Aerobic Oxidation Of Alcohols Research Articles

Highly dispersive Pd nanoparticles decorated strontium niobate nanosheets: Efficient and recyclable catalyst for base-free aerobic oxidation of benzyl alcohols in water

2D perovskite Sr2Nb3O10 (SNO) nanosheets were synthesized by cation exchange-assisted liquid exfoliation and applied as supports for the immobilization of palladium (Pd) nanoparticles through the electrostatic assembly with Pd(NH3)42+ precursors and successive in-situ photoreduction. Pd nanoparticles with an average diameter of 9.22 nm are uniformly dispersed on the surface of strontium niobate nanosheets. The obtained nanohybrid Pd-SNO could serve as an efficient heterogeneous catalyst for the atmospheric pressure oxidation of benzyl alcohol to benzaldehyde by using air as an oxidizing agent and water as the sole solvent at low temperature (80 °C). Furthermore, the catalyst could be easily separated from the reaction mixture by simple centrifugation and reused five times without significant degradation in catalytic activity under the investigated conditions. We believe that the synthetic strategy described in this work is a feasible means of developing effective noble metal/layered transition metal oxide hybrid catalysts for organic reactions.

Catalytic Oxidation of Benzyl Alcohol to Benzaldehyde on Au8 and Au6Pd2 Clusters: A DFT Study on the Reaction Mechanism

Density functional theory calculations were performed to investigate the reaction mechanism of the aerobic oxidation of benzyl alcohol to benzaldehyde catalyzed by Au and Au–Pd clusters. Two consecutive reaction mechanisms were examined with Au8 and Au6Pd2 clusters: (1) the oxidation of benzyl alcohol with dissociated O atoms on metal clusters generating benzaldehyde and H2O; and (2) oxidation with adsorbed oxygen molecules generating benzaldehyde and H2O2. The calculations show that the aerobic oxidation of benzyl alcohol energetically prefers to proceed in the former mechanism, which agrees with the experimental observation. We demonstrate that the role of Au centers around the activation of molecular oxygen to peroxide-like species, which are capable of the H–abstraction of benzyl alcohol. The roles of Pd in the Au6Pd2 cluster are: (1) increasing the electron distribution to neighboring Au atoms, which facilitates the activation of O2; and (2) stabilizing the adsorption complex and transition states by the interaction between positively charged Pd atoms and the π-bond of benzyl alcohol, both of which are the origin of the lower energy barriers than those of Au8.

A green, reusable and remarkable catalyst for selective aerobic oxidation of alcohols: Construction of Cu(BDC) on the surface of carboxymethyl cellulose fiber

Removing or reducing the amount of metal used in catalytic methods is one of the most important concerns of today's activists in the field of green chemistry. In the present paper, copper terephthalate metal-organic framework (MOF) is chemically attached to carboxymethyl cellulose fiber via an in-situ synthesizing method. The synthesized novel hybrid material (Cu(BDC)/CMC) was applied as an efficient, reusable, and environmentally benign heterogeneous catalyst for the aerobic oxidation of alcohols to the corresponding aldehydes and ketones with good yields under mild conditions. FT-IR, XRD, TGA, SEM, EDS, and TEM techniques confirmed successful construction of catalyst. Obtained results revealed that primary aromatic alcohols are easily converted to aromatic aldehydes in high yields (from 70 to 94 %) with the zero-order kinetics model without additional oxidation to carboxylic acids compared to secondary aromatic alcohols (yields: from 6 to 22). The outstanding advantages of the synthesized catalyst are a non‐hazardous catalyst, desired yields, good selectivity, operational simplicity, mild reaction conditions, and reusability. On the other hand, this catalytic system overcomes essential defects of copper terephthalate MOFs as a catalyst, such as poisoning, deactivation, and non-reusability nature.

