New aspects of the Brdicka reaction of low-molecular thiols; Voltammetry at low rate of potential scan

The catalytic evolution of hydrogen on mercury electrodes from solutions of thiols containing cobalt(II) ions can proceed in different ways according to the conditions of electrolysis: in the classical Brdicka current at - 1. 7 V, at HMDE in the "P" peak, especially with low rate of potential scan, a round - 1.25 V, or at HMDE at - 1.5 V after preelectrolysis at the foot of the Co(II) reduction step. The occurrence of the "P" peak is due to reactio n in the adsorbed state, preceded by ligand catalytic reduction of the coba lt thiol complex; evolution of hydrogen is catalyzed by unstable intermedia tes of the surface process.