Patent ID: 7897777

Claim:
A process for isolating d-threo isomer of methylphenidate hydrochloride comprising the steps of: (i) resolving a mixture comprising racemic threo-methylphenidate hydrochloride; less than or equal to about 1.0 equivalent (based on the amount of racemic threo-methylphenidate hydrochloride) of chiral acid selected from one or more di-0-0′-aroyl-D-tartaric acids, about 0.4 to less than 1.0 equivalent (based on the amount of racemic threo-methylphenidate hydrochloride) of one or more tertiary amine bases, and a solvent mixture comprising one or more lower alkanols and water, thereby forming a chiral acid-isomeric methylphenidate salt (ii) basifying the chiral acid-isomeric methylphenidate salt to obtain isomeric methylphenidate free base and (iii) converting the isomeric methylphenidate free base into isomeric methylphenidate hydrochloride having an enantiomeric excess of greater than about 90% and a yield of greater than about 35% based on racemic threo-methylphenidate hydrochloride.