1.0 g (3.04 mmol) of 2-[{4-(3-hydroxypropoxy)-3-methylpyridine-2-yl}methylthio]-1H-benzimidazole was dissolved in 100 ml of dichloromethane to obtain a solution. 580 mg of 90% m-chloroperbenzoic acid was added to this solution at -45° C. The obtained mixture was stirred for 2 hours. After the completion of the reaction, 470 mg of triethylamine was added to the reaction mixture. The obtained mixture was heated to -20° C., followed by the addition of 30 ml of a saturated aqueous solution of sodium hydrogencarbonate. The obtained mixture was stirred at a room temperature for 30 minutes and extracted with chloroform. The obtained chloroform layer was concentrated to obtain a crude product. This crude product was crystallized from dichloromethane/ether to obtain 830 mg of 2-[{4-(3-hydroxypropoxy)-3-methylpyridine-2-yl}methylsulfinyl]-1H-benzimidazole. This product was dissolved in 24 ml of 0.1N aqueous sodium hydroxide. The obtained solution was distilled together with ethanol to remove the water as an azeotropic mixture with ethanol and dried under vacuumizing with a vacuum pump. Ether was added to the obtained residue to precipitate a colorless crystal. This crystal was separated by filtration. Thus, 860 mg of the title compound was obtained (77%).
