[SH:1][C:2]1[CH:3]=[C:4]([CH:8]=[C:9]([S:18](=[O:21])(=[O:20])[NH2:19])[C:10]=1[O:11][C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1)[C:5]([OH:7])=[O:6].C(=O)([O-])O.[Na+].S(S([O-])=O)([O-])=O.[Na+].[Na+].[CH:35]([C:37]1[CH:42]=[CH:41][N:40]=[CH:39][CH:38]=1)=[CH2:36]>C(O)(=O)C>[O:11]([C:10]1[C:9]([S:18](=[O:21])(=[O:20])[NH2:19])=[CH:8][C:4]([C:5]([OH:7])=[O:6])=[CH:3][C:2]=1[S:1][CH2:36][CH2:35][C:37]1[CH:42]=[CH:41][N:40]=[CH:39][CH:38]=1)[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1A mixture of 3-mercapto-4-phenoxy-5-sulfamylbenzoic acid (1.7 g), sodium hydrogen carbonate (1 g), sodium dithionite (1 g), 4-vinylpyridine (0.8 ml) and saturated aqueous sodium hydrogen carbonate (17 ml) is stirred at 70°C. for 4 hours. After cooling, pH of the mixture is adjusted to 4.5 by addition of acetic acid. The precipitated material is collected by filtration, washed with water, and recrystallized from aqueous ethanol to yield 4-phenoxy-3-(4-pyridylethylthio)-5-sulfamylbenzoic acid.
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