Continuous Flow Aerobic Alcohol Oxidation Reactions Using a Heterogeneous Ru(OH)x/Al2O3 Catalyst

Mannel, David S.; Stahl, Shannon S.; Root, Thatcher W.

doi:10.1021/op5002676

Cited by 50 publications

(38 citation statements)

References 49 publications

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“…135 Stahl et al reported a continuous-flow setup for the aerobic oxidation of diverse benzylic and heterobenzylic alcohols. 152 The mesoscale reactor was constructed out of stainless steel tubing (6 mm OD, 76 mm length) and was packed with commercially available Ru(OH)x/Al2O3 (2.3 wt% Ru) catalyst. A diluted source of oxygen (8% in N2) was used as oxidant to stay below the flammability threshold of the solvent.…”

Section: Transition Metal-catalyzed Aerobic Oxidation Processes In Comentioning

confidence: 99%

“…Continuous flow aerobic alcohol oxidation using Ru(OH)x/Al2O3 as catalyst and O2 (8% in N2) as source of oxidant. 152 One major advantage of microreactors (compared to batch) is the increased heat-transfer characteristics. 19,154,155 This is attributed to the high surface-to-volume ratios of microchannels.…”

Section: Transition Metal-catalyzed Aerobic Oxidation Processes In Comentioning

confidence: 99%

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Liquid phase oxidation chemistry in continuous-flow microreactors

et al. 2016

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Continuous-flow liquid phase oxidation chemistry in microreactors receives a lot of attention as the reactor provides enhanced heat and mass transfer characteristics, safe use of hazardous oxidants, high interfacial areas, and scale-up potential. In this review, an up-to-date overview of both technological and chemical aspects of liquid phase oxidation chemistry in continuous-flow microreactors is given. A description of mass and heat transfer phenomena is provided and fundamental principles are deduced which can be used to make a judicious choice for a suitable reactor. In addition, the safety aspects of continuous-flow technology are discussed. Next, oxidation chemistry in flow is discussed, including the use of oxygen, hydrogen peroxide, ozone and other oxidants in flow. Finally, the scale-up potential for continuous-flow reactors is described.

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Section: Transition Metal-catalyzed Aerobic Oxidation Processes In Comentioning

confidence: 99%

Section: Transition Metal-catalyzed Aerobic Oxidation Processes In Comentioning

confidence: 99%

Liquid phase oxidation chemistry in continuous-flow microreactors

et al. 2016

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“…On one hand, local shortage of oxygen, caused by the low solubility of oxygen in solvents and poor mass transfer, could potentially limit the reaction rate [11][12][13][14][15][16][17][18][19]. On the other hand, an excess of oxygen might cause overoxidation of products or catalysts [11,[20][21][22]. Mixtures of oxygen and organic solvents under elevated temperatures and pressures could also raise serious safety issues [23].…”

Section: Introductionmentioning

confidence: 99%

A Novel Approach for Measuring Gas Solubility in Liquids Using a Tube‐in‐Tube Membrane Contactor

Cao

Kuhn

et al. 2017

Chem Eng & Technol

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A novel approach using a semipermeable Teflon AF-2400 tube-in-tube membrane contactor was developed for the measurement of gas solubility in organic solvents. This membrane ensures gas saturation of liquids in continuous flow at a specific pressure and temperature. After liquid decompression, the amount of gas outgassed was measured with a bubble meter and used for solubility calculation. The proposed method was applied to the measurement of oxygen solubility in toluene and benzyl alcohol. Validation experiments were initially performed by comparing the obtained oxygen solubility in toluene with literature data. With higher temperature, the solubility of oxygen in benzyl alcohol was found to increase, indicating that the oxygen-dissolving process is endothermic. Finally, an empirical correlation of Henry's law constant as a function of temperature was determined.

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“…The liquid residence time  (defined as bed volume/flow rate) was studied with gas flow through determining the system response to the introduction of cinnamaldehyde. The resulting residence time distribution for the normalised response F(t) 35 given by Equation 1, showed a step change, and hence near plug-flow behaviour with relatively little broadening from mixing or axial dispersion (Figure 1). This demonstrates that the catalyst bed was static and filled with well-distributed liquid.…”

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confidence: 99%

Platinum-catalysed cinnamaldehyde hydrogenation in continuous flow

2015

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Platinum is one of the most widely used hydrogenation catalysts. Here we describe the translation of batch reactions to continuous flow, affording tunable C=O versus C=C hydrogenation over a Pt/SiO2 catalyst, resulting in high steady state activity and singlepass yields in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol under mild conditions. Negligible catalyst deactivation occurs under extended flow operation due to removal of reactively-formed poisons from the reaction zone. Process intensification imparts a four-fold enhancement in cinnamyl alcohol productivity.Chemoselectivity underpins 21 st century catalysis, 1, 2 permitting the targeted modification of specific functional groups within complex starting materials, 3-7 notably from biomass-derived feedstocks. 8 Catalytic hydrogenation of organic compounds possessing multiple unsaturated bonds such as α,β-unsaturated aldehydes is particularly challenging, 9-11 necessitating active sites able to discriminate and preferentially activate closely related moieties. Platinum is widely employed in heterogeneously catalysed hydrogenation of diverse functional groups including C=C, 12 C≡C, 13 C=O, 13 C≡N, 14 NO2 15 and aromatics. 15 The selective hydrogenation of allylic and benzylic aldehydes to unsaturated alcohols is a commercially important industrial process within the flavour, fragrance, agrochemical and pharmaceutical sectors, 9, 16 in which active and selective heterogeneous catalysts for such transformations are essential to circumvent the greater thermodynamic stability of C=O relative to C=C bonds. 9 The liquid phase, selective hydrogenation of cinnamaldehyde (CinnALD) to cinnamyl alcohol (CinnOH) illustrated in Scheme 1 is of significant interest due to the widespread use of this allylic alcohol in perfumes and flavourants. [16][17][18][19] Platinum is a promising catalyst for this challenging reaction, in which hydrogenation of the C=C bond is both kinetically and thermodynamically more favourable than the C=O function, 20 and hence the influence of the physicochemical properties of platinum nanoparticles is a topic of much intensive recent investigation in batch reactors. Particle size effects upon CinnOH selectivity have proved controversial, with oleic acid/oleylamine stabilised mono-and bimetallic colloidal Pt nanoparticles reported to exhibit a strong size dependence of CinnOH selectivity, with low coordination sites favoring C=C hydrogenation, 21, 22 whereas Zhu and Zaera reported that CinnOH selectivity was insensitive to the size of silica supported Pt nanoparticles albeit over a narrow size range. 23 Guo et al have shown that confinement of Pt nanoclusters within the cavity of metal-organic frameworks also promotes CinnOH selectivity; with steric constraints on CinnALD believed to hinder C=C planar adsorption with consequent preferential C=O activation. 24 Kinetics of CinnALD hydrogenation are also a function of support properties 25 and hydrogenation pressure. We recently reported a detailed mechanistic study of the structura...

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Continuous Flow Aerobic Alcohol Oxidation Reactions Using a Heterogeneous Ru(OH)_x/Al₂O₃ Catalyst

Cited by 50 publications

References 49 publications

Liquid phase oxidation chemistry in continuous-flow microreactors

Liquid phase oxidation chemistry in continuous-flow microreactors

A Novel Approach for Measuring Gas Solubility in Liquids Using a Tube‐in‐Tube Membrane Contactor

Platinum-catalysed cinnamaldehyde hydrogenation in continuous flow

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