An azo coupling is an organic reaction between a diazonium compound and an aniline, phenol or other aromatic compound which produces an azo compound. In this reaction the diazonium salt is an electrophile and the activated arene is a nucleophile in an electrophilic aromatic substitution. In most cases, including the example below, the diazonium compound is also aromatic. The product will absorb longer wavelengths of light than the reactants because of increased conjugation.
Azo couplings are important in the production of dyes and pH indicators such as methyl red and pigment red 170. Prontosil and other sulfa drugs are also produced using this reaction.
Further reading
- J. L. Hartwell and Louis F. Fieser. "Coupling of o-tolidine and Chicago acid". Org. Synth.; Coll. Vol. 2: 145.
- H. T. Clarke and W. R. Kirner. "Methyl red". Org. Synth.; Coll. Vol. 1: 374.
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