5,6-diaminonaphthalene-1-sulphonic acid

5,6-Diaminonaphthalene-1-sulfonic acid is used as an intermediate for naphthotriazoles. A green pigment (C.I. Pigment Green 9) is obtained by treatment with iron(III) salts.

1-Aminonaphthalene-5-sulfonic acid is coupled with diazotized aniline, and the resulting isolated azo compound (purpurin base) is reduced by heating with zinc and ammonia at 100℃ and allowing ammonia and aniline to distill off. The product 5,6-diaminonaphthalene-1-sulphonic acid is isolated in 76 % yield by acidification of the screened liquors.