Electrochemical oxidn. of alkyl-pyridine(s) to carboxylic acids - in cell with anion exchange membrane, acid anolyte and more dilute acid catholyte

摘要

Electrochemical oxidn. of an alkylpyridine of formula (I) is effected in an acid medium at a Pb-contg. anode of an electrolytic cell, with anode and cathode compartments sepd. by an anion-exchange membrane. As catholyte, an aq. soln. of the same acid as used for the anolyte but in relatively dilute form is used. The prod. is recovered from the anolyte. R=1-6C alkyl; n=1, 2 or 3. The acid used is pref. H2SO4, with 10-50 wt.% acid in the anolyte and 0.1-5 wt.% in the catholyte. The anion-exchange membrane is pref. non-porous, and has a high degree of selectivity for the transfer of monovalent anions. (I) is typically alpha- or beta-picolines, 2,3- or 2,6-lutidines or 2-ethyl-5-methylpyridine to give respectively, picolinic, nicotinic, 2,3-, 2,6- or 2,5-pyridinedicarboxylic acids.