3-Amino-4-hydroxybenzenesulfonic acid diazotization, and Naphthalen-2-ol coupling.
Purification Methods
Convert the acid to the monosodium salt by precipitation with NaOAc/AcOH buffer of pH 4, then purify by precipitation of the free acid from aqueous solution with conc HCl, washing and extracting with EtOH in a Soxhlet extractor. The acid precipitates on evaporating the EtOH and is reconverted to the sodium salt as described for Chlorazole Sky Blue FF. Dry it at 110o. It is hygroscopic. [Coates & Rigg Trans Faraday Soc 57 1088 1961, Beilstein 16 II 127.]
