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

Chemically reversible electrochemical oxidation processes have been observed at mercury electrodes in dichloromethane in the presence of Et₃PbOAc (OAc^- = acetate), Et₃PbCl, Et₂PbCl₂, Me₃PbOAc, Me₃PbCl and Me₂PbCl₂. The trialkyl derivatives R₃PbX (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 [R₃PbHgPbR₃]²⁺. The oxidation process is therefore described by the equation 2 R₃PbX + 2 Hg ⇌ [R₃PbHgPbR₃]²⁺ + HgX₂ + 2 e^- On the longer time scale of controlled potential electrolysis, HgX₂ can react with R₃PbX and presumably [R₃PbHgR₃Pb]²⁺ to produce RHgX, inorganic lead(II) and electroactive R₂PbX₂. The dialkyl complexes R₂PbX₂ exhibit analogous oxidation processes of the kind 2 R₂PbX₂ + 2 Hg ⇌ [R₂XPbHgPbXR₂]²⁺ + HgX₂ + 2 e^- with short time domain experiments. However HgX₂ reacts with [R₂XPbHgPbXR₂]²⁺ and R₂PbX₂ 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.