A unique proton coupled electron transfer pathway for electrochemical reduction of acetophenone in the ionic liquid [BMIM][BF(4)] under a carbon dioxide atmosphere

Shu-Feng Zhao, La-Xia Wu, Huan Wang, Jia-Xing Lu, Alan Bond, Jie Zhang

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Abstract

The mechanism of electrochemical reduction of acetophenone in 1-butyl-3-methylimidazolium tetrafluroborate ([BMIM][BF(4)]) under nitrogen (N(2)) and carbon dioxide (CO(2)) atmospheres have been investigated using transient voltammetry, steady-state voltammetry, bulk electrolysis and numerical simulation. Under a N(2) atmosphere, acetophenone undergoes a one-electron reduction to the radical anion followed by rapid dimerization reactions with an apparent rate constant of 1.0 x 10(6) M(-1) s(-1). In contrast, under a CO(2) 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][BF(4)]. However, the presence of CO(2) enhances the C-2 hydrogen donating ability of [BMIM](+) due to strong complex formation between the deprotonated form of [BMIM](+), N-heterocyclic carbene, and CO(2), resulting in a thermodynamically favorable proton coupled electron transfer pathway.
Original languageEnglish
Pages (from-to)3461 - 3468
Number of pages8
JournalGreen Chemistry
Volume13
Issue number12
DOIs
Publication statusPublished - 2011

Cite this

@article{7cf9e7a31b5d404aa502cb50ad60f553,
title = "A unique proton coupled electron transfer pathway for electrochemical reduction of acetophenone in the ionic liquid [BMIM][BF(4)] under a carbon dioxide atmosphere",
abstract = "The mechanism of electrochemical reduction of acetophenone in 1-butyl-3-methylimidazolium tetrafluroborate ([BMIM][BF(4)]) under nitrogen (N(2)) and carbon dioxide (CO(2)) atmospheres have been investigated using transient voltammetry, steady-state voltammetry, bulk electrolysis and numerical simulation. Under a N(2) atmosphere, acetophenone undergoes a one-electron reduction to the radical anion followed by rapid dimerization reactions with an apparent rate constant of 1.0 x 10(6) M(-1) s(-1). In contrast, under a CO(2) 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][BF(4)]. However, the presence of CO(2) enhances the C-2 hydrogen donating ability of [BMIM](+) due to strong complex formation between the deprotonated form of [BMIM](+), N-heterocyclic carbene, and CO(2), resulting in a thermodynamically favorable proton coupled electron transfer pathway.",
author = "Shu-Feng Zhao and La-Xia Wu and Huan Wang and Jia-Xing Lu and Alan Bond and Jie Zhang",
year = "2011",
doi = "10.1039/c1gc15929a",
language = "English",
volume = "13",
pages = "3461 -- 3468",
journal = "Green Chemistry",
issn = "1463-9262",
publisher = "Royal Sciety of Chemistry",
number = "12",

}

A unique proton coupled electron transfer pathway for electrochemical reduction of acetophenone in the ionic liquid [BMIM][BF(4)] under a carbon dioxide atmosphere. / Zhao, Shu-Feng; Wu, La-Xia; Wang, Huan; Lu, Jia-Xing; Bond, Alan; Zhang, Jie.

In: Green Chemistry, Vol. 13, No. 12, 2011, p. 3461 - 3468.

Research output: Contribution to journalArticleResearchpeer-review

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T1 - A unique proton coupled electron transfer pathway for electrochemical reduction of acetophenone in the ionic liquid [BMIM][BF(4)] under a carbon dioxide atmosphere

AU - Zhao, Shu-Feng

AU - Wu, La-Xia

AU - Wang, Huan

AU - Lu, Jia-Xing

AU - Bond, Alan

AU - Zhang, Jie

PY - 2011

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N2 - The mechanism of electrochemical reduction of acetophenone in 1-butyl-3-methylimidazolium tetrafluroborate ([BMIM][BF(4)]) under nitrogen (N(2)) and carbon dioxide (CO(2)) atmospheres have been investigated using transient voltammetry, steady-state voltammetry, bulk electrolysis and numerical simulation. Under a N(2) atmosphere, acetophenone undergoes a one-electron reduction to the radical anion followed by rapid dimerization reactions with an apparent rate constant of 1.0 x 10(6) M(-1) s(-1). In contrast, under a CO(2) 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][BF(4)]. However, the presence of CO(2) enhances the C-2 hydrogen donating ability of [BMIM](+) due to strong complex formation between the deprotonated form of [BMIM](+), N-heterocyclic carbene, and CO(2), resulting in a thermodynamically favorable proton coupled electron transfer pathway.

AB - The mechanism of electrochemical reduction of acetophenone in 1-butyl-3-methylimidazolium tetrafluroborate ([BMIM][BF(4)]) under nitrogen (N(2)) and carbon dioxide (CO(2)) atmospheres have been investigated using transient voltammetry, steady-state voltammetry, bulk electrolysis and numerical simulation. Under a N(2) atmosphere, acetophenone undergoes a one-electron reduction to the radical anion followed by rapid dimerization reactions with an apparent rate constant of 1.0 x 10(6) M(-1) s(-1). In contrast, under a CO(2) 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][BF(4)]. However, the presence of CO(2) enhances the C-2 hydrogen donating ability of [BMIM](+) due to strong complex formation between the deprotonated form of [BMIM](+), N-heterocyclic carbene, and CO(2), resulting in a thermodynamically favorable proton coupled electron transfer pathway.

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