Breaking C-C Bonds via Electrochemically Mediated Hydrogen Atom Transfer Reactions

Bing Yan, Changxia Shi, Gregg Beckham, Eugene Chen, Yuriy Roman-Leshkov

Research output: Contribution to conferencePaperpeer-review


Cleaving inert SP3-SP3 carbon-carbon (C-C) bonds selectively remains a major challenge in organic chemistry and a main bottleneck in the chemical upcycling of recalcitrant polyolefin waste. Here, we present an electrochemical strategy using redox mediators to activate and break C-C bonds at room temperature and ambient pressure. Specifically, we use N-hydroxyphthalimide (NHPI) as a redox mediator that undergoes electrochemical oxidation to form the phthalimide-N-oxyl (PINO) radical to initiate hydrogen atom transfer (HAT) reactions with benzylic C-H bonds. The resulting benzylic carbon radical is readily captured by molecular oxygen to form a peroxy radical that decomposes into oxygenated C-C bond-scission fragments. This indirect, mediated approach for Csp3-Csp3 bond cleavage reduces the oxidation potential by > 1.2 V compared to the direct oxidation of the substrate, thereby eliminating deleterious side reactions, such as solvent oxidation, that may occur at high potentials. Studies with a bibenzyl model compound revealed a bifurcated reaction pathway following the initial HAT step. At a bibenzyl conversion of 61.0%, the C-C bond cleavage pathway generates benzaldehyde and benzoic acid products at 38.4% selectivity, and the C-H bond oxygenation pathway leads to 1,2-diphenylethanone and benzil products at 39.2% selectivity. Changes in reaction selectivity were investigated with various model compounds, including bibenzyl, 1,3-diphe-nylpropane, 1,4-diphenylbutane, and their derivatives. Product selectivity is correlated with the C-C bond strength of the reactant, with weaker C-C bonds favoring the C-C bond cleavage pathway. We also evaluated the mediated oxidation of oligo-meric styrene (Mn= 510 Da, OS510) which were converted into oxygenated products. Lastly, proof-of-concept depolymeriza-tion of polystyrene (PS, ~10,000 Da) into oxygenated monomers, dimers, and oligomers was demonstrated using NHPI-mediated oxidation.

Original languageAmerican English
StatePublished - 2021
Event2021 AIChE Annual Meeting - Boston, Virtual, United States
Duration: 15 Nov 202119 Nov 2021


Conference2021 AIChE Annual Meeting
Country/TerritoryUnited States
CityBoston, Virtual

Bibliographical note

Publisher Copyright:
© 2021 American Institute of Chemical Engineers. All rights reserved.

NREL Publication Number

  • NREL/CP-2A00-84065


  • benzoic acid
  • carbon
  • dimers
  • electrochemical oxidation
  • free radical reactions
  • hydrogen
  • hydrogen bonds
  • redox reactions
  • styrene


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