2-Hydroxynaphthalene-3,7-disulfonic acid [6361-38-2]. (3-hydroxynaphthalene-2,6- disulfonic acid), C10H8O7S2, Mr 304.3: the alkali-metal salts of 85 are readily soluble in water, but its barium salt is only sparingly soluble even at 100 ℃. Sulfonation with 20 % oleum at 85℃ gives mainly 2-hydroxynaphthalene-1,3,7-trisulfonic acid. Amination yields 2-aminonaphthalene-3,7-disulfonic acid, and caustic fusion yields 2,7-dihydroxynaphthalene-3-sulfonic acid. Diazo coupling takes place in the 1-position.
2-Hydroxynaphthalene-7-sulfonic acid is heated at 120℃ with concentrated sulfuric acid for 12 h, the mixture is poured into water, and the product is separated after liming out.
