Diazo Compounds

Diazo Compounds are a class of compounds which are characterised by the presence of two nitrogen atoms united to one another. The most important of the diazo-compounds are those of benzene derivatives and allied substances. The benzene diazo-compounds consist of the two nitrogens united on the one side to a benzene derivative and on the other to a monovalent radical - e.g. diazobenzene chloride is C₆H₅.N: N.Cl. These compounds are produced by the action of nitrous acid or a nitrite upon the salt of an amido-benzene derivative; thus from nitrate of aniline, C₆H₅NH₂.HNO₃ + HNO₂ = C₆H₅N: N.NO₃ (diazo-benzene nitrate) + 2OH₂. They are usually colourless, soluble crystalline bodies, but turn yellow or brown if exposed to the air. They are easily decomposed, and explode by concussion if heated.

They were discovered by Griess in 1859, and the discovery is one of the most fruitful and important of modern organic chemistry, as the compounds are invaluable in pure chemistry, since they furnish means of innumerable important synthetic and other reactions, and in applied chemistry, especially in the preparation of various dyes and coal-tar colours.