Anodically-Generated Alkyl Radicals Derived from Carboxylic Acids as Reactive Intermediates for Addition to Alkenes
Date
2023-05-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ChemElectroChem
Abstract
Electrochemically driven C−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.
Graphical Abstract available at: https://doi.org/10.1002/celc.202201099
Electrochemically driven C−C coupling: High anodic current density favors the formation of the undesirable radical self-coupling product. Low anodic current density favors the formation of the target product, but also leads to more solvent oxidation. Solvent oxidation at low current density can be suppressed by multiple methods to achieve high Faradaic efficiency of the target product at high selectivity.
Description
This article was originally published in ChemElectroChem. The version of record is available at: https://doi.org/10.1002/celc.202201099
Keywords
C−C coupling, electrochemistry, electrooxidation, electrosynthesis, radical addition
Citation
Ding, Haoran, and Marat Orazov. “Anodically‐Generated Alkyl Radicals Derived from Carboxylic Acids as Reactive Intermediates for Addition to Alkenes.” ChemElectroChem 10, no. 10 (May 12, 2023): e202201099. https://doi.org/10.1002/celc.202201099.