1-Aminonaphthalene-4,6-disulfonic acid [85-74-5]. (4-aminonaphthalene-1,7-disulfonic acid), Dahl’s acid II, C10H9NO6S2, Mr 303.3, and its alkali-metal salts are soluble in water; the calcium salt is soluble in aqueous ethanol. Caustic fusion at 180℃ yields 1-amino-6-hydroxynaphthalene-4-sulfonic acid, but at higher temperature 4,7-dihydroxynaphthalene1-sulfonic acid is formed. Sulfonation with 35 % oleum at 80℃ gives 1-aminonaphthalene-2,4,6-trisulfonic acid.
Naphthionic acid is sulfonated with 25 % oleum at 20℃ to give a 70 : 30 mixture of 1,4,7- and 1,4,6-trisulfonic acids, which is used as mixed Dahl’s acids.
