Polarographic reduction of benzazolylsubstituted pyridinium salts

Abstract

N-Methyl- and N-benzyl-substituted 2-, 3-, and 4-benzazolypyridinium (BAP) salts are reduced on a dropping mercury electrode (DME) to give a free radical in the first step and the corresponding dihydropyridine derivative in the second step. The free radicals of 2- and 4-BAP salts are distinguished by high stability as compared with other radicals with a pyridine structure owing to delocalization of the unpaired electron over the conjugated system and can be recorded by ESR spectroscopy. A peculiarity of the BAP salts is their facile reduction on the electrode; this is particularly true of the 2- and 4-benzoxazolyl- and benzothiazolyl-substituted salts.