Tuning the Reactivity of TEMPO during Electrocatalytic Alcohol Oxidations in Room-Temperature Ionic Liquids
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Otros documentos de la autoría: Delorme, Astrid E.; Sans, Victor; Licence, Peter; Walsh, Darren
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https://doi.org/10.1021/acssuschemeng.9b01823 |
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Título
Tuning the Reactivity of TEMPO during Electrocatalytic Alcohol Oxidations in Room-Temperature Ionic LiquidsFecha de publicación
2019-05-22ISSN
2168-0485Cita bibliográfica
DELORME, Astrid, et al. Tuning the Reactivity of TEMPO during Electrocatalytic Alcohol Oxidations in Room-temperature Ionic Liquids. ACS Sustainable Chemistry & Engineering, 2019, vol. 7, no 13, p.11691-11699Tipo de documento
info:eu-repo/semantics/articleVersión de la editorial
https://pubs.acs.org/doi/10.1021/acssuschemeng.9b01823Versión
info:eu-repo/semantics/publishedVersionPalabras clave / Materias
Resumen
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 ... [+]
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 < 1-phenylethanol < octanol < benzyl alcohol, and the RTIL 1-octyl-3-methylmidazolium bis(trifluoromethanesulfonyl)imide ([NTf2]−) shows clear selectivity toward 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. [-]
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ACS Sustainable Chemistry and Engineering, 2019, vol. 7, no 13Derechos de acceso
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