6,7-Dihydroxynaphthalene-2-sulfonic acid [92-27-3]. (2,3-dihydroxynaphthalene-6-sulfonic acid), dioxy R acid, C10H8O5S, Mr 240.2, is readily soluble in water. The sodium salt is sparingly soluble in cold water but readily soluble in hot water. Heating with dilute sulfuric acid at 190 C gives 2,3-dihydroxynaphthalene.
2-Hydroxynaphthalene-3,6- disulfonic acid is heated with 70 % caustic soda liquor for 4 h at 270℃, after which the reaction mixture is diluted with water and poured into excess hydrochloric acid. The precipitated product is filtered off and washed with brine; the yield is 90 %.
