Patent ID: 6100401
Filing Date: 2000-08-08
Classification: C07D

Abstract:
A process for preparing the d-threo isomer of methylphenidate hydrochloride directly from the racemic mixture of threo methylphenidate hydrochloride comprising the steps of:1) resolving d,l-threo methylphenidate hydrochloride with a preformed salt of 4-methylmorpholine and dibenzoyl-D-tartaric acid in the presence of a crystallization-inducing amount of pure dibenzoyl-D-tartrate salt seeds enriched with the d-threo isomer of methylphenidate to obtain a dibenzoyl-D-tartrate salt enriched with the d-threo isomer of methylphenidate;2) basifying the tartrate salt prepared in Step 1 to obtain the free base form of d-threo methylphenidate;3) converting the free base prepared in Step 2 into the hydrochloride salt form of d-threo methylphenidate in high optical purity; and4) recrystallizing the salt prepared in Step 3 to obtain the desired d-threo isomer in a higher optical purity.