AZOIMIDE or HYDRAZOIC ACID, a compound of nitrogen and hydrogen, first isolated in 1890 by Th. Cur tius, corresponding with diazoimino-benzene, (P. Griess, 1866), is prepared by adding ammonia to diazobenzene perbro mide.
Curtius found that either benzoylglycollic acid or ethyl ben zoate gave benzoylhydrazine with hydrazine hydrate. Benzoyl hydrazine gave a nitroso compound with nitrous acid, which changed spontaneously into benzoylazoimide by loss of water : The resulting benzoylazoimide was easily hydrolysed by boiling with alcoholic soda, when the addition of ether, precipitating sodium hydrazoate, was in a crystalline condition.
An improved method of preparation is based on the use of hippuric acid, which reacts with hydrazine hydrate to form hippurylhydrazine, and this sub stance is converted by nitrous acid into diazohippuramide, which is hydrolysed by the action of caustic alkalis with the production of salts of hydrazoic acid. To obtain the free acid it is best to hydrolyse the diazo hippuramide with dilute soda, the resulting liquid being distilled with dilute sulphuric acid. The pure acid may be obtained by fractional distillation as a colourless liquid with a penetrating odour causing throbbing of the temples; it boils at 30°C., and is extremely explosive. It is soluble in water, and the solution dissolves many metals (zinc, iron, etc.) with liberation of hydro gen and formation of salts (termed azoimides, azides or hydra zoates). The salts are explosive and readily interact with the alkyl iodides. In its properties hydrazoic acid shows some analogy with the halogen acids, since it forms difficultly soluble lead, silver and mercurous salts. The metallic salts all crystallize in the anhydrous condition and decompose on heating, leaving a residue of the pure metal. The acid is a "weak" acid, being ionized only to a very slight extent in dilute aqueous solution. Lead azide, is a powerful detonator employed in the mili tary services instead of mercury fulminate. (See EXPLOSIVES.) E. Noelting and E. Grandmougin (1891) obtained azoimide from 2 :4—dinitraniline, and from ortho- and para-nitro-anilines by converting either of these nitrated bases successively into diazomin salt, diazoperbromide and diazoimine, the last compound was hydrolysed by alcoholic potash and the resulting potassium azide distilled with dilute sulphuric acid.
W. Wislicenus (1892) prepared sodium azide by passing nitrous oxide over heated sodamide. The acid can also be obtained by the action of nitrous acid on hydrazine sulphate ; by the oxidation of hydrazine by hydrogen peroxide and sulphuric acid (A. W. Browne, 1905).
Ammonium azoimide, or and Hydrazine azoimide, are soluble, explosive salts.
Chloroazoimide, obtained by F. Raschig (1908), is a highly explosive colourless gas prepared by acidifying a mixture of sodium azide and hypochlorite with acetic or boric acid.
See Thorpe, Dictionary of Applied Chemistry, Azoimide, p. 496 (1921).