Catalytic Oxidation Of Alcohols Research Articles

Manganese(III) complexes stabilized with N-heterocyclic carbene ligands for alcohol oxidation catalysis.

The chemistry of N-heterocyclic carbenes with Earth-abundant manganese has largely focused on low-valent systems for reductive catalysis. Here, we have decorated imidazole- and triazole-derived carbenes with phenol substituents to access higher-valent Mn(III) complexes [Mn(O,C,O)(acac)], where acac = acetylacetonato, and O,C,O = bis(phenolate)imidazolylidene (1) or bis(phenolate)triazolylidene (2). Both complexes catalyze the oxidation of alcohols in the presence of tBuOOH as terminal oxidant. Complex 2 is slightly more active than 1 (TOF up to 540 h-1vs. 500 h-1), yet significantly more robust towards deactivation. Secondary and primary alcohols are oxidized, the latter with high selectivity and essentially no overoxidation of the aldehyde product to carboxylic acids unless the reaction time is substantially extended. Mechanistic investigations using Hammett parameters, IR spectroscopy, isotope labelling experiments, and specific substrates and oxidants as probes support the formation of a manganese(V) oxo system as the active species and subsequent turnover-limiting hydrogen atom abstraction.

Modulating the electronic structure of Co-Ni bimetal oxides on mesoporous silica for promoting selective oxidation of alcohol

The selective oxidation of alcohols by transition-metal-based catalysts provides a green route for the production of aldehydes. In this paper, mesoporous SBA-15 supported bimetallic NixCoy oxides were synthesized for the catalytic oxidation of alcohol using oxygen as the sole oxidant. The catalytic activity was highly related to the metal composition, of which the Ni1Co4/SBA-15 catalyst showed the best catalytic performance with high benzyl alcohol conversion of 96.2% and benzaldehyde selectivity of 98.3%. It was proposed that the electronic structure of the NixCoy/SBA-15 catalysts can be modulated by Ni/Co ratio, and high Co3+/Co2+ and Ni3+/Ni2+ ratios promoted the catalyst activity. Compared to the NixCoy nanocatalysts obtained by removing SBA-15 support, the NixCoy/SBA-15 exhibited a better benzyl alcohol oxidation performance, suggesting a diffusion enhancement by the mesoporous structure of SBA-15 support.

Bioinspired oxidation of benzyl alcohol: The role of environment and nuclearity of the catalyst evaluated by multivariate analysis

Inspired by copper-containing enzymes such as galactose oxidase and catechol oxidase, in which distinct coordination environments and nuclearities lead to specific catalytic activities, we summarize here the catalytic properties of dinuclear and mononuclear copper species towards benzyl alcohol oxidation using a multivariate statistical approach. The new dinuclear [Cu2(μ-L1)(μ-pz)]2+ (1) is compared against the mononuclear [CuL2Cl] (2), where (L1)− and (L2)− are the respective deprotonated forms of 2,6-bis((bis(pyridin-2-ylmethyl)amino)methyl)-4-methylphenol, and 3-((bis(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzaldehyde and (pz)− is a pyrazolato bridge. Copper(II) perchlorate (CP) is used as control. The catalytic oxidation of benzyl alcohol is pursued, aiming to assess the role of the ligand environment and nuclearity. The multivariate statistical approach allows for the search of optimal catalytic conditions, considering variables such as catalyst load, hydrogen peroxide load, and time. Species 1, 2 and CP promoted selective production of benzaldehyde at different yields, with only negligible amounts of benzoic acid. Under normalized conditions, 2 showed superior catalytic activity. This species is 3.5-fold more active than the monometallic control CP, and points out to the need for an efficient ligand framework. Species 2 is 6-fold more active than the dinuclear 1, and indicates the favored nuclearity for the conversion of alcohols into aldehydes.

