Sacrificial Anode-Free Electrosynthesis of α-Hydroxy Acids via Electrocatalytic Coupling of Carbon Dioxide to Aromatic Alcohols

Electrocarboxylation of organic compounds using CO₂ is a promising approach toward a sustainable low-carbon society, but it is desirable to avoid the use of conventional sacrificial anodes in terms of green chemistry. Here, we report a novel electrocarboxylation methodology operating in a simple undivided cell with a nonsacrificial anode, at which tetramethylpiperidine-1-oxyl (TEMPO)-mediated alcohol oxidation takes place. Aromatic alcohols can be oxidized with high efficiency to ketones or aldehydes at the anode in the presence of a small amount of water, and then converted to α-hydroxy acids in yields of up to 61% by coupling with CO₂ at the cathode. The electrocarboxylation mechanism comprising electron and proton transfers at the cathode is discussed along with experiments using various cathode materials. Electron and proton transfers are influenced by the hydrogen adsorption energy of the cathode material, which plays an important role in the electrocarboxylation efficiency.