Reaction of Amines with Nitrous Acid

Primary aromatic amines react with nitrous acid to give diazonium salts and this reaction is known as diazotisation.

Nitrous acid is an unstable compound and can not be stored, so it is prepared during the reaction by mixing sodium nitrite and hydrochloric acid. The reaction is specifically carried out at low temperature between 273 - 278 K. For example, aniline reacts with nitrous acid to give benzene diazonium chloride.

Primary aliphatic amines also react in a similar way but the diazonium salts formed are unstable and decompose to give alcohols and nitrogen gas. Thus, ethanamine gives ethanol when subjected to this reaction.