. xxi. 181. 3 Ibid. cxlv. 295. 4 Piria, ibid. Ivi. 64. B Schiff, ibid. cliv. 14. 6 Michael, Amer. Chern. Journ. i. 309. 7 Lisenko, Jahresber. Chem. 1864, 588. DERIVATIVES OF HELICIN. 289 which has the formula C13H16O7.SO3HNa, and forms a dazzling white, hygroscopic, crystalline mass.1 When it is moistened with one per cent, nitric acid, dried and heated to 110°-115°, it is converted into parahelicin, which is without doubt a polymeride; this substance is an amorphous, starchy, tasteless powder, which is scarcely soluble in water and alcohol, and has no action upon a solution of rosaniline reduced by sulphurous acid, whereas helicin forms a reddish violet crystalline compound with it. It dissolves in very dilute hydrochloric acid which has been slightly warmed, and is thus reconverted into helicin.2 Tetracetylhelicin, C13H12(C2H3O)4, was obtained by Schiff by heating helicin with acetyl chloride or acetic anhydride ; it crystallizes from hot alcohol in long, silky needles or prisms. Benzoylhelicin, C13H15(CO.C6H5)O7. Piria prepared this com- pound by the action of nitric acid on populin (p. 282),3 and Schiff by heating helicin with benzoyl chloride.4 It crystallizes in silky needles, which are slightly soluble in water, more readily in alcohol. Sodium amalgam and water reduce it again to populin; on boiling with water and magnesia it is decomposed into helicin and benzoic acid. Helico'idin, C26H34O14, is formed by dissolving salicin in nitric acid of sp. gr. 1'085 : 2C13Hi8O7 + O - C26H34O14 + H2O. It crystallizes from hot water in needles, and is very similar to helicin, from which it differs in being resolved by acids, &c., into dextrose, salicylaldehyde, and saligenin (Piria). Octacctylhclico'idin, C26H26(C2H3O)8O14, is obtained by heating helico'idin to 100° with acetic anhydride; it is insoluble in water, and crystallizes from alcohol in druse-like aggregates, melting at 80° (Schiff). Ortho-aldehydophenoxy acetic acid, C6H4(COH)OCH2.CO2H, is formed when equal molecules of salicylaldehyde and chloracetic acid are heated together and the fused mass treated with an excess of caustic soda solution of sp. gr. 12-1'3; the mixture is then heated on the water-bath until it has become almost solid, the acid precipitated by hydrochloric acid and 1 Schiff, Ann. Chern. Pharm. ccx. 126. 2 Ibid. Bet. Deutsch. Chem. Ges. xiv. 317. 3 Ann. Chem. Pharm. xcvi. 379. 4 Ibid. cliv. 23. 290 AROMATIC COMPOUNDS. re-crystallized from hot water. It forms large, yellow plates, which melt at 132°, and sublime when gradually heated. Like other aldehydes it reduces Fehling's solution and am- moniacal silver solution, and combines with phenylhydra- zine and acid sodium sulphite. Its salts are readily soluble and crystallize well; its ethyl ether forms needles melting at 1140.1 2166 Orthohydroxybenzidene compounds. These are obtained in a similar manner to the benzidene compounds. .OH Ortliohydroxybenzidene acetate, CGH4^ is formed \CH(OCO.CH3)2, when salicylaldehyde is heated to 150° with acetic anhydride; it crystallizes from alcohol in thick, hard, transparent tablets, which melt at 103°-104°, and distil with slight decom- position.2 Perkin has obtained the following compounds in a similar manner: yOCH3 Melting-point. CGH4y , lustrous prisms 75° \CH(OCO.CH3)2 zoc2h5 CGH4y , small prisms 88°-89° \CH(OCO.CH3)2 zoco.ch3 C6H4<^ , needles or pointed tablets 100°-101° \CH(O.CO.CH3)2 The last compound may also be obtained by heating salicyl- aldehyde to 180° with acetic anhydride.3 Tolerably concentrated caustic potash decomposes it into acetic acid and orthohydroxy- benzidene acetate, while it splits up on distillation into acetyl- salicylaldehyde and acetic anhydride.4 Orthohydroxybenzidenoxime, or Salicylaldoxime, CGH4(OH) CHzzzN.OH, is formed by the action of hydroxylamine on salicylaldehyde, and forms white crystals which dissolve readily in alcohol, ether and benzene, but are insoluble in petroleum spirit, and melt at 57°.5 Its compounds resemble those of benzaldoxime (p. 139). 1 Rbssing, Bar. Deutsch. Chem. Ges. xvii. 2988. 2 Perkin, Ann. Chem. Pharm. cxlvi. 371. 3 Barbier, Bull. Soc. Chim. xxxiii. 53. 4 Perkin, Ann. Chem. Pharm. cxlviii. 203. 5 Lach, Ber. Deutsch. Chem. Ges. xvi. 1782. HYDROSALICYLAMIDE. 291 Hydroxybenzidene-amidobenzoic acid, CGH4(OH)CH-NC6H4 CO2H, is prepared by mixing warm, dilute, aqueous solutions of salicylaldehyde and metamidobenzoic acid. It crystallizes in long, yellow needles, which are very soluble in alcohol and benzene. Its aqueous solution gives off salicylaldehyde on evaporation.1 Helicin combines with metamidobenzoic acid to form the analogous compound CGH4(OCGHnO5)CH=zNCGH4.CO2H, which crystallizes from alcohol in lustrous plates, melting at 142°;2 it is resolved into the preceding compound and grape sugar by heating with an aqueous solution of emulsin. Hydrosalicylamide, N2(CH.C6H4.OH)3. This compound, cor- responding to hydrobenzamide (p. 140), was prepared by Ettling by the action of ammonia on an alcoholic solution of salicylalde- hyde, and named by him salicylimide.3 It forms heavy, light yellow crystals, melting at 300°, and is insoluble in water, slightly in cold, more readily in hot alcohol, and decomposes into salicyl- aldehyde and ammonia when heated with concentrated caustic potash solution or strong acids. It absorbs three molecules of hydrochloric acid, forming a compound which decomposes in moist air into salicylaldehyde and ammonium chloride.4 As a phenol it forms metallic salts ; when an ammoniacal solution of copper acetate is added to its cold alcoholic solu- tion, the liquid becomes coloured emerald-green, and after a few minutes becomes decolourized, cruciform plates being de- posited, which after drying have a strong satin lustre; their composition is represented by the formula (C21H15N2O3)2Cu3 (NH3)2. They are almost insoluble in water and alcohol, and form a green solution in hydrochloric acid, from which they are reprecipitated by alkalis. They are not attacked by cold caustic potash, and decomposition only proceeds slowly on boiling; salicylaldehyde is formed when it is heated with strong acids. Orthobenzidencphenylhydrazine, C6H4(OH)CH-N9H.C6H5, crystallizes from hot, dilute alcohol in yellow needles or plates, melting at 142°-143°. When it is heated with chloracetic acid a colouring matter, C9H7NO3, is produced, which forms a deep bluish green solution in alcohol and is coloured cherry-red by alkalis.5 1 Schiff, Ann. Chem. Pharm. ccx. 114. 2 Ber. Deutsch. Chem. Ges. xii. 2032. 3 Ann. Chem. Pharm. xxxv. 261. 4 Bode, Jahresb. Chem. 1857, 318. B Fischer, Ber. Deutsch. Chem, Ges. xvii. 575 ; Bossing, ibid. 3004. 292 AROMATIC COMPOUNDS. SUBSTITUTION PRODUCTS OF SALICYL- ALDEHYDE. 2167 Chlorosalicylaldchyde, C6H3C1(OH)CHO, is formed by the action of chlorine on salicylaldehyde.1 It is insoluble in water, and crystallizes from alcohol in rectangular tablets. Bromosalicylaldchyde, C6H3Br(OH)CHO, is not only formed by the direct action of bromine2 but also when salicylaldehyde is treated with phosphorus pentabromide, the latter compound act- ing in the same manner as a mixture of bromine and phosphorus pentabromide.3 It crystallizes from ether in small plates, melt- ing at 98°-99°; its alcoholic solution is coloured violet by ferric chloride. Melting-point. Methylbromosalicylaldehyde, flat prisms ) 4, Q0 11 < -o C6H3Br(OCH3)CHO. J-113 -Mi o . Ethylbromosalicylaldehyde,4 sharp prisms 1 C6H3Br(OC2H6)CHO. J b 1 ~bb * a-Nitrosalicylaldchyde, C6H3(NO2)(OH)CHO, is formed, to- gether with the yS-compound, by boiling salicylaldehyde with dilute nitric acid ;5 the two substances are separated by means of their barium salts. a-Nitrosalicylaldehyde crystallizes in small yellow prisms, which melt at 105°-107°, while its barium salt, (C7H4NO4)2Ba + 2H2O, forms slightly soluble, yellowish red columns. ft-Nitrosalicylaldehyde forms needles, melting at 123°-125°; its barium salt, (C7H4NO4)2Ba + 6H2O, crystallizes in yellow prisms. Methylnitrosalicylaldcliyde, C6H3(NO2)(OCH3)CHO, forms fine, white needles, melting at 880.6 1 Piria, Ann. Chem. Pharm. xxx. 169 ; Lowig, Ben. Jahresb. xx. 311. 2 Piria ; Lowig, Pegg. Ann. xlvi. 57 ; Heberlein, Berz. Jahresb. xxv. 484. 3 Henry, Ber. Deutsch. Chem. Ges. ii. 274. 4 Perkin, Ann. Chem. Pharm. cxlv. 304. 5 Mazzara, Gazz. Chim. Itai. vi. 460. 6 Voswinkel, Ber. Deutsch. Chem. Ges. xv. 2027 ; Schnell, ibid. xvii. 1381. METAHYDROXYBENZALDEHYDE. 293 METAHYDROXYBENZALDEHYDE. 2168 This compound is formed, together with metahydroxy- benzyl alcohol, by the action of sodium amalgam on a faintly acid solution of metahydroxybenzoic acid. It can be more readily obtained from metamidobenzaldehyde by treating its well-cooled solution in hydrochloric acid with the calculated quantity of sodium nitrite and then heating.1 It crystallizes from hot water in white needles, melting at 104°; its aqueous solution is coloured a faint violet by ferric chloride, and it differs from the isomeric para-compound in giving a precipitate with lead acetate. Mcthylmetahydroxybenzaldehyde, C6H4(OCH3)CHO, is obtained by heating the aldehyde with caustic potash, methyl iodide and wood-spirit. It is an oily liquid, which boils at 230° and has a pleasant odour. Acetylmetahydroxybenzaldehyde, C6H4(OCO.CH3)CHO, is formed by the action of acetic anhydride on the potassium compound of the aldehyde, and is an oily liquid, boiling at 263.° Acetometahydroxybenzidene acetate, C6H4(OCO.CH3)CH(O. CO.CH3)2, is produced when the aldehyde is boiled with an excess of acetic anhydride. It is slightly soluble in water, readily in alcohol, and crystallizes in lustrous, white plates, melting at 7G.° Nitro-substitution products. The three following compounds are all formed by the direct nitration of the aldehyde; they may be separated by re-crystallization from hot water, chloro- form, &c. a-Nitrometahydroxybenzaldehyde, C6H3(NO2)(OHjCHO, crys- tallizes in yellowish plates, melting at 128°, which are slightly soluble in cold, more readily in hot water, and readily in chloroform and petroleum ether. ^-Nitromctahydroxybenzaldchyde forms needles which melt at 166°, and is more readily soluble in water than the a-compound, but only very slightly soluble in chloroform and benzene. y-Nitrometahydroxybcnzaldehyde melts at 138°, and crystallizes 1 Tiemann and Ludwig, Ber. Deutsch. Chem. Ges. xv. 2043 and 3052. 294 AROMATIC COMPOUNDS. in prisms, which dissolve readily in hot water, chloroform and benzene, but only with difficulty in petroleum ether. When these compounds are heated with caustic potash, wood- spirit and methyl iodide, their methyl ethers, C6H3(NO2)(OCH3) CHO, are formed (Tiemann and Ludwig); these can also be obtained by the nitration of metamethoxybenzaldehyde.1 a-Orthonitromethylmetahydroxy^^ crystallizes from chloroform in thick, yellow prisms, melting at 107°. {d-OrthonitTomethylmctaliydroxyhenzald^ forms white plates or needles, which melt at 82°-83°. These bodies are known to be orthonitro-compounds because they give the indigo reaction (p. 146). Metanitromethylmetahydroxybenzaldchyde crystallizes in needles or prisms, and melts at 98°. Paranitromrtliylmetcdiydroxybenzaldchyd was obtained by Ulrich by the oxidation of paranitromethoxycinnamic acid; it crystallizes in hair-like needles and melts at 62°. PARAHYDROXYBENZALDEHYDE. 2169 This body was first prepared by Bucking by heating the methyl ether, anisaldehyde, with hydrochloric acid.2 It may be synthetically obtained by the action of chloroform on an alkaline solution of phenol, salicylaldehyde being formed at the same time. In order to prepare it, 30 parts of chloroform are gradually added to a solution of 20 parts of phenol in 120 parts of water heated to 50°-60°; the liquid becomes coloured blue and then deep red, a considerable rise of temperature taking place, the use of an inverted condenser being thus rendered necessary. The mixture is finally boiled for half an hour, the excess of chloroform distilled off, an excess of sulphuric acid added, and the whole distilled in steam, salicylaldehyde passing over along with any free phenol, from which it is subsequently separated by means of acid sodium sulphite. The residual liquid is filtered while hot from the deep red coloured resin which is formed, and after cooling is extracted with ether; on evaporation of the ether, the parahydroxybenzaldehyde is left behind, and is then re-crystall- ized from boiling water.3 It is slightly soluble in cold, more readily 1 M. Ulrich, Ber. Deutsch. Chern. Ges. xviii. 2571. 2 Ibid. ix. 527. 3 Reimer and Tiemann, ibid. ix. 824 ; Tiemann and Herzfeld, ibid. x. 63. PARAHYDROXYBENZALDEHYDE. 295 in hot water, and readily in alcohol, ether, &c., and crystallizes in fine needles, which have a faint but pleasant aromatic odour, melt at 115°-116°, and sublime unaltered. Its aqueous solu- tion is coloured a dirty violet by ferric chloride ; if its ethereal solution be shaken up with a solution of acid sodium sulphite, combination ensues, but the double compound is readily soluble. Its solution is not easily attacked by oxidizing agents, but it is converted into parahydroxybenzoic acid by fusion with caustic potash at a low temperature. Methylparahydroxybenzaldehyde, C6H4(OCH3)CHO. Cahours prepared this compound by the oxidation of oil of anise seed,1 while Cannizzaro and Bertagnini obtained it by oxidizing anise alcohol (p. 284), and named it anisaldehyde.2 Piria then showed that it is also formed by distilling a mixture of calcium formate and calcium anisate (methylparahydroxybenzoate);3 and Tie- mann and Herzfeld obtained it by heating parahydroxybenz- aldehyde with methyl iodide, wood spirit and caustic potash. It may be most readily prepared from oil of anise, which consists for the most part of anethol, C3H5.C6H5.OCH3, the methyl ether of allylphenol. One part of this is brought into a cold solution of 2 parts of potassium dichromate, 3 parts of sulphuric acid, and 8 parts of water. As soon as the temperature ceases to rise, the mixture is diluted with half its volume of water and distilled, the quantity of liquid in the distilling flask being kept at its original volume by the gradual addition of water. The distillate is repeatedly rectified, the aldehyde coming over in the first portions, which are then shaken up with a concentrated solution of acid sodium sulphite. The crystals, which separate after some time, are washed with alcohol and decomposed by carbonate of soda solution.4 Anisaldehyde is a liquid which has an aromatic odour, boils at 247°-248°, and dissolves slightly in cold, more readily in hot water; it readily takes up oxygen from the air and is converted by alcoholic potash into a mixture of anise alcqhol and anisic acid. When heated with dilute hydrochloric acid to 200°, it decomposes into parahydroxybenzaldehyde and methyl chloride (Bucking). Acetylpardhydroxyljenzaldehyde, C6H4(OCO.CH3)CHO, is ob- tained by dissolving 2 parts of parahydroxybenzaldehyde and 1 part of caustic potash in water, evaporating and treating the 1 Ann. Chem. Phurm. Ivi. 307. 2 Ibid. xcviii. 189. 3 Ibid. c. 105. 4 Rossel, ibid. cli. 28. 296 AROMATIC COMPOUNDS. residue with acetic anhydride in presence of ether (Tiemann and Herzfeld). It is also formed by the action of acetic anhydride on the aldehyde,1 and is a liquid, boiling at 264°-205°, which forms an almost insoluble compound with acid sodium sulphite. Acetylparahydroxybcnzidene acetate, C6H4(OCO.CH3)CH(OCO. CH3)2, is prepared by heating the aldehyde with three times its weight of acetic anhydride. It is readily soluble in hot water and alcohol, and crystallizes from ether in flat prisms, melting at 93°-94° (Tiemann and Herzfeld). Parahydroxybenzaldoxime, CeH4(OH)CHz=NOH, forms odour- less, white needles.2 Chloroparahydroxybenzaldehydc, C6H3C1(OH)CHO, crystallizes from hot water in silky needles melting at 148°-149°; its aqueous solution is coloured violet by ferric chloride. Bromoparahydroxybcnzaldehyde, C6H3Br(OH)CHO, is almost insoluble in water, crystallizes from alcohol in long, strongly refractive needles, melting at 179°-180°, and does not give any colouration with ferric chloride. lodoparaliydroxybenzaldehyde, C6H3I(OH)CHO, is formed when parahydroxybenzaldehyde is boiled with iodine and dilute alcohol. It is slightly soluble in water, readily in alcohol, and separates from chloroform in white crystals, melting at 198°- 199°. On heating with caustic potash it yields protocatechuic acid.3 Nitroparahydroxybenzaldehyde, C6H3(NO2)(OH)CHO. Maz- zara obtained this substance by boiling the aldehyde with dilute sulphuric acid,4 and Herzfeld by adding concentrated nitric acid to a solution of parahydroxybenzaldehyde in concentrated sulphuric acid.5 It is soluble in boiling water and alcohol, and crystallizes in yellowish needles melting at 139°-140°. Its aqueous solution gives a fugitive red colouration with ferric chloride. It decomposes carbonates; the potassium salt, C0H3 (NO2)(OK)CHO + H2O, forms golden-yellow tablets. 1 Barbier, Bull. Soc. Chim. xxxiii. 54. 2 Lach, Ber. Deutsch. Chern. Ges. xvi. 1785. 3 Herzfeld, ibid. x. 2196. 4 Gaz. Chim. Itai. vii. 285. 5 Ber. Deutsch. Chern. Ges. x. 1269. SALICYLIC ACID. 297 ZOH HYDROXYBENZOIC ACIDS, C6H4< \co2h. Orthohydroxybenzoic Acid, or Salicylic Acid. 2170 The history of this important substance is of special interest because its genetic relations to the benzoyl and cinnamyl groups and to indigo blue were known at a very early period. Piria, who prepared it in 1838, by heating the aldehyde with caustic potash,1 pointed out that the radicals benzoyl and salicyl are different oxidation products of the hydrocarbon or radical C7H5 (p. 285). Marchand2 and Gerhardt3 found that it is also formed when salicin is melted with potash, and is converted by dilute nitric acid into nitrosalicylic acid, which is identical with indigotic or anilotic acid, a substance obtained by the action of nitric acid on indigo which had long been familiar to chemists. This compound on fusion with potash at a low temperature yields anthranilic acid (p. 237), while Cahours, by carrying out the operation at a higher temperature, obtained salicylic acid;4 it was obtained, together with acetic acid, in a similar manner from cumaric acid by Delalande, who remarked that this latter compound bears the same relation to cinnamic acid as salicylic to benzoic acid.5 Ettling, who prepared salicylic acid by oxidizing its aldehyde with potassium dichromate and sulphuric acid, found that it can also be obtained by heating the copper salt of this or of benzoic acid, and is therefore an oxidation product of the latter.6 Gerhardt had previously observed that salicylic acid decomposes on heating into phenol and carbon dioxide, just as anthranilic acid is split up into aniline and carbon dioxide. A series of relations was thus established among the following compounds: Benzene C6H6 Benzoic acid C7H6O2 Cinnamic acid C9H8O2 Phenol CgH6O Salicylic acid C7H6O3 Cumaric acid C9H8O3 Aniline c6h7n Anthranilic acid C7H7NO2 1 Ann. Chim. Phys. Ixix. 298 ; Ann. Chem. Pharm. xxx. 165. 2 Journ. Prakt. Chem. [1] xxvi. 396. 3 Ann. Chem. Pharm. xlv. 19. 4 Ibid. lii. 343. 5 Ibid. xlv. 336. 6 Ibid. liii. 77. 298 AROMATIC COMPOUNDS. Hofmann found that aniline is converted into phenol by the action of nitrous acid, and suomrested that anthranilic acid would probably yield salicylic acid when treated in a similar manner, this suggestion being experimentally verified by Gerland.1 Salicylic acid was obtained synthetically by Kolbe and Laute- mann by the action of carbon dioxide on a mixture of phenol and sodium.2 The former chemist found that it is also formed when carbon dioxide is passed over heated sodium phenate, half of the phenol being set free :3 /ONa 2CGH5.ONa + CO2 = C6H.< + CGH5OH. xCO2Na Ethyl salicylate may be prepared by the action of sodium on a mixture of phenol and ethyl chloroformate :4 zOH C6H5.ONa + C1CO2.C..H5 = CcH4( + NaCL \COo.C2H5 The acid is also formed, together with parahydroxybenzoic acid, when a mixture of tetrachloromethane and phenol is heated to 100° with alcoholic potash (Part III. p. 32).5 It may also be obtained by fusing orthocresol,6 toluene- orthosulphonic acid,7 &c., with caustic potash, as well as by heating copper benzoate to 180° with water,8 and when sodium is allowed to remain in contact with ethyl succinate for a long •time.9 It has also been observed as a product of the action of hydrogen dioxide on a solution of benzoic acid in sulphuric acid.10 Salicylic acid also occurs in nature. Lbwig and Weidmann detected it in the flowers of Spiraea Ulmaria, accompanied by salicylaldehyde, but did not actually identify it. Its methyl ether is contained in the ethereal oils of the various species of Gaultheria. 2171 It was formerly prepared exclusively from the winter- 1 Ann. Chern. Pharm. Ixxxvi. 147. 2 Ibid. cxv. 201. 3 Journ. Prakt. Chern. [2] x. 89. 4 Wilm and Wischin, Zeitschr. Chem. 1868, 6. 5 Reimer and Tiemann, Ber. Deutsch. Chem. Ges. ix. 1285. 6 Barth, Ann. Chem. Pharm. cliv. 360. 7 Wolkow, Zeitschr. Chem. 1870, 326. 8 Smith, Amer. Chem. Journ. ii. 338. 9 Herrmann, Ber. Deutsch. Chem. Ges. x. 646. 10 Hanriot, Compt. Bend. cii. 1250. SALICYLIC ACID. 299 green oil obtained from Gaultheria procumbens by saponifying with potash and decomposing the product with hydrochloric acid. It is now manufactured by Kolbe's process. The calculated quantity of pure phenol is dissolved in strong caustic soda solution, the whole evaporated to dryness and the residue rubbed into a dry powder; this is then gradually heated up to 180° in a metal retort in a current of carbon dioxide which has been previously warmed. After some time phenol com- mences to distil over, and is subsequently given off in larger quantity; the temperature is then raised to 200°, and the operation continued until no more phenol comes over. The residue is dissolved in water and fractionally precipitated with hydrochloric acid ; resinous and colouring matters are first thrown down, followed by tolerably pure acid, which is re-crystallized from water and purified by distillation with superheated steam.1 According to another patented process, carbonyl chloride, which is now manufactured on a large scale, is passed into a mixture of sodium carbonate and phenate heated to 140°, the temperature being finally raised to 200°.2 Various hypotheses were proposed to explain the course of the reaction which occurs when sodium phenate is heated in a stream of carbon dioxide. The correct explanation was found by R. Schmitt.3 Pure dry sodium phenate absorbs carbon dioxide with formation of sodium phenylcarbonate^^ldO .CO as a white powder which is instantly decomposed by water, phenol and sodium bicarbonate being formed. When heated in a closed tube to 120°-130°, it is converted quantitatively into monosodium salicylate. In Kolbe's reaction, this complete decom- position does not take place, and the monosodium salicylate reacts with the sodium phenate at a higher temperature, phenol being liberated : O.C6H5 C6H4.OH NaO.C6H5 4- CO, = | = | CO2Na CO,Na. C6H4.OH C6H4ONa | + NaO.C6H5 = | + C6H5.OH. CO2Na CO2Na Salicylic acid is, therefore, best prepared by bringing abso- lutely dry sodium phenate into an autoclave, pumping in rather 1 Rautert, Compt. Rend. viii. 537. 2 Ibid, xviii. Ref. 90. 3 Journ. Prakt. Chern. [2] xxxi. 397. 300 AROMATIC COMPOUNDS. more than the calculated quantity of carbon dioxide, the mass being kept cool during the absorption, or, better, adding it in the solid form, agitating for some time and then heating to 120°-130°.1 2172 Salicylic acid has a slightly acid, astringent and at the same time sweet taste; it dissolves slightly in cold, more readily in hot water, from which it crystallizes in fine needles, while it is deposited in monoclinic prisms from an alcoholic solution which is allowed to evaporate spontaneously. 100 parts of water dissolve at: 0° 15° 100° 0'085 • 0225 7'925 parts. Absolute alcohol and ether dissolve about half their weight of the acid;2 it is also readily soluble in chloroform, differing in this respect from its isomerides, and is dissolved by solutions of the acetates and citrates of the alkali metals.3 Its aqueous solution is coloured deep violet by ferric chloride; free acids, especially acetic and hydrochloric acids, hinder the re- action.4 It prevents the precipitation of copper salts by alkalis, while its isomerides have not this property.5 Strong boiling nitric acid converts it into picric acid, and chromic acid oxidizes it to water, carbon dioxide and a little formic acid.6 It melts at 155°-156°,7 and sublimes on gradual heating, but partially decomposes into carbon dioxide and phenol when rapidly heated. It is completely split up when heated to 250°-260° for two hours in a sealed tube; on cooling, the compound of these two substances, which has already been described, separates out (Part III. p. 102).8 This decomposition also occurs when the acid is heated for a long time to 220°-230° with water, and more rapidly in presence of hydrochloric acid at 140°-150°.9 Sodium amalgam only acts upon it in acid solu- tion ; a resinous substance, probably saliretin, being formed.10 In order to test the purity of salicylic acid, a piece the size of a pea 1 Bcr. Deutsch. Chern. Ges. xvii. Ref. 624 ; Schmitt, loo. cit. 2 On Solubility, &c., see Ost, Journ. Prakt. Chern. [2] xvii. 232 ; Bourgoin, Bull. Soc. Chim. xxix. 247 ; xxxi. 57. 3 Rother, Pharm. Journ Trans. 1886, 328. 4 Pagliani, Bcr. Deutsch. Chem. Ges. xii. 385. 5 Weith, ibid. ix. 342. 6 Kraut, Ann. Chem. Pharm. cl. 9. 7 Hiibner, ibid, clxii. 74. 8 Klepl, Journ. Prakt. Chan. [2] xxv. 464. 9 Grabe, ibid, cxxxix. 143. 10 Velden, Journ. Prakt. Chan. [2] xv. 164. THE SALICYLATES. 301 is ground up with five ccs. of concentrated sulphuric acid, in which it should form a perfectly colourless solution.1 Its alcoholic solution evaporated on a watch-glass should yield perfectly clear and colourless crystals : if they are yellow or brown, the sample contains admixed resins or colouring matters, while if they are pink or violet, iron is present. As salicylic acid decomposes so readily into carbon dioxide and phenol, Kolbe considered that it would, like the latter, be a powerful antiseptic, and subsequently verified this conclusion by experiment. It has very rapidly come into favour both for technical and household purposes, and is preferable to phenol because it has no smell and is not poisonous. Its isomerides, according to Kolbe, are not antiseptics.2 Salicylic acid is also employed in medicine, both for external and internal application. Several physicians have observed that the acid prepared from winter-green oil acts more powerfully than that obtained artificially, but this may possibly be due to the fact that the acid which first came into the market contained a considerable amount of impurity.3 2173 The Salicylates. Salicylic acid was first thought to be a monobasic acid, but was afterwards regarded as dibasic. Piria observes on this point: " Salicylic acid differs in a most striking manner from other monobasic acids in forming acid ethers, which are more fitly compared with the acid ethers of polybasic acids than with the neutral ethers. In the course of researches which I have instituted upon this question, I have succeeded in finding the cause of this exception, or rather in showing that the behaviour of this acid is not exceptional. Salicylic acid, which has hitherto been looked upon as monobasic, is actually dibasic, and very markedly so; it forms salts with two equivalents of a base so readily that it is singular that they have remained so long unnoticed. In the following, I shall call salts containing one equivalent of base, which have been previously described, acid salicylates, and those discovered by me, containing two equivalents of base, neutral salicylates." 4 This view was accepted by most chemists, but Kolbe con- sidered it to be a monobasic hydroxy-acid. Further researches have shown that it is both a monobasic acid and a phenol, and 1 Hager, Fresenius' Zeitschr, xvi. 259. 2 Journ. Prakt. Chern. [2] xi. 9. 3 Williams, Yearbook of Pharm. 1884, 424. 4 Ann. Chern,. Pharm. xciii. 262. 302 AROMATIC COMPOUNDS. therefore contains two hydrogen atoms which are easily replaced by metals. The salts thus obtained are usually called basic salicylates, while those formed by the replacement of the hydrogen of the carboxyl group are known as normal salicylates. The latter have recently been carefully examined by Milone.1 Potassium salicylate, C6H4(OH)CO2K, is obtained by dissolving the acid in potassium carbonate solution, evaporating and ex- tracting the residue with alcohol. It is deposited in needles on the spontaneous evaporation of its aqueous solution. When heated to 210°-220°, it decomposes quantitatively into basic potassium parahydroxybenzoate, phenol and carbon dioxide : /OH /OK 2C6H4< = C6H4< + C6H5.OH + CO2. \co2k xCO,K If a solution of one molecule of the acid and two molecules of caustic potash be evaporated to dryness, and the residue heated to 220°, the basic salt of parahydroxybenzoic acid is also formed, together with phenol: .OK /OK 2C6H4< + H.,0 = C6H4< -i- C6H5.OH + K2CO3. xCO2K " \co2k If, however, three or more molecules of potash are employed, the salicylic acid is not changed ; if four are taken, complete decomposition into carbon dioxide and phenol sets in at 300°, while in the presence of six molecules, the acid remains quite unaltered even at this temperature.2 Rubidium salicylate behaves in a precisely similar manner on heating.3 Sodium salicylate, C6H4(OH)CO2Na, forms silky tablets or a crystalline powder, and has an unpleasant sweet taste. It dissolves in its own weight of water and is used in medicine. On heating to above 200°, phenol and carbon dioxide are given off, the basic salt remaining behind, but not a trace of the para- acid is formed even at 300°. When salicylic acid is heated to this temperature with four molecules of caustic soda, it decom- poses into phenol and carbon dioxide, while if eight molecules are added the greater portion of it remains unaltered (Ost). 1 Gaz. Chim. Itai. xv. 219. 2 Ost, Journ. Prakt. Chem. [2] xi. 391. 3 v. d. Velden, ibid. [2] xv. 151. THE SALICYLATES. 303 Inversely, sodium parahydroxybenzoate is converted into basic sodium salicylate, phenol and carbon dioxide, when it is heated to 290° in a current of carbon dioxide,1 while hydroxy- isophthalic acid, CGH3(OH)(CO2H)2, and hydroxytrimesic acid, C6H.,(OH)(CO2H)3, are formed at temperatures above 800°. When equal molecules of salicylic acid and its normal salt are dissolved in alcohol and the solution concentrated, hard, clear crystals of C7HGO3 + C7H5NaO3 are obtained, which are converted by water into pseudomorphs of salicylic acid.2 Litlivum salicylate is converted into the basic salt at 300° without any formation of parahydroxybenzoic acid. Thallium salicylate, CGH4(OH)CO2T1, is obtained by neutra- lizing the acid with thallium carbonate ; its hot, concentrated solution deposits coarse needles on cooling. If the calculated quantity of thallium hydroxide be added to the solution, the basic salt, C6H4(OT1)CO2T1, separates out in yellow, nacreous, rhombic tablets, which are only very slightly soluble in water. This compound is also formed, together with phenol, when the normal salt is heated to 300°, while at a higher temperature the salicylic acid is partially converted into parahydroxybenzoic acid and hydroxyisophthalic acid (v. d. Velden). Ammonium salicylate, 2CGH4(OH)CO2NH4 + H2O, forms readily soluble, monoclinic crystals; when heated in a current of ammonia it decomposes into phenol and ammonium carbonate. The methylamine and aniline salts behave in a similar manner, while tetra-ethylammonium salicylate decomposes on heating into tri-ethylamine and ethyl salicylate.3 Calcium salicylate, (C7H5O3)2Ca 4- 2H2O, is readily soluble in water, and crystallizes in octohedra; when it is heated with a solution of calcium sucrate, or when salicylic acid is heated with an excess of milk of lime, the basic salt, C7H4O3Ca + H2O, is formed as a sandy, crystalline powder, which is almost insoluble in water and has an alkaline reaction (Piria). Barium salicylate, (C7H5O3)2Ba + H2O, is obtained by boiling the acid with water and barium carbonate; it crystallizes in stellate aggregates of silky needles. When baryta water is added to its boiling concentrated solution, the slightly soluble, alkaline, basic salt, C7H4O3Ba + 2H2O, separates out in small plates or needles. 1 Kupferberg, Joum. Prakt. Chem. [2] xiii. 104. 2 Hofmann, Arch. Pharm. [3] xii. 226. 3 Kupferberg, Joum. Prakt. Chem. [2] xvi. 437. 304 AROMATIC COMPOUNDS. Lead salicylate, (C7H5O3)2Pb + H2O, separates from boiling water in transparent crystals; when it is boiled with water, or when lead acetate is added to its hot solution, a slightly soluble, crystalline precipitate of C7H4O3Pb is formed. If, however, ammonia be added, and the solution boiled, the basic salt, 2(C7H4O3)Pb + 3PbO, is formed; it is a light powder consisting of micaceous plates. Copper salicylate, (C7H5O3)2Cu + 4H2O, is best prepared by decomposing the barium salt with copper sulphate ; it crystal- lizes in long, bluish green needles, which are readily soluble in water, and on boiling with it form the basic salt, C7H4O3Cu + H2O, which is a yellowish green powder. Basic copper potassium salicylate, C7H4O3Cu + C7H4O3K„ + 4H2O, is formed by adding salicylic acid to a solution of copper tartarate in tolerably strong caustic potash; a green mass of crystals is formed, which is dried on a porous plate and re- crystallized from a little lukewarm water. Small, emerald-green, rhombic tablets are thus obtained, which are insoluble in alcohol, and form a dark blue solution in caustic potash. When the aqueous solution is boiled it becomes colourless and deposits black copper oxide. Barium chloride produces, on standing, a green, crystalline precipitate of C7H4O3Cu + C7H4O3Ba + 4H2O. Silver salicylate, C7H5O3Ag, is a precipitate which crystallizes from boiling water in very lustrous, transparent needles. Borondisalicylic acid, B(OH)(OCcH4.CO2H)2, is not known in the free state; its sodium salt is formed, along with free boric acid, when four molecules of salicylic acid are added to a boiling solution of one molecule of borax, as well as by dissolving a mixture of equal molecules of boric acid, salicylic acid and sodium salicylate : ZOH HO - B< + HO.C6H..CO2H + HO.C6H4.CO2Na = \OH /OC6H4.COqH HO-B< " +2H2O. \OC6H4.CO2Na It forms crystalline crusts and is readily soluble in hot water and alcohol. Its aqueous solution turns turmeric paper brown, reddens litmus paper, and is coloured violet by ferric chloride; hydrochloric acid gives a precipitate of salicylic acid. Several METHYLSALICYLIC ACID. 305 other of its salts have been prepared; its barium salt is only slightly soluble in boiling water.1 2174 Methyl salicylate, C6H4(OH)CO2.CH3. Cahours, in 1843, found that winter-green oil, obtained from Gaultheria procumbens (Canadian tea), one of the Ericaceae, which occurs abundantly in the north of the United States and in Canada, consists of this compound together with small quantities of a terpene, and he prepared the ether by distilling salicylic acid with wood-spirit and sulphuric acid in order to compare the two products.2 Since as a phenol it forms metallic salts, it was called gaultheriaic acid and methylsalicylic acid, the latter name being now given to the following compound. The ethereal oils of Gaultheria punctata and Gaultheria leucocarpa, which grow on the summits of extinct volcanoes in Java,3 and of Andromeda Lechenaultii, one of the Ericaceag, which occurs abundantly in the Neilgherry Mountains in India,4 consist almost entirely of methyl salicylate. It is a liquid with a pleasant, refreshing odour, and boils at 217°. Winter-green oil is largely used in America as a perfume ; that obtained artificially, by heating salicylic acid with methyl alcohol and sulphuric acid, does not possess the fine odour of the natural product. Methylsalicylic acid, C6H4(OCH3)CO2H. Cahours obtained the methyl ether of this compound by the action of methyl iodide and caustic potash on winter-green oil. It is a liquid boiling at 244°-24G° (Schreiner). In order to prepare the acid, two parts of methyl salicylate are heated to 100°-120° with one part of caustic potash and three or four parts of methyl iodide, the product distilled in order to remove methyl alcohol and methyl iodide, and the residue then extracted with caustic soda and precipitated with hydrochloric acid. Any adhering salicylic acid is removed by boiling with an excess of milk of lime, insoluble basic calcium salicylate being precipitated, while calcium methylsalicylate remains in solution, and is then decomposed by hydrochloric acid.5 Methylsalicylic acid crystallizes from hot water in large, monoclinic tablets, and from alcohol in prisms, which melt at 98-5° and decompose above 200° into carbon dioxide and anisol. 1 Jahns, Arch. Pharm. [3] xii. 212. 2 Ann. Chern. Pharm. xlviii. 83 ; liii. 327. 3 de Vrij, Pharm. Journ. Trans. [3] ii. 503 ; Kohler, Ber. Deutsch. Chern. Ges. xii. 246. 4 Broughton, Pharm. Journ. Trans. [3] ii. 281. s Grabe, Ann. Chern. Pharm. cxxxix. 137. 306 AROMATIC COMPOUNDS. On heating with concentrated hydrochloric acid, it is resolved into salicylic acid and methyl chloride; hydriodic acid has a similar action. The sodium salt of the acid is formed, together with a little of the methyl ether and sodium salicylate, when winter-green oil is heated with sodium : C6H4.ONa C6H4.OH C6H4.OCH3 C6H4.OH I +1 =1 +1 CO2.CH3 CO2.CH„ CO2.CH3 CO2Na. Ai O At O Ai O At Two molecules of the sodium compound then react in a similar manner: C6H4.ONa CO2.CH3 C6H4.OCH3 CO2Na I +1 =1 +1 C09.CH3 CLELONa CO2Na C6H4.OCH3. At & O X Ai OxO ETHEREAL SALTS OF SALICYLIC ACID. Melting point. Boiling point. 2 Ethyl salicylate, C6H4(OH)CO2.C2H5, liquid - 223° 3 Propyl salicylate, C6H4(OH)CO2.C3H7, liquid - 239° 4 Amyl salicylate, C6H4(OH)CO2.C6HU, liquid - 270° 5 Ethylene salicylate, (C6H4(OH)CO2)2C2H4, needles 83° - 6 Propenyl salicylate, C6H4(OH)CO2C3H5(OH)2, liquid - - SALICYLIC ETHERS. Melting-point. 7 Ethysalicylic acid, C6H4(OC2H5)CO2H, gradually) 19-4° solidifying oil J 8 Isopropylsalicylic acid, C6H4(OC3H7)CO2H, liquid . - 9 Benzylsalicylic acid, C6H4(OC7H7)CO2H, small tablets 75° 10 Etbylenesalicylic acid, C6H4(OC6H4.CO2H)2, long ) 454°_452° needles J 1 Ann. Chern. Pharm. cxlii. 327. 2 Baly, ibid. Ixx. 269 ; Schreiner, ibid, cxcvii. 17 ; Gottig, Ber. Deutsch. Chem. Ges. ix. 1473. 3 Caliours, Jahresb. Chem. 1874, 333. 4 Drion, Ann. Chem. Pharm. xcii. 313. 5 Gilmer, ibid, cxxvii. 377. 6 Gottig, Ber. Deutsch. Chem. Ges. x. 1817. 7 Kraut, Ann. Chem. Pharm. cl. 1 ; Gottig, Ber. Deutsch. Chem. Ges. ix. 1474. 8 Kraut. 9 Perkin, Journ. Chem. Soc. xxi. 125. 10 Weddige, Journ. Prdkt, Chem. [2] xxi. 128. ETHYL METHYLSALICYLATE. 307 ETHEREAL SALTS OF SALICYLIC ETHERS. Boiling-point. 1 Ethyl methylsalicylate, C6H4(OCH3)CO2.C.2H5, . 260° 2 Methyl ethylsalicylate, C6H4(OC2H5)CO2.CH3, . 256°-257° 3 Ethyl ethylsalicylate, C6H4(OC2H5)CO2.C2H5, . 258°-259° 4 Methyl isopropylsalicylate, C6H4(OC3H7)CO2.CH3, 250° 5 Methyl benzylsalicylate, C6H4(OC7H7)CO2.CH3, above 320° Melting-point. 6 Ethyl ethylenesalicylate, C2H4(OC6H4.CO2C9H5)2,) 0-0 thick plates " - " Ji Phenyl salicylate, C6H4(OH)CO2.C6H5. Seifert7 obtained this compound by heating salicylic acid and phenol with phosphorus oxychloride: 2CfiH.rOH)CO2H + 2CJL.0H + POCL = 2C6H4(OH)CO2.C6H5 + 3HC1 + HPO3. A better yield is obtained by employing the sodium salts; this ethereal salt, known as salol, is manufactured by heating the product of the action of carbon dioxide on sodium phenate with phosphorus pentachloride or oxychloride : C6H4(OH)CO2Na + C6H5.ONa + PC15= C6H4(OH)CO2.C6H5 + 2NaCl + POC13. 2C6H4(OH)CO2Na + 2C6H5.ONa+POC13 = 2C6H4(OH)CO2.C6H6 + 3NaCl + NaPO3. Salol crystallizes in rhombic prisms, which are odourless and melt at 42°-42'5°; the dilute alcoholic solution, however, has a smell resembling that of winter-green oil. It is employed in medicine as a substitute for salicylic acid, because, as it is not decomposed until it reaches the duodenum, it does not attack the stomach like the former: when applied externally it has no corrosive action, and, on account of its lower melting-point, it can be more conveniently used for dressings, &c., than salicy1i'° acid. 1 Grabe ; Schreiner ; loc. cit. 2 Schreiner'; loc. tit. 3 Gbttig ; Schreiner ; loc. tit. 4 Kraut ; loc. tit. 5 Perkin ; loc. tit. 6 Weddige ; loc. tit. 7 Journ. Prakt. Chern. [2] xxxi. 462. 308 AROMATIC COMPOUNDS. Phenyl methylsalicylate, C6H4(OCH3)CO2.C6H5, was prepared by Seifert in a similar manner; it crystallizes in six-sided prisms, melting at 59°. Acetylsalicylic acid, C6H4(O.CO.CH3)CO2H, is formed by the action of acetyl chloride on salicylic acid or its sodium salt, and crystallizes from hot water in fine needles, melting at 118°- 118°'5. Its aqueous solution gives a violet colouration with ferric chloride ; when the acid is heated with ammonia, ammo- nium salicylate is formed, but no salicylamide (Kraut). Salicyl chloraldide, CgH4/ J>CH.CC13, is formed when Ver salicylic acid is heated to 130°-150° for a long time with an excess of chloral. It is insoluble in water, slightly soluble in alcohol and ether, and crystallizes from the latter in prisms, melting at 124°-1250.1 Disalicylic acid, (C6H4.CO2H)2O. This compound, which is also called salicylic anhydride, or salicylosalicylic acid, was ob- tained by Gerhardt by the action of phosphorus oxychloride on sodium salicylate.2 It is also formed when acetylsa'icylic acid is heated, or when salicylic acid is heated for a long time to 130°-140° with acetyl chloride.3 It is an amorphous mass, which dissolves in the alkaline carbonates and is reprecipitated by acids. It gives no colouration with ferric chloride; aqueous ammonia converts it into salicylamide and ammonium salicylate, while potassium salicylate is formed by the action of caustic potash. Salicylide, C7H4O2, is formed by heating salicylic acid with phosphorus oxychloride : ZOH z O x c6h4< = C6H 4 > + H2O. VO.OH \COZ It crystallizes from absolute alcohol in spherical aggregates of lustrous plates, which melt at 195°-200°; it gives no colour- ation with ferric chloride, and is converted into salicylic acid by the action of caustic potash.4 Tetrasalicylide, C28H18O9, is formed at the same time as the preceding compound, and is a resinous mass insoluble in alcohol. 1 Wallach, Ann. Chem. Pharm. cxcvii. 41. 2 Ibid. Ixxxvii. 159. 3 Kraut, ibid. cl. 13. 4 Schiff, ibid, clxiii. 220. SALICYLHYDROXYACETIC ACID. 309 Salicylhydroxyacetic acid, C6H4(OCH2CO2H)CO2H,is obtained by oxidizing ortho-aldehydophenoxyacetic acid (p. 289) with potassium permanganate. It crystallizes from hot water in white needles, melting at 186°-187°. It forms readily soluble salts which crystallize well.1 2175 The Action of Phosphorus Pentachloride upon Salicylic Acid. As already mentioned, Chiozza found, in 1852, that when salicylic acid is treated with phosphorus pentachloride and the product distilled, the distillate yields orthochlorobenzoic acid when treated with water (p. 217). Gerhardt repeated this experiment, and found that the liquid before distillation is salicyl chloride, C7H5O2C1, as it is converted by water into sali- cylic acid, and by alcohol into an ethereal salt of this; he also obtained it together with methyl alcohol by treating winter-green oil with phosphorus pentachloride.2 Drion made the further observations that only a trace of phosphorus oxychloride is formed in this reaction, and that a portion of the product is converted into chlorobenzoyl chloride by distillation.3 Couper, however, obtained different results. He acted upon one molecule of methyl salicylate with two molecules of phos- phorus chloride, and distilled the resulting liquid; the excess of the chloride came over first, followed by a liquid distilling between 285°-295°, to which he gave the name of salicyl trichlorophos- phate, explaining its formation by the following equation : C8H8O3 p PC15 = HC1 + CH3C1 + C7H4C13PO8. This compound, which he also obtained from salicylic acid, is decomposed by water into hydrochloric acid, phosphoric acid and salicylic acid : C7H4CLPO3 + 4H2O = 3HC1 + H PO. + C7HfiO3. • it o ti I v O When he submitted it to rapid distillation, a considerable quantity of hydrochloric acid was evolved, and the distillate consisted of a liquid boiling above 300°, which deposited large crystals of salicyl rnonochlorophosphate, C7H4C1PO4, when pre- served in a sealed tube; this substance, like the trichlorophos- phate, is converted into phosphosalicylic acid, C7H7PO6, in moist air. He therefore considered that the existence of salicyl 1 Rossing, Ber. Deutsch. Chem. Ges. xvii. 2988. 2 Ann. Chem. Pharm. Ixxxix. 363. 8 Ibid. xcii. 312. 310 AROMATIC COMPOUNDS. chloride, no analyses of which had been published, was very doubtful.1 Drion replied to this, that although the latter compound had not been obtained in a state of purity, its existence was proved by the fact that ethers of salicylic acid are formed by the action of alcohol upon it.2 Kolbe and Lautemann came to the same conclusion. Accord- ing to them, a mixture of chlorobenzoyl chloride, salicyl chloride and chlorosalicyl trichloride is obtained by distilling salicylic acid with phosphorus pentachloride.3 Kekule, who investigated this reaction at about the same period, found that when the product is heated to 180°-200° to remove phosphorus chloride and oxychloride, a liquid remained which yielded salicylic acid and traces of chlorobenzoic acid when decomposed by water. It also contained 3 per cent, of phosphorus, and considerably more chlorine than corresponds with the composition of salicyl chloride ; on dis- tillation he obtained considerable quantities of phosphorus oxychloride and chlorobenzoyl chloride, but not Couper's com- pound.4 It therefore became the generally accepted view, that the following compounds are formed by the action of phosphorus pentachloride on salicylic acid : Salicyl chloride. ZOH c6h4< \COC1 Chlorobenzoyl chloride. ZC1 c6h4< \coci Chlorobenzenyl trichloride. ZC1 (W \cci3. The salicyl chloride could not be obtained pure because it decomposed on distillation, and could not therefore be freed from chlorobenzoyl chloride and phosphorus oxychloride; according to Miquel, it adheres most obstinately to the latter.5 The solution of the problem was found by Anschutz, who, by bringing together equal molecules of salicylic acid and phos- phorus pentachloride, obtained an evolution of hydrochloric acid and a yellow liquid, which distilled under a pressure of 11 mm. as a colourless, refractive liquid, only a small quantity of residue being left. This has the composition of Couper's salicyl tri- 1 Ann. Chem. Pharm. cix. 369. 2 Ibid. cix. 373. 3 Ibid. cxv. 183. 4 Ibid, cxvii. 148. 6 Ann. Ghim. Phys. [5] xi. 304. ORTHOCHLOROCARBONYLPHENYL METAPHOSPHATE. 311 chlorophosphate and is orthocarbonylphenylphosphoryl chloride, formed according to the following equations : OH /OH c6h4 < + PC15 = C6H4< + POC13 + h2o. \CO.OH \COC1 The phosphorus oxychloride then acts upon the salicyl chloride just as it does upon phenol: OH /O.POC12 C6H4< + POC13 = C6H4< 4 HC1. XCOC1 XCOC12 The pure chloride distils at 285°-295° under the ordinary pressure. If it be submitted to slow distillation, a mixture of phosphorus oxychloride, orthochlorobenzoyl chloride and ortho- chlorotribenzenyl chloride is obtained, boiling at 270°-290°. If the distillation be now continued under diminished pressure, Couper's salicyl monochlorophosphate, or orthochlorocarbonyl- phenyl metaphosphate passes over; it is formed, together with orthochlorobenzoyl chloride, according to the following equation: /O.POC12 .Cl /OPO, 2C6H4< = C6H4< +c6h4< -+poci3. \COC1 \COC1 XCOC1 It boils at 187° under a pressure of 11 mm., and solidifies on cooling to crystals, which melt at 30°. The chloride is decomposed by a small quantity of water into hydrochloric acid, phosphoric acid and salicylic acid ; in moist air, on the other hand, or on distillation with anhydrous oxalic acid, it is converted into orthochlorocarbonylphenyl meta- phosphate : ZOPOC12 /OPO2 C6H4< +C2H2O4 = C0H4< "+2HC1+CO + CO2. \coci \coci It dissolves, however, in a large quantity of cold water, with formation of orthocarboxylphenylphosphoric acid, C6H4(CO.OH) OPO(OH)2, which on evaporation in a vacuum over soda lime gives a crystalline mass, which melts at 147° and is readily soluble in water. If the chloride be heated to 165°-170° with phosphorus pentachloride, benzenyltrichlorophosphoryl chloride, CgH^OPOCy 312 AROMATIC COMPOUNDS. CC13, is formed; it is a powerfully refractive liquid, which boils at 178°-179° under a pressure of 11-12 mm., and is not con- verted by water into hydroxybenzenyl trichloride, as might have been expected, but into phosphosalicylic acid. When it is heated with phosphorus chloride to 180°, ortho- chlor obenzenyl trichloride is formed A /OPOC1, /Cl C6H4< + PC15 = C6H4( + 2POC13. XCC13 \CC13 2176 Salicylamide, C6H4(OH)CO.NH2, is obtained by tbe action of concentrated ammonia on methyl salicylate;2 it cry- stallizes from ether in lustrous, yellow plates, melting at 142°,3 and sublimes when carefully heated. As a phenol it forms metallic salts; its ethers are formed when ammonia is allowed to act upon the ethers of salicylic acid. Bcnzoylsalicylamide, C6H5(O.CO.C6H6)NH2, is formed when salicylamide is heated to 180° with benzoyl chloride, or fused with benzamide.4 It is slightly soluble in alcohol, but almost insoluble in ether, and crystallizes in needles melting at 200°. Disalicylamide, (C6H4(OH)CO)2NH, is prepared by heating salicylic acid in a current of hydrochloric acid. It crystallizes in yellowish white needles, which resemble asbestos in appearance, and melt at 197°-199° with partial decomposition; it is in- soluble in water, but readily dissolves in alcohol and alkalis. The alcoholic solution is coloured red by ferric chloride.5 Salicylanilide, C0H4(OH)CO.NH(C6H5), is obtained by gently warming aniline with salicylic acid and then gradually adding phosphorus trichloride to the cooled mass. It crystallizes from dilute alcohol in small prisms, melting at 134°-135°; ferric chloride colours the solution violet.6 Salicyluric acid, CGH4(OH)CO.NH.CH2.CO2H. When salicylic acid is administered internally, it appears in the urine partly in an unaltered state and partly as salicyluric acid. This is slightly soluble in water, readily in alcohol, and crystallizes in fine needles, which melt at 160° and give a violet colouration with ferric chloride. On heating with concentrated hydrochloric acid, 1 Anschutz, Ann. Chem. Pharm. ccxxviii. 308, and private communication. 2 Limpricht, ibid, xcviii. 258. 3 Grimaux, Bull. Soc. Chim. xiii. 25. 4 Chiozza and Gerhardt, Jahresb. Chem. 1856, 502. 6 Schulerud, Journ. Prakt. Chem. [2] xxii. 298. 6 Kupferberg, ibid. [2] xvi. 442 ; Wanstrat, Ber. Deutsch. Chem. Ges. vi. 336. CHLOROSALICYLIC ACID. 313 it decomposes into salicylic acid and amido-acetic acid. Its barium salt forms prisms, which are only slightly soluble in water.1 Scdicylnitril, C6H4(OH)CN, is formed by heating the amide with phosphorus pentoxide, and is a colourless, crystalline substance, which melts at 195°, and on boiling with dilute caustic potash is converted into salicylic acid.2 Polysalicylnitril, (C7H5ON)X. Limpricht obtained this com- pound by heating salicylamide to 270°, and looked upon it as an imide of the dibasic salicylic acid.3 It is a yellow, crystalline powder, which melts at 280°-285° (Grimaux), and is only converted into salicylic acid by fusion with caustic potash. On heating with phosphorus pentachloride, orthochlorobenzonitril is formed.4 Benzoylsalicylnitril, C6H4(OCO.C6H5)CN, was prepared by Limpricht by heating benzosalicylamide, and called by him benzoylsalicylimide.5 Henry obtained it by heating the poly- nitril with benzoyl chloride. It crystallizes from hot alcohol in small, brittle, lustrous plates, melting at 148°-149°. The hot alcoholic solution is coloured red by ferric chloride. SUBSTITUTION PRODUCTS OF SALICYLIC ACID. 2177 Chlorosalicylic acid, C6H3C1(OH)CO2H (5:2:1), is formed by passing chlorine into a solution of salicylic acid in carbon disulphide,6 as well as by the action of nitrous acid upon ^-chloramidobenzoic acid.7 It may also be obtained by replacing the amido-group of the corresponding amidosalicylic acid by chlorine,8 and by heating parachlorophenol with tetrachloro- methane and alcoholic potash.9 It dissolves in 1100 parts of water at 20°, and in 80 parts at 100°, and crystallizes in small 1 Bertagnini, Ann. Chern. Pharm. xcvii. 249. 2 Grimaux, Bull. Soc. Chim. xiii. 26. 3 Ann. Chem. Pharm. xcviii. 261. 4 Henry, Ber. Deutsch. Chem. Ges. ii. 491. 5 Ann. Chem. Pharm. xcix. 250. 6 Hubner and Brenkeu, Ber. Deutsch. Chem. Ges. vi. 174. 7 Hubner and Weiss, ibid. vi. 175. 8 Schmitt, Jahresb. Chem. 1864, 385 ; Beilstein, Ber. Deutsch. Chem. Ges, viii. 816. 9 Hasse, ibid. x. 2190. 314 AROMATIC COMPOUNDS. needles,melting at 172°. The aqueous solutionis coloured violet by ferric chloride. Dichlorosalicylic acid, C6H2C12(OH)CO2H(3 :5 : 2 :1), may be prepared by heating salicylic acid with antimony pentachloride,1 as well as by the action of chlorine on a solution of salicylic acid in glacial acetic acid.2 It is also slightly soluble in boiling water, and crystallizes from dilute alcohol in small prisms, which melt at 214°, and are coloured dark violet by ferric chloride. Con- centrated nitric acid converts it into the same dichloronitrophenol as is formed by the nitration of a-dichlorophenol.3 a-Bromosalicylic acid, C6H;Br(OH)CO2H(3 : 2 ; 1), has been obtained from the corresponding amidobromobenzoic acid.4 It crystallizes in small, soluble needles, melting at 219°-220°, and gives a dark reddish blue colouration with ferric chloride. ^-Bromosalicylic acid (5:2:1) is formed by the direct bromination of salicylic acid,5 and also by treating /3-bromamido- benzoic acid with nitrous acid (Hubner and Heinzerling). It crystallizes from hot water in long needles, melting at 164°- 165° ; ferric chloride colours it violet. Three dibromosalicylic acids are also known.6 lodosalicylie acid, C6H3I(OH)CO2H(5 : 2 :1), has been prepared from the corresponding amido-salicylic acid by means of the diazo-reaction.7 It is almost insoluble in cold water, and crystal- lizes from alcohol in needles, which melt at 196°, and decompose into iodophenol and carbon dioxide when they are rapidly heated. The same acid had previously been obtained by Lautemann by treating salicylic acid with iodine and caustic potash solution,8 while Liechti9 and Demole,10 by the action of iodine and iodic acid on salicylic acid, prepared an iodosalicylic acid which is slightly soluble in cold, somewhat more readily in hot water, and crystallizes in needles, melting at 183°. Two isomeric acids are therefore produced by the direct action of iodine on salicylic acid,11 and probably in varying proportions. The following compounds are also formed in this reaction : 1 Lossner, Journ. Prakt. Chern. [2] xiii. 429. 2 Smith, Ber. Deutsch. Chern. Ges. xi. 1225. 3 Smith and Knerr, Amer. Chern. Journ. viii. 95. 4 Hiibuer and Heinzerling, Zeitschr. Chern. 1871, 709. 5 Henry, Ber. Deutsch. Chem. Ges. ii. 275 ; Hubner and Heinzerling. 6 Rollwage, ibid. x. 1707; Smith, ibid. 1706 ; Hiihner, ibid. 1706. 7 Goldberg, Journ. Prakt. Chem. [2] xix. 368 ; Hiibner, Ber. Deutsch. Chem. Ges. xii. 1347. 8 Ann. Chem. Pharm. cxx. 302. 9 Ibid. Suppl. vii. 136. 10 Ber. Deutsch. Chem. Ges. vii. 1437. 11 Fischer, Ann. Chem. Pharm. clxxx. 346. NITROSALICYLIC ACIDS. 315 Di-iodosalicylic acid, C6H2I2(OH)CO2H, is best obtained by the action of iodine and mercuric oxide upon an alcoholic solution of salicylic acid.1 It is slightly soluble in cold, more readily in hot water and alcohol, crystallizes in needles, melting at 220°-230°, and, like moniodosalicylic acid, is coloured violet by ferric chloride. Tri-iodosalicylic acid, C6HI3(OH)CO2H, is insoluble in water, and crystallizes from alcohol in yellow needles. 2178 Nitrosalicylic acids. In the year 1806, Fourcroy and Vauquelin obtained a volatile, crystalline acid, which they thought was benzoic acid, by treating indigo blue with dilute nitric acid. Chevreul recognized the individuality of this sub- stance, which was called indigotic acid, and it was then carefully examined by Buff,2 and correctly analysed by Dumas.3 Marchand4 confirmed the results obtained by Dumas, and found, as also did Gerhardt,5 that indigotic acid is identical with nitrosalicylic acid. Piria, by the action of nitric acid on salicin, obtained helicin and anilotic acid, which, according to Major, is identical with nitrosalicylic acid, although Piria himself was convinced that the two acids were different substances.6 In spite of this, it was generally assumed that only one nitrosalicylic acid existed, until Hubner found that two are formed by the nitration of salicylic acid.7 One of these is identical with anilotic acid, while indigotic acid proves to be a mixture of both.8 These acids are also formed when the vapour of nitric acid is passed into methyl salicylate.9 a-Nitrosalicylic acid, (CO2H : OH : NO2 = 1 : 2 : 5), may be obtained, in addition to the methods given above, by heating paranitrophenol with tetrachloromethane and alcoholic potash to 100°,10 by boiling e-nitro-amidobenzoic acid with caustic potash solution,11 and by passing nitrogen tetroxide into a cold aqueous solution of salicylic acid (Hubner). In order to prepare it, 100 parts of salicylic acid are dissolved in 800 parts of glacial acetic acid, 50 parts of pure nitric acid, of sp. gr. of 1'5, being then 1 Weselsky, Ann. Chem. Pharm. clxxiv. 103. 2 Schweigg, Journ. Chem. Phys. li. 38 ; liv. 163. 8 Ann. Chim. Phys. [3] ii. 224. 4 Journ. Prakt. Chem. xxvi. 385. 5 Ann. Chem. Pharm. xlv. 19. 6 Ibid, xcvii. 253. 7 Ibid. cxcv. 1. 8 Masino and Schiff, ibid, cxcviii. 256. 9 Smith and Knerr; Amer. Chem. Journ. viii. 99. 10 Hasse, Ber. Deutsch. Chem. Ges. x. 2188. 11 Griess, ibid. xi. 1730. 316 AROMATIC COMPOUNDS. gradually added in the cold; the solution is then diluted with two or three volumes of water, and the acid, which separates out after some time, purified by repeated crystallization from hot water. The barium salt of tbe /3-acid may be prepared from the mother-liquor; it is only slightly soluble in water. a-Nitrosalicylic acid crystallizes in long needles, which melt at 228° and dissolve in 1475 parts of water at 15°; it is more easily soluble in alcohol or hot water. Its solution is coloured blood-red by ferric chloride. Boiling nitric acid converts it into picric acid, and when its diethyl ether is heated to 130° with alcoholic ammonia, the amide of e-amidonitrobenzoic acid is obtained. On heating with lime it decomposes into carbon dioxide and paranitrophenol. Normal barium a-nitrosalicylate, (C7H4NO6)2Ba 4- dH^O,1 is obtained by heating the acid with water and barium carbonate ; it is readily soluble in water, and crystallizes in compact, yel- low needles which form fascicular aggregates. The basic salt, C7H3NO5Ba + 2H2O, is formed by boiling the acid with baryta water, and crystallizes in citron-yellow plates, w hich have a satin lustre and are only slightly soluble in water. (3-Nitrcsalicylic acid, or Anilotic acid, (CO2H:OH:NO2 = 1: 2:3), is formed in largest quantity by the action of the most concentrated nitric acid upon salicylic acid at a low temperature,2 and has also been obtained by heating orthonitrophenol with tetrachloromethane and alcoholic potash (Hasse). In order to prepare it, 10 grms. of salicylic acid are gradually brought into a mixture of 10 grms. of concentrated nitric acid with 10-12 grms. of glacial acetic acid at a temperature of about 6°. The solution is then poured into 250 ccm. of water and the precipitated acids separated by means of their barium salts. /3-Nitrosalicylic acid dissolves in 770 parts of water at 15'5°, readily in alcohol and ether, and crystallizes in long needles, which contain a molecule of water, and melt at 125°. The anhydrous acid melts at 144°; its solution is coloured blood-red by ferric chloride; on heating with lime it decomposes into carbon dioxide and orthonitrophenol, while the amide of ^-amido- nitrobenzoic acid is formed by the action of alcoholic ammonia on its diethyl ether. Normal barium -nitrosalicyl ate, (C7H4NO5).,Ba, crystallizes in golden yellow plates or compact, refractive needles, which are 1 Ann. Chern. Pharm. ccx. 344. 2 Schaumann, Ber. Deutsch. Chem. Ges. xii. 1346. DINITROSALICYLIC ACID. 317 only very slightly soluble in cold, more readily in hot water. Ammonia added to the solution produces a deep-red colouration and then a precipitate of the basic salt, 2C7H3NO5Ba+ 3H2O, in thick, blood-red needles. Dinitrosalicylic acid, C6H2(NO2)2(OH)CO2H. The methyl ether of this compound was obtained by Cahours by dropping winter-green oil into a mixture of fuming nitric and sulphuric acids.1 It crystallizes in yellow scales, which melt at 127°-128° (Salkowski), and are easily saponified by caustic potash. Sten- house then prepared dinitrosalicylic acid by the action of nitric acid on the aqueous extracts of Populus nigra and P. lalsam- ifera, which contain populin.2 It is also formed by the further nitration of both the mononitrosalicylic acids, their constitution being thus shown. It is best prepared by bringing 10 grms. of salicylic acid into 70 grms. of the most concentrated nitric acid at 0°, and pouring the clear solution into 300 ccm. of water; after standing for 24-36 hours the separated acid is filtered off, pressed, converted into the barium salt by boiling with water and barium carbonate, and re-precipitated by hydro- chloric acid.3 Dinitrosalicylic acid is readily soluble in cold, very readily in hot water, and crystallizes therefrom in thick, lustrous plates, or, on rapid cooling, in fine needles containing one molecule of water. Its solution is coloured dark-red by ferric chloride; on heating with water to 200° it decomposes into carbon dioxide and ordinary dinitrophenol. Potassium'dinitrosalicylate. When caustic potash is added in excess to the aqueous solution of the acid, the salt C6H2(NO2)2 (OK)CO2K + H2O is formed; it crystallizes in long, dark-red needles, which detonate violently when heated. Dilute hydro- chloric acid or nitric acid added to its solution precipitates the salt C6H2(NO2)2(OH)CO2K, which crystallizes from boiling water in compact, short, dark yellow needles. Barium dinitrosalicylate, C6H.,(NO2)2OBaCO2 + 3H2O, forms compact, yellow needles, which are only slightly soluble in cold water. 2179 a-Amidosalicylic acid, C6H3(NH2)(OH)CO2H, was ob- tained by Beilstein by reducing nitrosalicylic acid with tin and hydrochloric acid ;4 it is better, however, to employ acetic acid (Hubner). It crystallizes in needles which have a satin lustre, 1 Ann. Chern. Pharm. Ixix. 232. 2 Ibid. Ixxviii. 1. 3 Hubner, ibid. cxcv. 45. 4 Ann. Chern. Pharm. cxxx. 243. 318 AROMATIC COMPOUNDS. and are insoluble in alcohol and cold water, but slightly soluble in hot water; the solution soon decomposes in the air, a brown, amorphous substance being precipitated. Ferric chloride pro- duces a cherry-red colouration, followed by a brownish black precipitate. Amidosalicylic acid forms salts both with bases and acids; it decomposes on heating into carbon dioxide and paramidophenol.1 .CO Trimethylamidosalicylic acid, C6H3(OH)^ ^>0. This com- XN(CH3)3 pound, which may also be called hydroxybenzobetaine, is formed by the action of methyl iodide and caustic potash on amidosalicylic acid, and crystallizes from water in large, snow-white needles, often an inch in length, which contain four molecules of water, have a very bitter taste and are coloured reddish violet by ferric chloride. It combines with the mineral acids to form salts which crystallize well. Methyl dimethylamidosalicylate, C6H3(OH)N(CH3)2CO2CH3, is prepared by heating the preceding compound, after previously removing its water of crystallization. It forms rhombic prisms, and is decomposed on boiling with hydrochloric acid into methyl alcohol and dimethylamidosalicylic acid, which crystallizes in small, almost insoluble needles.2 ft-Amidosalicylic acid is not known in the free state; its hydrochloride crystallizes in needles which readily decompose (Hubner). Nitro-amidosalicylic acid, C6H2(NO2)NH2(OH)CO2H, is formed by the partial reduction of dinitrosalicylic acid ; it forms crystals, melting at 220°; a-nitrosalicylic is obtained3 when the amido- group is replaced by hydrogen. Diamidosalicylic acid, CGH2(NH2)(OH)CO2H, was prepared by Saytzew by the action of hydriodic acid on the methyl ether of dinitrosalicylic acid.4 It is very slightly soluble in cold, more readily in hot water, and crystallizes in small needles. It combines with acids to form salts which crystallize well; ferric chloride produces a brownish red colouration, followed by a black precipitate. Sulphosalicylic acid, C6H3(SO3H)(OH)CO2H, was obtained by Mendius by the action of sulphur trioxide on salicylic acid,5 and 1 Schmitt, Jahresber. 1864, 423. 2 Griess, Ber. Deutsch. Chem. Ges. xii. 2307. 3 Babcock, ibid. xii. 1345. 4 Ann. Chem. Pharm. cxxxiii. 321. 5 Ibid. ciii. DIAZOSALICYLIC ACID. 319 may also be prepared by heating salicylic acid with sulphuric acid.1 It crystallizes in long, thin, very soluble needles, which melt at 120°, and are coloured an intense reddish violet by ferric chloride. Its salts crystallize well; on fusion with caustic potash, no dihydroxybenzene is formed, the product consisting entirely of phenol and salicylic acid. Salicylsulphuric acid, C6H4(SO4II)CO2H. The potassium salt may be obtained by heating salicylic acid with caustic potash and potassium disulphate; it crystallizes in colourless, pointed prisms and is readily soluble in water, but insoluble in absolute alcohol. It gives no colouration with ferric chloride and is decomposed by dilute acids, including even acetic acid, into potassium sulphate and salicylic acid.2 ,N-N Diazosalicylic acid, C6H3(OH)^ | , is formed by passing ' xC0.0 nitrogen trioxide into an alcoholic solution of the hydrochloride of amidosalicylic acid. It crystallizes in fine needles and combines with acids to form salts which crystallize well ;3 iodosalicylic acid is formed on heating with hydriodic acid. Azobcnzenesalicylic acid, C6H5.N2.C6H3(OH)CO2H, is obtained by the action of diazobenzene nitrate on an alkaline solution of salicylic acid; it crystallizes in orange-red needles, which are insoluble in water, but dissolve readily in alcohol. Sulphuric acid converts it into a sulphonic acid, which is probably identical with the following compound.4 Saicylparazobenzencsulphonic acid, C6H4(SO3H)N2.C(.H3(OII) CO2H, is formed by bringing salicylic acid into a solution of paradiazobenzenesulphonic acid in caustic potash. It crystallizes in golden-yellow needles, which are only slightly soluble in hot water; barium chloride produces a yellow precipitate of (C1.iH„NoSOA,Ba, which is converted on boiling into irregular, six-sided, lustrous plates.5 1 Remsen, Ann, Chem. Pharm. clxxix. 107. 2 Baumann, Ber. Deutsch. Chem Ges. xi. 1914. 3 Schmitt, Jahresber. Chem. 1864, 384 ; Schmidt and Mittenzwey, Journ. Prakt. Chem. [2] xviii. 193 ; Goldberg, ibid. xix. 362. 4 Stebbins, Ber. Deutsch. Chem. Ges. xiii. 716. 8 Griess, ibid. xi. 2196. 320 AROMATIC COMPOUNDS. METAHYDROXYBENZOIC ACID. 2180 Gerland obtained this isom eride of salicylic acid by the action of nitrous acid on a hot solution of ordinary amidobenzoic acid, and gave it the name of oxybenzoic acid,1 by which it is still generally designated. It is also formed by fusing sulpho- benzoic acid,2 metachlorobenzoic acid,3 or metachlorocresol4 with caustic potash. In order to prepare it, 2 parts of potassium sulphobenzoate are fused with 5 parts of caustic potash and a little water, the melt acidified with sulphuric acid and the whole extracted with ether. The metahydroxybenzoic acid is left on evaporation in thick, white crusts which are purified by re-crystallization from hot water. Any adhering benzoic acid is finally removed by washing with carbon disulphide (Barth). Metahydroxybenzoic acid crystallizes in small prisms or needles, melting at 200°, which usually form warty aggregates. It dissolves at 0° in 265, and at 18° in 108'2 parts of water, has a sweet taste, is not coloured by ferric chloride and can be distilled without undergoing decomposition. It differs from its isomerides in being reduced by sodium amalgam in an acid solution to metahydroxybenzyl alcohol, and in blackening at 300° without a trace of phenol being formed; decomposition, accom- panied by the formation of small quantities of the latter, only occurs at higher temperatures.5 The Metahydroxylenzoates. The salts of the alkali metals are readily soluble and do not crystallize well; they are very stable and only decompose at a high temperature, very little phenol and no isomeric acid being formed. The basic salts do not combine with carbon dioxide at a high temperature (Kupferberg) ; when the acid is fused with an excess of sodium carbonate, decomposition sets in above 300°, the greater portion of the acid being completely burnt, and only a small quantity of phenol being therefore formed.6 If two molecules of the acid are heated 1 Ann. Chem. Pharm. Ixxxvi. 