Local pH Control Promotes Oxygen-Atom Transfer Electrosynthesis

Abstract Control of the local reaction environment at electrified interfaces is central to electrocatalysis, yet this principle has rarely been integrated into electro-organic synthesis. Electro-organic transformations are not governed by electron transfer alone; reaction turnover is often coupled to ion transfer and, in particular, proton transfer across aqueous, mixed, and nonaqueous media. Under high-rate operation, these fluxes polarize proton activity near electrodes. Although such concentration polarization is expected to be widespread and consequential, it has been largely neglected in electrosynthesis design. Here we establish a mechanistically distinct, oxygen-driven electrosynthetic pathway for Baeyer–Villiger oxidation (BVO) and use it to develop a local-pH design framework for electro-organic synthesis. Isotope labeling shows that O2 supplies the inserted oxygen atom, and radical trapping, operando EPR spectroscopy, rotating ring–disk electrode analysis, and H2O2-additivity experiments support a paired mechanism in which O2-derived hydroperoxyl-radical equivalents enter acetonitrile-assisted oxygen transfer while anodic oxidation of electrogenerated H2O2 sustains radical flux. This productive pathway is intrinsically coupled to proton activity: the proton-coupled electrode reactions that generate oxygenating equivalents also impose local pH gradients that attenuate reactive oxygen species availability, divert ketone substrates through α-enolization/tautomerization, and accelerate lactone hydrolysis under nominally neutral bulk conditions. Electrometric local pH estimations, together with molecular α-deuteration reporters and transport simulations, link these local pH swings to reaction performance. By tuning electrode spacing and convective flow, these opposing proton-activity gradients are attenuated, enabling high-yield BVO across diverse ketones at elevated substrate loading. The same local-pH control strategy is further extended to electrochemical epoxidation.