2-Hydroxynaphthalene-5,7-disulfonic acid [575-05-3]. (6-hydroxynaphthalene-1,3- disulfonic acid), C10H8O7S2, Mr 304.3, and its alkali-metal salts are readily soluble in water. Diazo coupling takes place in the 1-position.
The acid has some use as an azo coupling component and as an intermediate in the production of 2,5-dihydroxynaphthalene-7- sulfonic acid.
2-Aminonaphthalene-5,7-disulfonic acid is heated with 5 % sulfuric acid for 15 h at 185℃ under pressure. After liming out and removal of ammonia and calcium ions, the product is obtained as a solution of the sodium salt for further use.
