2,3,4,6-Tetra-O-benzyl-D-galactopyranosyl acetate (79.8 g) was dissolved in a mixed solution of toluene (160 mL) and isopropyl ether (520 mL) and then cooled to −10-0° C. To the solution was added a solution containing 2.0 equivalent amount of HBr in isopropyl ether (2.8 mmol/mL, about 100 mL). After the reaction solution was stirred at −10-0° C. for about 90 minutes, a 5% aqueous solution of sodium hydrogencarbonate was poured thereto and stirred to neutralize the excess HBr. The whole of the solution was transferred to a separatory funnel to cause separation into an aqueous layer and an organic layer. The aqueous layer obtained was discarded and the organic layer was washed with a 10% aqueous solution of sodium chloride twice. The organic layer was concentrated under reduced pressure, thereby giving a syrup product of 2,3,4,6-tetra-O-benzyl-α-D-galactopyranosyl bromide (Gal-Br).
