4,5-Dihydroxynaphthalene-1-sulfonic acid [83-65-8]. (1,8-dihydroxynaphthalene-4- sulfonic acid), dioxy Chicago acid, dioxy S acid, C10H8O5S, Mr 240.2, is sparingly soluble in water, but the sodium salt is readily soluble. Heating with dilute sulfuric acid at 150℃ gives 1,8-dihydroxynaphthalene.
1-Hydroxynaphthalene-4,8- disulfonic acid is heated with 82 % caustic soda liquor for 3 h at 235℃. The melt is poured into excess hydrochloric acid and sulfur dioxide is expelled. After cooling, the product is filtered off and washed with brine; the yield is 83 %.
