ANILINE, PHENYLAMINE or AMINOBENZENE, an organic base first obtained from the destructive distillation of indigo in 1826 by 0. Unverdorben, who named it Crystallin . In 1834, F. Runge isolated from coal-tar a sub stance which produced a beautiful blue colour on treatment with chloride of lime; this he named kyanol or cyanol. In 1841, C. J. Fritzsche showed that by treating indigo with caustic potash it yielded an oil, which he named aniline, from the specific name of one of the indigo-yielding plants, Indigo f era anil, anil being de rived from the Sanskrit nila, dark-blue, and nild, the indigo plant. About the same time N. N. Zinin found that on reducing nitroben zene a base was formed, which he named benzidam. A. W. von Hofmann investigated these variously prepared substances, and proved them to be identical, and thenceforth they took their place as one body, under the name aniline or phenylamine having the composition Pure aniline is a basic substance of an oily consistence, colourless, melting at —8° and boiling at 184° C; it dissolves in 31 parts of water. On exposure to air it absorbs oxygen and slowly resinifies, becoming deep brown in colour. It possesses a somewhat pleasant vinous odour and a burning aro matic taste ; it is highly poisonous, having a destructive action on the red corpuscles of the blood.
Aniline is a weak base and forms salts with the mineral acids. Aniline hydrochloride forms large colourless tables, which become greenish on exposure; it is the "aniline salt" of commerce. Al though aniline is but feebly basic, it precipitates zinc, aluminium and ferric hydroxides from their salts, and expels ammonia from ammonium compounds when warmed with them. When aniline hydrogen sulphate is baked at C sulphanilic acid, is produced. Anilides, compounds in which the amino-group is sub stituted by an acid radical, are prepared by heating aniline with certain acids; antifebrin or acetanilide (q.v.) is thus obtained from acetic acid and aniline. When aniline vapour and hydrogen are passed over finely divided nickel heated at 190° C., the reduction products, cyclohexylamine, dicyclohexylarine, and cyclohexyl aniline are produced. The oxidation of aniline has been carefully investigated. In alkaline solution azobenzene results, while ar senic acid produces the violet colouring matter, violaniline. Chromic acid converts it into quinone, while chlorates, in the presence of certain metallic salts (especially of vanadium), give aniline black. Hydrochloric acid and potassium chlorate give chloranil. Potassium permanganate oxidizes it, in alkaline solu tion to azobenzene ; Caro's acid, H2S05, converts it into nitro sobenzene. Hypochlorous acid gives para-amino-phenol and para amino-diphenylamine (E. Bamberger). Bleaching powder gives a purple coloration.
The great commercial value of aniline is due to the readiness with which it yields, directly or indirectly, valuable dyestuffs. The discovery of mauve in 1858 by Sir W. H. Perkin was the first of a series of dyestuffs which are now to be numbered by hundreds. Reference should be made to the articles DYES, SYNTHETIC; FUCHSINE; SAFRONINE; INDULINES, for more details on this sub ject. It is a starting-product for the manufacture not only of dyestuffs but of many drugs.
Aniline is manufactured by reducing nitrobenzene with iron borings and water slightly acidified with hydrochloric acid, the product being purified by steam distillation followed by distilla tion under reduced pressure. Monomethyl- and dimethyl-aniline are colourless liquids prepared by heating in an autoclave at 2 aniline, aniline hydrochloride and methyl alcohol, or aniline, methyl alcohol and about o.5% of iodine. They are of great im portance in the colour industry. Monomethylaniline boils at dimethylaniline at 192°. (See also AMINES.)