Azo coupling reactions are a major class of organic chemical reactions that are utilized to prepare several organic molecules, especially organic dyes such as methyl orange. Azo compounds are characterized by their colors due to possessing electronically conjugated systems within their chemical structure. They have a broad range of colors that depend on the structure of each dye.
Azo coupling reactions occur through the electrophilic attack of diazonium ions on electron rich aromatic rings containing compounds such as phenols and aromatic amines. Electrophilic diazonium ions should be freshly prepared just prior to use in azo coupling reactions as they are unstable. Moreover, their stability can be increased through their keeping in an ice bath.
Diazonium ions can be prepared through the reaction between sodium nitrite and primary aromatic amines in the acidic medium at low temperature as shown in the below scheme.
Figure 1. Diazonium ion formation.
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Azo coupling reaction is carried out through diazotization of some phenolic and aromatic amines compounds such as 1-naphthol, 2-naphthol & N,N-dimethylaniline to prepare some colored dyes such as methyl orange.
