grey to grey-brown granular powder
Sulfonation gives 1-amino-7-hydroxynaphthalene-4-sulfonic acid. The N-acetyl derivative is an important coupling component for after-chrome and metal-complex dyes, e.g., C.I. Mordant Black 38 and C.I. Acid Black 60.
The sodium salt of 1-aminonaphthalene-7-sulfonic acid is added to 80 % potassium hydroxide at 210℃, and the reaction is completed by heating for 6 h at 230℃. After dilution and careful acidification with hydrochloric acid, the acid solution is screened to remove impurities and neutralized to precipitate 159 in 80 % yield (mp 207℃).
