20 25 u00b0 c the weak suspension was stirred at room temperature for 3 hours to crystallize and was then filtered the filtered crystals were washed with 1 ml glacial acetic acid off white crystals of prasugrel hydrochloride form f were obtained yield 83 8 prasugrel hydrochloride form b 499 mg was suspended in 3 ml glacial acetic acid at room temperature 20 25 u00b0 c the resulting weak suspension was stirred at room temperature for 3 hours to crystallize and was then filtered the filtered crystals were washed with 1 ml glacial acetic acid and dried overnight at room temperature 20 25 u00b0 c off white crystals of prasugrel hydrochloride form f were obtained yield 80 9 prasugrel hydrochloride form b 1 001 g was dissolved in 4 ml glacial acetic acid at 40 u00b0 c cooled down to room temperature 20 25 u00b0 c and left to crystallize for 3 hours the filtered crystals were washed with 2 ml glacial acetic acid and 1 ml distilled water the crystals were dried overnight at room temperature 20 25 u00b0 c yellowish crystals of prasugrel hydrochloride form f were obtained yield 62 9 prasugrel hydrochloride form b 15 005 g was dissolved in 60 ml glacial acetic acid at 40 u00b0 c then cooled down to room temperature 20 25 u00b0 c and left to crystallize for 4 5 hours the resulting crystals were filtered and washed with 20 ml glacial acetic acid 5 15 ml in portions dried for 30 min at 30 u00b0 c 10 mbar and left overnight at room temperature 20 25 u00b0 c off white crystals of prasugrel hydrochloride form f were obtained prasugrel hydrochloride form.