How is Resorcine blue (CAS: 87495-30-5) typically synthesized?

Resorcine blue (CAS: 87495-30-5) is typically synthesized by the coupling of resorcinol with a diazonium salt. The process involves treating resorcinol with nitrous acid in the presence of an appropriate coupling agent to form the diazonium salt. Subsequently, this salt is coupled with a suitable aromatic amine to yield the desired blue dye. This method provides good yield and selectivity, although careful control of pH and temperature is necessary to achieve optimal results.