Skip to main content

Research Repository

Advanced Search

Tuning the Reactivity of TEMPO during Electrocatalytic Alcohol Oxidations in Room-Temperature Ionic Liquids

Delorme, Astrid E.; Sans, Victor; Licence, Peter; Walsh, Darren A.

Tuning the Reactivity of TEMPO during Electrocatalytic Alcohol Oxidations in Room-Temperature Ionic Liquids Thumbnail


Authors

Astrid E. Delorme

Victor Sans

DARREN WALSH DARREN.WALSH@NOTTINGHAM.AC.UK
Professor of Chemistry



Abstract

2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) is a promising, sustainable, metal-free mediator for oxidation of alcohols. In this contribution, we describe how the selectivity of TEMPO for electrocatalytic alcohol oxidations in room-temperature ionic liquids (RTILs) can be changed by design of the solvent medium. Cyclic voltammetry of TEMPO in a series of ammonium-, phosphonium-, and imidazolium-based RTILs reveals that the potential at which TEMPO is oxidized increases from 677 mV (vs. the potential of the decamethylferrocene/ decamethylferrocinium, dmFc/dmFc+, redox couple) to 788 mV as the H-bond basicity of the RTIL anions decreases. The increase in potential is accompanied by an increase in the rate constant for oxidation of benzyl alcohol from about 0.1 dm3 mol−1 s−1 to about 0.7 dm3 mol−1 s−1, demonstrating the ability to manipulate the reactivity of TEMPO by judicious choice of the RTIL anions. The rate of alcohol oxidation in a series of RTILs increases in the order 2-butanol < 1phenylethanol < octanol < benzyl alcohol, and the RTIL 1-octyl-3-methylmidazolium bis(trifluoromethanesulfonyl)imide ([NTf2]–) shows clear selectivity towards the oxidation of primary alcohols. In addition, the reaction kinetics and selectivity are better in [NTf2]–-based RTILs than in acetonitrile, often the solvent-of-choice in indirect alcohol electrooxidations. Finally, we demonstrate that electrolytic TEMPO-mediated alcohol oxidations can be performed using RTILs in a flow-electrolysis system, with excellent yields and reaction selectivity, demonstrating the opportunities offered by such systems.

Citation

Delorme, A. E., Sans, V., Licence, P., & Walsh, D. A. (2019). Tuning the Reactivity of TEMPO during Electrocatalytic Alcohol Oxidations in Room-Temperature Ionic Liquids. ACS Sustainable Chemistry and Engineering, 7(13), 11691-11699. https://doi.org/10.1021/acssuschemeng.9b01823

Journal Article Type Article
Acceptance Date May 22, 2019
Online Publication Date May 22, 2019
Publication Date Jul 1, 2019
Deposit Date Jun 14, 2019
Publicly Available Date May 23, 2020
Journal ACS Sustainable Chemistry & Engineering
Electronic ISSN 2168-0485
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 7
Issue 13
Pages 11691-11699
DOI https://doi.org/10.1021/acssuschemeng.9b01823
Public URL https://nottingham-repository.worktribe.com/output/2188265
Publisher URL https://pubs.acs.org/doi/10.1021/acssuschemeng.9b01823
Contract Date Jun 14, 2019

Files





You might also like



Downloadable Citations