143 ; xci. 189 ; Fischer, ibid, cxxvii. 138. 2 Barth, ibid, cxlviii. 30. 3 Denibey, ibid, cxlviii. 222. 4 Barth, ibid. cliv. 361. 5 Klepl, Journ. Prakt. Chem. [2] xxv. 464 ; xxvii. 159. 6 Barth and Schreder, Ber. Deutsch. Chem. Ges. xii. 1254. THE METAHYDROXYBENZOATES. 321 to 350° with three molecules of caustic baryta, no change takes place, but if seven molecules of the latter be employed, a complete decomposition into carbon dioxide and phenol occurs (Klepl). Ammonium mctahydroxybcnzoate, C6H4(OH)CO2NH4, crystal- lizes in needles which form fascicular aggregates. Calcium 'metahydroxybenzoate, (C6H4.OH.CO2)2Ca + 3H2O, forms readily soluble crystals. Barium metahydroxybenzoate, (C6H4.OH.CO2)2Ba, is an amor- phous, gummy mass; it has been found impossible to prepare a basic salt. Copper metahydroxybenzoate, (CcH4.OH.CO2)2Cu + H2O, crystal- lizes from hot water in greenish needles. Thallium metahydroxybenzoate, C6H4(OH)CO2T1, is prepared by neutralizing a hot solution of the acid with thallium carbonate ; it crystallizes on cooling in lustrous, colourless prisms. When a solution of the hydroxide is neutralized with the acid and an equal quantity of the hydroxide added to the neutral solution, the basic salt, C6H4(OT1)CO2T1, crystallizes on evaporation in yellowish prisms ; it is more readily soluble than the normal salt and has an alkaline reaction (Kupferberg). The methylamine salt decomposes into its constituents when heated, and the aniline salt behaves in a similar manner, a little hydroxybenzanilide being also formed, while tetra-ethy lammonium metahydroxybenzoate splits up into tri-ethylamine and ethyl metahydroxybenzoate. Ethyl metahydroxybenzoate, C6H4(OH)CO2.C2H5, is formed by the action of hydrochloric acid gas on an alcoholic solution of the acid,1 or by heating the normal potassium salt with ethyl iodide.2 It crystallizes from ether in tablets, melts at 72°, boils at 282°, and is converted by caustic soda into a crystalline mass of C6H4(ONa)CO2.C2H5, which is readily soluble in water and alcohol. Metameth oxybenzoic acid, C6H4(OCH3)CO2H, is obtained by heating metahydroxybenzoic acid with the calculated quantity of caustic potash and methyl iodide, and decomposing the ethereal salt thus formed with a solution of caustic potash in wood-spirit (Grabe and Schultzen). It is also formed by the oxidation of metacresyl methyl ether with potassium permanganate,3 and by 1 Grabe and Schultzen, Ann. Chem. Pharm. cxlii. 351. 2 Heintz, ibid, cliii. 337. 3 Oppenheim and Pfaff, Ber. Deutsch. Chem. Ges. viii. 887. 322 AROMATIC COMPOUNDS. the action of carbon dioxide on a mixture of metabromophenyl methyl ether and sodium.1 It crystallizes from hot water in long needles, which melt at 106°-107°, and sublime without decomposition. Meta-ethoxybenzoic acid, C6H4(OC2H5)CO2H, was prepared by Heintz from the ethyl ether; it is also formed by the decom- position of the sulphate of metadiazobenzoic acid with alcohol.2 It crystallizes in small needles, melting at 137°, which are scarcely soluble in cold, slightly in hot water, but readily in alcohol, and sublime undecomposed. Ethyl meta-ethoxybenzoate, C6H4(OC2H5)CO2.C2H5, is obtained by heating metahydroxybenzoic acid with two molecules of caustic potash and ethyl iodide; it is a liquid, boiling at 263°. Meta-acetoxybenzoic acid, C6H4(OCO.CH3)CO2H, is produced by the action of acetyl chloride on the acid (Heintz); it forms granular crystals melting at 127°, and gives amorphous salts. 2181 Metahydroxybenzoic acid behaves towards phosphorus pentachloride in a very similar manner to salicylic acid. Mctacarbonylphenylphosphoryl chloride, C6H4(OPOC12)COC1, is a colourless liquid, which boils at 168°-170° under a pressure of 11-12 mm. A yield of 57'5 per cent, of the theoretical quantity is obtained, and the unattacked acid may be extracted from the residue in the retort by boiling water or alkalis. Metacarboxy orthophosphoric acid, C6H4(CO2H)PO(OH)2, is formed when the chloride is treated with water, a considerable evolution of heat taking place, but no metahydroxybenzoic acid being reformed. It crystallizes in fine, white scales, which melt at 200°-201°, and are only decomposed by water at a tem- perature of 150°-160°, phosphoric and metahydroxybenzoic acids being formed. When the chloride is submitted to slow distillation, a portion passes over unchanged, together with phosphorus oxychloride> no metachlorobenzoyl chloride, C6H4C1(COC1), or metachloro- benzenyl trichloride, C6H4C1(CC13), being produced, and a black syrupy residue is left, which yields metahydroxybenzoic acid on boiling with water or alkalis, and therefore probably contains the compounds (C6H4(COC1)O)2POC1 and (CcH4(COC1)O)3PO. Metabcnzcnyltrichlorophosphoryl chloride, C6H4(OPOC12)CC13. is obtained in a similar manner to the corresponding salicylic acid derivative. It boils at 178° under a pressure of 11 mm., and is 1 Korner, Jahr ester. Chern. 1867, 414. 2 Griess, Zeitschr. Chem. 1866, 1. iodometahydroxybenzoic acid. 323 converted by water into metacarboxy phenylphosphoric acid, while on heating with phosphorus pentachloride to 180°, a portion is converted into metachlorobenzenyl trichloride.1 Metahydroxybenzamide, C6Ht(OH)CO.NH2, is formed when diazobenzamide nitrate is boiled with water 2 as well as by the action of ammonia on ethyl metahydroxy benzoate. It crystallizes from water in thin plates, which have a bitter taste and melt at 167°. Metahydroxybenzanilide, C6H4(OH)CO.NH(C6H5), is obtained m the same way as salicylanilide ; it crystallizes from dilute alcohol in needles, melting at 154°-155°, and combines with alkalis to form salts which crystallize well. It is not attacked by boiling alkalis, but is decomposed by them on fusion (Kupferberg). Metahydroxybenzuric acid, C6H4(OH)CO.NH.CH2.CO2H, occurs in the urine of the dog after metahydroxybenzoic acid has been administered ; it crystallizes in needles.3 Metahydroxybenzonitril, C6H4(OH)CN, is formed by boiling diazobenzonitril sulphate with water4 and by heating meta- hydroxybenzoic acid in a current of ammonia, first to 220°-230° and then to 300°-320°; the isomeric compounds are decomposed by this treatment into phenol and carbon dioxide, but yield no nitril.5 Metahydroxybenzonitril crystallizes from hot water in small plates and from alcohol in small, rhombic prisms; it has an intensely sweet and at the same time sharp taste, melts at 82°, and decomposes on heating with hydrochloric acid into ammonia and metahydroxybenzoic acid. SUBSTITUTION PRODUCTS OF METAHYDROXY- BENZOIC ACID. 2182 lodometahydroxybcnzoic acid, C6H3I(OH)CO2H. Weselsky obtained this substance by the action of iodine and mercuric oxide on an alcoholic solution of metahydroxybenzoic acid. It cry- stallizes in needles, which are only slightly soluble in cold water. Nitrometahydr oxybenzoic acids, C6H3(NO2)(OH)CO2H. Gerland found that the direct nitration of metahydroxybenzoic acid yields 1 Anschutz, private communication. 2 Griess, Zeitschr. Chem. 1866, 1. 3 Baumann and Heiter, Hoppe-Seyler's Zeitsehrift, i. 260. 4 Griess, Ber. Deutsch. Chem. Ges. viii. 859. 5 Smith, Journ. Prakt. Chem. [2] xvi. 218. 324 AROMATIC COMPOUNDS. a nitrohydroxybenzoic acid, which forms yellow, rhombic crystals, and has a repulsive, bitter taste ; it must be identical with one of those described below, since metahydroxybenzoic acid can only yield four mononitro-derivatives. The first three were prepared by Griess by boiling the corresponding nitro-amido- benzoic acids with caustic potash.1 a-Nitrometahydroxybenzoic acid, (CO2H : OH : NO2 = 1 :3 :6), is readily soluble in water, and crystallizes in thick, honey-yellow prisms or in needles containing one molecule of w7ater, which is given off at a few degrees above 100°. It melts at 169°, has a slightly acid taste, and is coloured a faint reddish brown by ferric chloride. The barium salt, C7H3NO5Ba + 6H2O, forms yellowish red prisms, which are readily soluble in water. ^-Nitrometahydroxybenzoic acid (1 : 3 :4), is slightly soluble in hot water, and crystallizes in long, yellow, four- or six-sided plates, melting at 230°. The barium salt, C7H3NO5Ba + H2O, is almost insoluble and crystallizes in yellowish red plates. y-Nitrometahydroxybenzoic acid (1:3: 2),is less soluble in water than the a-acid, has an intensely sweet taste, and crystallizes with one molecule of water in long, four-sided plates or large tablets, which melt at 178° and give a faint reddish brown colouration with ferric chloride. The barium salt, 2C7H3NO5Ba + 3H2O, also has a very sweet taste, and forms tolerably soluble reddish brown plates. T)-Niiromctahydr oxybenzoic acid (1:3: 5), was prepared by Grube from the corresponding nitro-amidobenzoic acid,2 and is a yellowish brown, crystalline precipitate. Its salts crystallize badly. Trinitrometahydroxybcnzoic acid, C6H(NO.2)3(OH)CO2H, is formed by heating diazo-amidobenzoic acid with ordinary strong nitric acid,3 and by the action of fuming nitric acid on metamido- benzoic acid.4 It crystallizes in large, almost colourless, rhombic prisms, which have a vitreous lustre, and are best obtained from solution in concentrated nitric acid ; it is readily dissolved by water, alcohol, and ether, forming intensely yellow solutions, which dye animal fabrics in the same way as picric acid. It melts when heated and then explodes. The barium salt, C7HN3O9Ba 4-3H9O, is tolerably soluble in water, but insoluble in alcohol, and crystallizes in thick, light yellow needles, which are very explosive. 1 Ber. Deutsch. Chem. Ges. xi. 1729. 2 Ibid. x. 1704. 3 Griess, Ann. Chern. Pharm. cxvii. 28. 4 Beilstein and Geitner, ibid, cxxxix. 11 THIOMETAHYDROXYBENZOIC ACID. 325 When metahydroxybenzoic acid is heated with sulphuric acid, three compounds isomeric with alizarin, C14H8O4, are formed.1 If the product be boiled with strong nitric acid, a trinitrometahy- droxybenzoic acid is produced among other products, which is readily soluble in water, and crystallizes in tablets or prisms con- tainino- one molecule of water, which is lost at 100°. It melts at 105° and then commences to sublime; when rapidly heated it detonates. The barium salt, C7HN3O9Ba + 2H2O, is readily soluble in water, and crystallizes in yellow needles, which explode at 299°.2 Thiomctahydroxyhenzoic acid, C6H4(SH)CO2H, is formed by the action of tin and hydrochloric acid on sulphobenzoyl chloride, C6H4(SO2C1)COC1. It is tolerably soluble in water, more readily in alcohol, and sublimes very easily in small plates, melting at 146°-147°. Dithiometaliydroxybenzoic acid, S2(CGH4.CO2H)2, is obtained by exposing the monothio-compound to the air in the moist state, or more rapidly by adding bromine water to its aqueous solution.3 Griess prepared it by decomposing diazobenzoic acid aurichloride with sulphuretted hydrogen :4 3C1N2CGH4.CO2H + 2H2S = S.CGH4.C09H | " + CGH5.CO9H 3HC1 + 3N9. SCgH4.CO2H It crystallizes in microscopic needles, which are scarcely soluble in water, more readily in alcohol, and melt at 242°-244°. Sbdpliometahydroxybenzoic acid, C6H3(SO3H)(OH)CO2H, is formed by the action of sulphur trioxide on metahydroxybenzoic acid ; it crystallizes in green, deliquescent needles, melting at 208°, is almost insoluble in ether and is coloured wine-red by ferric chloride.5 Isosulphometahydroxyhenzoic acid is obtained by dissolving the sulphate of diazobenzoic acid in warm sulphuric acid; it crystal- lizes in plates, which are readily soluble in water and alcohol. It is decomposed by strong nitric acid into trinitrometahydroxy- benzoic acid and sulphuric acid.6 1 Schunck and Romer, Ber. Deutsch. Chem. Ges. xi. 1167. 2 Schardinger, ibid. viii. 1490. 3 Hubner and Upmann, Zeitschr. Chem. 1870, 294 ; Frerichs, Ber. Deutsch. Chem. Ges. vii. 793. 4 Journ. Prakt. Chem. [2] i. 102. 5 Barth, Ann. Chem. Phctrm. cxlviii. 38 ; Senhofer, ibid. clii. 102. 6 Griess, Jahresber. Chem. 1864, 351. 326 AROMATIC COMPOUNDS. Disulphomctahydr oxybenzoic acid, C6H2(SO3H)2(OH)CO2H, seems to be formed when metahydroxybenzonitril is heated with fuming sulphuric acid;1 its barium salt is obtained by boiling the following compound with baryta water.2 Trisulphometahydr oxybenzoic acid, C6H(SO3H)3(OH)CO2H, is obtained by heating metahydroxybenzoic acid to 250° with a mix- ture of fuming sulphuric acid and phosphorus pentoxide. The free acid is a honey-yellow syrup; it is coloured an intense carmine-red by ferric chloride, and on fusion with caustic potash undergoes complete oxidation. Mctahydroxybcnzoylsulphiiric acid, C6H4(SO4H)CO2H, is found in the urine of men and dogs after the administration of meta- hydroxybenzoic acid (Baumann and Heiter). Its potassium salt is obtained in a similar manner to that of salicylsulphuric acid ; it forms deliquescent needles, and decomposes on boiling with hydrochloric acid or alcoholic potash into metahydroxy- benzoic acid and sulphuric acid.3 PARAHYDROXYBENZOIC ACID. 2183 Fischer obtained this acid by the action of nitrous acid on an aqueous solution of paramidobenzoic acid,4 and Saytzew by heating anisic acid (methylparahydroxybenzoic acid) with hydriodic acid.5 It is also formed when para-compounds such as anisic acid,6 paracresol,7 parasulphobenzoic acid,8 &c., are fused with caustic potash; it may be obtained by the same method from various resins, as gum benzoin, dragon's blood, aloes and acaroid resin.9 Kolbe prepared it synthetically by adding potassium to boiling phenol and at the same time passing in carbon dioxide; para- hydroxybenzoic acid alone is formed, while if the temperature be not allowed to rise above 130°-150°, salicylic acid is obtained. Parahydroxybenzoic acid may also be prepared by the action 1 Smith, Joum. Prakt. Chem. [2] xvi. 229. 2 Kretschy, Ber. Deutsch. Chern. Ges. xi. 858. 3 Baumann, ibid. xi. 1915. 4 Ann. Chern. Pharrn. cxxvii. 129. 5 Ibid, cxxvii. 145. 6 Barth, Zeitschrift. Chem. 1866, 650. 7 Barth, Ann. Chem. Pharm. cliv. 859. 8 Remsen, ibid clxxviii. 281. 9 Barth and Hlasiwetz, ibid, cxxxiv. 274 ; cxxxix. 78. PARAHYDROXYBENZOIC ACID. 327 of carbon dioxide on potassium phenate at 170°-210° j1 it is formed in small quantities, together with salicylic acid, when sodium phenate is treated in a similar manner at a lower temperature.2 The fact that normal potassium salicylate de- composes at 220° into carbon dioxide, phenol and basic potassium parahydroxybenzoate, has been already mentioned. Parahydroxy- benzoic acid is further obtained, together with a smaller quantity of salicylic acid,3 by heating tetrachloromethane to 100° with phenol and alcoholic soda.4 It is formed in theoretical amount when the potassium salt of paracresylsulphuric acid is oxidized with potassium per- manganate in alkaline solution.5 Paracresol is also converted into parahydroxybenzoic acid in passing through the animal organism, while metacresol is found in the urine as metacresyl- sulphuric. acid, and orthocresol is partly converted into ortho- cresylsulphuric acid and partly into hydrotoluquinone.6 In order to prepare parahydroxybenzoic acid, a mixture of equal molecules of caustic potash and phenol is heated in a current of hydrogen, the temperature being finally raised to 180°; carbon dioxide is then passed in until the theoretical quantity of phenol has distilled over, and the residue is then dissolved in water and decomposed by hydrochloric acid. The parahydroxybenzoic acid is boiled with animal charcoal and crystallized from hot water. It is thus obtained in small, monoclinic prisms, while it is deposited from dilute alcohol in larger crystals,7 containing one molecule of water, which is lost at 100°; it dissolves in 580 parts of water at 0°, and in 126 parts at 15°, and is readily soluble in hot water, alcohol and ether, but only slightly in chloroform, which is therefore employed to free it from salicylic acid. Its slight solubility in carbon disulphide is made use of in separating it from benzoic acid. It melts at 200° and when rapidly heated decomposes partly into carbon dioxide and phenol, and partly into other products, which will be described below. It decom- poses completely and readily into phenol and carbon dioxide on heating with dilute sulphuric acid in a sealed tube.8 Its aqueous solution gives an amorphous, yellow precipitate with ferric 1 Kolbe, Journ. Prakt. Chem. [2] x. 100. 2 Ost, ibid. [2] xx. 208. 3 Hasse, Ber. Deutsch. Chem. Ges. ix. 2186. 4 Reimer and Tiemann, ibid. ix. 1285. 8 Heymann and Konigs, ibid. xix. 704. 6 Baumann and Preusse, ibid. xix. 706. 7 Hartmann, Journ. Prakt. Chem. [2] xvi. 35. 8 Klepl, ibid. [2] xxv. 464. 328 AROMATIC COMPOUNDS. chloride. Phosphorus pentachloride converts it into parachloro- benzoyl chloride. The Parahydroxybenzoates. The normal sodium salt decom- poses completely at 240°-250° into carbon dioxide, phenol and the basic salt; when, however, it is heated to 280°-295° in a current of carbon dioxide, salicylic acid is obtained, while both hydroxy isophthalic acid and hydroxytrimesic acid are formed at temperatures above 340° (Kupferberg). When, on the other hand, the acid is heated with eight to ten parts of caustic soda, a partial decomposition into phenol and carbon dioxide sets in at 355° (Barth and Schreder), The salts of methylamine and aniline decompose at a higher temperature into phenol, carbon dioxide and the base, while that of tetra-ethylammonium decomposes on distillation into tri-ethylamine and ethyl para- hydroxybenzoate, the latter of which is then partially resolved into carbon dioxide and phenetol. Sodium parahydroxybenzoate, C6H4(OH/CO2Na + 5H2O, crys- tallizes from concentrated solutions in transparent tablets, which effloresce in the air. Potassixim parahydroxybenzoate, C6H4(OH)CO2K + 3H2O, is similar to the sodium salt, but is stable in the air. Ammonium parahydroxybenzoate, C6H4(OH)CO2NH4 + H2O, crystallizes in long prisms. Calcium parahydroxybenzoate, (C7H5Os)2Ca + 4H2O, forms fine needles grouped in stellate forms, and is very soluble. Bariu/m parahydroxybenzoate, (C7H5O3)2Ba + H2O, crystallizes in flat, lustrous needles or with two molecules of water in pointed rhombohedra; baryta water added to its solution pro- duces a precipitate of the basic salt, C7H4O3Ba, as a sandy, crystalline powder, which is scarcely soluble in cold water. Lead parahydroxybenzoate, (C7H5O3)2Pb + 2H2O, is a very characteristic salt, and is obtained by neutralizing the boiling aqueous solution of the acid with lead carbonate. It separates out on cooling in thin, iridescent plates which take a silver lustre on drying, and resemble those of benzoic acid. Copper parahydroxybenzoate, (C7H6O3)2Cu + 6H2O, crystal- lizes in small, bluish green needles, which become dull and insoluble on boiling with water. Silver parahydroxybenzoate, C7H5O3Ag + 2H.,O, crystallizes from hot water in small, lustrous plates. Methyl parahydroxybenzoate, C6H4(OH)CO2CH3, is formed by heating together equal molecules of parahydroxybenzoic acid, ANISIC ACID. 329 caustic potash and methyl iodide; it crystallizes from ether in large tablets, melts at 17° and boils at 2830.1 2184 Paramethoxybenzoicacid,oxAnisicacid,CeH.lic{OCH3)CO.2II. Cahours obtained this compound in 1839 by the oxidation of oil of anise-seed, and showed at the same time that it is formed from the " camphor " (anethol or allylphenol, C6H4(OH)C3H5), contained in this substance.2 Laurent, in 1841, prepared from tarragon oil (from Artemisia dracunculus\ the so-called dragonic acid {acide draconique), which, according to Gerhardt, is identical with anisic acid. This view was subsequently confirmed by Laurent, who also accurately determined its composition.3 At about the same time Persoz submitted oil of anise-seed, fennel oil, and star-anise oil {huile de badiane, from Illicium anisatum) to oxidation, and obtained two acids, which he named umbellic acid {acide ombellique} and badianic acid {acide badianique^d Hempel showed, however, that these are both anisic acid,5 the formation of which might have been expected, since the oils employed contain anethol.6 Anisic acid was at first looked upon as the homologue of salicylic acid ; Kolbe, however, considered it to be methoxy- benzoic acid, since it behaves very similarly to benzoic acid, and decomposes into anisol (phenyl methyl ether) and carbon dioxide when distilled with caustic baryta.7 In order to determine from which of the hydroxybenzoic acids it is derived, Saytzew heated it with hydriodic acid, and found that the product consists of parahydroxybenzoic acid. It was then thought probable that anisic acid and winter-green oil would have similar constitutions, but Grabe showed that the latter is the methyl ether of salicylic acid, while Ladenburg proved that in anisic acid the methyl group replaces the hydrogen of the phenol hydroxyl; by heating equal molecules of potassium parahydroxybenzoate and caustic potash with two molecules of methyl iodide, he obtained the methyl ether of paramethoxybenzoic acid (anisic acid) and prepared the free acid by saponifying with potash and decomposing the product with hydrochloric acid.8 Anisic acid may also be obtained by oxidizing orthocresyl methyl ether with chromic acid solution,9 1 Ladenburg and Fitz, Ann. Chern. Pharm. cxli. 247. 2 Ibid. xli. 66. 3 Ibid. xliv. 313. 4 Ibid. xliv. 311. 5 Ibid. lix. 104. 6 Cahours, ibid. xxxv. 312. 7 Lehrb. d. Organ. Chem. ii. 135. 8 Ann. Chem. Pharm. cxli. 241. 9 Korner, Zeitschr. Chem. 1868, 326. 330 AROMATIC COMPOUNDS. In order to prepare it, 1 part of oil of anise seed is poured into a solution of 5 parts of potassium dichromate in 10 parts of sulphuric acid and 20 parts of water, which is heated to 50°. The reaction is completed in a few minutes and the solution is then allowed to cool, the anisic acid filtered off and purified by precipitation with hydrochloric acid from solution in ammonia (Ladenburg and Fitz). It crystallizes in long monoclinic prisms or needles, melting at 184°, which dissolve in 2500 parts of water at 18°. It is tolerably soluble in boiling water and very readily in alcohol. On heating with hydriodic or concentrated hydrochloric acid, or on fusion with potash, it is converted into parahydroxy benzoic acid. Its salts, which crystallize well, have been chiefly investigated by Engelhardt and by Borella.1 Melting-point. Boiling-point. Methyl paramethoxybenzoate,2 C6H4(OCH3)CO2.CH3, scales . . 45°-46° 255° Ethyl paramethoxybenzoate,3 C6H4(OCH3)CO2.C2H5, liquid . - 250°-255° Ethyl parahydroxybenzoate,4 C6H4(OH)CO2.C2H5, crystals . 116° 297°-298° Para-ethoxybenzoic acid,5 C6H4(OC2H5)CO2H, needles . 195° - Ethyl para-ethoxybenzoate,6 CeH4(OC2H5)CO2.C2H5, liquid . - 275° Para-acetoxybenzoic acid, C6H4(OCO.CH3)CO2H, is formed when' parahydroxybenzoic acid is heated with acetic anhy- dride. It is slightly soluble in water, and crystallizes from chloroform in large plates, which have a silver lustre and melt at 185° (Klepl). Phenyl parahydroxybenzoate, C6H4(OH)CO2.C6H5, occurs in the products which are formed by the dry distillation of the acid. It is insoluble in water, but readily soluble in alcohol and chloro- form, from which it crystallizes in compact, rhombic tablets, which melt at 176°, dissolve readily in caustic soda, and are decom- 1 Gaz. Chim. Itai. xv. 304 ; Ann. Chem. Pharm. cviii. 240. 2 Ladenburg and Fitz, ibid. cxli. 252. 3 Cahours, ibid. Ivi. 310. 4 Grabe, ibid, cxxxix. 146 ; Hartmann, Journ. Pralct. Chem. [2] xvi. 50. 5 Ladenburg and Fitz ; Fuchs, Ber. Deutsch. Chem. Ges. ii. 624. 6 Ladenburg and Fitz. METHYL PARAMETHOXYBENZOATE. 331 posed by it even in the cold with formation of phenol and parahydroxybenzoic acid (Klepl). Paraphenoxybenzoic acid, C6H4(OC6H5)CO2H, is obtained by boiling the following compound with alcoholic potash, or by heat- ing it to 200° with concentrated hydrochloric acid. It is readily soluble in alcohol and ether, and crystallizes from chloroform in long prisms melting at 159'5°. When heated with caustic baryta it decomposes into carbon dioxide and diphenyl ether. Phenyl paraphcnoxybenzoate, C6H4(OC6H5)CO2 CGH5, is formed when parahydroxybenzide, which is described below, is heated to about 400°, preferably in a current of carbon dioxide. It crystallizes from dilute alcohol in fatty scales, which melt at 73°-78°, and sublime at a higher temperature, forming a vapour which smells like the geranium. 2185 Anhydrides of parahydroxybcnzoic acid. When para- hydroxybenzoic acid is submitted to dry distillation, only half of it is decomposed into carbon dioxide and phenol, which distils over accompanied by water, and phenyl parahydroxybenzoate; as the distillation is continued, the boiling acid suddenly becomes turbid, and a milky liquid settles in the retort, until at 350° the residue solidifies to a white amorphous mass.1 Parahydroxybenzoyl'parahydroxybcnzoic acid, zoco.c6h4.oh CeH 4^ • I*1 order to prepare this compound, the XCO2H distillation is stopped as soon as the acid has lost about 15 per cent, of its weight and before any turbidity has appeared. The residue is boiled with chloroform and water, and the compound then extracted with dilute alcohol and purified by re-crystal- lization. It forms short, microscopic needles, which melt at 261° and are rapidly converted into parahydroxy ben zoic acid in alkaline solution. As a monobasic acid it forms a barium salt, (C14H9O5)2Ba, which crystallizes in long plates containing water of crystallization. On heating with acetic anhydride, the mono- acetyl compound, C14H9(C2H3O)O5, is formed; it crystallizes in small plates, melting at 216'5°. Diparahydroxybenzoylparahydroxybenzoic acid, /OCO.C6H4O.CO.C6H4.OH C6H4\ , is contained in the residue ob- xco2h tained in the preparation of the preceding compound, and also in 1 Klepl, Journ. Prakt. Chem. [2] xxv. 525 ; xxviii. 193. 332 AROMATIC COMPOUNDS. the amorphous mass formed by the distillation of parahydroxy- benzoic acid, from which it may be extracted by absolute alcohol. It is a white, non-crystalline powder, which is slightly soluble in alcohol and ether, but insoluble in water and chloroform; it melts at 280°, and readily dissolves in alkalis, being gradually converted into parahydroxybenzoic acid, while it is not altered by boiling water. When the acid is suspended in a small quantity of water and treated with sufficient caustic soda to effect solution, the compound C21H13O7Na is precipitated in needles after some time. The acetyl compound, C91H13(C2H3O)O7, is formed by heating the acid with acetic acid ; it crystallizes in needles melting at 230°. Parahydroxybenzide, (C7H4O2)n, is the final product of the action of heat upon parahydroxybenzoic acid, and forms a white, amorphous powder, which is insoluble in the ordinary solvents, and carbonizes at 350° without previously melting. Boiling concentrated caustic potash converts it into parahydroxybenzoic acid ; on heating with concentrated sulphuric acid, parahydroxy- benzoylsulphuric acid is obtained, while parachlorobenzenyl trichloride is formed by the action of phosphorus chloride at 300° (p. 196). Anisic anhydride, (CcH4(OCH3'CO)2O, is obtained by the action of phosphorus oxychloride on sodium anisate. It crys- tallizes from ether in small, silky needles, which melt at 99° and volatilize at a higher temperature without decomposition.1 Mcthylparahydroxybenzoyl chloride, or Anisyl chloride, C6H4 (OCH3)COC1, is formed by the action of phosphorus penta- chloride on anisic acid.2 It forms long needles, which cannot be volatilized.3 Paracarbonylphenyl phosphoryl chloride, C6H4(OPOC12)COC1} is prepared by the action of phosphorus pentachloride on de- hydrated parahydroxybenzoic acid, the reaction being more violent than in the case of salicylic or metahydroxybenzoic acids. It boils at 176° under a pressure of 13-14 mm., and is a powerfully refractive liquid. Water converts it into paracarbonyl- orthophosphoric acid, CcH4(CO2H)PO(OH)2, which crystallizes in fine, white plates, melting at 200°; it is only decomposed by water at 150°-160°, parahydroxybenzoic and phosphoric acids being formed. When the chloride is distilled slowly under the ordinary pressure, it passes over almost unaltered, only a small 1 Pisani, Ann. Chem. Pharm. cii. 284. 2 Caliours, ibid. Ixx. 47. 3 Lossen, ibid, clxxv. 284. ANISIC ANHYDRIDE. 333 portion decomposing into phosphorus oxychloride and para- chlorobenzoyl chloride. The behaviour of this chloride towards a second molecule of phosphorus pentachloride is of considerable interest, since it differs from that of its isomerides inasmuch as no parabenzenyl- trichlorophosphoryl chloride is formed, but the compound decomposes into phosphorus oxychloride and parachlorobenzoyl chloride, the latter being then partially converted into para- chlorobenzenyl trichloride. The phenol-oxygen is therefore more readily replaced by chlorine when it occupies the para- position than when it is present in either an ortho- or meta-disubstituted compound.1 Parahydroxybenzaviide, CGH4(OH)CO.NH.2 + H.2O, is obtained by heating the ethyl ether with ammonia under pressure. It crystallizes from hot water in strongly lustrous, rhombic needles, which lose their water of crystallization at 100° and then melt at 162.° Anisamide, CGH4(OCH3)CO.NH2, was prepared by Cahours from the chloride by the action of ammonia; it crystallizes in prisms, melts at 137°-138°, sublimes in broad plates and boils at 295° (Henry). Parahydroxybenzanilidc, CGH4(OH)CO.NH(CGH5), is formed when the acid is heated with aniline and the product treated with phosphorus trichloride. It crystallizes from hot water in yellowish, lustrous plates, melting at 196°-197°. It forms salts of potassium and sodium, which are readily soluble and crystallize well (Kupferberg). Anisanilide, CGH4(OCH3)CO.NH(CGH5), was obtained by Lossen as a product of the distillation, of benzanishydroxamic acid (p. 340). It is slightly soluble in cold alcohol, and crystallizes in rhombic plates, melting at 168°-169°. Parahydroxybenzuric acid, CGH4(OH)CO.NH.CH2.CO2H, ap- pears, together with parahydroxybenzoylsulphuric acid, in the urine of the dog after the administration of parahydroxybenzoic acid ; it crystallizes in short prisms, which are tolerably soluble in water (Baumann and Heiter). Anisuric acid, C6H4(OCH3)CO.NH.CH2.CO2H, was obtained by Cahours from silver amido-acetate and anisyl chloride,2 and is also found in the urine after anisic acid has been taken;3 it 1 Anschutz, private communication. 2 Ann. Chern. Pharm. cix. 32. 3 Griibe and Schultzen, ibid, cxlii. 348. 334 AROMATIC COMPOUNDS. forms foliaceous crystals, which are readily soluble in hot water. Parahydroxybcnzonitril, C6H4(OH)CN, is formed when am- monium parahydroxybenzoate mixed with phosphorus pentoxide is distilled in a current of carbon dioxide (Hartmann), and by the action of ammonia on parahydroxybenzide mixed with pumice-stone and heated to 250° (Klepl). It crystallizes from hot water in rhombic tablets, which melt at 113°, and have a sweet but pungent taste; it forms a series of salts in which the phenol-hydrogen is replaced by the metal. Anisonitril, C6H4(OCH3)CN. Henry obtained this substance by distilling the amide with phosphorus pentachloride. It crystallizes from hot water in small needles, and from ether in long, white, lustrous prisms, has a penetrating, characteristic rank odour, melts at 56°-57°, and boils at 253°-254°.1 SUBSTITUTION PRODUCTS OF PARAHYDROXY- BENZOIC ACID. 2186 Chloroparahydroxybcnzoic acid, C6H3C1(OH)CO2H, (3:4:1), is formed by heating parahydroxybenzoic acid with antimony pentachloride,2 and by the action of alcoholic potash on orthochlorophenol at 125°-136°.3 It is slightly soluble in cold, more readily in hot water, and crystallizes in small needles, which melt at 169°-170°, and sublime without decomposition. Ferric chloride produces a brown precipitate in a concentrated solution; phosphorus pentachloride converts it into the chloride of a-dichlorobenzoic acid (Lossner). DiMoroparahydroxybenzoic acid, C6H2C12(OH)CO2H, has also been prepared by Lossner; it crystallizes in fine needles, which melt at 255°-256°. Dibromoparahydroxybcnzoic acid, C6H2Br2(OH)CO2H, (3:5: 4:1), has been obtained from dibromanisic acid. It is scarcely soluble in water, and crystallizes from alcohol in needles, which melt with decomposition at 266°-268°, but sublime at a lower temperature. A monobromoparahydroxybenzoic acid is not known; when bromine water is added to a solution of para- 1 Ber. Deutsch. Chem. Ges. ii. 666. 2 Lossner, Journ. Prakt. Chem. [2] xiii. 432. 3 Hasse, Ber. Deutsch. Chem. Ges. x. 2192. CHLOROPARAHYDROXYBENZOIC ACID. 335 hydroxy ben zoic acid, a precipitate of tribromophenol is produced (Barth and Hlasiwetz). lodoparahydroxybenzoic acid, 2C6H3I(OH)CO2H + H2O, is formed when parahydroxybenzoic acid is boiled with water, iodine and iodic acid; it crystallizes from hot water in small needles, which become anhydrous at 100° and then melt at 1920.1 Di-iodoparahydroxybenzoic acid, C6H2I2(OH)CO2H, is formed together with the preceding compound, and crystallizes in small needles, which are scarcely soluble in water, but readily in alcohol. Nitroparahydroxybenzoic acid, C6H3(NO2)(OH)CO2H, (3:4:1). Griess obtained this compound by the action of boiling potash on 8-nitro-amidobenzoic acid.2 It is also formed in small quantity, together with /3-nitro-salicylic acid, by heating orthonitrophenol with alcoholic potash and tetrachloromethane (Hasse). It crystal- lizes from boiling water in yellowish needles, melting at 185°. Its solution is not coloured by ferric chloride. Basic barium nitroparahydroxybenzoate, C7H3NO5Ba + H2O, is obtained by adding barium chloride to a hot, ammoniacal solu- tion of the acid. It forms yellowish red, lustrous plates. Dinitroparahydroxybenzoic acid, C6H2(NO2)2(OH)CO2H, (3:5: 1:4) is formed when a boiling solution of dinitroparamidobenzoic acid is treated with nitrous acid or with caustic potash. It is slightly soluble in cold, more readily in hot water, and crystallizes in large, thin tablets, which are coloured light yellow to bronze, and melt at 235°-237°.3 Its salts are coloured yellow oi' orange- red, and crystallize well. Barth has prepared a mono- and a di- nitro-acid by the action of nitric acid on parahydroxybenzoic acid, both of which seem to be different from the preceding compounds. Amidoparahydroxybenzoic acid, C6H3(NH2)(OH)CO2H. Barth obtained this substance bythe reduction of his nitroparahydroxy- benzoic acid. It crystallizes in needles and forms a sulphate which also crystallizes in needles, and gives a dark cherry-red colouration with concentrated nitric acid. Sulphoparahydroxybenzoic acid, C6H3(SO3H)(OH)CO2H, was prepared by Kblle by the action of sulphur trioxide on para- 1 Pelzer, Ann. Chem. Pharm. cxlvi. 288. 2 Ber. Deutsch. Chem. Ges. v. 856. 3 Salkowski, Ann. Chem. Pharm. clxiii. 36. 336 AROMATIC COMPOUNDS. hydroxybenzoic acid.1 It is also obtained when the latter, or parahydroxybenzide, is heated with concentrated sulphuric acid (Klepl), and forms deliquescent needles, which are insoluble in ether. Its solution is coloured blood-red by ferric chloride ; on fusion with potash, it yields protocatechuic acid. Acid potassium sidphoparahy dr oxybenzoate, C7H5SO6K + H2O, is a very characteristic salt, since it is even less soluble in water than acid potassium tartrate. It crystallizes from a hot solution in quadratic tablets or prisms, and from a less concentrated solution in rectangular plates which are obliquely striated (Klepl). Parahydroxybcnzoyl sulphuric acid, CGH4(SO4H)CO2H, occurs as an alkali salt in the urine of the dog after administration of parahydroxybenzoic acid. The potassium salt, CGH4(SO4K)CO2K, is obtained by heating an alkaline solution of parahydroxybenzoic acid with potassium disulphate, and crystallizes in lustrous plates or tablets, which decompose at 250° with formation of potassium sulphate and anhydrides of parahydroxybenzoic acid.2 SUBSTITUTION PRODUCTS OF ANISIC ACID. 2187 Chloranisic acid, C6H3C1(OCH3)CO2H, is formed by the action of chlorine on fused anisic acid, and crystallizes from dilute alcohol in needles or rhombic prisms, which melt at 176° and volatilize without decomposition.3 Dichlor anisic acid, CGH2C12(OCH3)CO2H, is obtained, together with chloranil, by heating anisic acid with hydrochloric acid and potassium chlorate; it crystallizes from alcohol in large needles melting at 1960.4 Bromanisic acid, CGH3Br(OCH3)CO2TI, is formed by the action of bromine on anisic acid (Cahours), the latter being kept covered with hot water.5 It crystallizes from alcohol in needles which melt at 213°-214° and sublime in small plates. Dibromanisic acid, C6H2Br2(OCH3)CO2H. Reinecke pre- pared this substance by heating anisic acid to 120° with bromine and water; it crystallizes in long needles melting at 207°. On 1 Ann. Chem. Pharm. clxiv. 150. 2 Baumann, Ber. Deutsch. Chan. Ges. xi. 1916. 3 Cahours, Ann. Chem. Pharm. Ivi. 312. 4 Reinecke, Zeitschr. Chem. 1866, 366. 6 Salkowski, Ber. Deutsch. Chem. Ges. vii. 1013. IODANISIC ACID. 337 further treatment with bromine, tribromanisol and tetrabromo- quinone are formed, while fuming nitric acid converts it into dibromonitro-anisol, C6H2Br2(NO2)OH, (3 : 5 : 4 :1), which was previously obtained by Korner in a different manner, the con- stitution of the acid being thus shown.1 When its sodium salt is distilled with lime, the methyl ether is formed, together with the basic sodium salt of dibromoparahydroxybenzoic acid :2 zCO2Na zCO2.OCH3 zCO2Na. 2C6H.,BrZ = C6H9Br.Z " + C6H2Br2< \QCH3 xOCH3 \QNa This ether crystallizes from alcohol in lustrous needles melting at 91-5°-92°. The dibromoparahydroxybenzoic acid is also obtained by heating dibromanisic acid with hydriodic acid.3 lodanisic acid, C6H3I(OCH3)CO2H, was prepared by Griess from diazo-amido-anisic acid,4 while Peltzer obtained it by heating anisic acid to 145°-150° with iodine and iodic acid.5 It crystallizes from alcohol in needles, which melt at 234'5°, and sublime in small plates. Nitro-anisic acid, C6H3(NO2)(OCH3)CO2H, was obtained by Cahours as a product of the action of nitric acid on anisic acid and anisol.6 In order to prepare it, anisol is allowed to drop into ten times its weight of warm nitric acid, of specific gravity 14, the mixture boiled for a short time, and the acid then precipitated by watei'; it is well washed and finally freed from an admixed oil by solution in ammonia and reprecipitatidii by hydrochloric acid.7 Nitro-anisic acid is slightly soluble in water, and crystallizes from alcohol in compact prisms melting at 189°. On heating with water to 220°, it decomposes into ortho- nitrophenol, methyl alcohol and carbon dioxide,8 while aqueous ammonia at 140°-170° converts it into 3-nitro-amidobenzoic acid.9 Its salts have been investigated by Engelhardt.10 Dinitro-anisic acid, C6H2(NO2)2(OCH3)OO2H. Salkowski and Rudolph prepared this substance by dissolving anisic acid in 1 Balbiano, Gaz. Chim. Itai. xiv. 9. 2 Ibid. xiii. 65. 3 Alessi, ibid. xv. 242. * Ann. Chem. Pharm. cxvii. 54. 5 Ibid, cxlvi. 302. 6 Cahours, ibid. xli. 71. 7 Salkowski, ibid, clxiii. 6. 8 Salkowski and Rudolph, Bar. Deutsch. Chem. Ges. x. 1254. 9 Salkowski, Ann. Chem. Pharm. clxxiii. 35. 10 Zinin, ibid. xcii. 327 ; Cahours, ibid. cix. 21. 338 AROMATIC COMPOUNDS. portions of 40 grammes at a time in a well-cooled mixture of sulphuric and nitric acids, 160 grammes of the former and 140 of the latter being required for each portion of anisic acid ; notwithstanding the low temperature, carbon dioxide is evolved and di- and tri-nitro-anisol are formed. The dinitro-anisic acid separates from the acid solution on standing, and is then dissolved in a cold, dilute solution of sodium bicarbonate, re-precipitated by alcohol and finally purified by re-crystallization from dilute alcohol. It forms yellowish needles melting at 181°-182°, and on boiling with caustic soda decomposes into methyl alcohol and dinitroparahydroxybenzoic acid, while it is immediately converted into chrysanisic acid by boiling, concentrated ammonia (p. 258). Amido-anisic acid, C6H3(NH2)(OCH3)CO2H, is obtained by reducing nitro-anisic acid with alcoholic ammonium sulphide.1 It is slightly soluble in water, readily in alcohol, and crystal- lizes in long, thin, four-sided prisms, which melt at 180° and are decomposed into carbon dioxide and anisidine when heated with caustic baryta (Part III. p. 249). Methyl amido-anisate, C6H3(NH2)(OCH3)CO2.CH3, was pre- pared by Cahours from the methyl ether of nitro-anisic acid by re- duction ; it crystallizes in prisms which readily dissolve in alcohol. Mcthylamido-anisic acid, C6H3(NH.CH3)(OCII3)CO2H. Griess obtained this substance by heating potassium amido-anisate with methyl iodide. It is slightly soluble in hot water and cold alcohol, but more readily in hot alcohol, and melts above 200°.2 Trimethylamido-anisic acid, or Trimethylanise-loetaineQ O3 4- 5H2O, is formed by the action of methyl iodide and caustic potash on anisic acid, and crystallizes from water in well- formed, vitreous prisms, which have a bitter taste and are neutral to litmus paper. It is completely converted by distillation into the metameric methyl ether of dimethylamido-anisic acid : /OCH3 /OCH3 C6H3-CO-O = C6H3-co.och3. VO v o \ o \ / \n(CH,)2 N (CH,), The latter substance is a yellowish liquid, which has a faint aromatic odour and boils at 2880.3 1 Zinin, Ann. Chem. Pharm. xcii. 327 ; Cahours, ibid. cix. 21. 2 Ber. Deutsch. Chern. Ges. n. 1042. 3 Griess, ibid, vi. 587. ANISENYLOXIME COMPOUNDS. 339 ANISENYLOXIME COMPOUNDS. 2i88 These bodies, which correspond to the benzenyloxime compounds (p. 207), are prepared in an exactly similar manner, anisyl chloride being gradually added to a solution of hydroxyl- amine hydrochloride, which is kept faintly alkaline by the addition of dilute carbonate of soda solution. A mixture of anishydrox- amic acid, di-anishydroxamic acid and anisic acid is thus obtained. Boiling water extracts from this a portion of the anisic acid and all the anishydroxamic acid, these being sub- sequently separated by means of their barium salts, that of the former being soluble while that of the latter is insoluble in water. The dry mixture of the two acids may also be extracted with warm absolute ether, in which anishydroxamic acid is almost insoluble. The di-anishydroxamic and anisic acids are separated by treatment with a cold solution of sodium carbonate, which dissolves the latter completely, while only a small portion of the former enters into solution. The liquid is filtered rapidly, because di-anishydroxamic acid is easily decomposed by carbon- ate of soda, the filtrate almost neutralized with hydrochloric acid, and then saturated with carbon dioxide, all the di-anis- hydroxamic acid present being thus precipitated.1 Anishydroxamic acid, CH3O.C6H4.C(OH)NOH, is slightly soluble in cold, readily in hot water and alcohol, but is almost insoluble in ether; it crystallizes in small plates, melting at 156°-157°, and is coloured deep violet by ferric chloride. The acid potassium salt, C8H8KNO3 + C8H9NO3, forms long, flat needles, which are tolerably soluble in cold water. Lead acetate produces a thick, white precipitate2 of C2H3O2PbC8H8NO3. Ethyl anishy dr oxamate, CH3O.C6H4.C(OH)NOC2H5, is formed by the action of anisyl chloride on ethylhydroxylamine ; it is insoluble in water, readily soluble in alcohol, less easily in ether, from which it crystallizes in tablets, which melt at 84° and have feeble acid properties. On heating with concentrated hydrochloric acid, it is split up into anisic acid and ethyl- hydroxylamine.3 Ethylanishydroxamic acid, CH3O.C6H4.C(OC2H5)NOH, is 1 Lessen, Ann. Chern. Pharm. clxxv. 284. 2 Hodges, ibid, clxxxii. 218. 3 Pieper, ibid, ccxvii. 16. 340 AROMATIC COMPOUNDS. obtained by heating the ethyl ether of anisbenzhydroxamic acid with caustic potash. It is precipitated by carbon dioxide as an oily liquid, which solidifies to a crystalline mass, melting at 32°. It is readily soluble in alcohol and ether, and decomposes on heating with hydrochloric acid into ethyl anisate and hydroxylamine.1 Dianishydroxamic acid, CH3O.CeH4.C(NO.CO.C6H4.OCH3)OII, is scarcely soluble in water and ether, slightly in alcohol, and crystallizes in needles, melting at 142°-143°. It is de- composed by baryta water into anisic acid and anishydroxamic acid. Bcnzanishydroxamic acid, C6HVC(NO.CO.C6H4.OCH3)OH, is formed by heating benzhydroxamic acid to 100° with anisyl chloride. It crystallizes from alcohol in needles or prisms, which melt at 131°-132°. On heating with baryta water, it decom- poses into anisic acid and benzhydroxamic acid, while boiling water splits it up into carbon dioxide, anisic acid and diphenyl urea. When heated alone, it yields carbon dioxide, phenyl isocyanate, anisic acid and anisanilide,C6H5.NH(CO.C0H4.OCH3). a-Ethylbenzanishydroxamatc, or Bcnzaniscthylhydroxylaminc, O6H5.C(NO.CO.C6H4.OCH3)OC2II5, is obtained by the action of ethyl iodide on silver benzanishydroxamate. It crystallizes from a mixture of ether and benzene in thick, monoclinic tablets, melting at 74° (Pieper). It is decomposed by caustic potash into anisic and a-ethylbenzhydroxamic acids, and by hydrochloric acid into anisic acid, ethyl benzoate and hydroxylamine. (3-Ethylbenzanishydroxamate is formed by the action of anisyl chloride on a- or /3-ethylbenzhydroxamic acid, and separates from ether in monoclinic crystals, melting at 89°. On heating with concentrated caustic potash solution, it decomposes into anisic acid and /3-ethylbenzhydroxamic acid, while on dry distillation it decomposes into benzonitril, anisic acid and aldehyde. Anisbenzhydroxaynic acid, CH3O.C6H4C(NO.CO.C6H5)OH, is obtained from anishydroxamic acid and benzoyl chloride; it crystallizes in needles or prisms, which melt at 147°-148°, and decompose at a higher temperature into carbon dioxide, benzoic acid, anisol isocyanate, CON.C6H4.OCH3, and benzoylanisidine, NH(CO.C6H5)C6H4.OCH3. Ethyl anisbenzhydroxamate, or Anisbenzethylhydroxylamine, CH3O.C6H4C(NO.CO.C6H5)OC3H5, crystallizes in short, four- sided, asymmetric pyramids, melts at 79° and is decomposed 1 Eisler, Ann. Chern. Pharm. clxxv. 338. DIBENZANISHYDROXYLAMINE. 341 by caustic potash into benzoic acid and ethylanishydroxamic acid. Benzethylanishydroxylaminc, C6H5C(NOC2H5)O.CO.C6H4. OCH3, is obtained by the action of anisyl chloride on the silver salt of ethylbenzhydroxamate, and separates from ether in asymmetric crystals, melting at 64°. It is decomposed by highly concentrated caustic potash into anisic acid and ethylbenzhydroxamate. A7i7seZA7/ZZ)en?Ay(ZmryZa??wic,CH3O.CGH4.C(NOC\H5)OCO.€^^ is formed when a solution of ethylanishydroxamate in caustic potash is treated with benzoyl chloride, and forms monosymmetric crystals, melting at 93°-94°. It is split up into benzoic acid and ethyl anishydroxamate on heating with caustic potash.1 2189 Hydroxylamine Derivatives containing three Acid Radicals are formed by the action of anisyl or benzoyl chloride on the silver salts of the dihydroxamic acids. They are insoluble in water and sodium carbonate solution, and only very slightly soluble in cold alcohol. On heating with hydrochloric acid, the radical which was last introduced is split off.2 NO.CO.C6H5 Dibenzanishydroxylamine, CqH5C; xO.CO.C6H4.OCH3 Melting-point. a) Long, monosymmetric needles or prisms . 110°-110'5° /3) Small crystals 109°-110° NO.CO.C6H4.OCH3 Benzanisbenzhydroxylamine, C6H5.C<; \o.co.c6h5 Melting-point. a) Short, asymmetric prisms 113°-114° /?) Long, rhombic prisms 124°-125° y) Monosymmetric tablets; decompose on fusion - NO.CO.C6H5 Anisdibenzhydroxylamine, CH3O.C6H4C\ \OCO.C6H5 Melting-point. a) Lustrous monoclinic tablets 137°-137'5° /9) Very small crystals, usually opaque . . . 109'5°-110'5° 1 Pieper, Ann. Chem. Pharm. ccxvii. 1. 2 Lossen, ibid, clxxxvi. 1. 342 AROMATIC COMPOUNDS. Anisbenzanishydroxylamine, NO.CO.C6H5 CH3O.C6H4.C< \oco.c6h4.och3 Melting-point. a) Very small, monosymmetric tablets .... 152°-153° /S') Monosymmetric tablets 148°-149° Dianisbenzhydroxylamine, ,NO.CO.C6H4.OCH3 ch3o.c6h4.c< xOCO.C6H5 Melting-point. Large, monosymmetric crystals with many faces . 147'5° ^NO.CO.C6H4.OCH3 BeNZDIANISHYDROXYLAMINE, CgH5.C\ \o.co.c6h4.och3 Melting-point. a) Short, asymmetric columns 137'5°-138'5° /3) Asymmetric tablets 137'5°-138° Lossen remarks concerning these compounds: " The twelve substances described above afford an additional proof of the well- established fact that there are two kinds of isomerism, which must be carefully distinguished from one another. Seven isomeric substances were obtained as the products of three different methods of preparation, three being yielded by one method and two by each of the others ; three further methods of preparation, different from the preceding, gave five isomeric bodies, two being formed by each method. Isomerides are, therefore, formed both by different methods and by one and the same method, but the difference between two compounds which are prepared by independent methods is not the same as that existing between the isomeric products of a single method." 1 The latter, in fact, always give the same decomposition products on treatment with hydrochloric acid or caustic potash. 1 Loc. cit. and Ber. Deutsch. Chern. Ges. xviii. 1189. PROTOCATECHUICALDEHYDE. 343 Thus benzoic acid and dianishydroxamic acid are obtained by the action of caustic potash upon the anisbenzanishydroxylamines, the same products, together with anisic acid and anisbenzhydrox- amic acid, being also formed from dianisbenzhydroxylamine, while the benzdianishydroxylamines are resolved into anisic acid and benzanishydroxamic acid. The dibenzanishydroxylamines under the same circumstances yield benzanishydroxamic acid, and not, as might have been expected, a compound metameric with this : NO.CO.C6H5 C6H5.C< +2K0H= \O.CO.C7H7O N°K c6h5.c< + ko.co.c6h5+h2o. xO.CO.C7H7O Lossen assumes that the decomposition first proceeds in this way, and that the compound formed changes into: .NO.CO.C7H7O c6h5.c^ \QK. " A similar exchange between a metal and an acid radical has often been observed." DIHYDROXYBENZYL AND DIHYDROXY- BENZOYL COMPOUNDS. 21 go Protocatechibicaldehyde, or a-Orthodihydroxybenzaldehyde, C6H3(OH)2CHO.(COH : OH : OH = 1: 3 : 4), was first prepared from piperonal (p. 347) and from vanillin or its methyl ether. Tiemann and Reimer found that it is also formed by the action of chloroform on an alkaline solution of catechol.1 In order to prepare it, a solution of 10 parts of the latter in 600 parts of 16 per cent, caustic soda solution is heated for 5-6 hours with 100 parts of chloroform in an apparatus connected with an inverted condenser, acidified with hydrochloric acid, allowed to cool, filtered from a black resinous substance and shaken out with 1 Ber. Deutsch. Chern. Ges. ix. 1269. 344 AROMATIC COMPOUNDS. ether. The aldehyde is extracted from the ethereal solution by means of acid sodium sulphite, liberated by dilute sulphuric acid, again dissolved in ether and the residue on evaporation re-crystallized from boiling toluene.1 It is readily soluble in water, alcohol and ether, very slightly in cold, more readily in boiling toluene, and crystallizes from water in flat, lustrous needles, melting at 150°. Ferric chloride added to its aqueous solution produces a green colouration, which becomes first violet and then red on the addition of sodium carbonate. Ammoniacal silver solution is immediately reduced by it. Vanillin, C6H3(OH)(OCH3)CHO(CHO : OCH3:OH = 1:3 : 4). The crystalline coating of vanilla (givre de vaniUe) was mistaken by Buchholz for benzoic acid, and by other chemists for cinnamic acid, although Bley had previously pointed out that it is a distinct substance. Gobley, who at first took it for cumarin, subsequently found with Vee, that it differs from this substance, and named it vanillin,2 while Stokkebye, who obtained analytical results differing from those of Gobley, termed it vanillaic acid.3 The correct formula of vanillin was determined by Carles, who investigated its properties and some of its derivatives,4 without being able to determine its relations to any known compounds. Tiemann and Haarmann, however, were successful in this, and prepared it artificially from coniferin, C10H12O8. This compound occurs in the cambium sap of the fir-tree, and is decomposed by emulsin in the presence of water into grape sugar and the compound C10H12O3, forming odourless crystals, which after standing in the air for some time have a faint smell of vanilla; Tiemann and Haarmann therefore oxidized it with chromic acid and thus obtained vanillin. On fusion with caustic potash it is converted into protocatechuic acid, and on heating to 200° with hydrochloric acid is decomposed into methyl chloride and proto- catechuicaldehyde, proving that it is the methyl ether of the latter.5 Reimer and Tiemann then obtained it by heating guaiacol (Part III. p. 134) with caustic soda and chloroform,6 the iso- meric metamethoxysalicylaldehyde being simultaneously formed (Tiemann and Koppe).7 1 Tiemann and Koppe, Ber. Deutsch. Chern.. Ges. xiv. 2015. 2 Jahresber. Chem. 1858, 534. 3 Ibid. 1864, 512. 4 Bull. Soc. Chim. xvii. 2. 5 Ber. Deutsch. Chem. Ges. vii. 608. 6 Ibid. ix. 424. 7 Ibid. xiv. 2023. VANILLIN. 345 The decomposition product of coniferin, referred to above, is coniferyl alcohol, C6H3(OH)(OCH3)CH~CH.CH2OH, and its conversion into vanillin by oxidation may readily be under- stood. The latter is formed in a similar manner from eugenol, C6H3(OH)(OCH3)CHzzCH.CH3, a substance which is found in oil of cloves. Vanilla contains 1'5-2'5 per cent, of vanillin and a little vanillic acid, C6H3(OH)(OCH3)CO2H, but no other aromatic compounds.1 It also occurs in Siam benzoin,2 in Asa fodida? and frequently in small quantities in beet-sugar,4 since the sugar' beet contains coniferin, which has also been found, together with vanillin, in asparagus.5 It is best obtained from coniferin. The trees containing this substance, Abies excelsa, A. pectinata, Pinus strobus, P. cembra, Larix europaea, and other pines and firs, are felled during the spring or early summer. The trunks are then sawn into pieces and freed from bark, the cambium sap being removed by means of a sharp knife. This is boiled with water, freed from albumen, and the clear liquid evaporated to one-fifth of its bulk. The crystals which separate after some time are filtered off, pressed and re-crystallized after having been boiled with animal charcoal. The aqueous solution is then allowed to flow into a warm mixture of potassium dichromate and dilute sulphuric acid, the whole being heated for several hours in a flask con- nected with an inverted condenser. After cooling, the solution is filtered to remove a small quantity of a resinous substance and extracted with ether. On evaporation a yellow oil is left, which solidifies after some days to crystals which are boiled with animal charcoal and re-crystallized from hot water.6 Vanillin can also be readily obtained by replacing the nitroxyl group in paranitromethylmetahydroxybenzaldehyde by hydroxyl, by the oxidation of ferulaic acid, C6H3(OH)(OCH3)CH2.CO2H, which can be prepared on the large scale without difficulty,7 and from olivil,8 C14H18O5, the crystalline constituent of the Lecca gum, or resin of the wild olive, which is used in Italy as 1 Tiemann and Haannann, Ber. Deutsch. Chem. Ges. viii. 1118 ; ix. 1287. 2 Jannasch and Rump, ibid. xi. 1635. 3 E. Schmidt, ibid. xix. Ref. 705. 4 Scheibler, ibid. xiii. 335 ; Lippmann, ibid. xiii. 662. 5 Lippmann, ibid. xvi. 44 ; xviii. 3335. 6 Tiemann and Haarmann, ibid. vii. 609 and 614. 7 M. Ulrich, ibid, xviii. Ref. 682. 8 Scheidel, ibid, xviii. 685. 346 AROMATIC COMPOUNDS. incense.1 This substance will be further described along with eugenol. Properties.-Vanillin forms white needles, generally occurring in stellate aggregates, which possess a very strong taste and smell of vanilla. It melts at 80°-81°, sublimes readily, boils at 285° without decomposition when heated in an atmosphere of carbon dioxide, and dissolves in 90-100 parts of water at 14°, and in 20 parts at 75°-80°. It is scarcely soluble in cold, more readily in hot petroleum spirit. Its aqueous solution is coloured bluish violet by ferric chloride ; if this solution be heated, white needles of dihydrovanillin separate out. This body, which will be described among the compounds containing two aromatic nuclei, has the following constitution :2 C6H2(OH)(OCH3)CHO CcH2(OH)(OCH3)CHO Vanillin is reduced in dilute alcoholic solution by sodium amalgam to vanillyl alcohol, C6H3(OH)(OCH3)CH2.OH, which crystallizes in prisms, melting at 115°.3 Vanillin has an acid reaction and forms salts, which have been investigated by Carles, and by Tiemann and Haarmann ; the former has also prepared bromine and iodine substitution compounds. 2191 Isovanillin, C6H3(COH)(OH)(OCH3) (1: 3: 4), is formed by heating opianic acid, C6H2(COH)(OCH3)2CO2H, to 160°-170° with dilute hydrochloric acid; it crystallizes from hot water in monosymmetric prisms, which possess a vitreous lustre, and its solution is not coloured by ferric chloride; it sublimes when heated, undergoing slight decomposition;4 its vapour has a pleasant smell, resembling that of vanilla and anise. Mcthylvanillin, or Dimcthylprotocatcchuicaldehydc, C6H3(OCH3)2 CHO, is formed by heating potassium vanillin with methyl iodide and wood-spirit.5 Beckett and Wright prepared it by distilling opianic acid with soda lime,6 It is slightly soluble in hot water, readily in alcohol, and crystallizes in needles, which smell like vanilla; it melts at 42°-43° and boils at 280°-285°. 1 Pelletier, Ann. Chern. Pharm. vi. 31 ; Sobrero, ibid. liv. 67. 2 Tiemann, Ber. Deutsch. Chern. Ges. xviii. 3493. 3 Ibid. viii. 1125 ; ix. 415 ; xviii. 1597. 4 Wegscheider, Monatsch. Chem. iii. 789. 5 Tiemann, Ber. Deutsch. Chem. Ges. viii. 1135- 6 Journ. Chem. Soc. 1876, i. 287. VANILLIN COMPOUNDS. 347 Acetylvanillin, C6H3(OCO.CH3)(OCH3)CHO, is obtained by the action of sodium vanillin on an ethereal solution of acetic anhydride. It crystallizes in large, flat needles, melting at 77°.1 Glucovanillin, or Vanillin glucoside, C6H3(OCH3)(OC6HnO5). CH0 + 2H.,0, is formed by the oxidation of coniferin with a dilute solution of chromic acid. It is tolerably soluble in water, less readily in alcohol, and crystallizes from dilute alcohol in white needles which lose their water at 100° and melt at 192°. It is readily decomposed by emulsin into grape sugar and vanillin, and is converted by sodium amalgam and water into glucovanillyl alcohol, C6H3(OCH3)(OC6HnO5)CH2.OH + H2O, which crys- tallizes in white needles, melting at 120°. When its aqueous solution is treated with a little emulsin and allowed to stand for four or five days at 30°-40°, vanillyl alcohol is formed, and can most easily be obtained pure by this method.2 Piperonal, or Methyleneprotocatechuicaldehyde, C6H3(O2CH9) CHO, was prepared by Fittig and Mielk by the oxidation of piperic acid, C6H3(O2CH2)C4H4.CO2H, with potassium per- manganate.3 It is slightly soluble in cold, more readily in hot water and forms long, thin, lustrous plates, which have a very pleasant smell, resembling that of the heliotrope ;4 it is on this account employed in perfumery.5 Piperonal melts at 37°, boils at 263° and forms a vapour which has a specific gravity of 5'18.6 A very characteristic reaction of this substance is that it decomposes into protocatechuicaldehyde and finely divided carbon when it is heated to 200° with dilute hydrochloric acid:7 /CHO /CHO = C6H3-OH + C. \o/ 2 \OH Oxidizing agents convert it into piperonylic acid, while sodium amalgam reduces it in boiling aqueous solution to piperonyl 1 Tiemann and Nagai, Ber. Deutsch. Chern. Ges. xi. 647. 2 Tiemann, ibid, xviii. 1595. 3 Ann. Chern. Pharm. clii. 35. 4 This same smell is possessed by " vanillon," a kind of vanilla, which forms thick, fleshy capsules, and is obtained from the West Indies. It is only employed in perfumery for the preparation of essence of heliotrope ; it contains no piperonal, but vanillin and an oil which is probably benzaldehyde. The perfumers in preparing essence of heliotrope add a little of this oil to the extract of vanillon. If a little be added to a solution of pure vanillin, both substances can be recognized by their smell for some time, but after standing for months, the mixture acquires the smell of heliotrope (Tiemann and Haarmann, Ber. Deutsch. Chem. Ges. ix. 1287.) 6 Chem. Zeit. 1884, 173. 6 Knecht, Ber. Deutsch. Chem. Ges. x. 1274. 7 Fittig and Remsen, Ann. Chem. Pharm. clxviii. 97. 348 AROMATIC COMPOUNDS. alcohol, C6H3(O2CH2)CH2.OH, which is slightly soluble in cold, more readily in hot water, and forms long, colourless crystals, melting at 510.1 Dichloropiperonal, C6H3(O2CC12)COH. When one molecule of piperonal is heated with three molecules of phosphorus pentachloride, the compound C6H3(O2CC12)CHC12 is formed- It is an oily liquid, which is decomposed by water into hydro- chloric acid and dichloropiperonal; the latter crystallizes from toluene in needles, which melt at 90° and undergo the following decomposition when heated with water : /CHO /CHO C6H3^-O\PP1 + 2H2O = C6H3^-OH + CO2 + 2HC1. \o/cc12 \OH Protocatechuicaldehyde was first prepared according to this method by Fittig and Remsen. 2192 /3 Mdhylorthodihydroxylenzaldehyde, or ^-Mdamdhoxy- salicylaldehydc, C6H3(OH)(OCH3)CHO (CHO: OH: OCH3= 1: 2: 3), is formed together with vanillin by heating guaiacol with caustic soda and chloroform. On distillation with steam it passes over first as a liquid, which smells like salicylaldehyde, boils at 264°-265° in a current of carbon dioxide, stains the skin yellow and forms a deep yellow solution in alkalis. Ferric chloride added to an alcoholic solution produces a green coloura- tion containing a shade of violet.2 Mdadihydroxyhcnzaldehyde, or ^-Rcsorcylaldehyde, C6H3(OH)2 CHO (CHO : HO : HO ~ 1: 2 : 4), is obtained, along with resorcyldialdehyde, C6H2(OH)2(CHO)2, by heating resorcinol with caustic soda and chloroform.3 It crystallizes from water in yellowish needles, which melt at 134°-135°; its solution is coloured reddish brown by ferric chloride. It is an unstable substance and gradually decomposes in moist air into a red powder. Orthomdhoxyparahydroxybenza Idehyde, C 6 H3 (0 H) (O CH3) CHO (CHO: OCH3: OH - 1 : 2 : 4), is formed, together with the following compound and two resorcyldialdehydes, by heating methylresorcinol with caustic soda and chloroform.4 It is readily soluble in alcohol, slightly in water and benzene, and crystallizes 1 Fittig and Remsen, Ann. Chem. Pharm. clix. 138. 2 Tiemann and Koppe, Ber. Deutsch. Chcm. Ges. xiv. 2020. 3 Tiemann and Lewy, ibid. x. 2212. 4 Tiemann and Parrisius, ibid. xiii. 2365. PARAMETHOXYSALICYLALDEHYDE. 349 from the latter in lustrous plates melting at 153°. Its aqueous solution is coloured a faint violet by ferric chloride. The acetyl- derivative, C6H3(OC2H3O)(OCH3)CHO, is formed by adding the potassium compound to an ethereal solution of acetic anhydride ; it crystallizes in needles, melting at 86°. Paramethoxysalicylaldehyde,, (COH : OH : OCH3 " 1: 2 : 4), may also be obtained by heating 7-resorcyldialdehyde with caustic potash and methyl iodide. It is almost insoluble in water and crystallizes in plates, which have a characteristic, pleasant, aromatic odour, melt at 62°-63° and are very readily volatile. It forms an intensely yellow solution in alkalis; ferric chloride produces a deep reddish yellow colouration in an alcoholic solution. Melting-point. Dimethyl-/3-resorcylaldehyde, needles 68°-69°. Diethyl-^-resorcylaldehyde, lustrous plates . . . 71°-72°. Paradihydroxybenzaldehyde, or Gentisinaldehyde, (CHO : OH : OH~1 : 2: 5), has been prepared from quinol by the action of chloroform and caustic soda. It is readily soluble in water and alcohol, and crystallizes in flat, lustrous yellow needles, melting at 99°; its aqueous solution is coloured a transient bluish green by ferric chloride and intensely yellow by alkalis.1 Methylparadihydroxybenzaldehyde, or Metamethoxysalicylalde- hyde, (CHO : OH : OCH3z=1 : 3 : 5), has been obtained from methylquinol.2 It is a yellow oil which has an aromatic odour, solidifies in a freezing mixture to a radiating mass and then melts at 4°; it boils at 247°-248° in a current of carbon dioxide. It stains the skin yellow, forms an intensely yellow solution in alkalis and in alcoholic solution is coloured a permanent bluish green by ferric chloride. Its acetyl-compound crystallizes in needles, melting at 63°. Melting- point. Dimethylparadihydroxybenzaldehyde, fine needles . .51° Ethylparadihydroxybenzaldehyde, thick, yellow prisms. 51'5° Diethylparadihydroxybenzaldehyde, small needles 3 . . 60° 1 Tiemann and Miiller, Ber. Deutsch, Chem. Ges. xiv. 1986. 2 Ibid. 1990. 3 Hantzsch, Journ. Prakt. Chem. [2] xxii. 464. 350 AROMATIC COMPOUNDS. /OH DIHYDROXYBENZOIC ACIDS, C6H3<-CO.OH \OH. 2193 The numbers appended designate the positions of the groups CO2H:OH:OH. Protocatechuic Acid, or Orthodihydroxybenzoic Acid (1:3:4). In the year 1859, Hesse, by the action of bromine on an aqueous solution of quinic acid, C7H12O6, obtained " carbohydro- kinonic acid," C7H6O4, which decomposed into hydroquinone and carbon dioxide on heating.1 Two years later Strecker found that an acid is formed by fusing piperic acid with potash, which resembles catechuic acid so closely that he at first thought that they were identical, but as he subsequently found less carbon in the new compound he named it protocatechuic acid.2 It decom- poses on heating into carbon dioxide and catechol, and should therefore be isomeric with Hesse's acid. All the other properties of the two acids, however, agreed so completely that most chemists assumed their identity, the more so as catechol had been previously found among the decomposition products of carbo- hydrokinonic acid. Fittig and Macalpine then proved decisively that they are identical, and that the differences observed by Hesse were due to some error.3 Protocatechuic acid has been obtained from various carbon compounds by fusion with caustic potash. Catechin or catechuic acid,4 the maclurin which occurs in fustic,5 and the luteolin obtained from woad also yield phloroglucinol, while many resins give parahydroxybenzoic acid in addition6 (p. 326). Its synthetical formation from sulphanisic acid,7 paracresol- 1 Ann. Chern. Pharm. cxii. 52 ; cxxii. 221. 2 Ibid, cxviii. 280. Strecker supposed that catechu contained two homologous acids, which he named deutero- and trito-catechuic acids ; but this view has not been confirmed. 3 Ibid, clxviii. 111. 4 Kraut and Delden, ibid, cxxviii. 285 ; Malin, ibid, cxxxiv. 118. 5 Barth and Pfaundler, ibid, cxxvii. 357. 6 Barth and Hlasiwetz, ibid. cxxx. 346 ; cxxxiv. 277 ; cxxxix. 78. 7 Malin, ibid. clii. 109. PROTOCATECHUIC ACID. 351 sulphonic acid,1 bromanisic acid, iodoparahydroxybenzoic acid, sulphoparahydroxybenzoic acid and sulphometahydroxybenzoic acid,2 is of theoretical interest. It is best prepared from East Indian kino, which is obtained by making incisions in the bark of Pterocarpus Marsupium ; the sap flows out and dries to a dark red, transparent mass, which is employed in medicine as an adhesive, and for many purposes as a substitute for catechu. One part of the finely-powered kino is then gradually brought into a well-stirred melt of three parts of caustic soda kept at a low temperature. When the mass has become coloured a light orange brown, it is dissolved in 20 parts of water, and the solution acidified with sulphuric acid, and allowed to stand for twenty-four hours. The filtrate is extracted with ether, the latter evaporated and the residue repeatedly crystallized from water.3 The aqueous solution of the acid may also be precipitated with lead acetate, the precipitate washed and finally decomposed by sulphuretted hydrogen (Barth and Hlasiwetz). According to Eijkman, protocatechuic acid occurs in the fruit of Illicutm rcligiosum^ It crystallizes in monoclinic needles, containing one molecule of water which is lost at 100°, and melts at 194°;5 it dissolves in 53-55 parts of water at 14° and in 3 5-3'7 parts at 75°-80°,6 is very soluble in alcohol, less so in ether, and almost insoluble in boiling benzene. Its aqueous solution is coloured an intense bluish green by ferric chloride, the colour being changed to dark red by the addition of sodium carbonate. The solutions of its salts are coloured violet by ferrous sulphate. It reduces an ammoniacal silver solution, but not Fehling's solution; on dry distillation, or when heated to 330°-350° with caustic soda, it decomposes into carbon dioxide and catechol. When nitrogen trioxide is passed into its ethereal solution, oxalic and dihydroxy- tartaric acids are formed (Part III. p. 58), together with smaller quantities of dinitrophenol, picric acid, dinitrodihydroxyquinone and nitroparahydroxybenzoic acid.7 Protocatechuic acid is produced along with benzoic acid when gum benzoin is fused with caustic potash; a compound of the 1 Barth, Ann. Chern. Pharm. cliv. 364. 2 Ibid. elix. 232. 3 Stenhouse, ibid, clxxvii. 188. 4 Ber. Deutsch. Chern. Ges. xviii. Ref. 281. 5 Barth and Schmidt, ibid. xii. 1265. 6 Tiemann and Nagai, ibid. x. 211. 7 Gruber, ibid. xii. 514. 