Dizonium coupling

Diazonium Coupling (Diazo Coupling, Azo Coupling)

An azo coupling is an organic reaction between a diazonium compound and another aromatic compound that produces an azo compound. Nitrogen is used to make a bridge between two benzene rings.

Dizonium compound + Aromatic compound = Azo compound

 

This is basically an electrophilic aromatic substitution reaction. Due to the positive charge on the terminal nitrogen of the -N=N⁺ group, dizonium cation may participate as an electrophile. As a result, two aromatic compounds are coupled by a -N=N- group. This is known as the azo group (diazo group). The corresponding reaction is called diazonium coupling (diazo coupling, azo coupling).

Examples of Coupling Reactions:

1)   Reaction with Phenol

Phenol is dissolved insodium hydroxide solution to give a solution of sodium phenoxide.

When this phenoxide ion reacts with dizonium ion, an azo compound is formed in which two benzene rings are linked by a nitrogen bridge.

2)   Reaction with Phenylamine (aniline)

The reaction of aniline with dizonium salt produced a yellow solid known as aniline yellow.

 

Uses: Azo coupling is the most widely used industrial reaction in the production of dyes, lakes and pigments. 

Limitation:  The electrophilicity of diazonium ions is only relatively weak, as their positive charge is delocalized over the two nitrogen atoms.

The unsubstituted benzenediazonium cation may react only with strongly activated aromatic compounds, such as phenolates and amines, The substitution normally occurs at the para position, except when this position is already occupied, in which case ortho position is favoured. .