Under stirring in an ice-bath, 1-tert-butoxycarbonyl-4-[2-(5,6-difluorobenzimidazol-2-ylthio)ethyl]piperazine (7.26 g, 18.22 mmol) was added to trifluoroacetic acid (50 mL) over 15 minutes and dissolved. After the mixture had been stirred for ten minutes under cooling with ice, ether (100 mL) and hexane (100 mL) were added thereto, and the formed crystals were collected through filtration. The crystals were recrystallized from ethanol-ether, to thereby yield 1-[2-(5,6-difluorobenzimidazol-2-ylthio)ethyl]piperazine tris(trifluoroacetic acid) salt (9.58 g, yield 82%) as a pale yellow powder.
