Fulminic Acid, CNOH

Fulminic Acid, CNOH, formed the subject of the first investigation of isomerism by Liebig and Wohler, since its salts were found to possess an identical qualitative and quantitative composition with those of cyanic acid. The mercuric salt of this acid is prepared by adding alcohol to a solution of mercury in excess of nitric acid; and the acid itself, which is exceedingly unstable, is obtained in ethereal solution when its mercuric salt, suspended in ether, is decomposed with dry hydrogen chloride. Fulminic acid is also formed and its silver salt obtained when aminomethylnitrosolic acid decomposes in presence of nitric acid and silver nitrate:

ONC(NH₂):N-OH → H₂O + N₂ + C:N-OH.

Methenylamino-oxime, when treated with nitric acid and silver nitrate, also yields silver fulminate:

CH(NH₂):N-OH → NH₃ + C:N-OH.

It has been shown by Nef and Scholl that the acid is carbyloxime, C=N-OH; Palazzo, however, regards it as tautomeric and a pseudo-acid:

HC≡N=O → C=N-OH.

It is named fulminic acid on account of its explosive properties, and its mercuric salt is much employed for the manufacture of detonators and explosive caps. In accordance with its explosive character, this acid is endothermic, the mercuric salt liberating 116,000 calories per gram molecule on its decomposition into mercury, nitrogen, and carbon monoxide. By the action of concentrated hydrochloric acid on mercuric fulminate the oxime of chloroformaldehyde, , results, whilst dilute acid produces hydroxylamine and formic acid. The spontaneous polymerisation of fulminic acid yields metafulminuric acid (isocyanuric acid), which is probably: