WHAT IS CLAIMED IS:
1. A process for the isolation of 4-amino-3-chloro-6-(4-chloro-2-fluoro-3- methoxyphenyl)pyridine-2-carboxylic acid which comprises:
(a) neutralizing an aqueous solution of an alkali metal or alkaline earth metal salt of 4- amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)pyridine-2-carboxylic acid with an excess of 85 - 99 percent formic acid at a temperature from about 45 to about 90 °C to produce an aqueous mixture of 4-amino-3-chloro-6-(4-chloro-2-fluoro-3- methoxyphenyl)pyridine-2-carboxylic acid;
(b) cooling the aqueous mixture of 4-amino-3-chloro-6-(4-chloro-2-fluoro-3- methoxyphenyl)pyridine-2-carboxylic acid to about 10 to about 25 °C to crystallize the 4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)pyridine-2-carboxylic acid, and
(c) collecting the crystalline 4-amino-3-chloro-6-(4-chloro-2-fluoro-3- methoxyphenyl)-pyridine-2-carboxylic acid.
2. A process for the preparation and isolation of 4-amino-3-chloro-6-(4-chloro-2- fluoro-3-methoxyphenyl)pyridine-2-carboxylic acid which comprises:
(a) contacting an ester of 4-amino-3-chloro-6-(4-chloro-2-fluoro-3- methoxyphenyl)pyridine-2-carboxylic acid of Formula I
in which
R1 represents H or C(0)CH3, and
R2 represents CrC12 alkyl or an unsubstituted or substituted C7-Cn arylalkyl
with an aqueous solution of an alkali metal or alkaline earth metal hydroxide in a C1-C4 alcohol at a temperature from about 45 to about 100 °C to produce an aqueous alcoholic
solution of the alkali metal or alkaline earth metal salt of 4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)pyridine-2-carboxylic acid,
(b) optionally removing most of the C1-C4 alcohol from the aqueous alcoholic solution of the alkali metal or alkaline earth metal salt of 4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)pyridine-2-carboxylic acid,
(c) neutralizing the aqueous solution of the alkali metal or alkaline earth metal salt of 4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)pyridine-2-carboxylic acid with an excess of 85 - 99 percent formic acid at a temperature from about 45 to about 90 °C to produce an aqueous mixture of 4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)pyridine-2-carboxylic acid,
(d) cooling the aqueous mixture of 4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)pyridine-2-carboxylic acid to about 10 to about 25 °C to crystallize the 4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)pyridine-2-carboxylic acid, and
(e) collecting the crystalline 4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)pyridine-2-carboxylic acid.