Benzenediazonium chloride

Benzenediazonium chloride is the diazonium compound of aniline. It is used in the preparation of azo compounds (e.g. azo dyes). It is synthesised from nitrous acid and aniline. Nitrous acid is prepared in situ due to the fact that it is not stable enough to be stored.

Synthesis
Preparation of nitrous acid:


 * NaNO2 + HCl → HNO2 + NaCl

The nitrous acid formed is reacted with aniline to give benzenediazonium chloride:


 * C6H5NH2 + HNO2 + HCl → [C6H5N+≡N][Cl−]

The temperature must be kept between 0-5 °C to avoid the product from reacting and forming dinitrogen.

Diazo coupling reactions
Benzenediazonium chloride can react with phenol or aniline, via diazo coupling reactions, to give azo compounds: