Aerobic Oxidation Of Alcohols Research Articles

Cover Feature: Surface‐Deactivated Core–Shell Metal–Organic Framework by Simple Ligand Exchange for Enhanced Size Discrimination in Aerobic Oxidation of Alcohols (Chem. Eur. J. 34/2020)

Surface deactivated (only pore-active) core–shell-type MOF (metal–organic framework) catalysts for aerobic oxidation of alcohols were synthesized via a simple postsynthetic ligand exchange (PSE) method. They contain TEMPO groups on the ligand as active sites at the core. The highly porous but catalytically inactive shell ensured the substrate size-selective permeability by sieving effects and induced all reactions to take place in the pore of the catalytically active core. More information can be found in the Communication by H. R. Moon, M. Kim, et al. on page 7568.

Facile Synthesis of Xanthenesdiones and Acridinediones through TEMPO/CuCl2 Catalyzed Aerobic Oxidation of Benzyl Alcohols and Cyclization with Cyclohexane-1,3-Dicarbonyl Compounds

A series of xanthenediones, 3 were synthesized from benzyl alcohols, 1 via TEMPO/CuCl2 catalyzed aerobic oxidation, and sequential cyclization with cyclohexane-1,3-dicarbonyl compounds has been achieved. Similarly, the acridine-diones, 5 were obtained using a similar strategy from various benzyl alcohols. The strategy offers a simple experimental procedure, ease of access, within short reaction period, without the use of any hazardous solvents, and expensive chemicals.

Synthesis of Schiff base-functionalized Fullerene Anchored Palladium Complex as a Recyclable Nanocatalyst in the Heck Reaction and Oxidation of Alcohols

The use of nanocarbon support materials such as fullerene (C60) helps the dispersion of catalysts and creats new method to develop nanomaterials as a result of its garbled structure Pd supported on Schiff base modified fullerene (C60LPd2+ and C60LPd0) were fabricated. The obtained catalysts were characterized by FT-IR, XRD, TEM, TGA and ICP. To investigate the catalytic properties, this catalyst was used in aerobic oxidation of alcohols and Heck coupling as model reactions. The results showed that the efficiency of catalyst has about 75% to 92% and 90% to 98% in these two reaction, respectively. The catalyst can be rapidly readily regained and reused at least 5 consecutive cycles without notable leaching and loss its catalytic actuality.

Surface-Deactivated Core-Shell Metal-Organic Framework by Simple Ligand Exchange for Enhanced Size Discrimination in Aerobic Oxidation of Alcohols.

Metal-organic frameworks (MOFs) are an attractive catalyst support for stable immobilization of the active sites in their scaffold due to the high tunability of organic ligands. The active site-functionalized ligands can be easily employed to construct MOFs as porous heterogeneous catalysts. However, the existence of active sites on the external surfaces as well as internal pores of MOFs seriously impedes the selective reaction in the pore. Herein, through a simple post-synthetic ligand exchange (PSE) method we synthesized surface-deactivated (only core-active) core-shell-type MOF catalysts, which contain 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) groups on the ligand as active sites for aerobic oxidation of alcohols. The porous but catalytically inactive shell ensured the size-selective permeability by sieving effects and induced all reactions to take place in the pores of the catalytically active core. Because PSE is a facile and universal approach, this can be rapidly applied to a variety of MOF-based catalysts for enhancing reaction selectivity.

Selective aerobic oxidation of benzyl alcohol on alumina supported Au-Ru and Au-Ir catalysts

Selective oxidation of benzyl alcohol to benzaldehyde with molecular oxygen was studied over sol-derived alumina supported bimetallic Au-Ru and Au-Ir (nominal atomic ratio 1:1) with respect to Au, Ru and Ir monometallic catalysts in both calcined and subsequently reduced states with and without equimolar K2CO3 in toluene at 80 °C. The Au and after an induction period also Au-Ru and Au-Ir samples had good activity and selectivity in the presence of K2CO3, the monometallic Ir and Ru ones showed negligible activity. The different pretreatments did not cause large difference in the catalytic performance, except the Ir containing samples, which were more active in reduced state.The samples were characterized by TEM, STEM-EDS, UV-Vis spectroscopy, XRD and TPR. The surface of the catalysts was investigated by XPS and CO adsorption followed by infrared spectroscopy. We confirmed the interaction between Au and both second metals, and a strongly decreased CO adsorption on gold in the bimetallic samples compared to the monometallic one. Based on the reaction rates related to the estimated Au and second metal surfaces in the bimetallic and corresponding monometallic catalysts synergetic effect is suggested for the calcined and reduced Au-Ru and reduced Au-Ir catalysts in reaction with base addition.

Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV-Vis/ATR-IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas-Liquid Phase Reactions.

Operando EPR, XANES/EXAFS, UV‐Vis and ATR‐IR spectroscopic methods have been coupled for the first time in the same experimental setup for investigation of unclear mechanistic aspects of selective aerobic oxidation of benzyl alcohol by a Cu/TEMPO catalytic system (TEMPO=2,2,6,6‐tetramethylpiperidinyloxyl). By multivariate curve resolution with alternating least‐squares fitting (MCR‐ALS) of simultaneously recorded XAS and UV‐Vis data sets, it was found that an initially formed (bpy)(NMI)CuI‐ complex (bpy=2,2′‐bipyridine, NMI=N‐methylimidazole ) is converted to two different CuII species, a mononuclear (bpy)(NMI)(CH3CN)CuII‐OOH species detectable by EPR and ESI‐MS, and an EPR‐silent dinuclear (CH3CN)(bpy)(NMI)CuII(μ‐OH)2 ⋅CuII (bpy)(NMI) complex. The latter is cleaved in the further course of reaction into (bpy)(NMI)(HOO)CuII‐TEMPO monomers that are also EPR‐silent due to dipolar interaction with bound TEMPO. Both Cu monomers and the Cu dimer are catalytically active in the initial phase of the reaction, yet the dimer is definitely not a major active species nor a resting state since it is irreversibly cleaved in the course of the reaction while catalytic activity is maintained. Gradual formation of non‐reducible CuII leads to slight deactivation at extended reaction times.

Synthesis of Ni2+ cation modified TS-1 molecular sieve nanosheets as effective photocatalysts for alcohol oxidation and pollutant degradation

Improvement of the charge separation of titanosilicate molecular sieves is critical to their use as photocatalysts for oxidative organic transformations. In this work, MFI TS-1 molecular sieve nanosheets (TS-1 NS) were synthesized by a low-temperature hydrothermal method using a tailored diquaternary ammonium surfactant as the structure-directing agent. Introducing Ni2+ cations at the ion-exchange sites of the TS-1 NS framework significantly enhanced its photoactivity in aerobic alcohol oxidation. The optimized Ni cation-functionalized TS-1 NS (Ni/TS-1 NS) provide impressive photoactivity, with a benzyl alcohol (BA) conversion of 78.9% and benzyl aldehyde (BAD) selectivity of 98.8% using O2 as the only oxidant under full light irradiation; this BAD yield is approximately six times greater than that obtained for bulk TS-1, and is maintained for five runs. The excellent photoactivity of Ni/TS-1 NS is attributed to the significantly enlarged surface area of the two-dimensional morphology TS-1 NS, extra mesopores, and greatly improved charge separation. Compared with bulk TS-1, Ni/TS-1 NS has a much shorter charge transfer distance. The as-introduced Ni species could capture the photoelectrons to further improve the charge separation. This work opens the way to a class of highly selective, robust, and low-cost titanosilicate molecular sieve-based photocatalysts with industrial potential for selective oxidative transformations and pollutant degradation.

ε-Caprolactone manufacture via efficient coupling Baeyer-Villiger oxidation with aerobic oxidation of alcohols

To avoid the use of peracids oxidant or highly concentrated hydrogen peroxide which is potentially hazardous and explosive, herein, a new route to ε-caprolactone was developed in which molecule oxygen was employed as the terminal oxidant. The commercial available N-hydroxyphthalimide and ammonium cerium nitrate were used as the key catalysts for the increased yield of ε-caprolactone. For instance, the selectivity of ε-caprolactone was obtained 92 % with 85 % conversion of cyclohexanone which was comparable to the strategies using highly concentrated hydrogen peroxide. The sacrificed alcohols were transformed into corresponding ketones which were also valuable chemicals. Furthermore, the efficiency of the alcohols was achieved to unprecedented 52 %. The Baeyer-Villiger oxidation of various other cycloalkanones was also examined. The substituent group effect on the efficiency of sacrificed alcohols was investigated in which weak electron-donating substituent induced nearly quantitative yield of ε-caprolactone. The reaction mechanism was studied with the help of electron paramagnetic resonance which indicated the existence of a radical pathway.

Aerobic Oxidation of Alcohols on a Gold Catalyst Supported on Ionic Liquid-Bridged Mesoporous Silica

Key words aerobic oxidation - alcohols - gold catalysis - nanoparticles - ionic liquids

TiO2 encapsulated Au nanostars as catalysts for aerobic photo-oxidation of benzyl alcohol under visible light

Gold nanostar (AuNS) particles, characterized by pointed tips emerging from a central core, exhibit localized surface plasmon resonance (LSPR) with strongly amplified electric field upon illumination. Compared to Au nanospheres and nanorods, the absorbance is enhanced with the absorption band extending from 500 to above 1000 nm. However, they are easily reshaped by Ostwald ripening and therefore difficult to use in any application. This study shows that the AuNS particles can be effectively stabilized by encapsulation with TiO2 using a low temperature method. The synthesis parameters and capping solution were optimized to form nanostars. The encapsulated Au nanoparticles promoted the aerobic oxidation of benzyl alcohol to benzaldehyde at ambient temperature under visible light irradiation. AuNS@TiO2 showed significantly higher photocatalytic activity than Au nanospheres, Au nanorods or bulk TiO2 due to its enhanced LSPR. Encapsulation of the colloidal nanoparticles with TiO2 confers robustness to the resulting heterogeneous catalyst with retention of the metal particle size, morphology and associated LSPR properties.

Hydroxyapatite‐supported Manganese Oxides as Efficient Non‐noble‐metal Catalysts for Selective Aerobic Oxidation of Alcohols

AbstractIn this article, hydroxyapatites (HAPs) with different Ca/P ratios have been synthesized as the supports to prepare the MnOx/HAP catalysts for the aerobic oxidation of alcohols. The catalytic activity is strongly influenced by the Ca/P ratio and the calcination temperature as they can affect the acid and basic properties and oxidation state of MnOx of the catalysts. The optimized catalyst MnOx/HAP‐10 can catalyze various primary alcohols to the corresponding aldehydes selectively with excellent conversion (up to 100 %), and can be easily recovered and reused at least four times without any appreciable loss of activity.

Sustainable and recyclable heterogenous palladium catalysts from rice husk-derived biosilicates for Suzuki-Miyaura cross-couplings, aerobic oxidations and stereoselective cascade carbocyclizations

A new eco-friendly approach for the preparation of sustainable heterogeneous palladium catalysts from rice husk-derived biogenic silica (RHP-Si and RHU-Si). The designed heterogeneously supported palladium species (RHP-Si-NH2-Pd and RHU-Si-NH2-Pd) were fully characterized and successfully employed as catalysts for various chemical transformations (C–C bond-forming reactions, aerobic oxidations and carbocyclizations). Suzuki-Miyaura transformations were highly efficient in a green solvent system (H2O:EtOH (1:1) with excellent recyclability, providing the cross-coupling products with a wide range of functionalities in high isolated yields (up to 99%). Palladium species (Pd(0)-nanoparticles or Pd(II)) were also efficient catalysts in the green aerobic oxidation of an allylic alcohol and a co-catalytic stereoselective cascade carbocyclization transformation. In the latter case, a quaternary stereocenter was formed with excellent stereoselectivity (up to 27:1 dr).

Role of bismuth on aerobic benzyl alcohol oxidation over ceria polymorph-supported gold nanoparticles

Relative differences in oxygen vacancy concentrations and defects in the exposed planes have major impact in catalytic activities of different ceria morphologies. Bi3+ has been chosen as an effective dopant to exploit oxygen mobility and lattice defects in ceria polymorphs for better catalytic performance. The characterization results revealed the nature of promotional interaction of bismuth on (110) and (100) exposed planes of gold-ceria nanorods and nanocubes, respectively, in the catalytic oxidation of benzyl alcohol. The Au/Bi-CeO2 nanorods show highest activity (TOF = 105 h−1) due to the highest amount of Frenkel-type lattice defects.

Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts.

In this review, we discuss selected examples from recent literature on the role of the support on directing the nanostructures of Au-based monometallic and bimetallic nanoparticles. The role of support is then discussed in relation to the catalytic properties of Au-based monometallic and bimetallic nanoparticles using different gas phase and liquid phase reactions. The reactions discussed include CO oxidation, aerobic oxidation of monohydric and polyhydric alcohols, selective hydrogenation of alkynes, hydrogenation of nitroaromatics, CO2 hydrogenation, C–C coupling, and methane oxidation. Only studies where the role of support has been explicitly studied in detail have been selected for discussion. However, the role of support is also examined using examples of reactions involving unsupported metal nanoparticles (i.e., colloidal nanoparticles). It is clear that the support functionality can play a crucial role in tuning the catalytic activity that is observed and that advanced theory and characterization add greatly to our understanding of these fascinating catalysts.

Synthesis and characterization of dimeric Schiff base CoII, NiII, CuII complexes for their catalytic application of aerobic oxidation of alcohol and interaction with biomolecules

Three new transition metal (Co(II), Ni(II) and Cu(II)) complexes of Schiff’s base ligand were prepared in situ by refluxing stoichiometric amounts of respective metal salts with 2-hydroxy-1-naphthaldehyde and 2-picolylamine. The structural feature of the synthesized complexes was derived from spectral (FT-IR, UV–Vis and ESI-mass) studies and elemental analysis. The single crystal X-ray diffraction analysis of complex 3 showed the structure as dimeric form [Cu(2-hnppa)Cl]2 and each copper atom is penta-coordinated. The calculated τ value of [Cu(2-hnppa)Cl]2 was 0.25 (where α = 157.84 and β = 172.18) indicating the square pyramidal geometry. Binding of these complexes (1–3) with calf thymus DNA was investigated by UV–Vis, fluorescence, viscosity measurements and computer aided molecular docking studies and the Kb value of complexes 1–3 were 2.4 × 105, 5.9 × 105 and 2.0 × 104M−1, respectively. The relative binding energies of the metal complexes 1–3 docked with DNA were −151.82, −151.86 and −151.80 eV, respectively. Complexes (1–3) exhibited a good binding capability with bovine serum albumin (BSA) with relatively high binding constant values. The complexes also act as a catalyst that enables efficient aerobic oxidation of a broad range of alcohols (benzyl alcohol, n-octanol) to the corresponding aldehydes at room temperature with ambient air as the oxidant.

Silica Encapsulated-Gold Nanoparticles as a Nano-reactor for Aerobic Oxidation of Benzyl alcohols and Tandem Oxidative A3 coupling Reactions in Water

In this work, the encapsulated-Au nanoparticles (NPs) into the silica hollow NPs were synthesized by microwave-assisted preparation of PEG-coated Au NPs, coating them with a layer of organically modified silica and removing the PEG around the Au NPs. The structure of these encapsulated NPs was characterized by TEM, SEM, XRD, FTIR, EDX, TGA, and ICP-OES. These NPs have shown excellent activities in the aerobic oxidation of benzyl alcohol derivatives and tandem oxidative A3 coupling reactions as a catalyst and reactor in the water at room temperature. Synthesis of a new silica/gold nanoparticles as catalytic nano-reactor for carrying out A3-coupling reaction in the water at ambient temperature

Gold nanoparticles onto cerium oxycarbonate as highly efficient catalyst for aerobic allyl alcohol oxidation

Au nanoparticles, generated by the metal vapor synthesis technique, were supported onto cerium oxycarbonate monohydrate (Ce2O(CO3)2·H2O) giving Au@Ce2O(CO3)2·H2O. The obtained heterogeneous catalyst was used in the aerobic allyl alcohol oxidation reaction performed in toluene, showing a notably higher catalytic substrate conversion and isomerization activity compared to Au onto ceria, which is the reference catalyst for this type of catalysis. Results originating from catalytic recycling experiments and PXRD, HRTEM and XPS measurements carried out on recovered Au@Ce2O(CO3)2·H2O, confirmed the stability of the catalyst under aerobic oxidation reaction conditions and hence its recyclability, without the need of a regeneration step.

Cyclohexene Promoted Efficient Biomimetic Oxidation of Alcohols to Carbonyl Compounds Catalyzed by Manganese Porphyrin under Mild Conditions

Summary of main observation and conclusionSelective oxidation of alcohols to corresponding carbonyl compounds is one of the most important processes both in academic and application research. As a kind of biomimetic catalyst, metalloporphyrins‐catalyzed aerobic oxidation of alcohols with aldehyde as hydrogen donator is gathering much attention. However, using olefins as another kind hydrogen donator for aerobic oxidation of alcohols has not been reported. In this study, a system comprising managenese porphyrin and cyclohexene for biomimetic aerobic oxidation of alcohols to carbonyl compounds was developed. The catalytic system exhibited excellent catalytic performance and selectivity towards the corresponding products for most primary and secondary alcohols under mild conditions. Based on the results obtained from experiments as well as in situ EPR (electron paramagnetic resonance) and UV‐vis spectroscopy, the role of cyclohexene was demonstrated.

Site-specific deposition creates electron-rich Pd atoms for unprecedented C−H activation in aerobic alcohol oxidation

Here, we demonstrate a photochemical strategy to site-specifically deposit Pd atoms on Au nanoparticles. The high-sensitivity low-energy ion scattering spectra combined with the X-ray photoelectron spectra reveal that the surface electronic structure of Pd can be continuously regulated by tailoring the Pd-to-Au molar ratio and the location of Pd atoms in AuPd nanoparticles. It is revealed that electron-rich Pd atoms are considerably more active than the net Pd atoms in aerobic alcohol oxidation. Remarkably, the catalyst with the most electron-rich Pd sites (binding energy downshift: 1.0 eV) exhibits an extremely high turnover frequency (˜500000 h−1 vs 12000 h−1 for that with net Pd atoms) for solvent-free selective oxidation of benzyl alcohol, which is, to the best of our knowledge, the highest value ever reported. Kinetic studies reveal that electron-rich Pd atoms can accelerate the oxidation of benzyl alcohol by facilitating C-H cleavage, as indicated by the significant reduction in the activation energy as compared to net Pd atoms.

Scalable Aerobic Oxidation of Alcohols Using Catalytic DDQ/HNO3

A selective, practical, and scalable aerobic oxidation of alcohols is described that uses catalytic amounts of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and HNO3, with molecular oxygen servin...