Azo coupling reaction of diazonium salts of aromatic amines
Benzene diazonium chloride couples with electron rich aromatic compounds like phenols and anilines to give azo compounds.
The azo compounds contain -N=N- bond and the reaction is called coupling reaction.
Benzene diazonium chloride + phenol gives p-Hydroxyazobenzene (colour yellow).
Benzene diazonium chloride + aniline gives p-Aminoazobenzene (orange).
Coupling occurs para to hydroxy or amino group.
All azo compounds are strongly coloured and are used as dyes.
Methyl orange is an important dye obtained by coupling the diazonium salt of sulphanilic acid with N,N-dimethylaniline.