General procedure for the synthesis of 1,8-naphthalenesulfonolactam from 1,8-naphthalenesulfonic acid potassium salt (CAS: 16619-06-0): 5 g of 1,8-naphthalenesulfonic acid potassium salt was pulverized and placed in a flask containing 15 g of POCl3. After installation of a reflux condenser, the reaction system is heated in an oil bath to 130°C. When the temperature reaches 100°C, HCl gas starts to be released, which has to be discharged through the flue. To facilitate the reaction, the flask was shaken periodically. After the release of irritating gases stops, the heating is continued until the reaction mixture no longer produces dye in the diazotization and color development test, usually for a reaction time of 3 hours. Due to the slurry-like consistency of the reaction mixture, caution is required to remove excess POCl3. Subsequently, the reaction mixture is quenched by slowly pouring it into an ice bath. The gray solid product was collected by diafiltration and washed repeatedly with water to remove most of the phosphoric acid. The crude product was dried and purified by recrystallization with benzene. Product melting point: 175-180°C; 1H NMR (DMSO-d6, 300 MHz) δ: 8.62 (d, 1H, J = 8.0 Hz), 8.12 (d, 1H, J = 8.0 Hz), 7.75-7.74 (m, 1H), 7.61 (d, 1H, J = 8.0 Hz), 7.32 (dd, 1H, J = 7.5, 6.7 Hz), 6.7 Hz), 6.7 Hz). 6.7 Hz), 6.90 (d, 1H, J = 6.8 Hz), 5.36 (s, 1H); MS (EI): m/z 206 (M++H).
