White, crystalline scales. Soluble in hot water. 1-Hydroxynaphthalene-3,8-disulfonic acid [117-43-1]. (8-hydroxynaphthalene-1,6- disulfonic acid), epsilon acid, C10H8O7S2, Mr 304.3: the sodium salt crystallizes as the hexahydrate and is readily soluble in water. Alkali fusion at 200 ℃ gives 1,8-dihydroxynaphthalene-3-sulfonic acid and amination with ammonia and ammonium chloride at 170℃ gives 6,8-diaminonaphthalene-1-sulfonic acid. Diazo coupling takes place in the 2-position and bromination in the 4-position. The 1,8-sultone is formed on dehydration with concentrated sulfuric acid.
