[S:1]([OH:11])(=[O:10])([C:3]1[CH:8]=[CH:7][C:6]([NH2:9])=[CH:5][CH:4]=1)=[O:2].N([O-])=O.[Na+].Cl.S(=O)(=O)(O)[NH2:18].S(C[NH:27][C:28]1[CH:36]=[CH:35][CH:34]=[CH:33][C:29]=1[C:30]([OH:32])=[O:31])(O)(=O)=O.[OH-].[Na+]>O>[NH2:27][C:28]1[CH:36]=[CH:35][C:34]([N:18]=[N:9][C:6]2[CH:5]=[CH:4][C:3]([S:1]([OH:11])(=[O:10])=[O:2])=[CH:8][CH:7]=2)=[CH:33][C:29]=1[C:30]([OH:32])=[O:31]Sulfanilic acid (8.65 g, 0.05 mol) and sodium nitrite (3.8 g) were dissolved in water (pH 8, 100 ml). This solution was added to a beaker containing ice (30 g) and concentrated hydrochloric acid (15 ml). After stirring for 15 minutes, sulfamic acid (0.5 g) was added. This diazonium salt solution was added to a solution of the 2-((sulfomethyl)amino)benzoic acid prepared in stage 1 in water (150 ml) at 0 to 5° C. The reaction mixture was stirred at 0-5° C. for 1.5 hours while the pH of the reaction medium was maintained at pH 4 to 4.5 by the addition of dilute sodium hydroxide solution. When the diazonium salt had been consumed the product was precipitated by the addition of 2M hydrochloric acid. The precipitate was collected by filtration and then dissolved in water (200 ml) adjusted to pH 12 with lithium hydroxide. The resultant solution was stirred at 70° C. for 2 hours, maintaining the pH by periodic addition of 2M lithium hydroxide solution. After cooling, the reaction mixture was adjusted to pH6 with 2M hydrochloric acid. The precipitated dye was collected by filtration as a brown solid (18 g).
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