Mechanism and kinetics of the aerobic oxidation of benzyl alcohol to benzaldehyde catalyzed by cobalt porphyrin in a membrane microchannel reactor

The highly efficient selective aerobic oxidation of benzyl alcohol to benzaldehyde catalyzed by cobalt porphyrin was achieved in a membrane microchannel reactor. The efficiency of benzyl alcohol oxidation was remarkably improved in the micro-structured chemical system, achieving a conversion and benzaldehyde selectivity of 82% and 98%, respectively, in 6.5 min. The classification and transfer of free radicals, as well as the oxygen-transfer mechanism, were determined by in situ EPR (electron paramagnetic resonance) and in situ UV–visible spectroscopy. Further kinetic studies revealed that the oxidation of benzyl alcohol follows the Michaelis–Menten kinetics, with Km = 0.133 mol/L.A mathematic kinetic model was proposed, and the kinetic model fitted the experimental data well. The mathematical model can predict the reaction process at a wide range of benzyl alcohol concentrations, which is beneficial for the process optimization and reactor design.

A new catalytic approach for aerobic oxidation of primary alcohols based on a Copper(I)-thiophene carbaldimines

• Novel in situ copper(I) iodide schiff base catalysts. • High activity for the aerobic oxidation of benzylic, allylic and aliphatic alcohols. • Quantitative yields for benzaldehyde in 3 h with a catalyst loading of 2.5 mol%. • Diol oxidation to the corresponding lactol. We report here novel Cu(I) thiophene carbaldimine catalysts for the selective aerobic oxidation of primary alcohols to their corresponding aldehydes and various diols to lactones or lactols. In the presence of the in situ generated Cu(I) species, a persistent radical (2,2,6,6-tetramethylpiperdine-N-oxyl (TEMPO)) and N-methylimidazole (NMI) as an auxiliary ligand, the reaction proceeds under aerobic conditions and at ambient temperature. Especially the catalytic system of 1-(thiophen-2-yl)-N-(4-(trifluoromethoxy)phenyl)methanimine (ligand L2 ) with copper(I)-iodide showed high reactivity for all kind of alcohols (benzylic, allylic and aliphatic). In the case of benzyl alcohol even 2.5 mol% of copper loading gave quantitative yield. Beside high activity under aerobic conditions, the catalysts ability to oxidize 1,5-pentadiol to the corresponding lactol (86% in 4 h) and N-phenyldiethanolamine to the corresponding morpholine derivate lactol (86% in 24 h) is particularly noteworthy.

Corrigendum to A new catalytic approach for aerobic oxidation of primary alcohols based on a Copper(I)-thiophene carbaldimines [Mol. Catal. 509 (2021), 111637

Corrigendum to A new catalytic approach for aerobic oxidation of primary alcohols based on a Copper(I)-thiophene carbaldimines [Mol. Catal. 509 (2021), 111637

Activating Metalloenzymes By Electricity: Bioelectrocatalytic Aerobic Oxidation in the Synthesis of Islatravir

Electrochemistry is a green and sustainable technique that has been widely applied in bioanalysis, organic synthesis and energy conversion. Despite the huge potential for green and selective synthesis, bioelectrochemistry is uncommon in synthetic organic applications. The recently disclosed fully biocatalytic cascade synthesis of the HIV drug islatravir represents a groundbreaking approach to pharmaceutical manufacturing. The first step in the synthesis is the biocatalytic desymmetrizing oxidation of ethynyl glycerol to (R)-ethynyl glyceraldehyde. This oxidation process requires 3 redox enzymes: Cu-dependent galactose oxidase (GOase) together with two auxiliary enzymes: catalase and horseradish peroxidase (HRP). While elegant, this three-enzyme system introduced a significant cost and protein burden. GOase is critical to achieving enantioselectivity, while HRP is proposed to facilitate generation of catalytically active intermediate through modification of the oxidation state of the GOase active site. Thus we sought electrochemical strategies to achieve enzyme activation and replace HRP. Here we disclose the development of bioelectrocatalytic aerobic oxidation of alcohols under mild conditions, using a water-soluble ferrocene derivative as the electrocatalyst. Mechanistic insights into the electrochemical activation of GOase were gathered by interrogating the enzyme redox properties and the electron transfer rates between GOase and the electrochemically generated oxidants.

Chemoselective and ligand‐free aerobic oxidation of benzylic alcohols to carbonyl compounds using alumina‐supported mesoporous nickel nanoparticle as an efficient recyclable heterogeneous catalyst

An economically efficient and operationally simple ligand‐free protocol for the chemoselective oxidation of benzylic alcohols to carbonyl compounds has been developed using alumina‐supported nickel nanoparticles as a stable recyclable heterogeneous catalyst along with potassium tert‐butoxide in the presence of aerial oxygen as an eco‐friendly oxidant. The aliphatic alcohols remained unaffected under the present condition. Excellent chemoselectivity has also been demonstrated through intermolecular and intramolecular competition experiments. This protocol accommodates a diverse range of substituents with the tolerance of various sensitive moieties during the reaction. The catalyst could be recovered by filtration and reused consecutively without any significant loss in the catalytic activity. Moreover, the heterogeneity of the catalyst has also been established by the “hot filtration method (Sheldon's test)”.

Expansion of Substrate Scope for Nitroxyl Radical/Copper-Catalyzed Aerobic Oxidation of Primary Alcohols: A Guideline for Catalyst Selection.

Four distinctive sets of optimum nitroxyl radical/copper salt/additive catalyst combinations have been identified for accommodating the aerobic oxidation of various types of primary alcohols to their corresponding aldehydes. Interestingly, less nucleophilic catalysts exhibited higher catalytic activities for the oxidation of particular primary allylic and propargylic alcohols to give α,β-unsaturated aldehydes that function as competent Michael acceptors. The optimum conditions identified herein were successful in the oxidation of various types of primary alcohols, including unprotected amino alcohols and divalent-sulfur-containing alcohols in good-to-high yields. Moreover, N-protected alaninol, an inefficient substrate in the nitroxyl radical/copper-catalyzed aerobic oxidation, was oxidized in good yield. On the basis of the optimization results, a guideline for catalyst selection has been established.

Biomimetic donor-acceptor motifs in carbon nitrides: Enhancing red-light photocatalytic selective oxidation by rational surface engineering

Oxidation, especially selective oxidation by a heterogeneous catalyst with molecular oxygen, is a core technology for the conversion of petrochemical feedstock to commodity chemicals and pharmaceuticals. Existing catalytic approaches for efficient aerobic oxidation normally rely on the engagement of organometallic centers or transition-metal nanoparticles. In light of the necessity to develop sustainable production methodologies, multiple approaches for the metal-free polymeric carbon nitride (PCN) photocatalytic selective oxidation have been evaluated. However, the insufficient visible light optical absorption, poor charge-carriers separation and the weak driving force towards oxidation reaction impart a serious restriction on the efficiency and selectivity of the organic photosynthesis, especially under extended wavelength solar light irradiation. Here, we report a surface engineering photochemical modification method to fabricate a donor-acceptor (D-A) functional carbon nitride photocatalyst (ECN) under ambient conditions. The well-developed d-A structure, preserved high crystallinity and enlarged π-conjugation framework of the hybrid semiconductor-molecule ECN samples favor the improvement of the optical absorption, as well as the enhanced separation and migration of the photo-generated charge carriers. As a result, the obtained ECN photocatalysts exhibited remarkable enhancement in the photocatalytic aerobic oxidation of alcohols, even under an extended light wavelength of 620 nm red-light irradiation. The photocatalytic aerobic sulfides and sp3 C–H oxidation reactions were also considerably accelerated over ECN and may serve as a direct approach for the construction of value-added sulfoxide and ketone products.

On-Demand Electrochemical Synthesis of Tetrakisacetonitrile Copper(I) Triflate and Its Application in the Aerobic Oxidation of Alcohols.

