Sulfanilic acid is a component in diazonium salt formation, used in azo dye production. sulfanilic acid and sodium nitrite in an acidic solution is a diazotization reaction. This reaction forms a diazonium salt, which is a crucial intermediate in the synthesis of various azo dyes and other organic compounds.

In acidic conditions ( by using hydrochloric acid), sodium nitrite (NaNO2) reacts with sulfanilic acid (4-aminobenzenesulfonic acid) to form a diazonium salt. Specifically, the amino group on sulfanilic acid is converted to a diazonium group (–N2+)

4-aminobenzenesulfonic Acid