Patent ID: 7777056
Filing Date: 2010-08-17
Classification: C07D

Abstract:
1. A process for preparation of a compound of formula (I), wherein R 1 and R 2 are methyl and R 3 is hydrogen or methyl, comprising the steps of, heating a compound of formula (II), wherein R 4 is hydrogen, NH 4 + or an alkali metal, in a solvent mixture consisting of toluene and methyl ethyl ketone in an inert atmosphere at a temperature between 60-85° C. and optionally in the presence of orthophosphoric acid or its alkali dihydrogen salts or alkali hydrogen salts of a dibasic acid, followed by optional neutralization of the reaction mixture with an organic base and obtaining compound of formula (I) in high purity and substantially free of impurities through a step of isolation and crystallization.