Selective synthesis of α,β-unsaturated aldehydes from allylic alcohols using oxidatively supplied hydrogen peroxide from electrochemical two-electron water oxidation

Abstract

Selective oxidation of allylic alcohols to α,β-unsaturated aldehydes using electrochemically formed hydrogen peroxide (H₂O₂) is performed in the presence of Pt black catalyst. In this reaction, H₂O₂ is oxidatively supplied from the electrochemical two-electron water oxidation (2e-WOR) of an aqueous KHCO₃/K₂CO₃ mixed solution at a fluoride-doped tin oxide (FTO) anode. Geraniol was oxidized to the corresponding geranial in 86% yield with 99% selectivity when the appropriate amounts of Pt black catalyst with one equivalent of H₂O₂ by 2e-WOR toward geraniol was employed in toluene solution at 60 °C. The H₂O₂ by 2e-WOR can oxidize various kinds of allylic alcohols to give the corresponding aldehydes in 64–89% isolated yields. The detailed tuning of the amounts of Pt black and the rate of introduction of H₂O₂ to the vessel allows the selective oxidation to proceed despite the low concentration of H₂O₂ derived by 2e-WOR.