352 AROMATIC COMPOUNDS. formula C7H6O3 + C7HfiO4+ 2H2O is formed, crystallizing in short prisms, and the two acids cannot be separated by re-crystallization or by fractional precipitation with lead acetate. On treatment with bromine, however, the parahydroxybenzoic acid is converted into tribromophenol, while the protocatechuic acid remains unaltered (Barth and Hlasiwetz). Barium protocatechuate, (C6H3(OH)2CO2)2Ba +• 5H2O, forms granular crystals ; when its solution is treated with concentrated baryta water, the basic salt separates out in warty crystals, which, softer drying at 130°, have the formula (C6H3(O2Ba)CO2)2Ba.1 Lead protocatechuate, (C(.H3(OH)2CO2)Pb + 2H2O. An amor- phous precipitate of (C6H3(OPb.OH)2CO2)2Pb is obtained by the addition of lead acetate to an aqueous solution of the acid; the solution of this in dilute acetic acid deposits the normal salt in small crystals. Methyl protocatcchmate, C6H3(OH)2CO2.CH3, crystallizes from hot water in needles, which melt at 1345°; ferric chloride colours its aqueous solution green.2 2194 Vanillic acid, C6H3(OCH3)(OH)CO2H,(CO2H: OCH3: OH - 1 : 3 :4), was first obtained by Tiemann by the oxidation of coniferin with potassium permanganate;3 it is also formed by the action of air on finely divided, moist vanillin,4 and has been prepared by various other reactions, which will be described below. It crystallizes in needles, melting at 207°,5 and sublimes without decomposition; it dissolves in 850 parts of water at 14°, and in 39 parts at 100°, is very readily soluble in alcohol, but somewhat less so in ether; it is not coloured by ferric chloride, and in the pure state is quite odourless.6 On heating with caustic soda and chloroform, vanillin is formed and only one aldehydo- vanillic acid,7 proving that the hydroxyl-group is in the para- position, since both ortho- and para-compounds may be formed in this reaction (p. 286). Methyl vanillate, C6H3(OCH3)(OH)CO2.CH3, crystallizes from dilute alcohol in lustrous needles, melts at 62°-63", and boils at 285°-2870.8 Vanillic acid glucoside, or Glucovanillic acid, (C6H3(OCH3) OC6HnO5)CO2H + H2O, is formed, together with glucovanillin,9 1 Barth, Ann. Chem. Ph arm. cxlii. 246. 2 P. Meyer, Ber. Deutsch. Chem. Ges. xi. 129. 3 Ibid. viii. 509. 4 Ibid. viii. 1123. 5 Ibid. ix. 414. 6 Ibid. x. 60. 7 Tiemann and Mendelsohn, ibid. ix. 1278. 8 Matsmoto, ibid. xi. 128. 9 Tiemann, ibid, xviii. 1595. ISOVANILLIC ACID. 353 by the action of potassium permanganate on coniferin, and crystallizes from hot water in fine prisms, which lose their water of crystallization at 100°, and melt at 210°-212°. It is decomposed by emulsin or by boiling with dilute acids into grape sugar and vanillic acid.1 Acetylvanillic acid, C6H3(OCH3)(OCO.CH3)CO2H, is formed by heating vanillic acid with acetic anhydride,2 and from eugenol acetate, C6H3(OCH3)(OC2H3O)C3H5, acetylferulic acid,3 C6H3(OCH3)(OC2H3O)C2H2.CO2H, acetylcreosol/ C6H3(OCH3) (OC2H3O)CH3 and acetylhomovanillic acid 5 by oxidation with potassium permanganate. It crystallizes from dilute alcohol in fine needles, which melt at 142°, and are decomposed on boiling with caustic potash into acetic and vanillic acids. Benzoylvanillic acid, C6H3(OCH3)(OCO.C6H5)CO2H, is pre- pared by the oxidation of benzoyleugenol, and crystallizes from dilute alcohol in small plates which have a peculiar surface lustre, and melt at 178°.6 Isovanillic acid, C6H3(OH)(OCH3)CO2H, (CO2H : OH: OCH3 "1:3:4). Tiemann found that when dimethylprotocatechuic acid is heated with dilute hydrochloric acid, vanillic acid and an isomeric methylprotocatechuic acid are formed,7 the latter being, as was proved by Beckett and Wright,8 identical with an acid which Matthiessen and Foster had previously ob- tained by heating hemipinic acid, C6H2(OCH3)2(CO2H)2, with hydrochloric acid.9 According to Matsmoto, who proposed the name isovanillic acid, it is most readily prepared by heating 2 parts of dimethylprotocatechuic acid to 160°-170° with a mixture of 25 parts of hydrochloric acid of specific gravity 1'2 and 50 parts of water for four to five hours. The product is repeatedly crystallized from water in order to remove vanillic and protocatechuic acids which are formed in the reaction, and is then freed from any unaltered dimethylprotocatechuic acid by conversion into the acetyl compound, which is then recrystallized and saponified by dilute caustic potash.10 1 Tiemann and Reimer, Ber. Deutsch. Chern. Ges. viii. 515. 2 Tiemann and Nagai, ibid. viii. 1142. 3 Tiemann, ibid. ix. 409. 4 Tiemann and Mendelsohn, ibid. x. 57. 5 Tiemann and Nagai, ibid. x. 201. 6 Kraaz and Tiemann, ibid. xv. 2068. 7 Ibid. viii. 513. 8 Journ. Chern. Soc. 1876, i. 302. 9 Proc. Boy. Soc. xii. 502. 10 Ber. Deutsch. Chern. Ges. xi. 125. 354 AROMATIC COMPOUNDS. Isovanillic acid crystallizes in lustrous, transparent prisms, melting at 250°, which dissolve in 1,700 parts of water at 14°, and in 1G0 parts at 100°. It is readily soluble in alcohol and ether; it gives no colour reaction with ferric chloride. Acetylisovanillic acid, C6H3(OCO.CH3)(OCH3)CO2H, crystal- lizes from dilute alcohol in scales, melting at 206°-207°. 2IQ5 Veratric acid or Dimethylprotocatechuic acid, C6H3(OCH3)2 CO2H. In the year 1839, E. Merck discovered veratric acid, C9H10O4,1 in the seeds of Veratrum Sabadilla, and W. Merck then observed that it decomposes into carbon dioxide and veratrol, C8H10O2, on heating with caustic baryta.2 By the oxidation of methyl eugenol, Grabe and Borgmann obtained bimethoxybenzoic acid,3 which was shown by Tiemann 4 and by Erlenmeyer and Wassermann5 to be identical with the di- methylprotocatechuic acid which Kblle had prepared by heating protocatechuic acid with caustic potash, methyl iodide and wood-spirit;6 Korner then showed that this compound is also identical with veratric acid, veratrol being dimethylcate- chol.7 Veratric acid is also formed when veratrin and pseudo- aconitine are heated with alcoholic potash.8 In order to prepare it, 1 part of methyleugenol, C6H3(OCH3)2C3H5, is shaken up with 10-15 parts of water, and a solution of 3'5 parts of potas- sium permanganate in 20-30 parts of water heated to 80-90° gradually added. The filtrate is concentrated by evaporation and precipitated with hydrochloric acid.9 Veratric acid dissolves in 2,100 parts of water at 14°, and in 160 parts at 100°, and crystallizes from a concentrated solution at a temperature above 50° in anhydrous needles, while crystals containing a molecule of water are obtained from very dilute solutions at any temperature below this. It melts at 174°-175° and can be sublimed. It dissolves readily in alcohol and ether; ferric chloride produces no colouration. Methyl veratrate, C6H3(OOH3)2CO2.CH3, is formed, together with methyl protocatechuate and methyl isovanillate, when protocatechuic acid is heated with caustic potash, methyl iodide and wood spirit,10 no methyl vanillate being formed.11 1 Ann. Chem. Pharm. xxix. 188. 2 Ibid, cviii. 60. 3 Ibid, clviii. 282. 4 Ber. Deutsch. Chem. Ges. viii. 514. 5 Ann. Chem. Pharm. clxxix. 366. 6 Ibid. clix. 240. 7 Ber. Deutsch. Chem. Ges. ix. 582. 8 Wright and Luff, Journ. Chem. Soc. 1878, i. 160 and 352. 9 Tiemann and Matsmoto, Ber. Deutsch. Chem. Ges. ix. 937. 10 Matsmoto, ibid. xi. 122. 11 Tiemann, Ber. Deutsch. Chem Ges. viii. 513. PIPERONIC ACID. 355 The ether is obtained pure when a solution of the acid in anhydrous methyl alcohol is saturated with hydrochloric acid, or when vanillic acid is heated with caustic potash and methyl iodide. It crystallizes in odourless needles, melts at 59°-60° and boils at about 300° (Matsmoto). Melting- point. Boiling- point. Ethyl veratrate,1 C6H3(OCH3)2CO2.C2H5. . . . . 43°-44° 295-296° Ethylvanillic acid,2 C6H3(OC2H5)(OCH3)CO2H . . . 193°-194° - Diethylprotocatechuic acid,3 C6H3(OC2H5)2CO2H, . . . . . 149° - Piperonic acid, C6H3(O.2CH2)CO2II, was prepared by Fittig and Mielk by the oxidation of piperic acid or piperonal with potassium permanganate,4 while Fittig and Remsen obtained it by heating protocatechuic acid with caustic potash and methy- lene iodide :5 O\ /OK / )CH2 C6H3<OK +CHJ2 = C6H3-Oz " +2KL \co2k \co2k It occurs in small quantity in Paracoto bark, which is collected on the river Mapiri in Bolivia, and has been detected in true Coto bark, which is also found in Bolivia.6 Piperonic acid is scarcely soluble in cold water, slightly in boiling water, from which it separates in small needles, or, on very gradual cooling, in characteristic crystals, which resemble in appearance small twisted threads of sewing cotton. It is also slightly soluble in ether and cold alcohol, separating from a hot alcoholic solution in larger crystals. It is obtained in the purest state by sublimation, which yields large, compact, glitter- ing prisms with acute terminal planes; it melts at 227*5°- 228 5°, but sublimes at a lower temperature. When it is heated with phosphorus pentachloride, a liquid chloride is formed which yields a chlorinated acid on decom- position with cold water; this substance is probably a dichloro- piperonic acid and is resolved on heating with water into 1 Tiemann and Matsmoto, Ber. Deutsch. Chern.. Ges. ix. 942. 2 Tiemann, ibid. viii. 1130 ; Wassermann, Ann. Chem. Pharm. clxxix. 379. 3 Kolle, ibid. clix. 245. 4 Kolle, ibid. clii. 40. 5 Ibid, clxviii. 93. 6 Hesse and Jobst, ibid, cxcix. 63. 356 AROMATIC COMPOUNDS. hydrochloric acid, carbon dioxide and protocatechuic acid. Piperonic acid is decomposed by dilute hydrochloric acid at 170°, or by water at 210°, into carbon dioxide and protocatechuic acid, so that it behaves in an analogous manner to its aldehyde 1 (p. 347). Potassium piperonate, C8H5O4K + H2O, crystallizes in long needles, which are readily soluble in water. Calcium piperonate, (C8H5O4)2Ca + 3H2O, is slightly soluble in cold, readily in hot water, and crystallizes in fascicular groups of needles or plates. Silver piperonate, C8H6O4Ag, is a granular precipitate, which crystallizes from hot water in large, narrow plates. Ethyl piperonate, C8H5O4.C2H5, is a mobile, strongly refractive liquid, which has a pleasant fruity odour (Jobst and Hesse). Ethylcneprotocatechuic acid, C6H3(O2C2H4)CO2H, is formed by heating protocatechuic acid with caustic potash and ethylene bromide.2 It is slightly soluble in cold water and crystallizes from a boiling solution in splendid, broad, lustrous needles. It dissolves in almost every proportion in alcohol, from which it separates on dilution in druses composed of short, lustrous prisms, which melt at 133'5°, and sublime in lustrous prisms when carefully heated. The calcium salt, (C9H7O4)2Ca +2H2O, crystallizes from hot water in well-developed, compact, monoclinic prisms. Bromoprotocatechuic acid, C6H2Br(OH)2CO2H, is prepared by triturating protocatechuic acid with bromine; it crystallizes from hot water in fine, rhombic needles, and is converted into gallic acid by fusion with potash.3 2196 Maclurin, C13H10O6 4- H2O, occurs in fustic {Morns, s. Ma- cher a tinctorial), and was described by Wagner as morintannic acid.^ Its correct formula has been determined by Hlasiwetz and Pfaundler.5 According to Wagner, the dirty yellow, crys- talline masses found in the centre of the logs consist almost entirely of impure maclurin, which can readily be purified by repeated crystallization from slightly acidified water. Bene- dikt employs as his raw material the muddy deposit which is obtained as a by-product in the manufacture of fustic extract, and which consists of maclurin and its calcium 1 Fittig and Remsen, Ann. Chem. Pharm. clix. 129. 2 Fittig and Macalpine, ibid, clxviii. 99. 3 Barth, ibid, cxlii. 246 ; Ber. Deutsch. Chem. Ges. viii. 1484. 4 Journ. Prakt. Chem. li. 82 ; lii. 449. 5 Ann. Chem. Pharm. cxxvii. 352. MACLURIN AND LUTEOLIN. 357 salt. It is ground up with dilute hydrochloric acid pressed, and repeatedly crystallized from hot water. In order to remove any adhering colouring matter, it is dissolved in water and treated with lead acetate. A current of sulphuretted hydrogen is then passed through the hot liquid, which is subsequently filtered and allowed to cool; the pure machirin is thus obtained as a light yellow, crystalline powder. It becomes anhydrous at 130°, and melts at 200°. On boiling with water and barium carbonate one molecule of carbon dioxide is evolved for every two molecules of maclurin present (Benedikt), while the salt C13H8PbO6 -I- H2O is deposited in yellow plates when lead acetate is added to the boiling solution (Hlasiwetz and Pfaundler). When maclurin is boiled with concentrated caustic potash solu- tion or heated to 120° with dilute sulphuric acid, it decomposes smoothly into protocatechuic acid and phloroglucinol. Benedikt therefore proposes the following formulae for maclurin and its lead salt:1 zOH C6H3-OH >0 C6H3^OH \CO.OH zOH C6H3<OH >0 C6H3-o-Pb XCO . o/ Luteolin, C.20H14O8, was discovered by Chevreul in weld (Reseda lutea}? and analyzed by Moldenhauer,3 who obtained numbers which led to the formula given above, while Paraf and Schiitzenberger calculated the composition 2C12H8O5+3H2O from the results of their investigation and somewhat unsatis- factory analyses.4 It is obtained by extracting the dried plant with water containing 5-6 per cent, of alcohol, concentrating the filtrate by evaporation and purifying the crude luteolin thus obtained by recrystallization from alcohol or a mixture of water and glycerol. It crystallizes in small, yellow needles, which dissolve in 14,000 parts of cold water, in 5,000 parts at 100° and in 37 parts of alcohol. It readily forms a deep yellow solution in alkalis, and dissolves in cold sulphuric acid forming a reddish yellow solution from which it is precipitated by water. A small 1 Ann. Chern. Pharm. clxxx. 114. 2 Berzelius, Jahresb. xi. 280. 3 Ann. Chem. Pharm. c. 180. 4 Cornet. Pend. lii. 92. 358 AROMATIC COMPOUNDS. quantity of ferric chloride produces a green colouration, which passes into brownish red on the addition of more of the reagent. Its hot aqueous solution dyes wool, mordanted with alum, a beautiful daffodil-yellow (Chevreul). On fusion with potash it is decomposed with evolution of hydrogen into phloroglucinol and protocatechuic acid :1 C20H14O8 + 3H2O = 2C7HGO4 + C6HgO3 + H2. Rochleder states, however, that the amount of phloroglucinol formed is much greater than corresponds to this equation. The formula of luteolin is by no means accurately determined and its constitution is quite unknown. SYMMETRIC METADIHYDROXYBENZOIC ACID OR a-RESORCYLIC ACID (1:3: 5). 2197 This substance is obtained by fusing /3-disulphobenzoic acid,2 metabromosulphobenzoic acid and parabromosulphobenzoic acid 3 with caustic potash. It crystallizes with one and a half molecules of water in needles or prisms, which melt at 232°- 233°, are tolerably soluble in cold, readily in hot water, alcohol and ether, and give no colouration with ferric chloride. On fusion with caustic soda it decomposes above 300° into resorcinol and carbon dioxide.4 A very characteristic reaction is that when heated with 4 parts of sulphuric acid to 140°, a deep red solution is formed from which water precipitates green flocks of anthrachrysone, C14H4(OH)4O2, which is a derivative of anthracene, and is also formed by the dry distillation of the acid. Lead acetate does not produce a precipitate when added to an aqueous solution of the acid. Ethyl a-resorcylate, CGH3(OH)2CO2.C2H5, crystallizes from water in long prisms which melt below 100°. Dimethyl-a-resorcylic acid, C6H3(OCH3)2CO2H, is formed when a-resorcylic acid is heated with caustic potash, methyl iodide and wood-spirit, and when dimethylorcinol is oxidized with potassium 1 Roehleder, Journ. Prakt. Chern, xcix. 433. 2 Earth and Senhofer, Ann. Chern. Pharm. clix. 217. 3 Bottinger, Ber. Deutsch. Chem. Ges. viii. 374. 4 Barth and Schreder, ibid. xii. 1258. RESORCYLIC ACIDS. 359 permanganate.1 It crystallizes from hot water in fine needles, which melt at 175°-176°. Diethyl-a-rcsorcylic acid, C6H3(OC2H5)2CO2H, was prepared by Barth and Senhofer from the acid by the action of ethyl iodide.2 It forms elongated prisms, which melt at 87°-88°, and are decomposed by distillation with lime into carbon dioxide and diethylresorcinol.3 a-Bromoresorcylic acid, C6H2Br(OH)2CO2H, is formed by the action of bromine water on an aqueous solution of a-resorcylic acid, and crystallizes from hot water in long needles, which melt at 253°, and give a yellowish brown colouration with ferric chloride. It gives the same reaction with sulphuric acid as a-resorcylic acid, and is converted into gallic acid by fusion with caustic potash (Barth and Senhofer). ASYMMETRIC METADIHYDROXYBENZOIC ACID OR ^-RESORCYLIC ACID, (1:2:4). 2198 This acid is formed when paracresolsulphonic acid,4 and a-disulphobenzoic acid5 are fused with caustic potash, and may also be obtained, together with a large amount of resorcinol, when its aldehyde is fused for a short time with caustic potash.6 It may also be prepared, together with 7-resorcylic acid and dihydroxyphthalic acid, CGH2(OH)2(CO2H)2, by heating 1 part of resorcinol with 4 parts of ammonium carbonate and 5 parts of water to 120°-130°,7 and still more readily by heating resorcinol in an open flask with a concentrated solution of potassium bicarbonate. It is very slightly soluble in cold water, and crystallizes from a hot solution in needles containing one and a half molecules of water, one of which is lost on exposure to the air (Fahlberg). It melts at 204°-206°, and simultane- ously decomposes into carbon dioxide and resorcinol. Its 1 Tiemann and Streng, Bar. Deutsch. Chem. Ges. xiv. 2002. 2 Ann. Chem. Pharm. clxiv. 121. 3 Barth, Ber. Deutsch. Chem. Ges. xi. 1569. 4 Ascher, Ann. Chem. Pharm. clxiv. 11. 5 Blomstrand, Ber. Deutsch. Chem. Ges. y. 1088 ; Fahlberg, Amer. Chem. Journ. ii. 196. 6 Tiemann and Reimer, Ber. Deutsch. Chem. Ges. xii. 997 ; Tiemann and Parrisius, ibid. xiii. 2358. 7 Brunner and Senhofer, ibid. xiii. 2356 ; Ber. Wien. Ahad. 1879, ii. 504. 360 AROMATIC COMPOUNDS. solution is coloured dark red by ferric chloride, and does not give a precipitate with lead acetate. Orthomethyl-^-rcsorcylic acid, C6H3(OH)(OCH3)CO2H(OCH3: OH = 2:4), is formed when the acetyl-derivative of its aldehyde is oxidized with potassium permanganate and the product decomposed by caustic potash. It is tolerably soluble in water, does not crystallize well, and gives no colouration with ferric chloride.1 Paramethyl-^-resorcy lie acid, (OH : OCH3=:2 : 4). The methyl ether is prepared by adding sodium to a solution of /8-resorcylic acid in wood-spirit and then heating with methyl iodide, the acid being obtained from this by boiling with caustic potash (Tiemann and Parrisius); it is also formed when sodium methyl- resorcinol is heated to 215° in a current of carbon dioxide :2 C6H4(OCH3)ONa + CO2 = C6H3(OCH3)(OH)CO2Na. It crystallizes from hot water in lustrous needles, which melt at 151'5°, and decompose into methylresorcinol and carbon dioxide when rapidly heated. Its aqueous solution is coloured an intense reddish violet by ferric chloride. Dimethyl-fi-resorcylic acid, C6H3(OCH3)2CO9H, is not readily formed by the further methylation of the preceding compound, but may be obtained by the oxidation of its aldehyde with potassium permanganate; it crystallizes from hot water in fine needles, melting at 108° (Tiemann and Parrisius). Diethyl-^-resorcy lie acid, C6H3(OO2H5)2CO2H, was prepared in a similar manner; it forms needles which melt at 99°.3 ADJACENT METADIHYDROXYBENZOIC ACID OR 7-RESORCYLIC ACID (1:2:6). 2igg The formation of this acid has already been mentioned ; it is very soluble in water, and crystallizes in fine, fascicular needles, which contain one molecule of water and commence to fuse at 140°, a partial decomposition into resorcinol and carbon dioxide occurring, which becomes complete at a higher tempera- 1 Tiemann and Parrisius, Ber. Deutsch. Chern. Ges. xiii. 2375. 2 Korner and Bertoni, ibid. xiv. 847. 3 Tiemann and Lewy, ibid. x. 2215. HYDROXYSALICYLIC ACID. 361 ture. Its aqueous solution is coloured a deep bluish violet by ferric chloride. y-Bromoresorcylic acid, C6H2Br(OH)2CO2H + H2O, is formed by the action of bromine on an ethereal solution of the acid. It is slightly soluble in cold water, readily in alcohol, and crystallizes in fine prisms, which lose their water at 100° and melt at 184° with decomposition. It is coloured violet by ferric chloride. Dimethyl-y-resorcylic acid, C6H3(OCH3)2CO2H. When meta- dinitrobenzene is treated with methyl alcohol and potassium cyanide, methoxy nitrobenzonitril^^^O2)(OCH3)CN, is formed; it crystallizes from chloroform in pliant needles, which melt at 171°, and are converted on heating with methyl alcohol and caustic potash into dimethoxybenzonitril, C6H3(OCH3)2CN, which crystallizes from alcohol in needles or rectangular tablets, melting at 118°. It boils at about 310°, and when heated with baryta water yields dimethyl-7-resorcylic acid, which forms crystals melting at 179°, and is converted into 7-resorcylic acid by heating with caustic potash. If methoxynitrobenzonitril is heated with caustic potash and ethyl alcohol, ethoxy methoxyl enzonitr it, C6H3(OCH3)(OC2H5) CN, is formed, and crystallizes from alcohol in prisms or tablets, melting at 66°. This compound is also formed when meta- dinitrobenzene is treated with ethyl alcohol and potassium cyanide, and the ethoxynitrobenzonitril, C6H3(NO2)(OC2H5)CN, thus formed, which melts at 137°, is heated with methyl alcohol and caustic potash. A new and simple proof is thus afforded of the identity of the positions 1 and 6 in the benzene nucleus.1 HYDROXYSALICYLIC ACID OR PARADIHY- DROXYBENZOIC ACID (1:2: 5). 2200 This isomeride has been prepared by fusing iodosalicylic acid with caustic potash;2 it is more readily obtained, however, by fusing bromosalicylic acid with caustic soda,3 and is also 1 Lobry de Bruyn, Ber. Deutsch. Chern. Ges. xviii. Ref. 148 ; Chern. Centralbl. 1884, 119 ; 1885/357. 2 Lautemann, Ann. Chern. Pharm. cxx. 311 ; Liechti, ibid. Suppl. vii. 144 ; Demole, Ber. Detdsch. Chem. Ges. vii. 1438 ; Goldberg, Journ. Prakt. Chem. [2] xix. 371. 3 Leppert and Rakowski, Ber. Deutsch. Chem. Ges. viii. 788. 362 AROMATIC COMPOUNDS. formed by the action of nitrous acid on a-amidosalicylic acid,1 and when quinol is heated with potassium bicarbonate, water and a little potassium sulphite.2 Hlasiwetz and Habermann, by fusing gentisin, C14H10O5, from Gentiana lutea, with caustic potash, obtained a dihydroxybenzoic acid, which they named gentisic acid, since they believed that it was different from those previously known;3 they subsequently found, however, that it is identical with hydroxysalicylic acid.4 It is readily soluble in water, alcohol and ether, crystallizes in needles or prisms, which melt at 196°-197°, and gives a deep blue coloura- tion with ferric chloride. It reduces Fehling's solution and ammoniacal silver solution on heating. On dry distillation it is resolved into carbon dioxide and quinol. Ethyl hydroxy salicylate, C(iH3(OH)2CO2.C2H6, crystallizes from hot water in needles, which have a pleasant fruity odour and melt at 75° (Goldberg). Methylhydroxysalicylic acid, C6H3(OCH3)(OH)CO2H.(CO2H : OH : OCH3-1 : 3 : 5), was prepared by Korner and Bertoni by the action of carbon dioxide on sodium methylquinol at 220°-225°,5 and named a-methylhydroyuinoneformic acid. Tiemann and Muller then obtained it by oxidizing the acetyl- derivative of the corresponding aldehyde with potassium per- manganate and saponifying the product with caustic soda.6 It crystallizes from hot water in long needles, melting at 142°, and gives a light blue colouration with ferric chloride. Dimethylhy dr oxy salicylic acid, C(.H3(OCH3)2CO2H, is formed by ihe oxidation of its aldehyde; it crystallizes from hot water ip silky needles, melting at 76°.7 When the reactions of the bodies just described are compared, it is found that protocatechuic acid, its aldehyde, and also catechol, which contain the hydroxyls in the ortho-position, give a green colouration with ferric chloride. Those com- pounds, on -the other hand, in which a hydroxyl is situated in the ortho-position with regard to a carboxyl, and which can therefore be considered as derivatives of salicylic acid, give a blue to dark red colouration, while those in which the hydroxyls are in the meta-position, give as little colouration as meta- hydroxybenzoic acid. 1 Goldberg, loc. cit. 2 Senhofer and Sarlay, Monatsh. Chem. ii. 448. 3 Ann. Chem. Pharm. clxxv. 66. 4 Ibid, clxxx. 343. 3 Ber. Deutsch. Chem. Ges. xiv. 848. 6 Ibid. xiv. 1997. 7 Ibid. 1993. GALLIC ACID. 363 According to theory, six dihydroxybenzoic acids can exist. In addition, to the five just mentioned, two others have been shortly described. One of these was obtained by Leeds by allowing toluene saturated with nitrogen peroxide to stand in a loosely covered vessel for a whole summer. It crystallizes from alcohol in small plates, which sublime at 170° without fusing and give no colouration with ferric chloride.1 Acscioxalic acid, C7H6O4, is the name given by Rochleder to a compound which he obtained, together with formic acid, oxalic acid and frequently protocatechuic acid, by boiling aesculetin, C9H6O4, with concentrated caustic potash or baryta water. It forms an extremely fine crystalline mass and gives a reddish brown colouration with ferric chloride, which is changed by sodium carbonate to purple-violet, while ferrous sulphate and a little carbonate of soda produce an intense blue colouration.2 TRIHYDROXYBENZOIC ACIDS, C6H2(OH)3CO2H. Gallic Acid. 2201 The history of this substance goes hand in hand with that of tannic acid. In the introduction to organic chemistry it has already been mentioned how Pliny states that paper dipped in an extract of nut-galls was used to ascertain whether verdigris was adulterated with green vitriol. He also informs us that the juice of nut-galls was used to recognize a kind of ahtmen, employed for dyeing wool black, which was either natural green vitriol or a mineral containing this salt. It was also known in very early times that certain parts of plants, which have an astringent taste, give a black colouration with bodies containing iron. In addition to nut-galls, Paracelsus enumerates the sap of oaks, alders, &c., which colour solutions of iron and copper black, and Libavius used this reaction in the analysis of mineral waters, which were coloured black in the presence of iron, but only darkened when containing copper; he thus discovered the presence of copper vitriol in the " Wein- brunnen " at Schwalbach. Tachenius states in Hippocrates chymicus, 1766, that tinc- ture of nut-galls produces various coloured precipitates with 1 Ber. Deutsch. Chem. Ges. xiv. 482. 2 Jahresb. Chem. 1867, 752. 364 AROMATIC COMPOUNDS. solutions of iron, copper, lead and mercury, and separates metallic gold from solutions of its salts. Other astringent plants have a similar action, which he compares with that of the volatile alkalis, since these remove acids from vitriols in a similar manner. Lemery takes the same view in his paper on the kinds of vitriol and the formation of ink, which is published in the Memoirs of the Paris Academy for 1707 ; nut-galls, according to him, are of an absorbent or alkaline nature, and therefore act like salt of tartar, lime-water, ammonia, &c. That the latter do not produce a black precipitate with iron is accounted for by the fact that the sulphurous particles present in nut-galls are absent in the alkalis. As a proof of this he mentions that when these absorbent substances are made to combine with sulphur, they do give a black precipitate with solutions containing iron. Bergman, on the other hand, suggested in 1775, that a vegetable acid is contained in astringent substances, and in his Elemens de Chymie 1777, published by Morveau, Maret, and Durand e, it is stated that on the dry distillation of nut-galls a substance sublimes which blackens solutions of iron and behaves as a true acid. In order to obtain it in a purer condition, Retzius, in 1783, treated the dried extract of nut-galls with cold water, and in this way obtained a substance which had the properties of an acid and effervesced with alkaline carbonates. In 1786, Scheele prepared gallic acid by exposing extract of nut- galls to the air in a warm place and frequently removing the film of mould which was formed. The crystalline precipitate which gradually separated out was purified by recrystallization. He observed that when gallic acid is heated a body sublimes which also precipitates iron salts, but which he considered to be different from gallic acid, a view which was also taken by Berthollet in his Statiquc chimique, 1803, while Fourcroy and Berzelius believed that the sublimate is the pure gallic acid, this being denied by Braconnot and also by Pelouze (Part III., p. 181). The astringent constituent of nut-galls, subsequently called tannic acid, was first recognized as a distinct substance by Deyeux in 1793, and more definitely by Seguin in 1795, after which Berzelius obtained it in a pure or almost pure con- dition. It had already been noticed that it is readily converted into gallic acid, but the relations of the two substances had not been explained, although many chemists had investigated the question. GALLIC AND TANNIC ACIDS. 365 Pelouze and Berzelius gave to tannic acid the formula C18H18O12, which was altered by Liebig to C18H16O12, since the latter explains in a simple manner its conversion into gallic acid in presence of water and oxygen: "From one atom of tannic acid and four atoms of oxygen, exactly two atoms of gallic acid and two atoms of carbonic acid are formed, while according to the formula CtoHtsO.,, two atoms of hydrogen remain over, and no one knows what becomes of them."1 At a later period he proposed the formula C18H10O9 + 3aq, which can be expressed as the sum of the formulae of anhydrous acetic acid and gallic acid; he had found that tannic acid can be converted into gallic acid without the intervention of oxygen by simply boiling for a few minutes with caustic potash, or better, dilute sulphuric acid.2 He could not, however, detect any acetic acid and suggested that an isomeride of this is formed, which, however, from the behaviour of tannic acid towards sulphuric acid, could not be a sugar3 as had been suggested by Stas.4 Wetherill, on the other hand, assumed that tannic and gallic acids were isomeric,5 while Mulder gave to the former the formula CuH10O9, according to which it forms two molecules of gallic acid by the assumption of the elements of water;6 subsequently, however, he altered his formula to C14H12O9, and looked upon gallic acid as an oxidation product.7 Tannic acid was then carefully investigated in Liebig's laboratory by Strecker, who succeeded in resolving it into grape sugar and gallic acid, expressing the reaction by the following equation :8 CaHaO„ + 4H2O = 3C,H„O5 + C„H12Oe. This view was almost universally accepted, the more so as other tannic matters had proved to be glucosides, and as the formation of gallic acid by fermentation received a simple explanation. According to Strecker's equation, 29 T per cent, of grape sugar should be formed, while he only obtained 15-22 per cent., and Rochleder found that by proper purification the amount can be reduced to 4 per cent, without altering the chemical and physical properties of the tannic acid to any 1 Ann. Chem. Pharm. x. 172. 2 Ibid. xxvi. 128. 3 Handb. Chem. 854. 4 Ann. Chem. Pharm. xxx. 205. 5 Journ. Prakt. Chem. xlii. 247. 6 Jahresb. Chem. 1848, 524. 7 Ibid. 1858, 261. 8 Ann. Chem. Pharm. xc. 328. 366 AROMATIC COMPOUNDS. important extent.1 His results confirmed those of Knop, who succeeded in converting 95 per cent, of the tannic acid into gallic acid, ellagic acid, C14H6O8, and a carbohydrate being also formed.2 Stenhouse had previously arrived at similar results, having found that by the use of sufficiently dilute sulphuric or hydrochloric acid almost the whole of the tannic acid can be converted into gallic acid.3 Rochleder then assumed that the sugar is formed from some admixture, and that tannic acid stands in the same relation to gallic acid as dextrin to grape sugar. Hlasiwetz remarks on this question : " If tannin is not a glucoside, it may perhaps be a digallic acid, which corresponds to gallic acid in the same way as diethylene alcohol to ordinary glycol, and it would then have the formula which was first proposed for it by Mulder : 2C7H6O6-H2O = C14H10O9. " The analyses of tannin and its salts agree with this com- position as well as can be expected in the case of a substance which is so difficult to purify." 4 Lowe, however, came to a different conclusion; he found that silver nitrate and arsenic acid are reduced by gallic acid with formation of ellagic acid and a substance which has all the pro- perties of tannic acid, so that he considered the latter to be an oxidation product of gallic acid.5 He subsequently found that the correct formula of tannic acid is C14H10O9, but assumed that gallic acid is not formed from it only by assumption of water, but that a molecular change takes place.6 Schiff, on the contrary, showed conclusively that arsenic acid and also phosphorus oxychloride simply exert a dehydrating action, and that the digallic acid thus formed is identical with tannic acid. This question will be more fully considered under the latter. 2202 Gallic acid occurs ready formed in nut-galls, sumach and divi-divi, the fruit of Caesalpinia coriaria} It is also found in the leaves of the red bear-berry (Arctostaphylos Uva ursi)} in China tea,9 and in red Biindner wine.10 Etti obtained it by heating 1 Chern. Centralbl. 1858, 579. 2 Pharm. Centralbl. 1855, 658. 3 Chem. Soc. Mem. i. p. 147. 4 Ann. Chern. Pharm. cxliii. 295. 5 Journ. Prakt. Chem. cii. Ill; ciii. 446. 6 Fresenius' Zeitschr. xi. 365. 7 Stenhouse, Chem. Soc. Mem. i. 137. 8 Kawalier, Jahresb. Chem. 1852, 683. 9 Hlasiwetz and Malin, Zeitschr. Chem. 1867, 271. 10 Simler, Jahresb. Chem. 1861. 923. GALLIC ACID. 367 kinoin, C14H12O6, with hydrochloric acid;1 it is also formed when di-iodoparahydroxybenzoic acid,2 bromoprotocatechuic acid,3 bromoveratric acid,4 and a-bromoresorcylic acid,5 are fused with caustic potash. According to Lautemann it is also formed in this way from di-iodosalicylic acid,6 but Demole failed to obtain it by this method,7 and it is probable that Lautemann's com- pound, which was only obtained in small quantity, is the isomeric pyrogallolcarboxylic acid. In order to prepare gallic acid, Scheele's method, which is stated by Liebig to give the best yield, is made use of. Finely powdered nut-galls are extracted with cold water and the solution allowed to stand in a warm place, the precipitated acid being recrystallized from boiling water. According to Braconnot, the entire nut-galls may be moistened with water in summer or allowed to stand in a warm place until they form a paste, which is then extracted with boiling water.8 The spores of Penicillium glaucum or Aspergillus niger are necessary to set up fermentation.9 Wittstein recommends the addition of beer yeast; he thus obtained almost 50 per cent, from Chinese nut-galls, while without the yeast the yield only amounted to 17 per cent.10 One hundred pounds of Turkish nut-galls, treated by Scheele's method, give 24 pounds of gallic acid.11 It crystallizes in silky needles or asymmetric prisms, containing one molecule of water, which is lost at 120°, has an acid, astringent taste, and dissolves in 130 parts of water at 12'5°, and in 3 parts at 100°. It is more readily soluble in alcohol, since 27'95 parts dissolve in 100 parts of absolute alcohol at 15°, and 18'90 parts in 100 parts of 90 per cent, alcohol, while 100 parts of ether only dissolve 2'5 parts.12 Gallic acid commences to melt above 220° and decomposes into carbon dioxide and pyrogallol when more strongly heated. It is readily oxidized, reduces Fehling's solution and the salts of the noble metals, and in alkaline solution absorbs oxygen. When 1 Ber. Deutsch. Chem. Ges. xi. 1881. 2 Barth and. Senhofer, ibid. viii. 1884. 3 Ibid. 4 Matmoso, ibid. xi. 140. 5 Barth and Senhofer, Ann. Chern. Bharm. clxiv. 118. 6 Ibid. cxx. 137. 7 Ber. Deutsch. Chem. Ges. vii. 1441. 8 Ann. Chim. Phys. ix. 181. 9 Tieghem, Zeitschr. Chem. 1868, 222. 10 Vierteljahrsschr. Pharm. ii. 72. 11 Steer, Jahresber. Chem. 1856, 482. 12 Bourgoin, Bull. Soc. Chim. xxix. 245. 368 AROMATIC COMPOUNDS. it is added to ferric chloride, a partial reduction ensues and a black-blue precipitate is formed, which dissolves in the excess of ferric chloride with a green colour. According to Etti, the colouration depends mainly on the concentration of the solutions, and varies between black-blue, black-green, blue, greenish and brownish green. An excess of gallic acid destroys the colour and effects complete reduction to ferrous chloride ; a solution of pure ferrous sulphate in absence of air is therefore not altered by it, but on exposure to air is coloured a bright blue, and deposits a black precipitate without becoming decolourized. Gallic acid in alcoholic or alkaline solution reduces paranitro- benzyl chloride to paranitrotoluene. Digallic acid and pyro- gallol have a similar action.1 It is converted by the action of potassium chlorate and hydrochloric acid into tricarballylic acid, C3H5(CO2H)3, and isotrichloroglyceric acid, CC13.C(OH)2.CO2H, which crystallizes in needles and is readily decomposed by alkalis into chloroform and oxalic acid.2 When gallic acid is heated with sulphuric acid, rufigallic acid or hexyhydroxyanthraquinone, C14H2O2(OH)6, is formed, while an acid solution of potassium permanganate produces hydrorufigallic acid, C14H8O5. Gallic acid is not precipitated by gelatine solution, and can thus be distinguished from tannic acid and other similar substances. 2203 The G-allates have been chiefly investigated by Buchner. Sodium gallate, C6H2(OH)3CO2Na + 3H2O, is obtained by adding alcoholic soda to a solution of the acid in alcohol as a granular, crystalline precipitate, which crystallizes from a very concentrated aqueous solution in pointed yellow plates. Potassium gallate, C6H2(OH)3CO2K + C6H2(OH)3CO2H + H2O, is a light, crystalline powder which is prepared in a similar manner to the sodium salt; the normal salt has not yet been obtained. Ammonium gallate, C6H2^OH)3CO2NH4 + U2O, is formed when ammonia is passed into a solution of the acid in absolute alcohol, and crystallizes from water in fine needles. When its solution is boiled, the acid salt, C6H2(OH)3CO2NH4 + C6H.2(OH)3 CO2H, is deposited on cooling in splendid crystals.3 It is also 1 Pellizzari, Gazz Chem. Itai. xiv. 481. 2 Schreder, Ann. Chem. Pharm. clxxvii. 282 ; see also Claisen and Antweiler, Ber. Deutsch. Chem. Ges. xiii. 1938. 3 Etti, Ber. Deutsch. Chem. Ges. xvii. 1821. SALTS OF GALLIC ACID. 369 formed when dry gallic acid is saturated with ammonia, the excess of the latter allowed to evaporate in a vacuum and the residue crystallized from water; it contains water of crystallization (Robiquet). Calcium gallate, (C7H5O5)2Ca + 3H2O, forms thin, crystalline crusts, consisting of needles. When lime-water is added to a solution of the acid a dirty green precipitate is produced. Barium gallate, (C7H5O5)2Ba + 3H2O, is obtained by neutra- lizing a boiling solution of the acid with barium carbonate ; it crystallizes in small plates, which do not readily redissolve in water. If the freshly-prepared solution be treated with baryta- water, a precipitate of C7H2O5Ba2 + 5H2O is formed, which rapidly becomes coloured dark blue on exposure to the air in the moist state (Hlasiwetz). Lead gallate. Lead acetate added to a hot solution of an excess of the acid produces a precipitate of 2C7H4O5Pb + H2O, which soon changes to a lustrous, crystalline powder. If, how- ever, an excess of the lead acetate be employed, a flocculent precipitate is formed, which becomes yellow and crystalline on boiling and has the formula C7H2O5Pb2 (Liebig). Iron gallate. A splendid blue precipitate is obtained when the acid is added to a mixture of three molecules of a ferrous salt with two molecules of a ferric salt.1 Ethyl gallate, 2C6H2(OH)3CO2.C2H5 + 5H2O, is formed when hydrochloric acid is passed into the alcoholic solution of the acid. It is slightly soluble in cold, readily in hot water and alcohol, and crystallizes in pointed prisms, which lose their water at 100°.2 It is slightly soluble in chloroform, from which it separates in anhydrous crystals.3 It behaves towards ferric chloride, silver nitrate, &c., in the same mannei- as the free acid, and on heating decomposes into alcohol and pyrogallol, accompanied, however, by other products.4 When acid sodium carbonate is added to its aqueous solution, small crystals of C6H2(OH)3CO2.C2H5 + C6H2(OH)2(ONa)CO2.C2H5, are formed, which are scarcely soluble in cold water (Ernst and Zwenger). Lead acetate added to an aqueous solution of the ether produces a finely divided precipitate of (C6H2(CO2.C2H5)O3)2Pb3 (Schiff). Triethyl gallic acid, C6H2(OC2H5)3CO2H. The ethyl ether of this substance is obtained by heating ethyl gallate with caustic 1 Barreswill, Compt. Rend. xvii. 739. 2 Grimaux, Bull. Soc. Chim. ii. 94. 3 Ernst and Zwenger, Ann. Chem. Pharm. clix. 28. 4 Schiff, ibid, clxiii. 209. 370 AROMATIC COMPOUNDS. potash, ethyl iodide and alcohol; water precipitates it from alco- holic solution in lustrous needles, which melt at 51° and are easily decomposed by alcoholic potash; hydrochloric acid separates the triethylgallic acid from the product as a crystalline precipitate. It is slightly soluble in cold, readily in hot water, and separates from the latter in crystals melting at 1120.1 Triacetylgallic acid, C6H2(OC2H3O)3CO2H, is prepared by boiling gallic acid with acetyl chloride and acetic anhydride. It is only slightly soluble in hot water, separates from alcohol in small, lustrous needles and gives no colouration with ferric chloride (Schiff). Bromogallic acid, C6HBr(OH)3CO2H, is obtained by triturating equal molecules of gallic acid and bromine.2 It separates from the hot, aqueous solution in monoclinic crystals, resembling those of gypsum ; its solution gives a splendid violet colouration with ferric chloride and a fiery red, soon changing to brown with ammonia. Dibromogallic acid, C6Br2(OH)3CO2H + H2O, is formed when an excess of bromine is employed (Grimaux). It crystallizes from hot water in long plates or needles, melting at 15O0.3 Ferric chloride produces a black-blue colouration; moist silver oxide decomposes it with formation of pyrogallol, carbon dioxide and silver bromide, while on heating with water and potassium silver cyanide it is reconverted into gallic acid :4 C6Br2(OH)3CO2H + 2AgCN + 4H9O = C6H2(OH3)CO2H + 2CO2 + 2NH3 + 2AgBr. Gallamidc, C6H2(OH)3CO.NH2. This compound, which is also called gallamic acid, is formed together with gallic acid when a solution of tannin in ammonia is rapidly boiled : HOX /OH >c6h2< HOZ ZCOX HOX /OH > + nh3 = >c6h2< + HOX /O z HOZ zCO.NH2 )c6h2/ HOZ ZCO.OH HOX /OH >c6h2z HOZ ZCO.OH. 1 Albrecht and Will, Bcr. Deutsch. Chem. Ges. xvii. 2098. 2 Hlasiwetz, Ann. Chem. Pharm. exlii. 249; Grimaux, Zeitschr. Chem. 1867,431. 8 Etti, Bcr. Deutsch. Chem. Ges. xi. 1182. 4 Priwoznik, ibid. iii. 645. TANNIC ACID. 371 In order to avoid oxidation, ammonium sulphite must be added to the solution or the operation must be conducted in an atmosphere free from oxygen.1 It crystallizes from hot water in large, colourless plates and decomposes on boiling with hydrochloric acid into gallic acid and ammonia. 2204 Digallic acid, Tannic acid or Tannin, C6H2(OH)3CO. OC6H2(OH)2CO2H. The name of tannic acids has been applied to a whole series of substances, which are weak acids, have an astringent taste, give black-blue or dark green compounds with salts of iron, and combine with animal skins to form leather, for which purpose they are largely employed. These bodies do not stand in any intimate chemical relation to each other, and the tannic acid derived from nut-galls, the constitution of which is known, is alone referred to here. The nut-galls in which it occurs are of two kinds : the ordinary, Turkish or Levant variety, which are produced by the puncture of the gall-fly (Cynips G-allae tinctoriae) in the young shoots of Quercus lusitanica, var. infectoria and probably some other species, and the Chinese or Japanese nut-galls, which are formed by a plant-louse (Aphis chincnsis} on the leaf-stalks and young twigs of Rhus semialata. In addition to these modes of occur- rence, tannic acid has hitherto only been observed in sumach, the leaves and twigs of Rhus coriaria.2 Stenhouse, who found that tannic acid from sumach is con- verted into gallic acid by dilute sulphuric acid, says: " Sumach, therefore, appears to approach the nature of nut-galls more closely than any of the other astringent substances. This fact is well known to Turkey-red dyers, who have long successfully employed sumach as a substitute for galls." In order to prepare tannin, the method of Pelouze was formerly employed, according to which the nut-galls are extracted with ordinary ether, containing both alcohol and water. The solution thus obtained separates into two layers, the upper of which consists of water and ether containing gallic acid and a little tannin, while the syrupy lower layer is a solution of tannin in water and ether and is evaporated to dryness. A mixture of 12 parts of ether and 3 parts of alcohol is now used for the extraction, 12 parts of water being added to the extract and the alcohol and ether removed by distillation. The 1 Knop, Jahresber. Chem. 1854,'431 ; Schiff and Pons, Ber. Deutsch. Chern: Ges. xv. 2591 ; xviii. 487 ; Etti, ibid. xvii. 1820. 2 Stenhouse, Chem. Hoc. Mem. i. 137 ; Lowe, Fres. Zeitschr. xii. 128. 372 AROMATIC COMPOUNDS. residual aqueous solution is then filtered and evaporated, the crude tannin being further purified by solution in water and treatment with animal charcoal.1 Pure tannin may also be obtained by extracting nut-galls with anhydrous ether, to which 5 per cent, of alcohol has been added (Schiff). While the tannin prepared by Pelouze's method contains more or less grape sugar or a substance yielding dextrose, this is not the case with that obtained by the more modern process, and hence it follows that tannin is not a glucoside, but that the older specimens contained, as was suggested by Rochleder, an admix- ture of sugar or a glucoside which was brought into solution by the water present.2 Schiff, as already mentioned, found that gallic acid is converted into tannic acid when it is heated with phosphorus oxychloride or when its solution is evaporated with arsenic acid. According to Freda, the product obtained by the latter method gives all the characteristic reactions of tannin, but is nothing more than gallic acid containing arsenic acid,3 while Schiff has shown that this is not the case, but that arsenic acid adheres to the tannin so obstinately that it cannot be removed without a simultaneous conversion of a portion of the latter into gallic acid.4 The constitution of tannin or digallic acid is expressed by the following formula: HOX .HO >c6h2< HOZ \CO^ HO\ / O / >c6h2z HOZ ZCO.OH. This explains in a simple manner its conversion into gallic acid by the assumption of water, its decomposition into gallamide and gallic acid by the action of ammonia and the formation of a penta-acetyl-derivative. The fact that when monobromocatechuic acid is heated with potassium gallate and alcohol, a substance is formed 1 Biedermann, Ber. Entw. Chem. Ind. ; 2 Halfte, p. 456. 2 Schiff, Ann. Chem. Pharm. clxx. 75. 3 Ber. Deutsch. Chern. Ges. xii. 1576. 4 Ibid. xiii. 454. PROPERTIES OF TANNIN. 373 which gives all the reactions of tannin, is also in favour of this formula:1 C6H.,(OH)3CO.OK + BrC6H2(OH)2CO.OH = C6H2(OH)3CO.O.C6H2(OH)2CO.OH + KBr. Properties.-Tannin is a colourless, amorphous mass, which is left on the evaporation of its solution in brittle, vitreous masses, which become coloured yellow in the light, even when exposed in closed vessels. It reddens litmus and has a very strong astringent taste, is readily soluble in water, less so in absolute alcohol, and almost insoluble in absolute ether. Finely-powdered tannin coagulates in ether which contains water, and then de- liquesces, so that it can be employed to detect the presence of water in ether. If water be slowly dropped into the vessel containing the thick solution covered by ether, a point is attained at which three layers are formed.2 This occurs when 100 ccms. of water and 150 ccms. of ether are present to 100 grms. of tannin ; the lowest layer contains most tannic acid, the middle layer some tannic acid and a large amount of water while the upper layer consists almost entirely of ether, but contains a little tannic acid.3 Tannin is insoluble in carbon disulphide, chloroform, petroleum ether, benzene, &c. Its aqueous solution gives a black-blue colouration and precipitate with ferric salts, a partial reduction taking place (Wackenroder); ferrous sulphate produces in a concentrated solution a white, gelatinous precipitate which becomes coloured blue in the air. When tannin is heated it darkens at 150°-160°, and at 215° decomposes into water, carbon dioxide and pyrogallol, which volatilize, while metagallic acid or melangallic acid is left behind; this substance alone is formed when tannic acid is rapidly heated to 250°, and is a black, amorphous, tasteless mass. Tannin very readily undergoes oxidation; strongly ozonized air produces complete combustion, oxalic acid being formed as an intermediate product (Schonbein); it reduces the salts of copper, silver, mercury, gold, &c. In alkaline solution it rapidly absorbs oxygen, the liquid becoming coloured dark. Tannin is precipitated from aqueous solution by dilute hydro- chloric acid, sulphuric acid, common salt, potassium chloride, 1 Hunt, Chem. News, lii. 49. 2 Bolley, Ann. Chem. Pharm. cxv. 63. 3 Luboldt, Jahresb. Chem. 1859, 296. 374 AROMATIC COMPOUNDS. potassium acetate and other salts, but not by nitric acid or sodium sulphate. Animal skin removes it from solution com- pletely ; it precipitates gelatine solution, egg albumen, alkaloids and other substances. The Tannates. Tannin decomposes carbonates and is a mono- basic acid, the salts of which are amorphous and difficult to prepare pure. Many of them are insoluble precipitates, such as the tannates of lead, copper, tin, and antimony, and these may be used for the quantitative estimation of the acid. Tannin, or rather the material containing it, is employed in medicine, dyeing, the manufacture of inks, the clarification of beer and wine, &c. It is not adapted for use as a tanning agent. Pcnta-acetyltannin, C14H5(C2H3O)5O9, is obtained by boiling tannin with acetic anhydride for one hour; it is insoluble in water and separates from boiling alcohol in white spherical or warty aggregates of crystals, which melt at 137°. Its solution is precipitated by lead acetate, but is not coloured by ferric chloride (Schiff). Kinoin, C14H12O6, was discovered by Etti in Malabar kino, the dried sap of Pterocarpus Marsupium (p. 351). It crystallizes in prisms, which are slightly soluble in cold, readily in hot water and alcohol; its solution is coloured red by ferric chloride. On heating to 120° with hydrochloric acid, it decomposes into methyl chloride, catechol and gallic acid : C14H1906 + H90 + HC1 = CH3C1 + C6H6O9 4- C7HcO5. It is therefore gaily Icatechol methyl ether, and probably has the following constitution : HOX .OH >c6h2( ho^ xCO.OC6H4.OCH3. Kino-red, C28H22On, is an astringent substance which also occurs in kino, and is formed by heating kinoin to 120°-130°. It is a red, resinous substance, which is slightly soluble in water, readily in alcohol and alkalis, gives a dirty-green colouration with ferric chloride, and precipitates gelatine solution. On heating to 160°-170°, it melts with loss of water and is converted into an amorphous red compound, which may also be obtained by heating kino-red with dilute hydro- chloric or sulphuric acids. On dry distillation, the larger SINAPIN. 375 portion becomes carbonized, phenol, catechol and a small amount of anisol or guaiacol being formed.1 2205 Sinapin, C16H23NO5. Henry and Garot discovered in the seeds of the white mustard, a crystalline compound, con- taining both sulphur and nitrogen, to which they gave the name of sulphosinapin,2 and which was subsequently recognized by Babo and Hirschbrunn as sinapin thiocyanate.3 Robiquet and Boutron Charlard, repeating the research of Henry and Garot, obtained another substance,4 which Will and Lauben- heimer named sinalbin, and which is resolved into acid sinapin sulphate, sinalbin mustard oil, and grape sugar, by the action of myrosin in aqueous solution (Vol. III., Part II., p. 393). Sinapin, which is generally classed among the alkaloids, is extremely deliquescent, but forms stable salts. Sinapin thiocyanate, C16H23NO5.HSCN, is obtained from the powdered seeds by first extracting them with ether and cold alcohol, and then boiling up with 90 per cent, alcohol. A very voluminous crystalline mass, which bears a strong resemblance to quinine sulphate, separates out on cooling. It crystallizes from a dilute, hot, aqueous solution in large, fascicular groups of needles, which melt at 176°,5 and are only slightly soluble in cold alcohol and water. Acid sinapin sulphate, C16H23NO5,H2SO4 + 2H2O, is obtained by adding sulphuric acid to a concentrated, hot solution of the thiocyanate ; it crystallizes in rectangular plates, has an acid reaction and is readily soluble in water. The normal sulphate may be prepared from the acid by neutralizing with baryta water and evaporating the filtrate; it forms an extremely soluble crystalline mass. The nitrate and hydrochloride of sinapin can be prepared from it by means of barium nitrate or chloride, and crystallizes in fine, very soluble needles. The hydrochloride combines with mercuric chloride to form the compound C16H23NO5,HC1 + HgCl2, which crystallizes from water in thin, lustrous prisms (Will and Laubenheimer). When the sulphuric acid is completely removed by baryta water from a solution of the sulphate, a solution of free sinapin is obtained which has a deep yellow colour, is alkaline to litmus, 1 Ber. Deutsch. Chem. Ges. xi. 1879. 2 Berzelius, Jahresber. vi. 242 ; xii. 263. 3 Ann. Chem. Pharm. Ixxxiv. 10. 4 Ibid. xii. 266. 6 Remsen and Coale, Amer. Chem. Journ. vi. 50. 376 AROMATIC COMPOUNDS. and precipitates the salts of the heavy metals. It decomposes on evaporation, the colour changing through green and red into brown and a noncrystalline residue being left. If sinapin thiocyanate be boiled with baryta water or caustic potash solution, it decomposes into thiocyanic acid, sinapic acid and a base, which was named sinkalin by Babo and Hirsch- brunn, but has since been identified as choline (Vol. III., Part II., p. 64). C16H23NO5,HSCN 4- 2H2O = HSCN + CnH12O5 + C15H15NO2. Sinapic acid, CnH12O5, is best prepared, according to Remsen and Coale, by boiling si napin with baryta water and decom- posing the precipitate, which is formed, with hydrochloric acid. It is only slightly soluble in cold water and alcohol, and crystal- lizes from a hot solution in small, yellowish, transparent prisms, melting at 192°. Its alkaline solution rapidly turns green, red, and brown in the air. The addition of alcohol to the freshly prepared solution of the potassium salt precipitates it in iridescent plates, which rapidly change after the removal of the alcohol. Calcium chloride and barium chloride produce white precipitates, and ferric chloride gives a rose-red or fine purple- red precipitate, a partial reduction being also effected. Lead salts added to a neutral solution of the acid produce a white precipitate, which soon becomes green and then brown, while the colourless precipitates yielded by the salts of silver and mercury, are rapidly reduced; the metal is immediately separated from gold solutions. The barium salt alone has been obtained in a condition suitable for analysis by precipitating a solution of the acid, neutralized by potash or ammonia, with barium chloride, or more readily by boiling the acid with baryta water in absence of air ; it has the composition C11H10BaO5. Babo says: " Since it is a matter of some difficulty to obtain another salt of the acid in a state fitted for analysis, and I could not spare too much material for this research, the question whether the acid is mono- or dibasic must remain for the present undecided." This point was settled by Remsen and Coale, who heated weighed amounts of the acid with calcium or barium carbonate and determined the amount of metal which had entered into solution; they found that sinapic acid is monobasic, and that the normal barium salt has the formula (CuIInO5)2Ba. SINAPIC ACID. 377 The insoluble barium salt is therefore a basic compound, corresponding to the basic salicylates, and sinapic acid should therefore be a hydroxy-acid, as is proved to be the case by the existence of the following compound. Acetylsinapic acid, C11H11(C2H3O)O5, is obtained by boiling the acid with acetic anhydride, and forms crystals, which are soluble in hot water and melt at 281°. When sinapic acid is heated on platinum foil, vapours are given off which smell like incense, and are also formed when the acid is fused with caustic potash, pyrogallol being among the products. According to Remsen and Coale, sinapic acid is probably butylenegallic acid: /Ox /OH c4h z >c6h2( \oz ZCO.OH. If this view be correct, the following formulae will represent the constitution of sinapin and its thiocyanate : ZOX ZOH c4h8< >c6h2z ZOZ zCO.OC2H4N(CH3)3OH. z(\ zoh c4h z >c6h2z ZOZ zCO.OC2H4N(CH3)3S.CN. If it be further assumed that sinalbin contains two molecules of water of crystallization, its constitution may be represented as follows : ,OX zOC6HuO5 c4h 8Z >c6h2z ZOZ ZCO.O.C2H4(CH3)3NO.SO2.OC6H4.CH2.NCS. Gallocyanin. This dye, which was discovered by Kochlin, and which is also known as solid-violet {violet solide), is manu- factured by heating nitrosodimethylaniline hydrochloride with gallic acid or tannin in alcoholic solution. It is a crystalline substance with a green metallic lustre, readily dissolves in alkalis, and yields salts which crystallize well, that with aniline forming small, green crystals. Gallocyanin forms a blue solution in concentrated sulphuric acid. It is used for dyeing cotton and in calico printing, since it forms a beautiful violet-black 378 AROMATIC COMPOUNDS. lake with chromium oxide, with which the material is mordanted. The shades produced are as bright as those of aniline violet, but much more stable towards light, alkalis and acids. In the presence of quercitron or similar yellow dyes, dark blue shades resembling indigo are produced and can be varied to the greenest shades of blue. It dyes silk and wool directly violet-blue, and is also used as an acid blue on azo-colours ; the goods are dyed in ponceau or some other shade, and the pattern is then printed on in the shape of a mixture of solid-violet, indophenol and an alkaline reducing agent, which effects the usual decomposition of the azo-colour, while the blue colours are reduced to leuco-compounds, which penetrate the fibre and on exposure to air produce a fast blue on a red ground.1 Gallocyanin belongs to the class of the indophenols, but its analysis has not yet been published. Its method of formation leads to the following constitution or some similar one (Part III., p. 331). Ik /CO2H )C=C< 0~C\ >C=zN.C6H4.N(CH3)2. >c=c< OHZ \0H PYROGALLOLCARBOXYLIC ACID. 2206 This compound is formed, together with gallocarboxylic acid, C6H(OH)3(CO2H)2,2 by heating pyrogallol to 130° with ammonium carbonate, or more simply by heating pyrogallol in an open flask with a concentrated solution of acid potassium carbonate.3 It crystallizes from hot water in silky needles of the composition 3C6H2(OH)3CO2H 4- H2O, which become anhydrous at 110° and have a markedly acid taste. One part dissolves at 12'5° in 767 parts of water ; it is readily soluble in alcohol, but less so in ether. On heating in a current of hydrogen, a gradual evolution of carbon dioxide accompanied by fusion sets in at 195°-200°, while it sublimes slowly, but without decomposition, in a current of carbon dioxide. Its aqueous solution is coloured 1 Kochlin, Chern. News, xlvii. 170; Pabst, Bull. Soo. Chim. xxxviii. 162 ; Chemikerzeit, ix. 1444. 2 Senhofer and Brunner, Monatsh. Chern., i. 468. 3 Kostanecki, Ber. Deutsch. Chern. Ges. xviii. 3202. PYROGALLOL CARBOXYLIC ACID. 379 violet by very dilute ferric chloride, while a strong solution pro- duces a greenish brown colouration; ferrous sulphate produces no immediate colouration, but the liquid becomes violet on stand- ing. The same colouration is produced by concentrated sulphuric acid which contains a trace of nitric acid. Baryta water and lime water produce blue precipitates which are at first so finely divided that the liquid appears clear. The acid is coloured dark brown by strong potash solution, especially on boiling. It reduces ammoniacal silver solution in the cold and imparts a green colour to Fehling's solution, reduction taking place on warming. It differs sharply from gallic acid in remaining unacted on by sulphuric acid at 140°, no rufigallic acid being formed; de- composition, accompanied by a violent evolution of gas, sets in, however, at a higher temperature. The Pyrogallolcarboxylates. The following salts are charac- teristic : Calcium pyrogallolcarboxylatc, (C7H5O5)2Ca + 4H2O, separates from a hot solution in hard, granular crystalline masses. Barium pyrogallolcarboxylate, (C7H5O5)2Ba + 5H2O, crystallizes from a hot solution in hard, yellow prisms. Basic lead pyrogallolcarboxylate, C7H2Pb2O5 + H2O, is a white, flocculent precipitate, which becomes anhydrous at 100°. Bthyl pyrogallolcarboxylate, 2CfiH2(OH)3CO2.C2H5 + 3H2O, is insoluble in cold water, but readily in alcohol and ether, and separates from a hot aqueous solution in crystals, which become anhydrous over sulphuric acid or at 100°, at which temperature they commence to sublime, and then melt at 102.° Ferric chloride colours the aqueous solution greenish brown. Triethylpyrogallolcarboxylic acid, C6H2(OC2H5)3CO2II. The ethyl ether of this substance is prepared by heating the preceding compound with caustic potash, ethyl iodide and alcohol. It is an odourless, volatile liquid, which is readily decomposed by alcoholic potash.1 The free acid is slightly soluble in cold, more readily in hot water and alcohol, and crystallizes in long, silky needles, melting at lOO'o0. It was first obtained from triethyl- daphnetic acid, C6H2(OC2H5)3C2H2.CO2H, by oxidation with potassium permanganate, its aldehyde C6H2(OC2H5)3CHO, being simultaneously formed as an oily liquid which gradually solidifies to a crystalline mass melting at 7O0.2 1 Will and Albrecht, Ber. Deutsch. Chem. Ges. xvii. 2100. 2 Ber. Deutsch. Chem. Ges. xvii. 1087. 380 AROMATIC COMPOUNDS. PHLOROGLUCINOLCARBOXYLIC ACID. This acid is obtained by heating phloroglucinol with acid potas- sium carbonate and water to 13O0.1 It crystallizes in needles, which contain a molecule of water and are only slightly soluble in water, more readily in alcohol, very readily in ether and have an acid taste. The water is lost at 100°, carbon dioxide being also slowly evolved. On boiling with water it is decomposed smoothly into phloroglucinol and carbon dioxide. Its aqueous solution is coloured an intense blue by ferric chloride, which soon changes to dirty brown, and its alkaline solution turns brown in the air. When its alcoholic solution is saturated with hydrochloric acid, carbon dioxide is evolved and phloroglucinol diethyl ether is formed (Part III., p. 187). HYDROXYQUINOLCARBOXYLIC ACID. The following derivatives of this acid are alone known : Triethylhydroxyquinolcarboxylic acid, C6H2(OC2H513CO2H, is formed by the oxidation of the two isomeric triethylaesculetic acids, C6H2(OC2H5)3C2H2.CO2H, with potassium permanganate, and crystallizes from hot water in fine needles, melting at 134°. Its aldehyde, C6H2(OC2H5)3COH, is also formed and crystallizes from alcohol in splendid pointed prisms, melting at 95°. Trimethylhydroxyquinolcarboxylic acid, CGH2(OCH3)3CO2H, resembles the ethyl compound and melts at 108°-109°.2 These compounds were at first considered as derivatives of phloroglucinolcarboxylic acid. When the triethylcompound is distilled with lime, however, a triethoxybenzene is obtained, which melts at 34°, and is therefore different from the triethyl ether of pyrogallol or phloroglucinol, so that it must be that of hydroxyquinol.3 1 Bar. Deutsch. Chem. Ges. xvii. 2103. 2 Will, ibid. xvi. 2112. 3 Will and Albrecht, ibid. xvii. 2108. QUINIC ACID. 381 CONSTITUTION OF THE TRIHYDROXY- BENZOIC ACIDS. According to theory, six of these compounds can exist, but only four are known : Pyrogallolcarboxylic acid. CO2H /\OH \/OH OH Phloroglucinolcarboxylic acid. co2h oh/Xoh OH Gallic acid. co2h OH\/OH OH Hydroxyquinolcarboxylic acids. co2h co.,h co2hx oh/^oh Aqh ^^.oh \/OH OH\/OH HOX/ OH The constitution of gallic acid is determined by its formation from bromoprotocatechuic acid and a-bromoresorcylic acid, whence it also follows that pyrogallol is an adjacent trihydroxy- benzene, and that in phloroglucinol the hydroxyls are symmetri- cally arranged (Part III., p. 181). The latter can only yield one carboxylic acid, so that the constitution of phloroglucinol- carboxylic acid is determined; this is confirmed by its formation from daphnetic acid, in which a hydroxyl is known to be in the ortho-position to the carboxyl. The constitution of the hydroxyquinolcarboxylic acid from aesculetic acid has not yet been determined. QU IN IC ACID, CGH7(OH)4CO2H. 2207 Count Claude de la Garaye, in 1746, obtained a crystal- line deposit1 from the extract of Peruvian bark, which became known as Sei essentiel de la Garaye. Hermbstiidt of Berlin showed in 1785 that this " Chinasalz " is a salt of lime,2 and Hofmann, an apothecary of Leer, in 1790 detected in it a 1 Chimie hydrmdique, Paris, 1746, 114. 2 Crell's Ann. ii. 115. 382 AROMATIC COMPOUNDS. characteristic acid, which he named " Chinasaure," 1 and which was carefully investigated by Vauquelin in 1806, who called it acide quinique? Its correct formula was determined by Liebig3 and Woskresensky.4 It occurs to the amount of 5-8 per cent, in true Peruvian bark, combined with alkaloids and lime. Stenhouse5 was unable to obtain the slightest trace from the false China nova s. surina- mensis (Buena magnifoUa) ; but Hlasiwetz subsequently showed that it is present, although only in small amount.6 Zwenger and Siebert have also detected it in bilberry leaves (Vac- cinium Myrtillus)^ and in coffee beans.8 They obtained an ounce of the acid from some baskets of bilberry leaves gathered in May, and one variety of Java coffee yielded 0'3 per cent. Loew discovered it in meadow hay,9 which contains about 0'6 per cent. Calcium quinate was formerly a by-product of the manufacture of quinine, but is not obtained by the method now in use.10 It is prepared by treating the powdered bark for two or three days with cold water, adding a little milk of lime to the extract, in order to precipitate tanning matters and the small quantity of alkaloids present, and evaporating the filtrate until it has the consistency of syrup. The calcium quinate which separates out after some weeks is purified by re-crystallization and decom- posed by sulphuric or oxalic acid. Quinic acid crystallizes in hard, transparent, monoclinic prisms or tablets, has a very soui' taste, and dissolves at 9° in 2'5 parts of water, more readily in alcohol, and scarcely at all in ether. It is optically active and its aqueous solution is loevorotatory. When it is heated it melts at 161'6°,11 and loses water at a higher temperature, forming quinide, C7H10O5, which separates from water in crystals resembling those of salammoniac, which have an acid reaction and combine with bases to form salts of quinic acid.12 It probably has the following constitution, C6H7(OH)4CO.OC6H7(OH)3CO2H. Quinic acid decomposes on dry distillation with formation of phenol, quinol, catechol, benzoic acid and other products.13 1 Crell's Ann. ii. 314. 2 Ann. Chim. lix. 162. 3 Ann. Chcm. Pharm. vi. 14. 4 Ibid. xxiv. 257. 5 Ibid. liv. 100. 6 Ibid. Ixxix. 144. 7 Ibid. cxv. 108. 8 Ibid. Suppl. i. 77. 9 Journ. Prakt. Chcm. [2] xix. 309. 10 Neues HandwMerb. ii. 532. 11 Hesse, Ann. Chern. Pharm. cxiv. 292. 12 Hesse, ibid. ex. 335. 13 Wohler, ibid. Ii. 146. QUINIC ACID. 383 When lead dioxide is added to its aqueous solution, carbon dioxide is evolved and the reaction may be carried on by heating the mixture, lead quinate and quinol being formed :1 C7H12Og+O = C6H6O2 + CO2+3H2O. When it is heated with manganese dioxide and sulphuric acid, quinone is formed, while protocatechuic acid may be obtained by evaporating a solution of the acid to which bro- mine has been added,2 or by fusing the acid with caustic potash,3 or caustic soda,4 as well as, together with a large amount of benzoic acid, by heating quinic acid to 150° with fuming hydrochloric acid.5 Fuming hydriodic acid reduces it at 120° to benzoic acid :6 C7H12O0 + 2HI = C7H6O2 + 4H2O +12. On heating with concentrated hydrochloric acid to 140°-150°, parahydroxybenzoic acid and quinol are formed; it dissolves when heated with sulphuric acid with evolution of carbon dioxide and formation of quinoldisulphonic acid (Hesse). Phosphorus chloride converts it into metachlorobenzoyl chloride (Grabe) : C7H12O6 + 5PCL = C7H.C12O + 5POCL + 8HC1. It is converted by the animal organism into hippuric acid (Lautemann). The whole behaviour of quinic acid points to the fact that it belongs to the aromatic addition-products.7 It is tetrahydroxy- hexhydrobenzoic acid, and, since it is optically active, must contain an asymmetric carbon atom, so that it has the following constitution: co2h CH HO.HC^ JcH.OH CH OH. 1 Hesse, Ann. Chern. Pharm. cxiv. 292. 