Pyridine carboxylic acids - by oxidation of alkyl pyridines

摘要

PROCESS FOR PYRIDINE CARBOXYLIC ACIDS BY OXIDATION OF ALKYLPYRIDINES. With 25-600% excess of aq. HNO3 at 230-350 degrees C under a pressure of up to 500 atmospheres (50-300 atmos. preferred) for 1-20 mins, adjusting to give an HNO3 concentration in the reaction mixture of 10-28%, the pyridine carboxylic acid crystallising from the mixture at 0-20 degrees C as the nitric-acid salt, separating the salt, dissolving it in water, adjusting to the isoelectric point with the original alkyl pyridine, separating the crystalline pyridine carboxylic acid from the mother liquor, combining the 2 mother liquors and recycling. Advantage of simple isolation of the required acid at the isoelectric point and no difficult treatment of mother liquors is involved as in customary process using HNO3 oxidation. Yields of 94% compared with 70% for usual processes.