To a methanol (427.4 kg) solution of (1S)-2,3,4,6-tetra-O-acetyl-1,5-anhydro-1-[3-(1-benzothien-2-ylmethyl)-4-fluorophenyl]glucitol (76.9 kg) was added a water (230 liters) solution of sodium hydroxide (26.9 kg) at a temperature of 25° C. or lower, followed by stirring at 40.0 to 49.1° C. for 4 hours. Water (850 liters) was added to the reaction mixture, and 12.9 kg of 38% hydrochloric acid was added thereto at a temperature of 25° C. or lower. The mixture was heated to 60° C., followed by stirring at 20.2 to 25.0° C. for 9.5 hours. The separated-out crystals were collected by filtration, washed with tap water (80 liters), and vacuum-dried to obtain, as white crystals, (1S)-1,5-anhydro-1-C-[3-(1-benzothiophene-2-ylmethyl)-4-fluorophenyl]-D-glucitol [52.7 kg, yield: 97.0%, purity: 99% (HPLC)].