2 Hesse, ibid. cc. 239. 3 Grabe, ibid, cxxxviii. 203. 4 Hesse, loo. cit. s Fittig and Hillebrand, ibid, cxciii. 197. 6 Ibid. cxxv. 9. 7 Grabe, Ann. Chem. Pharm. cxlvi. 66. 384 AROMATIC COMPOUNDS. It differs from quercitol (Part III. p. 194) in containing a carboxyl in the place of one hydroxyl. A different formula has been proposed by Lieben, who found that quinic acid yields iodoform when treated with iodine and caustic potash; he therefore assumes that its constitution must be expressed by the following or some similar formula :1 HO.CH CH, II I HO.C CH.OH HO.CH CH.CO2H. The Quinates. The salts of quinic acid are for the most part readily soluble in water, slightly in alcohol, and crystallize well. They have been investigated by Baup,2 Woskrensky, Hesse, and Clemm.3 Sodium quinate, C7HnO6Na + 2H2O, crystallizes in large, nacreous, rhombic prisms. Clemm was unable to obtain the potassium and ammonium salts in crystals; their solutions only gave syrupy residues on evaporation over sulphuric acid. Calcium quinate, (C7HuO6)2Ca + 10H2O, forms silky, rhombic plates, or long, concentrically-grouped prisms, which dissolve at 10° in 6 parts of water and are insoluble in absolute alcohol. Barium quinate, (C7H11O6)2Ba + GH2O, crystallizes, according to Henry and Plisson, in acute octohedral pyramids, while Baup always obtained it in dodecahedra formed by the combination of two pointed pyramids, and Clemm only as a partially crystalline mass. Lead quinate, (C7HuO6)2Pb, crystallizes in readily soluble needles; ammonia added to its solution produces a voluminous, hydrated precipitate which has the formula C7HsO6Pb2, after drying at 200°. Silver quinate, C7HnO6Ag, forms warty crystals, which readily dissolve in water and blacken in the light. Copper quinate, (C7H11O6)2Cu + 5H2O, crystallizes in light blue plates. Basic copper quinate, C7H10O6Cu + 2H2O, is obtained by boiling the aqueous solution of the acid with an excess of copper oxide: 1 Ann. Chern. Pharm. Suppl. vii. 232. 2 Ibid. vi. 1 ; Ann. Chim. Phys. [2] li. 56. 3 Ann. Chern. Pharm. ex. 345. ETHYL QUINATE. 385 it forms small, green crystals, which are only slightly soluble in cold water. Ethyl quinate, C6H7(OH)4CO2.C2H5, was obtained by Hesse by the action of ethyl iodide on the silver salt ; it is a viscid mass, which is readily soluble in water and alcohol, and has a very bitter taste. Ethyl tetracetylqidnate, C6H7(OCO.CH3)4CO.OC2H5, is formed by boiling the ethyl ether with acetic anhydride, and crystallizes from boiling water in plates; it separates from ethei' in large, rhombic crystals which melt at 135°, and sublime without decomposition (Fittig and Hilldebrand). 386 AROMATIC COMPOUNDS. THE XYLENE GROUP. 2208 It has been already mentioned under benzene (Part III. p. 66) that Mansfield in 1848 discovered that coal-tar naphtha contains, besides benzene, its homologues; of these he isolated the following (C = 6): Boiling-point. Toluol, C14H8 about 113°. Cumol, C18H12 143°-145°. Cymol, C20H14 170°--172°. He adds, it is interesting to note, " that tar-oil contains among its constituents the only four known members of the series C6 + n(C2H2). It seems, therefore, not improbable that the gap which still exists in this series (n = 5), corresponding to a substance whose boiling-point lies between those of toluol and cumol, will be filled by a compound to be obtained from tar-oil.1 Soon after this, Cahours discovered xylol (iryZ^ne),C8H10(C = 12), boiling at 128°-130°, along with toluol in crude wood-spirit ^vXov, wood),2 and Volkel found the same hydrocarbons in wood-tar.3 Church then stated that xylol is also contained in coal-tar oil, and boils at 126 2°,4 whereas Ritthausen5 and Hiltenkamp6 could only detect in it the hydrocarbons already discovered by Mansfield. Warren de la Rue and H. Muller then showed that Rangoon tar contains benzol and its homologues, which they were unable to isolate, but recognised by conversion into their characteristic nitro-compounds.7 Shortly before this time, Bussenius and Eisenstuck had investigated the rock oil from 1 Ann. Chern. Pharm. Ixix. 162. 2 Ibid. Ixxiv. 168 ; Ixxvi. 286. 3 Ibid. Ixxxvi. 331. 4 Phil. Mag. [4] ix. 256. 6 Journ. Prakt. Chem. Ixi. 74. 6 Ann. Chern. Pharm. xcv. 89. 7 Journ. Prakt. Chem. Ixx. 300. THE XYLENE GROUP. 387 Sehnde in Hanover, and discovered in it a new hydrocarbon, which they called petrol, CSH1O, its existence being proved by its characteristic trinitro-derivative;1 and Hugo Muller then showed that the hydrocarbon obtained from coal-tar and boiling at 140° is not cumol, but xylol, which also occurs in the oils from Burmah and Sehnde, trinitropetrol being identical with trinitro- xylol.2 In spite of this Bechamp repeated the statement that xylol boils at 126°-130c, adding that coal-tar also contains a "new" hydrocarbon boiling at 139°-140°.3 Mansfield's cumol was subsequently proved to be a mixture of trimethylbenzenes. After Fittig and Tollens had made the important discovery that the synthetic methylphenyl or methylbenzol is identical with toluol,4 it was supposed that ethylphenyl or ethylbenzol would be identical with xylol. This, however, was found not to be the case, since it boils as much as 7° lower than the latter, and does not yield a crystallized trinitro-derivative. Beilstein then investigated xylol more carefully; he fully con- firmed Muller's observations and found that on oxidation with chromic acid it yields dibasic terephthalic acid, C8H6O4.6 About this time Fittig prepared methylbenzyl, which he considered to be identical with xylol, by the action of sodium on a mixture of bromotoluol and methyl iodide.6 He also found that ethyl- phenyl is easily oxidized to benzoic acid and that its derivatives are completely different from those of xylol.7 Glinzer and Fittig then undertook a careful examination of methylbenzyl, or, as they now termed it, methyltoluol; like xylol it yielded terephthalic acid on oxidation, but the trinitro- derivatives proved to have different properties.8 A further investigation of the oxidation products of xylol showed that toluic acid, the next homologue of benzoic acid,9 is first formed, and this was also obtained from methyltoluol. In spite of this, however, the hydrocarbons were shown to be different, as the properties of their substitution products did not agree.10 Fittig and Velguth then obtained a third isomeric hydrocarbon, which they named isoxylol, by heating monobasic mesitylenic acid, C6H3(CH3)2CO2H, prepared by the oxidation of mesitylene, 1 Ann. Chern. Pharm cxiii. 151. 2 Zeitschr. Chern. 1864, 161. 3 Compt. Rend. lix. 47. 4 Ann. Chem. Pharm. cxxxi. 303 5 Ibid, cxxxiii. 32. 6 Ibid, cxxxiii. 47. 7 Ibid, cxxxiii. 222. 8 Ibid, cxxxvi. 303. 9 Yssel de Schepper and Beilstein, ibid, cxxxvii. 301. 10 Fittig, Ahrens and Mattheides, ibid, cxlvii. 15. 388 AROMATIC COMPOUNDS. C6H3(CH3)3, with lime. The substitution products of this body agreed so exactly with those of xylol, that the two hydro- carbons would have been considered identical had not their oxidation products been completely different. Isoxylol was not attacked by dilute nitric acid, while chromic acid oxidized it to isophthalic acid, the isomeride of terephthalic acid.1 Fittig soon found a very simple explanation of this exceptional and almost incredible fact. Xylol proved to be a mixture of methyltoluol or paraxylol with isoxylol, or, as it is now termed, metaxylol. Beilstein, who had looked upon it as a chemical individual, had only obtained in a pure state the difficultly soluble substitution products of metaxylol and the oxidation pro- ducts of paraxylol, which are most readily formed.2 The third isomeric dimethylbenzene, orthoxylol was then prepared syn- thetically and subsequently discovered in coal-tar by Jacobsen.3 According to Fittig, coal-tar naphtha contains a preponde- rating amount of metaxylene, while Jacobsen found 20-25 per cent, of orthoxylene, and 10-15 per cent, of paraxylene in a series of samples of xylene. In order to separate these, the coal-tar xylene, boiling at about 140°, is repeatedly shaken up with ordinary concentrated sulphuric acid, the ortho- and meta-compounds alone being dissolved. The solution is diluted with water and neutralized with chalk, the filtrate being then treated with a slight excess of sodium carbonate and concentrated by evaporation. The sodium orthoxylenesulphonate separates out on cooling in large prisms, which can readily be purified by re-crystallization. An additional crop of this salt can be obtained by further eva- poration, while the meta-salt remains in solution. The pure hydrocarbons are then obtained by heating the salts with concentrated hydrochloric acid. The portion of the crude xylene which does not dissolve in ordinary sulphuric is agitated with the slightly fuming acid, the mixture being gently heated; the paraffins are thus left undissolved, while paraxylenesulphonic acid is formed, which is only slightly soluble in dilute sulphuric acid, and is purified by re-crystallization (Jacobsen), the hydrocarbon being then obtained, as before, by the action of hydrochloric acid. The meta-compound alone may be extracted from crude xylene by boiling it for a considerable time with a mixture of 1 Ann. Chem. Pharm. cxlviii. 1. 2 Ibid, cliii. 265. 3 Ber. Deutsch. Chem. Ges. x. 1010. THE XYLENES. 389 one volume of concentrated nitric acid and two or three volumes of water, the ortho- and para-compounds being thus oxidized to the corresponding toluic acids, C6H4(CH3)CO2H, or their nitro- derivatives, while the meta-compound is scarcely attacked. When the evolution of red fumes ceases, the liquid is distilled with steam and the distillate agitated with caustic soda, washed with water, dried and distilled.1 Tn order to estimate the amounts of the three isomerides quantitatively, 100 c.c. of the crude xylene are boiled for half an hour to an hour with a mixture of 40 c.c. of nitric acid of sp. gr. 1'4 and 60 c.c. of water, the whole being repeatedly agitated. The unattacked portion is then washed with caustic soda and distilled with steam, the distillate is measured and shaken up with 1'5 vols. of concentrated sulphuric acid, the metaxylene being thus dissolved, while the paraffins remain behind and are measured in a graduated cylinder. The amount of paraxylene is found by thoroughly agitating 100 c.c. of the crude xylene with 120 c.c. of concentrated sul- phuric acid for half an hour, a mixture of paraffins and para- xylene being left undissolved ; this is then treated with an equal volume of fuming sulphuric acid, containing 20 per cent, of trioxide, which dissolves out the paraxylene. The amounts of paraxylene, metaxylene and paraffins are thus directly measured, the difference from 100 c.c. being that of the orthoxylene. In this way Levinstein has found in various samples of crude English and Scotch xylene :2 Paraxylene 3-10 per cent. Metaxylene 70-87 „ Orthoxylene 2-15 „ Paraffins 3-10 „ According to Reuter these methods of separation are not accurate, since nitric acid of the concentration employed also attacks metaxylene, and paraxylene dissolves in ordinary sulphuric acid, although to a much smaller extent than its isomerides. The resistance of the xylenes to the action of acids is, however, considerably increased by the presence of paraffins.3 1 Fittig and Velguth, Ann. Chem. Pharm. cxlviii. 10 ; Tawildarow, Zcitschr. Chern. 1870, 418 ; Bruckner, Ber. Deutsch. Chem. Ges. ix. 405. 2 Ibid. xvii. 444. 3 Ibid. xvii. 2028. 390 AROMATIC COMPOUNDS. When a mixture of the three xylenes is treated with bromine containing 1 per cent, of iodine, they are converted into the tetra- bromoxylenes, C6Br4(CH3)2, which yield the tetrabromophthalic acids quantitatively when heated with bromine and water to 160°-170°: C6Br4(CH3)2 + GBr2 + 4H2O = C6Br4(CO2H)2 +12HBr. Since these can readily be separated, the composition of the original mixture can be determined in this way.1 THE XYLENES, OR DIMETHYLBENZENES, C6H4(CH3)2. 220g Orthoxylene, (1: 2), was first prepared pure by the dis- tillation of paraxylic acid, C6H3(CH3)2CO2H, with lime ;2 it is also formed by the action of sodium on a mixture of ortho- bromotoluene and methyl iodide,3 and when a hot mixture of toluene and aluminium chloride is treated with methyl chloride. A small quantity of paraxylene is always formed in this reaction, together with still less metaxylene and a larger amount of the isomeric trimethylbenzenes.4 It has also been prepared from cantharidin, C10H12O4, which is the characteristic con- stituent of Spanish flies, and yields, pure orthoxylene when heated with phosphorus pentasulphide.5 It is a liquid which boils at 142°-143°,. solidifies in a freezing mixture to crystals, melting at - 28°,6 and is oxidized to ortho- toluic acid by heating with dilute nitric acid, while chromic acid produces complete combustion. When agitated with a boiling solution of potassium permanganate, however, it yields phthalic acid.7 A cold mixture of nitric and sulphuric acids converts it into liquid nitro-derivatives, and a single drop of orthoxylene can thus be distinguished from the para- and meta-compounds.8 1 Friedel and Crafts, Compt. rend. ci. 1218. 2 Bieber and Fittig, Ann. Chern. Pharm. clvi. 238. 3 Hubner and Jannasch, ibid. clxx. 117 ; Reymann, Bull. Soc. Chim. xxvi. 582. 4 Jacobsen, Bor. Deutsch Chem, Ges. xiv. 2624. 5 Piccard, ibid. xii. 580. 6 Colson, Ann. Chim. Phys. [6] vi. 128. 7 Claus and Pieszcek, Ber. Deutsch. Chem. Ges. xix. 3083. 8 Jacobsen, ibid. xix. 2518." ORTHOXYLENE. 391 Dihydro-orthoxylcne, or Cantharene, C6H6(CH3)2. The com- pound C10H12I2O3 is formed by the action of hydriodic acid on cantharidin, and is converted into Cantharene by heating with concentrated caustic potash; the latter boils at 134°, smells like camphor and oil of turpentine, rapidly absorbs oxygen from the air and is oxidized to orthotoluic acid by dilute nitric acid.1 Metaxylene (1 : 3) may be obtained pure by heating xylic acid C6H3(CH3)2CO2H (Bieber and Fittig), or the isomeric mesity- lenic acid (Fittig and Velguth) with lime, and by the action of sodium on a mixture of methyl iodide and meta-iodotoluene.2 It boils at 139'8° and has a specific gravity of 0'8780 at 0°, and of 0'8G60 at 15°; it solidifies when strongly cooled and then melts at - 54° to - 53°.3 It is only attacked with difficulty by dilute nitric acid, even on boiling; when, however, it is boiled for several hours with nitric acid of specific gravity 1'4, diluted with one and a half times its volume of water, metatoluic acid is obtained (Reuter), while chromic acid solution oxidizes it to isophthalic acid, which is also formed, together with metatoluic acid, by the action of potassium permanganate.4 Metaxylene, as already mentioned, occurs in various tars and petroleums, and it has also been found in that from the Caucasus.5 It forms a characteristic trinitro-derivative, which is only slightly soluble in alcohol and yields nitrodiamidometaxy- lene (p. 409) on partial reduction. These reactions serve to detect small quantities of metaxylene in petroleum, &c. Tetrahydrometaxylene, C6H8(CH3)2, is formed when camphoric acid, C8H14(CO2H)2, is heated to 200° with concentrated hydriodic acid,6 and has also been prepared from oxycamphoric acid, under which it will be mentioned. It is a liquid which boils at 119°, and is converted into trinitrometaxylene by a mixture of nitric and sulphuric acids. Hexhydrometaxylene, C6H10(CH3)2, is obtained by heating camphoric acid or metaxylene with hydriodic acid to 280°. It occurs in Baku petroleum (Beilstein and Kurbatow) and in essence of resin (Renard) ; it boils at 116°-120°, and also yields trinitrometaxylene with nitric and sulphuric acids.7 Paraxylene (1:4) is formed by the action of sodium on a 1 Piccard, Ber. Deutsch. Chern. Ges. xix. 1406. 2 Wroblewsky, Ann. Chern. Pharm. cxcii. 200. 3 Colson, loc. cit. 4 Claus and Burstert, Ber. Deutsch. Chem. Ges. xix. 3084. 5 Doroschenko, xviii. Ref. 662 ; Markownikow, Ann. Chem. Pharm. ccxxxiv. 89. 6 Wreden, Ann. Chem. Pharm. clxxxvii. 171. 7 Ibid, clxxxvii. 151. 392 AROMATIC COMPOUNDS. mixture of methyl iodide and parabromotoluene1 or paradi- bromobenzene.2 It boils at 136°-137°, and has a specific gravity of 0'8621 at 19'5°; when strongly cooled it solidifies to rhombic prisms resembling heavy spar,3 which melt at + 15°. Dilute nitric acid oxidizes it to paratoluic acid, while chromic acid or potassium permanganate give terephthalic acid. Paraxylene occurs in the petroleum from Galicia along with metaxylene.4 Hexhydroparaxylene, C6H10(CH3)2, is obtained by heating mono- bromocamphor, C10H15BrO, with zinc chloride to 150°-160°, and is a liquid boiling at 157'6°, which is converted into trinitropara- xylene by nitric and sulphuric acids.5 SUBSTITUTION PRODUCTS OF THE XYLENES. 2210 When one atom of hydrogen is replaced in the aromatic nucleus, six isomeric compounds may be formed. Metaxylene yields three, which are distinguished as symmetric = s, asym- metric = a, and adjacent (vicinus) = v. Two, asymmetric = a, and adjacent = v, are derived from orthoxylene, while paraxylene only yields one, which has therefore received no more particular designation. HALOGEN SUBSTITUTION PRODUCTS OF THE XYLENES. v-Chlororthoxylene, C6H3(CH3)2C1(1: 2:3), is formed, together with the following compound, when orthoxylene, to which 5 per cent, of iodine has been added, is treated with chlorine at 0°. In order to separate the two isomerides, they are converted into the sulphonic acids, the pure sodium salts of which are then decomposed by heating with concentrated hydrochloric acid. Adjacent chlor orthoxylene is a liquid boiling at 189'5°. a-Chlororthoxylene (1:2:4) boils at 191'5° and, like its isomeride, remains liquid at - 20°.6 1 Fittig and Glinzer, Ann. Chcm. Pharm. cxxxvi. 303. 2 V. Meyer, Ber. Deutsch. Chem. Ges. iii. 753 ; Jannasch, ibid. x. 1356. 3 Jacobsen, ibid. xvii. 2379. 4 Palewski, ibid, xviii. 1915. 6 R. Schiff, ibid. xiii. 1408. 6 Kriiger, ibid, xviii. 1755. XYLENE SUBSTITUTION-PRODUCTS. 393 The chlororthoxylenes are converted by oxidation into the corresponding chlorotoluic and chlorophthalic acids. According to Claus and Kautz, only one chlororthoxylene is formed, which boils at 205° and yields the following compounds on further chlorination :1 Dichlororthoxylene, C6H2C12(CH3)2, Melting- point. Boiling- point. crystalline mass . . . , + 3° 227° Trichlororthoxylene, C6HC13(CH3)2, lustrous needles . . . . 93° 265° Tetrachlororthoxylene, C6C14(CH3)2, long needles 215° - a-Chlorometaxylene, C6H3(CH3')2C1(1 : 3 :4), is formed when metaxylene is chlorinated at 0° in presence of iodine; the crude product, which distils between 185°-188°, is purified by con- verting it into the sulphonic acid and then preparing the sodium salt or chlorometaxylenesulphamide, C6H2(SO2.NH2)C1(CH3)2, from this. The latter crystallizes from hot alcohol in hard, com- pact, lustrous prisms melting at 195°. Both of these compounds yield pure chlorometaxylene when heated with hydrochloric acid. It boils at 186-5° and does not solidify at - 20°; it is oxidized to chlorometatoluic acid by chromic acid, while it is converted into ortho-homoparahydroxybenzoic acid by fusion with caustic potash.2 Chloroparaxylcnc, C6H3(CH3)9C1(1 : 4: 2), is obtained in a precisely similar manner to chlorometaxylene ; it boils at 186° and solidifies in a freezing mixture to a crystalline mass, which melts at + 2°. Dichloroparaxylene, C6H2(CH3)2C12, is only slightly soluble in cold, readily in hot alcohol, and crystallizes in flat needles or plates; it melts at 71° and boils at 2210.3 a-Brom orthoxylene, C6H3(CH3)2Br(l : 2 :4), is formed by the direct bromination of orthoxylene in the cold in the presence of iodine, no isomeride being produced,4 and more slowly when bromine alone is allowed to act in the dark, orthoxylyl bromide being obtained in the sunlight5 It boils at 214'5° and solidifies below 0° to a fibrous, crystalline mass, melting at - 0'2°. When heated with ethyl chloroformate and sodium amalgam, paraxylic acid, CfiH3(CH3)2CO2H, is formed. 7 box 6/ A L 7 1 Jacobsen, Ber. Deutsch. Chem. Ges. xviii. 1367. 2 Ibid, xviii. 1760. 3 Kluge, ibid, xviii. 2098. 4 Jacobsen, ibid. xvii. 2372. 5 Schramm, ibid, xviii. 1278. 394 AROMATIC COMPOUNDS. The following compounds are formed by the further action of bromine (Jacobsen): Solid dibromorthoxylene, (1 : 2 : 4 : 5), crystallizes from hot alcohol in large, rhombic plates, which melt at 88°; it readily sublimes in very large, thin plates, boils at 278° and yields symmetric tetramethylbenzene, C0H2(CH3)4, on treatment with sodium and methyl iodide. Liquid dibromorthoxylene boils at 277° and solidifies in the cold to a hard crystalline mass, melting at + 6'8°. Tetrabromorthoxylene, C6(CH3)2Br4, is formed when orthoxylene is allowed to drop into bromine containing 1 per cent, of alumi- nium bromide, the whole being kept at O0.1 It is very slightly soluble in alcohol, readily in benzene, and crystallizes in long, lustrous needles, which melt at 262°, or according to Blumlein at 254°-255°, and boil at 374°-375°. Jacobsen was unable to prepare tribromorthoxylene pure. a-Bromometaxylene, C6H3(CH3)2Br (1:3:4), is prepared like the ortho-compound; it is a liquid, which boils at 203°-204°, and is converted into the corresponding bromotoluic acid by oxi- dation,2 while xylic acid is formed by the action of carbon dioxide and sodium.3 s-Bromometaxylene, (1 : 3 :5), has been prepared from bromi- nated metaxylidine by the diazo-reaction. It boils at 204°, remains liquid at -20°, and is converted into symmetric dimethylethylbenzene by sodium and ethyl bromide.4 a-Dibromometaxylene, C6H2(CH3)2Br2, is formed when meta- xylene is allowed to stand in contact with an excess of bromine for twenty-four hours, the liquid being kept cool.5 It crystallizes from alcohol in colourless, nacreous plates, boils at 255°-256°, and melts at 720.6 ^-Dibromometaxylene was obtained by Wroblewsky, together with his monobromoxylene, as a liquid which boils at 252° and does not solidify at - 20°. Tetrabromometaxylcne, C6(CH3)2Br4, is formed when meta- xylene is allowed to stand for a long time in contact with a large excess of bromine. It is scarcely soluble in cold, slightly in boiling alcohol, but dissolves readily in benzene, 1 Bliimlein, Ber. Deutsch. Chern. Ges. xvii. 2492. 2 Fittig, Ann. Chern. Pharm. cxlvii. 31. 3 Kekule, ibid, cxxxvii. 186. 4 Wroblewsky, ibid, cxcii. 115. 5 Fittig, Ahrens and Mattheides, ibid, cxlvii. 24, 6 Fittig and Bieber, ibid. clvi. 236. NITRO-ORTHOXYLENES. 395 and crystallizes in fine needles which melt at 241° (Fittig and Bieber). Bromoparaxylene, CcH3(CH3)2Br (1:4: 2), is prepared by the action of bromine on cooled paraxylene in the presence of iodine, and is also formed when bromine is allowed to act alone in the dark (Schramm). It is a liquid, which boils at 205'5°, and some- times solidifies when strongly cooled, but frequently remains liquid until a crystal of the solid compound has been added, when it forms plates or tablets, melting at + 9°? Dibromoparaxylene, C6H2(CH3)2Br2 (1:4 : 2 : 5), boils at 261°, and crystallizes from alcohol in large plates or flat needles, melting at 75'5°. When these are allowed to remain in the mother liquor they are converted into transparent, asymmetric crystals, which closely resemble regular octohedra (Jacobsen). It is converted into symmetric tetramethylbenzene by the action of sodium and methyl iodide.2 In addition to this compound, a liquid dibromoparaxylene, which boils at 260°-264° and solidifies in a freezing mixture, is formed in small quantity. A tribromoparaxylene was not formed when the necessary quantity of bromine was added, the following substance being obtained together with the preceding compounds : Tetrabromoparaxylene, C6(CH3)2Br4, is very slightly soluble in alcohol, and crystallizes from hot toluene in long, fine needles, melting at 253°. NITRO-SUBSTITUTION PRODUCTS OF THE XYLENES. 22ii v-Nitro-orthoxylene, CeH3(CH3)2NO2 (1:2 :3), is formed, together with the following compound, when orthoxylene is treated in a freezing mixture with concentrated nitric and sulphuric acids; it is a liquid, which boils at 245°-247°.3 a-Nitro-orthoxylene (1 : 2 :4) is almost the sole product when pure nitric acid is employed ; it crystallizes from alcohol in long, brittle, light yellow, lustrous prisms, melts at 290° and boils at 280°.4 1 Jannasch, Ann. Chern. Pharm. clxxi. 82 ; Jacobsen, Per. Deutsch. Chem. Ges. xviii. 356. 2 Jannasch, ibid. x. 1357. 3 Nolting and Forel, ibid, xviii. 2669. 4 Ibid. xvii. 159. 396 AROMATIC COMPOUNDS. Dinitro-orthoxylene, C6H2(CH3)2(NO2)2, is formed, together with the following compound when orthoxylene is heated for a considerable time to 100° with a mixture of nitric and sul- phuric acids. It crystallizes from boiling alcohol in long, lustrous needles, melting at 71°. Trinitro-orthoxylcne, C6H(CH3)2(NO2)3, forms white, lustrous scales, which melt at 178°, and are almost insoluble in alcohol.1 v-Nitrometaxylene, (1 : 3 : 2) is obtained by the action of nitric and sulphuric acids on metaxylene in the cold.2 It has been prepared pure from the corresponding nitrometaxylidine by the diazo-reaction.3 It is a liquid boiling at 225°. a-Nitrometarylene (1:3:4) is formed in the preparation of the preceding compound, and in preponderating amount when pure, well-cooled nitric acid is employed. It is a light yellow liquid, which boils at 238° and does not solidify at - 20°.4 s-Nitrometaxylene (1: 3 : 5) is obtained from nitro-a-metaxy- lidine by dissolving it in absolute alcohol, adding two molecules of sulphuric acid, and then treating the well-cooled liquid with twice the theoretical quantity of ethyl nitrite in order to prevent the formation of the diazo-amido-compound. Ihe liquid is heated to boiling after standin" for some time, the alcohol driven off and the remainder distilled with steam. s-Nitrometaxylene boils at 263°, and crystallizes from alcohol in large, flat needles, melting at 74°--750.5 s-Dinitrometaxylene, C6H2(CH3)2(NO2)2 (1 : 3 : 4 :6), is readily prepared by heating metaxylene with fuming nitric acid; it crystallizes from hot alcohol in large, flat, colourless needles or lustrous prisms, melting at 93°.6 v-Dinitrometaxylene (1 : 3 : 4 : 2) is formed together with its isomerides when xylene is nitrated at a low temperature with a mixture of nitric and sulphuric acids ; it is readily soluble in alcohol, and crystallizes in scale-like plates, melting at 83°.7 Trinitrometaxylene, C6H(CH3)2(NO2')3 (1 : 3 :2 : 4 : 6). This characteristic compound, which has been previously mentioned 1 Drossbach. Bcr. Deutsch. Chern. Ges. xix. 2156. 2 Nolting and Forel, Bcr. Deutsch. Chern. Ges. xviii. 2668. 3 Grevingk, ibid. xvii. 2430. 4 Tawildarow, Zeitschr. Chan. 1870, 418 ; Harmsen, Ber. Deutsch.Chem. Ges. xiii. 1558. 6 Wroblewsky, Ann. Chem. Pharm. ccvii. 91 ; Thol, Ber. Deutsch. Chem. Ges. xviii. 359 ; Nolting and Forel. 6 Fittig, Ann. Chan. Pharm. cxlvii. 16 ; cxlviii. 5. 7 Grevingk, Ber. Deutsch. Chem. Ges. xvii. 2422. NITROXYLENES. 397 (p. 387), is formed when metaxylene or the preceding compounds are heated with a mixture of nitric and sulphuric acids. It is scarcely soluble in cold, very slightly in boiling alcohol, and crystallizes in fine, flat, colourless needles, melting at 1760.1 Nitroparaxylene, C6H3(CH3)2NO2, is obtained by allowing the calculated quantity of fuming nitric acid to drop into well-cooled paraxylene. It is a yellow liquid, which boils at 239° and does not solidfy at - 20°.2 a-Dinitroporaxylene, C6H2(CH3)2(NO2)2 (1 : 4 : 2 :6), is formed, together with its isomerides, when paraxylene is dissolved in cold, fuming nitric acid. It crystallizes from alcohol in very thin, lustrous needles, melting at 124°, and is deposited from glacial acetic acid in long, broad needles. /3-Linitroparaxylene (1: 4 : 2 : 3) is more readily soluble in alcohol, and crystallizes on gradual evaporation in monoclinic tablets, which resemble crystals of calcspar, and melt at 93°.3 It is a characteristic property of these two nitroxylenes that equal molecules of them combine to form a double compound, which can be crystallized from glacial acetic acid, but is de- composed by alcohol into its constituents.4 It forms transparent monoclinic prisms with sphenoid faces, and melts at 99'5°. y-Dinitroparaxylene (1:4:2:5) is slightly soluble in cold, more readily in hot alcohol, and forms long, yellow needles with a vitreous lustre, which melt at 147°-148°.5 Lellmann determined the constitutions of these three isomerides by the methods already described (Part III., p. 245); the first two, which are formed in largest quantity, were converted into the hydrochlorides of the corresponding diamines, their solutions evaporated with ammonium thiocyanate, and the residues heated to 120°, ground up with water, washed, dissolved in caustic soda, and these solutions heated with lead acetate. The a-compound gave a precipitate of lead sulphide while the /3-compound did not, and was thus proved to be an orthodiamine. He then prepared the free a-diamidoparaxylene, which is a crystalline mass, and combines with allyl mustard oil to form the compound C6H2(CH3)2(NH.CS.NH.C3H5)2, which crystallizes in 1 Luhmann, Ann. Chem. Pharm. cxliv. 276 ; Fittig, loc. cit. ; Grevingk, loc cit. 2 Jannasch, Ann. Chem. Pharm. clxxvi. 55 ; Nolting and Forel, loc. cit. 3 Fittig and Glinzer, Ann. Chem. Pharm. cxxxvi. 307 ; Fittig, Ahrens and Mattheides, ibid, cxlvii. 17. 4 Jannasch and Stiinkel, Bcr. Deutsch. Chem. Ges. xiv. 1146. 6 Lellmann, Ann. Chem. Pharm. ccxxviii. 250. 398 AROMATIC COMPOUNDS. small needles, melting without decomposition at 112'5°. It is therefore a metadiamine, and the 7-compound must, accordingly, contain the nitroxyl groups in the para-position. Trinitroparaxylene, C6H(CH3)2(NO2)3 (1 : 4 : 2 :3 :5), may readily be prepared by nitrating with a mixture of nitric and sulphuric acids, the whole being gently heated at the close of the operation. It crystallizes from alcohol in stellate aggregates of dazzling white needles, which melt at 139°-14O0.1 XYLENESULPHONIC ACIDS, C6H3(CH3)2SO3H. * V O' O/ O 2212 Orthoxylenesulphonic acid (1:2:4) is formed by dis- solving orthoxylene in tolerably hot sulphuric acid. It crystal- lizes from a somewhat dilute acid solution with two molecules of water in long, rectangular tablets or thicker, flat prisms with pointed ends. Its salts crystallize extremely well. "When its potassium salt is heated with sodium formate, paraxylic acid is foimed. Sodium orthoxylenesulphonate, CGH2(CH3)2SO3Na + 5H2O, separates from a concentrated solution in flat prisms, the size of which seems only to be limited by that of the containing vessel; they soon effloresce on exposure to the air. Orthoxyleneszdphonic chloride, C6H3(CH3)2SO2C1, crystallizes from ether in prisms, melting at 51°-52°. Orthoxylenesulphonamide, C6H3(CH3)2SO2.NH2, separates from hot alcohol in prisms, which melt at 1440.2 a-Mctaxylcncsulphonic acid (1:3:4) is formed, together with a small quantity of the isomeric compound, when metaxylene is dissolved in sulphuric acid. It separates on the addition of a little water in large plates or prisms, which contain two molecules of water. Xylic acid is formed when potassium salt is heated with sodium formate (p. 391). Sodium metaxylenesulphonate, C6H3(CH3)2SO3Na, crystallizes from water in scales, and from alcohol in small plates possessing a silver lustre. a-Metaxylenesulphonic chloride solidifies in the cold to a radiating mass, or to prisms which melt at 34°. 1 Fittig and Glinzer; Nolting and Geissmann, Ber. Deutseh. Chern. Ges. xix. 144. 2 Jacobsen, ibid. x. 1010 ; xi. 22. XYLENOLS. 399 a-Metaxylenesulphamide crystallizes from water in long pointed needles and melts at 137°. v-Metaxylenesulphonic acid (1:3:2) has not been prepared pure; its calcium salt when heated with sodium formate yields a xylic acid, which decomposes on distillation with lime into carbon dioxide and metaxylene. Its chloride is an oily liquid, and the amide crystallizes in needles, melting at 95°-96.1 Paraxylencsulphonic acid is formed when paraxylene is dis- solved at a gentle heat in slightly fuming sulphuric acid. It crystallizes with two molecules of water in large plates or very long, flat prisms. Sodium paraxylenesulphonate, C6H3(CH3)2SO3Na + H2O, crys- tallizes in large, flat, striated prisms, which do not effloresce in the air. Paraxylencsulphonic chloride forms flat prisms, which melt at 24°-26° Paraxylenesulphamide is readily soluble in alcohol, slightly in boiling water, from which it crystallizes in splendid, long needles, melting at 147°-148° (Jacobsen). HYDROXY-XYLENES, OR XYLENOLS, C6H3(CH3)2OH. 2213 After Dusart, Kekule and Wurtz had shown that sulphonic acids are converted into phenols by fusion with potash, the last-named of these chemists applied the reaction to xylene, and discovered the interesting fact that this hydrocarbon yields two isomeric phenols, a solid and a . liquid xylenol. This iso- merism is explained by him as due to the different positions of the hydroxyl with relation to the two methyl groups. " This isomerism," he adds, "could, according to Kekule's beautiful theory, also exist in xylene itself, as a result of a different arrangement of the side chains in the nucleus."2 After this supposition had been proved correct and these xylenes were known, it was seen that six xylenols must exist, and these have all now been prepared. Jacobsen obtained four of them from 1 Jacobsen, Ann. Chern. Pharm. clxxxiv. 188 ; loc. cit. 2 Ann. Chem. Pharm. cxlvii. 372 ; see also Wroblewsky, Zeitschr. Chern. 1868, 232. 400 AROMATIC COMPOUNDS. the sulphonic acids just described,1 and the two others have been prepared from the xylidines by means of the diazo-reaction.2 Like ordinary phenol, they readily form tribromo-derivatives. The xylenols also occur in coal-tar. They have not, in- deed been isolated, but their derivatives have been prepared from it. The tar obtained as a by-product from blast furnaces which are worked with coal seems to be especially rich in xylenols; the creosote oil fraction, boiling at 210°-240°, when distilled over heated zinc dust, yielded a mixture of hydrocarbons, which consisted chiefly of metaxylene.3 a-Orthoxylenol (1:2:4) crystallizes from hot water in very long needles and from very dilute alcohol in rhombic pyramids, melting at 62'5°;4 it boils at 225° and forms an aqueous solution which is not coloured by ferric chloride. a-Tribromorthoxylenol, C6Br3(CH3)2OH, crystallizes from alcohol in fine, snow-white, matted needles, melting at 169°. v-Orthoxylenol (1:2:3) crystallizes from water in white needles, melts at 75° and boils at 218°; its aqueous solution is coloured blue by ferric chloride, but is not affected by bleaching-powder solution. a-Mctaxylenol (1:3:4) is, according to Jacobsen, a strongly refractive liquid, which smells like phenol, boils at 211'5° and becomes viscid at -20°, without, however, solidifying. These are also the properties of the liquid xylenol discovered by Wurtz, while Stadel and Holz showed that the xylenol prepared from pure a-metaxylidine solidifies at the ordinary temperature.6 Jacobsen, on reinvestigation, found that his preparation crystal- lized after repeated cooling or on the addition of a small crystal.6 It forms white needles, melting at 26°. It dissolves slightly in water, yielding a solution which is coloured blue by ferric chloride; the alcoholic solution, on the other hand, is coloured a splendid dark green, which passes into blue when water is added. a-Metaxylenyl methyl ether, C6H3(CH3)2OCH3, is a liquid which has a faint smell resembling that of benzene, and boils at 192°. 1 Ber. Deutsch. Chern. Ges. xi. 23. 2 Thol, ibid, xviii. 359, 2561 ; Nolting and Forel, ibid, xviii. 2668. 3 Smith, Coutts and Brothers, Journ. Chem. Soc. 1886, i. 17. 4 Jacobsen, Ber. Deutsch. Chem. Ges. xvii. 161. 5 Ber. Deutsch. Chem. Ges. xviii. 2921. 6 Ibid, xviii. 3463. PARA XYLENOL. 401 a-Mctaxylenyl acetate, C6H3(CH3)2O.CO.CH3, is a liquid boiling at 226°, which has a faint odour of oil of bergamot. Melting-point. a-Bromometaxylenol, C8H8Br.OH, oily liquid ... - a-Dibromometaxylenol, C8H7Br2.OH, fine, colourless ) ^$0 needles ) a-Tribromometaxylenol, C8H6Br3.OH, long, colourless ) wqo needles j v-Metaxylenol (1:3 : 2) crystallizes in silky plates or long, flat needles, melts at 74'5°, boils at 211°-212°, and gives no colouration with ferric chloride. v-Tribromometaxylenol crystallizes from hot alcohol in long, light yellow needles, melting at 175°. s-Metaxylenol (1:3: 5) is deposited from solution in hot water or from sublimation in splendid white needles, melting at 68°. It boils at 219'5°, and gives no colouration with ferric chloride. s-Tribromometaxylenol crystallizes from alcohol or benzene in fine, white needles, melting at 166°. Paraxylenol (1 : 4 : 2) has been prepared from paraxylidine ;1 it melts at 74'5°, sublimes in needles at a slightly higher temperature, boils at 211'5° and crystallizes from hot water or very dilute alcohol in large, flat needles. It gives no colouration with ferric chloride. The solid compound prepared by Wurtz was almost pure paraxylenol. Melting-point. Monobromoparaxylenol, C8H8Br.OH, colourless, flex- ) $70 ible needles ) Tribromoparaxylenol, C8H6Br3.OH, deep golden) yellow needles J The great similarity existing between para- and v-meta- xylenol is somewhat remarkable (Jacobsen). A xylenol occurs in crude creosote, which boils at 220°, does not crystallize, and on heating with potash and methyl iodide yields a methyl ether, boiling at 200°.2 This substance is pro- bably a mixture, and, from its high boiling-point, would seem to consist chiefly of a-orthoxylenol.3 1 Nolting, Witt and Forel, Ber. Deutsch. Chern. Ges. xviii. 2664. 2 Marasse, Ann. Chem. Pharm. clii. 75 ; Tiemann and Mendelsohn, Ber, Deutsch. Chem. Ges. x. 57. 3 Nolting, Witt and Forel, ibid, xviii. 2664. 402 AROMATIC COMPOUNDS. Robiquet, by the distillation of aloes with lime, obtained a liquid which he called alo'isol. This substance has been shown by Rembold to be a mixture, the portion soluble in alkalis having the composition of a xylenol.1 DIHYDROXY-XYLE N E S, C6H2(CH3)2(OH)2. 2214 Homorcinol, or Paraxylorcinol (1:4 :2 : 6), was obtained by Stenhouse from Usnca barbata and Cladonia rangiferina and named by him /3-orcin,2 a name which was subsequently changed by him and Groves into beta-orcinol. It is a decom- position product of the barbatic acid, C19H20O7, which occurs in these lichens.3 Lamparter has succeeded in obtaining it, together with orcinol, from Bocella fuciformis.^ Its constitution was determined by Kostanecki, who prepared it from a-nitroparaxylidine, by first converting it into nitroxylenol, reducing this to amidoxylenol, and finally passing from this to paraxylorcinol by means of the diazo-reaction.5 It is less soluble in water than orcinol, and is deposited in quadratic crystals, melting at 163°. It possesses a slightly sweet taste, boils at 277°-280°, and is coloured red by ammonia in presence of air more rapidly than orcinol. Its aqueous solution gives with ferric chloride a light carmine-red colouration, quite distinct from the purple-red produced with orcinol. Like the latter it yields a red solution with a beautiful green fluorescence when heated with chloroform and caustic soda (Kostanecki). Nitrosoparaxylorcinol, C6H(CH3)2(OH)O(NOH), is formed by the action of nitrosy 1 sulphate (Part III. p. 171) on an aqueous solution of paraxylorcinol, as a lustrous, orange-red precipitate, which crystallizes from glacial acetic acid in small, lustrous, red prisms. Metaxylorcinol (1: 3 : 4 :6) is obtained from s-nitro-a-meta- xylidine. It is readily soluble in water, has an acid taste, melts at 125° and boils at 276°-279°. It crystallizes from chloroform in brilliant white, monosymmetric plates, which can also be obtained by sublimation. No red colouration is produced by exposure to ammonia and air.6 1 Ann. Chern. Pharm. cxxxviii. 186. 2 Phil. Trans. 1848, 63. 3 Ibid, cciii. 285. 4 Ibid, cxxxiv. 243. 5 Ber. Deutsch. Chem. Ges. xix. 2318. 6 Pfaff, ibid. xvi. 611 and 1135 ; Kostanecki, loc. cit. TRIHYDROXY-XYLENES. 403 Gundelach, by heating chlorometaxylenesulphonic acid to 230°-250° with caustic potash, obtained a dihydroxy-xylene which should be identical with metaxylorcinol, since, according to Jacobsen, the side chains of the sulphonic acid have the following arrangement: CH3: CH3: Cl: SO3H = 1 : 3 :4 : 6.1 It crystallizes in microscopic prisms, which are tolerably soluble in water, melt at 120° and are coloured deep red by ammoniacal air.2 This compound is probably impure metaxylorcinol. The following dihydroxy-xylenes have been prepared by the reduction of the xyloquinones: Paraxyloquinol, or Hydrophlorone (1 :4 : 2 : 5), is readily soluble in alcohol, slightly in boiling water and benzene, and crystallizes in nacreous plates or tablets, which melt at 210° and sublime in long needles. It reduces silver solution and is re-oxidized to the quinone by ferric chloride. The diethyl ether, C8H8(OC2H5)2, is formed by heating it with ethyl bromide and caustic potash; it forms lustrous plates, which melt at 105°-106°, and have an odour resembling that of peppermint (Stiidel and Holz). Metaxyloquinol (1 : 3 : 2 : 5) sublimes in needles and melts at 149°. Orthoxyloquinol (1: 2 :3 : 6) crystallizes from water in crusts, which melt at 221° with decomposition. TRIHYDROXY-XYLENES. 2215 Trihydroxy metaxylene, C6H(CH3)2(OH)3, is formed by the reduction of hydroxymetaxyloquinone (p. 404) with sulphurous acid. It is tolerably soluble in cold, readily in hot water, and crystallizes in colourless or yellowish transparent tablets, con- taining a molecule of water, which is lost at 80°, the anhydrous compound melting at 121°-122°. It is reduced to metaxylene when heated with zinc-dust. Oxidizing agents readily convert it into the quinone ; if the aqueous solution be merely allowed to evaporate in the air, the quinhydrone crystallizes out in long needles resembling those of potassium permanganate. Triacetoxy metaxylene, C6H(CH3)2(O.CO.CH3)3, is obtained by the action of acetyl chloride, and crystallizes from alcohol in colourless, lustrous prisms, which melt at 99°, and sublime without decomposition when carefully heated. 1 Ber. Deutsch. Chem. Ges. xviii. 1762. 2 Bull. Soc. Chim. xxviii. 343. 404 AROMATIC COMPOUNDS. THE XYLOQUINONES, C6H2(CH3)2O2. 2216 Paraxyloquinone, (1:4:2: 5). Rommier and Bouilhon, by oxidizing the fraction of crude cresol boiling between 195°- 220° with sulphuric acid and manganese dioxide, obtained two isomeric quinones, C8H8O2, and gave to the one, which is formed in largei' quantity and melts at 60°-62°, the name of phlorone, and to the other, melting at 125°, that of metaphlorone.1 Accord- ing to Gorup-Besanez and v. Rad, phlorone is also formed by the oxidation of wood-tar creosote.2 Nietzki then obtained para- xyloquinone by the oxidation of crude xylidine and of paradi- amidoxylene with potassium dichromate and sulphuric acid, and found that its properties agree with those of metaphlorone ;3 Carstanjen then showed that phlorone is a mixture of toluquinone with paraxyloquinone, and that the latter yields paraxylene on heating with zinc-dust.4 It is best prepared from paraxylidine in the same way as benzoquinone from aniline.5 Paraxyloquinone is only slightly soluble in water and cold alcohol; it crystallizes from hot alcohol in splendid golden- yellow needles, which melt at 123'5° and readily sublime. Orthoxyloquinone (1: 2 : 3 :6) has been prepared from v-ortho- xylidine by oxidation; it is slightly soluble in water, more readily in alcohol, and sublimes in yellow needles, which melt at 55°. Metaxyloquinone (1 :3 : 2 : 5) is formed by the oxidation of v- and s-metaxylidine, and crystallizes in splendid yellow needles, melting at 73°. Hydroxymetaxyloquinone, C6H(CH3)2(OH)O2, is formed when diamidomesitylene, C6H(CH3)3(NH2)2, is distilled with potassium dichromate and dilute sulphuric acid. It crystallizes from hot water or ether in orange-red needles, has a characteristic smell resembling that of benzoquinone, melts at 103°, and sublimes very readily in splendid, lustrous, deep golden-yellow needles. Its aqueous solution is instantly coloured a splendid reddish violet by the addition of any alkaline substance, and this reaction is so delicate that the slightest traces of the quinone 1 Compt. Rend. Iv. 214. 2 Zeitschr. Chem. [2] iv. 560 ; Ann. Chern. Pharm. cli. 158. 3 Ber. Deutsch. Chem. Ges. xiii. 470. 4 Journ. Prakt. Chem. [2] xxiii. 421. 5 Nolting and Forel, Ber. Deutsch. Chem. Ges. xviii. 2668. AMIDOXYLENES. 405 can be detected by it. Insoluble carbonates also produce this colouration; thus, if a 0T per cent, solution of the quinone be shaken up with calcium carbonate, the colouration produced is so deep that even a thin layer of the liquid appears quite opaque. The presence of calcium carbonate can thus be shown in very small quantities of mineral waters ; free carbonic acid does not affect the colouration, so that the quinone forms a valuable indicator for alkalimetry. It forms salts, which readily decompose on warming or on exposure to the air in presence of an excess of the base. The potassium salt, CSH7(OK)O2, crystallizes from hot alcohol in small, black needles, 1 mgrm. of which is sufficient to impart a deep red colour to a litre of water.1 AMIDO-DERIVATIVES OF THE XYLENES. The Amidoxylenes, or Xylidines, C6H3(CH3)2NH2. 2217 Cahours gave the name of xylidine to the homologue of toluidine and aniline which he obtained from his xylene (p. 386), by nitrating it and submitting the nitroxylene formed to reduc- tion. This, substance and the xylidine obtained by Church in the same manner was obviously a mixture of toluidines and xylidines, while that prepared by Deumelandt from xylene boiling at 140° consisted chiefly of a-metaxylidine, as was also the case with that prepared by Hofmann and Martins by heating paratoluidine hydrochloride to 300° with methyl alcohol. It only became possible to obtain the six xylidines after the three xylenes had been obtained in the pure condition and the six nitroxylenes prepared from these. A mixture of them is manu- factured on the large scale from tar-xylene, and the purity and composition of commercial xylidine is therefore dependent on that of the latter. Specimens now come into the market containing as much as 25 per cent, of paraxylidine in addition to ordinary metaxylidine.2 The commercial product is employed in the manufacture of azo-colours and of the cumidines, C6H2(CH3)3NH2, which are obtained by heating the hydrochlorides with wood-spirit. 1 Fittig and Siepermann, Ann. Chem. Pharm. clxxx. 27. 2 Nolting, Witt and Forel, Bar. Deutsch. Chem, Ges. xviii. 2664 ; Stadeland Holz, ibid, xviii. 2919. 406 AROMATIC COMPOUNDS. v-Orthoxylidine (1:2: 3) is formed when solid dibromortho- xylene is nitrated, the nitrodibromorthoxylene reduced to dibromo- xylidine, and the bromine removed by treatment with sodium amalgam and water.1 It is a liquid which boils at 223°; its hydrochloride is tolerably soluble in water, and crystallizes in white needles, containing a molecule of water. The sulphate is only slightly soluble. v-Acdorthoxylide, C6H3(CH3)2NH(CO.CII3), crystallizes from hot benzene in white needles, melting at 134°.2 a-Orthoxylidine, (1:2:4) melts at 49° and boils at 226°. It is tolerably soluble in hot water, readily in alcohol, and crystal- lizes when caused to solidify quickly or when rapidly deposited from solution, in transparent, vitreous tablets, while it may be obtained by the gradual evaporation of its petroleum-ether solution in thick, monoclinic crystals. Its aqueous solution is not coloured by bleaching powder; the solutions of its salts colour pine-wood an intense yellow. The hydrochloride is readily soluble in water, but only slightly in hydrochloric acid, and crystallizes with one molecule of water in long, very thin prisms. a-Acdorthoxylide crystallizes from hot water containing a little alcohol in long, thin, vitreous prisms, which melt at 99°. The base is converted by the diazo-reaction into a-ortho- xylenol.3 v-Mdaxylidine (1:3:2) was first obtained by Schmitz by heating /3-amidomesitylenic acid, C6H2(CH3)2(NH2)CO2H, with lime.4 Grevingk,5 and Nolting and Forel,6 then prepared it from v-nitrometaxylene. It is a liquid boiling at 214°. Its hydrochloride crystallizes in thin, anhydrous, monoclinic plates, which are readily soluble in water. v-Acetmetaxylide crystallizes from benzene in white needles, which melt at 176 8°. It is not attacked by caustic potash solution, sulphuric acid, or hydrochloric acid, on heating in an open vessel, but is decomposed by the last of these at 150°. a-Metaxylidine (1:3:4) has been known for a longer period than any of its isomerides and is therefore also called ordinary metaxylidine. It is formed by the distillation of a-amidomesity- lenic acid with lime (Schmitz) and by the reduction of a-nitro- 1 Thol, Ber. Deutsch. Chem. Ges. xviii. 2561 ; Wroblewsky, ibid, xviii. 2904. xix. 235 ; Jacobsen, ibid, xviii. 3166. 2 Nolting and Forel, ibid, xviii. 2668. 3 Jacobsen, ibid. xvii. 159. 4 Ann. Chem. Pharm. cxciii. 377. 5 Ber. Deutsch. Chem. Ges. xvii. 2422. 6 Ibid xviii. 2676. XYLIDINES. 407 metaxylene.1 It may also be readily obtained from commercial xylidine by converting this into the hydrochloride and purifying by re-crystallization. In order to obtain it perfectly pure, the acet- xylide is prepared, purified by re-crystallization, and decomposed with sulphuric acid. The other xylidine can also be easily obtained pure in this way. It is a liquid boiling at 212°. The hydrochloride is only slightly soluble in cold water, and crystallizes in anhydrous, rhombic tablets; the hydrobromide crystallizes even better, forming splendid prisms (Stadel and Holz). a-Acetmetaxylide crystallizes from benzene in white needles melting at 129°; impurities cause a considerable lowering of the melting-point. s-Metaxylidine (1:3:5) is obtained by the reduction of the corresponding nitroxylene ;2 it is a liquid boiling at 220°. Its hydrochloride and nitrate crystallize in large, anhydrous needles; 4'66 parts of the latter dissolve in 100 parts of water at 13°. s-Acetmetaxylide crystallizes from alcohol in large, flat needles, melting at 140'5°. Paraxylidine (1 :4 : 2) may be prepared in the usual way by the reduction of nitroparaxylene,3 and also from commercial xylidine; the latter is run into fuming sulphuric acid containing sufficient trioxide to convert the bases into sulphonic acids, the mixture being well stirred and then heated on the water-bath. The solution is allowed to cool and the solid mass pressed under water to separate the metaxylidinesulphonic acid in the crystalline state. The sodium salt of paraxylidinesulphonic acid is then prepared from the mother-liquor by neutralizing it with lime, filtering, removing the calcium with carbonate of soda, and concentrating the filtrate. It separates in splendid, nacreous plates, which are freed from any adhering traces of the readily soluble salt of the metaxylidinesulphonic acid by washing with a little cold water. Pure paraxylidine is then obtained by the dry distillation of the salt.4 It is a liquid boiling at 215°; its hydrochloride and nitrate crystallize in flat needles or large tablets, and the sulphate, which is only slightly soluble, forms small plates. Acetparaxylide crystallizes from hot water or toluene in long lustrous needles, melting at 139°. 1 Tawildarow, Zeitschr. Chem. 1870, 418 ; Nolting and Forel, loc. cit. 2 Wroblewsky, Ann. Chem. Pharm. ccvii. 95 ; Thol, Per. Deiitsch. Chem. Ges. xviii. 359 ; Nolting and Forel, loc. cit. 3 Schaumann, Ber. Deutsch. Chem. Ges. xi. 1537 ; Nolting and Forel, ibid. xviii. 2680. 4 Nolting, Witt and Forel, xviii. 2664. 408 AROMATIC COMPOUNDS. NITROXYLIDINES, C6H2(CH3)2(NH2)2NO2. 2218 s-Nitro-a-mdaxylidine (1 : 3 : 4 : 6) is formed by the reduction of s-dinitrometaxylene with ammonium sulphide, and crystallizes from hot water or alcohol in orange-red needles, while it separates on the gradual evaporation of its alcoholic solution in thick, deep red crystals, which melt at 1230.1 v-Nitro-a-metaxy Udine (1: 3 : 4 : 2) has also been prepared from v-dinitrometaxylene, and forms golden-yellow needles, which melt at 78°.2 a-Nitro-a-metaxylidine (1:3:4: 5). In order to prepare this compound, a-acetmetaxylide is treated with concentrated nitric acid in the cold, and the product decomposed by heating with sulphuric acid, diluted with half its volume of water. It crystallizes from alcohol in long, red needles, which melt at 76°.3 A small quantity of s-nitro-a-metaxylidine is formed at the same time (Nolting and Forel). a-Nitro-s-mdaxyUdine (1 :3 : 5 : 4) is obtained by the nitration of s-metaxylidine with a mixture of nitric and sulphuric acids; it crystallizes in yellow needles, which melt at 54°, and readily volatilize with steam (Nolting and Forel). a-Nitroparaxylidine (1 : 4 : 2 :6) has been prepared by the reduction of a-dinitroparaxylene with ammonium sulphide, and crystallizes from alcohol in long, golden-yellow needles, melting at 960.4 ^-NitroparaxyUdine has not yet been obtained, as the cor- responding dinitroparaxylene is immediately reduced to the diamine by ammonium sulphide. y-NitroparaxyUdine (1: 4 : 2 : 5) is formed by the nitration of paraxylidine with a mixture of sulphuric and nitric acids, and forms brownish yellow, lustrous crystals, which are readily soluble in alcohol and melt at 142°.5 Dinitroparaxylidinc, C6H(CH3)2(NO2)2NH2 (5:2: 3), is ob- tained by the long-continued heating of trinitro paraxylene with 1 Fittig, Ahrens and Mattheides, Ann. Chem. Pharm. cxlvii. 18. 2 Grevingk, Ber. Deutsch. Chern. Ges. xvii. 2425. 3 Hofmann, ibid. ix. 1295 ; Wroblewsky, Ann. Chem. Pharm. ccvii. 91 ; Thbl, Ber. Deutsch. Chern. Ges. xviii. 359 ; Nolting and Forel, ibid, xviii. 2677. 4 Fittig, Ahrens and Mattheides, Ann. Chem. Pharm. cxlvii. 22. 6 Nolting, Witt and Forel, Ber. Deutsch. Chem. Ges. xviii. 2664. DIAMIDO XYLENES. 409 alcoholic ammonia. It crystallizes from glacial acetic acid in yellow needles, which melt at 202°-203°, and are converted by the diazo-reaction into a-dinitroparaxylene.1 DIAMINES AND TRIAMINES OF THE XYLENES, C6H2(CH3)2(NH2)2. 2219 a-Diamidometaxyknc, C6H2(CH3)2 (NH2)2 (1 : 3 : 4 : 5), is formed by the reduction of a-nitro-a-metaxylidine,2 and amido- azo-a-metaxylene.3 It crystallizes from hot benzene in small, white plates, which melt at 77°-78°, and are readily soluble in alcohol. s-Diamidometaxykvie (1: 3 : 4 : 6) has been prepared from s-dinitrometaxylene and the corresponding nitroxylidene; it sublimes in white crystals, melting at 104°. v-Diamidometaxykne (1 : 3 : 4 : 2) sublimes in white needles and melts at 64°. Nitrodiamidometaxykne, C6H(CH3)2(NH2)2NO2, is formed by the reduction of trinitrometaxylene with ammonium sulphide and was first described by Bussenius and Eisenstuck as nitro- petroldiamine (p. 387). It is slightly soluble in cold, more readily in boiling water and readily in alcohol, from which it crystallizes in lustrous, ruby-red prisms, an inch in length, which melt at 212°-213°.4 Triamidometaxykne, C6H(CH3)2(NH2)3 (1 : 3 : 2 :4 : 6), has been obtained by reducing trinitrometaxylene with hydrochloric acid and stannous chloride; it crystallizes in white needles, which decompose at about 140° without melting. Diamidometaxylene contains the amido-groups in the ortho- position, and gives all the characteristic reactions of the ortho- diamines (Nolting and Forel); the two other diamidometa- xylenes are metadiamines, and therefore yield azo-dyes when their hydrochlorides are treated with sodium nitrite, as does also triamidometaxylene. The colour prepared from v-diamido- metaxylene dyes silk reddish brown, that from s-diamidometa- xylene, yellowish brown, while the derivative of the triamine 1 Nolting and Geissmann, Ber. Deutsch. Chem. Ges. xix. 144. 2 Hofmann, ibid. ix. 1298. 3 Nolting and Forel, ibid, xviii. 2683. 4 Fittig and Velguth, Ann. Chern. Pharm. cxlviii. 6. 410 AROMATIC COMPOUNDS. produces a grey shade of olive. With diazobenzenesulphonic acid, on the other hand, the v-diamine gives a light yellowish red colouring matter, while that from the s-diamine is darker and that from the triamine a dark, red-black. The shades produced on silk, however, are in the inverse relation ; the lightest coloured dye gives the darkest shade, then follows that of the s-diamine, while the substance prepared from the triamine dyes an almost pure golden yellow.1 a-Diamidoparaxylene, C6H2(CH3)2(NH2)2 (1:4 :2 :6), sublimes in white needles, melting at 101'5°-102'5°; its hydrochloride gives a brown colouring matter with sodium nitrite; it forms chrysoidines with diazo-salts and a dye analogous to toluylene- blue (p. 82) with nitrosodimethylaniline. ^-Diamidoparaxylene (1 :4 : 2 : 3) sublimes in small needles, melting at 75°; sodium nitrite, added to the solution of its hydrochloride, precipitates an azimido-compound (Part III. p. 270),2 while ferric chloride produces a deep red colouration. y-Diamidoparaxylene (1 : 4 : 2 : 5). Nietzki prepared this com- pound by the action of zinc and hydrochloric acid on the amido- azoxylene, C6H3(CH3)2.N2.C6H2(CH3)2NH2, prepared from com- mercial xylidine.3 Nolting and Forel then obtained it from amido-azoparaxylene, and showed that Nietzki's compound consists of amido-azometaparaxylene.4 It is also formed by the reduction of 7-nitroparaxylidine. It is slightly soluble in cold, readily in hot water and alcohol, but less readily in benzene, from which it crystallizes in white needles, melting at 146'5°- 147°. It yields paraxyloquinone on oxidation. XYLYL COMPOUNDS. 2220 When an atom of hydrogen in the methyl group of one of the xylenes is replaced by another element or radical, com- pounds of the monovalent radical xylyl, CH3.C6H4.CH2, are ob- tained ; this radical has also been called tolyl, because the monobasic acids, CH3.C6H4.CO2H, which correspond to the xylyl alcohols, CH3.C6H4.CH2.OH, and which decompose into toluene and carbon dioxide when heated with lime, have received 1 Grevingk, Ber. Deutsch. Chem. Ges. xvii. 2442. 2 Nolting and Geissmann, ibid. xix. 144. 3 Ibid. xiii. 470. 4 Ibid, xviii. 2685. XYLYL COMPOUNDS. 411 the name of toluic acids. The term tolyl has, however, been also applied to the group C7H7, and it is therefore preferable to designate the derivatives of the xylenes as xylyl compounds.1 The use of this term is open to the objection that the acids, (CH3)2C6H3.CO2H, are called xylic acids, because they stand to xylene in the same relation as the toluic acids to toluene and benzoic acid to benzene.2 In order to avoid this confusion of terms, it has been proposed to give the name of tolyl to the group CH3.C6H4 and to desig- nate the xylyl alcohols according to Kolbe's nomenclature as tolyl carbinols,3 the toluic acids being called tolylformic acids. In the sequel, however, the names which are in general use will be retained. Chlorine acts upon boiling xylene in the same way as on toluene, substitution taking place in the methyl group. The first xylyl-compounds were obtained from tar-xylene, but they have now been prepared from the pure hydrocarbons.4 Bromine acts on the xylenes at the boiling-point in a similar manner;5 an energetic reaction also takes places in the sunlight, O 1 O' the first product consisting of a mixture of xylyl bromides.6 XYLYL ALCOHOLS, CH3.C6H4.CH2.OH. Orthoxylyl alcohol was prepared by Raymann by the action of sodium amalgam and water on orthotolualdehyde, which he had prepared from the chloride. It is slightly soluble in water, readily in alcohol, and crystallizes in needles, melting at 54°. According to Colson, who prepared it by heating the bromide with water, it melts at 34 2° and boils at 217°.7 Metaxylyl alcohol has been obtained both from the acetate and bromide ; it is a liquid, which boils at 215° and has a faint odour. Mctaxylyl ethyl ether, CH3.C6H4.CH2.O.C2H5, is a liquid and boils at 202°. 1 Jahresb. Chern. 1866, 605. 2 Kekule, Ann. Chem. Pharm. cxxxvii. 186. 3 Beilstein, Org. Chem. 1084. 4 Raymann, Bull. Soc. Chim. xxvi. 532 ; xxvii. 498 ; Gundelach, ibid. xxvi. 43. s Radziszewski and Wispek, Ber. Deutsch.Chem. Ges. xv. 1743 ; xviii. 1279. 6 Schramm, ibid, xviii. 1272. 7 Colson, Bull. Soc. Chim. xliii. 6 ; Ann. Chim. Phys. [6] vi. 115. 412 AROMATIC COMPOUNDS. Mctaxylyl acetate, CH3.C6H4 CH2O.CO.CH3, was prepared by Volrath by heating the chloride obtained from tar-xylene with silver acetate.1 Radziszewski and Wispek then prepared it from the pure bromide. It is a liquid which boils at 226° and possesses an aromatic odour resembling that of apples. Paraxylyl alcohol was obtained by Cannizzaro from paratolu- aldehyde by the action of alcoholic potash, and was named toluenyl alcohol. It crystallizes in white needles, and is slightly soluble in cold, more readily in hot water, from which it sepa- rates in oily drops which solidify to fine needles, melting at 58'5°-59'5° and boiling at 217°. Hydrochloric acid converts it into the liquid chloride.2 Paraxylyl ethyl ether is a liquid which has a similar smell to benzyl alcohol and boils at 203° (Radziszewski and Wispek). Xylyl chlorides, CH3.C6H4.CH2C1. These compounds are colour- less liquids. Orthoxylyl chloride Metaxylyl chloride Melting- point. Boiling- point. 197°-199° 195°-196° Xylyl bromides, CH3.C6H4.CH2Br. Orthoxylyl bromide, rhombic prisms 21° 216°-217° Metaxylyl bromide, liquid .... - 212° -215° Paraxylyl bromide, long needles . . 35'5 218°-220° XYLYLAMINES. These have been prepared by heating the xylyl chloride from tar-xylene with ammonia,3 and are therefore more or less pure meta-compounds. Monoxylylamine, CH3.CJd4.CH2.NH2, is an oily, alkaline liquid which boils at 196° and smells strongly of herring brine; its hydrochloride is readily soluble in water and alcohol, and crystallizes in needles. Dixylylamine, (CH3.C6H4.CH2')2NH, is a similar liquid, which decomposes above 210°; its hydrochloride forms white needles, which are only slightly soluble in cold, readily in hot water and alcohol. 1 Ann. Chern. Pharm. cxliv. 261. 2 Ibid, cxxiv. 252. 3 Jannasch, ibid, cxlii. 303 ; Pieper, ibid. cli. 129. THE TOLUALDEHYDES. 413 Trixylylamine, (CH3.C6H4.CH2)3N, is a thick, colourless oil, which has a characteristic odour and a faint alkaline reaction. The hydrochloride crystallizes in loose groups of needles, which are insoluble in water, but slightly soluble in cold and readily in hot alcohol. It decomposes into xylyl chloride and dixylyl- amine hydrochloride when heated in a current of hydrochloric acid gas. THE TOLUALDEHYDES. 222i Chromy 1 chloride combines with the xylenes, as with benzene and toluene, to form compounds which are decomposed by water with formation of the tolualdehydes.1 3CH8.C6H4CH(OCrCl2.OH)2+3H2O = 3CH3.C6H4.CHO + 2CrO3+Cr2(OH)6 + 6HC1. Orthotohtaldehyde vas first prepared by boiling orthoxylyl chloride with water and lead nitrate ; it is a yellowish, strongly refractive liquid, which smells like benzaldehyde and boils at 200°.2 Metatolualdehyde has been obtained in a similar manner from metaxylyl chloride;3 it possesses a similar smell and boils at 199°. It combines with phenylhydrazine to form metaxyli- denehy dr azine, CH3.C6H4.CH.N2H.C6H5, which crystallizes from alcohol in thick, yellow prisms, melting at 91°. Orthonitrometatolualdehyde, CH3.C6H3(NO9)CHO, is formed when the aldehyde is allowed to drop into a cold mixture of nitric and sulphuric acids. It is a yellowish liquid, volatile with steam, and is converted into methylindigo when warmed with caustic soda and acetone.4 Paratolualdehyde was prepared by Cannizzaro by the distilla- tion of a mixture of calcium formate and calcium paratoluate, and is a liquid which boils at 204° and possesses a smell re- sembling that of peppermint.5 1 Etard, Ann. Chim. Phys. [5] xxii. 218, 1881 ; Bornemann, Ber. Deutsch. Chem. Ges. xvii. 1462. 2 Raymann, Bull. Soc. Chim. xxvii. 498. 3 Lauth and Grimaux, ibid. vii. 234 ; Gundelaeh, ibid. xxvi. 44. 4 Meister, Lucius and Bruning, Ber. Deutsch. Chem. Ges. xvi. 817 ; Bornemann, loc. cit. 5 Ann. Chem. Pharm. cxxiv. 254. 414 AROMATIC COMPOUNDS. /CH3 THE TOLUIC ACIDS, CcH4Z ZCO2H 2222 Orthotoluic acid was first obtained by Bieber and Fittig by oxidizing orthoxylene with dilute nitric acid.1 It may also be easily prepared from its nitril, and its ethyl ether is formed by the action of ethyl chlorocarbon ate on a mixture of ortho- iodotoluene and sodium amalgam.2 It is best prepared by heating phthalide with phosphorus and hydriodic acid :3 /CH2X zch3 C6H4< " >0 + 2III = C6H4< +12. xC0z \C0.0H It crystallizes in long, lustrous needles, which melt at 102°, and are slightly soluble in cold, more readily in hot water and very readily in alcohol. It is completely burnt by chromic acid solution, while dilute nitric acid4 and alkaline permanganate 5 convert it into phthalic acid. Calcium orthotoluate, (C8H7O2)2Ca + 2H2O, crystallizes in small needles, which are readily soluble in water but only slightly in alcohol. Ethyl orthotoluate, CSH7O2.C2H5, is a liquid which boils at 219'5°, and has an aromatic odour.6 Orthotoluyl chloride, CH3.C6H4.COC1, is a liquid which boils at 211° (Ador and Rilliet). Orthotoluamide, CH3.C6H4.CONH.,, crystallizes from boiling water in fine, silky needles, melting at 138°. Orthotolunitril, CH3.C6H4.CN, is formed by the distillation of potassium orthoxylenesulphonate with potassium cyanide,7 and also when orthotolyl mustard oil is heated for an hour with copper filings.8 It is a colourless, strongly refractive liquid boiling at 203°-204°, which is converted into the amide by heating with alcoholic potash, and into the acid by concentrated hydrochloric acid at 180°-200°. 1 Ann. Cham. Pharm. clvi. 242. 2 Kekule, Ber. Deutsch. Chem. Ges. vii. 1007. 3 Giabe.t&id. xix. 778. 4 Weith, ibid. vii. 1057. 5 Piccard, ibid. xii. 579. 6 Ador and Rilliet, ibid. xii. 2298. 7 Fittig and Ramsay, Ann. Chem. Pharm. clxviii. 246. 8 Weith, Ber. Deutsch. Chem. Ges. vi. 418. THE TOLUIC ACIDS. 415 Chlororthotoluic acids, CQH3C1(CH3)CO2H, are obtained by oxidizing the chloroxylenes with dilute nitric acid :1 Cl ch3 CO2H Melting-point. 4 : 2 : 1 compact prisms . . . .... 130° 4 : 1 : 2 compact prisms . . . .... 166° 3 : 2 : 1 needles .... 154° a-Bromorthotoluic acid, C6H3Br(CH3)CO2H (4:1: 2), is formed by the oxidation of brom orthoxylene, and crystallizes from hot alcohol in stellate aggregates of flat needles, which melt at 174°-176°-2 ^-Bromorthotoluic acid (3:1:2) is obtained by the action of bromine on orthotoluic acid. It is scarcely soluble in cold, slightly in boiling water, but readily in alcohol, and crystallizes in long needles, melting at 1670.3 Nitro-orthotohtic acids, C6H3(NO2)(CH3)CO2H. The first of these is formed, together with the second, by the nitration of orthotoluic acid,4 and, together with the third, when nitro- orthoxylene is oxidized.5 The last also occurs, according to Racine, in the products of the nitration of orthotoluic acid.6 no2 ch3 CO„H Melting-point. a) 4 : 1 : 2 needles or microscopic prisms . 179° 6 : 1 : 2 needles 145° 7) 4 : 2 : 1 long, lustrous needles . . . . 152° Amido-orthotohcic acids, C6H3(NH2)(CH3)CO2H: nh2 ch3 co2h a) 4 : 1 : 2 small prisms . . 196° 6 : 1 : 2 small, lustrous needles . . . . 191° 7) 4 : 2 : 1 long, flat needles . . . . . 153° The last of these acids decomposes into carbon dioxide and metatoluidine when it is heated with lime (Jacobsen). Sulphorthotoluic acid, C6H3(SO3H)(CH3)CO2H (1:2: 3), is obtained by heating orthotoluic acid to 160° with sulphuric 1 Kriiger, Ber. Deutsch. Chem. Ges. xviii. 1755. 2 Jacobsen, ibid. xvii. 2372. 3 Jacobsen and Wierss, ibid. xvi. 1956. 4 Fittig and Bieber, Ann. Chem. Pharm. cxlvi. 245 ; Fittig and Ramsay, ibid. clxviii. 250 ; Jacobsen and Wierss, Ber. Deutsch. Chem. Ges. xvi. 1956. 5 Jacobsen, ibid. xvii. 162. 6 Ibid, xviii. 3450. 