To a obtained solution of the sodium salt of 3-hydroxy-1-adamantylmethyl difluorosulfoacetate, 17.2 parts of chloroform, and 2.9 parts of a 14.8 mass % aqueous triphenyl sulfonium chloride solution were added, and the mixture was stirred for 15 hours, and then an organic layer was separated from the resultant solution, and an aqueous layer was subjected to extraction with 6.5 parts of chloroform. Organic layers were combined and washed with an ion-exchanged water, and the obtained organic layer was concentrated. To the concentrated solution, 5.0 parts of tert-butyl methyl ether was added, and the resultant mixture was stirred and filtered to obtain, as a white solid, 0.2 parts of triphenylsulfonium 1-((3-hydroxy-1-adamantyl)methoxycarbonyl)difluoromethane sulfonate (B1-2).
