1-Hydroxynaphthalene-8-sulfonic acid

1-Hydroxynaphthalene-8-sulfonic acid [117-22-6]. (8-hydroxynaphthalene-1-sulfonic acid), C10H8O4S, Mr 224.2, crystallizes as the monohydrate with mp 106℃. Sulfonation gives 1-hydroxynaphthalene-4,8-disulfonic acid, and alkali fusion with potassium hydroxide at 230℃ yields 1,8-dihydroxynaphthalene. Coupling with diazo compounds occurs in the 2- position.

The naphthosultone is usually satisfactory as an intermediate for further processing; however, for azo dye preparation the free naphthol must be used, for example, in C.I. Acid Black 54 and C.I. Acid Blue 158.

1-Aminonaphthalene-8-sulfonic acid is diazotized over 16 h at 50℃ and then heated to 80 ℃. After cooling, the precipitated naphthosultone is filtered off and washed. The sultone is heated with dilute sodium hydroxide at 100℃, which causes ring opening; the product is isolated after salting out.