AN′IL. [Fr., Sp., L.] The indigof′era anil of botanists—one of the plants yielding ‘indigo’—a native of America, but now largely cultivated in the East Indies. See Indigo (and below).
AN′ILINE[64] (-een). [Eng., Fr.] C6H7N. Syn. Phenyl′amine; Anili′na, Anili′num, &c., L. A peculiar volatile organic base first noticed by Unverdorben in empyreumatic bone-oil, and afterwards obtained by Runge from coal-tar, and by Fritzsche, Zinin, A. W. Hofmann, and others, as a product of various reactions, processes, and decompositions, particularly those attending the destructive distillation of organic bodies.
[64] For a detailed account of the methods of preparing aniline commercially, and of the dyes obtained therefrom, see ‘Dictionnaire de Chimie,’ par A. Wurtz.
Prep. Aniline is now almost invariably obtained, on the large scale, either directly or indirectly from coal-tar or indigo; and chiefly from the basic oil or naphtha, or the nitrobenzol, of which the former is the principal source. The following are the leading commercial and experimental processes:
1. From COAL-TAR or COAL-TAR NAPHTHA:—The basic oil or basic portion of coal-tar or coal-tar naphtha, forming the latter, denser, and least volatile products of the distillation or rectification of these substances, is strongly agitated, for some time, along with hydrochloric acid in slight excess, a glass globe, or, on the large scale, a suitable vessel of lead, or of enamelled iron, being employed for the purpose; the clear portion of the liquid (containing the hydrochlorates of the bases present) is then decanted and carefully evaporated over an open fire until acrid fumes begin to be disengaged, when it is again decanted or filtered; the clear liquor, or filtrate is next treated with potash or milk of lime in excess, by which the bases—chiefly aniline and chinoline—are liberated under the form of a brownish oil; the whole of the resulting mixture is now submitted to distillation, the portion which passes over at or about 360° Fahr., and which consists chiefly of crude aniline, being collected separately; the product is purified by rectification and recollection, once or oftener, at the same temperature, and, lastly, by fresh treatment with hydrochloric acid and careful distillation with excess of potash, or milk of lime, as before.
2. From NITROBENZOL:—a. (Zinin.) An alcoholic solution of nitrobenzol, after saturation with ammonia, is treated with sulphuretted hydrogen, until, after some hours, a precipitation of sulphur takes place; the brown liquid is then repeatedly saturated with fresh sulphuretted hydrogen, until no more sulphur separates, the reaction being aided by occasionally heating or distilling the mixture; an excess of acid is next added, and, after filtering the liquid, and the removal of the alcohol and unaltered nitrobenzol by ebullition or distillation, the residuum is lastly distilled with caustic potash, in excess. The ANILINE found in the receiver may be rendered quite pure by forming it into oxalate of aniline, repeatedly crystallising the salt from alcohol, and finally distilling it with excess of caustic potassa, as before.
The following is a cheaper and more convenient process; and probably the best, or one of the best, that has yet been invented for obtaining aniline:—
b. (M. Béchamps.) From nitrobenzol distilled along with basic protacetate of iron; or, what is better, by distilling a mixture of iron-filings, 2 parts, and acetic acid, 1 part, with about an equal volume of nitrobenzol, the reaction being assisted, whenever the effervescence flags, by the application of a gentle heat. The liquor found in the receiver consists of aniline and water, from which the first, forming the lower portion, is obtained, after sufficient repose in a separator; or more easily, by adding a very little ether, which by dissolving in the aniline, causes it to rise to the surface, when it is at once decanted. A very spacious glass or earthenware retort must be employed in the process, as the mass swells up violently; and it must be connected with the receiver, on the small scale, by means of a Liebig’s condenser, and, on the large scale, by an ordinary worm-pipe and tub, kept in good action by a sufficient flow of cold water.
The apparatus for carrying out Béchamp’s method was devised by Nicholson, and is exhibited in the subjoined plate.
“It consists essentially of a cast-iron cylinder (A) of 10 hectolitres (220 cubic gallons) capacity. A stout iron tube is fitted to this