Electrochemistry of aromatic diselenides and ditellurides in aprotic media. Preceding formation of mercury-containing compounds

Abstract

The reduction of aromatic diselenides and ditellurides on the mercury electrode in nonaqueous media proceeds quite differently from the reduction of aromatic disulphides. Using various electrochemical techniques, electrochemiluminescence and ICP (Inductively Coupled Plasma) emission spectrometry, it has been proven that in the case of ditellurides and diselenides, a spontaneous chemical pre-reaction with mercury, precedes the electron transfer process. In a heterogeneous reaction a stable, mercury-containing soluble compound is formed. A substance with the formula Hg(ArSe) 2 has been isolated as yellowish crystals and its composition was proven by 1H, 13C and 77Se NMR and Mass Spectroscopy. These formally Hg(II) compounds are reduced in a first, more positive cathodic wave with a consumption of one-third of the electrons involved in the total process. The whole two-step mechanism is discussed on the basis of the present experimental material as well as on earlier findings with analogue sulphur compounds. In the case of diphenyl disulphide, the chemical pre-reaction with mercury electrode was found to be nearly negligible. In coulometric experiments an improved electrolytical cell of own construction was tested and found to be advantageous.