Polarographic Reduction of Hydrogen Ion in Non-aqueous Solvents

Sommary-_The polarographic reduction of hydrogen ion, furnished by dissociation of a Brransted acid or present in the undissociated Brsnsted acid, is reviewed for the situation where a solvent other than water is involved. INTRODUCTION THE electrochemical reduction of hydrogen ion in aqueous solution has long been a major problem in electrochemistry, as indicated by the voluminous literature on the subject. The difhculty and complexity involved are well indicated by Frumkin’s reviews of one aspect of the situation, that of hydrogen overpotential and adsorption phenomena.l* The additional problems introduced when non-aqueous media are used, are well presented in Kolthotf’s recent revietil of polarography in inert organic solvents; the debt of the present authors to this study will be apparent to the reader. Other useful sources of data on polarography include two monographs by Charlot and collaborators.s*10 BockrisE has described the rates of hydrogen evolution in a variety of solvents at a number of different electrodes. The present review is primarily concerned with the phenomenological aspects of the polarographic reduction of hydrogen ion, furnished by the dissociation of a Bronsted acid or present in the undissociated Brsnsted acid, when a solvent other than water is involved; the available literature on hydrogen ion reduction in non-aqueous media is generally not sufBciently systematic and detailed to allow more than general correlations to be made. Because of the limited and fragmentary data available, hydrogen ion reduction in fused salt media will not be considered. Reference will be made to non-polarographic electrochemical data, where the latter illuminate the polarographic situation. The polarographic reduction of hydrogen ion in aqueous solution will be briefly reviewed to furnish a basis for comparison.