[SH:1][C:2]1[NH:3][C:4]2[CH:10]=[CH:9][CH:8]=[CH:7][C:5]=2[N:6]=1.[C:11]([OH:19])(=[O:18])[C:12]([CH2:14][C:15]([OH:17])=[O:16])=[CH2:13].S(=O)(=O)(O)O>O>[N:3]1[C:4]2[CH:10]=[CH:9][CH:8]=[CH:7][C:5]=2[NH:6][C:2]=1[S:1][CH2:13][CH:12]([C:11]([OH:19])=[O:18])[CH2:14][C:15]([OH:17])=[O:16]47.4 g of 2-mercaptobenzimidazole and 40.7 g of itaconic acid, mixed in finely powdered form, are introduced into 150 ml of 70% aqueous sulfuric acid in the course of 1 hour. The temperature is kept at 40° to 43°, with stirring. The mixture is then allowed to react completely at the above temperature over a period of 11/2 hours and the reaction mixture is diluted with water and ice to about 2 liters. The product is precipitated by addition of 30% aqueous sodium hydroxide solution to pH 4 and filtered off. After washing with water and drying in vacuo at about 30°, 92.5 g of 3-(benzimidazol-2-ylthio)-propane-1,2-dicarboxylic acid are obtained in the form of a dihydrate of melting point 113° (decomposition), corresponding to 97% of theory.
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