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Electrochemically driven CÀ C coupling has the potential to reduce the cost and environmental impact of some organic syntheses currently accomplished through thermochemical methods. Here, we use electrochemical oxidation of carboxylic acids as a source of reactive carbon-centered radicals that enable radical addition to alkenes in the anode boundary layer. We demonstrate an optimization of reaction conditions to suppress the thermodynamically favored, but synthetically undesirable radical self-coupling in favor of radical addition to styrene. In methanol solvent, 88 % selectivity and 72 % Faradaic efficiency for targeted functionalized benzenes are achieved. For low current densities, iridium anodes outperform platinum, gold, palladium, and glassy carbon anodes. With constant potential or constant current electrolyses, the deposition of organic by-products on the catalyst surface leads to anode passivation. We show that periodic cathodic current pulses effectively regenerate the catalyst. Lastly, we confirm the role of free radicals in the reaction mechanism with a radical trap.

This study employed the well-known organic electrochemical reaction, Kolbe electrolysis, as a source of alkyl radicals that readily add to the double bond of styrene. With conventional Kolbe electrolysis conditions, a complex set of products forms when an alkene (e.g., styrene) is introduced. Optimizing the interplay of the electrochemical processes, diffusion, and boundary-layer reactions leads to high selectivity and Faradaic efficiency of a single addition product, 1-methoxyheptylbenzene. To accomplish this, radical self-coupling, which results in the undesired Kolbe dimer product, is minimized at low current densities. However, under such conditions, the anode is less positively polarized, resulting in a lower surface coverage by the negatively charged carboxylates. This protective adlayer reduces solvent oxidation and its loss leads to lower Faradaic efficiency for the desired chemistry. Multiple strategies are presented to mitigate solvent oxidation and improve the Faradaic efficiency at lower potentials. The most significant finding is that the system can thus be optimized to target maximal selectivity (88 %) or Faradaic efficiency (72 %) for the desired product. The cover art highlights the co-adsorption of solvent and carboxylate on the anode, while the desired C-C coupling reaction occurs in the solution above.

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