416 AROMATIC COMPOUNDS. acid ; it forms a fibrous crystalline mass, which dissolves readily in water, but only slightly in dilute sulphuric acid. Disulphorthotoluic acid, C6H2(SO3H)2(CH3)COaH, is formed when orthotoluic acid is heated to 170° with disulphuric acid; it forms microscopic needles, which are extremely soluble in water (Jacobsen and Wierss). Parasulphamido-orthotohbic acid, C6H3(SO2.NH2)(CH3)CO2H (4:2: 1), is formed, together with the following compound, when orthoxylenesulphamide is oxidized with an alkaline solution of potassium permanganate. It is slightly soluble in cold, readily in hot water, and crystallizes in long needles, which melt at 217°. Its potassium salt crystallizes in large, compact rhombohedra. Mdasulphamido-orthotoluic acid (4:1:2) is less soluble in hot water than the isomeric acid, and forms long, brittle needles, melting at 243°. Its potassium salt is extremely soluble, and can only be obtained in a crystalline state by exposing its concentrated solution over sulphuric acid for a long time.1 2223 Mdatoluic acid is obtained by the oxidation of metaxy- lene with nitric acid2 or potassium permanganate.3 Richter prepared it from orthonitrotoluene by converting this into bromometatolunitril by heating with alcohol and potassium cyanide (p. 217), and treating the acid obtained from this with sodium amalgam and water.4 It has also been obtained from mesitylene, or symmetric trimethylbenzene, by oxidizing this to uvitic acid, C6H3(CH3)(CO2H)2, and heating the calcium salt of the latter with half its weight of slaked lime to above the melting-point of lead.5 In order to prepare it, metaxylene is heated to 130°-150° for one or two days with a mixture of one volume of nitric acid and two volumes of water, and the product distilled with steam, isoph- thalic acid and nitro-compounds being left behind (Bruckner). Metatoluic acid is more readily soluble in water than its isomerides, and crystallizes, when its solution is rapidly cooled, in long, fine needles, while it is deposited on gradual evaporation in clear, well-formed prisms. It melts at 108°-109°, and readily sublimes. Calcium metatoluate, (C8H-O2)2Ca-|-3H.,O, crystallizes in aggre- gates of lustrous needles, similar to those of calcium benzoate. 1 Jacobsen, Ber. Deutsch. Chern. Ges. xiv. 38. 2 Ahrens, Zeitschr. Chem. 1869 ; 106 ; Tawildarow, Ber. Deutsch. Chem. Ges. iv. 410 ; Bruckner, ibid. ix. 405. 3 Schrotter, KekuWs Org. Chem. iii. 701. 4 Ber. Deutsch. Chem. Ges. v. 424. 6 Bottinger and Ramsay, ibid. ix. 405. NITROMETATOLUIC ACIDS. 417 Ethyl metatoluate, C8H7O2.C9H5, is a liquid, which boils at 224-5 -226-50.1 Metatoluyl chloride boils at 218° (Ador and Rilliet). Metatohmitril, C6H4(CH3)CN, has been obtained by heating metatolyl mustard oil with copper dust as a liquid which smells like benzonitril, and is converted into metatoluic acid by heating with concentrated hydrochloric acid to 180°-200°.2 Chlor omctatoluic acid, C6H3C1(CH3)CO2H (4:3: 1), is formed by boiling a-chlorometaxylene with chromic acid,3 as well as by replacing the amido-group of amidometatoluic acid by chlorine.4 It is only very slightly soluble in water, and sublimes in dazzling white needles, which melt at 209°-210°. a-Bromometatoluic acid, C6H3Br(CH3)CO2H (4:3: 1), is obtained by the oxidation of bromometaxylene 5 and of a-bromo- isocymene,6 as well as, together with the /3-acid, by the bromina- tion of metatoluic acid.7 It separates from hot alcohol as a crystalline powder or in small thick prisms, which melt at 209°-210°. ^-Bromometatoluic acid (4:1:3) is formed by the oxidation of /?-bromo-isocymene, and separates from hot glacial acetic acid as a faintly lustrous, crystalline powder, melting at 152°-1530.8 Nitrometatoluic acids, C6H3(NO2)(CH3)CO2H. Two of these are formed by the nitration of metatoluic acid,9 and both the others by the oxidation of the corresponding nitrometaxylene,10 while the third has also been obtained by the oxidation of nitro- isocymene :11 no2 ch3 co2h Melting-point. a) 4 : 1 : 3 compact prisms 219° ft 2 : 1 : 3 compact prisms 182° 7) 6 : 1 : 3 lustrous needles or crystalline powder . . 214° 8) 5 : 1 : 3 silky needles 167° 1 Ador and Rilliet, Ber. Deutsch. Chem. Ges. xii. 2300. 2 Wei th and Landolt, ibid. viii. 719. 3 Volrath, Ann. Chem. Pharm. cxliv. 266 ; Jacobsen, Bcr, Deutsch. Chem. Ges. xviii. 1760. 4 Beilstein and Kriisler, Ann. Chem. Pharm. cxliv. 181. 5 Fittig, Ahrens and Mattheides, ibid,, cxlvii. 32. 6 Kelbe, Ber. Deutsch. Chem. Ges. xv. 39. 7 Jacobsen, ibid. xiv. 2351. 8 Kelbe and Czamomski, Ann. Chem. Pharm. ccxxxv. 291. 9 Jacobsen, Ber. Deutsch. Chem. Ges. xiv. 2353. 10 Kreusler and Beilstein, toe. cit. ; Remsen and Kuhara, Amer. Chem. J (mm. iii. 424 ; Thbl, Ber. Deutsch. Chem. Ges. xviii. 359. 11 Kelbe and Warth, Ann. Chem. Pharm. ccxxi. 161. 418 AROMATIC COMPOUNDS. Amidometatoluic acids, CGH3(NH2)(CH3)CO2H, have been prepared by the reduction of the first three nitro-acids with tin and hydrochloric acid : Melting-point. NH„ CH. C09H a) 4 : 1 : 3 long, thin, colourless plates . 172° & 2 : 1 : 3 small, flat prisms 132° 7) 6 : 1 : 3 long needles 167° a-Sulphamidometatoluic acid, CGH3(SO2.NH2)(CH3)CO2H (4:3:1), is formed when a-metaxylenesulphamide is oxidized with chromic acid or potassium permanganate ; it crystallizes from hot water in long needles, melting at 254°.1 v-Sulpliamidometatoluic acid (2:3:1) has been obtained by the oxidation of v-metaxylenesulphamide, and forms crystals which melt at 202°-203° (Jacobsen). 2224 Paratoluic acid was prepared by Noad in 1847 by the oxidation of cymene, CH3.CGH4.C3H7, with nitric acid; * it is formed in this way from many other hydrocarbons which con- tain two side-chains in the para-position, such as paramethyl- ethylbenzene,3 paraxylene,4 &c. The latter is also converted into the acid by the action of potassium permanganate5 and of chromyl chloride.6 Oil of turpentine and its isomerides, which must be looked upon as dihydroxycymenes, and various deriva- tives of these are also oxidized to paratoluic acid by dilute nitric acid.7 Kekule obtained it synthetically by the action of carboa dioxide on a mixture of sodium and parabromotoluene,8 while Wurtz obtained the ethyl ether by employing ethyl chloro-car- bonate.9 It has also been synthetically prepared by many of the reactions previously mentioned (Part III., p. 30). The cymene which is contained in Roman cumin oil and which can easily be obtained from camphor, is employed as the starting point in the preparation of the acid. It is heated for a con- siderable time in an apparatus connected with an inverted con- denser with a mixture of 1 vol. of nitric acid of spec. gr. 1'38 1 Iles and Remsen, Bcr. Deutsch. Chern. Ges. x. 1044 ; xi. 229 and 88; Jacobsen, ibid. xi. 895 ; Coale and Remsen, Amer. Chem. Journ. iii. 205. 2 Chem. Soc. Mem. iii. 425. 3 Jannasch and Dieckmann, Bcr. Deutsch. Chem. Ges. vii. 1514. 4 Yssel de Schepper and Beilstein, Ann. Chem. Pharm. cxxxvii. 306. 5 Berthelot, Bull. Soc. Chim. vii. 134. 6 Carstanjen, Ber. Deutsch. Chem. Ges. ii. 635. 7 Hirzel, Zeitschr. Chem. 1866, 205 ; Mielk, Ann. Chern. Pharm. clxxx. 49 : Hempel, ibid, elxxx. 74 ; Kobig, ibid. cxcv. 106. 8 Ibid, cxxxvii. 184. 9 Ibid. Suppl. vii. 127. PARATOLUIC ACID. 419 and 4 vols. of water, then neutralized with caustic soda and boiled in order to remove unattacked cymene and nitro-products. It is then precipitated with hydrochloric acid and the precipitate freed from nitroparatoluic acid, &c., by boiling with tin and hydrochloric acid. The product always contains terephthalic acid, which remains behind on treatment with water. The paratoluic acid is finally purified by distillation with steam.1 It crystallizes in needles, which are slightly soluble in cold, more readily in hot water, and very readily in alcohol and ether; it molts at 180°, boils at 274°-275°,2 and is readily volatile with steam. It is converted into terephthalic acid by oxidation. All its salts are soluble in water. Calcium paratohtate, (C8H7O2)2Ca + 3H2O, crystallizes from hot water in dazzling white needles, which resemble those of calcium benzoate. Methyl paratoluate, C8H7O2.CH3, forms crystals which have a very pleasant, penetrating odour; it melts at 32° and boils at 217° (Fischli). Ethyl paratoluate, C8H702.CoH5, is a liquid, which boils at 228°, has a bitter taste and a smell resembling that of ethyl benzoate (Noad). Phenyl paratoluate, C8H7O2.C6H5. When paratoluyl chloride is heated with sodium salicylate, a viscid mass of paratoluyl- salicylic acid, CH3.C6H4CO.OC6H4.CO2H, resembling turpentine, is formed and decomposes into phenyl paratoluate and carbon dioxide on distillation with lime. It forms white plates, which have a nacreous lustre, smell like the geranium and melt at 71° 72°s Paratoluyl chloride, CH3.C6H4.COC1, is a strongly refractive liquid, boiling at 2180.4 Paratoluamide, CH3C6H4.CO.NII2, crystallizes from hot water in needles or plates, which melt at 151° (Fischli). Paratohtylamido-acetic acid, CH3.C6H4.CO.NH.CH2.CO2H, which is also called toluric acid, occurs in the urine after the administration of paratoluic acid. It is slightly soluble in cold, readily in hot water and alcohol, and crystallizes in nacreous plates or rhombic tablets, which melt at 1GO°-165°, and are 1 Dittmar and Kekule, Ann. Chern. Pharm. clxii. 339 ; Briickner, ibid. ccv. 113. 2 Fischli, Ber. Deutsch. Chern. Ges. xii. 615. 3 Kraut, Chern. Centralbl. 1859, 84. 4 Cahours, Ann. Chern. Pharm. cviii. 316 ; Bruckner, ibid. ccv. 114 ; Ador and Rilliet, Ber. Deutsch. Chern. Ges. xii. 2298. 420 AROMATIC COMPOUNDS. decomposed into paratoluic acid and amido-acetic acid by con- tinued boiling with hydrochloric acid.1 Schultzen and Naunyn, after taking coal-tar xylene, found in the urine a toluric acid, which did not crystallize but was only obtained as a colourless liquid;2 this substance probably con- sists entirely or chiefly of the meta-compound. Paratolunitril, CH3.C6H4.CN, is best prepared by distilling paratoluic acid with potassium thiocyanate (Part III., p. 197). It is a powerfully refractive liquid, smelling like benzonitril, boils at 217'8° and solidifies at a low temperature to a mass, which melts at 28'5°.3 Chloroparatoluic acid, C6H3C1(CH3)CO2H (3:4:1), is formed by the oxidation of chlorocymene, CcH3C1(CH3)C3H7, with dilute nitric acid.4 It is slightly soluble in hot water, readily in alcohol, and crystallizes in large plates melting at 194°-196°. a- Bromoparatohtic acid, CcH3Br(CH3)CO2H (3:4: 1), has been obtained by the oxidation of orthobromocymene,5 bromethyl - methylbenzene,6 and bromoparaxylene,7 and is also formed when paratoluic acid is allowed to stand in contact with dry bromine.8 It is almost insoluble in cold, slightly soluble in hot water and readily in alcohol, crystallizing in needles, which melt at 204°. Bromoparatoluic acid, which is formed by the oxidation of metabromocymene, crystallizes from alcohol in plates melting at 196°9 Dibromoparatoluic acid, C6H2Br2(CH3)CO2H (3 : 6 : 4 : 1), is obtained by oxidizing solid dibromoparaxylene with a solution of chromium trioxide in acetic acid. It is only very slightly soluble in water, and crystallizes from alcohol in stellate aggregates of needles, which melt at 195°.10 lodoparatoluic acid, CcH3I(CH3)CO2H, was obtained by Griess together with amidoparatoluic acid, by the action of hydriodic acid on diazo-amidotoluic acid, it is slightly soluble in water, readily in alcohol, and crystallizes in white plates or needles. 1 Kraut, Ann. Chern. Pharm. xcviii. 360. 2 Zeitschr. Chern. 1868, 29. 3 Paterno and Pisati, Bor. Deutsch. Chem. Ges. viii. 441 ; see also Volrath, Zeitschr. Chem. 1866, 489 ; Hofmann, Ann. Chem. Pharm. cxlii. 126 ; Merz, Zeitschr. Chem. 1868, 33 ; Weith, Ber. Deutsch. Chem. Ges. vi. 421. 4 Kekule and Fleischer, ibid. vi. 1090 ; v. Gerichten, ibid. x. 1250 ; xi. 368. g Landolph, Bor. Deutsch Chem. Ges. v. 268. e Fittica, Ann. Chem. Pharm. clxxii. 312. 7 Morse and Remsen, Ber. Deutsch. Chem. Ges xi. 225. 8 Jannasch and Dieckmann, Ann. Chem. Pharm. clxxi. 83. 9 Kelbe and Koschnitzky, ibid. xix. 1730. 10 Schultz, ibid, xviii. 1762. NITROPARATOLUIC ACIDS. 421 a-Nitroparatoluic acid, C6H3(NO2)(CH3)CO.?H (3:4-1), is formed by the action of fuming nitric acid on cymene1 or paratoluic acid.2 It is slightly soluble in cold, more readily in hot water and readily in alcohol, from which it crystallizes m light yellow, monoclinic prisms, which melt at 189° -190°. fi-Nitroparatoluic acid (2 : 4 :1) is obtained by the oxidation of liquid nitrocymene with chromic acid solution (Landolph, Fittiea). It is scarcely soluble in cold, slightly in hot water, and only with difficulty in alcohol, crystallizing in small plates or needles, which sublime without melting when heated. Accord- ing to Widman and Bladin, the so-called liquid nitrocymene consists chiefly of paratolylmethylketone,3 and the acid prepared from it is therefore probably not a nitrotoluic acid. ft-Nitroparatolunitril, C6H3(NO2)(CH3)CN, is obtained by heating the diazo-compound of metanitroparatoluidine with potassium cuprocyanide; it melts at 99°-100.04 a-Amidoparatoluic acid, C6H3(NH2)(CH3)CO2H (3:4:1), is tolerably soluble in water and crystallizes in hair-like needles, which melt at 164°-165° (Ahrens). 7)^o-amWoZmcacAZ,CO2H.C6H3(^^ CO2H, is formed by the action of nitrogen trioxide on an alcoholic solution of the amido-acid. It forms yellow microscopic prisms, which are insoluble in water and alcohol, and is decomposed by the haloid acids with formation of substituted toluic acids.5 Sidphoparatohiic acid, C6H3(SO3H)(C1I3)CO2H (2 :1:4), has been prepared by the action of sulphur trioxide on paratoluic acid,6 and by the oxidation of thiocymene, C6H3(SH)(CH3)C3H7 7 and cymene-orthosulphonic acid.8 It crystallizes in small plates which contain two molecules of water and are stable in the air. Srdphamidoparatohtic acid, C6H3(SO2.NH2)(CH3)CO2H, is formed by the oxidation of paraxylenesulphamide9 or cymene- sulphamide,10 and crystallizes from hot water in long needles which melt at 167°.11 1 Noad, Chern. Soo. Mem. iii. 431 ; Ahrens, Zeitschr. Chem. 1869, 102 ; Landolph, Ber. Deutsch. Chem. Ges. vi. 936 ; Fittiea, ibid. vi. 938. 2 Ann. Chem. Pharm. clxviii. 250. 3 Ber. Deutsch. Chem. Ges. xix. 584. 4 Leukart, ibid. xix. 417. 5 Griess, Ann. Chem. Pharm. cxvii. 58. 6 Fischli, Ber. Deutsch. Chem. Ges. xii. 615. 7 Flesch, ibid. vi. 478 ; Bechler, Journ. Prakt. Chem. [2] viii. 170. 8 Remsen and Burney, Amer. Chem. Journ. ii. 405 ; Baur and Meyer, Ann. Chem. Pharm. ccxx. 18. 9 Ahrens, Zeitschr. Chem. 1869, 102 ; Landolph, Ber. Deutsch. Chem. Ges. vi. 936; Fittiea, ibid. vi. 938. 10 Ann. Chem. Pharm. clxviii. 250. 11 Iles and Remsen, Ber. Deutsch. Chem. Ges. xi. 230 ; Hall and Remsen, ibid. xii. 1433. 422 AROMATIC COMPOUNDS. HYDROXYTOLUALDEHYDES, C6H4(OH)(CH3)COH. 2225 These compounds are formed when the cresols are heated with caustic soda solution and chloroform, homosalicyl- aldehydes being formed, which are volatile with steam. Ortho- and meta-cresol also yield homologues of parahydroxybenz- aldehyde, which are not volatile with steam, but this is not the case with paracresol, since in the chloroform reaction the alde- hyde-group always takes up either the ortho- or para-position with respect to the hydroxyl.1 Parahomosalicylaldehyde or Orthohyd roxym etatohcaldchyd e (COH : OH : CH3 = 1 : 2 : 5) is slightly soluble in water, readily in alcohol, and crystallizes from dilute alcohol in six-sided plates which have a nacreous lustre, and melt at 56°. It boils at 217°-218°, has a powerful, almost repulsive aromatic odour, and gives a deep blue colouration with ferric chloride. It is converted by the action of water and sodium amalgam into homosaligenin or orthohydroxymetaxylyl alcohol, C6H3(OH) (CH3)CH2.OH, which crystallizes from hot water in lustrous plates, melts at 105° and, like saligenin, gives a deep blue colouration with ferric chloride. Orthohomosalicylaldehyde or Orthohydroxy metatolualdehyde (1 : 2 : 3) is an oily liquid, which has a smell resembling both salicyl- aldehyde and oil of bitter almonds, solidifies on cooling to crystals which melt at 17°, and gives a bluish colouration with ferric chloride. Mctahomosalicylaldehyde or Orthohydroxyparatolualdehydc (1 : 2 :4) forms crystals, which melt at 54° and have a pleasant aromatic odour. It boils at 222°-223° and gives a violet colouration with ferric chloride, Orthohomoparahydroxybenzaldehydc or Parahydroxymetatolu- aldchydc (1:4:3) crystallizes from hot water in pointed prisms, which occur chiefly in twinned forms, resembling gypsum. It melts at 115° and gives a bluish violet colouration with ferric chloride. Metahomoparahydroxybenzaldeh ydc or Parahydroxy orthotolu- aldehyde (1:4:2) crystallizes in lustrous plates, melts at 110° and gives a light rose-red colouration with ferric chloride. 1 Tiemann and Schotten, Bcr. Deutsch. Chem. Ges. xi. 770. HYDROXYTOLUIC ACIDS. 423 Menyanthol, CSHSO. An amorphous substance, called meny- anthin, C30H46O14, which has an intensely bitter taste, occurs in the common buckbean {Menyanthes trifoliata) and is decom- posed by heating with dilute sulphuric acid into grape sugar and menyanthol. This substance is a liquid which smells like benzaldehyde, reduces ammoniacal silver solution, and is con- verted into a crystalline acid on exposure to the air or on fusion with caustic potash.1 It is probably identical with orthohomo- salicylaldehyde. HYDROXYTOLUIC ACIDS, C6H3(OH)(CH3)CO2H. 2226 Kolbe and Lautemann, after finding that salicylic acid is formed by the action of carbon dioxide on a mixture of phenol and sodium, prepared its homologue, cresotic acid, from the cresol which boils at 12O0.2 The three cresotic acids were then pre- pared from the isomeric cresols,3 and, on account of their similarity to salicylic acid, were also called homosalicylic acids. Ihle has shown that, like their lower homologue, they may be obtained by passing carbon dioxide over the heated sodium cresols.4 These compounds and the other hydroxytoluic acids, the ten of which are all known, are also formed by reactions similar to those employed for the preparation of the hydroxybenzoic acids and other hydroxy-acids (Part III., p. 32). The dimethyl ethers, O6H3(CH3)(OCH3)CO2.CH3, are formed by heating the acids with caustic potash and methyl iodide, and these are converted by saponification into the methoxytoluic acids, C6H3(CH3)(OCH3)CO2H.5 The numbers appended in brackets give the position of the side chains in the order CO2H : OH : CH3. Parahomosalicylic acid, a-Cresotic acid or a-Orthohydroxymeta- ioluic acid (1:2: 5), may be obtained, in addition to the methods just described, by fusing /3-metaxylenol6 or ^-bromometatoluic acid7 with caustic potash, by the action of nitrous acid on the 1 Kromayer, Jahresb. Chern. 1861, 749. 2 Ann. Chem. Pharm. cxv. 203. 3 Engelhardt and Latschinow, Zeitschr. Chem. 1869, 622 ; Biedermann, Ber. Deutsch. Chem. Ges. vi. 325 ; Kekule, ibid. vii. 1006. 4 Journ. Frakt. Chem. [2] xiv. 454. 6 Schall, Ber. Deutsch. Chem. Ges. xii. 822. 6 Jacobsen, ibid. xi. 374. 7 Ibid. xiv. 2347. 424 AROMATIC COMPOUNDS. amidometatoluic acid which melts at 1720,1 and by heating para- cresol with caustic soda and tetrachloromethane.2 It crystallizes from hot water in very long needles or rhombic prisms, melting at 151°, and is readily volatile with steam. Its aqueous solution is coloured an intense violet-blue by ferric chloride ; it decom- poses into paracresol and carbon dioxide when heated to 180° with hydrochloric acid, while a remarkable reaction occurs when its calcium salt is heated with lime, orthocresol being formed (Jacobsen). Methylparahomosalicylic acid forms long, thin needles, melting at 67°. Orthohomosalicylic acid, {3-Cresotic acid, or v-Orthohydroxymeta- toluic acid (1 : 2 :3) is also formed by fusing v-sulphamidometa- toluic acid with caustic potash3 and by the action of nitrous acid on the amidometatoluic acid melting at 132° (Jacobsen). It crystallizes from hot water in long, flat needles, which melt at 163°-164°. It decomposes into orthocresol and carbon dioxide when heated with hydrochloric acid to 210°; ferric chloride colours its aqueous solution deep violet. Mcthylorthohomosalicylic acid crystallizes in feathery needles and melts at 81°. a-Mctahomosalicylic acid, y-Cresotic acid, or Orthohydroxypara- toluic acid (1:2:4) is also obtained by fusing paraxylenol with caustic potash (Jacobsen), and, together with metahomopara- hydroxybenzoic acid, when metacresol is heated with tetrachloro- methane and caustic soda (Schall). It crystallizes from water in needles and from alcohol in monoclinic prisms, which melt at 177°,4 and are volatile with steam. On heating with hydro- chloric acid to 170°, it decomposes into metacresol and carbon dioxide ; ferric chloride produces a deep violet colouration in its aqueous solution. a-Mcthylmetahomosalicylic acid crystallizes in plates, which melt at 103°-104°. ^-Metahomosalicylic acid (1:2:6) has been obtained from /9-bromorthotoluic acid. It is slightly soluble in cold, readily in hot water, very freely in alcohol, crystallizes in long needles, melting at 168°, and is tolerably volatile with steam. Its solution is coloured a deep blue-violet by ferric chloride; 1 Ber. Deutsch. Chem. Ges. xiv. 2352. ; Panaotovid, Journ. Prakt. Chem. [2] xxxiii. 63. 2 Schall, ibid. xii. 821. 3 Ber. Deutsch. Chem Ges. xi. 902. 4 Oppenheimer and Pfaff, ibid. viii. 889. PARAHOMOMETAHYDROXYBENZOIC ACID. 425 on heating to 200° with concentrated hydrochloric acid, it decomposes into metacresol and carbon dioxide.1 2227 Parahomomdahydroxybenzoic acid or Mdahydroxyortho- toluic acid (1 : 5 : 2) is formed by fusing metasulphamido-ortho- toluic acid,2 a-bromorthotoluic acid,3 or the chlororthotoluic acid melting at 166°/ with caustic potash, and from /3-amidortho- toluic acid by means of the diazo-reaction.5 It is slightly soluble in cold, readily in hot water, crystallizes in transparent prisms, which melt at 172° and sublime in needles, and is also volatile with steam. Ferric chloride, added to its cold saturated solution or to that of its ammonium salt, produces a light brown precipitate soluble in a large quantity of hot water. It is not attacked by concentrated hydrochloric acid even at 220°. Mdahomomdahydroxyljcnzoic acid or s-Hydroxytoluic acid (1: 3 :5). Fuming sulphuric acid converts metatoluic acid into two isomeric sulphonic acids, which yield a mixture of symmetric hydroxymetatoluic acid and parahomosalicylic acid on fusion with caustic potash; the latter may be removed by distillation with steam, while the former differs from all its isomerides in not being volatile. Symmetric hydroxytoluic acid is tolerably soluble in cold, readily in hot water, and crystallizes in fascicular aggregates of needles, which melt at 208°; it solidifies to hard, transparent prisms and sublimes in stellate groups of needles. Solutions of the acid and of its salts give a fawn-coloured precipitate with ferric chloride, which dissolves in a large excess of the reagent, forming a dark brown solution. It is not attacked by concentrated hydrochloric acid at 230°, and yields metacresol when distilled with lime.6 s-Trinitrohydroxytoluic acid, C6(NO9)3(OH)(CH3)CO2H + H20 Warren de la Rue, by heating the colouring matter of cochineal with nitric acid, obtained nitrococcusic acid, which possesses the same composition as the trinitro-anisic acid prepared by Cahours, but is obviously not identical with it.7 Gmelin states that it is isomeric with the latter and also with methyltrinitrosalicylic acid.8 It differs from both of these by being dibasic, and Strecker on this account suggested that it might be trinitrocresotic acid.9 oo o 1 Jacobsen, Ber. Deutsch. Chern. Ges. xvi. 1962. 2 Ibid. xiv. 38. 3 Ibid. xvii. 2375. 4 Kriiger, ibid, xviii. 1758. 5 Jacobsen and Wierss, ibid. xvi. 1959. 6 Jacobsen, ibid. xiv. 2357. 7 Ann. Chern. Pharm. Ixiv. 23. 8 Handb. Org. Chern, iii. 398. 9 Lehrb. Org. Chem. v. Aufl. 727. 426 AROMATIC COMPOUNDS. Liebermann and Dorp found that it decomposes into carbon dioxide and trinitrometacresol when heated with water to 18O0,1 and therefore considered it to be a trinitro-derivative of the then unknown symmetric hydroxytoluic acid. After the dis- covery of the latter, Kostanecki and Niementowski showed that on solution in warm nitric acid it is converted into nitrococcusic acid.2 It crystallizes from hot water in colourless, rhombic plates, which are yellow when not perfectly pure, and form a yellow solution in water which dyes animal fabrics and the skin an intense yellow. It melts with decomposition between 170° and 180°, and detonates at a higher temperature. Its salts are soluble in water and detonate violently on heating. a-Orthohomometahy dr oxybenzoic acid or Metahydroxyparatoluic acid (1:3:4) is formed by fusing paratolulylsulphonic acid,3 chloroparatoluic acid, bromoparatoluic acid 4 or sulphamidopara- toluic acid5 with caustic potash, as well as by the action of nitrous acid on amidoparatoluic acid.6 It crystallizes in long needles, melting at 206°-207°, is slightly soluble in cold, readily in hot water, and volatilizes with steam. Ferric chloride gives no colouration, and hydrochloric acid has no action upon it at 270°. On distillation with lime it decomposes into orthocresol and carbon dioxide. [3-Orthohomonietahydroxybenzoic acid (1:3:2) was obtained by Jacobsen from sulphorthotoluic acid. It crystallizes from hot water in long needles with a vitreous lustre, which melt at 183°, are volatile with steam, and are not attacked by hydro- chloric acid at 200°-210°. It yields orthocresol on distillation with lime. Ferric chloride, added to an aqueous solution of the acid or one of its salts, produces a heavy, bulky, light brown precipitate. (3-Methylorthohomomctahydroxybenzoic acid crystallizes in long, fine needles, and melts at 146°.7 2228 Mctahomoparahydroxybcnzoic acid or Parahydroxy ortho- toluic acid (1:4:2) is obtained by fusing the aldehyde with caustic potash.8 It is also formed, together with a small quantity of metahomosalicylic acid, when metacresol is heated 1 Ann. Chcm. Pharm. clxiii. 99. 2 Ber. Deutsch. Chcm. Ges. xviii. 250. 3 Flesch, ibid. vi. 481. 4 v. Gerichten, ibid. xi. 368. 5 Hall and Remsen, ibid. xii. 1433. 6 Fittica, ibid. vii. 927 ; v. Gerichten and Rossler, ibid. xi. 705. 7 Jacobsen, ibid. xvi. 1962. 8 Schrotten and Tiemann, ibid. xi. 778. DIHYDROXYTOLUALDEHYDES. 427 with tetrachloromethane and concentrated caustic soda solution,1 and when parasulphamido-orthotoluic acid2 or the chlorortho- toluic acid which melts at 130° 3 is fused with caustic potash. It crystallizes from hot water in small needles which contain half a molecule of water of crystallization; this is lost at 100° and the anhydrous residue then melts at 177°-178°. Ferric chloride produces no colouration, but gives a reddish brown precipitate withits salts, which dissolves in an excess of the reagent forming a dark-brown solution. On heating to 200° with hydrochloric acid it decomposes into carbon dioxide and metacresol. Methylmetahomoparahydroxybenzoic acid crystallizes in long needles and melts at 176°. Orthohomoparahydroxybenzoic acid or Parahydroxy metatoluic acid (1 : 4 : 3) is formed by fusing the aldehyde,4 a-sulphamido- toluic acid 5 a-bromometatoluic acid,6 or chlorometatoluic acid 7 with caustic potash, and together with a small quantity of orthohomosalicylic acid by heating orthocresol with tetrachloro- methane and caustic soda (Schall). It crystallizes from hot water in small needles, containing half a molecule of water, which is lost at 100°; the anhydrous acid melts at 171°-173°, and is volatile with steam. Ferric chloride produces no coloura- tion; on heating with hydrochloric acid to 180°-185° it decomposes into carbon dioxide and orthocresol. Methylorthohomoparahydroxybenzoic acid forms microscopic silky needles, melting at 192°-193°. DIHYDROXYTOLUALDEHYDES, C6H2(CH3)(OH)2CHO. 2229 Para-orsellincddeJ^ : OH : OH : CH3 = 1: 2 :4 : 6). This compound, which is also known as orcylaldehydc, is formed together with two orcendialdehydes, C0H(CH3)(OH)2(CHO)2, by heating orcinol with caustic potash and chloroform ; it crystallizes from hot water in fascicular or stellate aggregates of needles, which melt at 177°-178°. Its aqueous solution is coloured reddish brown by ferric chloride.8 The constitution of this body 1 Schall, Ber. Deutsch. Chern. Ges. xii. 819. 2 Jacobsen, ibid. xiv. 40. 3 Kruger, loc. cit. 4 Schotten and Tiemann. 5 Jacobsen, ibid. xi. 897. 6 Jacobsen, ibid. xiv. 2351. 7 Ibid, xviii. 1760. 8 Tiemann and Helkenberg, ibid. xii. 999. 428 AROMATIC COMPOUNDS. has not been determined, but since resorcinol is converted by the above reaction into /3-resorcylaldehyde, in which the alde- hyde group takes the para-position with regard to one hydroxy] and the ortho-position to the other, this is probably also the case with orcylaldehyde. Mctahomomethoxysal.icylaldchyde (1 : 2 : 3 :5) has been obtained from creosol and chloroform, and forms an oily liquid, which possesses a smell resembling that of salicylaldehyde, and, like the latter, forms a deep yellow coloured solution in alkalis. Ferric chloride produces a deep green colouration.1 DIHYDROXYTOLUIC ACIDS, CH,.C6H2(OH)2CO2H. ' O V JU \ Ju At 2230 In the year 1830, Heeren investigated the lichens Rocclla tinctoria and Lecanora tartarea, which are employed in Holland for the manufacture of litmus and archil, and found in them a characteristic, colourless, crystalline substance, which is converted into a red dye by the united action of air and ammonia, and which he therefore named erythrin (epvZpo?, red). On boiling with a solution of ammonium carbonate, it was con- verted into the amorphous erythrinLitter. In order to obtain erythrin in larger quantities, he extracted the lichens with alcohol, but found that the erythrin was thus converted into a similar substance, which was, however, unsuitable for the pre- paration of the dye, and which he namedpseudoerythrin? He also found rocellic acid in the lichens which he examined (Pt. II. p. 289). Kane, however, obtained different results; in extracting the lichens with hot alcohol he obtained erythrylin, insoluble in water, and a soluble crystalline compound, which is identical with pseudoerythrin and is not an accidental product, but one of the most important of the whole series. He therefore transferred the name erythrin to this substance and assumed that Heeren's erythrin was a mixture of erythrylin with other bodies. When its solution is exposed to the air, erythrinbitter or amarythrin is formed, and this converted after several months' exposure into crystalline telerythrin, to which he gave this name in contradis- tinction to erythrylin, since the word reXo? denotes the end, and the beginning of the series.3 1 Tiemann and Koppe, Ber. Deutsch. Chem. Ges. xiv. 2026. 2 Schweigger's Journ. lix. 313. 3 Phil. Trans. 1840, 273. DIHYDROXYTOLUIC ACIDS. 429 Schunck then investigated many varieties of Lecanora and Variolaria from the Vogelsberg, and found in them a crystalline compound, which, like Heeren's erythrin, is converted into a red dye by exposure to the air, but has a different composition, and which he therefore named lecanorin? On boiling with baryta water, it decomposed into carbon dioxide and orcinol, which had already been prepared from these species of lichens by Robiquet, while on boiling with alcohol it was converted into Heeren's pseudoerythrin.2 Rochleder and Heldt, who detected lecanorin in Evernia Prunastri, showed that it is also converted into pseudo- erythrin by the action of hydrochloric acid and alcohol; the latter substance must therefore be looked upon as the ethyl ether of lecanorin, or as it is more suitably called, lecanoric acid? This compound was then carefully examined by Schunck,4 who also submitted the substances contained in Rocella tinctoria var. fuciformis from Madagascar and Angola to a new investiga- tion. The most important of these is erythric acid, which yields the colouring matter. This is so readily converted into the ethyl ether or pseudoerythrin by boiling with alcohol, that the latter is always obtained when the lichens are extracted with boiling alcohol. This compound has the same composition as ethyl-lecanoric acid, and appears to be identical with it-a fact which admits of the simple explanation that erythric acid is a copulated compound of lecanoric acid and orcinol. On boiling with alcohol, orcinol is set free and the lecanoric acid combines with the ethoxyl residue.5 Erythric acid is converted by boiling with water into picro- erythrin, the properties of which are not identical either with those of Heeren's erythrinbitter or of Kane's amarythrin; they approach most closely to those of telerythrin. Stenhouse, who investigated a South American sample of Rocella tinctoria, found in it a-orsellic acid, which is decomposed by boiling with milk of lime or baryta into orcinol and a-orsellinic acid, while Schunck's lichen, which is R. Montagnei, contains erythric acid, which yields picroerythrin and erythrelinic acid, which is very similar to a-orsellinic acid. According to Schunck, picroerythrin is decomposed by boiling with an excess of lime or 1 Ann. Chern. Pharm. xli. 157. 2 Ibid. xlv. 250. 3 Ibid, xlviii. 1. 4 Ibid. liv. 261. 5 Ibid. Ixi. 64. 430 AROMATIC COMPOUNDS. baryta into carbon dioxide and orcinol, but Stenhouse has shown that erytliroghccin is also formed.1 Stenhouse also discovered a ^-orsellic acid in Bocella tinctoria from the Cape of Good Hope, but this was shown by Gerhardt, who was subsequently confirmed by Stenhouse himself, to be identical with the a-acid. In " Remarks on the Preceding Communication," Strecker observes : Stenhouse has made us acquainted with a series of acids which are of special interest, both on account of their similar properties and analogous reactions, and from the fact of their occurrence in the same plants. It is for this reason desirable that the changes undergone by these compounds should be represented by formulae, and for this purpose it is necessary to sub- stitute new expressions for some of the empirical formulae given by Stenhouse, since the former agree equally well with the experimental results and are also capable of representing the decompositions and reactions of the substances in question. a-Orsellic acid, then, is converted into two molecules of orsellinic acid, the elements of water being taken up : C1cH14O7 + H2O = 2C8H8O4. The former can also form orcinol with loss of carbon dioxide: C1cH14O7 + H2O = 2C7H8O4 + 2CO2. The conversion of orsellinic acid into orcinol takes place with the separation of carbon dioxide : C8H8O4 = C7H8O2 + CO9. o o 4 / o Z Z Erythric acid is resolved into picroerythrin and erythrelic acid, which is undoubtedly orsellinic acid : ^20^22^10 + H2O - C12H16O7 + C8H8O4. Finally, picroerythrin decomposes into carbon dioxide, orcinol and erythroglucin: C12H1cO7 + h2o = co2 + c7h8o2 + C4H10O4. He adds that erythnc acid can yield twice as much orsellinic acid as given by the equation, but Stenhouse considers this as improbable. In this case the formula of the former would be C14H15O7:2 2C8H8O4 + C12H8O7 = 2C14H15O7 + H2O. 1 Stenhouse, Phil. Trans. 1848, 63. 2 Ann. Chern. Phann. Ixviii. 108. ERYTHRIN AND PICROERYTHRIN. 431 Gerhardt came to the conclusion that orsellic acid has the formula C16O14O7, and is identical with lecanoric acid,1 while Schunck expressed the opinion that the ethyl ether of orsellinic acid is identical with that of lecanoric acid, just as is the case with erythrin and pseudoerythrin.2 Hesse then undertook a new investigation of these lichen substances. He ascertained that the Angola lichen, which comes into the market under many names, is Rocdla fuciformis, and retained Heeren's name of erythrin for the chromogen con- tained in it, since it scarcely possesses the properties of an acid. His analysis gave him results in accordance with Strecker's second formula, which, however, he doubled and wrote C28H30O14. The acid obtained from it by decomposition proved as Strecker had correctly foreseen, to be identical with orsellinic acid.3 Stenhouse confirmed these observations, and adopted the same formula for erythrin, giving equations to explain its changes and decompositions,4 but, in spite of this, Strecker's first formula has been shown to be correct. Aftei' it had been recognized that erythroglucin or erythrol as it is now called, is an alcohol, Berthelot suggested that erythrin is the orsellinic ether of this, and de Luynes has observed that it is in fact the di-acid ether of this alcohol, picro- erythrin being the mono-acid derivative.5 Orsellinic acid has proved to be a dihydroxytoluic acid, and the compounds in question have, therefore, the following constitution : Erythrin: CH3.C6H2(OH)2CO.(X >C4H6(OH)2. CH3.C6H2(OH)2CO.Oz Picroerythrin: CH3.C6H2(OH)2CO.OC4H6(OH)3. Further investigations conducted by Hesse have finally decided that the archil lichens which occur in commerce consist chiefly of two species. Rocdla fuciformis (Acharius) comprises those from Lima, Angola, Mozambique, Zanzibai' and Ceylon; this contains erythrin alone, while Ilocclla tinctoria (De Candolle), 1 Compt. Rend. Chim. 1849, 127. 2 Phil. Mag. xxxiii. 249. 3 Ann. Chem. Pharm. cxvii. 297. 4 Proc. Hoy. Roc. xii. 263. 5 Ann. Chem. Pharm. cxxxii. 355. 432 AROMATIC COMPOUNDS. which comes from Cape Verde and the neighbouring islands, contains a chromogen, lecanoric acid,1 which is identical with orsellic acid. Stenhouse remarks on this point that the South American lichens examined by him are also Rocella tinctoria. They are sent into the market under the name of Valparaiso lichens, but are seldom exported to England, while the Lima lichens (Rocella fuciformis) are sent there in large quantities.2 Lecanoric acid is monobasic and stands in the same relation to orsellic acid as glycoIlic acid to glycoglycollic acid : /OH CH3.CGH<OH \CO\ / o / CH3.C6H2^OH \co2h. 2231 Orsellinic acid, CH3.C6H2(OH)2CO2H + H2O, is readily- prepared from erythrin by heating it on the water bath with baryta water until barium carbonate commences to separate. A few drops of the solution are then tested with hydrochloric acid at short intervals, and as soon as a gelatinous precipitate is no longer formed, hydrochloric acid is added to the solution, the orsellinic acid being thus soon precipitated. It crystal- lizes from acetic acid in stellate aggregates of needles, and separates from dilute alcohol as a crystalline mass, which is readily soluble in water, becomes anhydrous at 100°, and melts at 176°, a gradual decomposition into carbon dioxide and orcinol accompanied by violent frothing, taking place. The same decomposition occurs on boiling with water or alkalis. Its aqueous solution is coloured purple-violet by ferric chloride, and gives an amorphous precipitate with an ammoniacal solution of lead acetate. Barium orsellinate, (C8H7O4)2Ba, is extremely soluble in water, and crystallizes from dilute alcohol in hydrated prisms, which decompose even at 100° with formation of barium carbonate. Methyl orsellinate, C8H7O4(CH3), is formed by boiling lecanoric acid (Schunck) or erythrin (Stenhouse) with methyl alcohol, and crystallizes in lustrous needles, or flat, pointed prisms, which 1 Ann. Chem. Pharm cxxxix. 22. 2 Journ. Cliem. Soc. v. 221. LECANORIC ACID. 433 are readily soluble in water. It dissolves in alkalis and is reprecipitated by acids. Ethyl orsellinate, C8H7O4(C2H6). The formation of this ether, which was described by Heeren as pseudoerythrin, has been frequently referred to in the preceding pages. It is slightly soluble in cold, readily in hot water and alcohol, and crystallizes in needles or small plates, which melt at 132°. Its aqueous solution is precipitated by lead acetate. Amyl orsellinate, C8H7O4(C5H1]), is prepared by boiling erythrin with amyl alcohol. It is scarcely soluble in water, readily in alcohol and ether, from which it crystallizes in vitreous prisms, melting at 760.1 Orsellinic acid is decomposed by the action of bromine into carbon dioxide and tribrom orcinol; if, however, the substances are mixed in ethereal solution, substitution products are formed. Dibromorsellinic acid, C8H6Br2O4, is slightly soluble in hot water, readily in alcohol and ether, and crystallizes in small, white prisms; its alcoholic solution is coloured a splendid dark blue by ferric chloride, and blood-red by bleaching powder (Hesse). Phosphorsellinic acid, C40H36P4O24. When orsellinic acid is gradually heated with phosphorus oxychloride to 90°-100°, the liquid becomes coloured brown, violet-green, and, finally, indigo- blue. If it be now allowed to drop into ice water, phosphorsellinic acid separates out, and may be purified by repeated solution in water and precipitation with hydrochloric acid or common salt. It is an amorphous, indigo-blue powder, which takes a cupreous lustre under strong pressure and readily forms deep blue solutions in water and alcohol. The solution in 20,000 parts of water has the colour of a concentrated solution of copper sulphate and a distinct violet colouration is visible when 50,000 parts of water are employed. It dissolves in alkalis, lime water and baryta water with a violet-red colour; the salts of the heavy metals produce bluish violet, flocculent precipitates. Phosphorsellinanilide, C40H34(C6H5.NH)2P4O22, is formed by boiling the acid with aniline and alcohol; it is a dark violet powder, which is insoluble in water, but forms a splendid violet solution in alcohol.2 2232 Lecanoric acid or Diorsellinic acid, C16H14O7 + H2O, is, according to Hesse, best prepared from the R. tinctoria from Cape Verde. The lichens are extracted with ether, and the greenish 1 Hesse, Ann. Chern. Pharm. cxxxix. 22. 2 Schiff, ibid, ccxxviii. 56. 434 AROMATIC COMPOUNDS. white, crystalline residue left after the evaporation of the ether dissolved in milk of lime, filtered, precipitated with sulphuric acid and crystallized from alcohol. It is scarcely soluble in cold water, but dissolves in 2,500 parts of boiling water, more readily in alcohol and ether, and crystallizes in needles or prisms, which become anhydrous at 100°, melt at 153°, and simultaneously decompose with evolution of carbon dioxide. The alcoholic solution is coloured dark purple-red by ferric chloride and is not precipitated by lead acetate; copper acetate, however, produces a pale, apple-green precipitate on standing (Schunck). It reduces ammoniacal silver solution on heating, and is converted on boiling with water into orsellinic acid, and with alcohol into its ether. Barium lecanorate, (C16H13O7)2Ba, separates from hot alcohol in small, star-shaped aggregates of needles. Substitution products are formed by the action of bromine on an ethereal solution : Melting- point. Dibromolecanoric acid, C16H12Br2O7, small white prisms . 179° Tetrabromolecanoric acid, C10H10Br4O7, pale yellow prisms 157° Both these bodies evolve carbon dioxide on fusion; their alcoholic solutions are coloured purple-red by ferric chloride and blood-red by bleaching powder (Hesse). Erythrin, 2C20H2,O10 + 3H2O. In order to prepare this sub- stance, 1 part of R. fuciformis is macerated for twenty minutes with 10 parts of milk of lime containing 1'6 per cent, of lime, filtered and precipitated immediately with hydrochloric acid. The re- sidue is treated a second time with milk of lime, which is then employed for the extraction of a new quantity of lichen. The precipitate is redissolved in milk of lime, the filtrate treated with carbon dioxide and the precipitated mixture of calcium carbonate and erythrin gently warmed with alcohol; hot water is then added to the solution until a permanent turbidity is produced. The erythrin separates on cooling in spherical crystalline masses, which become anhydrous at 100° and melt at 137°. It is slightly soluble in cold water, with difficulty in ether, but readily in alcohol; ferric chloride added to the alcoholic solution produces a purple-violet colouration, which changes on further addition to a brownish red precipitate. Picroerythrin, C12H16O7 + 3H2O, is the first product of the decomposition of erythrin by boiling water, alcohols or alkalis, EVERNIC ACID. 435 When erythrin is dissolved in milk of lime it decomposes in the course of a day or two with formation of picroerythrin, which is also obtained pure when erythrin is boiled for some hours with amyl alcohol. It crystallizes in silky prisms, which readily effloresce, melt at 158° and have a slightly sweet and intensely bitter taste. It is exceptionally soluble in hot water and under- goes no change when boiled with absolute alcohol. Ferric chloride produces a purple-violet colouration. 2233 In connection with these compounds, the following, which are to some extent homologous with them, may be mentioned here. Evernic acid, C17H16O7. According to Rochleder and Heldt, lecanoric acid occurs in Evcrnia Prunastri; Stenhouse, how- ever, could not detect it in lichens grown in Scotland, but found in them evernic acid, together with usnic acid, C18H1SO7, thus proving either that the German and Scotch lichens contain different compounds, or, what is much more probable, that the German chemists had not investigated the true Evcrnia Pru- nastri^ a view which is supported by the fact that Hesse, who examined this lichen collected in various parts of Germany, always found evernic acid in it.2 It is almost insoluble in water, but dissolves easily in alcohol, and crystallizes in spherical aggregates of needles, which melt at 164°. Everninic acid, C9H10O4, is formed, together with carbon dioxide and orcinol, when evernic acid is boiled with lime water or baryta water. It is tolerably soluble in hot water, readily in alcohol, and crystallizes in flat, lustrous needles, resembling those of benzoic acid. It melts at 159°, and on further heating emits a penetrating odour and yields a colourless sublimate. Ferric chloride colours the aqueous solution violet. Earbatic a.cid, C19H20O7. This substance, which stands in the same relation to homorcinol (p. 402) as evernic acid to orcinol, occurs with usnic acid in Usuta barbata. It crystallizes from benzene in long plates, needles, or short prisms, which melt at 168°, and decompose at a higher temperature with evolution of carbon dioxide and formation of homorcinol.3 ^-Erythrin or Homo-erythrin, C21H.24O]0 + H2O, was discovered in a stunted specimen of R. fuciformis* It crystallizes in 1 Ann. Chem. Pharm. Ixviii. 83 ; civ. 56. 2 Ibid, cxvii. 297. 3 Stenhouse and Groves, Journ. Chem. Soc. 1880, 407. 4 Menschutkin, Bull. Soc. Chim. [2] ii. 424 ; Lamparter, Ann. Chem. Pharm, cxxxiv. 234. 436 AROMATIC COMPOUNDS. concentrically arranged needles, which are very readily soluble in alcohol. On boiling with baryta water it is resolved into carbon dioxide, erythrol and homorcinol: c13h16o6 + 2H2O=co2+c4h10o4 + C8H10O2. It is not homologous with picroerythrin, but is the anhydride of such a compound, which would probably have the following constitution : /CO.OX (CH3)2C6H(OH)< >C4H6(OH)2. \ O / Picroroccllin, O27H29N3O5, was found along with erythrin by Stenhouse and Groves in a variety of P. tinctoria, which pro- bably came from western Africa. It is insoluble in water, tolerably soluble in hot alcohol, and crystallizes in long, lus- trous prisms, which melt at 192°-194°, and have an intensely bitter taste. On oxidation with chromic acid, benzoic acid is obtained together with a liquid smelling like benzaldehyde. On dry distillation it yields water, ammonia, and xanthoroceUin, C21H17N2O2, which is also obtained by heating picrorocellin with dilute acids, and crystallizes from alcohol in long, yellow needles, melting at I830.1 2234 Para-orsellinic acid, C6H2(CH3)(OH)2CO2H 4- H2O, is prepared by heating orcinol with 4 parts of ammonium car- bonate and 4 parts of water for 10-15 hours to the boiling- point of amyl alcohol,2 or by passing carbon dioxide over the potassium compound of orcinol at 250°-26O0.3 It crystallizes from dilute alcohol in fine, hard needles, which dissolve in about 660 parts of cold water; the solution is coloured blue by ferric chloride. On heating the acid it loses water at 100° and commences to melt at about 150° with evolution of carbon dioxide, which is also given off when the acid is simply boiled with water; on dry distillation it decomposes completely with formation of orcinol. Barium para-orscllinatc, (CsH7O4)2Ba + 6H2O, crystallizes in four-sided tablets, which are readily soluble in water. Paraphosphorsellinic acid is formed as a chromegreen powder by heating para-orsellinic acid with phosphorus oxychloride (p. 433). 1 Ann. Chem. Pharm. clxxxv. 14. 2 Brunner and Senhofer, Monatsh. xiii. 1643. 8 Schwarz, Ber. Deutsch. Chem. Ges. xiii. 1643. CRESORSELLINIC ACID. 437 Cresorcinolcarboxylic acid, C6H2(CH3)(OH)2CO2H + H.2O, is formed when cresorcinol is heated in a small flask with 4 parts of potassium or sodium bicarbonate for half an hour. It is slightly soluble in cold, readily in hot water and alcohol, and crystallizes in very long, thin, lustrous prisms, which lose their water at 100° and melt at 208° with decomposition. Its solution is coloured bluish violet by ferric chloride and is not precipitated by lead acetate.1 Cresorsellinic acid, C6H2(CH3)(OH)2CO2H (1 :2:4:6), is pre- pared by fusing disulphorthotoluic acid with caustic potash. It is slightly soluble in cold, readily in hot water, and crystallizes in long, hard, vitreous needles, which melt at 245°. It reduces ammoniacal silver solution on heating and Fehling's solution on boiling; its aqueous solution is coloured dark brown by ferric salts, a ferrous compound being formed. On heating with sulphuric acid the liquid assumes a splendid stable magenta colour; water precipitates from it yellow flocks, which form an intense golden- yellow solution in alkalis. It therefore gives a similar reaction to that which is characteristic of the analogous a-resorcylic acid (p. 358). When it is heated to 220°-225° with hydrochloric acid, dark flocks separate out, which form a reddish brown solution in alcohol; on the addition of a little alkali, the liquid takes a splendid dark green fluorescence, which disappears when an excess of alkali is added, a deep purple-red solution being formed. Cresorcinol is formed when the acid is distilled with slaked lime.2 Three carboxylic acids are derived from cresorcinol: co2h co2h co2h OH^^.OH ^^.OH chJ^J OH^yoH OH The last of these expresses the constitution of cresorsellinic acid, which is a derivative of orthotoluic acid. The second probably represents that of cresorcinolcarboxylic acid, since the readiness with which it is formed supports the conclusion that the carboxyl takes up the same position in the nucleus in the case of cresorcinol as it does in the analogous formation of /3-resorcylic acid from resorcinol (p. 359). 1 Kostanecki, Ber. Deutsch. Chem. Ges. xviii. 3202. 2 Jacobsen and Wierss, ibid. xvi. 1956. 438 AROMATIC COMPOUNDS. The constitution of para-orsellinic acid, and therefore that of orsellinic acid, follows from these considerations (Kostanecki): Orsellinic acid. co2h OH^^OH ''cH3 Para-orsellinic acid. co2h ^OH. 2235 Homohydroxysalicylic acid, C6H2(CH3)(OH)2CO2H, is prepared by heating 40 grms. of toluquinol for thirty-six hours in a bath of oil of turpentine with 130 grms. of potassium bicarbonate, 110 ccs. of water, and 40 ccs. of a saturated solution of potassium sulphite. It dissolves in 1,366 parts of water at 8°, more readily in hot water, and crystallizes from dilute alcohol in microscopic, acute rhombic plates, while, when prepared from the ammoniacal salt by precipitation with hydro- chloric acid, it separates as a crystalline powder containing half a molecule of water. Ferric chloride produces an azure-blue colouration, which passes into a beautiful green on standing or on the addition of an excess of the chloride; it reduces Fehling's solution on warming, but a neutral silver solution in the cold. It is decomposed at 210°-220" into carbon dioxide and toluquinol.1 Barium homohydroxysalicylate, (C8H7O4)2Ba + 2H2O, forms fine prismatic needles, readily soluble in water. Creosolcarboxy lie acid, C6H2(CH3)(OCH3)(OH)CO2H (1:3:4:5). According to the researches of Kostanecki, only those phenols which contain hydroxyl groups in the meta-position are con- verted into carboxylic acids by boiling with the alkali bicar- bonates, and as creosol does not belong to this class of bodies, the corresponding acid is prepared by adding sodium, warming gently and passing in a current of carbon dioxide. Creosolcarboxylic acid crystallizes from a mixture of chloroform and benzene in concentrically arranged needles, which melt at 180°-182° and sublime when carefully heated. It is readily soluble in alcohol, ether and chloroform, but only slightly in water and scarcely at all in benzene and petroleum ether; its solution is coloured deep blue by ferric chloride. The barium salt crystallizes in small, anhydrous needles, which are only slightly soluble in water. 1 Brunner, Monatsh. Chem. ii. 458. XYLYLENE ALCOHOLS. 439 Methyl creosolcarboxylate, C6H4(CH3)(OCH3)(OH)CO2.CH3, forms small, rhombic prisms, melts at 92° and gives a bluish green colouration with ferric chloride.1 ,ch2.oh XYLYLENE ALCOHOLS, C6H4< \ch2.oh 2236 Orthoxylylene alcohol was first prepared by the action of sodium amalgam on a boiling solution of phthalyl chloride, C6H4.C2O2C12 (p. 458), in glacial acetic acid, and named phthal- alcohol.2 It is also obtained by boiling its bromide with a solution of sodium carbonate 3 or potassium carbonate.4 It is tolerably soluble in water, readily in alcohol, and crystallizes in rhombic tablets, which have a bitter taste and melt at 04'5°. Concentrated sulphuric acid imparts to them a red colour and then converts them into a resinous mass. Potassium permanganate or chromic acid oxidize it to phthalic acid, while it is reduced to orthoxylene by heating with hydriodic acid and amorphous phosphorus. Orthoxylylene ethyl ether, C6H4(CH2OC2H6)2, is obtained by boiling the bromide with alcoholic potash, and is a very pleasant- smelling, oily liquid, which boils at 247°-249° (Leser). Orthoxylylene chloride, C6H4(CH2C1)2, is formed when ten ccs. of orthoxylene are heated to 190° with .35 grms. of phos- phorus pentachloride,5 as well as by heating the alcohol with hydrochloric acid, and separates from ether in crystals, which melt at 54'8° and readily sublime. Its vapour attacks the eyes with great violence. Raymann, by the action of chlorine on boiling orthoxylene, obtained an isomeric substance, which crystallizes in tablets and melts at 103°.6 These properties correspond with those of paraxylylene chloride, and the hydrocarbon employed by Ray- mann must have contained paraxylene, which is much more readily attacked by chlorine and bromine than its isomerides. This property can be made use of to detect even traces of paraxylene > in the presence of the ortho- and meta- compounds; the 1 Wende, Ber. Deutsch. Chem. Ges. xix. 2324. 2 Hessert, ibid. xii. 642. 3 Baeyer and Perkin, xvii. 122. 4 Colson, Ann. Chim. Phys. [6] vi. 104. 5 Colson and Gautier, Bull. See. Chim. xlv. 6 ; Colson, Ann. Chim. Phys. [6] vi. 108. 6 Bull. Soc. Chim. xxvi. 553. 440 AROMATIC COMPOUNDS. mixture is treated at the boiling point with sufficient bromine to form the monobromo-derivatives; any paraxylene present is converted into paraxylylene bromide, which separates out on cooling.1 Orthoxylylene bromide, C6H4(CH2Br)2 is obtained when or- thoxylene is heated with the calculated quantity of bromine to 150°-155°, or when the latter is allowed to drop into the boil- ing hydrocarbon, the temperature being gradually raised to 180°. It is also formed when orthoxylene is treated with bromine in the sunlight,2 and crystallizes from chloroform in splendid, rhombic pyramids, which melt at 94'9°, and dissolve in 5 parts of ether. Orthoxylylene iodide, C6H4(CH2I)2, is prepared by heating the alcohol with phosphorus and hydriodic acid, and crystallizes from ether in splendid, well-formed yellowish prisms, melting at 109°-110°.3 Orthoxylylene acetate, C6H4(CH2O.CO.CH3)2, is formed by the action of acetyl chloride on the alcohol; it is a crystalline mass, which melts at 37° and boils without decomposition. /CH2\ Orthoxylylene sulphide, C6H4\ yS, is obtained by heating XCH/ the bromide with an alcoholic solution of potassium sulphide, and is a colourless liquid which smells like mercaptan and solidifies in large crystals at about 0° (Leser). Diphenylorthoxylylenediamine, C6H4(CH2.NH.CcH5)2, is pre- pared by the action of aniline on the bromide. It crystallizes from alcohol in small plates, melting at 172°, and dissolves in concentrated hydrochloric acid, but is reprecipitated by water. Metaxylylene alcohol, C6H4(CH2.OH)2. This compound, which is also known as isophthalalcohol, is prepared by heating the bromide with a solution of carbonate of potassium. It is readily soluble in water and separates from ether as an oily liquid, which solidifies to microscopic, twinned crystals, melting at 46°-47°.4 Metaxylylene ethyl ether is obtained by heating the bromide with alcoholic potash, and is an oily liquid, which boils at 247°-249°, and is oxidized by chromic acid to isophthalic acid.5 1 Radziszewski and Wispek, Ber. Deutsch. Chem. Ges. xviii. 1279. 2 Schramm, ibid, xviii. 1272. 3 Leser, ibid. xvii. 1824. 4 Colson, Ann. Chim. Phys. [6] vi. 109. 5 W. H. Perkin, jun., Private communication. METAXYLYLENE CHLORIDE. 441 Metaxylylene, chloride, C6H4(CH2C1)2, is prepared by heating the alcohol with hydrochloric acid (Colson); it is also formed when metaxylene is heated with phosphorus pentachloride, the yield being, however, very poor (Colson and Gautier). It crystallizes in pointed prisms, melts at 34° and boils at 250°- 25 50.1 Metaxylylene bromide, CeH4(CH2Br)2, forms long, prismatic needles, melting at 77°, and is obtained by heating metaxylene with bromine (Colson, Radziszewski and Wispek), as well as by bringing these two substances together in the sunlight (Schramm). Paraxylylene alcohol, C6H4(CH2.OH)2, was prepared by Gri- maux by heating the chloride or bromide with 30 parts of water to 170°-180°, and was named tollylene glycol.2 It crystallizes in lustrous needles, which melt at 112°-113°, are readily soluble in water, alcohol and ether, and are converted by oxidation into terephthalic acid. Paraxylylene mono-ethyl ether, C6H4(CH2.OH)CH2.O.C2H5, is formed when the chloride is heated with alcoholic potash ; it is a pleasant-smelling liquid which boils at 250°-252°.3 Paraxylylene chloride, CcII4(CH2C1)2, is prepared by the action of chlorine on boiling paraxylene,4 or by heating the alcohol with hydrochloric acid. It may also be obtained in a similar manner to the ortho-compound by heating paraxylene with phosphorus pcntachloride (Colson and Gautier). It crystallizes from alcohol in pointed, rhombic tablets, melts at 100° and boils with decomposition at 240°-250°. Paraxylylene bromide, C6H4(CH2Br)2, is obtained by passing bromine vapour into paraxylene or by heating the alcohol with hydrobromic acid; it boils at 240°-250°, and crystallizes from chloroform in plates, which melt at 143'5°,5 and dissolve in about 50 parts of ether. Paraxylylene iodide, C0H4(Cll2I)2, is prepared by heating Ihe alcohol with hydriodic acid ; it forms fine needles, which melt at 170°, and rapidly become coloured yellow in the air. Paraxylylene acetate, C6H4(CH2.O.CO.CH3)2, is formed when the chloride is heated to 150° with an alcoholic solution of sodium acetate. It is readily soluble in alcohol and ether, and 1 Bull. Soc. Chim. xliii. 6. 2 Ann. Chem. Pharm. civ. 338. s Grimaux, Bull. Soc. Chim. xvi. 193. 4 Grimaux, Zeitschr. Chem. 1867, 381. 5 Radziszewski and Wispek, Ber. Deutsch. Chem. Ges. xviii. 1280 ; Low, ibid. xviii. 2072. 442 AROMATIC COMPOUNDS. crystallizes from the latter in hard, lustrous plates, which have a pungent, camphor-like taste, and melt at 47°. Paraxylylene monobenzoate, C(.H4.(CH2.OCO.C6H5)CH2.OH, is obtained by heating the chloride with an alcoholic solution of sodium benzoate, and crystallizes in long, thin needles, melting at 73°_74° HYDROXYMETHYLBENZOIC ACIDS, /C02h C6hZ xCH2.OH 2237 These compounds are isomeric with the hydroxytoluic acids, from which they differ in being alcohols while the latter are phenols. Parahydroxymethylbenzoic acid was prepared by Dittmar and Kekule, who named it oxy methylphenylformic acid, by heating paratoluic acid with bromine at 160°-'170°, and boiling the product with baryta water. It crystallizes in white plates or flat needles, which are more readily soluble in water than para- toluic acid, melt a few degrees higher and sublime in feathery needles.1 Orthohydroxy methylbenzoic acid was first prepared by Hessert, who named it " Bcnzolorthoalcoholsaure" by the action of alkalis on phthalide, which is its anhydride. Acids precipitate it as a fine powder, which is slightly soluble in cold water, readily in alcohol, has a strongly acid reaction, and melts at 118°, being thus converted into the anhydride, which is also formed when the acid is simply boiled with water. Silver orthohydroxymethylbenzoate, C8H-O3Ag, crystallizes from water in small octohedra. Phthalide, C8H6O2, was obtained by Kolbe and Wischin, who prepared it by the action of zinc and hydrochloric acid on phthalyl chloride, C8H4O2C12, and named it phthalaldchyde, C6H4(COH)2.2 It is also formed by the action of phosphorus and hydriodic acid on the chloride,3 and when orthoxylidene chloride is boiled with water and lead nitrate.4 Hessert has proved 1 Ann. Chern. Pharm. clxii. 337. 2 Zeitschr. Chem. 1866, 315. 3 Baeyer, Ber. Deutsch. Chem., Ges. x. 123. 4 Raymann, Bull. Soc. Chim. x. 1180. PHTHALIDE. 443 that it is not the aldehyde of phthalic acid but the anhydride or lactone of the preceding compound.1 Its formation was explained by the following reactions : /COCI /CH2.0H C6H4< + 4H = CfiHZ " + HC1. \COC1 ZCOC1 /CH2.0H /CH.,. c6h4< " = c6hz >0 + HCl. ZCOC1 \ co z It has since been shown that phthalyl chloride has not the constitution assumed above (p. 460), and the formation of phthalide is now represented much more simply : zCCU /CH.,X C6n/ >0 + 4H = C6H4( " >0 + 2HC1. \COZ zcoz This is confirmed by the observation of Hjelt,who found that it is also obtained when bromine is passed into orthotoluic acid heated to 140°; the brominated acid which is first formed being decom- posed as follows:2 zCH2Br /CH2X C6HZ " =C6H4< >0 + HBr. XCO.OH ZCOZ It crystallizes from boiling water in needles which smell like cinnamon, melts at 73° and boils at 290° (Griibe). It does not combine with hydroxylamine,3 gives no compounds with the acid sulphites of the alkalis and does not reduce ammoniacal silver solution (Hessert). It is oxidized to phthalic acid by alkaline permanganate, while it is reduced to orthotoluic acid on heating with phosphorus and hydriodic acid, and to orthoxylene together with a little toluene by heated zinc dust. Monobromophthalide is formed by the action of bromine vapour on heated phthalide ; it crystallizes in plates, melting at 86°, and is converted into phthalaldehydic acid (p. 447) when heated with water ; it has, therefore, the following constitution :4 zCHBr c6h4( > O. ZCO 1 Ber. Deutsch. Chem. Ges. x. 1445 ; xi. 237. 2 Ibid. xix. 412. 3 Lach, ibid. xvi. 1782. 4 Racine, ibid. xix. 778. 444 AROMATIC COMPOUNDS. Dibromophthalidc, C8H4Br2O2, is obtained, together with dibromonaphthoquinone, by the oxidation of a-dibromo- naphthalene with chromic acid, and crystallizes from boiling alcohol in hard, white prisms, which sublime in needles and melt at 187'5°; it does not reduce ammoniacal silver solution and only dissolves slowly in boiling caustic soda solution.1 It has the following constitution : CBr HC^^C-CH2 I II > O. HC C- CO CBr Guareschi obtained dichlorophthalide in a similar manner from dichloronaphthalene; it resembles the bromine compound, and melts at 163°.2 Hydrophthalide,, C8H8O2, is formed together with phthalyl- pinacone, C1CH18O4, by the action of sodium amalgam on an acid solution of phthalide, and is a syrupy mass, extremely soluble in all solvents ; it probably has the following constitution (Hessert) : /CH2 c6h4( > o. \CH.0H Phthalimidine, C8H7NO, is obtained by heating phthalide with zinc ammonium chloride, or by treating it at its boiling- point with ammonia : /CO /C-NH c6h4< >o + nh3 = c6h4< >0 +h2o. \ch2 \ch2 It may be more simply prepared by the action of tin and hydrochloric acid on phthalimide, CcII4(C2O2)NH. It is readily soluble in alcohol and hot water, crystallizes in prisms or needles, melts at 150° and boils at 337°. When sodium nitrite is added to its solution in hydrochloric acid, yellow needles of nitrosoplithalimidine separate out; they melt at 156°, 1 Guareschi, Ann. Chern. Pharm. ccxxii. 282. 2 Ber. Deutsch. Chem. Ges. xix. 1155. METHYLPHTHALIMIDINE. 445 and are rapidly converted into orthohydroxymethylbenzoic acid by the action of aqueous caustic soda: ZC=N -NO zCO2Na C6H4< >0 +NaOH = C6H4< + N2. xCH2 xCHq.OH Hydrochloric acid precipitates either the free acid or phthalide from this solution according to the temperature, and the latter substance is in fact most conveniently prepared in this way from phthalimide, which can itself be readily obtained from phthalic acid.1 Methylphthalimidine, C8H6O(NCH3), is formed by the action of tin and hydrochloric acid on methylphthalimide, and is readily soluble in water, alcohol and ether, from which it crystallizes in large tablets, melting at 120°; it boils without decomposition at about 300°.2 Phenylphthalimidine or Phthalide-anil is prepared by heating phthalide to 200°-220° with aniline : /CO x ,C=N.C6H5 c6h4( >0+h.7n.c6h5=c6h4< >0 +h20. \ch/ " \ch2 It crystallizes from alcohol in silvery plates, melting at 160° (Hessert). Phthalidehydr azide, C14H12N2O, is formed by heating phthalide with phenylhydrazine for some time : /CH2 /CH„ c6h4< >o+n2h3.c6h5=c6h/ >o +h2o. XCO \C=N2H.C6H5 It crystallizes from hot water or alcohol in needles, which possess a silver lustre, and melt at 16 5°.3 Paranitrophthalide, C8H5(NO2)O2, is prepared by dissolving 20 grms. of phthalide in 200 grms. of sulphuric acid, and running in a solution of rather more than the calculated quantity of potassium nitrate in 80 grms. of sulphuric acid, the solution being well cooled during the operation. It forms long, colourless needles, which melt at 141°, and are almost insoluble in cold water, but dissolve slightly on boiling, more readily in alcohol, 1 Grabe, Ber. Deutsch. Chern. Ges. xvii. 2598 ; xviii. 1408. 2 Grabe and Pictet, ibid, xviii. 1173. 3 V. Meyer and Miinchmeyer, ibid. xix. 1706 and 2132. 446 AROMATIC COMPOUNDS. and readily in benzene. Alcoholic potash produces a charac- teristic violet colouration, while aqueous potash forms a yellow solution. Dilute sulphuric acid precipitates paranitrohydroxy- methylbenzoic acid, C6H3(NO2)(CH.,.OH)CO2H, from the cool solution. This body crystallizes in microscopic needles united in stellate forms, and is extremely soluble in ether, readily in alcohol and hot water. It melts at 129°, and decomposes at a higher temperature into water and nitrophthalide. Par amidophthalide, C8H5(NH2)O2, is obtained by the reduc- tion of the preceding compound, and is almost insoluble in water, but dissolves slightly in alcohol, and more readily in chloroform, from which it crystallizes in short prisms, melting at 178°. Its hydrochloride forms needles which are readily soluble in water. It also dissolves in alkalis, salts of para- amidohydroxymethylbenzoic acid being formed. The free acid has not yet been prepared. When paranitrophthal ide is heated with hydriodic acid and phosphorus, 7-amido-orthotoluic acid is formed.1 Orthonitrophthalidc was prepared by Beilstein and Kurbatow, together with the corresponding nitrophthalic acid, by oxidizing a-nitronaphthalene with a solution of chromium trioxide in acetic acid. They mention that the substance obtained has the formula of nitrophthalaldehyde, but must possess a different constitution, because it is only attacked with difficulty by the oxidizing mixture just named.2 Its properties prove that it is actually orthonitrophthalide.3 It crystallizes in small plates, melting at 136°, is much more readily soluble in alcohol and chloroform than the para-com - pound, and forms a yellow solution in alkalis. On heating in a sealed tube with dilute hydrochloric acid, it is smoothly con- verted into v-nitrophthalic acid (Honig). 1 Honig, Ber. Deutsch. Chern. Ges. xviii. 3447. 2 Ann. Chern. Pharm. ccii. 217. 3 Guareschi, ibid. ccxxii. 283 ; Honig, loc. cit. PHTHALALDEHYDE. 447 ALDEHYDES, C6H4(CHO)2, AND ALDEHYDO- ACIDS, C6H4(COH)(COOH). 2238 Phthalaldehyde. When orthoxylene is submitted at the boiling-point to the continued action of chlorine, or is heated to 195° with eight parts of phosphorus pentachloride, orthoxylidene tetrachloride, C6H4(CHC12)2, is formed ; it crystallizes from ether in large asymmetric prisms, melts at 89° and boils at 273°-274°. On heating with water it is converted into phthalaldehyde, which is also formed by the oxidation of phthal alcohol, and is an oily liquid, which has not yet been prepared pure since it so readily passes into the isomeric phthalide (Hjelt). According to Colson and Gautier, phthalaldehyde is a yellow crystalline substance melting at 52°. Ammonia produces a deep blue or yellow colouration, followed by a brown precipitate.1 Phtha.laldehydic acid is prepared by heating monobromo- phthalide with water :2 /CHBix /CHO C6H4< >O + H2O = C6H4< +HBr. \ CO z \CO.OH It may also be obtained by heating orthoxylene to 200 with 12'5 parts of phosphorus pentachloride and boiling the product, xylidenyl pentachloride, C6H4(CHC12)CC13, with water (Colson and Gautier). It forms lemon-yellow crystals, which melt at 98° to 100°, and are readily soluble in water. Its phenylhydrazine compound crystallizes in fine, yellow needles. Isophthalaldehyde is prepared in a similar manner from meta- xylidene tetrachloride, C6H4(CHC12)2, which is a liquid boiling at 273°. It is an oily liquid which, as well as its solution in water, gives a green colouration with ammonia, followed by a brown precipitate (Colson and Gautier). Terephthalaldehyde, C6H4(CHO)2, was obtained by Grimaux from paraxylylene chloride, C6H4(CH2C1)2, by boiling with lead nitrate and water,3 while Low prepared it by the same method from paraxylylene bromide.4 1 Hjelt, Bar. Deutsch. Chem. Ges. xviii. 