Anodically-Generated Alkyl Radicals Derived from Carboxylic Acids as Reactive Intermediates for Addition to Alkenes

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Author(s)Ding, Haoran
Author(s)Orazov, Marat
Date Accessioned2023-05-16T19:20:21Z
Date Available2023-05-16T19:20:21Z
Publication Date2023-05-12
DescriptionThis article was originally published in ChemElectroChem. The version of record is available at: https://doi.org/10.1002/celc.202201099
AbstractElectrochemically 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.
SponsorWe thank Dr. Rameswar Bhattacharjee and Dr. Stavros Caratzoulas from the group of Prof. Dionisios G. Vlachos for the calculation of the ionization energy discussed in mechanistic insights section of the manuscript. We acknowledge and thank the University of Delaware, Department of Chemical and Biomolecular Engineering for providing startup funding for the research group of Prof. Marat Orazov.
CitationDing, 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.
ISSN2196-0216
URLhttps://udspace.udel.edu/handle/19716/32757
Languageen_US
PublisherChemElectroChem
KeywordsC−C coupling
Keywordselectrochemistry
Keywordselectrooxidation
Keywordselectrosynthesis
Keywordsradical addition
TitleAnodically-Generated Alkyl Radicals Derived from Carboxylic Acids as Reactive Intermediates for Addition to Alkenes
TypeArticle
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