When primary aromatic amine is treated with nitrous acid in a cool solution, product is unstable compound, known as diazonium salt.
This reaction is known as diazotisation. Diazonium salts have the structure
Mechanism of diazotisation:
Illustration . Why ice cold condition have to be maintained in the diazotisation reaction of aniline?
Solution. Because benzene diazonium chloride is unstable and decomposes to give phenol above 278 K.
(i) mineral acid is added in excess in diazotization of arylamines.
(ii) Aryl diazonium ions are more stable than alkyl diazonium ions. Explain
Reactions of diazonium salts:
These salts give substitution reactions and coupling reactions as follows: