Reversible oxidation processes in dichloromethane for triethyl-, diethyl-, trimethyl-, and dimethyllead compounds at mercury electrodes

Abstract

Chemically reversible electrochemical oxidation processes have been observed at mercury electrodes in dichloromethane in the presence of Et 3PbOAc (OAc − = acetate), Et 3PbCl, Et 2PbCl 2, Me 3PbOAc, Me 3PbCl and Me 2PbCl 2. The trialkyl derivatives R 3PbX (R  Et, Me; X −  OAc −, Cl −) give rise to a reversible oxidation process involving transfer of one electron, exchange of alkyl groups and X − and formation of a mercury-lead complex, which in its simplest form can be represented as [R 3PbHgPbR 3] 2+. The oxidation process is therefore described by the equation 2 R 3PbX + 2 Hg ⇌ [R 3PbHgPbR 3] 2+ + HgX 2 + 2 e − On the longer time scale of controlled potential electrolysis, HgX 2 can react with R 3PbX and presumably [R 3PbHgR 3Pb] 2+ to produce RHgX, inorganic lead(II) and electroactive R 2PbX 2. The dialkyl complexes R 2PbX 2 exhibit analogous oxidation processes of the kind 2 R 2PbX 2 + 2 Hg ⇌ [R 2XPbHgPbXR 2] 2+ + HgX 2 + 2 e − with short time domain experiments. However HgX 2 reacts with [R 2XPbHgPbXR 2] 2+ and R 2PbX 2 on longer time domain experiments such as controlled potential electrolysis or dc polarography to generate inorganic lead(II) and RHgX. The existence of reversible polarographic processes implies that it may be possible to develop extremely sensitive analytical methods for the determination of these toxic and environmentally significant compounds based on procedures incorporating (i) extraction into non-polar solvents, (ii) high performance liquid chromatography and (iii) electrochemical oxidative detection without the need to remove oxygen as is required when using previously described reduction processes.