2-Hydroxynaphthalene- 4 -sulfonic acid [6357-85-3]. (3-hydroxynaphthalene-1- sulfonic acid), C10H8O4S, Mr 224.2, and its salts are extremely soluble in water and difficult to isolate. It undergoes nitrosation and couples with diazo compounds in the 1-position. Sulfonation with oleum gives 2-hydroxynaphthalene-4,8-disulfonic acid. Amination with ammonia under pressure gives 2-aminonaphthalene-4-sulfonic acid.
2-Hydroxynaphthalene-4,8- disulfonic acid is heated with dilute sulfuric acid at 190℃ for 10 h in an autoclave under pressure. After cooling, a small quantity of 2-naphthol is filtered off and sulfuric acid is removed by liming. The resulting solution of the calcium salt of the product is converted to the sodium salt, which is used directly as a solution or evaporated to isolate the product.
