GB610619A - Process for the separation of isomeric substituted quinoline carboxylic acids and esters thereof - Google Patents

Abstract

5- and 7-chloro-4-hydroxy-3-methylquinoline-2-carboxylic acids, or esters of such acids, are separated from mixtures comprising them by treatment with a non-oxidizing strong acid at a temperature and acid concentration at which the 5-chloro isomer dissolves or remains in solution and at which the 7-chloro isomer is insoluble or precipitates. By "non-oxidizing strong acid" is meant an inorganic or organic acid which is at least as strong as formic acid and which is not an oxidizing agent. The 5-chloro isomer may be separated from the acid solution. The isomeric acids or esters may be separated with concentrated hydrochloric acid at an elevated temperature, or the isomeric acids may be separated with sulphuric acid of a concentration between or in the neighbourhood of 50 to 70 per cent or with concentrated formic acid, e.g. by heating the mixture of isomeric acids until dissolution is complete, and cooling to separate the 7-chloro isomer. The isomeric esters may be heated with concentrated sulphuric acid, e.g. of a concentration between or in neighbourhood of 50 to 70 per cent to effect saponification and on cooling the 7-chloro acid separates out. The mixture of isomeric esters used for the process of the invention may be obtained by the cyclization of the condensation product of meta-chloraniline and oxalo-propionic acid ethyl ester, or the mixture of acids used for the process of the invention may be obtained by the alkaline saponification of the resulting mixture of isomeric esters. The diethyl ester of m-chloro phenyliminomethyl succinic acid is prepared by condensing in the cold m-chloraniline and the diethyl ester of oxalo-propionic acid.