Synthesis and Tuning of Gold Nanoparticles Supported on Polymorphic Semicrystalline Nanoporous Polymer for Catalytic Aerobic Oxidation of Alcohols

AbstractThe wide and complex tunability of gold nanoparticles (AuNPs) supported on nanoporous, semicrystalline, and polymorphic polymer matrices consisting of syndiotactic polystyrene (sPS) or multiblock syndiotactic polystyrene‐co‐cis‐1,4 poly(butadiene) (sPSB) is herein described and correlated with the performances in aerobic oxidation of (±)‐1‐phenylethanol. Impregnation or deposition‐impregnation synthetic methods yielded AuNPs of middle size (10–20 nm) on the surface of polymer grains. The co‐precipitation method leads to small AuNPs (4–5 nm) homogenously dispersed in the support with quantitative entrapment of the gold. Thermal or solvent annealing afforded modifications of polymer crystalline phase and AuNPs morphology. The annealing with chloroform/water mixture increases the crystallinity of the nanoporous forms and converts compact γ and β phases into the nanoporous ϵ and δ phases. The thermal treatment of the AuNPs‐sPS(B) catalysts afford defective NPs with enhanced catalytic activity. The solvent‐induced formation of the nanoporous forms improves permeability to solvents and reactants and, in turn, the catalytic properties.

Hemilabile Amine-Functionalized Efficient Azo-Aromatic Cu-Catalysts Inspired by Galactose Oxidase: Impact of Amine Sidearm on Catalytic Aerobic Oxidation of Alcohols.

A series of azo-aromatic copper(II) complexes, [1a-g] and a Cu(I) complex, [1h], with varying amine-functionalized hemilabile pincer-like [HL1-3] and [L1,2], methyl-substituted azo [L3], and imine [L4] ligands, were synthesized and characterized. These complexes were investigated for aerobic oxidation of a variety of aromatic alcohols in the presence of 2.0 mol % precatalysts [1a-g], cobaltocene (2.0 mol %), N-methyl imidazole (NMI) (8.0 mol %), and TEMPOH (2.0 mol %) at room temperature. The Cu(I) complex (1h) acted as a catalyst in the absence of cobaltocene. To understand the mechanism, detailed experimental and theoretical studies have been performed with the representative complex [1a], which has suggested a new kind of mechanism involving a Cu(II)/Cu(I) redox couple. Cobaltocene acts as a reductant to [1a] to generate a Cu(I) complex, which activates dioxygen in the presence of NMI. TEMPOH transfers a hydrogen atom to the activated dioxygen with the generation of TEMPO•, which further participates in α-C-H bond activation in the Cu(II)-alkoxide intermediate in an intermolecular fashion in the catalytic cycle. The amine sidearm in the ligand backbone of the complexes has a significant role in catalytic activity. Complexes with amine sidearms are more effective than complexes without them. Moreover, the aliphatic secondary amine sidearm is more efficient among the amine sidearm than the aromatic secondary amine and tertiary amines. The amine sidearm that remained coordinated to the Cu(II) center is hemilabile, and it facilitates alcohol coordination in the catalytic process. Alcohol coordination was the rate-limiting step, and it was supported by the isotope effect study on benzyl alcohol, substitution effect on the amine moiety of the ligands, and DFT calculation. The hemilabile amine sidearm of the coordinated ligand also acted as a base in deprotonating the alcoholic O-H proton and acted as an acid in releasing H2O2 during the catalysis.

