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Issue 12, 2011
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A unique proton coupled electron transfer pathway for electrochemical reduction of acetophenone in the ionic liquid [BMIM][BF4] under a carbon dioxide atmosphere

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Abstract

The mechanism of electrochemical reduction of acetophenone in 1-butyl-3-methylimidazolium tetrafluroborate ([BMIM][BF4]) under nitrogen (N2) and carbon dioxide (CO2) atmospheres have been investigated using transient voltammetry, steady-state voltammetry, bulk electrolysis and numerical simulation. Under a N2 atmosphere, acetophenone undergoes a one-electron reduction to the radical anion followed by rapid dimerization reactions with an apparent rate constant of 1.0 × 106 M−1s−1. In contrast, under a CO2 atmosphere, the electrochemical reduction of acetophenone is an overall two-electron transfer chemically irreversible process with the final electrolysis product being 1-phenylethanol, instead of the anticipated 2-hydroxy-2-phenylpropionic acid resulting from an electrocarboxylation reaction. A proton coupled electron transfer pathway leading to the formation of 1-phenylethanol requires the presence of a sufficiently strong proton donor which is not available in neat [BMIM][BF4]. However, the presence of CO2 enhances the C-2 hydrogen donating ability of [BMIM]+ due to strong complex formation between the deprotonated form of [BMIM]+, N-heterocyclic carbene, and CO2, resulting in a thermodynamically favorable proton coupled electron transfer pathway.

Graphical abstract: A unique proton coupled electron transfer pathway for electrochemical reduction of acetophenone in the ionic liquid [BMIM][BF4] under a carbon dioxide atmosphere

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Publication details

The article was received on 30 Jul 2011, accepted on 16 Sep 2011 and first published on 28 Oct 2011


Article type: Paper
DOI: 10.1039/C1GC15929A
Green Chem., 2011,13, 3461-3468

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    A unique proton coupled electron transfer pathway for electrochemical reduction of acetophenone in the ionic liquid [BMIM][BF4] under a carbon dioxide atmosphere

    S. Zhao, L. Wu, H. Wang, J. Lu, A. M. Bond and J. Zhang, Green Chem., 2011, 13, 3461
    DOI: 10.1039/C1GC15929A

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