Recent advances in green catalytic oxidations of alcohols in aqueous media

Sheldon, Roger A.

doi:10.1016/j.cattod.2014.08.024

Cited by 185 publications

(109 citation statements)

References 127 publications

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“…Green catalytic and electrocatalytic processes are of considerable interest for sustainable chemical processes [1]. Controlling molecular electrocatalyst reactivity within a microporous host environment (here the host is a highly rigid polymer of intrinsic microporosity, PIM [2]) offers opportunities for (i) improved selectivity due to host-substrate interactions, (ii) increased reactivity due to modified catalystsubstrate interaction and (iii) control over catalyst density and co-catalyst effects.…”

Section: Introductionmentioning

confidence: 99%

Polymer of Intrinsic Microporosity Induces Host-Guest Substrate Selectivity in Heterogeneous 4-Benzoyloxy-TEMPO-Catalysed Alcohol Oxidations

et al. 2015

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The free radical 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4B-TEMPO) is active as an electrocatalyst for primary alcohol oxidations when immobilised at an electrode surface and immersed into an aqueous carbonate buffer solution. In order to improve the catalytic process, a composite film electrode is developed based on (i) carbon microparticles of 2-12 μm diameter to enhance charge transport and (ii) a polymer of intrinsic microporosity (here PIM-EA-TB with a BET surface area of 1027 m 2 g −1 ). The latter acts as a highly rigid molecular framework for the embedded free radical catalyst with simultaneous access to aqueous phase and substrate. The resulting mechanism for the oxidation of primary alcohols is shown to switch in reaction order from first to zeroth with increasing substrate concentration consistent with a kinetically limited process with competing diffusion of charge at the polymer layer-electrode interface (here the BLEk^case in Albery-Hillman notation). Reactivity optimisation and screening for a wider range of primary alcohols in conjunction with DFT-based relative reactivity correlation reveals substrate hydrophobicity as an important factor for enhancing catalytic currents. The PIM-EA-TB host matrix is proposed to control substrate partitioning and thereby catalyst reactivity and selectivity.

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Section: Introductionmentioning

confidence: 99%

Polymer of Intrinsic Microporosity Induces Host-Guest Substrate Selectivity in Heterogeneous 4-Benzoyloxy-TEMPO-Catalysed Alcohol Oxidations

et al. 2015

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“…The electrochemistry of nitroxyl based free radicals is of broader interest and often seen as an alternative to metal-based catalysis (organo-catalysis [20,21]). TEMPO derivatives alone or combinations of TEMPO with metals [22,23] or with enzymes [24] provide versatile tools in bio-mass conversion [25,26,27] and in electrosynthetic processing [28].…”

mentioning

confidence: 99%

Hydrodynamic Rocking Disc Electrode Study of the TEMPO‐mediated Catalytic Oxidation of Primary Alcohols

et al. 2016

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The hydrodynamically thinned diffusion layer at a sinusoidally rocking disc is approximately uniform and can be expressed in terms of a diffusion layer thickness δRoDE=9.0D13ν16Θf with D, the diffusion coefficient of the redox active species, v, the kinematic viscosity, Θ, the total rocking angle (here 90 degrees), and f, the rocking frequency (ranging here from 0.83 to 25 Hz). For the one‐electron oxidation of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) in aqueous carbonate buffer pH 9.5, it is shown that there is quantitative agreement between the expression for the diffusion layer thickness and experimental data. Next, for seven primary alcohols, the catalytic TEMPO‐mediated oxidation mechanism is investigated under rocking disc conditions. Chemical rate constants are evaluated (by varying the diffusion layer thickness) employing the DigiElch4.F simulation package. Trends in the chemical rate constants (compared with DFT calculations) suggest enhanced reactivity for methanol versus higher primary alcohols and for aromatic versus non‐aromatic primary alcohols. Rocking disc voltammetry allows quantitative mechanistic analysis in the laminar flow regime.

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“…18,19,54 However, the conversions obtained with 4 S were optimal under a moderate oxygen pressure of 2 bar instead of the 30 bar of air employed with the phenanthroline complex (6.3 bar partial pressure of oxygen). We performed additional tests to study the performance of 4 S in the oxidation of other alcohols under the conditions optimized for 1-phenylethanol (Scheme 5).…”

Section: Scheme 4 Catalytic Oxidation Of 1-phenylethanolmentioning

confidence: 99%

Synthesis of water-soluble palladium(ii) complexes with N-heterocyclic carbene chelate ligands and their use in the aerobic oxidation of 1-phenylethanol

et al. 2017

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The synthesis of palladium(ii) complexes containing N-heterocyclic carbene chelate ligands is reported. These chelate ligands have methylene or ethylene ring bridges and sulfonate, carbonate or ammonium functionalities to render the complexes soluble in water. Bis- [(bis-NHC)PdX] (X = Cl, Br or I) and tetra-carbene [(bis-NHC)Pd] complexes have been prepared and the crystal structures of two of them have been determined. The NHC ligand is coordinated to the metal center in normal (C2-bound) or abnormal (C4-bound) mode. Processes involving the formation of NHC-Pd bonds or the transfer of NHC ligands have been explored in water. The behavior of the bis-carbene complexes as catalysts for the aerobic oxidation of 1-phenylethanol is also discussed.

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Recent advances in green catalytic oxidations of alcohols in aqueous media

Cited by 185 publications

References 127 publications

Polymer of Intrinsic Microporosity Induces Host-Guest Substrate Selectivity in Heterogeneous 4-Benzoyloxy-TEMPO-Catalysed Alcohol Oxidations

Polymer of Intrinsic Microporosity Induces Host-Guest Substrate Selectivity in Heterogeneous 4-Benzoyloxy-TEMPO-Catalysed Alcohol Oxidations

Hydrodynamic Rocking Disc Electrode Study of the TEMPO‐mediated Catalytic Oxidation of Primary Alcohols

Synthesis of water-soluble palladium(ii) complexes with N-heterocyclic carbene chelate ligands and their use in the aerobic oxidation of 1-phenylethanol

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