Patent ID: 8552030

Claim:
A process for preparation of d-threo-Ritalinic acid & l-threo-Ritalinic acid of formulas I & II and their salts by resolution of dl-threo-ritalinic acid of formula III using ester of tartaric acid of formula IV which comprises (i) dissolving dl-threo-ritalinic acid in a solvent, water mixture (60:40) and adding a solution of an ester of tartaric acid dissolved in a first organic solvent to the solution at a temperature in the range from −10° C. to 100° C. for a period ranging from 5 minutes to 5 hours to obtain a resulting mass; (ii) heating the resulting mass to reflux for a period ranging from 15 minutes to 24 hours and filtering through a hyflo bed, cooling filtrate to a temperature in the range of −10° C. to 40° C. to obtain a slurry containing solid mass of d-threo-ritalinic acid-tartaric acid ester salt; (iii) maintaining the slurry for a period ranging from 30 minutes to 24 hours and filtering to obtain a first mother liquor, separating d-threo-ritalinic acid-tartaric acid ester salt; (iv) adding to the first mother liquor, concentrated or dilute hydrochloric acid along with toluene and concentrating under vacuum by maintaining the temperature at 40° C. to 100° C. to obtain an organic residue; (v) adding a second organic solvent to the organic residue; (vi) cooling the second organic solvent added to the organic residue to a temperature in the range of −15° C. to 40° C. and filtering to get l-threo-ritalinic acid hydrochloride and the second mother liquor containing a resolving agent; (vii) adding a third organic solvent along with organic or inorganic acids to the d-threo-ritalinic acid-tartaric acid ester salt and removing water present in the acids to obtain a concentrated mass; (viii) adding a fourth organic solvent to the concentrated mass at a temperature range of −10° C. to 25° C. and filtering the d-threo-ritalinic acid hydrochloride and separating a third mother liquor containing the resolving agent; and (ix) concentrating the second and third mother liquors, basifying and acidifying and filtering the resolving agent.