An on-demand electrochemical synthesis of copper(I) triflate under both batch and continuous flow conditions has been developed. A major benefit of the electrochemical methodology is that the only byproduct of the reaction is hydrogen gas, which obviates the need for workup and purification, and water is not incorporated into the product. Upon completion of the electrochemical synthesis, solutions are directly transferred or dispensed into reaction mixtures for the catalytic oxidation of benzyl alcohol with no requirement for workup or purification.

Highly Efficient and Selective Aerobic Oxidation of Cinnamyl Alcohol under Visible Light over Pt-Loaded NaNbO3 Enriched with Oxygen Vacancies by Ni Doping

NaNbO3 enriched with oxygen vacancies by Ni doping was successfully synthesized via a polymerized complex method and applied as a photocatalyst in the oxidation of cinnamyl alcohol (CA) to cinnamal...

Additive-free aerobic C-H oxidation through a defect-engineered Ce-MOF catalytic system

Ce-UiO-66 MOF, namely cerium-organic framework was prepared through a fast and efficient method under ultrasonic radiation. After preparation, it was identified using some different microscopic and spectroscopic techniques such as PXRD, FT-IR, TG/DTA, BET, BJH, and FE-SEM. The catalytic activity of Ce-UiO-66 MOF was checked in aerobic oxidation of methyl arenas, alcohols and styrene derivatives in a sustainable circumstance with no additives. Moreover, its catalytic activity was surveyed influenced by a number of variables in the ultrasonic synthesis method. Some parameters such as solvent, base, temperature, amount of the catalyst and time were also tested to optimize the aerobic oxidation reaction. After the 10th run, the recycled Ce-MOF showed an acceptable efficiency, which proved its high reusability and stability under optimized conditions. Furthermore, the Ce-UiO-66 was investigated structurally by PXRD method which demonstrated the catalyst stability after the aerobic oxidation reaction. • Aerobic oxidation of methyl arenes, alcohols, and styrene derivatives. • Simple and efficient synthesis method for defect-engineered Ce-MOF preparation. • Using a non-precious metal catalyst for the aerobic oxidation process. • Air as a green oxidant for the oxidation process. • Using inert solvents to increase oxygen solubility and efficiency.

The superiority of cuprous chloride to iodide in the selective aerobic oxidation of benzylic alcohols at ambient temperature

Cuprous halides, best described as (CuX)n (X = Cl−, Br−, and I−) in their solid state, catalyse selective aerobic oxidation of alcohols with the assistance of both NMI (N‐methylimidazole) and TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl), and the iodide generally demonstrates the highest activity, for example, in the oxidation of 1‐octanol at ambient temperature under 24 h' reaction. However, in the aerobic oxidation of benzylic alcohols, the chloride showed superiority to the iodide in that the aerobic oxidation was quantitatively completed within 3 h at ambient temperature whereas the iodide showed only about half the activity of the chloride analogue. By probing the system using electrochemistry, electric conductivity, and 1H NMR titration, it was revealed that the surprising anomaly was due to the difference in the rate of forming active species, [Cu (NMI)2X(MeCN)], from the polymeric solid in a two‐stage process. Substrates expansion of 11 benzylic alcohols indicated that CuCl/NMI/TEMPO system demonstrated quantitative conversion of benzylic alcohols into corresponding aldehydes within 3 h and showed great tolerance to the substituents on the phenyl ring of the substrates. Furthermore, electron‐withdrawing substituent was beneficial to the oxidation and could offset the steric effect at orthro‐substituent. Such a behaviour suggested that in the catalysis, increasing the acidity of the hydroxyl group (OH) of the substrates could ease the oxidation, which implied that the deprotonation via an internal pathway might be one of the rate‐determining steps. Our results also showed that the anion halide participated actively in the catalysis by coordinating to Cu(I) in the active species.

