The preparation of Sodium 4-amino-1-naphthalenesulfonate is as follows:To a suspension of 4-amino-l -naphthalene sulfonic acid (10.Og, 44.8 mmol) in 10 ml MeOH was added 5 N NaOMe (9 ml). The mixture was sonicated to effect complete solution. The solvent was evaporated to provide the sodium salt of -amino-1- naphthalene sulfonic acid as a white solid. This solid was suspended in 100 ml acetic anhydride and heated at 110 °C for 2 1/2 h. Adding some MeOH to the cooled mixture and co-evaporating with 3x100 ml toluene gave the Na-salt of 4-acetamidonaphthalene-l -sulfonic acid as a white powder.
