Diazo coupling is useful to prepare dyes. Diazo coupling reactions mainly composes of Diazonium Salts. The diazonium salts the class of organic compounds with general formula R−N2+X− where X is an organic or inorganic anion (for example, Cl–, Br–, BF4–, etc.) and R is an alkyl or aryl group.
The chemical method used to transform a primary aromatic amine into the amine‘s equivalent diazonium salt is generally called diazotization. The preparation of these diazonium salts typically includes the reaction of an aromatic amine-containing nitrous acid in the presence of another compound. They find application in the dye and pigment industries and are used to produce dyed fabrics.