Kinetic Control of Oxygenation and Dehydrogenation for Selective Maleic Acid Production from Electrochemical Furfural Conversion

Abstract

Electrochemical synthesis offers a promising route toward renewable-energy-based chemical production and a sustainable carbon cycle. Maleic acid (MA) production from biomass-derived furfural (FF) via electrochemical oxidation (FFOR) represents a valuable model system for multi-step electro-organic oxidation reactions. However, oxygenation and dehydrogenation are conventionally treated as indistinguishable oxidation processes, obscuring key factors and the rational design of complex electro-organic reactions. Herein, we decouple oxygenation and dehydrogenation kinetics in FFOR, identify the key controlling factors for each step, and demonstrate that independent regulation enables high selectivity with 81.0% yield using a PbOx anode. Employing (bi)carbonate electrolytes moderates •OH-mediated oxygenation, improving carbon efficiency. 2,2,6,6-Tetramethylpiperidine 1-oxyl (TEMPO) mediator selectively accelerates dehydrogenation of the key intermediate (5-hydroxy-2(5H)-dihydrofuran-2-one, HFN, or cis-β-formylacrylate, FAA–) to MA without perturbing FF-to-HFN/FAA– oxidation, shifting the rate-determining step. Mechanistic studies reveal that oxidation by TEMPO+ promotes oxoammonium-mediated proton transfer, driving the selective dehydrogenation toward MA. Systematic control of pH, cation/anion, and TEMPO concentration demonstrates that these factors strongly influence kinetics between •OH-mediated oxygenation and TEMPO-mediated dehydrogenation, with selective MA production achieved under their optimal balance. These mechanistic insights highlight strategies for the rational design of electro-organic synthesis by independently controlling oxygenation and dehydrogenation pathways under complex aqueous conditions.