2879 ; xix. 411 ; Colson and Gautier, Bull. Soc. Chim. xlv. 6 and 506. 2 Baeine, Ber. Deutsch. Chern. Ges. xix. 778. 3 Jahrsber, Chem. 1876, 490 ; Colson and Gautier, loc. cit. 4 Ann. Chem. Pharm. ccxxxi. 361. 448 AROMATIC COMPOUNDS. It is also formed, when paraxylene is heated to 190° with eight parts of phosphorus pentachloride, and the paraxylidene tetrachloride which is thus formed boiled with water for some time. The latter forms well-developed crystals, melting at 93°. Terephthalaldehyde is only very slightly soluble in cold ether, but readily in alcohol and tolerably freely in hot water, from which it crystallizes in fine needles, melting at 116°. It forms a readily soluble compound with acid sodium sulphite. Con- centrated caustic soda solution decomposes it with formation of parahydroxymethylbenzoic acid, paraxylylene alcohol and tere- phthalic acid : /CHO /CH„ .OH c6h4< +h2o=cgh4( XCHO \CO.OH. /CH2.OH /CH2.OH /CO.OH 2C6H4( ~ =C6H4( " +C6H4< XCO.OH \CH2.OH xCO.OH. Terephthalaldehyde is also obtained when paraxylylene bro- mide is dissolved in cold, concentrated nitric acid. The com- pound C24H20Br2O4 is simultaneously formed ; it is insoluble in water, but dissolves readily in ether, from which it crystallizes in stunted needles, which melt at 80° and are converted into tere- phthalaldehyde, paraxylylene alcohol and hydrobromic acid, by heating with water: /CHO c6h4( \CHBr.O.CH2X >C6H4 + 2H2O = /CHBr.O.CH/ C6H4( \CHO /CHO HO.CH.?X 2C6H4< + >C6H4 + 2HBr. \CHO HO.CH/ It is noteworthy that concentrated nitric acid exerts an oxidizing action upon paraxylylene bromide, and does not effect nitration as in the case of benzyl chloride.1 Xylylidencdiamine, C8H8N2, is deposited in very brittle, 1 Low, Ber. Deutsch. Chem. Ges. xviii. 2072. HYDROBENZAMIDE TRIALDEHYDE. 449 vitreous crystals when an alcoholic solution of terephthalaldehyde is saturated with ammonia and allowed to stand: ZCHO ZCH=NH C„H/ +2NH3 = C6H4< +2H2O. 'CHO \CH=NH It is also formed when dry ammonia is passed over the aldehyde, but is decomposed again by acids, or even on boiling with water, into ammonia and the aldehyde. Hydrobenzamide trialdehyde, N2(CH.C6H4.CHO)3, is formed by the action of aqueous ammonia on terephthalaldehyde, as a white powder consisting of matted microscopic needles, which is insoluble in water and alcohol and is dissolved by acids, the aldehyde being set free.1 Nitroterephthalaldehyde, C6H3(NO2)(CHO)2. In order to pre- pare this substance, a solution of the aldehyde heated to 150° is treated with an equal quantity of potassium nitrate dissolved in sulphuric acid, kept at a temperature of 110°-115° for 10-15 minutes, poured into water and then extracted with ether. It is very readily soluble in alcohol, with greater difficulty in hot water and ether, crystallizing from the latter in rhombohedra, which melt at 86° and sublime in large needles. A blue indigo derivative is formed when it is heated with caustic soda and acetone (p. 146) (Low). Terephthalaldehydic acid, CGH4(CHO)CO2H, is formed, together with terephthalic acid, by the oxidation of the aldehyde with chromic acid solution. It is only slightly soluble in ether and chloroform, and still less readily in hot water, from which it crystallizes in needles, which melt at 246° and sublime in well- formed needles. It forms a barium salt which is readily soluble in water, as well as a scarcely soluble silver salt, and only reduces ammoniacal silver solution after continued boiling. The ethyl ether, C6H4(CHO)CO2.C2H5, forms groups of pointed needles, easily reduces ammoniacal silver solution on heating, and gives all the reactions of benzallehyde (Lbw). Hydrobenzamidctricarboxylic acid, N2(CH.C6H4.CO2H)3 is not formed by the action of ammonia on the aldehydo-acid, but by the oxidation of the trialdehyde with potassium permanganate. It crystallizes in nacreous, rhombohedral tablets (Oppenheimer). Nitroterephthalaldehydic acid, C6H3(NO2)(CHO)CO2H(2:1: 4, 1 Oppenheimer, Ber. Deutsch. Chern Ges. xix. 574. 450 AROMATIC COMPOUNDS. is prepared in a similar manner to nitrophthalaldehyde. It is readily soluble in hot water, and crystallizes from it in large, four-sided needles, which melt at 160°. On heating with caustic soda solution and acetone it is converted into indigocarboxylic acid, C16H8N2O2(CO2H)2, a reaction which proves that the nitroxylyl-group stands in the ortho-position with respect to the aldehyde group. In its preparation a small quantity of the isomeric acid (NO2: COH : CO2H -3 :1 : 4), which melts at 184°, is also formed (Low). /CO2H THE PHTHALIC ACIDS, C6HZ xCO2H. 223g In the year 1836, Laurent prepared naphthalic acid (acide naphtalique), C10H0O5, by boiling naphthalene tetrachloride, C1OH8C14, with nitric acid,1 and Marignac, who was subsequently confirmed by Laurent, proposed for it the formula C8H6O4. The latter chemist found that it is also obtained, together with other products, by boiling naphthalene with nitric acid, oxalic acid being always simultaneously formed.2 Since it no longer belongs to the naphthalene series, he named it phthalic acid (acidc phtalique).3 It decomposes on distillation with lime, as was shown by Marignac, into carbon dioxide and benzene.4 During his investigation of the colouring matter of madder root, Schunck found that alizarin is converted by oxidation into alizaric acid, CLH.,,0-,5 which, according to Gerhardt,6 con • firmed by Strecker and Wolff,7 is identical with phthalic acid. The naphthesic acid (acide naphtesique), C10HGO4, which Laurent had obtained by the action of potassium dichromate and sulphuric acid on naphthalene,8 was also recognized as phthalic acid by Scheibler 9 and F. Lossen, the latter of whom found that it is also formed by the action of potassium permanganate on naphthalene.10 An isomeric substance was prepared by Cailletet 1 Ann. Chim. Phys. Ixi. 114 ; Ann. Chem. Pharm. xix. 38. 2 Ibid, xxxviii. 13. 3 Ibid. xli. 107. 4 Ibid. xlii. 215. 5 Ibid. Ixvi. 197. 6 Compt. Rend. Trav. Chim. 1849, 222. 7 Ann. Chem. Pharm. Ixxv. 12. 8 Revue Scient. xiv. 560 ; Compt. Rend. xxi. 36. 9 Ber. Deutsch. Chem. Ges. i. 125. 10 Zeitschr. Chem. x. 419 ; Ann. Chem. Pharm. cxliv. 71. THE PHTHALIC ACIDS. 451 in 1847, by heating oil of turpentine (essence de tMbenthine') with dilute nitric acid, and named on this account terephthalic acid (acide t^r^phtalique).1 Five years previously, Persoz had obtained cumino-cyminic acid (acide cumino-cyminique') by the oxidation of the ethereal oil contained in the seeds of Roman cumin (Cuminum Cyminum), but had not analysed it.2 Hofmann, in attempting to purify cumic acid, C10H12O2, by treatment with dilute sulphuric acid and potassium dichromate, found that it is thus oxidized to insolinic acid, C9H8O4, which he also obtained from Roman cumin oil, and which, as he pointed out, is very similar to terephthalic acid,3 these being afterwards shown by H. Muller and Warren de la Rue to be identical.4 Fittig then prepared a third acid by the oxidation of isoxylene and named it isophthalic acid.5 The methods employed in the determination of the position of the carboxyl groups in these three acids have already been described in detail (Part III., p. 38). Quite recently, however, Nolting has added a very simple proof of their constitution. The three acids can be quantitatively obtained by the oxidation of the three dimethylbenzenes with an alkaline solution of potassium permanganate. Paraxylene yields terephthalic acid and on nitration gives only one mononitroxylene, while ortho- xylene is oxidized to phthalic acid and yields two nitro-deriva- tives. Finally, three nitroxylenes can be obtained from isoxylene, which corresponds to isophthalic acid. The position of the carboxyls is, therefore, in : Phthalic acid 1:2 Isophthalic acid 1:3 Terephthalic acid 1:4 This proof is exactly analogous to that employed by Kbrner to determine the positions of the bromine atoms in the three dibromobenzenes, and by Griess in ascertaining the constitution of the diamidobenzenes (Part III., pp. 47, 48).6 1 Ann. Chim. Phys. [3] xxi. 28. 2 Journ. Prakt. Chem. xxiv. 55 ; Compt. Rend, xxxiii. 433. 3 Ann. Chem. Pharm. xcvii. 197. 4 Ibid. exxi. 86. 5 Ibid, cxlviii 11. 6 Ber. Deutsch. Chem. Ges. xviii. 2687. 452 AROMATIC COMPOUNDS. PHTHALIC ACID. 2240 This acid is most simply formed by the oxidation of orthoxylene or orthotoluic acid 1 with potassium permanganate or dilute nitric acid.2 Carius found that it is also obtained in small quantity when benzene or benzoic acid is treated with manganese dioxide and concentrated sulphuric acid in the cold,3 diphenylbenzene, CcH4(C6H5)2, being probably the intermediate product (Part III.,p. 76). According to Guyard, it is also formed when a mixture of salicylic, formic and sulphuric acids is heated.4 Phthalic acid is manufactured from naphthalene, C10H8, which is first converted into the tetrachloride, C1OH8C14, by passing chlorine through the fused hydrocarbon, the plant shown in section and elevation in Figs. 2 and 3 being employed. The mass becomes heated to such an extent that the iron vessel containing it has to be cooled by water, the temperature being kept below 160°-170°, above which carbonization takes place. The tetrachloride is also manufactured by grinding naphthalene with water and potassium chlorate, making up the paste into balls, and bringing these, after drying, into concentrated hydro- chloric acid. The chlorate may be replaced by bleaching powder which is mixed with naphthalene and pressed into cakes. One part of the chloride is then heated with 5-6 parts of nitric acid of sp. gr. 135 in flat stoneware retorts placed in an air-bath (Figs. 4 and 5). The vapours which are evolved are condensed and employed in a subsequent operation. The acid may be finally purified by crystallization, but the product is usually distilled and thus immediately converted into the anhydride. The yield amounts to 30 per cent, on the naphthalene.5 Phthalic acid is also formed when naphthalene is heated to 130° with 20 parts of nitric acid of sp. gr. 1T5, 40 percent of the theoretical yield being obtained.6 1 Weith, Ber. Deutsch. Chem. Ges. vii. 1057. 2 Piccard, ibid. xii. 579. s Ann. Chern. Pharm. cxlviii. 60. 4 Bull. Soc. Chim. xxix. 248. 6 Schultz, Steinkohlenthecr, S. 540 ; s. E. Fischer, Ber. Deutsch. Chem. Ges. xi. 735 ; Depouilly, Ann. Chem. Pharm. cxxxvii. 373. 6 Beilstein and Kurbatow, Ann. Chem. Pharm. ccii. 215. PHTHALIC ACID. 453 Fig. 2. 454 AROMATIC COMPOUNDS. Fig. 3. PHTHALIC ACID. 455 Properties. It crystallizes from hot water in thin plates or lustrous, rhombic prisms,1 which dissolve in 180 parts of water at 11-5°. 100 parts of ether absolute alcohol 90 per cent, alcohol, dissolve at 15° 0'684 1008 11'70 parts.2 Fig. 4. Varying statements have been made as to the melting-point of the acid, the discrepancies being due to the fact that it loses water on heating, the anhydride being formed. According to 1 Scheibler, Ber. Deutsch. Chern. Ges. i. 125; Groth, Jahresher. Chern. 1870, 5. 2 Bourgoin, Bull. Boe. Chim. xxix. 247. 456 AROMATIC COMPOUNDS. Lossen, this takes place at 184°, while Ador states that the unbroken crystals melt at 213°, but the powder at 203°.1 It is completely burned by chromic acid solution on heating,2 and on this account cannot be prepared by means of this reagent from orthoxylene or other ortho-compounds which possess two side chains. On distillation with lime it decomposes into carbon Fig. 5. dioxide and benzene, but if the temperature be not allowed to rise above 330°-350°, it is converted into benzoic acid, which was formerly manufactured in this way (p. 155). 2241 The normal phthalates of the alkali metals are readily soluble in water and crystallize in small plates or scales. Acid ammonium phthalate, C8H5O4(NH4), separates on the spontaneous evaporation of a solution of the normal salt in six- 1 Ann. Chem. Pharm. clxiii. 230. 2 Fittig and Bieber, ibid. clvi. 242 SALTS OF PHTHALIC ACID. 457 sided, rhombic tablets, prisms or pyramids, which dissolve very readily in water but only slightly in alcohol. Calcium phthalate C8H4O4Ca + H2O, is tolerably soluble in water and crystallizes in lustrous, rhombic prisms.1 Acid barium phthalate, (C8H5O4)2Ba, is readily soluble in hot water and crystallizes in small, rhombic prisms. Normal barium phthalate, C8H4O4Ba, is obtained by preci- pitating the normal ammonium salt with barium chloride, or by mixing hot solutions of the acid and caustic baryta; it forms small, white scales or silky needles, which are only slightly soluble in hot water. On evaporating the solution, a basic salt separates out in crystalline crusts (Carius, Hermann). Lead phthalate, C8H4O4Pb, is a precipitate, consisting of scaly crystals. Copper phthalate, C8H4O4Cu + H2O, crystallizes in lustrous blue, rhombic prisms, which dissolve readily in hot water (Hermann). Silver phthalate, C8H4O4Ag2, forms a light, crystalline powder, which is tolerably soluble in water and detonates when rapidly heated. Ethers of phthalic acid are formed by the action of hydrochloric acid on the alcoholic solution of the acid and by that of an alco- holic iodide upon the silver salt. The two following have been prepared, and are both odourless liquids:2 Boiling-point. Methyl phthalate, C6H4(CO2.CH3)2 280° Ethyl phthalate, C6H4(CO2.C2H5)2 294° Phthalyl oxide or Phthalic anhydride, (C6H4.CO2)2O, is formed when the acid is heated alone or with acetyl chloride : /CO.OH C6H4< +ch3.coci = XCO.OH /C°\ C6H4< >0 + ch3.co.oh + HC1. ZCOZ The anhydride remains behind in splendid prisms after the acetic acid and excess of acetyl chloride have been removed.3 It is manufactured by subliming phthalic acid in a current of 1 Hermann, Ann. Chern. Pharm. cli. 77. 2 Grabe and Born, ibid, cxlii. 344 ; Grabe, Per. Deutsch. Chem. Ges. xvi. 860. 3 Anschutz, ibid. x. 235 ; Ann. Chem. Pharm. ccxxvi. 1. 458 AROMATIC COMPOUNDS. air, or better, of carbon dioxide, the apparatus shown in Fig. 6 being employed.1 It is thus obtained in long, white, pliant, rhombic needles, while on rapid heating it distils as a liquid and then solidifies to a hard, crystalline mass. It melts at 128° and boils at 284'5° (Schultz, Griibe), is only very slightly soluble in cold, more readily in hot water, and is reconverted into phthalic acid when boiled with water for a long time, more rapidly in presence of alkalis. It is reduced by zinc dust and acetic acid to phthalide, di- phthalyl (v. post) and zinc phthalate being also formed.2 It is employed in the manufacture of dyes and of many other com- pounds, as it very readily enters into chemical reactions. Thus it combines with the acid anhydrides, forming with acetic zC=CH.CO.2H anhydride, phthalylacetic acid, CGH4; >0 XC0 It also combines with the aromatic hydrocarbons in presence of aluminium chloride, forming acids ; thus benzene yields benzoyl- benzoic acid : ZCOX /CO.OH c6h4( >0+c6h6=c6h4< xcoz xco.cjl. b d A specially characteristic property is that of combining with phenols on heating to form phthaleins, water being eliminated. As already mentioned, resorcinol yields fluorescein in this way, the formation of this substance, which is employed as a test for the presence of the phenol in question, taking place in the following manner: .OH zc6h/ co C\ z° / I OTT / I 4\ C„H4/o +2C6H4<q| =C8H/o 'OH+ 211,0. CO CO 2242 Phthalyl chloride, C8H4O2C12, was first prepared by Hugo Muller from phthalic acid by the action of phosphorus penta- 1 Schultz, Steinkohlentheerc. 9 Wislicenus, Ber.Deutsch. Chem. Ges. xvii. 2178. PHTHALYL CHLORIDE. 459 Fig. 6.-Apparatus for the Sublimation of Phthalic Anhydride. Cast iron cylinder to receive the crude phthalic acid : it is surrounded by a wrought iron cylinder b, which is partially filled with oil, phenanthrene, &c.-K. Fire.-e. Ventilating fan to drive the vapours into the wooden chests g, which are covered with sacking.-h. Coarse wire grating.-i. Light, movable trap, covering the exit of the current of air.-The working doors are shown in the figure by dotted lines. 460 AROMATIC COMPOUNDS. chloride.1 From analogy with other acid chlorides it would be formed according to the following equation : zC0.0H /COCI C0H4Z 4- 2PC15 = C6H z 4-2POCL 4- 2HC1. zC0.0H ZCOC1 Careful investigation, however, has shown that it does not possess this constitution. It is formed in two stages : /CO.OH ZCOX C6H4z 4-PC15 = C6H4z )O4-POC13 + 2HC1. zC0.0H ZCOZ /COX /CC12X C6H4z >0 + PC15 = C6H4z >0 4- POC13. ZCOZ ' z COz It is also obtained, therefore, when equal molecules of phthalic anhydride and phosphorus pentachloride are heated together for 12 hours at 17O0.2 In order to prepare it, phthalic acid is boiled with rather more than two molecules of phosphorus chloride for 5-6 hours and then distilled.3 It is an oily liquid, which boils at 268° and solidifies at about 0°. It is only slowly decomposed by boiling water and even boiling caustic soda solution. On heating with finely-divided silver, diphthalyl, which will be subsequently described, is obtained, its formation taking place according to the following equation: / C° \ ZCO\ C6H4< >0 C6HZ >0 ZCC12Z z C z + 4 Ag = || + 4 AgCl. /CC12\ / c x C6H4z >0 C6H4z >0 z CO z ZCOZ The proof that it possesses this constitution rests not only on the whole behaviour of the substance, which shows it to be a dilac- 1 Zeitschr. Chem. 1863, 257. 2 Claus and. Hoch, Ber. Deutsch. Chern. Ges. xix. 1187. 3 Wischin, Ann. Chem. Pharm. cxliii. 259. PHTHALYL CHLORIDE. 461 tone, but also on the fact that it is formed when phthalide is heated with phthalic anhydride :1 ZCO x . /COX C6H4< >0 C6H4< >0 XCH 2Z z C z 11+ h2o. /C°\ / c K ^H4< >0 c6hz )o xcoz xcoz The following compounds have been prepared by the action of sodium methylate and ethylate on phthalyl chloride: /C(OCH3)2 Boiling-point. C6H4< >0 280° XCO /C(OC2H5)2 C6H4z >0 294° XCO These are liquids which boil at the same temperature as the isomeric phthalic ethers, from which they differ only in possess- ing a slightly lower specific gravity. That they are actually distinct bodies is shown by the fact that tetrachlorophthalic acid yields compounds which differ both in crystalline form and melt- ing point from those derived from its chloride.2 The corresponding phenyl ether, C6H4(CO)C(OC6H5)2O, is prepared by heating the chloride with phenol, and crystallizes from alcohol in small prisms, melting at 7O0.3 When phthalyl chloride is heated in a sealed tube with phosphorus pentachloride to 210°-220°, two isomeric chlorides, C8H4C14O, are formed, both of which crystallize in monosym- metric forms; the one melts at 47°, and the other, which is also a product of the action of phosphorus pentachloride on phthalide, at 88°. Theory, indeed, allows the formation of two isomeric tetrachlorides : /CC12\ C6H4Z >0 xcciz /COCI c6hz zcci3. The compounds in question, however, exhibit an identical chemical behaviour. On heating with concentrated sulphuric acid, or on boiling with alcoholic potash, they are converted into 1 Grabe and Guye, Ber. Deutsch. Chern. Ges. xvii. 2851. 2 Grabe, Ber. Deutsch. Chern. Ges. xvi. 860. 3 Schreder, ibid. vii. 705 ; v. Gerichten, ibid. xiii. 419. 462 AROMATIC COMPOUNDS. phthalic acid, and phenol combines with them to form the phenyl ether mentioned above. These facts seem to indicate a case of physical isomerism, but all endeavours to convert either of the compounds into the other have proved unsuccessful (v. Gerichten). According to Claus and Hoch, the tetrachloride, which melts at 88° and boils at about 274°, is alone obtained and is best prepared by heating for 15 hours at 245°. Carbonyl chloride and orthoclilorobenzoyl chloride are also formed in the reaction.1 A compound is formed by the action of zinc ethyl on phthalyl chloride, which is looked upon by Wischin as phenylenediethyl- acetone, C6H4(CO.C2H5)2. It separates from ethereal solution in splendid crystals, which possess a pleasant, fruity smell, and melt at 52°. Wischin was, however, unable to obtain a com- pound of it with acid sodium sulphite, and V. Meyer has shown that it is not a ketone, since it does not form a hydroxylamine compound.2 The constitution of this compound can readily be explained in accordance with the present views in regard to phthalyl chloride, and is as follows : C2H5\ /C2H5 > C < C6H4( >0. zC0z Succinyl chloride (Part II., p. 191) has obviously an analogous constitution to phthalyl chloride, and its reduction to the anhydride or lactone of 7-hydroxybutyric acid (Part. IL, p. 169) thus receives a simple explanation: /CC12\ /CH2x C2H4z >0 + 4H = C2H z >0 + 2HC1. ZCO z ZCO z Phthalyl sulphide or Thiophthalic anhydride, C8H4O2S, is formed by the action of potassium hydrosulphide on phthalyl chloride 3 or its phenyl ether :4 /CC12\ ,CSX C6H4Z )O + 2KSH = C6H 4Z >0 + 2KC1 + SH2. z CO z ZCOZ It crystallizes from alcohol in small plates or needles, melts at 114° and boils at 284°. 1 Bcr. Deutsch. Chem. Ges. xix 1187. 2 Ibid. xvii. 817. 3 Sehreder, ibid. vii. 705. 4 Grabe and Zschokke, ibid. xvii. 1175. PHTHALAMIC ACID. 463 2243 Phthalimide, C8H4O2(NH), is obtained by heating acid ammonium phthalate :1 zC0.0NH4 / C=NH c6h4< =C6H4< >o + h.,o. ZCO.OH ZCO It is also formed by the action of ammonia on the anhydride, chloride,2 or sulphide,3 as well as by heating phthalic acid with ammonium or potassium thiocyanates.4 It is insoluble in cold water, slightly soluble on boiling, and crystallizes from ether in six-sided prisms, w'hich melt at 228°5 and sublime in small plates. It is decomposed on heating with slaked lime into carbon dioxide and benzonitril,6 and is reduced to phthalimidine (p. 444) by tin and hydrochloric acid. When phthalimide is heated with aniline or one of its homologues, ammonia is evolved and the corresponding substi- tuted phthalimide formed. If a phenol be substituted for the amine, ammonia is also evolved, and a substance belonging to the class of phthaleins is produced. These bodies are identical with those prepared from phthalic anhydride.7 Potassium phthalimide, C8H4O2(NK), is obtained in white plates by adding alcoholic potash to an alcoholic solution of phthal- imide (Cohn). Silver phthalimide, C8H4O2(NAg), is formed as a heavy, white precipitate when silver nitrate is added to an aqueous solution of the potassium salt, or when an alcoholic solution of phthalimide is treated with an ammoniacal silver solution (Laurent). Phthalamic acid, C6H4(CO.NH2)CO2H. Marignac prepared the ammonium salt of this acid by dissolving anhydrous naph- thalic acid (phthalic acid) in ammonia, and named it naphthal- amide? It was also obtained by Laurent, who added ammonia to a hot, alcoholic solution of the anhydride .9 ,cox zco.nh2 C6H4< >0 + 2NH3 = C6H4< XCOZ ZCO.ONH4 1 Laurent, Ann. Chern. Pharm. xli. 110. 2 Kuhara, Amer. Chern. Journ. iii. 26. 3 Grabe and Zschokke, loo. cit. 4 Ossian Aschan, Ber. Deutsch. Chern. Ges. xix. 1398. 6 Cohn, Ann. Chern. Pharm. ccv. 301. 6 Laurent, Jahresb. Chern. 1868, 549. 7 Hall, Private Communication. 8 Ann. Chern. Pharm. xlii. 219.< 9 Ann. Chiin. Phys. [3] xxiii. 117. 464 AROMATIC COMPOUNDS. The barium salt is formed when phthalimide is boiled with baryta water (Kuhara), and the potassium salt by the continued boiling of potassium phthalimide with water.1 It may be more simply prepared by the action of 25 per cent, caustic potash solution on phthalimide.2 When concentrated hydrochloric acid is added to the solution, the phthalamic acid is gradually deposited in short, well developed, transparent prisms, which melt at 148°- 149° and decompose at a slightly higher temperature into water and phthalimide. It has an acid taste, is tolerably soluble in cold water and is gradually converted by it into acid ammonium phthalate, the change taking place rapidly on boiling (Aschan). Pthyl phthalimide, C6H4O2(NC2H5), is prepared by the distilla- tion of phthalic anhydride with aqueous ethylamine; it crystal- lizes in needles or prisms, melts at 78'5° and boils at 276°-278°.4 Acetphthalimide, C8H4O2(NCO.CH3), is formed by heating phthalimide with acetic anhydride for some time. It crystallizes in large octohedra and is decomposed by boiling water or by alkalis in the cold into acetic acid and phthalimide.5 Phthaluric acid is obtained by heating phthalic anhydride with amido-acetic acid: /COX C6H4< >O + NH2.CH2.CO2H = \coz /C=N.CH2.CO2H c6h4< >0 +h20. XCO It crystallizes from hot water in long, thin needles, which melt at 191°-192°, and are decomposed on boiling with con- centrated hydrochloric acid into phthalic and amido-acetic acids.6 Phenylphthalimide or Phthalanil, C8H4O2(NC6H6), is prepared by distilling phthalic acid with aniline; it crystallizes from alcohol in needles, which melt at 205°, but sublime at a lower temperature.7 On boiling with ammonia and alcohol, it is con- verted into phthalanilic acid, or phenylphthalamic acid : /C=NC6H6 zCO.NH.CeH5 c6h4< >0 +h2o=c6h4( \co \CO.OH. 1 Landsberg, Ann. Chem. Pharm. ccxv. 198. 2 Ossian Aschan, Ber. Deutsch. Chem. Ges. xix. 1401. 3 Michael, ibid. x. 1646. 4 Wallach and Kamenski, ibid. xiv. 171. 5 Ossian Aschan, ibid. xix. 1400. 6 Drechsel, Journ. Prakt. Chem. [2] ccxxvii. 418. 7 Gerhardt and Laurent, Ann. Chem. Phys. [2] xxiv. 189 ; Dobner, Ann. Chem. Pharm. ccx. 267. DIPHENYLPHTHALEIN. 465 This substance crystallizes from hot water or alcohol in small plates, which melt at 192° and decompose into water and phthalanil at a highei' temperature. Analogous compounds are obtained from the substitution products of aniline1 and its homologues,2 from the amido- phenols,3 and from the amidobenzoic acids.4 Diphenylphthalamic acid is formed when equal molecules of phthalic anhydride and diphenylamine are heated together: /COX zCO.N(C6H5)2 C6H4 >O+NH(C6H5)2=C6H4< CO CO.OH. It is insoluble in water and crystallizes from alcohol in wTarty masses of small, lustrous prisms, which melt at 147°-148°.5 If two molecules of diphenylamine are employed, the so-called diphenylphthalein is formed ; it is also obtained by the action of the base on phthalyl chloride,6 and is tolerably soluble in alcohol, more readily in benzene, from which it crystallizes in large prisms, melting at 238°. It has the following constitu- tion : (C6II5)2N /N(C3H5)2 > C < C6H4< >0 co The aromatic diamines form two series of compounds with phthalic anhydride:7 /C=N.C6H4.NH2 c6h4< >0 xco /C=H.C6H4.N=a C6H4< >0 o< >c6h4. xco coz When orthamidothi ophen ol is heated with phthalic anhydride or phthalyl chloride, the compound C20H12N2S2 is formed, and probably has the following constitution : C6II4 >c.c6h4.c< >c6ii4. xsz xsz 1 Gabriel, Ber. Deutsch. Chern. Ges. xi. 2260; Frohlich, ibid. xvii. 1801 and 2679. 2 Michael, ibid. x. 579. 3 Ladenburg, ibid. ix. 1528. 4 Gabriel loc. cit. 6 Piutti, Gaz. Chim. Itai. xiii. 542 ; xiv. 470. 6 Lellmann, Ber. Deutsch. Chern. Ges. xv. 830. 1 Biedermann, ibid. x. 1160. 466 AROMATIC COMPOUNDS. It crystallizes from alcohol in thin needles or thick prisms, which melt at 112°; it is a weak base and forms a hydrochloride which is only slightly soluble and crystallizes well, but is readily decomposed by water.1 2244 Phthalyldiamide. Phthalylmalonic ether is formed by the action of phthalyl chloride on sodmalonic ether, and reacts with ammonia to form malonamide, alcohol and phthalyldi- amide :2 /C=C(CO.OC2H5)2 CA< >0 + 4NH3 = xco znh2 / c ^nh2 CH2(CO.NH2)2 + 2HO.C2HZC6Hz >0 . ZCOZ This body may also be obtained in a similar manner from ph thalylacet o-acetic ether,3 and by allowing phthalimide to stand for some hours in contact with concentrated ammonia.4 It forms a glittering powder, consisting of microscopic, very refractive rhombohedra, only slightly soluble in water and alcohol, and is decomposed into ammonia and phthalimide when heated with either of these. It fuses at 219°-220°, when carefully heated, forming a clear liquid, but ammonia is given off and the residue finally consists of phthalimide. Plitlialylhydroxylamine, N(C8H4O2)OH,is formed when phthalyl chloride and sodium carbonate are alternately added to a con- centrated solution of hydroxylamine hydrochloride, so that the liquid is always kept alkaline : zCCU ZC=N.OH C6H4< >O + H2N.OH = C6H4< >0 +2HC1. XCOZ XX) It is insoluble in ether, but dissolves slightly in water, more readily in boiling alcohol, from which it crystallizes in small plates or needles, which, after drying, form a yellow powder, melting at 230° with decomposition. It is an acid, decomposes carbonates and forms a red solution in alkalis. Alcoholic potash ' Hofmann, Ber. Deutsch. Chem. Ges. 13, 1233. 2 Wislicenus, ibid. xvii. Eef. 529. 3 Billow, Ann. Chem. Pharm. ccxxxvi. 188. 4 Ossian Oschan, Ber. Deutsch. Chem. Ges. xix. 1398. ETHYLPHTHALYLHYDROXYLAMINE. 467 added to its solution in alcohol precipitates the potassium salt, N(C8H4O2)OK, which consists, as does the sodium compound, of an amorphous red powder. The silver compound is obtained by double decomposition as a dark-red precipitate, the barium and lead salts being light red and yellowish red precipitates, while the copper salt, which is only thrown down from a concentrated solu- tion, is green, and the aluminium and mercury salts are yellow. Ethylphthalylhydroxylamine, N(C8H4O2)OC2H5, is obtained by treating the silver salt with ethyl iodide. It forms large crystals which melt at 103°-104° and boil at 270°. Phthalylhydroxylamine decomposes on dry distillation into phthalic anhydride, ammonia and nitrogen; a boiling solution of caustic potash resolves it into phthalic acid and hydroxylamine, while orthamidobenzoic acid is formed when it is heated in alcoholic solution with one molecule of potash : ,C=N.0H zNH2 C6H4< >0 +KOH = C6H4< + C02. \co XCO.OK Hydroxyphthalamic acid is formed when an alcoholic solution of phthalylhydroxylamine is heated with potash for a short time : yC=N.OH /CH=N.OH C6H4< >0 +KOH=zC6H4/ \co XCO.OK Potassium hydroxyphthalamate separates out on cooling ; it is readily soluble in water, and is deposited on evaporation in hard, yellow crystals. The lead salt is thrown down when lead acetate is added to a solution of the potassium salt; it has the following constitution : ZCH-N.OX c„h/ ,Pb. \co-(y When this is suspended in water and treated with sulphuretted hydrogen, a solution of the free acid is formed, which reddens lit- mus and, like that of the potassium salt, is coloured violet by ferric chloride. The solution of the acid decomposes gradually on standing, more rapidly when heated, with separation of phthalyl - hydroxylamine. Phthalylhydroxylamine shows great similarity to the nitrolic 468 • AROMATIC COMPOUNDS. acids, which, like the former, are colourless but are coloured red by the slightest trace of an alkali, and have a similar constitu- tion :1 Phthal ylhydroxylamine ZC=N.OH C3H / >0 ^co Ethylnitrolic acid. N.OH ch3.< \no2. Benzenylazoximebenzenylcarboxylic acid, C15H10N2Os, is formed when phthalic anhydride is fused with benzenylamidoxifme: .N.OH ZCOX C6H5.OC +c6h4< >0= nii2 xco c6h5.c< >c.c6h4.co2h+ii2o. It crystallizes from hot alcohol in lustrous needles melting at 151°.2 Orthocyanobenzoic acid, C6H4(CN)CO2H, is obtained by add- ing orthodi azobenzoyl chloride to a hot solution of copper sul- phate and cuprous cyanide ; it is a thick, viscous liquid, which has not hitherto been prepared pure, since it readily changes into the isomeric phthalimide, phthalamic acid being probably formed as an intermediate product: ZCN zCO.NH2 c6hZ +h20=c6h4; xco.oii co.on This is then resolved into phthalimide and water.3 The conversion may however be simply explained by an intermolecular change:4 /C=NH c6h4< =c6hZ >0 CO-OH CO Ethyl orthocyanobenzoate, C6II4(CN)CO2.C2IIg, is prepared by diazotizing the ethyl ether of orthamidobenzoic acid and treat- ing the product in the manner just described; it crystallizes in thick needles, melting at 70°.5 It is gradually attacked when 1 Cohn, Ann. Client. Pharm. ccv. 295. 2 Schulz, Ber. Deutsch. Chem. Ges. xviii. 2463. 3 Sandmeyer, ibid, xviii. 1496. 4 Liebermann, ibid. xix. 2283. 6 Muller, ibid. xix. 1491. DIHYDROPHTHALIC ACID. 469 heated with hydroxylamine in alcoholic solution, phthalimide- oxime being formed : ,C=N zCz=NH C6H4< + H2N.OH = C6H4< >0 +HO.C2H5. \CO.OC2H5 xC=N.OH The latter crystallizes from dilute alcohol in needles, which melt at 250° and are converted into phthalimide by boiling with ferric chloride and hydrochloric acid. 2245 Dihydrophthalic acid, C6H6(CO2H)2, is formed when a cold alkaline solution of phthalic acid is treated with sodium amalgam,1 or better when the operation is carried on at the boiling point.2 It crystallizes in hard, rhombic tablets, which are only slightly soluble in cold, more readily in hot water, and readily in alcohol. It is a strong dibasic acid; on heating with soda lime it decomposes into carbon dioxide, hydrogen and benzene, while the action of phosphorus pentachloride upon it yields hydrochloric acid, carbon dioxide, phosphorus oxychloride and benzoyl chloride. Bromine acts upon its aqueous solution in the following manner (Grabe and Born): ADDITION PRODUCTS OF PHTHALIC ACID. C6H6(CO2H)2 + Br2 = C6H5.CO2H + CO2 + HBr. On heating with sulphuric or nitric acids, benzoic acid is also formed, together with phthalic acid, while ethyl benzoate, pro- bably accompanied by ethyl formate, is produced when hydro- chloric acid is passed into its alcoholic solution. Hydrophthalic acid can be heated to 200° without undergoing any alteration ; at a higher temperature, however, it decomposes with formation of phthalic anhydride. All these reactions may be simply explained if we ascribe the following constitution to the acid : CH HC^CH-CO2H i HC' JCH-CO2H CH 1 Grabe and Born, Ann. Chem. Pharm. cxlii. 330. 2 Baeyer, Ber. Deutsch. Chem. Ges, xix. 1807. 470 AROMATIC COMPOUNDS. Tctrahydrophthalic acid, C6H8(CO2H)2. The anhydride of this acid, C8H8O3, is formed by the distillation of hydropyromellitic acid, C6H6(CO2H)4, and crystallizes from ether in hard, lustrous plates, which melt at 68° and sublime readily. It is insoluble in cold water, but dissolves in hot water with formation of the acid, which crystallizes in large plates, and is readily soluble in water, being, however, converted into the anhydride when the solution is heated to about 1000.1 Dibromotetrahydrophthalic acid, C6H6Br2(CO2H)2, is obtained by the combination of dry bromine with dihydrophthalic acid, and crystallizes in rhombohedra (Baeyer). Hexhydrophthalic acid, CcH10(CO2H)2, is formed when tetra- hydrophthalic acid or dihydrophthalic acid2 is heated to 230° with hydriodic acid, or when the former is treated with sodium amalgam and water, while dihydrophthalic acid is not attacked by these re-agents (Baeyer). It is slightly soluble in cold, somewhat more readily in hot water, and crystallizes in small prisms or plates, which melt at 203°-205° without forming an anhydride. Bromomalophthalic acid, C6H8Br(OH)(CO2H)2, is prepared by adding bromine to an aqueous solution of tetrahydrophthalic acid, a dibromide being first formed, which is then decomposed by water: C6H8Br2(CO2H)2 + H2O = C6H8Br(OH)(CO2H)2 + HBr. It is readily soluble in water and crystallizes in small rhombic prisms or tablets. On heating with baryta water it is converted into the following compound.3 Tartrophthalic acid, C6H8(OH)2(CO2TI)2 is best obtained by dissolving the anhydride of tetrahydrophthalic acid in boiling water, and adding to one part of the anhydride rather more than an equal amount of bromine, the mixture being then heated on the water bath and treated with baryta water until the liquid has a permanent alkaline reaction. The barium salt is obtained on concentration in plates, from which the tartrophthalic acid is prepared by means of sulphuric acid. It crystallizes from a con- centrated solution in colourless prisms containing two molecules of water, which are lost in a vacuum. On heating with hydri- odic acid it is converted into hexhydrophthalic acid, the 1 Baeyer, Ann. Chern. Pharm. clxvi. 344. 2 Mierski, Ber. Deutsch. Chem. Ges. iv. 558. 3 Baeyer, Ann. Chem. Pharm. clxvi. 354. CHLOROPHTHALIC ACIDS. 471 relation existing between these two bodies being similar to that between succinic and tartaric acids, while tetrahydrophthalic acid corresponds to fumaric acid. HALOGEN SUBSTITUTION PRODUCTS OF PHTHALIC ACID. 2246 Chlorine does not act upon free phthalic acid, even in the presence of iodine ; substitution takes place, however, when the gas is passed into an alkaline solution of the acid. Auerbach obtained in this way a monochlorophthalic acid, which crystal- lized from benzene in needles, melted at 149°-150°, was readily soluble in alcohol and remained on the evaporation of this solu- tion as a syrup which gradually solidified. On heating, it yielded an anhydride boiling at 140°-1430.1 Kruger obtained different results by oxidizing the two chioro-orthotoluic acids with potas- sium permanganate in faintly alkaline solution.2 v-Chlorophthalic acid, C6H3C1(CO2H)9(3 : 1 : 2), is also formed by the oxidation of the dichloronaphthalene melting at 107°, and crystallizes from hot water in stellate groups of silky needles, which melt at 184° and yield an anhydride which sublimes in long needles and melts at 122°-123°.3 a-Chlorophthalic acid (4:1:2) has also been prepared by the oxidation of e-dichloronaphthalene 4 and by the action of phos- phorus pentachloride on the corresponding sulphonic acid.5 It is more readily soluble in water and alcohol than the v-acid, and crystallizes in silky needles, which melt at 130°-134° (Kruger) but according to Claus and Ree at 148°. It decom- poses on distillation into water and the anhydride, which crystallizes in lustrous, asymmetric tablets, and melts at 96°-97°. Dichlorophthalic acid. C6H2C12(CO2H)2, is obtained by heating dichloronaphthalene tetrachloride, C1OC1.2H6C14,6 and /3-dichloro- naphthalene 7 with nitric acid. It is readily soluble in alcohol and hot water, and crystallizes in compact prisms, which melt at 1 Jahresb. Chem. 1880, 862. 2 Ber. Deutsch. Chem. Ges. xviii. 1758. 3 Guareschi, ibid. xix. 134. 4 Alen, Bull. Soc. Chem. xxxvi. 434 ; Claus and Deline, Ber. Deutsch. Chem. Ges. xv. 319 ; Claus and Muller, ibid, xviii. 3073. 5 Bee, ibid, xviii. 3359 ; Inaugzirald. Bern. 1886. 8 Faust, Ann. Chem. Pharm. clx. 64. 7 Atterberg, Ber. Deutsch. Chem. Ges. x. 574. 472 AROMATIC COMPOUNDS. 183°-185°. Its anhydride melts at 187° and forms crystals which are very similar to those of benzoic acid. Trichlorophthalic acid, C6HC13(CO2H)2, which has been pre- pared by the oxidation of /3-pentachloronaphthalene with nitric acid, forms a yellowish, crystalline mass, and is converted on heating into the anhydride which melts at 157° and sublimes in long needles.1 Tetrachlorophthalic acid, CC14(CO2H)2. was obtained from a-pentachloronaphthalene. It is also formed by the action of chlorine on phthalic acid in presence of antimony chloride,2 and crystallizes from water in small plates or hard, thick prisms, which melt at 250° and form an anhydride, which crystallizes in long needles, melting at 245°; these are insoluble in cold water but gradually dissolve in hot water, the acid being re- formed.3 Ethyl tctrachlorophthalate, C6C14(CO2C2H5)2, is prepared by heating the silver salt with ethyl iodide; it forms large prisms which melt at 60°. An isomeric compound is obtained when the acid is treated with phosphorus chloride and the tetrachloro- phthalyl chloride formed submitted to the action of sodium ethylate (p. 461); it crystallizes in tablets and melts at 124°.4 v-Bromophthalic acid, C6H3Br(CO2H)2 (3:1:2), is formed when phthalic acid is heated with bromine and water to 180°; it is an indistinctly crystalline powder which melts at 138°-140° and yields an anhydride melting at 60°-65°.5 a-Bromophthalic acid (4 :1 : 2) is obtained by the oxidation of bromonitronaphthalene, C1()H6Br(NO2),6 tetrabromo-^-naphthol7 and dibromamidonaphthalene8 with potassium permanganate. It crystallizes in white, prismatic needles, which melt at 175°- 176° and are converted into an anhydride melting at 131°-132°. a-Dibromophthalic acid, C6H2Br2(CO2H)2 (3:6 :1:2), was pre- pared by Guareschi by the oxidation of a-dibromonaphthalene with nitric acid. It separates from hot water as a crystalline powder, which melts at about 135° with decomposition; on further heating the anhydride sublimes in light, nacreous needles melting at 207'5°-208°. 1 Atterberg and Widmann, Ber. Deutsch. Chem. Ges. x. 1843. 2 Ibid, xviii. Ref. 676. 3 Grabe, Ann. Chem. Pharm. cxlix. 18. 4 Grabe, Ber. Deutsch. Chem. Ges. xvi. 860. 8 Faust, Ann. Chem. Pharm. clx. 62; Pechmann, Ber. Deutsch. Chem. Ges. xii. 2126. 6 Guareschi, Ann. Chem. Pharm. ccxxii. 262. 7 A. J. Smith. Journ. Chem. Soc. 1879, i. 792. 8 Meldola, ibid. 1885, i. 511 ; see also Stallard, ibid. 1886, i. 187. NITROPHTHALIC ACIDS. 473 {B-Dibromophthalic acid is formed by the oxidation of penta- bromo-a-naphthol, and crystallizes from hot water in needles which melt at 206° and are thus converted into the anhydride, which sublimes in long needles and melts at 208°. The salts of this acid are, with the exception of those of the alkali metals, only slightly soluble in water.1 Tribromophthalic acid, C6HBr3(CO2H)2, is prepared from penta- bromo-/3-naphthol; it is almost insoluble in cold water and crystallizes from hot water in lustrous plates which melt at 190°-191° and are converted at a higher temperature into the anhydride, which sublimes in white plates and melts at 157°.2 Tetrabromophthalic acid, C6Br4(CO2H)2, was obtained by Blum- lein as a product of the oxidation of tetrabromorthoxylene ; it is almost insoluble in the ordinary solvents, and crystallizes from boiling water in lustrous needles, and on the evaporation of its solution in benzene in prisms, which melt at 266° and are thus converted into the anhydride, which sublimes in small, lustrous needles, melting at 258°-259°. Its salts are for the most part insoluble, or only slightly soluble, in water. NITROPHTHALIC ACIDS. 2247 v-Nitrophthalic acid, C6H3(NO2)(CO2H)2 (3:2:1), is formed by the continued boiling of naphthalene with nitric acid,3 by the action of a mixture of nitric and sulphuric acids on phthalic acid4 and by the oxidation a-nitronaphthalene with potassium permanganate 5 or of a-dinitronaphthalene with nitric acid.6 In order to prepare it, one part of nitronaphthalene is dissolved in 7 parts of 90 per cent, acetic acid, and to this are gradually added 5 parts of chromium trioxide ; water is then added and the solu- tion extracted with chloroform to remove the orthonitrophthalide which is always formed. The acid liquid is then treated with barium carbonate, and the insoluble barium nitrophthalate de- composed by carbonate of soda. The solution of the sodium salt is then acidified and the nitrophthalic acid extracted with 1 Bliimlein, Ber. Deutsch. Chern. Ges. xvii. 2485. 2 Flessa, ibid. xvii. 1479. 3 Laurent, Ann. Chern. Pharm. xli. 110 ; Marignac, ibid. xlii. 7. 4 Faust, ibid. clx. 57. 5 Guareschi, Ber. Deutsch. Chern. Ges. x. 294. 6 Aguiar, ibid. v. 899. 474 AROMATIC COMPOUNDS. ether.1 It crystallizes from this in light yellow, monoclinic prisms, which are slightly soluble in cold, more freely in hot water, and readily in alcohol. It decomposes on heating into water and the anhydride; in a small sealed tube it melts at 218° (Miller). Acid ethyl v-nitrophthalate, C6H3(NO2)(CO2C2H5)CO2H, is ob- tained by passing hydrochloric acid into an alcoholic solution of the acid; it crystallizes from hot water in long needles, melting at 110'5°. Normal ethyl v-nitrophthalate, C(.H3(NO2)(CO2C2H5)2, is pre- pared from the silver salt by the action of ethyl iodide, and crystallizes from alcohol in long, rhombic prisms, melting at 45° (Miller). a-Nitrophthalic acid, C6H3(NO2)(CO.,H)2-|-II2O (4:2:1), is formed, together with the preceding compound, by the nitration of phthalic acid.2 In order to prepare it, 50 grms. of phthalic acid are heated with 75 grms of sulphuric acid and the same amount of fuming nitric acid for two hours on the water bath; 120 grms. of water are then added, and the whole allowed to stand for twelve hours in the cold. The precipitate is washed and extracted with ether, the residue after the evaporation of this consisting of a mixture of the two acids accompanied by a little picric acid. It is re-crystallized from water, to remove the greater portion of the v-acid, the mother liquor evaporated to dryness, and the residue dissolved in alcohol and treated with hydrochloric acid gas, which converts the v-acid into the acid and the a-acid into the normal ether. These are separated by car- bonate of soda solution, and the normal ether then converted into the potassium salt by the action of alcoholic potash; this is then acidified with hydrochloric acid and the free acid ex- tracted with ether. It may be still more easily obtained by heating paranitrophthalide with dilute nitric acid to 140°.3 It crystallizes in small needles, which are readily soluble in water and alcohol, effloresce in the air, lose their water at 100°, and then melt at 161°. Acid ethyl a-nitrophthalate, C(.H3(NO2)(CO2.C2H5)CO2H, is formed in small quantity when an alcoholic solution of the acid is treated for a short time with hydrochloric acid, and crystallizes from water, in long, thin needles, which melt at 127°-128°. 1 Beilstein and Kurbatow, Ann. Chcm. Pharm. ccii. 217. 2 Miller, ibid, ccviii. 223. 3 Honig, Ber. Deutsch. Chcm. Ges. xvii. 3447. AMIDOPHTHALIC ACIDS. 475 Normal ethyl a-nitrophthalatc, C6H3(NO2)(CO2.C2H5)2, is in- soluble in water and crystallizes from alcohol in lustrous tablets, which melt at 34°. a,-Nitrophthalic anhydride, C8H3(NO2)O3, is obtained by heat- ing the acid to 170° and subliming the residue in a current of air at 210°, in the form of fascicular crystals, which melt at 114° and are readily soluble in ether and hot water. If the aqueous solution be evaporated, a-nitrophthalic acid is deposited. Dinitrophthalic acid, C6H2(NO2)2(CO2H)2 (5 : 3 : 2 :1), is formed when dinitrophthalene is heated to 150° with nitric acid of sp. gr. 1'15 in a sealed tube, small quantities of nitro- phthalic acid, s-dinitrobenzoic acid, and picric acid being also formed. It crystallizes in large prisms, which are readily soluble in water and alcohol, and melt at 22G0.1 /CO2H AMIDOPHTHALIC ACIDS, C6H NII2 . \CO2H 2248 v-Amidophthalic acid. When the v-nitro-acid is treated with tin and hydrochloric acid in the cold, needles of the com- pound C6H3(NH2.ClH)(CO2H)2 + SnCl2+2H2O are formed. If the hydrochloric acid solution of this be treated with sulphuretted hydrogen and evaporated, carbon dioxide is given off and meta- amidobenzoic acid formed. Ethyl v-amidophthalate, C6H3(NH2)(CO2.C2H5)2, is prepared by treating a well-cooled alcoholic solution of the ether of the nitro-acid with hydrochloric acid and zinc dust. It is a yellow liquid, which decomposes on heating and forms a splendid blue, fluorescent solution in ether (Miller). a-Amidophthalic acid. When the a-nitro-acid is reduced, no carbon dioxide is evolved, but no double tin salt is formed. On removing the tin and evaporating, however, carbon dioxide is evolved just as in the case of the v-acid, and metamidobenzoic acid formed. If the reduction be carried on by means of zinc dust and acetic acid, a double compound of zinc acetate and zinc amido- phenate is formed, which has probably the constitution C6H3 (NH2)(CO2H)CO2.Zn.O.CO.CH3, and crystallizes in fine, white 1 Beilstein and Kurbatow, Ann. Chem. Pharm. ccii. 224. 476 AROMATIC COMPOUNDS. needles, which form an almost colourless solution in hot water, while its solution in acetic acid is coloured yellow and has a green fluorescence. It dissolves in caustic soda, but the solution decomposes on heating, zinc carbonate is deposited and the amidophthalic acid decomposed.1 Ethyl a-amidophthalate was first prepared by Baeyer but mistaken for the v-compound2 until Miller showed that it is derived from the a-acid.3 This substance is obtained in a similar manner to the isomeric compound; it is insoluble in water, slightly soluble in dilute acid, readily in alcohol, from which it crystallizes in monoclinic prisms, which melt at 95°; the dilute ethereal solution shows a faint blue fluorescence. /CO2H SULPHOPHTHALIC ACIDS, CJL- SO3H. 6 '\co'h 224g a-Sulphophthalic acid (1:4:2) is obtained by heating phthalic acid or phthalic anhydride with strong, fuming sul- phuric acid,4 and by the oxidation of /3-naphthalenesulphamide, C10H7SO2.NH2, and dinitronaphtholsulphonic acid, C10H4(NO2)2 (OH)SO3H.5 It remains as a syrup when its solution is evaporated on the water bath, but solidifies after heating for some time to a mass consisting of stellate groups of sharply pointed prisms; these contain a molecule of water, which is lost at 140°, a brownish syrup being formed, which often solidifies on standing. On heating to 180°, the anhydride, C6H3(C2O3) SO3H, is formed as a hard, brown, very hygroscopic mass. The normal barium salt crystallizes in plates or silky needles, slightly soluble in water; when it is dissolved in the necessary amount of hydrochloric acid, the monacid salt, C6H3(CO2BaSO3) CO2H+2H2O, is formed, and crystallizes from hot water in large needles; it is converted by solution in an excess of hydrochloric acid into the diacid salt, (C6H3(CO2H)2SO3)2Ba-|-5H2O, which also crystallizes in lustrous needles. 1 Bernthsen and Semper, Ber. Deutsch. Chem. Ges. xix. 164. 2 Ibid. x. 124 and 1079. 3 Ibid. xi. 1191. 4 Low, Ann. Chem. Pharm. cxliii. 249 ; Ree, Ber. Deutsch. Chem. Ges. xviii. 1629 ; Inaugurald. Bern. 1886 ; Ann. Chem. Pharm. ccxxxiii. 216. 6 Grabe, Ber. Deutsch. Chem. Ges. xviii. 1126. SULPHAMICPHTHALIC ACIDS. 477 When the monacid ammonium salt is heated, the ammonium salt of a-sulphophthalimide is formed ; it crystallizes in mono- symmetric prisms, and is decomposed on heating with formation of phthalimide: /C=NH c n Z >0 /C=NH L«\co = C6H4< >0 + so2 + nh2 + h2o. xSO3NH4 xCO a-Sidphamidophthalic acid, C6H3(SO3.NH2)(CO2H)2. When a-sulphophthalic anhydride is treated with phosphorus penta- chloride, the monochloride, C6H3(SO2C1)(CO2H)2, is formed, and is converted by ammonia into the amide, which crystallizes from water in small, transparent prisms (Ree). v-Sidphophthalic acid (1:3: 2) is formed when a-naphthalene- sulphamide is oxidized with potassium permanganate. The first product is the anhydride of sulphamidophthalic acid, which yields the sulphonic acid on heating with hydrochloric acid: /CO /CO2H c6h3<so >ah +2H2o=c6h<so3h +nh3. \co2h \co2h It is readily soluble in water, and forms salts which crystallize well.1 The normal barium salt, (C6H3(CO2)2Ba.SO3).2Ba-|-8H2O, crystallizes in transparent tablets. Sidphamidophthalic anhydride, or Sidphinidephthalic acid, C8H5NSO3+ 2H2O, crystallizes from hot water in needles, which become anhydrous at 155.° Alkalis do not convert it into sul- phamicphthalic acid ; it is a dibasic acid, the hydrogen of the imide-group being easily replaced by metals. Normal potassium sidphinidephthalate, C8H3K2NSO3, is very readily soluble in water and dries to an elastic mass, from which semi-crystalline, spherical masses separate on standing. Acid potassium sulphinidephthalate, C8H4KNSO3 + H2O, is only slightly soluble in cold, readily in hot water, and crystallizes in long acute prisms, which rapidly lose their water at 100°. Normal silver sulphinidephthalate, C8H3Ag2NSO3 + H2O, is a white precipitate, which is scarcely soluble in boiling water, but dissolves in a hot solution of potassium nitrate and separates out again on cooling, o o 1 Remsen and Comstock, Amer. Chem. Journ. v. 106 ; Stokes, ibid. vi. 262. 478 AROMATIC COMPOUNDS. Acid silver sulphinidcphthalate, C8H4AgNSO3 + H2O, is formed when the normal salt is heated with nitric acid, or when silver nitrate is added to a dilute boiling solution of the acid potassium salt. It crystallizes on cooling in long, pliant needles, which become anhydrous below 135°. The silver salt is converted into the methyl ether by treat- ment with methyl iodide. Normal methyl sulphinidcphthalate, CgH3(CH3)2NSO3, crys- tallizes from alcohol in colourless needles, which melt at 180° and readily sublime in iridescent plates. Acid methyl sulphinidcphthalate, C8H4(CH3)NSO3, separates from an alcoholic or hot aqueous solution in long, striated prisms, or long, narrow tablets, which melt at 190'7°-191'7° and readily volatilize. When it is successively treated with phosphorus trichloride and methyl alcohol the dimethyl ether is formed. In order to determine the constitution of the acid sulphinide- phthalates, the acid potassium salt was heated with phosphorus pentachloride, the compound C8H3C13SO2NPOC12 being formed ; it crystallizes in small prisms, and is converted by methyl alcohol into the trimethyl ether, C8H4(CH3)3NSO6, which separates from hot water in needles or long narrow prisms, which melt at 140'5°- 141'5°. The constitution of these compounds is expressed by the following formulae : C#H^s8'2>™k \coci ZC(OCH3) c6h3<-so2 \co.och3 Since the monomethyl ether is converted into the diethyl ether by the action of phosphorus chloride for a short time, followed by the treatment described above, it follows that in the first of these, and therefore in the acid sulphinidephthalates, it is the hydrogen of the imido-group which is replaced (Stokes): C6H34o >NCH» + PC15 = \CO.OH C6hAo>NCH3 +HC1 + POCL. \coci C6H34o >NCH3 + II0.CII3=C6H34^ +HCL \coci \co.och3 ISOPHTHALIC ACID. 479 ISOPHTHALIC ACID OR METAPHTHALIC ACID. 2250 This compound is formed by the oxidation of meta- xylene,1 metatoluic acid,2 and other meta-compounds with two side-chains containing carbon. It has also been obtained by fusing potassium metasulphobenzoate3 and potassium meta- bromobenzoate4 w'ith sodium formate (Part III. p. 31), and has been found among the products of the oxidation of colophony with nitric acid.5 In order to prepare it, metaxylene is converted into metaxylylene diethyl ether, and this is then oxidized with chromic acid solution, the reaction proceeding very smoothly.6 It dissolves in 7,800 parts of water at 25° and in 460 parts at 100°, crystallizing in hair-like needles, which usually extend through the whole liquid, and are readily soluble in alcohol.7 It melts at above 300° and sublimes without decomposition. Potassium isophthalate, C8H4O4K2, is readily soluble in water, less readily in alcohol, from which it crystallizes in fascicular groups of needles. Calcium isophthalate, 2C8H4O4Ca + 5H2O, is scarcely more soluble in hot than in cold water and forms fine needles. Barium isophthalate, 2C8H4O4Ba + 7H2O, is readily soluble in water and crystallizes from a concentrated solution in lustrous needles, which effloresce in the air.8 Silver isophthalate, C8H4O4Ag2, is an amorphous precipitate, which, like mercury thiocyanate, forms a voluminous vermiform mass on heating. Methyl isophthalate, C8H4(CO2.CH3)2, has been prepared from the silver salt by means of methyl iodide. It crystallizes from dilute alcohol in long fine needles, melts at 64°-65°, and distils without decomposition.9 Ethyl isophthalate, C6H4(CO2.C2H5)2, has been obtained by the action of hydrochloric acid on an alcoholic solution of the acid. 1 Fittig and Velguth, Ann. Chern. Pharm. cxlviii. 11. 2 Weith and Landolt, Ber. Deutsch. Chern. Ges. viii. 721. 3 V. Meyer, Ann. Chem. Pharm. clvi. 275. 4 Ador and Meyer, ibid. clix. 16. 8 Fittig and Storss, ibid, cliii. 284. 6 W. H. Perkin, jun. Private communication. 7 Fittig and Storss, Ann. Chem. Pharm. cliii. 284. 8 Kelbe, ibid. ccx. 20. 9 V. Meyer, Ber. Deutsch. Chem. Ges. iv. 262 ; Baeyer, Ann. Chem.. Pharm. clxvi. 340. 480 AROMATIC COMPOUNDS. It is a liquid which possesses a faint but pleasant odour, boils at about 285°, and solidifies at 0° to a dazzling white, radiating mass (Fittig and Storss). Phenyl isophthalate, C6H4(CO2.C6II5)2, is formed when phenol is heated with the chloride ; it crystallizes in long, fine needles which melt at 120° and are only slightly soluble in alcohol.1 Isophthalyl chloride, C6H4(COC1)2, is obtained by the distilla- tion of the acid with phosphorus chloride as an oily liquid, which boils at 276° and solidifies to a radiating, crystalline mass, melting at 41° (Schreder). Isophthal amide, C6H4(CO.NH2)2, is formed by the action of ammonia on the chloride and is a light, white powder, which melts at 265°, is slightly soluble in alcohol, but scarcely dissolves in any other of the ordinary solvents. On heating with phosphorus pentoxide it is converted into isophthalonitril.2 Metacyanobenzoic acid, C6H4(CN)CO2H, is obtained by allow- ing a hydrochloric acid solution of metadiazobenzoic acid to run into a solution of copper sulphate and cuprous cyanide: /N-NCI ZCN 2C6H4< + Cu2(CN)2 = 2C6H4< + Cu2Cl2 + 2N2. xco2h \co2h It is readily soluble in alcohol and hot water, and crystallizes from the latter in microscopic, arborescent needles, which after drying form a dull white powder and melt at 217°. Boiling caustic soda solution readily converts it into iso- phthalic acid.3 Ethyl metacyanobenzoate, C6H4(CN)CO.C2II5, crystallizes in fine, matted needles, which melt at 48°. Ecnzenylamidoximemetacarboxylic acid, is prepared by heating metacyanobenzoic acid for a long time with an alcoholic solution of hydroxylamine, and forms crystals which are readily soluble in alcohol and hot water, and melt at 200°. It is formed according to the equation : CN C^ C6H / + H2N.OH = C^/ ^n.oh. xco2h \co2h 1 Schreder, Ber. Deutsch. Chern. Ges. vii. 708. 2 Beyer, Journ. Prakt. Chem. [2] xxii. 351. 3 Sandmeyer, Ber. Deutsch. Chem. Ges. xviii. 1496. CHLORO-ISOPHTHALIC ACID. 481 The ethyl ether is prepared in a similar manner from the corresponding ether of metacyanobenzoic acid and crystallizes from hot water in needles, which melt at II80.1 Isophlhalonitril, C6H4(CN)2, is formed by the distillation of potassium benzenemetadisulphonate with potassium cyanide,2 or of potassium metabromosulphonate with dehydrated potassium ferrocyanide;3 it forms fine needles, which melt at 160°-161°, are only very slightly soluble in water, somewhat more readily in alcohol, and are converted into isophthalic acid by heating with alkalis. ADDITION PRODUCTS OF ISOPHTHALIC ACID. Tetrahydro-isophthalic acid, C6H8(CO2H)2,is prepared by boil- ing an alkaline solution of isophthalic acid with sodium amalgam for some time, and crystallizes from hot water in needles, which melt at 199°. Its dimethyl ether is an oily liquid.4 SUBSTITUTION PRODUCTS OF ISOPHTHALIC ACID. 2251 Chloro-isophthalic acid, 2C6H3C1(CO2H)2 + H2O, has been obtained from the amido-acid by means of the diazo- reaction, and crystallizes from hot water in long, very fine needles, which become anhydrous at 120°, and melt at 278° (Beyer). lodo-isophthalic acid, C6H3I(CO2H)2 (4:3: 1), is formed by the oxidation of acetyliodotoluene, CH3.CO.C6H3I.CH3, which will be subsequently described. It is scarcely soluble in cold, only very slightly in boiling water, and crystallizes from hot acetic acid in small, white needles, which melt at 203°-204°, but sublime in white, lustrous flocks, without previously melting, when carefully heated. On fusion with caustic potash, para- 1 Muller, Ber. Deutsch. Chcm. Ges. xix. 1491. 2 Barth and Senhofer, ibid. viii. 1481 ; Ann. Chcm. Pharm. clxxiv. 235. 3 Limpricht, ibid, clxxx. 92. 4 Baeyer, Ber. Deutsch. Chem. Ges. xix. 1806. 482 AROMATIC COMPOUNDS. hydroxybenzoic acid is formed, while it yields benzoic acid when reduced in alcoholic solution by sodium amalgam.1 Nitro-isophthalic acid, 2C6H3(NO2)(CO2H)2 + 8H2O, is pre- pared by heating isophthalic acid with fuming nitric acid for some time;2 it is slightly soluble in cold, very readily in boiling water and alcohol, and crystallizes in thin, lustrous plates, re- sembling those of benzoic acid, which readily lose their water and melt with slight decomposition at 248°-249°. Its salts, some of which crystallize well, have been fully examined by Beyer. Methyl nitro-isophthalate, C6H3(NO2)(CO2.CH3)2, is formed when hydrochloric acid is passed into an alcoholic solution of the acid, and crystallizes in fine, lustrous needles, which melt at 121'5°, and yield a vapour which smells like aniseed. Ethyl nitro-isophthalate, C6H3(NO2)(CO2.C2H5)2, forms fine needles or transparent prisms, which melt at 83'5°. Amido-isophthalic acid, C6H3(NH2)(CO2H)2, is readily obtained from the nitro-acid by reduction with tin and hydrochloric acid. It is only slightly soluble in cold water and alcohol, crystallizing from hot water in lustrous plates and from alcohol in prisms. It combines with acids and bases forming compounds which have been investigated by Beyer. Its ethers are obtained by the reduction of the corresponding nitro-compounds. Methyl amido-isophthalate, C6H8(NH2)(CO2.CH3)2, crystallizes from wood-spirit in thin, yellowish plates or tablets, which melt at 176°. Ethyl amido-isophthalate, C6H3(NH2)(CO2.C2H5)2, forms thin plates or fascicular needles, melting at 118°. Its ethereal solution has a splendid violet fluorescence. s-Sulpho-isophthalic acid, CH3(CO2H)2SO3H + 2H2O (1 : 3 :5), is prepared by the action of sulphur trioxide on isophthalic acid,3 and by heating the latter to 200° with fuming sulphuric acid.4 It is very readily soluble in water, but only slightly in dilute sulphuric acid, and crystallizes in long needles or transparent, four-sided, pointed, rhombic columns, which effloresce in dry air, but deliquesce in very damp air. The anhydrous acid melts at 257°-258°, a slight discolouration taking place. a-Sulpho-isophthalic acid, C6H3(CO.2H)2SO3H + 2H2O (1:3: 4), is obtained by the oxidation of an alkaline solution of a-meta- 1 Klingel, Bar. Deutsch. Chern. Ges. xviii. 2701. 2 Fittig and Storss, ibid, cliii. 285 ; Beyer, Journ. Prakt. Chem. [2] xxv. 465. 3 Heine, Bar. Deutsch. Chem. Ges. xiii. 491. 4 Lonnies, ibid. xiii. 703. TEREPHTHALIC ACID. 483 xylenesulphonic acid,1 or metatoluylsulphamic acid 2 with potas- sium permanganate. It is readily soluble in water, and crystallizes from dilute sulphuric acid in flat, very hygroscopic needles melting at 235°-240°. TEREPHTHALIC ACID. 2252 Paraphthalic acid is readily formed by the oxidation of those para- compounds which possess two side-chains containing carbon, such as paraxylene,3 cymene, or methylpropylbenzene, CH3.C6H4.C3H7, cuminol or cuminaldehyde, COH.C6H4.C3H7,4 paratoluic acid,5 &c. Caillot, as already mentioned, obtained it from oil of turpentine, C10H16, which is closely related to cymene. The isomerides of this, oil of cajeput, oil of citron, and the thymene contained in thymian, all yield terephthalic acid on oxidation,6 and it is also formed when potassium parasulpho- benzoate is fused with sodium formate.7 In order to prepare it, a mixture of 100 grms. of paraxylene, which need not be pure, 400 grms. of potassium dichromate and 550 grms. of sulphuric acid, diluted with two volumes of water, is heated for several days in a flask connected with a reflux condenser until the solution has become coloured a pure green ; the unattacked xylene is then distilled off, and the solution filtered from the precipitated acid, which is dissolved in dilute carbonate of soda and precipitated by hydrochloric acid. The acid is obtained pure by repeating this process two or three times. Cymene, which is easily prepared by distilling camphor with phosphorus pentoxide, may be employed instead of paraxylene, or Roman cumin oil, a mixture of cymene and cuminol, may be used. Terephthalic acid is a tasteless powder, which appears crystal- line under the microscope, is insoluble in ether and chloroform, and scarcely soluble in water and alcohol ; the hot, saturated, aqueous solution has an acid reaction, and deposits the acid on 1 Jacobsen and Lonnies, Ber. Deutsch. Ckem.Ges. xiii. 1556. 2 Coale and Remsen, Amer. Chem. Journ. iii. 214. 3 Beilstein, Ann. Chem. Pharm. cxxxiii. 40. 4 Muller and Warren de la Rue, ibid. cxxi. 87. 5 Beilstein and Yssel de Schepper, ibid, cxxxvii. 308. 6 Schwanert, ibid, cxxxii. 260. 7 Remsen, Ber. Deutsch. Chem. Ges. v. 379. 484 AROMATIC COMPOUNDS. cooling as an indistinctly crystalline powder. It sublimes when heated without previously melting. Ammonium terephthalate, C8H4O4(NH4)2, is deposited on the evaporation of its solution in small, lustrous crystals. Calcium terephthalate, C8H4O4Ca + 3H2O, separates from hot water in small crystals, which dissolve in 1,214 parts of water at 6°. Barium terephthalate, C8H4O4Ba + 4H2O, is deposited from a rapidly cooled solution as a white, granular powder; by gradual evaporation it is obtained in small, concentrically arranged tablets, which dissolve in 355 parts of water at 5°. Silver terephthalate, C8H4O4Ag2, is an amorphous precipitate, which blackens in the light. Methyl terephthalate, C8H4O4(CH3)2, is formed by the action of the chloride on methyl alcohol,1 and crystallizes from hot alcohol in large flat prisms, which melt at 140° and are volatile without decomposition. By means of this compound the smallest quantity of terephthalic acid can be detected. The substance is treated with phosphorus chloride and then with methyl alcohol, water being finally added and the methyl compound extracted with ether. On the evaporation of the latter characteristic crystals of the compound are obtained. Ethyl terephthalate, C6H4(CO2.C2H5)2, forms white odourless prisms, which resemble those of urea and melt at 44°. The following ethereal salts have been prepared by Beyer, some by means of the chloride, the remainder from the silver salt:2 Melting- point. Propyl terephthalate, C6H4(CO2.C3H7)2, long needles .... 31'0° Isopropyl terephthalate, C6H4(CO2.C3H7)2, lustrous plates . 55'5° Isobutyl terephthalate, C6H4(CO2.C4H9)2, needles 52'5° The normal butyl ether is liquid, while the tertiary butyl ether is only formed with great difficulty, and has not yet been obtained in considerable amount. Muller and Warren de la Rue have prepared the amyl ether; it crystallizes in scales, which are melted even by the warmth of the hand. Phenyl terephthalate, C6H4(CO2.C6H5)2, crystallizes from alcohol in fine needles, melting at 1910.3 1 Warren de la Rue and Muller ; Schwanert, loc. cit. 2 Ber. Deutsch. Chern. Ges. x. 1742. 3 Schreder, ibid. vii. 707. TEREPHTHALAMIC ACID. 485 Terephthalyl chloride, C6H4(COC1.).„ is formed by the distilla- tion of the acid with phosphorus pentachloride and is a crys- talline mass, which has a somewhat sharp odour resembling cinnamon, melts at 78° (Schreder) and boils at 259° (Beyer). Terephthalamide, C6H4(CO.NH2)2, is obtained by the action of ammonia on the chloride, as a white amorphous powder, which is insoluble in all solvents (Warren de la Rue and Muller). Terephthalamic acid, C6H4(CO.NH2)CO2H, is obtained as the product of all reactions by which paracyanobenzoic acid might be prepared, as the elements of water are taken up by the latter according to the following equation : ZCN ZCO.NH2 c6h4( +h20=c6h4< \CO.,H XCO.,H Tereph thalamic acid crystallizes in indistinct, microscopic plates, which are slightly soluble in cold, readily in hot water and alcohol, melt at 214°, and are converted into terephthalic acid by boiling with caustic soda (Sandmeyer). Ethyl paracyanobenzoate, C6H4(CN)CO2.C2H5, is prepared from ethyl paramidobenzoate and crystallizes in needles, melting at 54°. On heating with an alcoholic solution of hydroxylamine, the ethyl ether of benzenylamidoximeparacarboxylic acid, CcH4 (CO2H)C(NH2)NOH, is formed ; it melts at 135° and yields the free acid which melts above 3300.1 The meta- and para-cyano- benzoic acids and their ethers, therefore, behave towards hydro- xylamine like other nitrils, while the ortho-compounds differ from these. Terephthalonitril, C6H4(CN)2, is prepared by heating terephtha- lamide with phosphorus pentoxide (Warren de la Rue and Muller) or by distilling potassium benzeneparadisulphonate,2 potassium parachlorobenzenesulphonate,3 or potassium para- bromobenzenesulphonate 4 with potassium cyanide or dehydrated potassium ferrocyanide.5 It is insoluble in water, slightly soluble in cold, readily in hot alcohol, and crystallizes in needles or lustrous prisms, which melt at 215° and readily sublime. It is 1 Muller, Bcr. Deutsch. Chem. Ges. xviii. 2485 ; xix. 1491. 2 Garrick, Zcitschr. Chem. 1869, 551. 3 Nolting, Bcr. Deutsch. Chem. Ges. viii. 1110. 4 Irelan, Zcitschr. Chem. 1869, 164 ; Barth and Senhofer, Ann. Chem. Pharm. 174, 242. 8 Limpricht, ibid, clxxx. 88. 