13306-42-8

1-Aminonaphthalene-5,7-disulfonic acid [13306-42-8]. (5-aminonaphthalene-1,3- disulfonic acid), C10H9NO6S2, Mr 303.3, and its sodium salt are very soluble in water. Caustic fusion produces 1-amino-5-hydroxynaphthalene-7-sulfonic acid, and sulfonation (40 % oleum, 130 C) yields 1-aminonaphthalene2,5,7-trisulfonic acid.

1-Aminonaphthalene-5-sulfonic acid in sulfuric acid solution is treated with 65 % oleum, and the mixture is heated at 120℃ for 4 h. The sulfonation mass, which contains mainly the 2,5,7-trisulfonic acid, is diluted with water, and the batch is heated at 130℃ for 10 h to cause desulfonation. The product crystallizes on cooling and, after isolation, is deacidified by treatment of the solution with lime. The final sodium salt solution is used directly for production of 1-amino-5-hydroxynaphthalene-7-sulfonic acid.