Overcoming the Potential Window-Limited Functional Group Compatibility by Alternating Current Electrolysis

Abstract

The functional group compatibility of an electrosynthetic method is typically limited by its potential reaction window. Here, we report that alternating current (AC) electrolysis can overcome such potential window-limited functional group compatibility. Using alkene heterodifunctionalization as a model system, we design and demonstrate a series of AC-driven reactions that add two functional groups sequentially and separately under the cathodic and anodic pulses, including chloro- and bromotrilfuoromethylation as well as chlorosulfonylation. We discovered that the oscillating redox environment during AC electrolysis allows the regeneration of the redox-active functional groups after their oxidation or reduction in the preceding step. As a result, even though redox labile functional groups such as pyrrole, quinone, and aryl thioether fall in the reaction potential window, they are tolerated under AC electrolysis conditions, leading to synthetically useful yields. The cyclic voltammetric study has confirmed that the product yield is limited by the extent of starting material regeneration during the redox cycling. Our findings open a new avenue for improving functional group compatibility in electrosynthesis and show the possibility of predicting the product yield under AC electrolysis from voltammogram features.

Electrochemical reduction of benzoic acid esters using water as a H/D source

“…In recent years, alternating current electrolysis has emerged as a promising protocol for electrochemical synthesis because it can overcome the thermodynamic limitation of the electron process by regulating its kinetics. 10 Among the alternating current electrolysis methods reported to date, the rapid alternating polarity (rAP) current method 11 and the asymmetric-waveform alternating current method 12 show unique advantages of reversing the chemoselectivity, stabilizing the catalyst, improving the current efficiency, and so on.…”

Organoboron-Promoted Electrochemical Chlorosulfonylation of Alkenes with Sulfonyl Chlorides

“…To overcome these issues, metal-catalysts, − redox-mediators, , microfluidic setups, and alternating current electrolysis , have been developed to enhance the stability or diffusion rate of reactive intermediates. Regarding chlorosulfonylation, Lei and co-workers reported a Mn-based catalyst acting as both a redox mediator and chlorine atom transfer reagent to achieve chlorosulfonylation of alkenes and alkynes through convergent paired electrolysis (Scheme B) .…”

Physico-chemical principles of AC electrosynthesis

“…The latter has the advantage of introducing additional controllable parameters such as oscillation frequency and waveform shape, creating more opportunities for reaction control [15][16][17][18][19][20][21]. In particular, this has been useful in minimising loss of electrocatalysts [22][23][24][25][26], achieving paired electrosynthesis [24,[27][28][29][30][31], and improving chemical selectivity [26,28,[32][33][34][35][36][37][38][39][40][41][42][43]. These benefits are also transferrable to the manufacturing industry -recently, Hioki et al used AC to upgrade biomass-derived carboxylic acids into valuable polymers [40], setting yet another milestone in green engineering.…”

“…Importantly, the reaction outcome in these early explorations was highly sensitive to the reaction and AC parameters with no definitive qualitative trends identified. Furthermore, assumptions of reaction irreversibility played an important role in these studies, bypassing the consideration of reversible reactions mediated by alternating polarity [38,39,43,56].…”

“…We show that for products with the same stoichiometry, switching from DC to square waves (also termed rapid alternating polarity or rAP) can completely invert chemoselectivity control towards the pathway involving more electrons, facilitating over-oxidation/over-reduction. * joelyuen@ucsd.edu This occurs via a selective reverse reduction/oxidation of the less-oxidised/less-reduced product, a possibility proposed only experimentally by Rodrigo et al [43]. In contrast, sinusoidal waves minimise over-oxidation/overreduction, while for branched reactions of different product stoichiometries, square (sine) AC favours pathways containing fewer (more) products.…”