486 AROMATIC COMPOUNDS. converted into terephthalic acid by boiling with an aqueous, or more rapidly with an alcoholic, solution of potash. It is, how- ever, better to decompose it by heating to 160° with hydrochloric acid (Limpricht). ADDITION PRODUCTS OF TEREPHTHALIC ACID.1 2253 Tetrahydroterephthalic acid, C6H8(CO2H)2. In order to prepare this substance, 5 grms. of terephthalic acid are dissolved in a little caustic soda solution and boiled for twenty hours, 500 grms. of 4 per cent, sodium amalgam being gradually added. It is scarcely soluble in cold water and requires 120 parts of boiling water for solution, from which it crystallizes on cooling in small, arborescent prisms, which melt above 300° and sublime. Its silver salt is a white amorphous precipitate which blackens in the light. Methyl tetrahy drotcr ephthalate, C6H8(CO2.CH3)2, is formed by the action of methyl iodide on the silver salt, as well as by passing hydrochloric acid into a solution of the acid in wood- spirit. It is thus obtained as an oily liquid, which smells of fennel and soon solidifies in large prisms, melting at 39°. It crystallizes from ether, in which it forms a blue fluorescent solution, in long needles. Hexhydroterephthalic acid, C6H10(CO2H)2,is obtained by heating the tetrahydro-acid to 240° for six hours with concentrated hydriodic acid. It is even less soluble in water than the tetra- hydro-compound and crystallizes from hot water in small prisms, melting at about 295°. It is very stable towards alkaline per- manganate solution, while the tetrahydro-derivative is oxidized to oxalic acid by this even in the cold. Its methyl ether melts at 58° and resembles the preceding compound, but does not give a fluorescent solution. Dibromohcxhydroterephthalic acid, C6H8Br2(CO2H)2 + H2O, is best prepared by treating finely divided tetrahydroterephthalic acid for several hours with an ethereal solution of bromine, the mixture being agitated at intervals, and repeating this operation until the acid is almost completely dissolved. The solution is Baeyer, Ber. Deutsch. Chem. Ges. xix. 1805. TETRAHYDROTEREPHTHALIC ACID. 487 then decolourized with sulphur dioxide and the acid extracted by carbonate of soda solution. It is precipitated from the latter by hydrochloric acid in granular, cubic crystals. Its methyl ether is formed by the combination of bromine with the ether of tetrahydroterephthalic acid, and crystallizes in large prisms melting at 73°. Tetrahydrophthalic acid behaves towards bromine in the same manner as cinnamic and fumaric acids. When the brominated acid is heated with caustic soda solution, a dihydroterephthalic acid is formed, which resembles terephthalic acid very closely. A syrupy acid is however formed by the action of freshly pre- cipitated silver oxide, which is probably a dihydroxyhexhydro- terephthalic acid, and is converted by the action of bromine into tetrabromocatechol: C6H8(OH)2(CO2H)2 + 7Br2 = C6Br4(OH)2 + 2CO2 +1 OHBr. The constitution of tetrahydrophthalic acid is proved by the formation of this substance, and may also be deduced from the following considerations. Phthalic acid only assumes two atoms of hydrogen when acted upon by sodium amalgam and water, while isophthalic and tere- phthalic acids combine with four. The simplest explanation of this fact is that the double linking of two carbon atoms is con- verted into a single one, if at least one of these be combined with a carboxyl group. The following formulae are thus arrived at: Dihydrophthalic acid. CH HC^CH-CO2H HC^/CH-CO2H CH Tetrahydro-isophthalic acid. CH-CO2H H2(Z^|CH2 HC^/CH-CO2H CH Tetrahydroterephthalic acid. CH-CO2H h2cz^ch H2C\/CH CH-CO2H Dihydroxyhexhydroterephthalic acid. CH-CO2H h2c/\ch.oh H2C\/CH.OH CH-CO2H 488 AROMATIC COMPOUNDS. SUBSTITUTION PRODUCTS OF TERE- PHTHALIC ACID. 2254 Chlorotercphthalic acid, C6H3C1(CO2H), is prepared from amidoterephthalic acid, and is slightly soluble in hot water, more readily in alcohol. It is crystalline, and melts above 300°. The chloride, C6H3C1(COC1)2, obtained by the action of phosphorus chloride, is also crystalline and boils at about 300°. By treating this with ammonium carbonate, the amide, CeH3Cl(CO.NH2)2, is formed, and crystallizes from alcohol in crusts, melting above 300°. Methyl chlor otcrephthalate, C6H3C1(CO2.CH3)2, forms silky plates, melting at 60.°1 Bromotcrcphthalic acid, C0H3Br(CO2H)2 + H2O, is formed by the action of potassium permanganate on an alkaline solution of bromoparatoluic acid. It is almost insoluble in cold water, and crystallizes from hot water in dazzling white, microscopic needles, which melt at 304°-305°. Phosphorus pentachloride converts it into the chloride, C6H3Br(COCl)2, an oily liquid, which boils at 304'5°-305'5°, is only gradually decomposed by water, and combines with aqueous ammonia to form the amide, C6H3Br(CO.NH2)2, which crystallizes from hot water in small needles, melting at 270°. Methyl broYMterephthalatc, C6H3Br(CO2.CH3)2, crystallizes in concentrically arranged groups of needles, melts at 42° and boils at above 300°.2 Dibromotcrcphthalic acid, C6H2Br2(CO2H)2, is prepared by heat- ing dibromocymene, C6H2Br2(CH3)C3H7, for some time with nitric acid,3 and by the oxidation of dibromotoluic acid with potassium permanganate.4 It crystallizes from hot, dilute alcohol in small plates, which have a satin lustre, do not melt even at 320°, and sublime at a higher temperature with decomposition. Ethyl dibromoterephthalatc crystallizes from alcohol in nacreous plates, melts at 121° and boils at about 335°. Nitroterephthalic acid, C6H3(NO2)(CO2H)2, is formed by treat- ing terephthalic acid with a mixture of fuming sulphuric and 1 Ahrens, Ber. Deutsch. Chem. Ges. xix. 1634. 2 Fischli, ibid. xii. 619. 3 Claus and Wimmel, ibid. xiii. 902. 4 Schultz, ibid, xviii. 1762. CHLOROTEREPHTHALIC ACID. 489 nitric acids, and crystallizes in prisms • it separates from hot water in cauliflower dike masses, which melt at 2700.1 Methyl nitroterephthalate, C6H3(NO2)(CO2.CH3)2, crystallizes from ether in splendid prisms, which melt at 70°.2 Nitroterephthalamide, C6H3(NO2)(CO.NH2)2, was obtained by Warren de la Rue and Muller in well formed prisms by the nitration of terephthalamide. Amidoterephthalic acid, C6H3(NH2)(CO2H)2, is formed by the reduction of the nitro-acid with tin and hydrochloric acid, and crystallizes in thin, lemon-yellow prisms or moss-like forms, which are only slightly soluble in cold water and alcohol, and decompose on heating without melting. Their aqueous or alkaline solutions, and those of their salts and ethers, which latter are crystalline bodies but have not been described in detail, show a remarkable blue fluorescence, while acidified solutions of the acid do not possess this property. Methyl amidoterephthalate, CcH3(NH2)(CO2CH3)2, forms crystals, melting at 126°; its alcoholic and ethereal solutions also show a strong blue fluorescence (Ahrens). Diamidotercphthalic acid, C6H2(NH2)2(CO.,H)2, is not known in the free state; its ethyl ether has been prepared from succinosuccinic ether (Pt. III., p. 146). When the latter is heated with ammonium acetate, a di-imide is formed, which crystallizes in shining, yellow needles, melting at 181°. Dicthyl- diamidoterephthalate is obtained by the action of bromine on its solution in sulphuric acid : co2.c2h5 co2.c2h, " A O । " o CH C hn=c/\ch2 h2n-c,^\ch +2HBr. H2C\/C=NH HC \/C -nh2 CH C I I co2c2h5 co2c2h6 It crystallizes from hot alcohol in lustrous golden needles of the colour of potassium dichromate, which melt at 168°. Its brown alcoholic or ethereal solution shows a golden-yellow fluorescence. It forms slightly soluble salts with hydrochloric and sulphuric acids. 1 Warren de la Rue and Muller, Ann. Chern. Pharm. cxxi. 90 ; Burckhardt, Ber. Deutsch. Chern. Ges. x. 144. 2 Ahrens, ibid. xix. 1634. 490 AROMATIC COMPOUNDS. When a solution of its diazo-compound in hydrochloric acid is heated with an acid solution of cuprous chloride, an acid is formed which is probably dichloroterephthalic acid, since it is converted into terephthalic acid by the action of sodium amalgam and water.1 Sulphoterephthalic acid, CeH3(SO3H)(CO2H)2, is obtained by heating terephthalic acid with fuming sulphuric acid,2 and by the oxidation of sulphoparatoluic acid, paratoluylsulphamic acid, or paraxylenesulphonic acid with potassium permanganate.3 It forms a hygroscopic mass, and yields salts which are soluble in water, but insoluble in alcohol. HYDROXYMETHYLHYDROXYBENZOIC ACID, /OH C6H3^C0oH \ch"2oh. 2255 These compounds, which are simultaneously alcohols and phenols, are formed by the action of sodium amalgam on the aldehydo-acids, which are described below.4 Orthohydroxymethylsalicylic acid (1:2:6) is precipitated by acids from its alkaline solution as an oil, which solidifies after some time to hard, white crystals; it is readily soluble in hot waler, alcohol and ether, and crystallizes from the latter in transparent prisms, which melt at 142°. Its aqueous solution is coloured an intense bluish-violet by ferric chloride. Paxahydroxymethylsalicylic acid (1:2: 4) is slightly soluble in alcohol and ether, and crystallizes from the latter in long prisms, which melt at 160° with decomposition. Ferric chloride colours the solution violet. Orthohydroxymethylparahydroxylcnzoic acid (1:4:2) is a white powder, which does not melt below 270°, and gives no colouration with ferric chloride. 1 Baeyer, Ber. Deutsch. Chern. Gen. xix. 428. 2 Ascher, Ann. Chern. Pharm. clxi. 2 ; Schoop, Ber. Deutsch. Chem. Ges. xiv. 223. 2 Hall and Remsen, ibid. xii. 1434 ; Burney and Remsen, Amer. Chern. Journ. ii. 405 and 413. 4 Reimer, Ber. Deutsch. Chem. Ges. xi. 790. ALDEHYDOHYDROXYBENZOIC ACIDS. 491 ALDEHYDOHYDROXYBENZOIC ACIDS, ZOH C6H3^COoH \COH 2256 These are prepared by heating the hydroxybenzoic acids with caustic soda and chloroform: zONa C6H4< 4 3NaOH + CHCL = COsNa /ONa C.H3<COH + 3NaCl + 2H.O. \C02Na They are converted by reduction into the preceding alcohol- acids, and by fusion with caustic potash into the hydroxyphthalic acids. They combine, like other aldehydes, with the sulphites of the alkali metals. Ortho-aldehydosalicylic acid . (1 : 2 : 6) is obtained, together with the following compound, from salicylic acid. It crystallizes in fine, matted needles, which dissolve at 23°-25° in 1,500- 1,600 parts, or at 100° in 15-16 parts of water. The aqueous solution is coloured deep yellow by caustic soda, and red by ferric chloride, and the alcoholic solution shows a faint, bluish violet fluorescence. It melts at 179° and sublimes without decomposition when carefully heated. On distillation with slaked lime it decomposes into salicylaldehyde and carbon dioxide. The copper salt is a gelatinous precipitate, which is soluble in ammonia; on boiling the solution a light blue precipitate of C8H4O4Cu is thrown down. Para-aldehydosalicylic acid (1:2:4) forms long, fine needles, which melt at 248°-249°, and dissolve in 2,600-2,700 parts of water at 25°, and in 145-150 parts at 100°. Its aqueous solution is not coloured by caustic soda, while ferric chloride produces a deep cherry-red colouration. On distillation with lime, parahydroxybenzaldehyde is formed; its copper salt is also soluble in ammonia, but is not precipitated on boiling.1 Ortho^ddehydoparahydroxybenzoic acid (1:4:2), was obtained by Reimer and Tiemann from parahydroxybenzoic acid; it 1 Reimer and Tiemann, Ber. Deutsch. Chem. Ges. ix. 1268, x. 1562. 492 AROMATIC COMPOUNDS. crystallizes from hot water in thin, arborescent prisms, which melt at 243°-244°, and sublime in splendid, white needles. Its aqueous solution is coloured deep yellow by caustic soda and brownish red by ferric chloride. Salicylaldehyde is formed when it is distilled with caustic lime. Ortho-aldehy dometahy dr oxybenzoic acid (1:3: 6) is obtained, together with the following compound, from metahydroxybenzoic acid. It crystallizes in needles, which melt at 234°, and are slightly soluble in hot water and readily in alcohol. Its aqueous solution is coloured violet by ferric chloride and deep yellow by caustic soda. On boiling with caustic soda it is only decomposed at a high temperature, phenol being formed. Para-aldchy dometahy dr oxybenzoic acid (1 : 3 :4) has only been obtained as a syrup; it is very unstable and reduces Fehling's solution readily. On fusion with caustic potash it is converted into a-hydroxyisophthalic acid.1 /OH HYDROXYPHTHALIC ACIDS, C6H3/CO.,H. \co2h 2257 a-Hydroxyphthalic acid (4:1: 2). When the ethyl ether of a-amidophthalic acid is dissolved in dilute sulphuric acid, treated with sodium nitrite and then heated to 100°, the ether of a-hydroxyphthalic acid separates out as a yellowish oil, which yields the free acid on saponifying with potash; it is purified by precipitating the neutral solution with basic lead acetate and removing the lead by sulphuretted hydrogen.2 It is also obtained by oxidizing the sulphamido-orthotoluic acids with potassium permanganate and fusing the residue with potash,3 and is formed when para-aldehydometahydroxybenzoic acid,4 a-chlorophthalic acid,5 and a-sulphophthalic acid 6 are fused with caustic potash or soda. It is tolerably soluble in cold, very readily in hot water and alcohol, and crystallizes in large stellate groups of pointed prisms which melt at about 185°, the anhydride being formed ; on heating with dilute hydrochloric acid to 180°, it decomposes 1 Landshoff and Tiemann, Ber. Deutsch. Chcm. Ges. xii. 1334. 2 Baeyer, ibid. x. 1079. 3 Jacobsen, ibid. xiv. 42. 4 Tiemann and Landshoff, ibid. xii. 1337. 5 Kruger, ibid, xviii. 1759. 6 Griibe, ibid, xviii. 1130 ; Ree, InaugUrald. Bern. 1886. HYDROXYPHTHALIC ACIDS. 493 into carbon dioxide and metahydroxybenzoic acid (Ree). Its aqueous solution is coloured reddish yellow by ferric chloride. When the acid is heated with resorcinol, hydroxyfluorescein is obtained, which forms a dark, yellowish red solution in caustic potash, and is slightly soluble in water with a yellowish green fluorescence; acids separate it from its alkaline solution as a yellow precipitate. a-Hydroxy phthalic anhydride, C8H4O4, sublimes in feathery needles, when the acid is heated and melts at 165°-166°. a-Methylhydroxyphthalic acid, C6H3(OCH3)(CO2H)2, is formed by the oxidation of methylparahydroxyorthotoluic acid with potassium permanganate, and crystallizes from water in stellate groups of needles, which lose water on heating, forming the anhydride, which sublimes in long needles and melts at 930.1 vHIyd/roxyorthophthalic acid (3:1:2) is prepared by gently fusing v-methylhydroxyphthalic acid with potash, and by means of the diazo-reaction from the product of reduction of a-nitro- phthalic acid, which contains amidophthalic acid. It separates from hot water as a compact, crystalline mass, consisting of short, hard prisms, which are partly converted by heating into the anhydride, melting at 145°-148°, and are partly de- composed into phenol and carbon dioxide. Its aqueous solution is coloured a deep cherry-red by ferric chloride. When it is heated to 200° with resorcinol, hydroxyfluorescein is formed. Dinitro-v-hydroxyphthalic acid, C6H(NO2)2(OH)(CO2H)2, was first obtained by the action of nitric acid on jugion, a hydroxy- naphthoquinone, C10H5(OH)O2, which occurs in green walnut shells (Juglans regia}, and was called jugionic acid. It may also be prepared by the nitration of v-hydroxyphthalic acid ; it is exceptionally soluble in water, alcohol and ether, and separates from petroleum ether in small crystals. Its acid potassium salt, C8H3KN2O9, crystallizes in yellow, rhombic plates, which detonate violently on heating. It can be recrystallized from nitric acid or dilute sulphuric acid without undergoing decomposition.2 v-Mcthylhydroxyphthalic acid has been prepared by the oxidation of v-methylorthohomometahydroxybenzoic acid; it is tolerably soluble in water, and crystallizes in microscopic prisms, which melt at 160°, and are thus converted into the anhydride, which sublimes in needles and melts at 87°.3 1 Schall, Ber. Deutsch. Chern. Ges. xii. 829. 2 Bernthsen and Semper, ibid, xviii. 210 ; xix. 164. 3 Jacobsen, ibid. xvi. 1962. 494 AROMATIC COMPOUNDS. 2258 a-Hydroxyisophthalic acid (4:1:3) is formed, together with a large quantity of hydroxytrimesic acid, C6H2(OH)(CO2H)3, when carbon dioxide is passed over disodium salicylate heated to 370°-3800.1 It may be obtained in a similar manner from parahydroxybenzoic acid, which first changes into salicylic acid.2 It is also formed by the oxidation of para-aldehydosalicylic acid or ortho-aldehydoparahydroxy benzoic acid with potassium per- manganate, and when this acid,3 a-metaxylenol,4 or a-metaxylene- sulphonic acid,6 is fused with potash. When an alkaline solution of salicylic acid is heated to 120°-130° with tetrachloromethane, a-hydroxyisophthalic acid is obtained, together with a little v-hydroxyisophthalic acid.6 In order to prepare it, phenol is dissolved in an alkaline solu- tion which contains one molecule of potash to three of soda, the mass evaporated and carbon dioxide passed over the dry residue for some time at 120°-160°, the temperature being finally raised to 300°-320°. The chief product of the reaction is a-hydroxy- isophthalic acid accompanied by parahydroxybenzoic acid and hydroxytrimesic acid, almost two-thirds of the phenol coming over unchanged. The residue is decomposed with hydrochloric acid, and the a-hydroxyisophthalic acid repeatedly recrystallized from water.7 It forms long needles, which cross each other at an angle of 60°, melt at 305°-306°, and dissolve at 10° in 5,000, at 24° in 3,000, and at 100° in 160 parts of water. It is readily soluble in alcohol and ether, but not in chloroform, by means of which it can be separated from hydroxytrimesic acid. Its aqueous solution is coloured a deep cherry-red by ferric chloride. On heat- ing to 200° with hydrochloric acid, it decomposes into phenol and carbon dioxide, while on dry distillation it yields salicylic acid, phenol and carbon dioxide. When its disodium salt, C6H3 (OH)(CO2Na)2, is heated to 250°, the trisodium salt, C6H3(ONa) (CO2Na)2, is obtained, together with phenol and carbon dioxide, while the potassium salt yields a large amount of parahydroxy- benzoic acid when heated to 280°-300° (Ost). a-Methoxy isophthalic acid, C6H3(OCH3)(CO2H)2, is formed by 1 Ost, Journ. Prakt. Chem. [2] xiv. 99. 2 Kupferberg, ibid. [2] xvi. 42S. 3 Tiemann and Reimer, Ber. Deutsch. Chem. Ges. x. 1571. 4 Jacobsen, ibid. xi. 377. 5 Jacobsen and Remsen, ibid. xi. 377. 6 Hasse, ibid. x. 2195. 7 Ost, Journ. Prakt. Chem. [2] xv. 301. HYDROXYTEREPHTHALIC ACID. 495 the oxidation of a-metaxylenyl monomethyl ether,1 or methyl- parahomosalicylic acid2 with potassium permanganate, and crystallizes from hot water in microscopic needles, melting at 261° (Schall). Dimethyl a-hy dr oxy isophthalate, C6H3(OH)(CO2.CH3)2, forms large, flat needles which melt at 96° (Jacobsen). Diethyl a-hydroxyisophthalatc, C6H3(OH)(CO2.C2H6)2, crystal- lizes in fine needles, which melt at 52° and are soluble in caustic soda (Ost). v-Hydroxyisophthalic acid (2:1:3) is formed when ortho- aldehydosalicylic acid3 or sulphamido-isophthalic acid 4 is fused with potash. It crystallizes in hair-like needles, which melt at 243°-244°, dissolve in 700 parts of water at 24°, and in 35-40 parts at 100°. Ferric chloride produces a cherry-red colouration ; the aqueous and alcoholic solutions show a bluish violet fluorescence, which is destroyed by alkalis. The acid de- composes on heating, the chief portion being resolved into salicylic acid and carbon dioxide. r-Methoxy isophthalic acid, C6H3(OCH3)(CO2H)2, is prepared by the oxidation of methylorthohomosalicylic acid and crystallizes from water in prisms, which melt at 216°-218°, turning brown and subliming at the same time (Schall). s-Hydroxyisophthalic acid (5:1:3) is obtained by fusing s-sul- pho-isophthalic acid with potash, and by means of the diazo- reaction from amido-isophthalic acid. It crystallizes from hot water, in which it readily dissolves, in fascicular groups of needles with two molecules of water, which are lost at 100°. It melts at 288° and sublimes in broad, lustrous needles, which dissolve in 3280 parts of water at 5° and are coloured a faint yellow by ferric chloride. It decomposes into phenol and carbon dioxide on distillation with lime :5 Melting- point. Dimethyl s-hydroxyisophthalate, C6H3(OH)(CO2.CH3)2, fine needles 160° Diethyl s-hydroxyisophthalate, C6H3(OH)(CO2.C2H5)2 mono- clinic prisms 103° 225g Hydroxyterephthalic acid (2:1:4) was prepared by Warren de la Rue and Muller from amidoterephthalic acid by 1 Jacobsen, Ber. Deutsch. Chern. Ges. xi. 898. 2 Schall, ibid. xii. 828. 3 Tiemann and Riemer, ibid. x. 1570. 4 Jacobsen. s Heine, Ber. Deutsch. Chem. Ges. xii. 494 ; Lonnies, ibid. xiii. 705. 496 AROMATIC COMPOUNDS. the action of nitrous acid.1 It is also formed when paraxylenol,2 bromoterephthalic acid,3 ortho-aldehydometahydroxybenzoic acid,4 or metahydroxyparatoluic acid 5 is fused with caustic potash. In order to prepare it, amidoterephthalic acid is dissolved in dilute sulphuric acid, treated with sodium nitrite and boiled.6 It forms a powder, which is slightly soluble in hot water, readily in alcohol, and sublimes on heating with partial decomposition without previously melting. Its aqueous solution is coloured an intense violet-red by ferric chloride. When it is mixed with sand and submitted to dry distillation, it decomposes into carbon dioxide and phenol, and on heating with hydrochloric acid to 220° is resolved into carbon dioxide and metahydroxybenzoic acid, while fusion with an excess of caustic potash converts it into salicylic acid, together with a smaller amount of metahy- droxybenzoic acid.7 Methoxyterephthalic acid, C6H3(OCH3)(CO2TI)2, is formed by the oxidation of methylmetahomosalicylic acid8 and crystallizes from hot water in small prisms, which melt at 277°-279°, and are resolved into methyl chloride and hydroxyterephthalic acid by hydrochloric acid at 160°. Dimethyl Ayc?raryfcr^A£AaZa/e,C6H4(OH)(CO2.CH3)2, is obtained by passing hydrochloric acid into a solution of the acid in methyl alcohol, and crystallizes in splendid, silky needles, which melt at 94° and are soluble in hot water, readily in alcohol. Ferric chloride gives a somewhat fainter colouration than with the free acid. When the ethereal solution is shaken up with caustic soda solution, the sodium compound, C6H3(ONa)(CO2.CH3)2, is formed as a white paste. On heating the acid with caustic soda, methyl iodide and wood-spirit, the trimethyl ether, CGH3 (OCH3)(CO2.CH3)2, is obtained as an oily, pleasant-smelling liquid. Dimethyl acetoxy tercphthlate, C6H3(OCO.CH3)(CO2.CH3)2, is prepared by heating the dimethyl ether with acetyl chloride, and crystallizes from alcohol in cauliflower-like masses of fine needles, melting at 76° (Burckhardt). Dinitrohydroxytcrephthalic acid, C6H(NO2)(OH)(CO2H)2, is 1 Ann. Chem. Pharm. cxxi. 96. 2 Jacobsen, Ber. Deutsch. Chem. Ges. xi. 570. 3 Fischli, ibid. xii. 621. 4 Tiemann and Landshoff, ibid. xii. 1336. 5 Hall and Remsen, ibid. xii. 1433. 6 Burckhardt, x. 144. 7 Barth and Schreder, xii. 1260. 8 Schall, ibid. xii. 828. HYDROXYMETHYLDIHYDROXYBENZOIC ACIDS. 497 formed by the action of a mixture of concentrated nitric acid and fuming sulphuric acid on hydroxy terephthalic acid. It is readily soluble in water, from which it separates in golden yellow, trans- parent crystals, resembling those of calc-spar, which are, like the yellow and red salts of the acid, explosive.1 HYDROXYMETHYLDIHYDROXYBENZOIC ACIDS, zch2.oh c6h2(0H)2< " . \CO.OH 2260 In 1832, Couerbe detected meconin,2 C10H10O4, in opium, and Wohler and Liebig, in 1842, obtained opianic acid,3 C10H10O5, by the oxidation of narcotin or opian, which is also an opium alkaloid. This acid was more closely investigated by Wohler, who found that it is converted by further oxidation into hemipinic acid, C5H5O3. He assumed that in its formation one molecule of opianic acid took up oxygen and formed tw'o mole- cules of hemipinic acid ; he says: " It contains a radical which consists of half the radical of opianic acid, and this is referred to in its name." 4 Anderson, who also investigated the products of oxidation of narcotin, obtained a substance, opianyl, in addition to these acids, and pointed out that it shows an interesting relation to opianic and hemipinic acids when the formula of the latter of these is doubled, as his and Laurent's5 researches had shown to be necessary. " For we have as follows : Opianyl C10H10O4, Opianic acid . . . C10H10O5, Hemipinic acid . C10H10O6, as though these three compounds were different oxidation pro- ducts of the same radical." 6 He subsequently found that opianyl is identical with me- conin.7 Matthiessen and Foster then made the important observation, 1 Burckhardt, Ben Deutsch. Chem. Ges. xii. 1273. 2 Ann. Chim. Phys. xlix. 44 ; 1. 337 ; lix. 148. 3 Ann. Chem. Pharm. xliv. 126. 4 Ibid. 1. 1. 5 Compt. Bend. xx. 1118. 6 Ibid. Ixxxvi. 179. 7 Ibid, xcviii. 44. 498 AROMATIC COMPOUNDS. that when opianic acid is evaporated with caustic potash solution it is resolved into meconin and hemipinic acid : 20,^0,=CwHM04 + c10hwo6- They also found that opianic acid is reduced to meconin by the action of water and sodium amalgam : CWHWOS+2H = C10HwO4 + H2O. These highly characteristic reactions receive, according to them, a simple explanation, if it be assumed that a very un- stable hydrate of meconin, C10Hi2O5, is first formed. The de- composition of opianic acid then becomes quite analogous to that of benzaldehyde into benzyl alcohol and benzoic acid, and the reduction of the former also corresponds to that of benzalde- hyde to benzyl alcohol. By heating hemipinic acid with concentrated hydriodic acid, they obtained carbon dioxide, methyl iodide and hypogallic acid, according to the equation : C10H10O6+2HI = CO2 + 2CH3I + C7H6O4. If hydrochloric acid be employed, mdhylhypogallic acid,Q>^.9Qi is first formed, and is converted into hypogallic acid by further heating. Hemipinic acid, therefore, as well as opianic acid and meconin, contains two methyl groups, and the three bodies in question are derivatives of the still unknown normal compounds : Normeconin .... C8H6O4, Noropianic acid . . C8H6O5, Norhemipinic acid . C8H6O6, as they may be shortly designated, ordinary meconin being thus dimethylnormeconin, &c. They then succeeded in converting the latter, as well as opianic acid, into mcthylnormeconin, C9H8O4, and methylnor- opianic acid, C9H8O5, by heating with hydrochloric or hydriodic acid. They finally considered hemipinic acid to be dimethyl- dihydroxyterephthalic acid and looked upon opianic acid as the corresponding aldehydo-acid,1 but, as shown by Matthiessen and Wright, the former can be readily converted into an anhydride, and must therefore be dimethyldihydroxy phthalic acid. 1 Phil. Trans. 1863, 345 ; Journ. Chem. Soc. [2] i. 342 ; ibid. vi. 357. MECONIN AND OPIANIC ACID. 499 Liebermann and Chojnacki proposed the following formula for opianic acid : /COH C6H2(OCH3)2Z ZCO.OH and this was confirmed by the researches of Beckett and Wright, who also found that hypogallic acid is identical with protocatechuic acid. In the case of meconin there were two possibilities; it might be either hemipinic aldehyde or the anhydride of an alcoholic acid: .COH C6H2(OCH3)2Z \COH ZCH.,X C6H2(OCH3)2< )O. \co z The facts that it is formed from opianic acid by the action of nascent hydrogen, and cannot be re-oxidized to opianic acid, while the latter is converted into meconin and hemipinic acid by heating with canstic potash, are in favour of the latter view. Beckett and Wright then proved that this view is correct, and their results were confirmed by the researches of Hessert.1 Hemipinic acid is dimethylcatecholdicarboxylic acid, and can readily be converted into protocatechuic acid or catecholcarboxylic acid, in which the side-chains have the position CO2H: OH: OH = 1:3:4. Since hemipinic acid is simultaneously a derivative of phthalic acid, the second carboxyl group must be either in position 2 or 6; in the latter case it would yield only one acid methyl ether, while in the former two such compounds would be possible. Wegscheider has now found that two such isomerides exist,2 and he has also obtained isovanillin by heating opianic acid with dilute hydrochloric acid,3 while Beckett and Wright found that methylvanillin is formed when sodium opianate is distilled with soda-lime. It follows from these facts that the constitutions of the three compounds in question are represented by the following formulae : Meconin. XHz>0 rv \/0CH3 och3 Opianic acid. COH ^XcO.OH \/OCH3 och3 Hemipinic acid. CO.OH Z^CO.OH \/0CH3 och3 1 Journ. Chem. Soc. 1876, i. 164, 281, 461. 2 Monatsh. Chem. iii. 348. 3 Ibid. hi. 798. 500 AROMATIC COMPOUNDS. Meconin therefore stands to hemipinic acid in the same rela- tion as phthalide to phthalic acid. 2261 Meconinic acid or Hy dr oxy me thy Idimeth oxy benzoic acid, CcH2(OCH3)2(CH2.OII)CO2H, is not known in the free state. When its lactone, meconin, is dissolved in baryta water, barium meconinate, (C10HnO5)2Ba, is formed, and is left on evaporation as a gummy mass 1 (Kessert), while Prinz obtained it in fine, silky needles.2 This salt, however, yields meconin on decom- position with a strong acid. The copper and silver salts are precipi- tates, which decompose on heating with formation of meconin. Meconin, C10H10O4, as already mentioned, occurs in opium. Anderson obtained it, accompanied by other products, by the oxidation of narcotin with nitric acid, and it is also formed by the reduction of opianic acid. In order to prepare it, the mother liquor of the opium alka- loids is extracted with ether, the solution evaporated, and the residue washed with hydrochloric acid and re-crystallized from water (Anderson). It forms white, lustrous needles, which have a bitter taste, melt at 102°-102°'5 (Wright), and when carefully heated sublime in splendid needles. It is readily soluble in alcohol and ether, and requires 22 parts of boiling water and 700 parts of water at 15'5° for solution. On heating with concentrated sulphuric acid, a purple-coloured solution is formed. It forms ethers when heated with stearic or benzoic acids, as was shown by Berthelot, who concluded from this that it is an alcohol.3 Chloromeconin, C10TI9ClO4, was prepared by Anderson by the action of chlorine on fused meconin or on its aqueous solution. It crystallizes in colourless needles, which are scarcely soluble in cold, somewhat more readily in hot water, and more freely in alcohol, melt at 175° and sublime without decomposition. Bromomeconin, C10H9BrO4, crystallizes from alcohol in colour- less needles, melting at 1G7°. lodomeconin, C10H9IO4, is formed by the action of chloride of iodine on an aqueous solution of meconin, and forms long crystals or needles, which melt at 112°, and decompose when more strongly heated. Nitromeconin, C19H9(NO2)2O4,is obtained by dissolving meconin in cold, concentrated nitric acid, and precipitating with water. It crystallizes from alcohol in white needles or prisms, which 1 Ber. Deutsch. Chem. Ges. xi. 240. 2 Journ. Prakt. Chem. [2] xxiv. 373. 3 Ann. Clam, Phys. [3] Ivi. 51 ; Ann. Chem. Pharm. cxii. 356. MECONINIC ACID. 501 melt at 160°, and sublime when carefully heated. It forms a yellow solution in hot alkalis and is not re-precipitated by acids, nitromeconinic acid being probably formed. Amidomeconin, C10H9(N H2)O4, is prepared by warming the preceding compound with iron filings and acetic acid. It is precipitated by water as a yellowish powder, which is only slightly soluble in benzene, and melts at 171°. Methyl normeconin, C6H2(OCH3)(OH)C2H2O2, is formed when meconin is heated with hydrochloric or hydriodic acid (Mat- tbiessen and Foster), and when meconin or narcot'n is carefully fused with caustic potash (Beckett and Wright). It crystallizes from hot water in prisms, which melt at 125°; ferric chloride colours the aqueous solution a beautiful blue, which is converted into red by the addition of ammonia. On further fusion with potash it is converted into protocatechuic acid. y\r-Meconin. When hemipinimide, which will be further de- scribed below, is boiled with tin and hydrochloric acid, hemi- pinimidine is formed: /CO /CH2 (CH3O),CgH.< >0 + 4H = (CH3O)2< >0 +H„o. 'C=NH " XC=NH This substance crystallizes from benzene in small plates, which melt at 181°, and are converted into nitrosohemipinimidine, C]0H10O3N(NO), by the action of sodium nitrite on their solution in hydrochloric acid. The latter compound crystallizes from hot alcohol in silky, yellow needles, and dissolves in caustic soda solution with evolution of nitrogen. Hydrochloric acid added to this solution precipitates A/r-meconin, which crystallizes from hot water in colourless needles, melting at 123°-124°. Its isomerism with meconin is shown by the following formula: X°>o iZX|CH2 \/och3 och3 Nitro-y^-meconin, C10H9(NO2)O4, crystallizes in splendid, yellowish needles, which melt at 166°. Amido-y^-meconin, C10H9(NH2)O4, resembles amidomeconin, but is readily soluble in benzene, and melts at 1650.1 1 Salomon, Ber. Deutsch. Chern. Ges. xx. 883. 502 AROMATIC COMPOUNDS. Mcconiosin, C8H10O2, also occurs in opium, and crystallizes in plates, which melt at 88° and dissolve in 27 parts of cold water, and in almost every proportion in boiling water. On heating with sulphuric acid a splendid green solution is formed.1 ALDEHYDODIHYDROXYBENZOIC ACIDS, ZCOH C6H2(OH)2/ \CO.OH 2262 Noropianic acid, 2C8H6O5 + 3H2O, was obtained by Wright, together with methyl iodide, by boiling opianic acid with four times its weight of 50 per cent, hydriodic acid. It is readily soluble in water and crystallizes in fine prisms, which become anhydrous at 100° and melt at 171°. Its solution is coloured greenish blue by ferric chloride, the addition of ammonia or carbonate of sodium changing the colour to brownish red. It reduces ammoniacal silvei' solution in the cold and forms a yellow or brown solution in alkalis. The lead salt is a canary-yellow precipitate.2 Methylnor opianic acid, C6H2(OCH3)OH(COH)CO2H, was prepared by Matthiessen and Foster from opianic acid by heating it with hydrochloric or hydriodic acid. In order to prepare it, hydrochloric acid is passed into a warm solution of 50 grms. of opianic acid in 600 cb. cms. of strong hydrochloric acid until no opianic acid separates after standing for about two days. The solution is then concentrated, the paste of crystals thus obtained dissolved in water, the solution neutralized exactly with ammonia and treated with barium chloride, which produces a brown precipitate. The addition of ammonia to the filtrate precipitates the barium salt of the acid, which is then washed and decomposed with sulphuric acid.3 It is readily soluble in water and crystallizes in nacreous plates, long prisms, of transparent vitreous columns, which contain different amounts of water, but all readily effloresce in the air. The anhydrous acid melts at 154°; its aqueous solution is coloured dark blue by ferric chloride, and on the addition of ammonia light red. 1 T. and H. Smith, Pharm. Journ. Trans. [3] viii. 981. 2 Journ. Chern. Soc. 1877, ii. 545. 3 Prinz, Journ. Prakt. Chem. [2] xxiv. 368. OPIANIC ACID. 503 As a phenol-acid it forms two series of salts. Silver methylnoropianatc, C9H7O5Ag, is a gelatinous precipitate, which becomes crystalline on standing. It is soluble in hot water and separates in crystals when the solution is cooled. Barium methylnoropianate, C9H0O5Ba + H2O, is also thrown down in the gelatinous state and changes into granular crystals on standing. Chloromethylnoropianic acid, C6HC1(OCH3)OH(COH)CO2H, is obtained by the action of potassium chlorate and hydrochloric acid on methylnoropianic acid, and crystallizes from hot water in large, lustrous needles, which melt at 206° (Prinz). Nitromethylnoropianic acid, C6H(NO2)(OCH3)OH(COH)COoH + h2o, is formed when methylnoropianic acid is treated with dilute nitric acid (Matthiessen and Foster). It is also obtained by heating nitro-opianic acid for some time with hydrochloric acid. It crystallizes in radiating needles, which lose their water at 120° and melt at 2030.1 2263 Dimethylnoropianic acid or Opianic acid, CGH2(OCH3)2 (COH)CO.,H, was prepared by Wohler and Liebig from narcotin by boiling it with dilute sulphuric acid and manganese dioxide. Blyth found that it is also formed by heating with platinum chloride,2 and Anderson obtained it by oxidizing narcotin with dilute nitric acid. In order to prepare it according to the method proposed by Matthiessen and Foster, 100 grms. of narcotin are heated with 1,500 grms. of water and 150 grms. of sulphuric acid until the mixture boils; 150 grms. of finely powdered pyrolusite, corresponding to 90 grms. of manganese dioxide, are then added somewhat rapidly and the hot solution filtered. Opianic acid separates out on cooling and is purified by recrystallization. Wohler, in order to obtain it perfectly colour- less, dissolved it in sodium hypochlorite, heated to boiling, and then added an excess of the hypochlorite. The decolourization may also be effected, according to Prinz, by passing the gases evolved from nitric acid and arsenic trioxide through the hot solution; and it may also be obtained perfectly white by running potassium permanganate into the hot solution acidified with sulphuric acid until it becomes sherry-yellow.3 The portion which is left in the mother-liquor from its preparation can be 1 Elbel, Bar. Deutsch. Chem. Ges. xix. 2306. 2 Ann. Chem. Pharm. 1. 29. 3 Prinz, Journ. Prakt. Chem. [2] xxiv. 353. 504 AROMATIC COMPOUNDS. removed by ether, which does not dissolve the colouring matter (Wegscheider). It is slightly soluble in cold, readily in hot water, alcohol and ether, and crystallizes in thin, narrow prisms or silky needles, which melt at 150° (Wegscheider) and decompose on further heating, giving off a vapour which smells like vanilla (Wohler). It has a faint acid reaction and a slightly bitter taste. Sodium amalgam and water reduce it to meconin, while on evaporation with caustic potash it is converted into the latter and hemipinic acid (Matthiessen and Foster, Beckett and Wright). When its sodium salt is heated with soda lime methylvanillin is formed, and isovanillin when it is heated with dilute sulphuric acid to 160°-170°. Concentrated sulphuric acid converts it on heating into a red colouring matter, which Anderson mistook for alizarin, C14H8O4, but which was shown by Liebermann and Chojnacki to be the closely allied substance rufiopin,1 C14H8O6. The salts of opianic acid have been investigated by Wohler and Wegscheider.2 Potassium opianatc. C10H9O5K, is readily soluble in water and crystallizes in several forms, which differ in the amount of water they contain. It crystallizes from ordinary alcohol in compact, white prisms containing two and a half molecules, or transparent, rhombic tablets with one molecule of water of crystallization. Barium opianatc, (C10H9O5)2Ba + 2H2O, forms a radiating mass of prisms, which are readily soluble in water and effloresce when kept in a warm place. Lead opianatc, (C10H9O5)2Pb + 2H2O, is only slightly soluble, and forms very lustrous, transparent crystals, apparently of the same form as sphenite. Silver opianatc, 2C10H9O5Ag + H2O, is described by Wohler as forming short prisms, which readily become coloured yellow. Wegscheider found that when the acid is rapidly dissolved in presence of silver carbonate, complete saturation does not take place, and that reduction ensues on boiling. On precipitating the potassium salt with silver nitrate, he found that the greater portion of the silver salt was removed by washing, and therefore prepared it by mixing concentrated solutions of silver fluoride and potassium opianate. The tough, amorphous, yellowish pre- cipitate changes on stirring into hemispherical or warty masses consisting of small prisms, which can be completely washed with a small quantity of water. 1 Ann, Chern. Pharm. clxii. 321. 2 Monatsh. Chern. iii. 348. OPIANIC ANHYDRIDE. 505 Methyl opianate, C10H9O5(CH3), was prepared by Wegscheider from the silver salt by the action of methyl iodide. It is also formed, as found by Liebermann and Kleemann, when opianic acid is boiled with methyl alcohol.1 It crystallizes from alcohol in flat, monosymmetric needles, and from ether in thick, vitreous tablets or short prisms, which melt at 102° and partially sublime on careful heating. It rapidly decomposes into methyl alcohol and opianic acid when boiled with water, the latter being ob- tained pure by this method (Liebermann and Kleemann). Ethyl opianate, C10H9O5(C2H5), is readily formed, according to Wohler, by saturating a hot, alcoholic solution of opianic acid with sulphur dioxide, while it could not be prepared by means of hydrochloric acid. Anderson, however, noticed its formation when hydrochloric acid was added to an alcoholic solution of the potassium salt, and Prinz prepared it by the action of the chloride on absolute alcohol. According to Liebermann and Kleemann, it may be most simply obtained by boiling the acid with absolute alcohol. It crystallizes from alcohol in needles or fine prisms, which melt at 92° and sublime when carefully heated. 2264 Opianic anhydride, C20HlsO9. Wohler found that opianic acid undergoes a remarkable change when it is kept in a state of fusion for some time, becoming insoluble in water, and he assumed that it is thus converted into an isomeric modi- fication, while Matthiessen and Wright concluded that it loses water and forms the compound C40H38O19.2 Wegscheider, on the other hand, considered the substance to be formed from three molecules of opianic acid, and named it triopianide, C30H18Ou.3; Liebermann has, however, found 4 that it is formed when opianic acid is heated for two hours at 160° in a current of air, and explains the reaction by the following equation : 2(CH3O)2(COH)C6H2,CO.OH = (CH3O)2(COH)C6H2.COX >0 + h2o. (CH3O)2(COH)C6H2.COz Opianic anhydride is also obtained when opianic acid is heated with phosphorus pentachloride, and crystallizes from hot acetone in needles, which melt at 234°. 1 Ber. Deutsch. Chem. Ges. xx. 881. 2 Ann. Chern. Pharm. Suppl. vii. 63. 3 Monatsh. Chem. iv. 262. 4 Ber. Deutsch. Chem. Ges. xix. 2286. 506 AROMATIC COMPOUNDS. On heating with caustic potash and a little water, it decom- poses into meconin and hemipinic acid, while on boiling with caustic potash solution, or when it is dissolved in sulphuric acid and the solution poured into water, it is reconverted into opianic acid. Acctylopianic acid. When aromatic aldehydes or aldehydo- acids are heated with acetic anhydride and anhydrous sodium acetate, the aldehyde group CHO is converted into the acrylic acid residue CH~CH-CO2H. Opianic acid does not behave in this way, but forms acetylopianic acid, which crystallizes from hot water in needles melting at 120°-121°. It is insoluble in cold alkalis and is only decomposed on boiling, acetic and opianic acids being formed; it therefore does not contain a carboxyl group, and its constitution must be expressed by the following formula : /CO (CH3O)2C6H2< >0 \ch.o.co.ch3 It appears, therefore, that opianic acid can behave not only as an ortho-aldehydo-acid, but also as a lactone.1 The one form can pass into the other according to the circumstances of the case: /CO.OH ,00 (CH3O)2C6H2/ = (CH3O)2C6H2< >0 . XCHO \CH.0H Opianyl sulphurous acid, C6H2(OCH3)2(CHO.SO3H2)CO,H, is formed when opianic acid is dissolved in a hot aqueous solution of sulphur dioxide: ZCHO (CH3O)2C6.H2< + SO(OH)2 = XCO.OH on .<011 (ch3o)2c6hZ os°2H- XCO.OH On evaporation at a gentle heat, the compound is left as a fine crystalline mass, which is resolved into its constituents by water. Its solution has a characteristic bitter taste, and leaves a persistent, sweet after-taste. 1 Liebermann and Kleemann, Ber. Deutsch. Chem. Ges. xix. 2287. THIO-OPIANIC ACID. 507 Barium opianylsulpliite, (C10H10O5.SO3H)2Ba + 3H2O, is pre- pared by dissolving barium carbonate in a freshly-made solution of the acid, and crystallizes in lustrous, rhombohedral tablets. Lead opianylsulphite, (C10H10O5.SO2H)2Pb +6H2O, is prepared in a similar manner, and forms very lustrous, four-sided prisms or six-sided tablets (Wohler). These salts correspond to the ethidene sulphites (Part II. p. 73). 2265 Thio-opianic acid, (CH3O)2C6H2(CHS)CO2TI, was ob- tained by Wohler by passing sulphuretted hydrogen into a warm solution of opianic acid; it forms a yellow powder which crystal- lizes from alcohol in fine, transparent, yellowish prisms, which melt below 100° and resemble opianic acid in forming an anhydride. Chloropianic acid, (CH3O)2CHC1(COH)CO2H, is formed by the action of potassium chlorate on a hot solution of opianic acid in hydrochloric acid, and crystallizes from hot water in small prisms melting at 210°-211° (Prinz). Bromopianic acid, (CH3O)2C6HBr(COIT)CO2H, is prepared by adding bromine to a boiling solution of opianic acid (Prinz) and by triturating opianic anhydride with bromine (Wegscheider). It crystallizes from hot water in small, arborescent needles which melt at 204°. Nitro-opianic acid, (ClI3O)2C6H(NO2)(COH)CO2H, is formed, together with nitrohemipinic acid, by the action of concentrated nitric acid on opianic acid. It is only slightly soluble in water, and crystallizes in lustrous yellow prisms, melting at 166°. Its salts are readily soluble in water and crystallize well. Opianylphcnylhyd/razide, C16H14N2O3, is obtained by mixing hot solutions of opianic acid, phenylhydrazine hydrochloride, and sodium acetate (Part III. p. 283) : WjC6W8 = C16HuN2O3+2H2O. It crystallizes from alcohol in almost colourless needles, which melt at 175°, and are insoluble in alkalis, but dissolve in con- centrated hydrochloric acid, from which solution they are pre- cipitated by water. It is therefore a weak base, and is very stable, being unattacked by concentrated sulphuric acid even at 130°; it has probably the following constitution : xCO-N.C6H5 (CH3O).,C6hZ I XCH-N 508 AEOMATIC COMPOUNDS. Phcnylhydrazine nitro-opianic acid, C1GHl5N3OG, is formed in a similar manner, according to the equation : /CO.OH (CH3O)2CGH (no2) / + nh2 -nh.c6h6 XCHO /CO.OH (CH3O)2C6H(NO2)< +h20. \CH-N-NHC6H5 It crystallizes in splendid, carmine-red needles, which melt at 184°, and form a red solution in alkalis. Acids convert it into nitro-opianylphcnylhydrazidc, C1GH13N3O5, which crystallizes in yellow, silky needles, melting at 173°, is insoluble in alkalis, and behaves as a weak but stable base.1 When it is boiled with alcoholic potash, it decomposes into methyl alcohol and nitromethylnorcpianylvhcnylliydrazidc, C15HuN3O5, which has also been prepared from methylnor- opianic acid.2 This substance crystallizes in glittering, yellow plates, melting at 191°, and since it is a phenol, behaves as a weak acid. Amido-cpianylphcnylhydrazidc, C1GH15N3O3, is obtained by the reduction of the nitro-compound with tin and hydrochloric acid. It crystallizes in fine needles, and oxidizes in the air to amido- hemipinylphenylhydrazide. 2266 Isonoropianic acid, CGH2(OH)2(COH)CO9H(CO2H: OH : OH : COH 1 : 3 : 4 : 5), is formed when the following compound is heated to 170°-180° with hydrochloric acid. It is tolerably soluble in cold, readily in hot water, and crystallizes in yellowish needles, which melt with decomposition a few degrees above 240°. Its aqueous solution is coloured yellow by alkalis and dark green by ferric chloride, this colour being instantly changed to reddish violet by the addition of ammonia. It reduces ammoniacal silver solution in the cold, and Fehling's solution on boiling.3 Methylisonoropianic acid or Aldehydovanillic acid, CGH9(0CH3) (0H)C0H(C09H), is formed, together with vanillin, when vanillic acid is heated with caustic soda and chloroform. It is readily soluble in alcohol, very slightly in cold, somewhat more readily in boiling water, from which it crystallizes in fine, silky needles, which melt at 221°-222°. As an aldehydo-acid 1 Liebermann, Ber. Deutsch. Chcm. Ges. xix. 763. 2 Elbe!, ibid. xix. 2306. 3 Mendelsohn and Tiemann, ibid. x. 393. ISOPIANIC ACID. 509 it combines with acid sodium sulphite; caustic soda colours the solution an intense yellow, while ferric chloride produces a dirty reddish violet colouration. Its constitution follows from the fact that, in the synthesis of aldehydes or aldehydo-acids from phenols by means of chloro- form, the aldehyde group always takes either the ortho- or para- position with regard to the hydroxyl. Since the latter is occupied in vanillic acid, the aldehyde group must lie next the hydroxyl, and the two groups are thus found in aldehydovanillic acid in the same relation as in salicyl aldehyde-a view which is confirmed by its behaviour towards caustic soda and ferric chloride.1 As a phenol it forms two series of salts.2 Methyl aldehydovanillate, C6H2(OCH3)OH(COH)CO2.CH3, is prepared by heating the acid with caustic potash, wood-spirit and methyl iodide, and forms yellow needles, which melt at 134°-135°, and are soluble in carbonates of the alkalis. Isopianic acid, C6H2(OCH3)2(COH)CO2H. The methyl ether of this compound is formed together with the foregoing com- pound. It crystallizes from boiling water in fine needles, which melt at 98°-99°, and are insoluble in the alkali carbonates. It is readily saponified by hot caustic potash solution. The free acid, which is precipitated by acids from this product, crystallizes from water in fine needles, melting at 210°-211°, which give no colouration with caustic soda or ferric chloride. It forms a slightly soluble compound with acid sodium sulphite.3 Quercimcric acid, C8H6O5 + II2O. This substance, which is very similar to isonoropianic acid, was obtained by Hlasiwetz and Pfaundler by fusing quercitin with caustic potash. It forms crystalline granules or small prisms, is readily soluble in water, and reduces Fehling's solution and salts of silver. Ferric chloride produces a blue colouration in the aqueous solution, and an alkaline solution turns red in the air. On farther fusion with potash protocatechuic acid is formed.4 1 Bcr. Deutsch. Chem. Ges.ix. 1278. 2 Mendelsohn and Tiemann, ibid. x. 395. 3 Ibid. x. 397. 4 Jahresber. 1864, 560. 510 AROMATIC COMPOUNDS DI HYDROXYPHTHALIC ACIDS, C6H2(OH)2(CO2H)2. 2267 Ilcmipinic acid or Dimethoxy orthophthalic acid, C6H2 (OCH3)2(CO2H)2, is, as already mentioned, a product of the oxidation of opianic acid, and has also been obtained by the oxidation of the alkaloids contained in opium, oxynarcotiu and narcem.1 It is readily soluble in alcohol, very slightly in cold, more freely in boiling water, from which it crystallizes in colour- less, distorted prisms with acute basal planes, containing two molecules of water which are lost below 100°. The anhydrous acid melts at 180°, and sublimes in lustrous plates, resembling those of benzoic acid (Wohler). Crystals containing half a molecule of water are obtained by the spontaneous evaporation of its solution, while those deposited from a supersaturated solution contain one molecule (Matthiessen and Foster). It has a faint acid and slightly astringent taste, is decomposed into carbon dioxide and dimethylcatechol on heating with soda-lime, and is converted into rufiopin by hot sulphuric acid. Dilute hydrochloric acid decomposes it at 160°-170° into methyl chloride, carbon dioxide, isovanillic acid and protocatechuic acid (Wegscheider). Its aqueous solution is coloured yellowish brown by ferric chloride, and gives a white precipitate with lead acetate. Normal potassium hcmipincdcN\(^^ is very soluble in water and does not easily crystallize. Acid potassium hcmipinate, C10H9O0K, forms thick, six-sided tablets, which are readily soluble in water and alcohol, and have an acid reaction. Normal silver hcmipinate, C10H8O6Ag2, is a white precipitate, insoluble in water. Acid a-methyl hcmipinate, C6Ho(OCH3)2(CO2.CH3)CO2H + H2O(OCH3: OCH3: CO2CH3: CO2H = 4 : 3:2 :1), is prepared by oxidizing methyl opianate with potassium permanganate, and crystallizes from hot water in lustrous, narrow, flat needles, which readily effloresce and when completely dehydrated melt at 121°-122°. Its solution gives a yellowish brown precipitate with ferric chloride. 1 Beckett and Wright, Journ. Chem. Soc. 1876, i. 461. HEMIPINIC ACID. 511 Acid ^-methyl hemipinate, CflH2(OCH3)2(CO2H)CO2.CH3 (4 :3 : 2 :1), is formed by passing hydrochloric acid into a solu- tion of hemipinic acid in methyl alcohol. It is readily soluble in water and crystallizes from alcohol in arborescent needles or stellate groups of prisms, and from benzene or chloroform in rhombic tablets, which melt at 137°-138°. Its solution is not precipitated by ferric chloride (Wegscheider). Acid ethyl hemipinate, 2C6H2(OCH3)2(CO2.C2PI5)CO2H + 3H2O, was prepared by Anderson by passsing hydrochloric acid into the alcoholic solution of the acid. It is also formed by heating hemipinic anhydride with 90 per cent, alcohol (Matthiessen and Wright) and crystallizes from hot water in fascicular groups of needles, melting at 141°-142° (Wegscheider). Its solution is precipitated by ferric chloride, so that it cor- responds to the a-methyl ether, and not, as might have been expected from its formation, to the ^-compound. Hemipinic anhydride, C10H8O5, is formed when the acid is heated for an hour to 180° (Beckett and Wright), by the action of phosphorus pentachloride on the acid (Prinz) and by the distillation of the methyl ether (Wegscheider). It crystallizes from absolute alcohol, benzene, and xylene in lustrous needles, which melt at 167° and readily sublime. On heating with zinc dust and glacial acetic acid it is reduced to -^-meconin (Salomon). 2268 Nitrohemipinic acid, C6H(NO2)(OCH3)2(CO2H)2 + H2O, is best prepared by boiling nitro-opianic acid with pure nitric acid. It is also formed when meconin or T/r-meconin is heated under pressure with nitric acid (Salomon), and crystallizes from hot water in hard, yellow, vitreous prisms which lose water on heating, melt at 155°, and are converted into the anhydride at 160°-165°; the latter crystallizes from benzene incompact, light yellow prisms, and melts at 145°? Amidohemipinic acid, C6H(NH2)(OCH3)2(CO2H)2, was first prepared from its anhydride and was then obtained by Grune by reducing nitrohemipinic acid with caustic soda and ferrous sulphate. The free acid is only known in its aqueous solution, which is coloured yellow, showing a fine green fluorescence, has an acid reaction and decomposes on evaporation. Barium amidohemipinate, C10II9NO6Ba, is obtained by boiling the anhydride with baryta water; it is a golden coloured crys- talline powder, which dissolves in dilute acids, but is insoluble in water. 1 Griine, Bar. Deutsch. Chem. Ges. xix. 2299. 512 AROMATIC COMPOUNDS. Anhydro-amidohemipinic acid was prepared by Prinz by the action of an acid solution of stannous chloride on a boiling solution of nitro-opianic acid and was named azo-opianic acid.1 Liebermann then pointed out that this substance is probably the anhydride or anthranil of amidohemipinic acid :2 /CO.OH (CH3O)2C6H<NH 0 Xco^ The accuracy of this view was proved by Grime. It crystallizes from alcohol in fine, colourless needles, which melt at 200° with decomposition. When its solution in concentrated hydrochloric acid is evaporated, the hydrochloride separates in stellate groups of prisms, which lose their hydrochloric acid on drying. Its potassium salt, (CH3O)2CH(CONH)CO2K, is a crystalline powder, insoluble in alcohol. When it is boiled with acetic anhydride and anhydrous sodium acetate the acetyl-compound is formed, and crystallizes in needles which form an aqueous solu- tion possessing a blue fluorescence. It readily decomposes with formation of free acetic acid, and has the following con- stitution : .CO (CH3O)2C6H(CO2H)/ I xN.C2H3O Amidohcmipinylplienylhydrazide is formed by the continued boiling of anhydro-amidohemipinic acid with alcohol, phenyl- hydrazine hydrochloride, and sodium acetate, and also by the oxidation of amido-opianylphenylhydrazide in the air : zCO-NC6H6 (CH3O)2CcHr"CH=N + 0 = XNH2 co-nc6h5 (CH3O)2C6H-C = N + H2O. It crystallizes from benzene or alcohol in small, vitreous, honey- yellow crystals belonging to the tetragonal system, which melt at 222.°3 1 Journ. Prakt. Chem. [2] xxiv. 362. 2 Ber. Deutsch. Chern. Ges. xix. 351. 8 Liebermann, ibid. xix. 2275. HEMIPINIMIDE. 513 Diazohemipinic acid, (CH3O)2C6H(CO2H)<^q_q>, is ob- tained by the addition of hydrochloric acid to a cooled solu- tion of sodium amidohemipinate and sodium nitrite. It forms a light yellow, crystalline powder, which explodes by percussion or on heating. When it is dissolved in warm hydrochloric acid, the chloride, (CH3O)2C6H(CO2H)2N2C1, separates on cooling in long needles, which are instantly converted by water into their constituents (Grune). Opianoxime anhydride, C10H9NO4, is formed when an alcoholic solution of opianic acid and hydroxylamine hydrochloride is allowed to stand: /CO.OH C6H2(OCH3)2< + h2n.oh = XCOH /CO-0 C6H2(OCH3)2< I + 2H2O. \CH=N It crystallizes from benzene in long needles, which on careful heating melt at 114°-115°, and are converted into acid ammonium hemipinate by boiling with water.1 Hemipinimide, C10H9NO4. This compound, which corresponds to phthalimide, is formed when ammonium hemipinate is heated and when an alcoholic solution of opianic acid is boiled with hydroxylamine hydrochloride, the foregoing compound being first formed and then undergoing an intramolecular change, which also occurs when it is rapidly heated to 117°; the temperature rises suddenly to 260°, and the liquid solidifies on cooling to crystals of hemipinimide : /CO-O /CO C6H2(OCH3)2< | = C6H2(OCH3)a< >0 , \CH=N \C=NH It crystallizes from hot water in splendid needles, which melt at 228°-230° and readily sublime. Its aqueous solution has a fine blue fluorescence. When it is triturated with a cold alcoholic solution of potash, potassium hemipinimide, C10H8O4(NK), is formed as a crystalline powder, whose aqueous solution gives a white precipitate of silver hemipinimide, C10H8O4(NAg), with silver nitrate. 1 Liebermann, Ber. Dnitsch. Chern. Ges. xix. 2923. 514 AROMATIC COMPOUNDS. Ethyl hemipinimide, C10H8O4(NC2H5), is obtained when the potassium compound is heated to 150° with ethyl iodide. It crystallizes from hot water or benzene in needles, which melt at 96°-98°. The solution also shows a blue fluorescence.1 2269 Methylnorhemipinic acid, C6H2(OCH3)OH(CO2H)2 + 2H2O (4 : 3 : 2 :1), is formed by heating hemipinic acid with hydriodic acid for a short time,2 and by heating acid a-methyl hemipinate with hydrochloric acid. It forms warty crystals, which are readily soluble in water and alcohol. It reduces ammoniacal silver solution in the cold and Fehling's solution on heating, gives a deep blue colouration with ferric chloride, and melts at 152°-155° with decomposition. It separates from ether as an anhydrous powder, which melts at 223°-225° with evolution of gas (Wegscheider). On dry distillation it decom- poses into iso vanillic acid and carbon dioxide, and is converted into protocatechuic acid by fusion with potash. In its preparation from hemipinic acid, the compound C9HgO4 + 2H2O is formed as a by-product. It crystallizes in lustrous prisms or thin tablets, which melt at 148°. Its aqueous solution is coloured lilac by ferric chloride. This substance, which Liechti named opinic acid, might be methylnorhemipinic anhydride, but this is considered doubtful by Beckett and Wright since it contains water of crystallization, and they assume that it corresponds to salicylide and has the following constitution: /CO2H C6H(OCH3)^-CO xO-> Nitromethylnorhemipinic acid, CeH(NO2)(OCH3)OH(CO„H)2, is formed when methylnorhemipinic acid is evaporated with dilute nitric acid, and crystallizes from alcohol in almost white, silky needles, which are readily soluble in water, and melt at 220°.3 Amidomcthylnorhemipinic acid, CcH(NH2)(OCH3)OH(CO2H)2, is not known in the free state; its barium salt separates in lustrous, dull yellow plates when the anhydro-acid is boiled with baryta water. Anhydro-amidomethylnorhemipinic acid, (CH3O)(OH)C6H(CO2H)<^^i>O, is prepared by adding 1 Liebermann, Ber. Deutsch. Chern. Ges. xix. 2287. 2 Beckett and Wright, toe. cit. ; Liechti, Ann. Chcm. Pharm. Suppl. vii. 149. 3 Elbel, Ber. Deutsch. Chcm. Ges. xix. 2306. DIHYDROXYISOPHTHALIC ACID. 515 stannous chloride and hydrochloric acid to a boiling, saturated solution of nitromethylnoropianic acid, and crystallizes in silky needles, which melt at 174°-175° with decomposition. On boiling with acetic anhydride and sodium acetate, the diacetyl compound is formed: CH3OX zCO )C6H(CO2H)< I CH3.CO.Oz zN.CO.CH3 It crystallizes in needles, melting at 205°, and yields a solution in alcohol which has a blue fluorescence. Acetic anhydride is set free on standing, the monoacetyl derivative, C6H(OCH3) (OC2H3O)(CO2H)(CONH), being formed. This body melts at 198° and does not form a fluorescent solution in alcohol. Isohemipinic acid, CflH2(OCH3)2(CO2H)2, is formed by the oxi- dation of methyl isopionate with potassium permanganate. The methyl ether is thus obtained, which crystallizes in needles melting at 167°, and yields the acid on saponification. The latter forms white needles, which are scarcely soluble in cold, more readily in hot water, and melt at 245°-246° (Mendelsohn and Tiemann). 2270 Dihydroxyisophthalic acid, or Dcsorcinoldicarhoxylic acid, C6H2(OH)2(CO2H)2. When resorcinol is heated with caustic soda and chloroform, dihydroxyisophthalaldehyde, C6H2(OH)2 (COH)2, is formed, which is almost insoluble in cold water, but dissolves readily in alcohol and ether, from which it is removed by agitation with acid sodium sulphite without forming a difficultly soluble compound. It crystallizes from hot water in long, strongly refractive needles, which melt at 127° and readily sublime. It forms a yellow solution in alkalis. On fusion with caustic potash resorcinoldicarboxylic acid is formed ; this crys- tallizes from water in fine, white needles, which decompose on heating into resorcinol and carbon dioxide.1 Its constitution has not been accurately determined, but the position of the side- chains is probably OH : OH : CO2H : CO2H = 1: 3 : 4 : 6, since in this arrangement the carboxyls stand in both the ortho- and the para-relation to the hydroxyls. Dihydroxy terephthalic acid, (OH: OH: CO2H: CO2H=1:4:2:5). This body, which is also known as quinoldicarhoxylic acid, is ob- tained by passing air into an alkaline solution of succinosuccinic ether (Part II. p. 190; III. p. 146) and decomposing the pro- 1 Lewy and Tiemann, Ber. Deutsch. Chem. Ges. x. 2210. 516 AROMATIC COMPOUNDS. duct with sulphuric acid.1 It may also be readily prepared by saponifying the ether, and crystallizes from hot water in brownish yellow, hair-like needles, but from alcohol in deep yellow plates, while it separates from ether in rhombic tablets or prisms, which are coloured greenish yellow and show a light blue fluorescence. Ahot supersaturated solution, however, first deposits asymmetric white and green crystals, the latter of which are less acutely pointed than the former. On further cooling the rhombic prisms appear and replace the asymmetric crystals when the solution is again gently warmed. If, however, the latter are isolated, the white plates are converted on cooling into the green, which again become white on warming, so that by alternate heating and cooling the same crystal can be obtained in either modification an in- definite number of times. Since the shape of the crystal alters with the colour, it can be made to present the appearance of a concertina,, alternately elongated and compressed by causing the changes of temperature to follow one another rapidly.2 The aqueous solution of the acid shows a f.int emerald green fluorescence, while that of the alcoholic solution is light blue ; it is coloured a pure deep blue by ferric chloride. When rapidly heated the acid decomposes with formation of quinol and other products.3 Normal sodium dihydroxy terephthalate, C6H4O2(CO2Na)2 + 2H2O, crystallizes on the spontaneous evaporation of its aqueous solution, in flat, light brown prisms. Acid sodium dihydroxy terephthalate, C6H4O2(CO2Na)CO2H 4- 2H2O, forms light yellow, lustrous prisms. Basic sodium dihydroxytercphthalatc, C6H2(ONa)2(CO2Na)2 + 12H2O. The acid dissolves in caustic soda forming a deep yellow solution with a strong green fluorescence; on the addition of very concentrated caustic soda the basic salt separates in large transparent crystals, which possess a large number of faces and appear a faint greenish yellow by transmitted, but light blue by reflected light. 2271 Diethyl dihydroxyterephthalate, CcH4O2(CO2.C2H5)2, is formed by the addition of bromine to a solution of succinosuccinic ether in carbon disulphide,4 and by the action of sodium on an ethereal solution of dibromaceto-acetic ether,5 CH3.CO.CBr2.CO2. C2H6. The latter formation corresponds to that of succino- 1 Herrmann, Ber. Deutsch. Chem. Ges. x. 111. 2 Lehmann, Zeitsch. Kryst. x. 3 ; Herrmann, Ber. Deutsch. Chem. Ges. xix. 2229. 3 Herrmann, Ann. Chem. Pharm. ccxi. 335. 4 Herrmann, ibid. ccxi. 372; Ber. Deutsch. Chem. Ges. xvi. 1411; Duisberg, ibid. xvi. 133 ; Ebert, Ann. Chem. Pharm. ccxxix. 45. 5 Wedel, ibid, ccxix. 71. DIHYDROXYTEREPHTHALIC ACID. 517 succinic ether from monobromaceto-acetic ether. It crystallizes from ether in short, thick prisms or long flat needles, and from benzene in rectangular, rhombic tablets, which have the colour of uranium glass and show a light blue fluorescence. It melts at 133°-133'5° and sublimes at a higher temperature in lustrous, green, flat plates possessing a beautiful blue fluorescence. Its alcoholic solution is coloured bluish green by traces of ferric chloride. It dissolves in alkalis forming a deep yellow solution, with which a concentrated solution of an alkali produces a deep orange-red precipitate. Diethyl diacetoxyterephthalate, C6H2(OCO.CH3)2(CO2.C2H5)2, is prepared by heating the ethyl ether with acetyl chloride, and crystallizes from alcohol in colourless, lustrous plates, which melt at 115° (Wedel). Monethyl dihydroxyterephthalate, C6H2(OH)2(CO2.C2H5)CO2H. When the diethyl ether is dissolved in dilute caustic potash and the unattacked portion removed after some time by acetic acid, barium chloride precipitates the barium salt of the acid ether from the filtrate; this salt can readily be recrystallized from hot water, and hydrochloric acid added to its solution precipitates the mono-ethyl ether of dihydroxyterephthalic acid. It is a strong monobasic acid, crystallizes from hot water in fine, yellow needles, and is deposited on the evaporation of its alcoholic solu- tion in light yellow, transparent, vitreous prisms, which melt at 184°. Its solution is coloured bluish violet by ferric chloride. If the diethyl ether is boiled with alcoholic hydrochloric acid and zinc, it is again reduced to succinosuccinic ether, which can therefore be regarded as the ether of a dihydroxydihydrotere- phthalic acid. The latter is formed in the first stage of the reaction, but immediately changes into the isomeric compound:1 h^^co2.c2h5 c HOOTCH HC\/COH c h/\co2.c2h5 h^zco2.c2h5 C OC/^CH, H2c'\Zlco c h/\co2.c2h5 The latter formula is rendered probable by the formation of the substance from bromaceto-acetic ether, CH3.CO.CHBr.CO2.C2H5, which occurs with elimination of hydrobromic acid ; it also forms a 1 Bar. Deutsch. Chern. Ges. xix. 428. 518 AROMATIC COMPOUNDS. di-imide, is converted into an oximido-compound by hydroxyl- amine (Baeyer), and yields both a phenylhydrazide and a di- phenylhydrazide.1 On the other hand it yields a diacetyl-com- pound on heating wi th acetyl chloride (Wedel), which is more readily obtained by adding sodium ethylate to its ethereal solution, a rose-coloured precipitate of C6H4O2Na2(CO2.C2H5)2 being formed, which is immediately converted by acetyl chloride into the com- pound C6H4(OC2H3O)2(CO2.C2H5)2 (Baeyer). The latter com- pounds must be looked upon as derivatives of the dihydroxy- dihydroterephthalic acid into which succinosuccinic ether or quinonetetrahydrodicarboxylic acid so readily changes. Dihydroxyterephthalic acid also probably exists in two forms, as quinoldicarboxylic acid, C6H2(OH)2(CO2H)2, and as quinonedihydrodicarboxylic acid, C6O2H4(CO2H)2, which readily change into one another. The latter formula is required by its formation from dibromaceto-acetic ether, while its ■whole behaviour corresponds to the former. It may be assumed that the green modification is the quinone-acid, while the colourless is the quinol derivative (Herrmann). A similar case has been observed by Baeyer with regard to phloroglucinol, which forms a trioxime with hydroxylamine, the trihydroxybenzene being converted into triketohexhydrobenzene (Part III. p. 186.): 2 Phloroglucinol. OH C HOZ\CH HO-C^/C-OH CH Triketohexhydrobenzene. CO H2C/\,CH2 oc\/co ch2 Analogous cases have long been known to chemists; among the simplest are nitrous acid and cyanic acid, which are exceed- ingly unstable in the free state, but yield stable modifications of two kinds: Methyl nitrite. ch3-o-n=o Potassium cyanate. K-O-C=N Nitromethane. /X CH3-> XOZ Methyl isocyanate. CH - N~C~0 1 Knorr, Ber. Deutsch. Chem. Ges. xvii. 2055. 2 Ibid, xviii. 3454 ; xix. 159, 1800. TRI- AND TETRA-HYDROXYPHTHALIC ACIDS. 519 The constitution of these compounds can therefore be repre- sented with equal accuracy by different structural, or, as Laar1 names them, tautomeric formulae. The atoms are in continual motion within the molecule, and one form is converted into the other when the light and most rapidly moving atoms of hydrogen are more strongly attracted by one or other of the remaining atoms. If, however, the hydrogen be replaced by a heavier atom or molecule, the latter no longer escapes from the sphere of attraction, and the mobile form is converted into a stable one. TRIHYDROXYPHTHALIC ACIDS, C6H(OH)3(CO2H)2. 