The reduction mechanism at the mercury electrode in a 0.9 M NaClO4+0.1 M HClO4 supporting electrolyte of an hydroxytriphenylmethane: Eriochrome Cyanine R

Abstract

The reduction mechanism at a mercury electrode of Eriochrome Cyanine R, in a 0.9 M NaClO4+0.1 M HClO4 supporting electrolyte, has been investigated by several electrochemical techniques. By means of coulometry at constant potential and cyclic voltammetry it was demonstrated that a radical is formed, which suffers disproportionation, after the first electron transfer. The results of the cyclic voltammetric investigation and the impedance measurements evidenced the intrinsic reversible nature of the electron transfers. Apparent irreversible polarographic behaviour is a consequence of the existence of chemical reactions following the electron transfers. The impedance measurements demonstrated the strong adsorption of the Ox and Red form of Eriochrome Cyanine R as well as of the radical formed. On the basis of the experimental data a reduction mechanism is proposed.