Electrodeposition of shaped PtIr alloy nanocrystals with high–index facets for the electro–catalytic oxidation of alcohols

Pt–group metal nanocatalysts enclosed with high–index facets have sufficient kink and step atoms on the surface, which could act as efficient sites for fuel cell reactions. Besides surface structure, alloying was another efficient strategy to obtain nanoparticles with excellent catalytic performance. So how about combining the surface structure of high–index facet with alloying to prepare Pt–based nanocatalysts? In this work, we have synthesized alloyed PtIr tetrahexahedral (THH) nanocrystals (NCs) with high–index facets (730) by electrodeposition. And PtIr trioctahedral (TOH) NCs with high–index facets (441) could be obtained by simply decreasing the upper limit potential (EU) of square–wave potential (SWP) with other condition keeping the same as that for the synthesis of PtIr THH NCs. The successful synthesis of alloyed PtIr NCs with high–index facets mainly lied in the repetitive adsorption/desorption of oxygenated species on the surface of nanoparticles. The prepared PtIr THH NCs exhibited excellent electrocatalytic activity and stability towards ethylene glycol oxidation reaction (EGOR) and glycerol oxidation reaction (GOR). Among the nano–catalysts, the peak in the forward scan of PtIr THH NCs for EGOR and GOR were 19.9 mA∙cm−2 and 17.6 mA∙cm−2, respectively, which were 9.5 and 6.8 times higher than those of commercial Pt/C. The excellent electro–catalytic performance of alloyed PtIr NCs could mainly be attributed to the surface structure effect of high–index facets and synergetic effect of the alloy structure. This work could provide a new idea for designing highly efficient nanocatalysts for fuel cells by combing surface structure effect and alloying effect together.

Activating Pd Nanoparticles on Oxygen-Doped g-C3N4 for Visible Light-Driven Thermocatalytic Oxidation of Benzyl Alcohol.

Direct oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) using O2 as the oxidant has crucial significance under mild conditions in industrial manufacturing. Herein, an efficient and ecofriendly Pd/O-g-C3N4 heterojunction catalyst using oxygen-doped g-C3N4 (O-g-C3N4) with a porous surface as the support is developed for visible light-driven thermocatalytic oxidation of BzOH to BzH by using O2 as the sole oxidant. The obtained Pd/O-g-C3N4 exhibits visible light-enhanced catalytic performance under visible light irradiation with BzOH conversion and BzH yield of 89.4 and 76.6%, respectively, which are 1.96 and 1.83 times higher than those for the catalyst in the dark. Oxygen doping, as well as Pd deposition, can significantly narrow the band gap of g-C3N4, thereby enhancing its visible light harvesting ability. The resulting heterojunction interface between Pd nanoparticles and O-g-C3N4 might promote separation of the photogenerated e--h+ pairs. In addition to achieving considerable BzOH conversion and BzH yield, Pd/O-g-C3N4 also exhibits impressive stability. The current study provides potential applications for the green and efficient catalytic oxidation of other alcohols to corresponding aldehydes using O2 as the oxidant.

Reusable Copper Catechol‐based Porous Polymers for the Highly Efficient Heterogeneous Catalytic Oxidation of Secondary Alcohols

AbstractNew catechol‐based porous polymers were synthesized and used as platforms for the heterogenization of molecular Cu complexes. The resulting Cu@CatMP‐1 materials proved to be highly stable and performing catalysts for the oxidation of secondary alcohols with turnover numbers up to 6000, about 1 to 2 orders of magnitude higher than the current relevant state of the art, using catalyst loadings as low as 25 ppm of Cu. The solid catalyst proved to be recyclable for over 10 runs without detectable metal leaching and has been scaled to the gram scale. The coordination of Cu to catechol within the polymer has been evidenced by X‐ray absorption spectroscopy.

Structures of lactaldehyde reductase, FucO, link enzyme activity to hydrogen bond networks and conformational dynamics.