2272 G allocarboxylic acid, C8H6O7 + 3H2O, is formed, together with pyrogallolcarboxylic acid (p. 378), when pyrogallol or gallic acid is heated to 130° with ammonium carbonate. It requires 3,000 parts of water at 0° for solution, and crystallizes from hot water in very fine needles, which become anhydrous at 180° and melt above 270° with evolution of carbon dioxide. Dilute ferric chlorides colour its solution violet, while the concentrated reagent produces a greenish brown colouration. When heated in the air with water and an excess of calcium carbonate, the latter is coloured reddish violet, and when an ammoniacal solu- tion of the acid is mixed with a solution of bicarbonate of calcium, a deep violet coloured precipitate is formed, which may therefore be obtained with spring water containing calcium carbonate.2 tetrahydroxyphthalic acids, C6(OH)4(CO2H)2. 2273 Tetrahydroxyterephthalic acid. When an ethereal or alcoholic solution of ethyl dihydroxy terephthalate is treated with anhydrous nitrogen trioxide, it is converted into ethyl dihydr- oxy qrtinoneterephthalate, C6O2(OH)2(CO2.C2H6)2, crystallizing in yellow prisms, which are slightly soluble in cold water, alcohol and ether, more readily in chloroform. The solutions have a 1 Her. Deutsch. Chern. Ges. xviii. 648 ; xix. 730. 2 Brunner and Senhofer, Monatsh. Chem. i. 468. 520 AROMATIC COMPOUNDS. deep yellowish rod colour. When the ether is heated with caustic soda, a basic salt of dihydroxyquinoneterephthalic acid is formed, and immediately decomposes on the addition of acids into carbon dioxide and dihydroxy quinone, CcO2H2(OH)2, which forms small, black-brown crystals. Nitranilic acid, CbO2(NO2)2(OH)2, is always formed if di hydroxy terephthalic acid be submitted to the same treatment. Ethyl tetrahydroxyterephthalate, C6(OH)4(CO2.C2H5)2, is ob- tained by passing sulphur dioxide into a faintly alkaline solution of the dihydroxyquinone ether, and crystallizes from hot chloro- form in golden yellow plates, melting at 178°. It is converted by cold caustic soda solution into sodium tetrahydroxytere- phthalate, C6(OH)4(CO2Na)2, which crystallizes in yellow prisms. On decomposition with sulphuric or hydrochloric acid, tetra- hydroxyphthalic acid yields carbon dioxide and tetrahydroxy- benzene, CgH2(OH)4, which forms yellow needles, melting at 1480.1 1 Loewy, Ber. Deutsch. Chern. Ges. xix. 2385. INDEX INDEX. A. Acetbromamide, 113 Acetmetamidobenzoic acid, 248 Acetmetatoluide, 62 a-Acetmetaxylide, 407 s-Acetmetaxylide, 407 v-Acetmetaxylide, 406 Acetmethylparatoluide, 65 Acetometahydroxy benzidene acetate, 293 Acetortho-amidobenzoic acid, 239 Acetorthotoluide, 59 a-Acetorthoxylide, 406 v-Acetorthoxylide, 406 Acetoxime benzyl ether, 98 Acetparamidobenzoic acid, 253 Acetparatoluide, 66 Acetparaxylide, 407 Acetphthalimide, 464 Acetylbenzenylaniidoxime 214 Acetyliso vanillic acid, 354 Acetylmetahydroxybenzaldehyde, 293 Acetylopianic acid, 506 Acetylorthamidobenzaldehyde, 149 Acetylparahydroxybenzaldehyde, 295 Acetylparahydroxy benzidene acetate, 296 Acetylparamidobenzaldehyde, 150 Acetylsalicylic acid, 308 Acetyl salicylaldehyde, 288 Acetylsinapic acid, 377 A cetyl vanillic acid, 353 Acetylvanillin, 347 Acid ammonium hippurate, 189 Acid ammonium phthalate, 456 Acid barium hydroxamate, 208 Acid barium orthosulphobenzoate, 268 Acid bariumphthalate, 457 Acid calcium benzarsenate, 277 Acid ethyl hemipinate, 511 Acid ethyl metasulphobenzoate, 271 Acid ethyl a-nitrophthalate, 474 Acid ethyl v-nitrophthalate, 474 Acid metatoluidine oxalate, 61 Acid a-methyl hemipinate, 510 Acid 0-methyl hemipinate, 511 Acid methyl sulphinidephthalate, 478 Acid paratoluidine oxalate, 64 Acid potassium benzarsenate, 277 Acid potassium benzhydroxamate, 208 Acid potassium benzophosphinate, 276 Acid potassium hemipinate, 510 Acid potassium sulphinidephthalate, 477 Acid potassium sulphoparahydroxy- benzoate, 336 Acide quiniquc, 382 Acid silver sulphinidephthalate, 478 Acid sinapin sulphate, 375 Acid sodium benzhydroxamate, 208 Acid sodium dihvdroxyterephthalate, 516 Addition products of isophthalic acid, 481 Addition products of phthalic acid, 469 Addition products of terephthalic acid, 486 Adjacent Dinitroparatoluidine, 71 Adjacent metadihydroxybenzoic acid, 360 Aes-cioxalic acid, 363 Aldehydes, 447 Aldehydovanillic acid, 508 Aldebydohydroxy benzoic acids, 491, 502. Alizaric acid, 450 Allyl benzoate, 162 Aloisol, 402 Amarine, 140 Amarythrin, 428 Amido-anisic acid, 338 Amido-azotoluenes, 77 Amidobenzenyl-phenylene-amidine,206 Amidobenzoic acid percyanide, 248 Amidobenzylamines, 120 Amido-derivatives of the xylenes, 405 Amidohemipinic acid, 511 Amidohemipinylphenylphydrazide, 512 Amido-isophthalic acid, 482 Amidomeconin, 501 Amidometa-azotoluene, 78 Amidometatoluic acids, 418 524 INDEX. Amidomethylnorhemipinic acid, 514 Amido-opianylphenylhydrazide, 508 Amidortho-azotoluene, 77 3-Amido-orthocresol, 26, 51 7-Amido-orthophenol, 26 Amido-orthotoluic acids, 415 Amido-i//-meconin, 501 a-Amidoparacresol, 20 3-Amidoparacresol, 30 7-Amidoparacresol, 30 Amidoparahydroxybenzoic acid, 335 a-amidoparatoluic acid, 421 Amidophenylmetabenzoglycocyamine, 253 Amidophthalic acids, 475 a-Amidophthalic acid, 475 ®-Amidophthalic acid, 475 a-Amidosalicylic acid, 317 3-Amidosalicylic acid, 318 Amido-substituted benzylamines, 116 Amidosulphobenzoic acids, 275 Amidoterephthalic acid, 489 Amidotoluenes, 54 Amido-uramidobenzoyl, 242 Amidoxylenes, 405 Ammonium benzidene sulphate, 137 Ammonium benzoate, 160 Ammonium gallate, 368 Ammonium metahydroxybenzoate, 321 Ammonium parahydroxybenzoate, 328 Ammonium salicylate, 303 Ammonium terephthalate, 484 Amyg-dalacese, 131 Amygdalin, 130 Amyl benzoate, 162 Amyl hippurate, 191 Amyl orsellinate, 433 Amyl salicylate, 306 Anhydrides of parahydroxybenzoic acid, 331 Anhydro-amidohemipinic acid, 512 Anhydro - amidomethylnorhemipinic acid, 514 Anhydrobenzodiamidobenzene, 205 Anhydrous benzoic acetic acid, 167 Aniletic acid, 316 Anilido-ethoxytolu-quinone anilide, 49 Anilidohydroxytol-Uquinone, 49 Anilidohydroxytoluquinone anilide, 49 Aniline, 297 Aniline lourde speciale, 56 Aniline oil, 55 Aniline orange, 31 Anis-amide, 333 Anis-anilide, 333 Anisbenzanishydroxylamine, 312 Anisbenzethylhydroxylamine, 340 Anisbenzhydroxamic acid, 340 Anis-dibenzhydroxylamine, 341 Anise alcohol, 284 Anisenyloxime compounds, 339 Anisethylbenzhydroxylamine, 341 Anishydroxamic acid, 339 Anisic acid, 329 Anisic acid, substitution products of, 336 Anisic anhydride, 332 Anisonitril, 334 Anisuric acid, 333 Anisyl chloride, 332 Anthranil, 240 Anthranilcarboxylic acid, 240 Anthranilic acid, 297 Antimony derivatives of toluene, 86 Archil, 42 Arsendiparatolyl chloride, 85 Arsendiparatolyl trichloride, 85 Arsenditolyl oxide, 85 Arsenic Compounds of Benzyl, 125 Arsenic derivatives of toluene, 84 Arsenobenzoic acid, 277 Arsenorthotolyl chloride, 85 Arsenorthotolyl dioxide, 86 Arsenorthotolyl oxide, 85 Arsenparatolyl chloride, 84 Arsentolyl oxide, 85 Arsentribenzoic acid, 278 Arsen tritolyl dichloride, 85 Asymmetric diamido-azotoluene, 80 Asymmetric dibenzyl thiocarbamide, 124 Asymmetric dibenzyl urea, 123 Asymmetric ethylbenzoyl urea, 178 Asymmetric metadihydroxybenzoic acid, 359 Asymmetric diphenylbenzenylamidine, 204 Azo-aceto-acetic benzoic acid, 267 Azobenzenesalicylic acid, 319 Azobenzoic acids, 265 Azo-derivatives of benzoic acid 265 Azo-derivatives of toluene, 75 Azomalonic-benzoic acid, 268 Azonitromethanebenzoic acid, 267 Azo-orcin, 52 Azophenylmethyl, 181 Azo-opianic acid, 512 Azotoluenes, 75 a-Azotoluidine, 79 3-Azotoluidine, 79 Azoxybenzoic acids, 265 a-Azoxy toluidine, 7 8 Azoxy toluidine, 79 4 B. Badianic acid, 329 Barbatic acid, 402, 435 Barium amidohemipinate, 511 Barium benzoate, 161 Barium benzylsulphonate, 108 Barium chloro benzylsulphonate, 108 Barium diamidobenzoate, 259 Barium a-dinitrobenzoate, 234 Barium 3-dinitrobenzoate, 234 Barium y-dinitrobenzoate, 234 INDEX. 525 Barium 8-dinitrobenzoate, 235 Barium e-dinitrobenzoate, 235 Barium dinitrosalicylate, 317 Barium gallate, 369 Barium hippurate, 189 - Barium homohydroxysalicylate, 438 Barium isophthalate, 479 Barium lecanorate, 434 Barium meconinate, 500 Barium metabromobenzoate, 224 Barium metahydroxybenzoate, 321 Barium metanitrobenzoate, 231 Barium methylnoropianate, 503 Barium opianate, 504 Barium opianylsulphite, 507 Barium ornithurate, 193 Barium orsellinate, 432 Barium orthobromobenzoate, 223 Barium orthonitrobenzoate, 230 Barium parabromobenzoate, 224 Barium parahydroxybenzoate, 328 Barium paranitrobenzoate, 232 Barium para-orsellinate, 436 Barium protocatechuate, 352 Barium pyrogallolcarboxylate, 379 Barium quinate, 384 Barium salicylaldehyde, 287 Barium salicylate, 303 Barium terephthalate, 484 Basic barium nitroparahydroxybenzo- ate, 335 Basic copper potassium salicylate, 304 Basic copper quinate, 384 Basic lead pyro-gallolcarboxylate, 379 Basic sodium dihydroxyterephthalate, 516 Benzaldehyde, 129 Benzaldehyde-green, 135 Benzaldehyde oxyiodide, 137 Benzaldoxime, 139 Benzamic acid, 246 Benzamide, 172, 199 Benzamide hydrochloride, 174 Benzanilide, 174 Benzanilidimidocbloride, 203 Benzanisbenzhydroxylamine, 341 Benzanishydroxamic acid, 340 Benzarsene chloride, 277 Benzarsene iodide, 277 Benzarsenic acids, 277 Benzarsenious acid, 277 Benzdianishydroxylamine, 342 Benzene, 297 Benzenyl alcohol, 194 Benzenyl amidines, 195 Benzenylamidophenate, 206 Benzenylamidothiophenate, 206 Benzenylamidoxime, 212 Benzenylamidoximemetacarboxylic acid, 480 Benzenylamidoximeparacarboxylic acid, 485 Benzenylazoximebenzenylcarboxylic acid, 468 Benzenylazoxime carbinol, 215 Benzenylazoxime propenylcarboxylic acid, 215 Benzenyl compounds, 194 Benzenylethoxime chloride, 213 Benzenylethenylazoxime, 214 Benzenyl ethyl ether, 196 Benzenyloxime compounds, 207 Benzenyloximic acid, 208 Benzenyl triacetate, 196 Benzenyl tribromide, 196 Benzenyl trichloride, 195 Benzenyltrichlorophosphoryl chloride, 311 Benzethylanishydroxylamine, 341 Benzethylbenzhydroxylamine, 209 Benzhydroxamic acid, 208 Benzhydroxamide, 212 Benzhydroxylamine, 207 Benzidene-acetamide, 143 Benzidene-aniline, 140 Benzidene-aniline cyanhydrate, 141 Benzidene benzoate, 163 Benzidene benzobromohydrin, 170 Benzidene benzochlorohydrin, 169 Benzidene compounds, 136 Benzidene diacetate, 137 Benzidene dibromide, 136 Benzidene dichloride, 136 Benzidene dichlorochromic acid, 6 Benzidene diethyl ether, 136 Benzidene di-iodide, 137 Benzidenedimethylparadiamido- benzene, 142 Benzidened ipheny Ihyd razine, 141 Benzidenedi-ureide, 143 Benzidene-orthodiamidobenzene, 141 Benzideneparadiamidobenzene, 142 Benzidenephenylamine hydrochloride, 143 Benzidenephenyl hydrazine, 141 Benzidenephenyldiamine, 142 Benzidene sulphide, 138 Benzidenetetra-ureide, 143 Benzidenetri-ureide, 143 Benzidene ureides, 143 Benzidene urethane, 143 Benzidenoxime, 139 Benzimido-acetic ether, 201 Benzimido-amide, 202 Benzimido-ethers, 200 Benzimido-ethyl ether, 201 Benzimido-isobutyl ether, 201 Benzimido-thiobenzyl ether, 202 Benzimido-thio-ethyl ether, 201 Benzoene, 3 Benzoene monochlore, 7 Benzoic acid, 7, 108, 151, 297, 383 Benzoic acid, azo-derivatives of, 265 Benzoic acid, nitro-substitution pro- ducts of, 227 Benzoic acid, salts and ethers of, 160 Benzoic anhydride, 166 Benzoleic acid, 159 526 INDEX. Benzonitril, 122, 197 Benzonitril and its derivatives, 197 Benzophosphine chloride, 276 Benzophosphinic acid, 275 Benzolorthoalcoholsame, 442 Benzortho-amidobenzoic acid, 239 a-benzothio-aldehyde, 138 0-benzothio-aldehyde, 138 7-benzothio-aldehyde, 139 Benzo-trichloride, 195 Benzoxamidine, 213 Benzoyl, 285 Benzoyl acetyl oxide, 167 Benzoylaniline, 174 Benzoylanthranil, 241 Benzoylazobenzene, 180 Benzoylbenzenylamidoxime, 214 Benzoyl-benzoic acid, 458 Benzoylbenzoximic acid, 209 Benzoyl bromide, 169 Benzoyl chloride, 168 Benzoyl derivatives of amines and amido-bases, 174 Benzoyl dioxide, 167 Benzoyldiphenylamine, 175 Benzoyldiphenylhydrazine, 181 Benzoyl disulphide, 171 Benzoyl ethylbenzhydroxamate, 209 Benzoyl fluoride, 170 Benzoy 1-glycollic acid, 165 Benzoyl group, 128 Benzoylguanidine, 243 Benzoylguanidine, nitrate, 243 Benzoyl, halogen compounds of, 168 Benzoylhelicin, 289 Benzyl hydrosulphide, 138 Benzoyl iodide, 170 Benzoyl-lactic acid, 165 Benzoylmethylaniline, 175 Benzoylmethylpyrogallol dimethyl ether, 164 Benzoy Initranilines, 175 Benzoyl, nitrogen compounds of, 172 Benzoy lornithine, 193 Benzoylorthotoluide, 175 Benzoyl oxide, 166 Benzoyl, oxides of, 166 Benzoy Iparatoluide, 175 Benzoyl peroxide, 167 Benzoylphenylhydrazine, 179 Benzoylpropylpyro - gallol dimethyl ether, 164 Benzoy]pyro-gallol dimethyl ether, 164 Benzoylsalicin, 282 Benzoyl salicylaldehyde, 288 Benzoylsalicylamidc, 312 Benzoylsalicylnitril, 313 Benzoyl sulphide, 171 Benzoylsulphimide, 269 Benzoyl, sulphur compounds of, 170 Benzoyl thiocyanate, 172 Benzoyl thio-urea, 179 Benzoyl urea, 178 Benzoylvanillic acid, 353 Benzyl, 89 Benzylacetamide, 121 Benzyl acetate, 97 Benzyl alcohol, 7, 89 ; properties, 93 ; substitution products of, 98 Benzylamidine, 202 Benzylamine, 112 ; properties, 113 Benzylamine hydrochloride, 113, 114 Benzylamine nitrite, 114 Benzylamines, 110 Benzylamines, amido-substituted, 116 Benzylamines, substitution products of, 118 Benzylam moniu m benzyl carbamate, 113, 114 Benzylaniline, 117 Benzyl, arsenic compounds of, 125 Benzyl benzoate, 162 Benzylbenzoyl thio-urea, 179 Benzyl bromide, 97 Benzyl bromophenyl ether, 95 Benzyl carbamate, 123 Benzyl-carbimide, 122 Benzyl chloride, 7, 96 Benzyl chlorophenyl ether, 95 Benzylcyananmide, 121 Benzylcyanuramide, 121 Benzyl-Derivatives of the Acid-Amides and. Allied Bodies, 121 Benzyldimethylselenine tri-iodide, 110 Benzyldimethylsulphine iodide, 106 Benzyl dimethylsulphine platinichlor- ide, 107 Benzyl dioxysulphide, 107 Benzyl diphenylamine, 117 Benzyl diselenide, 109 Benzyl disulphide, 107 Benzyl, ethereal salts of, 96 Benzyl ethers, 94 Benzylethoxy 1 chloride, 100 Benzyl ethyl ether, 94 Benzyl ethyl sulphide, 106 Benzyl group, 89 Benzyl hydrosulphide, 105 Benzylhydroxyammonium chloride, 98 Benzyl iodide, 97 Benzyl-isocyanate, 122 Benzyl isocyanurate, 122 Benzyl isothiocyanate, 122 Benzylmetamine, 121 Benzyl methyl ether, 94 Benzyl mercaptan, 105 Benzyl mustard oil, 122 Benzyl nitrate, 97 Benzyl, nitrogen bases of, 110 Benzyl orthocresyl ether, 95 Benzyl oxalate, 98 Benzyl oxide, 94 Benzyl oxysulphide, 107 Benzyl paracresyl ether, 95 Benzylphenylamine, 117 Benzyl phenyldimethylammonium chloride, 117 Benzyl phenyl ether, 95 INDEX, 527 Benzyl phosphine, 124 Benzylphosphonium iodide, 124 Benzylquinol, 96 Benzylsalicylic acid, 306 Benzyl salicylaldehyde, 287 Benzylselenic acid, 109 Benzyl selenide, 109 Benzyl, selenium compounds of, 109 Benzyl selenocyanate, 123 Benzyl, silicon compounds of, 127 Benzyl sulphide, 106 Benzylsulphonamide, 109 Benzylsulphonic acid, 108 Benzylsulphonic chloride, 108 Benzyl, sulphur compounds of, 105 Benzyl thiocarbamide, 124 Benzyl thiocyanate, 122 Benzyl thiobenzoate, 171 Benzyl urea, 123 Benzyl urethane, 123 Beta-orcinol, 402 Boron and Silicon derivatives of Tolu- ene, 87 Boron disalicylic acid, 304 Bromamidobenzoic acids, 255 Bromanisic acid, 336 Bromine substitution products, 41 Bromine substitution products of tolu- ene, 10 Bromobenzidenedichlorochromyl chlo- ride, 11 Bromobenzylbenzoate, 170 Bromogallic acid, 370 Bromomalophthalic acid, 470 Bromomeconin, 500 Bromometacresol, 27 a-Bromometatoluic acid, 417 5-Bromometatoluic acid, 417 a-Bromometaxylene, 394 s-Bromometaxylene, 394 a-Bromometaxylenol, 401 Bromonitrobenzoic acids, 236 Bromonitrotoluenes, 19 Bromoparacresol, 29 Bromoparahydroxybenzaldehyde, 296 a-Bromoparatoluic acid, 420 3-Bromoparatoluic acid, 420 Bromoparaxylene, 395 a-Bromophthalic acid, 472 v-Bromophthalic acid, 472 Bromopianic acid, 507 Bromoprotocatechuic acid, 356 a-Bromoresorcylic acid, 359 7-Bromoresorcylic acid, 361 Bromorthocresol, 25 a-Bromorthotoluic acid, 415 3-Bromorthotoluic acid, 415 a-Bromorthoxylene, 393 Bromosalicylaldehyde, 292 a-Bromosalieylic acid, 314 £J-Bromosalicylic acid, 314 Bromosulphobenzoic acids, 274 Bromoterephthalic acid, 488 , Bromotoluidines, 68 Butyl benzoate, 162 Butyl hippurate, 191 C. Caffeol, 281 Calcium benzarsenite, 278 Calcium benzoate, 160 Calcium dibenzarsenite, 278 Calcium difluorbenzoate, 227 Calcium gallate, 369 Calcium hippurate, 189 Calcium isophthalate, 479 Calcium metachlorobenzoate, 220 Calcium metahydroxybenzoate, 321 Calcium metatoluate, 416 Calcium ornithurate, 193 Calcium orthochlorobenzoate, 218 Calcium orthotoluate, 414 Calcium parachlorobenzoate, 221 Calcium parahydroxybenzoate, 328 Calcium paratoluate, 419 Calcium phthalate, 457 Calcium piperonate, 356 Calcium pyrogallolcarboxylate, 379 Calcium quinate, 382, 384 Calcium salicylate, 303 Calcium terephthalate, 484 Cantharene, 391 Carbanilamide, 246 Carbanilidic acid, 246 Carbimidamidobenzoic acid, 250 Carbimidamidobenzoyl, 242 Carbohydrokinonic acid, 350 Carbonyl chloride, 462 Carbonyl dibenzenylamidoxime, 215 Carbotriphenyltriamine, 204 Carboxamidocyanamidobenzoyl, 241 Carboxamidobenzoic acid, 251 Carboxylcyanamidobenzoyl, 241 Catechol, 36 Chloranisic acid, 336 Chloramidobenzoic acids, 254 Chlorine substitution products, 41 Chlorine substitution products of toluene, 7 Chlorobenzol, 136 Chlorobenzoyl chloride, 310 Chlorobenzenyl trichloride, 310 Chlorodracylic acid, 221 Chloro-isophthalic acid, 481 Chloromeconin, 500 Chlorometatoluic acid, 417 Chlorometaxylenesulphamide, 393 Chloromethylnoropianic acid, 503 a-Chlorometaxylene, 393 Chloromichmic acid, 219 Chloroniceinic acid, 219 Chloronitrotoluenes, 19 Chloronitrobenzoic acids, 236 Chloroparacresol, 29 Chloroparahydroxy benzaldehyde, 296 Chloroparahydroxybenzoic acid, 334 Chloroparatoluic acid, 420 528 INDEX, Chloroparatoluidine, 8 Chlorophthalic acid, 393 a-Chlorophthalic acid, 471 v-Chlorophthalic acid, 471 Chloroparaxylene, 393 Chloropianic acid, 507 Chlororthotoluic acids, 415 a-Chlororthoxylene, 392 r-Chlororthoxylene, 392 Chlorosalicylaldehyde, 292 Chlorosalicylic acid, 313 Chlorosulphobenzoic acids, 274 Chloroterephthalic acid, 488 Chlorotoluene, 7 Chlorotoluic acid, 393 Chlorotoluidines, 68 Choline, 376 Cinnamein, 90 Cinnamic acid, 90, 135, 297 Cinnamone, 135 Colophonin hydrate, 7 Colophonin, 6 Coniferyl alcohol, 345 Copper benzoate, 161 Copper hippurate, 190 Copper metahydroxybenzoate, 321 Copper parahydroxybenzoate, 328 Copper phthalate, 457 Copper quinate, 384 Copper salicylaldehyde, 287 Copper salicylate, 304 Coumaim, 186 Creosol, 32 Creosote, 32 et seq. a-Cresol, 23 3-Cresol, 23 7-Cresol 24 Cresolcarboxy]ic acid, 438 Cresorcinol, 47, 437 Cresorcinolcarboxylic acid, 437 Cresorsellinicacid, 437 Cresotic acid, 423 a-Cresotic acid, 423 0-Cresotic acid, 424 7-Cresotic acid, 424 Cresyl alcohol, 23 Cresyl benzoate, 164 Cresyl hydrate, 23 Cudbear, 44 Cumaric acid, 297 Cumic acid, 451 Cumino-cyminic acid, 451 Cumol, 386 Cyanobenzylamine, 121 Cyanocarbimidobenzoic acid, 249 Cyanocarboxamidobenzoic acid, 249 Cynanphenin, 199 Cymene, 4 Cymol, 386 D Diacetortho-a'midobenzoic acid, 239 Diacetotoluquinol, 48 Diamidobenzoic acids, 258 Diamidobenzoic acids, action of nitrous acid on the, 263 a-Diamidobenzoic acid, 258 /3-Diamidobenzoic acid, 259 3-Diamidobenzoic acid, 267 7-Diamidobenzoic acid, 259 8 Diamidobenzoic acid, 259 8-Diamidobenzoic acid hydrochloride, 259 3-Diamidobenzoic acid sulphate, 259 Diamido benzylsulphonic acid, 109 Diamidocresol, 79 Diamidohydro-acridine ketone, 245 a-Diamidometaxylene, 409 v- Diamidometaxylene, 409 s-Diamidometaxylene, 409 a-Diamidoparaxylene, 410 3-Diamidoparaxylene, 410 7-Diamidoparaxylene, 410 Diamidosalicylic acid, 318 Diamido terephthalic acid, 489 a-Diamidotoluene, 72 j8-Diamidotoluene, 72 7-Diamidotoluene, 73 8-Diamidotoluene, 74 a-Diamidotoluene di-hydrochloride, 72 3-Diamidotoluene hydrochloride, 73 7-Diamidotoluene hydrochloride, 73 a-Diamidotoluene monohydrochloride, 72 a-Diamidotoluene sulphate, 72 /CDiamidotoluene sulphate, 73 7-Diamidotoluene sulphate, 73 Diamidotoluenes, 72 Diamidotriphenylmethane, 135 Diamines and Triamines of the Xylenes, 409 Dianilidotoluquinone, 49 Dianilidotoluquinone anilide, 49 Dianisbenzhydroxylainine, 342 Dianishydroxamic acid, 340 Diazo-amidobenzene, 18 Diazo-amidotoluene, 74 Diazo-amidotoluic acid, 421 Diazobenzene-amidobenzoic acid, 262 Diazobenzoic acid, 260 Diazobenzoic acid nitrate, 260 Diazobenzoic acid seminitrate, 260 Diazo-derivatives of benzoic acid, 260 Diazo-derivatives of toluene, 74 Diazohemipinic acid, 513 Diazo-imidobenzoic acids, 263 Diazooenzene-amidotoluene, 74 Diazo-salicylie acid, 319 Diazotoluene nitrate, 74 Diazotoluene sulphate, 74 Diazoxy benzoic acid, 267 Dibenzamide, 176 Dibenzamide hydrate, 177 Dibenzanilide, 177 Dibenzanishhydroxylamine, 341 Dibenzarsene iodide, 278 Dibenzarsenic acid, 278 Dibenzarsenious acid, 278 INDEX. 529 Dibenzenylazoxime, 214 Dibenzenyltriamine, 202 Dibenzhydroxamic acid, 209 Dibenzhydroxylamine, 207 Dibenzidenediamidobenzoic acid, 142 Dibeuzidenemetadiamidotoluene, 142 Dibenzidene-orthodiamidotoluene, 142 Dibenzimido-oxide, 197 Dibenzoarsenic acid, 85 Dibenzobenzoximate, 211 Dibenzoylcatechol, 164 Dibenzoylphenylhydrazine, 180 Dibenzoylquinol, 164 Dibenzoylrescorcinol, 164 Dibenzoyl urea, 179 Dibenzenylamidine, 202 Dibenzylamine, 114 Dibenzylamine hydrochloride, 115 Dibenzylamine nitrate, 115 Dibenzylarsenic acid, 126 Dibenzylarsine trichloride, 125 Dibenzylcatechol, 96 Dibenzylcyanimide, 122 Dibenzyl ether, 94 Dibenzylguanidine, 121 Dibenzyloxamide, 121 Dibenzylphosphine, 125 Dibenzylquinol, 96 Dibenzylresorcinol, 96 Dibenzyl sulphone, 107 Dibenzyltolylamine, 118 Dibenzyltoluidine, 118 Dibromanisic acid, 336 Dibromobenzoic acids, 224 Dibromo-gal lie acid, 370 Dibromohexhydroterephthalic acid, 486 Dibromolecanoric acid, 434 a-Dibromometaxylene, 394 £-Dibromometaxylene, 394 a-Dibromometaxylenol, 401 Dibromoparacresol, 29 Dibromoparahydroxybenzoic acid, 334 Dibromoparatoluic acid, 420 Dibromoparaxylene, 395 a-Dibromophthalic acid, 472 3-Dibromophthalic acid, 473 Dibromophthalide, 444 Dibromorcinol, 41 Dibromorsellinic acid, 433 Dibromorthoxylene, solid, 394 liquid, 394 Dibromoterephthalic acid, 488 Dibromotoluenes, 11 Dibromotetrahydrophthalic acid, 470 Dichloraniaic acid, 336 Dichlorobenzaldehyde, 144 Dichlorobenzenyl trichloride, 196 a-Dichlorobenzoic acid, 221 0-Dichlorobenzoic acid, 222 7-Dichlorobenzoic acid, 222 3-Dichlorobenzoic acid, 222 e-Dichlorobenzoic acid, 222 Dichlorobenzidene chloride, 145 Dichlorobenzoic acids, 221 Dichlorobenzyl alcohol, 100 Dichlorobenzyl chloride, 101 Diehlorohippuric acid, 220 Dichloroparacresol, 29 Dichloroparahydroxybenzoic acid, 334 Dichloroparaxylene, 393 Dichlorophthalic acid, 471 Dichloropiperonal, 348 Dichlororthocresol, 25 Dichlororthoxylene, 393 Diehloro-salicylic acid, 314 Dichlorosilicon orthoditoluide, 87 Dichlorotoluene hexchloride, 10 Dichlorotoluenes, 9 Dichlorotoluquinone, 27, 50 Dicinnyl ketone, 135 Dicyanamidobenzoyl, 241 Diethylbenzamide, 174 Diethylbenzylamine, 116 Diethyl diacetoxyterephthalate, 517 Diethyldiamidoterephthalate, 489 Diethyldibenzylammonium iodide, 117 Diethyl a-hydroxyisophthalate, 495 Diethyl s-hydroxyisophthalate, 495 Diethyl dihydroxyterephthalate, 516 Diethylorthotoluidine, 59 Diethylparadihydroxy benzaldehyde, 349 Di-ethylparatoluidine, 65 Diethylprotoeatechuic acid, 355 Diethyl-3-resorcylaldehyde, 349 Diethyl-a-resorcylic acid, 359 Diethyl-3-resorcylic acid, 360 Difluorbenzoic acid, 227 Digallic acid, 371 Dihydro-orthoxylene, 391 Dihydrophthalic acid, 469, 487 Dihydrotoluene, 6 Dihydroxybenzoic acids, 350 Dihydroxybenzyl and Dihydroxy- Benzoyl compounds, 343 Dihy droxyhexhydroterephthalic acid, 487 Dihydroxyisophthalaldehyde, 515 Dihydroxyisophthalic acid, 515 Dihydroxyphthalic acids, 510 Dihydroxyquinone, 520 Dihydroxy terephthalic acid, 515 Dihydroxytoluenes and allied bodies, 31 Dihydroxytolualdehydes, 427 Dihydroxytoluic acids, 428 Dihydroxytoluquinone, 49 Dihydroxy-xylenes, 402 Di-iodoparacresol, 29 Di-iodoparahydroxybenzoic acid, 335 Di-iodosalicylie acid, 315 Dimetatolyl carbamide, 63 Dimetatolyl thiocarbamide, 63 Dimethoxybenzonitril, 361 Dimethoxyorthophthalic acid, 510 Dimethyl acetoxyterephthlate, 496 530 INDEX. Dimethylamidophenylhydroxy tri- chlorethane, 151 Dimethylbenzamide, 174 Dimethylbenzenes, 390 Dimethyldiamidotoluene, 62 Dimethyldihydroxyphthalic acid, 498 Dimethyl a-hydroxyisophthalate, 495 Dimethyl s-hydroxyisophthalate, 495 Dimethylhydroxysalicylic acid, 362 Dimethyl hydroxyterephthalate, 496 Dimethylmetamidobenzoic acid, 247 Dimethylmetatoluidine, 61 Dimethylmethylene benzoate, 163 Dimethylnoropianic acid, 503 Dimethylorthotoluidine, 58 Dimethylparadihydroxybenzaldehyde, 349 Dimethylparamidobenzaldehyde, 150 Dimethylparamidobenzoic acid, 253 Dimethylparatoluidine, 65 Dimethylparatolyl phosphine, 84 Dimethyltolylphosphine oxide, 84 Dimethylphenylenebenzenylamide am- monium iodide, 205 Dimethylphosphine-oxide benzoic acid, 277 Dimethylprotocatechuic acid, 354 Dimethylprotocatechuicaldehyde, 346 Dimethyl-jS-resorcylaldehyde, 349 Dimethyl-a-resorcylic acid, 358 Dimethyl-3-resorcylic acid, 360 Dimethyl-7-resorcylic acid, 361 Dinitro-amidobenzoic acids, 257 Dinitro-anisic acid, 337 Dinitro-anthranilic acid, 257 a-Dinitrobenzoic acid, 234 j8-Dinitrobenzoic acid, 234 7-Dinitrobenzoic acid, 234 3-Dinitrobenzoic acid, 235 e-Dinitrobenzoic acid, 235 Dinitrobenzoic acids, 234 Dinitrobenzysulphonic acid, 109 Dinitro-diphenylamine-orthocarboxylic acid, 245 Dinitro-v-hydroxyphthalic acid, 493 Dinitrohydroxyterephthalic acid, 496 s-Dinitrometaxylene, 396 v-Dinitrometaxylene, 396 a-Dinitro-orcinol, 41 3-Dinitro-orcinol,, 42 Dinitro-orthamidobenzoic acid, 257 Dinitro-orthocresol, 26 a-Dinitro-orthotoluidine, 71 Dinitro-orthoxylene, 396 Dinitroparacresol, 30 Dinitroparahydroxybenzoic acid, 335 Dinitroparamidobenzoic acid, 258 Dinitroparaxylidine, 408 a-Dinitroparaxylene, 397 jS-Dinitroparaxylene, 397 7-Dinitroparaxylene, 397 Dinitrophthalic acid, 475 Dinitrosalicylic acid, 317 7-Dinitrotoluene, 17 Dinitrotoluene, ordinary, 16; sym- metric, 17 Dinitrotoluenes, 16 Dinitrotoluidine, 18 3-Dinitrotoluidine, 71 7-Dinitrotoluidine, 71 Dinitrotoluidines, 71 7-Dinitrotolylphenylamine, 18 Diorsellinic acid, 433 Di-orthotolylamine, 59 Di-orthotolylcarbamide, 59 Di-orthotolyl thiocarbamide, 60 Diparahydroxybenzoylparahydroxy- benzoic acid, 331 Diparatolylamine, 66 Diparatolylarsenic acid, 85 Diparatolyl carbamide, 66 Diparatolylhydrazine, 7 5 Diparatolylnitrosamine, 66 Diparatolyl thiocarbamide, 67 Diphenylbenzene, 452 Diphenylbenzenylamidine, 204 Diphenylorthoxylylenediamine, 440 Diphenylparamidobenzenylamidine,204 Diphenyl phthalamic acid, 465 Diphenylphthalein, 465 Diphenyl thiobenzamide, 178 Diphthalyl, 458, 460 Disalicylamide, 312 Disalicylic acid, 308 a-Disulphobenzoic acid, 274 0-Disulphobenzoic acid, 274 Disulphobenzoic acids, 274 Disulphometahydroxybenzoic acid, 326 Disulphorthotoluic acid, 416 Dithiobenzoic acid, 172 Dithiometahydroxybenzoic acid, 325 Dixylylamine, 412 Dragonic acid, 329 Drupacese, 131 E. Erythrelinic acid, 429 Erythric acid, 429 Erythrinbitter, 428 Erythrylin, 428 Erythrin, 428, 431, 434 j8-Erythrin, 435 Erythroglucin, 430 Ethereal salts of Benzyl, 96 Ethereal salts of salicylic acid, 306 Ethereal salts of salicylic ethers, 307 Ethers of benzoic acid, 160 Ethers of benzyl with the dihydroxy- benzenes, 95 Ethers of phthalic acid, 457 Ethidenedibenzamide, 176 Ethoxycarbimidamidobenzoic acid, 250 Ethoxycyanamidobenzoyl, 242 Ethoxymethoxybenzonitril, 361 Ethoxynitrobenzonitril, 361 Ethyl amido-isophthalate, 482 INDEX. 531 Ethyl a-amidophthalate, 476 Ethyl v-amidophthalate, 475 Ethyl anisbenzhydroxamate, 340 Ethyl anishydroxamate, 339 Ethylanishydroxamic acid, 339 a-Ethylbenzanishydroxamate, 340 3-Ethylbenzanishydroxamate, 340 Ethyl benzenylamidoximecarboxylate, 214 Ethenylbenzenylazoxime, 214 a-Ethylbenzhydroxamic acid, 211 Ethyl benzhydroxamate, 209 Ethyl benzoate, 161 Ethyl benzoyl-glycollate, 165 Ethyl benzoyl-lactate, 165 Ethylbenzoyl thio-urea, 179 Ethyl-benzylamidine, 202 Ethylbromosalicylaldehyde, 292 Ethylene benzoate, 162 Ethyl-3-diamidotoiuene, 73 a-Ethyl dibenzhydroxamate, 210 3-Ethyl dibenzhydroxamate, 210 Ethyl dibenzylamine, 117 Ethyl dibromoterephthalate, 488 Ethyl dihydroxy quinoneterephthalate, 519 Ethylenebenzamide, 174 Ethyleneprotoeateehuic acid, 356 Ethylene salicylate, 306 Ethylene salicylic acid, 306 Ethyl ether of benzenylamidoxime, 213 Ethyl ethylenesalicylate, 307 Ethyl ethylsalicylate, 307 Ethyl gallate, 369 Ethyl hemipinimide, 514 Ethyl hippurate, 190 /3-Ethylhydroxamic acid, 211 Ethyl hydroxysalicylate, 362 Ethyl isophthalate, 479 Ethyl metacyanobenzoate, 480 Ethyl meta-ethoxybenzoate, 322 Ethyl metahydroxybenzoate, 321 Ethyl metanitrobenzoate, 231 Ethyl metasulphamidobenzoate, 272 Ethyl metasulphobenzoic acid, 271 Ethyl metatoluate, 417 Ethyl methylsalicylate, 307 Ethyl nitro-isophthalate, 482 Ethylnitrolic acid, 468 Ethyl opianate, 505 Ethyl orsellinate, 433 Ethyl orthobenzoate, 194 Ethyl orthocyanobenzoate, 468 Ethyl orthonitrobenzoate, 230 Ethyl orthotoluate, 414 Ethylorthotoluidine, 59 Ethyl paracyanobenzoate, 485 Ethylparadihydroxy benzaldehyde, 349 Ethyl para-ethoxybenzoate, 330 Ethyl parahydroxybenzoate, 330 Ethyl paramothoxybenzoate, 330 Ethyl paranitrobenzoate, 232 Ethyl paratoluate, 419 Ethylparatoluidine, 65 Ethyl phthalate, 457 Ethyl phthalimide, 464 Ethylphthalylhydroxylamine, 467 Ethyl piperonate, 356 Ethyl pyro-gallolcarboxylate, 379 Ethyl quinate, 385 Ethyl a-resorcylate, 358 Ethyl salicylaldehyde, 287 Ethyl salicylate, 306 Ethyl terephthalate, 484 Ethyl tetracetylquinate, 385 Ethyl tetrachlorophthalate, 472 Ethyl tetrahydroxyterephthalate, 520 Ethyl thiobenzoate, 171 Ethyltolyl carbamate, 67 Ethylvanillic acid, 355 Ethyl veratrate, 355 Ethy salicylic acid, 306 Evernic acid, 435 Everninic acid, 435 F. Ferric benzoate, 161 Fluorine substitution products of toluene, 13 Formortho-amidobenzoic acid, 239 Fluotoluene, 13 G. Gallamide, 370 Gallates, the, 368 Gallic acid, 363, 381 Gallocarboxylic acid, 519 Gallocyanin, 377 Gentisic acid, 362 Gentisinaldehyde, 349 Glucovanillic acid, 352 Glucovanillin, 347 Glucovanillyl alcohol, 347 Guanidodibenzoic acid, 250 H. Halogen compounds of benzoyl, 168 Halogen substitution products, 118 Halogen substitution products of benzoic acid, 216 Halogen substitution products of phthalic acid, 471 Halogen substitution products of the Toluidines, 67 Halogen substitution products of the Xylenes, 392 Helicin, 288 Helicoidin, 289 Hemipinic acid, 497, 510 Hemipinic anhydride, 511 Hemipinimide, 513 Hemipinimidine, 501 532 INDEX. Heptacarbure quadrihydrique, 3 Hexbromobenzene, 12 Hexchloroxylone, 34 Hexhydrometaxylene, 391 Hexhydroparaxylene, 392 Hexhydrophthalic acid, 470 Hexhydroterephthalic acid, 486 Hexhydrotoluene, 7 Hexmethyl-8-diamidobenzoic acid, 259 Hexnitrodiparatolylamine, 66 Hipparin, 175 Hippuramide, 191 Hippuramido-acetic acid, 191 Hippurates, the, 189 Hippurgly coll amide, 192 Hippuric acid, 181, 383 ; properties, 188 Homocatechol, 31 Homocatechol dimethyl ether, 32 Homocatechol monomethyl ether, 32 Homo-erythrin, 435 Homohydroxysalicylic acid, 438 Homopyrocatechin, 31 Homorcinol, 402 Homosalicylic acids, 423 Homosaligenin, 422 Hydrazenebenzoic acids, 264 Hydrazine-derivatives of Toluene, 75 Hydrazobenzoic acids, 265 a-Hydrazotoiuidine, 79 0-Hydrazotoluidine, 79 Hydrobenzamide, 139, 140 Hydrobenzamide trialdehyde, 449 Hydrobenzamidetricarboxylic acid, 449 Hydrobenzoic acid, 159 Hydrobenzuric acid, 192 Hydrobenzyluric acid, 192 Hydrophlorone, 403 Hydrophthalide, 444 Hydrosalicylamide, 291 Hydroxybenzaldehydes, 285 Hydroxybenzidene-amidobenzoic acid, 291 Hydroxybenzoic acids, 297 Hydroxy benzyl alcohols, 279 Hydroxybenzyl group, 279 Hydroxybenzyluric acid, 192 a-Hydroxyisophthalic acid, 494 s-Hydroxyisophthalic acid, 495 u-Hydroxyisophthalic acid, 495 Hydroxyisophthalic acid, 303 Hydroxylamine derivatives containing three acid radicals, 341 Hydroxymetaxyloquinone, 404 Hydroxymethylbenzoic acids, 442 Hydroxymethyldihydroxybenzoic acids, 497 Hydroxymethyldimethoxybenzoic acid, 500 Hydroxy tn ethylhydroxybenzoic acid, 490 u-Hydroxyorthophthalic acid, 493 Hydroxyphthalamic acid, 467 a-Hydroxyphthalic acid, 492 Hydroxyphthalic acids, 492 a-Hydroxyphthalic anhydride, 493 Hydroxyquinolcarboxylic acid, 380, 381 Hydroxysalicylic acid, 361 Hydroxyterephthalic acid, 495 Hydroxytolualdehydes, 422 s-Hydroxytoluic acid, 425 Hydroxytoluic acids, 423 Hydroxytoluquinonoxime, 52 Hydroxytrinesic acid, 303, 494 Hydroxy-xylenes, 399 Hypogallic acid, 498 I. Imide of metadiazobenzoic acid, 264 Insolinic acid, 451 lodamidobenzoic acids, 255 lodanisic acid, 337 Iodine substitution products, 41 Iodine substitution pioducts of Toluene, 13 lodo-isophthalic acid, 481 lodomeconin, 500 lodometahydroxybenzoic acid, 323 lodonitrobenzoic acids, 237 lodoparacresol, 29 lodoparahydroxybenzaldehyde, 296 lodoparahydroxybenzoic acid, 335 lodoparatoluic acid, 420 lodosalicylic acid, 314 lodotoluenedisulphonic acid, 22 Iodo toluidines, 68 Iron gallate, 369 Isobutyl hippurate, 191 Isobutyl terephthalate, 484 Isodiazoxybenzoic acid, 267 Isohemipinic acid, 515 Isonitrosobenzyl ether, 98 Isonoropianic acid, 508 Isophthalalcohol, 440 Isophthalaldehyde, 447 Isophthalic acid, 451, 479 Isophthalic acid, addition products of, 481 Isophthalic acid, substitution products of, 481 Isophthalamide, 480 Isophthalonitril, 481 Isophthalyl chloride, 480 Isopianic acid, 509 Isopropyl benzoate, 162 1 sopropylsalicylie acid, 306 Isopropyl terephthalate, 484 Isorcinol, 47 Isosulphometahydroxybenzoic acid, 325 Isotrichloroglyceric acid, 368 Isovanillic acid, 353 Isovanillin, 346 Isoxylol, 387 INDEX. 533 J. Juglonic acid, 493 K. Kinoin, 374 Kino-red, 374 L. Lead benzoate, 161 Lead benzyl mercaptide, 106 Lead benzylsulphonate, 108 Lead dithiobenzoate, 172 Lead gallate, 369 Lead hippurate, 190 Lead opianate, 504 Lead opianylsulphite, 507 Lead parahydroxybenzoate, 328 Lead phthalate, 457 Lead proto-catechuate, 352 Lead quinate, 384 Lead salicylaldehyde, 287 Lead salicylate, 304 Lecanoric acid, 429, 432, 433 Lecanorin, 429 Lithium salicylate, 303 Litmus, 45 Luteolin, 357 M. Maclurin, 356 Magnesium hippurate, 189 Maluchite-green, 135 Mandelic acid, 131 Meconin, 497, 500 ^-Meconin, 501 Meconinic acid, 500 Meconiosin, 502 Menyanthin, 423 Menyanthol, 423 Mercuric benzamide, 174 Mercuric benzoate, 161 Mercury benzyl mercaptide, 105 Mercury derivatives of Toluene, 87 Mercury orthotolyl, 88 Mercury paratolyl, 88 Meta-acetobenzyl acetate, 283 Meta-acetoxybenzoic acid, 322 Meta-azotoluene, 76 Meta-benzamoxalic acid, 248, 249 Metabenzenyltrichlorophosphoryl chloride, 322 Metabenzobetaine, 248 a-Metabenzo-creatine, 252 /3-Metabenzo-creatine, 252 Metabenzoglycocyamine, 251 Metabenzosarcosine, 247 Metabromobenzaldehyde, 145 Metabromobenzoic acid, 223 Metabromobenzyl bromide, 102 Metabromotoluene, 11 Metacarbamidobenzoic acid, 251 Metacarbonylphenylphosphoryl chloride, 322 Metacarboxyorthophosphoric acid, 322 Metachlorobenzaldehyde, 144 Metachlorobenzoic acid, 219 Metachlorobenzonitril, 220 Metachlorobenzoyl chloride, 220, 383 Metachlorohippuric acid, 220 Metachlorotoluene, 8 Metacresol, 24, 27 Metacresyl benzoate, 164 Metacresyl oxide, 27 Metacyanobenzoic acid, 480 Metadiamidobenzylarnine, 120 Metadiazo-amidobenzoic acid, 262 Metadiazobenzamide nitrate, 261 Metadiazobenzoic acid, 261 Metadiazobenzoic acid imide, 264 Metadiazobenzoic acid nitrate, 261 Metadiazobenzoic acid perbromide, 261 Metadiazobenzoic acid platinichloride, 261 Metadiazobenzoic acid sulphate, 261 Metadiazobenzonitril nitrate, 262 Metadihydroxybenzaldehyde, 348 Metadinitrobenzylamine, 119 Metadithiobenzoic acid, 272 Metaditolylamine, 62 Meta-ethoxybenzoic acid, 322 Metafluorbenzoic acid, 226 Metafluorhippuric acid, 226 Metaguanidobenzoic acid, 251 Metahomometahydroxybenzoic acid, 425 Metahomomethoxycalicylaldehyde, acid, 428 Metahomoparahydroxybenzaldehyde, 422 Metahomoparahy droxybenzoic acid, 426 Metahomosalicylaldehyde, 422 a-Metahomosalicylic acid, 424 jS-Metahomosalicylic acid, 424 Metahydrazinebenzoic acid, 264 Metahydrazobenzoic acid, 266 Metahydrazotoluene, 76 Metahydroxybenzaldehyde, 293 Metahydroxybenzamide, 323 Metahydroxybenzanilide, 323 Metahydroxybenzenylamidoxime, 216 Metahydroxy benzoates, 320 Metahydroxybenzoic acid, substitution products of, 323 Metahydroxybenzonitril, 323 Metahydroxybenzoic acid, 320 Metahydroxybenzoylsulphuric acid, 326 Metahydroxybenzuric acid, 323 Metahydroxybenzyl acetate, 283 Metahydroxybenzyl alcohol, 283 534 INDEX Metahydroxybenzyl diacetate, 283 Metahydroxyorthotoluic acid, 425 Metahydroxyparatohiic acid, 426 Meta-iodobenzoic acid, 225 Meta-iodotoluene, 13 Metamethoxybenzoic acid, 321 Metamethoxysalicylaldehyde, 349 jB-Metamethoxysalicylaldehyde, 348 Metamidobenzaldoxime, 150 Metamidobenzaldehyde, 150 Metamidobenzamide, 247 Metamidobenzenylamidoxime, 216 Metamidobenzoic acid, 246, 248, 252 Metamidobenzoic acid hydrochloride, 247 Metamidobenzonitril, 247 Metamidobenzylphenylamine, 120 Metamidoparamethyltoluidine, 73 Metamidoparazotoluene, 78 Metanitrobenzaldehyde, 147 Metanitrobenzaldoxime, 147 Metanitrobenzamide, 231 Metanitrobenzenylamidoxime, 216 Metanitrobenzidene bromide, 147 Metanitrobenzidene chloride, 147 Metanitrobenzoic, 230 Metanitrobenzoic acid, 228 Metanitrobenzonitril, 232 Metanitrobenzoyl chloride, 231 Metanitrobenzyl alcohol, 104 Metanitrobenzylamine, 119 Metanitrobenzylamines, 119 Metanitrobenzyl chloride, 104 Metanitrobenzylphenylamine, 119 Metanitrohippuric acid, 232 Metanitromethylmetahydroxybenzalde- hyde, 294 Metanitro-orthotoluidine, 69 Metanitropara-ethyltoluidine, 71 Metanitroparamethyltoluidine, 71 Metanitroparatoluidine, 7 0 Metanitro toluene, 16 Metaphlorone, 404 Metaphthalic acid, 479 Metasulphamidobenzoic acid, 272 Metasulphamido-orthotoluic acid, 416 Metasulphobenzamide, 271 Metasulphobenzoates, 270 Metasulphobenzoic acid, 269 Metasulphobenzoyl chloride, 271 Metathiocresol, 31 Meta thiohydrobenzoic acid, 272 Metatolualdehyde, 413 Metatoluic acid, 416 Metatoluidine, 60 Metatoluidine hydrochloride, 61 Metatohiidine nitrate, 61 Metatoluidine sulphate, 61 Metatolunitril, 417 Metatoluyl chloride, 417 Metatoluylenediamine, 72 Metatolyl carbamide, 63 Metatolyl mustard oil, 63 Metatolylstibine, 86 Metatolyl thiocarbamide, 63 Metatriamidobenzylamine, 120 Metatrinitrobenzylamine, 119 Meta-uramidobenzoic acid, 250 Meta-urethanebenzoic acid, 251 Metaxylene, 388, 389, 391 a-Metaxylenesulphamide, 399 a-Metaxylenesulphonic acid, 398 u-Metaxylenesulphonic acid, 399 a-Metaxylenesulphonic chloride, 398 a-Metaxylenol, 400 s-Metaxylenol, 401 v-Metaxylenol, 401 a-Metaxylenyl acetate, 401 Metaxylidenehydrazine, 413 Metaxylidene tetrachloride, 447 Metaxylylene alcohol, 440 Metaxylylene bromide, 441 Metaxylylene chloride, 441 Metaxylylene ethyl ether, 440 a-Metaxylenyl methyl ether, 400 a-Metaxylidine, 406 s-Metaxylidine, 407 u-Metaxylidine, 406 Metazobenzoic acid, 266 Metazoxybenzoic acid, 266 Methenylamidorthocresol, 26 Metaxyloquinol, 403 Metaxyloquinone, 404 Metaxylorcinol, 402 Metaxylyl acetate, 412 Metaxylyl alcohol, 411 Metaxylyl bromide, 412 Metaxylyl chloride, 412 Metaxylyl ethyl ether, 411 a-Methoxyisophthalic acid, 494 v-Methoxyisophthalic acid, 495 Methoxynitrobenzonitril, 361 Methoxy terephthalic acid, 496 Methyl aldehydovanillate, 509 Methyl amido-anisate, 338 Methylamido-anisic acid, 338 Methyl amido-isophthalate, 482 Methyl amido-terephthalate, 489 Methylbenzene, 3 Methyl benzoate, 161 Methylbenzoylphenylhydrazine, 180 Methylbenzyl, 387 Methyl benzylsalicylate, 307 Methylbromosalicylaldehyde, 292 Methyl bromoterephthalato, 488 Methyl chloroterephthalate, 488 Methylcinnyl ketone, 135 Methyl cresolcarboxylate, 439 Methyl-/3-diamidotoluene, 73 Methyldibenzoylphenylhydrazine, 180 Methyl dimethylamidosalicylate, 318 Methylenedibenzamide, 175 Methyleneprotocatechuicaldehyde, 347 Methyl ethylsalicylate, 307 Methyl hippurate, 190 a-Methylhydroquinoneformic acid, 362 a-Methylbydroxyphthalic acid, 493 u-Methylhydroxyphthalic acid, 493 INDEX. 535 Methylhydroxysalicylic acid, 362 Methylhypogallic acid, 498 Methyl iodide, 36 Methyl isocyanate, 518 Methylisonoropianic acid, 508 Methylisophthalate, 479 Methyl isopropylsalicylate, 307 Methylmetahomoparahydroxy benzoic acid, 427 a-Methylmetahomosalicylic acid, 424 Methylmetahydroxy benzaldehyde, 293 Methylmetamidobenzoic acid, 247 Methylmetatoluidine, 61 Methyl nitrite, 578 Methyl-nitro-isophthalate, 482 Methylnitrosalicylaldehyde, 292 Methyl nitroterephthalate, 489 Methylnorhemipinic acid, 514 Methylnormeconin, 498, 501 Methylnoropianic acid, 498, 502 Methyl opianate, 505 Methyl orsellinnte, 432 3-Methylorthodihydroxybenzaldehyde, 348 a- Methylorthobenzogly cocy amidine, 243 /3-Methylorthohomometahydroxyben- zoic acid, 426 Methylorthohomoparahydroxybenzoic acid, 427 Methylorthohomosalicylic acid, 424 Methylorthotoluidine, 58 Methylorthotolylnitrosamine, 58 Methylparadihydroxy benzaldehyde, 349 Methylparahomosalicylic acid, 424 Methylparahydroxy benzal dehyde, 295 Methylparahydroxybenzoate, 295, 328 Methylparahydroxybenzoyl chloride, 332 Methyl paramethoxybenzoate, 330 Methyl paratoluate, 419 Methylparatoluidine, 64 Methylphthalate, 457 Methylphthalimidine, 445 Methylprotocatechuate, 352 Methylpyrogallic acid, 53 Methylpyrogallol, 53 Methylpyrogallol dimethyl ether, 54 Methyl salicylaldehyde, 287 Methyl salicylate, 305 Methyl salicylic acid, 305 Methyl terephthalate, 484 Methyl tetrahydroterephthalate, 486 Methyltoluol, 387 Methyl vanillate, 352 Methylvanillin, 346 Methyl veratrate,354 Monamidobenzoic acids, 237 Monethyl dihydroxyterephthalate, 517 Monobromobenzoic acids, 223 Monobromoparaxyknol, 401 Monobromophtbalide, 443 Monobromorcinol, 41 Monobromotoluenes, 10 Monochlorobenzoic acids, 217 Monochlorobenzenyl trichloride, 196 Monochlorotoluenes, 8 Monofluorbenzoic acids, 226 Monohydroxytoluenes and allied bodies, 23 Mono-iodobenzoic acids, 225 Mono-iodorcinol, 41 Mononitrobenzoic acids, 229 Mononitrotoluenes, 13 Monosulphobenzoic acids, 268 Monoxylylamine, 412 Morintannic acid, 356 N. Naphthalamide, 463 Naphthalic acid, 450 Naphthesic acid, 450 Nitradiazobenzoic acid, 262 Nitranilic acid, 520 e-Nitro-amidobenzamide, 257 a-Nitro-amidobenzoic acid, 256 j8-Nitro-amidobenzoic acid, 256 7-Nitro-amidobenzoic acid, 256 8-Nitro-amidobenzoic acid, 256 e-Nitro-amidobenzoic acid, 257 f-Nitro-amidobenzoic acid, 257 •jj-Nitro-amidobenzoic acid, 257 Nitro-amidobenzoic acids, 255 Nitro-amidosalicylic acid, 318 Nitro-anisic acid, 337 Nitrobenzinic acid, 227 Nitrobenzoene, 4 Nitrobenzoic acids, 233 Nitrobenzylsulphonic acid, 109 Nitrococcusic acid, 425 Nitro-diamidometaxylene, 409 Nitro-dimethylmetatoluidine, 62 Nitro-dracyl, 4 Nitro-dracylie acid, 228 Nitrogen bases of benzyl, 110 Nitrogen compounds of benzoyl, 172 N itrohemipinic acid, 511 Nitro-isophthalic acid, 482 Nitromeconin, 500 Nitro-rp-meconin, 501 Nitrometacresol, 27 a-Nitrometahydroxybenzaldehyde, 293 j8-Nitrometahydroxybenzaldehyde, 293 7-Nitrometahydroxybenzaldehyde, 293 Nitrometahydroxybenzoic acids, 323 a-Nitrometahydroxybenzoic acid, 324 3-Nitrometahydroxybenzoic acid, 324 7-Nitrometahydroxybenzoic acid, 324 77-Nitrometahydroxybenzoic acid, 324 Nitrometatoluic acids, 417 a-Nitrometaxylene, 396 s-Nitrometaxylene, 396 r-Nitrometaxylene, 396 a-Nitro-a-metaxylidine, 408 s-Nitro-s-metaxylidine, 408 j'-Nitrol-a-metaxylidine, 408 536 INDEX. a-Nitro-s-metaxylidine, 408 Nitromethane, 518 Nitromethylnoropianylhydrazide, 508 Nitromethylnoropianic acid, 503 Nitromethylnorhemipinic acid, 514 Nitro-opianic acid, 507 Nitro-opianylphenylhydrazide, 508 a-Nitro-orcinol, 41 3-Nitro-orcinol, 41 a-Nitro-orthocresol, 25 3-Nitro-orthocresol, 26, 51 7-Nitro-orthocresol, 26 Nitro-orthotoluic acids, 415 a-Nitro-orthoxylene, 395 v-Nitro-orthoxylene, 395 a-Nitroparaeresol, 30 3-Nitroparacresol, 30 Nitronarahy dr oxy benzoic acid, 335 Nitroparahydroxy benzaldehyde, 296 a-Nitroparatoluic acid, 421 3-Nitroparatoluic acid, 421 3-Nitroparatolunitril, 421 Nitroparaxylene, 397 a-Nitroparaxylidine, 408 3-Nitroparaxylidine, 408 7-Nitroparaxylidine, 408 a-Nitrophthalic acid, 474 v-Nitrophthalic acid, 473 Nitrophthalic acids, 473 a-Nitrophthalicanhydride, 475 a-Nitro-salicylaldehyde, 292 3-Nitrosalicylaldehyde, 292 Nitrosalicylic acids, 315 a-Nitrosalieylic acid, 315 3-Nitrosalicylic acid, 316 Nitrosodibenzylamine, 116 Nitroso-dimethylmetatoluidine, 62 Nitrosohemipinimidine, 501 Nitrosomethylmetanitrobenzene, 147 Nitrosomethylnitrobenzene, 147 Nitrosomethylparatoluidine, 65 Nitrosometracresol, 51 Nitrosoparaxylorcinol, 402 Nitrosophthalimidine, 444 Nitro-substitution products, 41, 293 Nitro-substitution products of benzoic acid, 227 Nitro-substitution products of toluene, 13 Nitro-substitution products of the xylenes, 395 Nitrosulphobenzoic acids, 275 Nitroterephthalamide, 489 Nitro-terephthalaldehyde, 449 Nitroterephthalaldehydic acid, 449 Nitro-terephthalic acid, 488 Nitrotoluene, 13 3-Nitrotoluene, 15 Nitrotoluidine, 15 Nitrotoluidines, 69 Nitro-uramidobenzoyl, 242 Nitroxylidines, 408 Norhemipinic acid, 498 Normal barium hydroxamate, 208 Normal barium metasulphobenzoate, 270 Normal barium a-nitrosalicylate, 316 Normal barium 0 nitrosalicylate, 316 Normal barium parasulphobenzoate,273 Normal barium phthalate, 457 Normal calcium benzamoxalate, 245 Normal ethyl metasulphobenzoate, 270 Normal ethyl a-nitrophthalate, 475 Normal ethyl v-nitrophthalate, 474 Normal lead metasulphobenzoate, 270 Normal methyl sulphinidephthalate, 478 Normal potassium hemipinate, 510 Normal potassium metasulphobenzoate, 270 Normal potassium sulphinidephthalate, 477 Normal silver hemipinate, 510 N ormal silver sulphinidephthalate, 477 Normal sodium dihydroxy terephtha- late, 516 Normeconin, 498 Noropianic acid, 498, 502 O. Octyl benzoate, 162 Octacetylhelicoidin, 289 Oil of bitter almonds, 132 Opianic acid, 497, 503 Opianic anhydride, 505 Opianoxime anhydride, 513 Opianyl, 497 Opianylphenylhydrazide, 507 Opianyl sulphurous acid, 506 Opinic acid, 514 Orcein, 44 a-Orcein, 44 3-Orcein, 44 Orcin, 37 /3 Orcin, 402 Orcinol, 37, 429 ; properties, 39 Orcinol acetate, 40 Orcinolazobenzene, 40 Orcinol diethylcarbonate, 40 Orcinol dimethyl ether, 40 Orcinol monomethyl ether, 40 Orcinol, substitution products of, 41 Orcylaldehyde, 427 Ornithine, 193 Ornithuric acid, 192, 193 a-Orsellic acid, 429 Orsellinic acid, 432, 438 a-Orsellinic acid, 429 Orthamidobenzaldoxime, 149 Orthamidobenzaldehyde, 149 Orthamidobenzyl alcohol, 105 Ortho - aldehydometahydroxybenzoic acid, 492 Ortho - aldehydoparahydroxybenzoic acid, 491 INDEX. 537 Ortho • aldehydophenoxyacetic acid, 289 Ortho-aldehydosalicylic acid, 491 Ortho-amidobenzamide, 240 Ortho-amidobenzoic acid, 237 Ortho-amidobenzoic acid, hydrochlor- ide, 239 Ortho-amidobenzonitril, 240 Ortho-amidopara-azotoluene, 78 Ortho-azobenzoic acid, 265 Ortho-azotoluene, 75 Ortho-azoxybenzoic acid, 265 Ortho-azoxytoluene, 77 Orthobenzamoxalic acid, 244 Orthobenzidenephenylhydrazine, 291 a-Orthobenzocreatinine, 243 j8-Orthobenzocreatinine, 244 Orthobenzoglycocyamidine, 243 Orthobenzoic acid, 194 Orthobenzoylhydrazide, 264 Orthobenzyl thioformate, 106 Orthobromobenzaldehyde, 145 Orthobromobenzoic acid, 223 Orthobromobenzyl alcohol, 102 Orthobromo-benzyl amine, 118 Orthobromobenzyl bromide, 102 Orthobromotoluene, 10 Orthocarbonylphenylphosphoryl chlo- ride, 311 Orthocarboxylphenylphosphoric acid, 311 Orthochlorobenzaldehyde, 143 Orthochlorobenzidene chloride, 143 Orthochlorobenzoic acid, 144, 217 Orthochlorobenzonitril, 218 Orthochlorobenzoyl chloride, 218, 462 Orthochlorocarbonylphenyl metaphos- phate, 311 Orthochloroparanitrotoluene, 19 Orthochlorotoluene, 8 Orthocresol, 24, 25 Orthocresyl benzoate, 164 Orthocresyl oxide, 25 Orthocyanobenzoic acid, 468 Orthodiazobenzoic acid nitrate, 261 Orthodiazobenzoic acid seminitrate, 261 Orthodibromo-benzylamine, 119 a-Orthodihydroxybenzaldehyde, 343 Orthodihydroxybenzoic acid, 350 Orthodin itrotoluene, 17 Orthofluorbenzoic acid, 226 Orthofluorhippuric acid, 226 a-Orthohomometahydroxybenzoic acid, 426 3-Orthohomometahydroxybenzoic acid, 426 Orthohomoparahydroxybenzaldehyde, 422 Orthohomoparahydroxybenzoic acid, 427 Orthohomosalicylaldehyde, 422 Orthohomosalicylic acid, 424 Orthohydrazinebenzoic acid, 264 Orthohydrazobenzoic acid, 265 Orthohydroazotoluene, 75 Orthohydroxybenzaldehyde, 285 Orthohydroxybenzidene acetate, 290 Orthohydroxybenzidene compounds, 290 Orthohydroxybenzidenoxime, 290 Orthohydroxybenzoic acid, 297 Orthohydroxybenzyl alcohol, 279 Orthohydroxybenzyl ethyl ether, 280 Orthohydroxybenzyl glucoside, 281 Orthohydroxybenzyl methyl ether, 280 Orthohydroxymetatolualdehyde, 422 a-Orthohydroxymetatoluic acid, 423 Orthohydroxymetaxylyl alcohol, 422 Orthohydroxymethylbenzoic acid, 442 Orthohydroxymethylparahydroxy ben- zoic acid, 490 Orthohydroxymethylsalicylic acid, 490 Orthohydroxyparatolualdehyde, 422 Orthohydroxyparatoluic acid, 424 Orthohydroxymetatolualdehyde, 422 i'-Orthohydroxymetatoluic acid, 424 Ortho-iodobenzoic acid, 225 Ortho-iodotoluene, 13 Orthomethoxybenzyl alcohol, 280 Orthomethoxyparahydroxy benzalde- hyde, 348 Orthomethyl-j3-resorcylic acid, 360 Orthonitrobenzoyl chloride, 230 Orthonitrobenzyl alcohol, 104 Orthonitrobenzaldehyde, 146, 240 Orthonitrobenzaldoxime, 146 Orthonitrobenzoic acid, 228, 229 Orthonitrobenzonitril, 230 Orthonitrobenzyl chloride, 105 Orthonitrobenzyl iodide, 105 Orthonitrometatolualdehyde, 413 a-Orthonitrometatoluidine, 70 3-Orthonitrometatoluidine, 70 a-Orthonitromethylmetahydroxybenz- aldehyde, 294 3-Orthonitromethylmetahydroxybenz- aldehyde, 294 a-Orthonitro-orthotoluidine, 69 3-Orthonitro-orthotoluidine, 69 Orthonitroparatoluidine, 70 Orthonitrophthalide, 446 Orthonitrotoluene, 15 Orthosulphamidobenzoic acid, 268 Orthosulphobenzoic acid, 268 Orthothiocresol, 31 Orthotolualdehyde, 413 Orthotoluamide, 414 Orthotoluic acid, 414 Orthotoluidine, 57 Orthotoluidine hydrobromide, 58 Orthotoluidine hydrochloride, 58 Orthotoluidine nitrate, 58 Orthotoluidine oxalate, 58 Orthotoluidine sulphate, 58 Orthotolunitril, 414 Orthotoluyl chloride, 414 538 INDEX. Orthotoluylarsenic acid, 86 Orthotoluylenediamine, 72 Orthotolyl carbamide, 59 Orthotolyl isocyanate, 59 Orthotolyl mustard oil, 60 Orthotolylphosphenilic acid, 84 Orthotolylphosphenylous acid, 84 Orthotolylphosphorus dichloride, 84 Orthotolylstibine, 86 Orthotolyl thiocarbamide, 59 Orthotribromo-bcnzylamine, 119 Ortho-uramidobenzoic acid, 243 Orthoxylene, 388, 389, 390 a-Orthoxylenol, 400, 401 v-Orthoxylenol, 400 Orthoxylenesulphonamide, 398 Orthoxylenesulphonic acid, 398 Orthoxyienesulphonie chloride, 398 Orthoxylidene tetrachloride, 447 a-Orthoxylidine, 406 v-Orthoxylidine, 406 Orthoxyloquinol, 403 Orthoxyloquinone, 404 Orthoxylyl alcohol, 411 Orthoxylyl bromide, 412 Orthoxylyl chloride, 412 Orthoxylylene acetate, 440 Orthoxylylene alcohol, 439 Orthoxylylene bromide, 440 Orthoxylylene chloride, 439 Orthoxylylene ethyl ether, 439 Orthoxylylene iodide, 440 Orthoxylylene sulphide, 440 Orthrin, 128 Orthylene, 439 Oxalamidobenzoic acid, 249 Oxalanthranilic acid, 244 Oxides of benzoyl, 166 Oxybenzonitrisulphuric acid, 199 Oxybenzuramic acid, 250 P. Para-acetobenzyl acetate, 284 Para-acetoxybenzoic acid, 330 Para-aldehydometahydroxybenzoic acid, 492 Para-aldehydosalicylic acid, 491 Para-amidohydroxymethylbenzoic acid, 446 Para-amidopara-azotoluene, 78 Para-azotoluene, 76 Parabenzidene sulphide, 138 Parabenzophosphenilic acid, 84 Parabromobenzaldebyde, 145 Parabromobenzoic acid, 224 Parabromobenzyl acetate, 102 Parabromobenzyl alcohol, 101 Parabromobenzyl bromide, 101 Parabromotoluene, 11 Paracarbamidobenzoic acid, 254 Paracarbonylorthophosphoric acid, 332 Paracarbonylphenylphosphoryl chlor- ide, 332 Parachlorobenzal deb yde, 144 Parachlorobenzoic acid, 9, 221 Parachlorobenzoic acid, 221 Parachlorobenzyl acetate, 101 Parachlorobenzyl alcohol, 99, 100 Parachloro-benzylaniine, 118 Parachlorobenzyl bromide, 101 Parachlorobenzyl chloride, 100 Parachlorobenzyl ethyl ether, 100 Parachlorobenzyl hydrosniphide, 106 Parachlorometacresol methyl ether, 32 Parachlorometatoluene, 19 Parachlororthonitrotoluene, 19 Parachlorotoluene, 9 Paracresol, 23, 24, 25, 28 Paracresyl benzoate, 164 Paracresyl oxide, 28 Paradiamidobenzylamine, 120 Paradiazo-amidobenzoic acid, 263 Paradiazobenzoic acid nitrate, 262 Paradichloro-benzylamine, 118 Paradihydroxybenzaldehyde, 349 Paradihydroxybenzoic acid, 361 Paradi-iodo-benzylamine, 118 Paradinitrobenzylamine, 119 Para-ethoxybenzoic acid, 330 Parafluorhippuric acid, 227 Parafluorbenzoic acid, 226 Parahomometahydroxybenzoic acid, 425 Parahomosalicylaldehyde, 422 Parahomosalicylic acid, 423 Parahydrazobenzoic acid, 266 Parahydrazotoluene, 76 Parahydroxybenzaldehyde, 294 Parahydroxybenzaldoxime, 296 Parahydroxy benzamide, 333 Parahydroxybenzanilide, 333 Parahydroxybenzide, 332 Parahydroxybenzoates, 328 Parahydroxybenzoic acid, 108 Paradroxybenzoic acid, 326 ; substitu- tion products of, 334 Parahydroxybenzonitril, 334 Parahydroxybenzoylparahydroxy-ben- zoic acid, 331 Parahydroxybenzoyl sulphuric acid, 336 Parahydroxybenzuric acid, 333 Parahydroxybenzyl acetate, 284 Parahydroxybenzyl alcohol, 283 Parahydroxybenzyl methyl ether, 284 Parahydroxybenzyl thio-carbimide, 284 Parahydroxymetatoluic acid, 427 Parahydroxymetatolualdehyde, 422 Parahydroxymethylbenzoic acid, 442 Parahydroxymethylsalicylic acid, 490 Parahydroxyorthotolualdehyde, 422 Parahydroxyorthotoluic acid, 426 Parahydroxyphenylacetonitril, 284 Para-iodobenzaldehyde, 146 Para-iodobenzoic acid, 225 INDEX. 539 Para-iodobenzyl alcohol, 102 Para-iodo-benzylamine, 118 Para-iodobenzyl bromide, 102 Para-iodotoluene, 13 Paraleucaniline, 148 Paraleucotoluidine, 77 Paramethoxybenzoic acid, 329 Paramethoxybenzylamine, 284 Paramethoxybenzyl chloride, 284 Paramethyl-3-resorcylic acid, 360 Paramethoxysalicylaldehyde, 349 Paramidobenzaldehyde, 150 Paramidobenzaldoxime, 150 Paramidobenzamide, 253 Paramidobenzanitril, 253 Paramidobenzoic acid, 253 Paramidobenzoic acid hydrochloride, 253 Paramidobenzylphenylamine, 120 Paramidodiazobenzoic acid, 263 Paramidophthalide, 446 Paranitrobenzaldehyde, 148 Paranitrobenzaldoxime, 149 Paranitrobenzamide, 232 Paranitrobenzidene bromide, 148 Paranitrobenzidene chloride, 148 Paranitrobenzoic acid, 232 Paranitrobenzonitril, 233 Paranitrobenzoyl chloride, 232 Paranitrobenzyl acetate, 104 Paranitrobenzyl alcohol, 99, 103 Paranitrobenzylamines, 119 Paranitrobenzyl bromide, 99, 103 Paranitrobenzyl chloride, 103 Paranitrobenzyl hydrosulphide, 106 Paranitrobenzyl iodide, 103 Paranitrobenzyl nitrate, ] 03 Paranitrobenzyl oxalate, 104 Paranitrobenzyl thiocyanate, 123 Paranitrobenzylyphenylamine, 119 Paranitro-diamidotriphenylmethane, 148 Paranitrohippuric acid, 233 Paranitrohydroxymethylbenzoic acid, 446 Paranitromethylmetahydroxybenzalde- hyde, 294 Paranitrotoluene, 15, 16 Paranitro-orthotoluidine, 69 Paranitrophthalide, 445 Para-orsellinaldehyde, 427 Para-orsellinic acid, 436, 438 Paraphenoxy benzoic acid, 331 Paraphosphorsellinic acid, 436 Pararosaniline, 148 Pararosotoluidine, 77 Parasulphamidobenzoic acid, 273 Parasulphamido-orthotoluic acid, 416 Parathiocresol, 31 Paratolualdehyde, 413 Paratoluamide, 419 Paratoluylenediamine, 73 Paratoluic acid, 418 Paratoluidine, 63 Paratoluidine hydrobromide, 64 Paratoluidine hydrochloride, 64 Paratoluidine nitrate, 64 Paratoluidine phenate, 64 Paratoluidine sulphate, 64 Paratolunitril, 420 Paratoluylamido-acetic acid, 419 Paratoluyl chloride, 419 Paratolylbenzoyl thio-urea, 179 Paratolylboron chloride, 87 Paratolyl carbamide, 66 Paratolylhydrazine, 75 Paratolyl mustard oil, 67 Paratolylphosphenilic acid, 83 Paratolylphosphenylous acid, 83 Paratolylphosphine, 84 Paratolylphosphonium iodide, 84 Paratolylphosphorus dichloride, 83 Paratolylphosphorus oxychloride, 83 Paratolylphosphorus tetrachloride, 83 Paratolylsilicic acid, 87 Paratolylsilicon chloride, 87 Paratolylsilieon oxide, 87 Paratolylstibine, 86 Paratolylstibine bromide, 86 Paratolylstibine chloride, 86 Paratolylstibine hydroxide, 86 Paratolylstibine iodide, 86 Paratolylstibine oxide, 86 Paratolyl thiocarbamido, 67 Paratolyl thiocarbimides, 67 Paratolyl urethane, 67 Paratriamidobenzylamino, 120 Paratribromo-benzylamine, 118 Paratrichloro-benzylamine, 118 Paratri-iodo-benzylamine, 118 Paratrinitrobenzylamine, 119 Para-uramidobenzoic acid, 254 Paraxylyl alcohol, 412 Paraxylenol, 401 Paraxylene, 388, 389, 391 Paraxylenesulphamide, 399 Paraxylenesulphonic acid, 399 Paraxylenesulphonic chloride, 399 Paraxylidine, 407 Paraxylidene tetrachloride, 448 Paraxyloquinol, 403 Paraxyloquinone, 404 Paraxylorcinol, 402 Paraxylylene acetate, 441 Paraxylylene alcohol, 441 Paraxylyl bromide, 412 Paraxylylene bromide, 441 Paraxylylene chloride, 441 Paraxylylene iodide, 441 Paraxylylene monobenzoate, 442 Paraxylylene mono-ethyl ether, 441 Paraxylyl ethyl ether, 412 Parazobenzoic acid, 266 Penta-acetyl tannin, 374 Pentabromobenzoic acid, 225 Pentabromorcinol, 41 Pentabromotoluene, 12 Pentachlorobenzidene chloride, 8, 145 540 INDEX. Pentachlorobenzyl alcohol, 100 Pentachlorobenzyl chloride, 101 Pentachlororcinol, 41 Pentachlorotoluene, 10 Pentachloroxy lone, 34 Persio, 44 Peruvin, 90 Petrol, 387 Phenol, 297 Phenylacetamide, 113 Phenylacetonitril, 113 Phenylaceturic acid, 186 Phenylamido-acetonitril, 113 Phenylbenzaldehydine, 141 Phenylbenzaldehydine hvdrochloride, 141 Phenylbenzenylamidine, 203 Phenyl benzoate, 163 Phenylbenzoyl thio-urea, 179 Phenylchlorocarbylethyl ether, 100 Phenylchloroform, 195 Phenylene benzoate, 164 Phenylenebenzenylamidine, 205 Phenylenediethylacetone, 462 Phenylenenitrobenzeny]amidine, 206 Phenylhydrazine nitro-opianic acid, 508 Phenylhydroxyacetic acid, 132 Phenylhydroxyacetonitril, 113, 131 Phenyl isophthalate, 480 Phenylorthotolylamine, 59 Phenylmetabenzoglycocyamine, 252 Phenylmethyl, 89 Phenyl methylsalicylate, 308 Phenylnitro-ethylene, 135 Phenylorthotolyl thiocarbamide, 60 Phenyl paraphenoxybenzoate, 331 Phenyl parahydroxybenzoate, 330 Phenyl paratoluate, 419 Phenylparatoluidine, 65 Phenylparatolylamine, 65 Phenylphthalimide, 464 Phenylphthalimidine 445 Phenylpropionic acid, 186 Phenylpropio nitril, 122 Phenyl salicylate, 307 Phenyl terephthalate, 484 Phenylthiobenzamide, 178 Phenylthiobenzoate, 171 Phloroglucinol, 357 Phloroglucinolcarboxylic acid, 380, 381 Phlorone, 404 Phosphorsellinanilide, 433 Phosphorsellinic acid, 433 Phosphorus compounds of benzyl, 124 Phosphorus derivatives of toluene, 83 Phosphorus pentachloride and its action upon salicylic acid, 309 Phospho-salicylic acid, 309 Phthalalcohol, 439 Phthalaldehyde, 442, 447 Phthalaldehydic acid, 447 Phthalamic acid, 463 Phthalamil, 464 Phthalanilic acid, 464 Phthaleins, 458 Phthalic acid, 439, 451, 452 Phthalic acid, addition products of, 469 Phthalic acid, halogen substitution products of, 471 Phthalic acids, 450 Phthalic anhydride, 457 ; apparatus for the sublimation of, 459 a-Phthalicsulphamic acid, 477 Phthalide, 442, 458 Phthalide-anil, 445 Phthalidehydrazide, 445 Phthalimide, 463 Phthalimide oxime, 469 Phthalimidine, 444 Phthalinic acid, 464 Phthalylacetic acid, 458 Phthalyl chloride, 458 Phthalyldiamide, 466 Phthalylhydroxylamine, 466, 468 Phthalyloxide, 457 Phthalyl sulphide, 462 Picranyl, 129 Picroerythrin, 429, 431, 434 Picrorocellin, 436 Piperonal, 347 Piperonic acid, 355 Piperonyl alcohol, 347 Polysalicylnitril, 313 Pomacese, 131 Populin, 282, 317 Potassium benzidene sulphite, 137 Potassium benzoate, 160 Potassium benzyl sulphonate, 108 Potassium chlorobenzylsulphonate, 108 Potassium cyanate, 518 Potassium dibenzhydroxamate, 210 Potassium dinitroparacresate, 31 Potassium dinitrosalicylate, 317 Potassium gallate, 368 Potassium hemipinimide, 513 Potassium hippurate, 189 Potassium hydroxyphthalamate, 467 Potassium isophthalate, 479 Potassium opianate, 504 Potassium parahydroxybenzoate, 328 Potassium phthalimide, 463 Potassium piperonate, 356 Potassium salicylaldehyde, 287 Potassium salicylate, 302 Potassium thiobenzoate, 170 Potassium a-toluquinonoximate, 51 Potassium tribenzarsenate, 278 Proin, 128 Propenyl salicylate, 306 Propyl benzoate, 162 Propylene, 24 Propylene benzoate, 163 Propyl salicylate, 306 Propyl terephthalate, 484 Protocatechuic acid, 350, 357 INDEX. 541 Protocatechuicaldehyde, 343 Protonitrobenzoine, 13 Pseudoerythrin, 428 Pseudotoluidine, 55 Pyrogallocarboxylates, 379 Pyrogallolcarboxylic acid, 378, 381 Q. Quercimeric acid, 509 Quinates, the, 384 Quinic acid, 186, 381 Quinoldicarboxylic acid, 515, 518 Quinonedihydrodicarboxylic acid, 518 Quinonoxime benzoate, 165 E. Resorcinoldicarboxylic acid, 515 3-Resorcylaldehyde, 348 a-Resorcylic acid, 358 jS-Resorcylic acid, 359, 437 7-Resorcylic acid, 360 Retinaphtha, 3 Ribbon Litmus, 46 S. Saccharin, 269 Safranine, 80 Salicin, 281 Salicyl, 285 Salicyl alcohol, 279 Salicylaldehyde, 285 ; properties, 286 Salicylaldehyde, substitution products of, 292 Salicylaldoxime, 290 Salicylamide, 312 Salicylates, 301 Salicyl chloraldide, 308 Salicyl chloride, 310 Salicyl hydride, 285 Salicylhydroxyacetic acid, 309 Salicylic acid, 108, 157, 297 Salicylic acid, ethereal salts of, 306 Salicylic acid, substitution products of, 313 Salicylic ethers, 306 Salicylic ethers, ethereal salts of, 307 Salicylide, 308 Salicyl monochlorophosphate, 309 Salicylnitril, 313 Salicylparazobenzenesulphonic acid, 319 Salicylsulphuric acid, 319 Salicyluric acid, 312 Saligesion, 279 Sal i retin, 280 Salireton, 280 Salol, 307 Salts and ethers of benzoic acid, 160 Selenium compounds of benzyl, 109 Silicon compounds of benzyl, 127 Silicon paratolyl, 87 Silicon tetrabenzyl, 127 Silicotetrabenzylmethane, 127 Silver benzarsenate, 277 Silver benzarsenite, 278 Silver benzoate, 161 Silver benzophosphinate, 276 Silver hemipinimide, 513 Silver hippurate, 190 Silver isophthalate, 479 Silver metasulphobenzoate, 270 Silver methylnoropianate, 503 Silver opianite, 504 Silver orthohydroxymethylbenzoate, 442 Silver parahydroxybenzoate, 328 Silver phthalate, 457 Silver phthalimide, 463 Silver piperonate, 356 Silver quinate, 384 Silver salicylate, 304 Silver terephthalate, 484 Sinalbin, 377 Sinapic acid, 376 Sinapin, 375 Sinapin thiocyanate, 375 Sodium arsenetribenzoate, 278 Sodium benzidene sulphite, 137 Sodium benzoate, 160 Sodium gallate, 368 Sodium hippurate, 189 Sodium metanitrobenzoate, 231 Sodium metaxylenesulphonate, 398 Sodium orthoxylenesulphonate, 398 Sodium parahydroxybenzoate, 328 Sodium paraxylenesulphonate, 399 Sodium phenylenecarbonate, 299 Sodium quinate, 384 Sodium salicylate, 302 Sodium tetrahydroxyterephthalate, 520 Sodium a-toluquinonoximate, 51 Spineic acid, 285 Spiroyl hydride, 285 Spiroylous acid, 285 Spiroyhvasserstoffsaure, 285 Strontium hippurate, 189 Substitution products of benzyl alcohol and its derivatives, 98 Substitution products of anisic acid, 336 Substitution products of benzidene compounds, 143 Substitution products of benzylamines, 118 Substitution products of isophthalic acid, 481 Substitution products of metahydroxy- benzoic acid, 323 Substitution products of parahydroxy- benzoic acid, 334 Substitution products of salicyl-alde- hyde, 292 542 INDEX. Substitution products of salicylic acid, 313 Substitution products of terephthalic acid, 488 Substitution products of the xylenes, 392 Sulphamicphthalic anhydride, 477 Sulphamidobenzonitril, 272 a-Sulphamidometatoluic acid, 418 r-Sulphamidometatoluic acid, 418 Sulphamidoparatoluic acid, 421 Sulphinidephthalic acid, 477 Sulphobenzoic acid, 20 Sulphobenzoyl hydride, 138 a-Sulpho-isophthalic acid, 482 s-Sulpho-isophthalic acid, 482 Sulphometahydroxybenzoic acid, 325 Sulphoparahydroxybenzoic acid, 335 Sulphoparatoluic acid, 421 a-Sulphophthalic acid, 476 u-Sulphophthalic acid, 477 Sulphophthalic acids, 476 Sulphorthotoluic acid, 415 Sulphosalicylic acid, 318 Sulphoterephthalic acid, 490 Sulphur compounds of benzoyl, 170 Sulphur compounds of benzyl, 105 Symmetric a-diamido-azotoluene, 79 Symmetric /3-diamido-azotoluene, 79 Symmetric dibenzyl thiocarlamide, 124 Symmetric dibenzyl urea, 123 Symmetric dinitroparatoluidine, 71 Symmetric diphenylbenzenylamidine, 203 Symmetric ethylbenzoyl urea, 178 Symmetric metadihydroxy benzoic acid, 358 T. Tannates, 374 Tannic acid, 365, 371 Tannin, 371 ; properties, 373 Tartrophthalic acid, 470 Taurylic acid, 23 Telerythrin, 428 Terephthalaldehyde, 447 Terephthalaldehydic acid, 449 Terephthalamic acid, 485 Terephthalamide, 485 Terephthalic acid, 451, 483 ; addition products of, 486 ; substitution pro- ducts of, 488 Terephthalonitril, 485 Terephthalyl chloride, 485 Tetrabromolecanoric acid, 434 Tetrabromometaxylene, 394 Tetrabromomethane, 12 Tetrabromoparaxylene, 395 Tetrabiomophthalic acid, 473 Tetrabromorthoxylene, 394 Tetrabromoluenes, 12 Tetracetylhelicin, 289 Tetrachlorobenzal chloride, 8 Tetrachlorobenzidene chloride, 145 Tetrachlorobenzoic acid, 222 Tetrachlorobenzyl alcohol, 100 Tetrachlorobenzyl chloride, 101 Tetrachlorobenzenyl trichloride, 196 Tetrachlorocreocone, 36 Tetrachloroguaiacone, 36 Tetrachlorophthalic acid, 472 Tetrachlororthoxylene, 393 Tetrachlorotoluene, 10 Tetrachlorotoluquinone, 50 Tetrahydro-isophthalic acid, 481, 487 Tetrahydrometaxylene, 391 Tetrahydrophthalic acid, 470 Tetrahydroterephthalic acid, 486 Tetrahydrotoluene, 6 Tetrahydroxyhexhydrobenzoic acid, 383 Tetrahydroxyphthalic acids, 519 Tetrahydroxy terephthalic acid, 519 Tetrasalicylide, 308 Thallium metahydroxybenzoate, 321 Thallium salicylate, 303 Thiobenzaldine, 140 Thiobenzamide, 177 Thiobenzanilide, 178 Thiobenzoic acid, 170 Thiobenzoic anhydride, 171 Thiocresolo, 31 Thiometahydroxybenzoic acid, 325 Thio-opianic acid, 507 Thiophthalic anhydride, 462 Thiotoluidine, 72 Tolualdehydes, the, 413 Tolubenzaldehydine, 142 Toluene 3 et seq., properties, 5 Toluene, amido-derivatives of, 54 Toluene, antimony derivatives of, 86 Toluene, arsenic derivatives of, 84 Toluene, azo-derivatives of, 75 Toluene, boron and silicon derivatives of, 87 Toluene, diazo-derivatives of, 74 Toluenedisulphonic acids, 22 a-Toluenedisulphonic acid, 22 /3-Toluenedisulphonic acid, 22 y-Toluenedisulphonic acid, 22 Toluene group, 3 Toluene, hydrazine derivatives of, 75 Toluene, mercury derivatives of, 87 Toluene, phosphorus derivatives of, 83 Toluenemetasulphonamide, 21 Tolunemetasulphonic acid, 21 Toluenemetasulphonic chloride, 21 Toluenemonosulphonic acids, 20 Tolucneparasulphonamide, 21 Tolueneparasul phonic acid, 21 Tolueneparasulphonic chloride, 21 Toluene-orthosulphonic acid, 21 7-Toluenesulphonic acid, 22 Toluenesulphonic acids, 20 Toluenetrisulphonic acids, 22 Toluenyl alcohol, 412 Toluhydroquinone, 48 INDEX. 543 Toluic acids, 414 Toluidine, 4, 14, 111 Toluidinedisulphonic acid, 22 Toluidines, 54 Toluidines, halogen substitution pro- ducts of the, 67 Toluol, 386 Toluquinhy drone, 50 Toluquinol, 48 Toluquinol dimethyl ether, 48 Toluquinol monomethyl ether, 48 Toluquinone, 49 a-Toluquinone chlorimide, 51 Toluquinone, substitution products, 50 a-Toluquinonoxime, 50 j8-Toluquinonoxime, 51 j8-Toluquinonoxime acetate, 51 Toluquinon oxime compounds, 50 Toluric acid, 419 Tolusafranine, 80 Tolusafranine hydrochloride, 81 Tolusafranine nitrate, 81 Tolusafranine picrate, 81 Toluylene-blue, 82 Toluylene-red, 82 Toluylene-violet, 82 Tolyl, 410 Tolylarsenic acid, 85 Tolylboric acid, 87 Tolylenediamines, 72 Triacetoxymetaxylene, 403 Triacetylgallic acid, 370 Triamido-azobenzoic acid, 264 Tri-amidobenzoic acid, 260 Triamidometaxylene, 409 Tribenzhydroxylamine, 207 Tribenzhydroxylamine, 211 a-Tribenzhydroxylamine, 212 3-Tribenzhydroxylamine, 212 7-Tribenzhydroxylamine, 212 Tribenzidenediamine, 139 Tribenzo-arsenic acid, 85 Tribenzoyl phi oro-glucinol, 164 Tribenzylamine, 110, 115 Tribenzylamine, hydrochloride, 116 Tribenzylamine nitrate, 116 Tribenzylamine sulphate, 116 Tribenzylarsine, 126 Tribenzylarsine dichloride, 125 Tribenzylarsine oxide, 126 Tribenzarsenic acid, 278 Tribenzarsenious acid, 278 Tribenzylarsonium iodide, 126 Tribromobenzoic acids, 225 a-Tribromometaxylenol, 401 s-Tribromometaxylenol, 401 v-Tribromometaxylenol, 401 Tribromoparaxylenol, 401 Tribromophthalic acid, 473 Tribrom orcinol, 41 a-Tribromorthoxylenol, 400 Tribromotoluenes, 12 Tribromotoluquinone, 50 a-Trichlorobenzaldehyde, 145 3-Trichlorobenzaldehyde, 145 a-Trichlorobenzidene chloride, 145 /3-Trichlorobenzidene chloride, 145 a-Trichlorobenzoic acid, 222 £-Triehlorobenzoic acid, 222 7-Trichlorobenzoic acid, 222 Trichlorobenzoic acids, 222 Trichlorobenzyl alcohol, 100 Trichlorobenzyl chloride, 101 Trichlorobenzenyl trichloride, 196 Trichlorophthalic acid, 472 Trichlororcinol, 41 Trichlororthoxylene, 393 a-Trichlorotoluene, 10 /3-Trichlorotoluene, 10 Trichlorotoluquinone, 50 Triethyl benzylammonium iodide, 116 Triethylgallic acid, 369 Triethylhydroxyquinolcarboxylic acid, 380 Triethylpyrogallolcarboxylic acid, 379 Trihydroxybenzoic acids, 363 Trihydroxybenzoic acids, constitution of, 381 Trihydroxymetaxylene, 403 Trihydroxyphthalic acids, 519 Trihydroxytoluenes, 53 Trihydroxy-xylenes, 403 Tri-iodorcinol, 41 Tri-iodosalicylic acid, 315 Triketohexhydrobenzene, 518 Trimethylamido-anisic acid, 338 Trimethylamidobenzoic acid, 248 Trimethylamidosalicylic acid, 318 Trimethyl anise-betaine, 338 Trimethylene benzoate, 163 Trimethyl ether, 478 Trimethylhydroxyljuinolcarboxylic acid, 380 Trimethylorthotolylammonium iodide, 59 Trimethylparatolylammonium iodide, 65 Trimethyl phosphobenzobetaine, 276 Trinitro-amarine, 148 Trinitrobenzene, symmetric, 18 Trinitrobenzoic acid, 235 Tri nitrohydrobenzamide, 148 Trinitrometahydroxybenzoic acid, 324 s-Trinitrohydroxy toluic acid, 425 Tri nitrometacresol, 28 Trinitrometaxylene, 396 Trinitroparaxylene, 398 Trinitrophenyl benzoate, 164 Trinitro-orcinol, 42 Trinitro-orthoxylene, 396 a-Trinitrotoluene, 17 /3-Trinitrotoluene, 18 7-Trinitro toluene, 18 Trinitrotoluenes, 17 Triopianide, 505 Triparatolylarsine, 85 Triphenylbenzylphosphonium chloride, 125 544 INDEX Trisulphometahydroxybenzoic acid, 326 Trixylylamine, 413 Tuluol, 4 U. 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