Electrochemical Hydroxylation of Arenes Catalyzed by a Keggin Polyoxometalate with a Cobalt(IV) Heteroatom

Alexander M. Khenkin; Miriam Somekh; Raanan Carmieli; Ronny Neumann

doi:10.1002/anie.201801372

Electrochemical Hydroxylation of Arenes Catalyzed by a Keggin Polyoxometalate with a Cobalt(IV) Heteroatom

Alexander M. Khenkin, Miriam Somekh, Raanan Carmieli, Ronny Neumann

Weizmann Institute of Science, Israel

Research output: Contribution to journal › Article › peer-review

16 Citations (Scopus)

Abstract

The sustainable, selective direct hydroxylation of arenes, such as benzene to phenol, is an important research challenge. An electrocatalytic transformation using formic acid to oxidize benzene and its halogenated derivatives to selectively yield aryl formates, which are easily hydrolyzed by water to yield the corresponding phenols, is presented. The formylation reaction occurs on a Pt anode in the presence of [Co^IIIW₁₂O₄₀]⁵⁻ as a catalyst and lithium formate as an electrolyte via formation of a formyloxyl radical as the reactive species, which was trapped by a BMPO spin trap and identified by EPR. Hydrogen was formed at the Pt cathode. The sum transformation is ArH+H₂O→ArOH+H₂. Non-optimized reaction conditions showed a Faradaic efficiency of 75 % and selective formation of the mono-oxidized product in a 35 % yield. Decomposition of formic acid into CO₂ and H₂ is a side-reaction.

Original language	English
Pages (from-to)	5403-5407
Number of pages	5
Journal	Angewandte Chemie - International Edition
Volume	57
Issue number	19
DOIs	https://doi.org/10.1002/anie.201801372
Publication status	Published - May 4 2018

Keywords

C−H bond activation
electrocatalysis
oxidation
polyoxometalate
radicals

ASJC Scopus subject areas

Catalysis
Chemistry(all)

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title = "Electrochemical Hydroxylation of Arenes Catalyzed by a Keggin Polyoxometalate with a Cobalt(IV) Heteroatom",

abstract = "The sustainable, selective direct hydroxylation of arenes, such as benzene to phenol, is an important research challenge. An electrocatalytic transformation using formic acid to oxidize benzene and its halogenated derivatives to selectively yield aryl formates, which are easily hydrolyzed by water to yield the corresponding phenols, is presented. The formylation reaction occurs on a Pt anode in the presence of [CoIIIW12O40]5− as a catalyst and lithium formate as an electrolyte via formation of a formyloxyl radical as the reactive species, which was trapped by a BMPO spin trap and identified by EPR. Hydrogen was formed at the Pt cathode. The sum transformation is ArH+H2O→ArOH+H2. Non-optimized reaction conditions showed a Faradaic efficiency of 75 % and selective formation of the mono-oxidized product in a 35 % yield. Decomposition of formic acid into CO2 and H2 is a side-reaction.",

keywords = "C−H bond activation, electrocatalysis, oxidation, polyoxometalate, radicals",

author = "Khenkin, {Alexander M.} and Miriam Somekh and Raanan Carmieli and Ronny Neumann",

note = "Funding Information: This research was supported by the Israel Science Foundation grant # 763/14 and the Israel Ministry of Science and Technology. R.N. is the Rebecca and Israel Sieff Professor of Organic Chemistry.",

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doi = "10.1002/anie.201801372",

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AU - Khenkin, Alexander M.

AU - Somekh, Miriam

AU - Carmieli, Raanan

AU - Neumann, Ronny

N1 - Funding Information: This research was supported by the Israel Science Foundation grant # 763/14 and the Israel Ministry of Science and Technology. R.N. is the Rebecca and Israel Sieff Professor of Organic Chemistry.

PY - 2018/5/4

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N2 - The sustainable, selective direct hydroxylation of arenes, such as benzene to phenol, is an important research challenge. An electrocatalytic transformation using formic acid to oxidize benzene and its halogenated derivatives to selectively yield aryl formates, which are easily hydrolyzed by water to yield the corresponding phenols, is presented. The formylation reaction occurs on a Pt anode in the presence of [CoIIIW12O40]5− as a catalyst and lithium formate as an electrolyte via formation of a formyloxyl radical as the reactive species, which was trapped by a BMPO spin trap and identified by EPR. Hydrogen was formed at the Pt cathode. The sum transformation is ArH+H2O→ArOH+H2. Non-optimized reaction conditions showed a Faradaic efficiency of 75 % and selective formation of the mono-oxidized product in a 35 % yield. Decomposition of formic acid into CO2 and H2 is a side-reaction.

AB - The sustainable, selective direct hydroxylation of arenes, such as benzene to phenol, is an important research challenge. An electrocatalytic transformation using formic acid to oxidize benzene and its halogenated derivatives to selectively yield aryl formates, which are easily hydrolyzed by water to yield the corresponding phenols, is presented. The formylation reaction occurs on a Pt anode in the presence of [CoIIIW12O40]5− as a catalyst and lithium formate as an electrolyte via formation of a formyloxyl radical as the reactive species, which was trapped by a BMPO spin trap and identified by EPR. Hydrogen was formed at the Pt cathode. The sum transformation is ArH+H2O→ArOH+H2. Non-optimized reaction conditions showed a Faradaic efficiency of 75 % and selective formation of the mono-oxidized product in a 35 % yield. Decomposition of formic acid into CO2 and H2 is a side-reaction.

KW - C−H bond activation

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KW - polyoxometalate

KW - radicals

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Electrochemical Hydroxylation of Arenes Catalyzed by a Keggin Polyoxometalate with a Cobalt(IV) Heteroatom

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