1.71 g (4 mmol) of 3-(5-chloro-2-methoxybenzamido)-6-sulfamoyl-7-methoxychroman were heated at 80° C. for 30 minutes in 10 ml of dry DMSO after addition of 0.4 g (10 mmol) of freshly powdered sodium hydroxide and 1.05 g (6 mmol) of N-methyltrichloroacetamide. The cooled reaction mixture was introduced into ice-water, clarified with active charcoal and acidified to pH 1. The precipitate was filtered off with suction, dried and recrystallized twice from ethanol. The product had a melting point of 256°-257° C.