Pd-Based Polysaccharide Hydrogels as Heterogeneous Catalysts for Oxidation of Aromatic Alcohols

Immobilization of Pd(OAc)2(TPPTS)2 in various renewable polysaccharides hydrogels, yielded heterogeneous catalysts that were successfully used, for the first time, in the aerobic oxidation of benzylic alcohol. The new catalysts were easily removed from the reaction mixture and recycled with some loss of activity. Among all tested polysaccharides, iota-carrageenan was found to be the most suitable support, using calcium chloride as a gelation agent.

Comparative study of size-selected gold clusters (Au38) and gold nanoparticles over porous cerium-based metal–organic frameworks with UiO-66 architecture for aerobic oxidation of cinnamyl alcohol

The catalytic activity of the size-selected gold clusters Au38(SCH2CH2Ph)24 (abbreviated with Au38) in 3-D nanoporous Ce-metal–organic framework (Ce–UiO-66) was studied. The Au38 nanoclusters were in situ immersed in Ce–UiO-66 with a loading percentage of 1 wt%. The Au38@Ce–UiO-66 catalyst demonstrated excellent catalytic activity for aerobic oxidation of cinnamyl alcohol. The oxidation reaction was tested from 40 to 100 °C utilizing O2 gas (30 ml min−1) as an oxidizing agent in atmospheric pressure. 0.1 mol% of the Au38@Ce–UiO-66 catalyst achieved 65% cinnamyl alcohol conversion at 100 °C within an hour with 100% selectivity toward cinnamaldehyde in toluene. In the case of using an aqueous solvent instead of an organic solvent (toluene), the conversion was increased to 75% under the same reaction condition. The cinnamyl alcohol conversion was increased gradually by increasing the reaction time over Au38@Ce–UiO-66 catalyst, where the conversion was enhanced to 93% after 5 h of heating at 100 °C in water. The catalytic activity of the Au38@Ce–UiO-66 catalyst was largely enhanced after oxygen thermal pretreatment at 100–200 °C, where the catalyst achieved 990 h−1 turnover frequency (TOF) after O2-pretreatment at 175 °C with 92% cinnamaldehyde and 8% cinnamic acid selectivity. The unique atomic packing structure and electronic properties of the size-selected gold nanoclusters (Au38) are responsible for their extraordinary catalytic activity. Moreover, the support (Ce–UiO-66) has a big role in the catalyst activity, since it has a high ability to absorb large quantities from oxygen on the Ce(III)/Ce(IV) centers and generate active oxygen species such as superoxo and peroxo species on the catalyst surface, which help in oxidation of cinnamyl alcohol. For comparison, gold nanoparticles were loaded over the same support, where the Au(III) ions were reduced by two different reduction methods utilizing NaBH4 in the absence of the ligand and hydrogen reduction at 200 °C, 4 h. The particle size of the Au38 clusters and gold nanoparticles over Ce–UiO-66 was investigated by a high-resolution transmission electron microscope (HR-TEM). The charge of the gold clusters and nanoparticles was zero as confirmed by X-ray photoelectron spectroscopy (XPS). The crystallinity and surface texture properties of the prepared catalysts and the pure support were measured by powder X-ray diffraction analysis and N2 gas sorption isotherm at − 196 °C, respectively.

Catalytic study of the copper-based magnetic nanocatalyst on the aerobic oxidation of alcohols in water

Catalytic study of the copper-based magnetic nanocatalyst on the aerobic oxidation of alcohols in water

Insights into the Structure-Activity Relationship in Aerobic Alcohol Oxidation over a Metal-Organic-Framework-Supported Molybdenum(VI) Catalyst.

