Polarographic study of catalytic hydrogen waves caused by substances formed in a preceding reduction process

Abstract

Pyridine and mercapto derivatives formed in the reduction of 4,6-dimethyl-2-benzimidazolyl 5-methyl-2-pyridylmethyl sulfoxide, 1-methyl-2-benzimidazolyl 2-pyridylmethyl sulfoxide, 2-imidazolyl 2-pyridyl-methyl sulfide and 2-inudazolin-2-yl 2-pyridylmethyl sulfide are shown to give catalytic hydrogen waves at the DME in aqueous ethanol. All the products resulting from the reduction of the sulfoxides can act as catalysts and consequently two catalytic waves appear in the polarograms. The sulfides show only one catalytic wave corresponding to the product 2-methylpyridine. The behaviour of the catalytic waves investigated in this paper is shown to be a function of the adsorptivity of the catalysts and their polarization in the high electric field of the double layer. Difference in electrochemical behaviour between the catalysts formed in the reduction processes of the sulfoxides and sulfides, and bulk experiments with the same catalysts, also reveal, the influence of the starting compound on the catalytic waves. Formation of surface-active polymeric species in the reduction of the pyridine derivatives is also verified and their influence on the catalytic waves is discussed.