Chemistry

CHEMISTRY] ).

Diamines.—Thediamines contain two amino-groups and are of importance because two of them are identical with the pto maines produced by the putrefactive action of bacteria on albumen and other related substances. Ethylenediamine, may be prepared by heating ethylene dibromide with alcoholic am monia to 100° C (F. S. Cloez, 1853) ; or by the action of tin and hydrochloric acid on cyanogen (T. Fairley, 1864) . It is an alkaline liquid, which when anhydrous boils at 116.5 ° C. Nitrous acid con verts it into ethylene oxide. It combines directly with many metallic salts. (S. F. Jorgensen, 1889.) Trimethylenediamine, prepared by the action of ammonia on tri methylene bromide (E. Fischer, 1884) is a liquid which boils at 135-136° C. Tetramethylenediamine (putrescine), is prepared by reducing ethylene dicyanide (succinonitrile) with sodium in absolute alcoholic solution (A. Ladenburg, 1886).

It melts at 2 7 ° C and is easily soluble in water. Pentamethylene diamine (cadaverine), is prepared by reducing trimethylene cyanide in ether solution by zinc and hydrochloric acid (A. Ladenburg, 1883). Cadaverine is a syrup at ordinary temperatures and boils at 178-179° C. It is readily soluble in water and alcohol, but only slightly soluble in ether.

Aromatic Amines.

Thearomatic amines in some respects re semble the aliphatic amines, since they form salts with acids, and double salts with platinum chloride, and also distil without decom position. On the other hand, they are much weaker bases than the aliphatic amines, their salts undergoing hydrolytic dissociation in aqueous solution. The primary aromatic amines may be prepared by the reduction of the nitro-hydrocarbons, the reducing agents used being either alcoholic ammonium sulphide (N. Zinin), zinc and hydrochloric acid (A. W. Hofmann), an alcoholic solution of stannous chloride containing hydrochloric acid (R. Anschutz, 1886), tin and hydrochloric acid, or on the manufacturing scale iron and water acidified by hydrochloric acid. They may also be obtained by the reduction of nitroso compounds and of azo- and hydrazo-compounds and of hydrazones, by distilling the amino acids with lime, by heating phenols with ammonio-zinc chloride (V. Merz, 188o), and by heating the secondary and tertiary bases with concentrated hydrochloric acid to about 18o° C. At about 300-400° C the alkyl chloride formed in this reaction attacks the benzene nucleus and replaces hydrogen by an alkyl group or groups, forming primary amines homologous with the original amine ; thus methylaniline hydrochloride is converted into para and ortho-toluidine hydrochloride, and phenyltrimethylammonium iodide is converted into mesidine hydriodide.

The primary aromatic amines are colourless liquids or crystal line solids which are sparingly soluble in water, but readily soluble in the common organic solvents. When heated with alkyl or aryl iodides they are converted into secondary and tertiary amines. When heated with concentrated sulphuric acid they become sul phonated. They form condensation products with aldehydes, benzaldehyde and aniline giving rise to benzylideneaniline, and when heated with organic acids forming ani lides. They give the isonitrile reaction (see above) when warmed with chloroform and a caustic alkali, and form alkyl thioureas when heated with an alcoholic solution of carbon bisulphide. When warmed with a solution of nitrous acid, they are converted into phenols; if, however, nitrous acid be added to an ice-cold solution of a primary amine in excess of mineral acid, a diazonium salt is formed (see ANILINE, AZO-COMPOUNDS and DIAzo-COMPouNDs).

The secondary amines may be of two types—namely, the purely aromatic amines, and the mixed secondary amines, which contain an aromatic residue and an alkyl group. The purely aromatic amines are obtained by heating the primary amines with their hy drochlorides, and, in some cases, by heating a phenol with a primary aromatic amine and a catalyst (anhydrous zinc chloride or 1 of iodine). The mixed secondary amines are prepared by the action of alkyl iodides on the primary amines, or by heating salts of the primary amine with alcohols under pressure. (See ANILINE.) The mixed secondary amines have basic properties, but the purely aromatic secondary amines are only very feeble bases. Both classes readily exchange the imide hydrogen for acid radicals and give nitrosamines with nitrous acid.

The tertiary amines may also be of two types, the purely aromatic and the mixed type. The mixed tertiary amines are produced by the action of alkyl halides on the primary amines. The simplest aromatic tertiary amine, triphenylamine, is prepared by the action of brombenzene on sodium diphenylamine (C. Hey drich, 1885).

Benzylamine, may be prepared by reducing benzonitrile in alcoholic solution with zinc and acetic acid (O. Mendius, 1862), or by metallic sodium (E. Bamberger, 1887). It can also be obtained together with di- and tri-benzylamines by the action of ammonia on benzyl chloride (S. Cannizzaro, 1865) . It is a liquid which boils at 183° C, has a strongly alkaline reaction, and is miscible in all proportions with water, alcohol and ether. Diphenylamine, the simplest representative of the true aromatic secondary amines is prepared by heating aniline and aniline hydrochloride for some hours to 2Io-24o° C (Ch. Girard and G. de Laire, 1866). It crystallizes in white plates, which melt at 45° C and boil at 302° C.

Aromatic Diamines.

Thesimplest aromatic diamines are prepared by reducing the three nitranilines. Ortho-phenylenedia mine, crystallizes from water in plates, which melt at I o2-103 ° C and boil at 2 5 6-2 58 ° C. The ortho-diamines are characterized by the large number of condensation products they form (see IMINAZOLES, QUINOXALINES, etc.). Meta-phenylenedia mine crystallizes in rhombic plates which melt at 63° C and boil at 287° C. It is easily soluble in water and alcohol. Para-phenyl enediamine may be prepared as above, and also by the reduction of aminoazobenzene. It crystallizes in tables which melt at 14o° C and boil at 267° C. When heated with io% hydrochloric acid to 18o° C the three diamines yield the corresponding dihydroxy benzenes (J. Meyer, 1897). The three classes of aromatic diamines may be distinguished by their behaviour towards nitrous acid. The ortho-compounds condense to azimino benzenes, the meta-compounds yield azo-dyestuffs and the para-compounds yield bis-diazo compounds of the type XN2.C6H4.N2X. (See DIAZo