Isocyanides

(isonitriles, carbylamines), organic compounds with the general formula R—N≡C structural isomers of the cyanides (esters of hydrocyanic acid, R—C≡N).

Isonitriles are colorless liquids with a specific, offensive odor. They are extremely toxic. The properties of some of them are given in Table 1.

Isocyanides are insoluble in water but soluble in alcohol and ether. They are resistant to the action of alkalies, but dilute acids rapidly hydrolyze them to primary amines (RNH2) and formic

acid (HCOOH). Mercuric oxide oxidizes them to isocyanates (R—N=C=0). When treated with sulfur they form esters of isothiocyanic acid (R—N=C=S). Treatment with chlorine yields carbylamine chloride (R—N=CCl2). Catalytically activated hydrogen reduces them to a methylamino group . Heat isomerizes isocyanides to cyanides.

Isocyanides can be prepared by treating a mixture of chloroform (CHCI3) and a primary amine (RNH₂) with an alcoholic alkali solution. The reaction provides a very sensitive qualitative means of detecting both amines and chloroform (as well as bromoform, CHBr₃), since the isocyanide formed is readily detected by its powerful characteristic smell (Hofmann test). Isocyanides are also prepared by the action of POCI₃ on formic acid monoalkylamides and by alkylating (by means of alkyl iodides) the silver, mercury, or lead salts of hydrocyanic acid (HCN).

Certain isocyanides are used to synthesize various nitrogen-containing substances (amides, nitriles, amino acids). Isocyanides were discovered by A. Hofmann in 1866.