3-Chloro-4-hydroxybenzenesulfonic acid is prepared by chlorination of 4-hydroxybenzenesulfonic acid or by sulfonation of 2-chlorophenol with 98% sulfuric acid. The compound can be converted by nitration into 3-chloro-4-hydroxy-5-nitrobenzenesulfonic acid, from which 3-amino-5-chloro-4- hydroxybenzenesulfonic acid is obtained by reduction. The sulfonic acid group is eliminated easily at 180 – 190℃.
