How is 4-Amino-3-hydroxy-1-naphthalenesulfonic acid (CAS: 116-63-2) typically synthesized?

4-Amino-3-hydroxy-1-naphthalenesulfonic acid is typically synthesized through a multi-step process involving the sulfonation of naphthalene, followed by nitration and reduction steps. The nitration introduces the sulfonic acid group and the amino group is introduced via reduction of the nitro group. Commonly used catalysts include sulfuric acid, and the process requires careful temperature and pH control to achieve high selectivity and yield.