A Review on Traditional and Modern Methods for the Synthesis of Aromatic Azo Compounds

Aromatic azo compounds are "derivatives of diazene/diimide", wherein the two hydrogens are substituted by phenyl groups. Azo compounds are very important universal scaffolds that show multiple applications in many areas of science, mainly chemical industries, where they are used in the synthesis of organic dyes, pigments, food additives, indicators, etc. They also remarkably exhibit various potential applications in the fields of pharmaceuticals, electronics, optics, etc., because of their fascinating photophysical properties. Moreover, several azo compounds have been strongly utilized as chemosensors, diagnostic probes, radical initiators, nanotubes, and building blocks of various polymers as well as natural products. This interesting and immense importance of the azo compounds has attracted the attention of researchers to establish novel synthetic routes to synthesize these important scaffolds. In organic chemistry, azo compounds can be synthesized by various methods utilizing coupling reactions with the aid of a catalyst or sometimes in the absence of it. The main purpose of writing this review was to provide a summary of the synthesis of both symmetric and asymmetric azobenzenes via various traditional and recently developed oxidative azo-coupling reactions.