489-78-1

1-Amino-5-hydroxynaphthalene-7-sulfonic acid [489-78-1].  (8-amino-4-hydroxynaphthalene-2-sulfonic acid), M acid, C10H9NO4S, Mr 239.2, and its sodium salt are sparingly soluble in water. Coupling with diazo compounds takes place under acidic and alkaline conditions, but a bisazo derivative cannot be obtained. Reaction with bisulfite gives 4,8-dihydroxynaphthalene-2-sulfonic acid.

1-Aminonaphthalene-5,7-disulfonic acid is heated with concentrated sodium hydroxide for 16 h at 172 – 176℃. After the reaction mixture is quenched, acidified, and purged of sulfur dioxide, the product is isolated in 80 % yield.