Electrochemical hydrogenation of α-arylvinylphosphonic acids on platinum and palladium modified with adatoms

A general characteristic of cathodic reduction of alpha-phenylvinylphosphonic acid and its methyl- and chloro-parasubstituted derivatives on Pt/Pt, Pd/Pt, and Pd/Pt modified with Cd and Cu adatoms, is given. At effective pressures of about 10(3)-10(4) Pa the processes occur at high rates and at some potentials are limited by the reactant diffusion from the bulk solution. In the presence of Cd and Cu adatoms two reduction waves (presumably, single-electron) may be isolated, i.e. the hampering by adatoms is more pronounced for a second successive stage of the process. At low effective hydrogen pressures the hydrogenation rate is higher on Pd electrodes, which possess a larger sorption capacity. Potential intervals where the reduction of substituted reactants may be complicated by destruction, are found. It is shown that alpha-phenylvinylphosphonic acid undergoes a complete reduction with a current efficiency of 100% in both hydrochloric- and sulfuric-acid solutions. Conditions where the reduction of alpha-(4-chlorophenyl)vinylphosphonic acid proceeds largely without destruction are found. Prospects for use of electrochemical reduction as a preparative method of a selective production of alpha-arylethylphosphonic acids are considered.