Selective Toluene Electrooxidation to Benzyl Alcohol

We report a novel electrocatalytic approach that couples water oxidation with toluene oxidation in wet DMF or DMSO electrolyte. Electrocatalytic oxidation of water, a sustainable oxygen atom source, favored hydroxyl (^·̇OH) radical formation over hydrogen peroxide and oxygen evolution because the organic solvent molecules suppressed O-O bond formation via hydrogen bonding. Water oxidation was catalyzed by laser-synthesized [NiFe]-(OH)₂ nanosheets supported on hydrophilic carbon fiber paper anodes, enhancing water oxidation activity and toluene oxygenation efficiency. Under optimized conditions in wet DMF electrolyte, toluene oxidation achieved 100% selectivity for benzyl alcohol at an unprecedented conversion yield of 87%. In wet DMSO electrolyte, 100% selectivity for benzyl alcohol was obtained, albeit with significantly lower conversion yield. Combined experimental and computational results reveal a new mechanistic pathway, based on electrocatalytic water oxidation to ^·OH radicals and protons. Protonation of DMF enabled the formation of H⁺-DMF-^·OH radical complexes stabilized by hydrogen bonding among the radical, protonated and unprotonated DMF molecules, and water. This radical stabilization played a crucial role in promoting benzyl alcohol production. In contrast, DMSO consumed ^·OH radicals to form methanesulfinic acid, limiting benzyl alcohol generation. The wet organic solvent environment additionally prevented overoxidation beyond the alcohol by stabilizing radical intermediates through hydrogen bonding networks, effectively arresting the reaction after the first oxygenation. Likewise, benzyl alcohol oxidation yielded benzaldehyde, with no overoxidation to benzoic acid. Our findings establish fundamental design principles for selective hydrocarbon oxidations by leveraging solvent-mediated interactions, with broad implications for sustainable chemical synthesis.