Revisiting Alternating Current Electrolysis for Organic Synthesis

Abstract

This review summarizes the recent advancements in alternating current (AC)-driven electroorganic synthesis since 2021 and discusses the reactivities AC electrolysis provides to achieve new and unique organic transformations.

Keywords: Alternating current; Direct current; Electroorganic synthesis; Reaction selectivity.

Fig. 1.. Timing electro/chemical reactions by AC frequency.

(A)-(B) The one-electron and two-electron pathways of amine oxidation that produce cyanation and arylated products. (C) Cyclic voltammograms (CV) of 1 in the presence and absence of base at 0.02 (top) and 5 V/s (bottom) and their equivalent AC frequencies showing the degree of oxidation shifts from two-electron oxidation to one-electron oxidation according to the peak current comparison (i₀ vs i₁). Adapted with permission from[7], copyright (2022) by American Chemical Society. (D) AC-driven heterodifunctionalization and functional group tolerance of the AC method compared to the DC conditions. (E) AC electrolysis provides a redox-neutral environment where the redox-active functional groups can undergo reversible redox conversion, overcoming the potential window-limited functional group compatibility. (F) CV of aryl thioether at different scan rates showing the reversibility of thioether redox chemistry improves at higher scan rates. Adapted with permission from[8], copyright (2023) by American Chemical Society. (G) Illustration showing reaction outcome difference by applying DC and rAP. (H) Proposed mechanism and (I) CV of piperidine 7 and PivOH at 50 and 400 mV/s. Adapted with permission from[13], copyright (2021) by American Chemical Society.

Fig. 2.. Controlling solution pH by AC electrolysis.

(A) Photographs of reaction pH change under DC (top) and rAP condition (bottom) using bromophenol blue as the pH indicator. (B) Comparison of reaction mechanisms under DC and rAP. (C) Cyclic voltammograms of carboxylic acid with or without a base (Me₄N·OH). Adapted from[14], copyright (2023) American Association for the Advancement of Science.

Fig. 3.

(A) Schematic diagram elucidating the underlying mechanism that benefits AC electrolysis by time-resolved mapping of short-lived reactive intermediates using time-resolved operando mass spectrometry. (B)Electrochemical oxidative homo-coupling of DMA. Real-time recording of the ion intensity changes under (top) DC and (bottom) AC conditions. Adapted from[20], copyright (2023) Wiley-VCH. (C) Product selectivity changes as a function of AC pulse duration during electrochemical CO₂ reduction (CO₂RR). (D) The catalytic Cu species on an electrode surface under AC and DC conditions and their effect on CO adsorption and C₂₊ product selectivity during CO₂RR. Adapted from[23], copyright (2023) by American Chemical Society.

Scheme 1.

Schematic of the AC-driven electroorganic transformations developed since 2021.