2-Hydroxy-3,6-naphthalenedisulfonic acid

2-Hydroxynaphthalene-3,6-disulfonic acid [148-75-4]. (3-hydroxynaphthalene-2,7- disulfonic acid), R acid, C10H8O7S2, Mr 304.3, is readily soluble in water and ethanol. Although the sodium salt (R salt) is soluble in water, it can be precipitated by sodium chloride. The barium salt is sparingly soluble in cold water but is 8 % soluble in boiling water. Whereas sulfonation with 20 % oleum yields 2-hydroxynaphthalene3,6,8-trisulfonic acid, the reaction with Na2SO3– MnO2 gives 2-hydroxy-1,3,6-trisulfonic acid. Alkali fusion with sodium hydroxide gives 2,3-dihydroxynaphthalene-6-sulfonic acid and some 2,3-dihydroxynaphthalene. Amination (Bucherer) produces 2-aminonaphthalene-3,6- disulfonic acid. Diazo coupling and nitrosation take place in the 1-position.