Azo coupling

Azo coupling is electrophilic aromatic substitution reaction with the aryldiazonium salts ( diazo component) with activated aromatics ( = coupling component ), β -dicarbonyl compounds, pyrazoles and 2- pyridinones reacted ( " coupled " ) to be. Due to the only low electrophilicity of the diazonium ion, the coupling can only take place as a second substitution in a strong M Erstsubstituenten and this preferred by the M effect in the para position.

General reaction equation:

Where X is usually Cl.

C azo couplings at temperatures ranging from 0 ° C to 5 ° carried out, since the diazonium salts used are faster decomposition at higher temperatures. Work is underway in the weakly acidic to moderately alkaline range depending on the starting material.

Characteristic of this reaction is the formation of an azo bond (Ar -N = N- Ar ', derivatives of diazene, H -N = N -H). The resulting azo compounds have strong absorption bands in the visible light range, and are therefore dyes. Many of them are widely used as so-called azo dyes.

Reaction mechanism

Following the example of the azo coupling reaction of N, N-dimethylaniline is represented as a diazotized aromatic -activated benzene derivatives to the dye butter yellow: