AMINES, in chemistry, derivatives of ammonia (q.v.) in which one or more of the three hydrogen atoms are replaced by alkyl or aryl groups. The replacement of one hydrogen atom by one alkyl or aryl group gives rise to primary amines; of two hydrogen atoms by two groups to secondary amines; of three hydrogen atoms by three groups to tertiary amines. The tertiary amines possess the power of combining with one molecular pro portion of an alkyl iodide to form quaternary ammonium salts. The structural relations of these compounds may be shown thus: Aliphatic Amines.—These compounds possess properties very similar to those of ammonia, the lowest members of the series being combustible gases readily soluble in water. The next higher members of the series are liquids of low boiling point also readily soluble in water, the solubility and volatility, how ever, decreasing with the increasing carbon content of the mole cule until the highest members of the series are odourless solids of high boiling point and are insoluble in water. They are all strong bases, readily forming salts with the mineral acids, and double salts with the chlorides of gold, platinum and mercury. They are ionized in aqueous solution to a much greater extent than ammonia, the quaternary ammonium bases being the most ionized.
Many methods have been devised for the preparation of primary amines, methylamine having been isolated in 1849 by A. Wurtz on boiling methyl isocyanate with caustic potash, The other methods are:— the reduction of nitriles with alcohol and sodium (A. Ladenburg, 1886) ; heating the esters of nitric acid with alcoholic ammonia at zoo° C (0. Wallach, 1881) ; the action of reducing agents on nitro-paraffins; the action of zinc and hydrochloric acid on alde hyde-ammonias ; the reduction of phenylhydrazones and oximes of aldehydes and ketones with sodium amalgam in the presence of alcohol and sodium acetate (J. Tafel, and H. Goldschmidt, 1886) the acidic hydrolysis of the isonitriles, R•NC-f- 2H,0 = heating the mustard oils with a mineral acid; the hydrolysis of the alkyl phthalimides (S. Gabriel, 1887) ; distil lation of the amino-acids with baryta ; the action of bromine and caustic potash on the acid-amides (A. W. Hofmann, 1885) ; and the hydrolysis of substituted urethanes (Th. Curtius, 1894).
The secondary amines are prepared, together with the primary and tertiary, by the action of ammonia on the alkyl iodides (see below), or by the hydrolysis of para-nitroso derivatives of tertiary aromatic amines, such as para-nitrosodimethylaniline, thus: By the action of ammonia on the alkyl iodides a complex mix ture of primary, secondary and tertiary amines, along with a quaternary ammonium salt, is obtained, the separation of which is difficult. The method worked out by A. W. Hofmann in 185o for the ethylamines is as follows:—the mixture is distilled with caus tic potash, when the primary, secondary and tertiary amines dis til over, and the quaternary ammonium salt remains behind un affected. The aqueous solution of the amines is now shaken with diethyl oxalate, when the primary amine forms a crystalline dial kyloxamide and the secondary amine an insoluble liquid, which is an ethyl dialkyloxamate, the tertiary amine not reacting: -{- = -}- -? = The tertiary amine is then distilled off, the residual products separated by filtration and finally hydrolysed by a caustic alkali.
A more general method due to 0. Hinsberg (189o) consists in treating the mixed bases with benzene sulphonic chloride (or p toluene sulphonic chloride). The primary base gives an acidic de rivative, soluble in aqueous alkali, the secondary base furnishes the compound, insoluble in alkali, whereas the tertiary base does not react, the process is applicable to both aliphatic and aromatic amines.
The primary, secondary and tertiary amines may be readily distinguished by their behaviour with various reagents. Primary amines when heated with alcoholic potash and chloroform yield isonitriles, which are readily detected by their offensive smell. The secondary and tertiary amines do not give this reaction. With nitrous acid, the primary amines yield alcohols, the secondary amines yield nitrosamines and the tertiary amines do not react : -}- ONOH = R.OH -I- -}- H.,0 ; ONOH = R,N•NO + The condensation with benzene sulphonic chlo ride in the presence of alkali also furnishes a method of diagnosis (see above). Primary amines heated with carbon disulphide in alcoholic solution are converted into mustard oils, when the dithiocarbamate first produced is heated with a solution of mer curic chloride. Primary and secondary amines condense with o-xyxylene dibromide giving two and one molecular proportions of hydrogen bromide, respectively. Tertiary aliphatic amines form additive compounds with this reagent (Scholtz 1898).
Methylamine, occurring in Mercurialis perennis, in bone-oil and herring brine, is also a decomposition product of many alkaloids. At ordinary temperatures it is a gas with a strong ammoniacal smell, burns readily and is exceedingly soluble in water. Dimethylamine found in Peruvian guano, is a heavy vapour which liquefies at 7° C and has a strong fish-like smell. Trimethylamine is a vapour very similar to dimethylamine, but liquefies at 3.2-3.8° C. It is usually ob tained from "vinasses," the residue obtained from the distillation of beet sugar alcohol. The three methylamines can be ob tained from ammonia and form aldehyde solution and a suitable separation for each of the three has been devised by E. Werner (191 7) . Tetramethylammonium iodide, N the chief prod uct obtained by the action of methyl iodide on ammonia (Hof mann), crystallizes in quadratic prisms and has a bitter taste. By warming its aqueous solution with an excess of silver oxide, it is converted into tetramethylammonium hydroxide which crystallizes in hygroscopic needles, and has a very alkaline reaction. This hydroxide forms many crystalline salts, absorbs carbon dioxide and precipitates many metallic hydroxides. On dry distillation it is decomposed into trimethylamine and methyl alcohol. If the nitrogen atom in a quaternary ammonium salt is in combination with four different groups, then the molecule is asymmetric, and the salt can be resolved into optically active enantiamorphous isomerides (W. J. Pope, 1901 [see STEREO