[NH2:1][C:2]1[C:3](S(O)(=O)=O)=[CH:4][CH:5]=[C:6](S(O)(=O)=O)[CH:7]=1.[C:16](#[N:18])[CH3:17]>O>[C:2](#[N:1])[C:7]1[C:17](=[CH:3][CH:4]=[CH:5][CH:6]=1)[C:16]#[N:18]A solution of aniline 2,5 disulphonic acid (27.5 g) in water (250 ml) was added to intermediate E (63.2 g) in acetonitrile (800 ml) and heated at 40° C. and at pH 5 to 7 overnight. The reaction solvent was removed under reduced pressure, water (50 ml) was added and then brine (60 ml) the solid which precipitated of filtered off, washed with 10% brine and dried to give product (91.1% strength, 22 g).
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