Copper (II) sulphate pentahydrate (0.122 g, 0.0005 mol) and glucose monohydrate (1.6 g, 0.008 mol) are added to a mixture of bromaminic acid sodium salt (38.2 g, 0.1 mol) and p-toluenesulphonamide (18.8 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, 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 99% yield of 1-amino-4-(4'-methylphenylsulphonamido)-anthraquinone-2-sulphonic acid sodium salt - a product of formula I where M denotes sodium and R denotes a group of formula IV. Analysis shows that the filtrate and washing liquid contain only 0.0025 mol of copper per mol of bromaminic salt starting material. Part of the solid product (25.5 g, 0.054 mol) is added to a solution of sodium hydroxide (62 g, 1.55 mol) in methanol (200 ml). The mixture is heated under reflux for 10 hours, then diluted with water to a volume of 900 ml at 70° C. 98% sulphuric acid is added to reduce the pH of the mixture to 6.0-7.0 and the mixture is heated at 70° C.-75° C. for 30 minutes. The solid product obtained is filtered off and washed with water at 40° C. (1000 ml) to give a substantially quantitative yield of 1-amino-4-(4'-methylphenylsulphonamido)-2-methoxyanthraquinone (C.I. Disperse Red 86). Analysis shows that the filtrate and washings contain only 0.0015 mol of copper per mol of bromaminic salt, while the product contains only 0.001 mol of copper per mol of bromaminic salt.