A group-III iron containing 1,2-propanediol oxidoreductase, FucO, (also known as lactaldehyde reductase) from Escherichia coli was examined regarding its structure-dynamics-function relationships in the catalysis of the NADH-dependent reduction of (2S)-lactaldehyde. Crystal structures of FucO variants in the presence or absence of cofactors have been determined, illustrating large domain movements between the apo and holo enzyme structures. Different structures of FucO variants co-crystallized with NAD+ or NADH together with substrate further suggest dynamic properties of the nicotinamide moiety of the coenzyme that are important for the reaction mechanism. Modelling of the native substrate (2S)-lactaldehyde into the active site can explain the stereoselectivity exhibited by the enzyme, with a critical hydrogen bond interaction between the (2S)-hydroxyl and the side-chain of N151, as well as the previously experimentally demonstrated pro-(R) selectivity in hydride transfer from NADH to the aldehydic carbon. Furthermore, the deuterium kinetic isotope effect of hydride transfer suggests that reduction chemistry is the main rate-limiting step for turnover which is not the case in FucO catalysed alcohol oxidation. We further propose that a water molecule in the active site - hydrogen bonded to a conserved histidine (H267) and the 2'-hydroxyl of the coenzyme ribose - functions as a catalytic proton donor in the protonation of the product alcohol. A hydrogen bond network of water molecules and the side-chains of amino acid residues D360 and H267 links bulk solvent to this proposed catalytic water molecule.

Vanadium Supported on Titanium Pillared Montmorillonite Clay for the Selective Catalytic Oxidation of Benzyl Alcohol

Vanadium Supported on Titanium Pillared Montmorillonite Clay for the Selective Catalytic Oxidation of Benzyl Alcohol

One pot synthesis of chromium incorporated SBA-16 under acid medium-Application in the selective oxidation of benzyl alcohol derivatives

Cr-SBA-16 mesoporous silica heterogeneous catalysts (Si/Cr = 7, 14, and 28) were successfully synthesized by one-pot hydrothermal method at low acidic medium. The catalysts were characterized by means of X-ray diffraction (XRD), N 2 adsorption-desorption at 77 K, Fourier Transform Infrared (FTIR), X-ray photoelectron (XPS) and Diffuse Reflectance UV–Vis (DRS) Spectroscopies, Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) techniques. Herein, Cr-SBA-16 catalysts are evaluated in the selective catalytic oxidation of benzyl alcohol derivatives using H 2 O 2 as oxidant. From XPS and UV–Vis (DRS) spectroscopies the molar ratios between Cr 6+ /Cr 3+ are found to increase versus chromium loading in the following order: Cr-SBA-16(28) < Cr-SBA-16(14) < Cr-SBA-16(7). Hence the highest Cr 6+ in tetrahedrally environment is observed for Si/Cr = 7. We demonstrated for the first time that the selective catalytic oxidation of benzyl alcohol (BzOH) using H 2 O 2 over Cr-SBA-16 occurs through noncompetitive adsorption mechanism and the reaction is pseudo-first order to BzOH. The activity of the reaction depends on the symmetry of chromium species, herein, high activity is observed for tetrahedral chromium species in Cr-SBA-16(7). The absence of any chromium ions in the filtrate shows no chromium leaching from the silica framework.

Efficient catalytic oxidation of benzyl alcohol by tetrasubstituted cobalt phthalocyanine-MWCNTs composites

In this paper, the tetra-[α-(p-formyl) phenoxy] phthalocyanine cobalt (II)/multiwalled carbon nanotubes (CoPc/MWCNTs) composites were prepared through the π-π interactions between CoPc and MWCNTs. UV–vis spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy were employed to characterize the structures of the prepared CoPc/MWCNTs composites. Its catalyzed oxidation properties were studied by carrying out the oxidation reaction of benzyl alcohol. The catalytic efficiency of these compounds under different reaction parameters such as catalyst dosage, temperature, time and various organic solvent was investigated.

