Patent ID: 7795439

Claim:
A method for the in-situ removal of impurities from a saponified solution of a pyridine-2,3-dicarboxylic acid ester, said method comprising the steps of: providing a saponified solution comprising the product produced by adding a base to a pyridine-2,3-dicarboxylic acid ester; reacting said saponified solution with an amount of an oxidizing agent effective to remove impurities, thereby providing a purified saponified solution; and collecting said purified saponified solution; wherein said pyridine-2,3-dicarboxylic acid ester is a compound of the formula wherein R 4 and R 6 are each independently H, C 1 -C 6 alkyl, C 1 -C 6 alkenyl, phenyl or substituted phenyl; R 5 is H; halogen; C 1 -C 6 alkyl optionally substituted with one or more C 1 -C 4 alkoxy groups; C 1 -C 6 alkenyl; phenyl or substituted phenyl; and R 2 and R 3 are each independently C 1 -C 6 alkyl, phenyl or substituted phenyl; and wherein said oxidizing agent is selected from the group consisting of peroxides, peroxyacids, and hypohalite salts.