The understanding of structure-activity relationships at the atomic level has played a profound role in heterogeneous catalysis, providing valuable insights into designing suitable heterogeneous catalysts. However, uncovering the detailed roles of how such active species' structures affect their catalytic performance remains a challenge owing to the lack of direct structural information on a specific active species. Herein, we deposited molybdenum(VI), an active species in oxidation reactions, on the Zr6 node of a mesoporous zirconium-based metal-organic framework (MOF) NU-1200, using solvothermal deposition in MOFs (SIM). Due to the high crystallinity of the NU-1200 support, the precise structure of the resulting molybdenum catalyst, Mo-NU-1200, was characterized through single-crystal X-ray diffraction (SCXRD). Two distinct anchoring modes of the molybdenum species were observed: one mode (Mo1), displaying an octahedral geometry, coordinated to the node through one terminal oxygen atom and the other mode (Mo2) coordinated to two adjacent Zr6 node oxygen atoms in a tetrahedral geometry. To investigate the role of base in the catalytic activity of these Mo centers, we assessed the activity of Mo-NU-1200 for the aerobic oxidation of 4-methoxybenzyl alcohol as a model reaction. The results revealed that Mo-NU-1200 exhibited remarkably higher catalytic reactivity under base-free conditions, while the presence of base inhibited the catalytic reactivity of this species. SCXRD studies revealed that the molybdenum binding motifs (structures of the supported metal on the Zr6 node in the MOF) changed over the course of the reactions. Following the oxidation without base, both pristine coordination modes (Mo1 and Mo2) evolved into a new coordination mode (Mo3), in which the molybdenum atom coordinated to two adjacent oxygen atoms from the Zr6 node in an octahedral geometry, while in the presence of base, the pristine Mo1 coordination mode evolved entirely into the pristine Mo2. This study demonstrates the direct observation of an active species' structural evolution from metal installation to subsequent catalytic reaction. As a result, these subtle structural changes in catalyst binding motifs led to distinct differences in catalytic activities, providing a compelling strategy for elucidating structure-activity relationships.

Selective Aerobic Oxidation of Benzyl Alcohols with Palladium(0) Nanoparticles Suspension in Water

This study concerns one of the rare applications of a suspension of palladium nanoparticles in water for oxidation reactions. The aqueous suspension containing well dispersed nanoparticles of 3.85 nm was obtained following a straightforward procedure involving the reduction of Na2PdCl4 with NaBH4 in the presence of PVP as stabilizing agent. In the way of oxidative catalytic valorisation of lignin, the aqueous suspension was directly applied as catalytic medium for the selective oxidation of vanillic alcohol into vanillin (80 °C, O2, 1 h) with more than 90% yield. Reusability of the catalytic medium has been demonstrated, acting as “quasi-homogeneous catalyst”. More sophisticated lignin-derived substrates like veratryl alcohol and hydrobenzoin gave yields of 50–80% to the respective aldehyde and ketone. In parallel, this as-synthesized suspension was directly used to prepare a Pd/TiO2 catalyst, the latter showing less efficiency for the catalytic transformations.

Au/TiO2-Catalyzed Benzyl Alcohol Oxidation on Morphologically Precise Anatase Nanoparticles.

Au nanoparticles (NP) on TiO2 have been shown to be effective catalysts for selective oxidation reactions by using molecular oxygen. In this work, we have studied the influence of support morphology on the catalytic activity of Au/TiO2 catalysts. Two TiO2 anatase supports, a nanoplatelet-shaped material with predominantly the {001} facet exposed and a truncated bipyramidal-shaped nanoparticle with predominantly the {101} facet exposed, were prepared by using a nonaqueous solvothermal method and characterized by using DRIFTS, XPS, and TEM. Au nanoparticles were deposited on the supports by using the deposition-precipitation method, and particle sizes were determined by using STEM. Au nanoparticles were smaller on the support with the majority of the {101} facet exposed. The resulting materials were used to catalyze the aerobic oxidation of benzyl alcohol and trifluoromethylbenzyl alcohol. Support morphology impacts the catalytic activity of Au/TiO2; reaction rates for reactions catalyzed by the predominantly {101} material were higher. Much of the increased reactivity can be explained by the presence of smaller Au particles on the predominantly {101} material, providing more Au/TiO2 interface area, which is where catalysis occurs. The remaining modest differences between the two catalysts are likely due to geometric effects as Hammett slopes show no evidence for electronic differences between the Au particles on the different materials.