Selective deoxygenation of biomass-derived carbonyl compounds on Zn via electrochemical Clemmensen reduction

For reductive upgrading of lignocellulosic biomass intermediates containing carbonyl groups, deoxygenation is critical to increase the energy density and storage lifetime of bio-oils. However, electrochemical reduction that cleaves the C=O bond by hydrogenolysis to form an alkane is extremely challenging because the C=O bond more readily undergoes hydrogenation to form an alcohol and the resulting alcohol C–O bond is more difficult to cleave by hydrogenolysis. In traditional organic chemistry, the Clemmensen reduction uses Zn as a reductant to convert aldehydes and ketones to alkanes. Here we demonstrate the feasibility of the electrochemical Clemmensen reduction, which uses Zn not as a stoichiometric reductant but as an electrocatalytic cathode in an electrochemical cell. The factors that affect the electrochemical hydrogenolysis and hydrogenation pathways on Zn and the mechanistic reasons why Zn is particularly good at hydrogenolysis are elucidated, revealing the advantages of electrochemical Clemmensen reduction. The electrochemical deoxygenation of carbonyl groups by hydrogenolysis is challenging as the competing hydrogenation usually prevails. Now the electrochemical Clemmensen reduction is proposed, achieving the selective hydrogenolysis of various carbonyl compounds using Zn as the electrocatalyst in a mildly acidic solution.