US Patent 7259261 Racemization and enantiomer separation of clopidogrel

Processes for separation of enantiomers of clopidogrel, and converting one enantiomer of clopidogrel to another enantiomer of clopidogrel are provided. The enantiomers are separated by crystallizing the (S) enantiomer as camphor sulfonate salt from a hydrocarbon, or a mixture of a hydrocarbon and a co-solvent, preferably DMF:toluene. The (R) enantiomer is then racemized and recycled by reaction with a catalytic amount of a base, preferably with t-butoxide.