Patent ID: 7164025

Claim:
A process for obtaining single enantiomer d-threo-methylphenidate or l-threo-methylphenidate, which comprises resolution of a mixture of the d-threo-methylphenidate and l-threo-methylphenidate enantiomers; racemisation of the unwanted enantiomer, to give a mixture of all four stereoisomers, wherein the racemisation comprises reacting the unwanted enantiomer with an acid; enriching said mixture following racemisation wherein the d-threo and l-threo stereoisomers of methylphenidate are enriched over said d-erythro and l-erythro stereoisomers of methylphenidate; and separation of said d-erythro and l-erythro stereoisomers, to leave the said mixture of d-threo-methylphenidate and l-threo-methylphenidate enantiomers for resolution.