Double-layer structure and mechanism of electrode reactions Part III. Diethylfumarate reduction on mercury from aqueous solutions

Abstract

Kinetic measurements of diethylfumarate (DEF) electroreduction to diethylsuccinate in aqueous solutions of pH ranging from 1 to 10 were carried out by the polarographic technique under different experimental conditions, and DEF adsorption was measured by the chronocoulometric technique. The rate changes produced by changes in pH, in buffer concentration, in the potential d at the outer Helmholtz plane or in the charge density σi at the inner Helmholtz plane due to specifically adsorbed iodide ions, were thoroughly examined. The effects of these changes are amenable to a straightforward interpretation if the overall electrode process is assumed to be controlled by an enol-keto transformation of the enol form of diethylsuccinate for 1<ph<3, by the heterogeneous protonation stepR−→+H+RH(with RэDEF) for 5<pH<6.5, by the heterogeneous protonation stepR2−→+H+RH− for 7.5<pH<10 and by both preceding protonation steps for 6.5<pH<7.5.