Copper (II) sulphate pentahydrate (0.16 g, 0.00064 mol) and lactose monohydrate (2.9 g, 0.008 mol) are added to a mixture of bromaminic acid sodium salt (38.2 g, 0.1 mol) and benzene sulphonamide (17.3 g, 0.11 mol) in water (250 ml) containing sodium carbonate (3.8 g) and sodium bicarbonate (19.0 g). The mixture which has a pH of 8.5-9.0, is heated to 70° C. and stirred at this temperature for 5 hours. The resulting mixture is diluted with water to a volume of 750 ml and cooled to 40° C. The solid product is filtered off and washed with a solution of sodium chloride (12 g) in water (1300 ml) to give a 95% yield of 1-amino-4-phenylsulphonamido-anthraquinone-2-sulphonic acid sodium salt, a product of formula I where M denotes sodium and R denotes a group of formula III.