Synthesis and characterization of Merrifield resin-supported vanadium complexes for the catalytic oxidation of straight-chain aliphatic alcohols

Two Schiff-base ligands [hynd-ap] (I) and [hynd-ae] (II) were prepared by reacting 2-hydroxynapthaldehyde with 2-aminophenol and aminoethylethanolamine, respectively. By systematically using the prepared Schiff-base ligands (I) and (II), a number of vanadium(IV) and (V) complexes were prepared and thoroughly characterized. Single crystal X-ray analysis, UV–Vis, FT-IR spectra and mass studies indicate that both the dioxidovanadium(V) complexes [VO2(hynd-ap)] (4) and [VO2(hynd-ae)] (5) exist in the monomeric form in the solid-state as well as in solution. The dioxidovanadium(V) complexes 4 and 5 were grafted on imidazole modified chloromethylated polystyrene, giving PS-im-[VO2(hynd-ap)] (6) and PS-im-[VO2(hynd-ae)] (7), for application in the catalytic oxidation of a series of primary aliphatic alcohols. Both the supported catalysts showed excellent catalytic performance towards this range of alcohols. A maximum of 98% substrate conversion to 1-proponal was observed in the presence of 6. Irrespective of the substrate, catalyst 6 shows better substrate conversion than 7 under the optimized reaction conditions. It has been observed that the catalytic performance of both the supported catalysts reduces slightly on increasing the number of carbon atoms in the alcohols, except for EtOH.

Catalytic oxidation of benzyl alcohol over MnO2: Structure-activity description and reaction mechanism

Activity evaluation of metal oxide catalysts with different crystal structures has been an important prerequisite for industrial applications. This work systematically elucidates the structure-activity relationship of α-, β-, γ- and δ-MnO2 catalysts toward the selective oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). Exposed surfaces of MnO2 are evaluated by a combined theoretical and experimental investigation. On this basis, a catalytic activity descriptor is established considering the surface energies, formation energies of oxygen vacancies (OVs), O2 adsorption energies, and areal densities of OVs and unsaturated Mn. Inspired by this, we fabricate β-MnO2 with a high surface area and it delivers the highest BA conversion among all MnO2. Furthermore, a developed Mars-van Krevelen (MvK) mechanism is proposed to describe the BA oxidation process on the β-MnO2 (110) surface. The research paradigm opens a door to the rational design of metal oxide catalysts.

A convenient and highly efficient catalytic oxidation of alcohol to acid using CoCl2-[Cemim]Br under mild conditions

Herein we first reported on the CoCl2 supported ionic liquid [Cemim] Br-catalysed conversion of aliphatic and aromatic alcohol to acid using hydrogen peroxide as an oxidant. The oxidation reaction proceeded selectively with good yields in comparison to various other solvents. This method as appealing way for greener oxidation system includes mild reaction condition, short reaction time, less poisonous catalyst and oxidant under optimal condition give well to good yields.

Catalytic Magnesium-Oppenauer Oxidation of Alcohols

Abstract A catalytic magnesium-Oppenauer oxidation reaction was developed. When a solution of alcohols in toluene was successively treated with 15–30 mol % of EtMgBr and 1.0 equiv. of trifluoromethyl ketone (oxidant), a hydride transfer-type oxidation reaction (Oppenauer oxidation) occurred to give corresponding ketones in good chemical yields (up to 85%). It was noteworthy that even a weakly basic alkoxide derived from trifluoromethyl ketone worked as an efficient Brønsted base to deprotonate the starting material (alcohols) at ambient temperature (25 °C). The efficiency of the present method was highlighted by applying the method to substrates having a nitrogen atom, which were sensitive to various oxidation conditions.

Phyto-Assisted Assembly of Metal Nanoparticles in Chitosan Matrix Using S. argel Leaf Extract and Its Application for Catalytic Oxidation of Benzyl Alcohol.

The design and synthesis of eco-friendly solid-supported metal nanoparticles with remarkable stability and catalytic performance have gained much attention for both industrial and environmental applications. This study provides a novel, low-cost, simple, and eco-friendly approach for decorating cross-linked chitosan with gold nanoparticles (AuNPs), greenly prepared with Solenostemma argel (S. argel) leaf extract under mild conditions. Glutaraldehyde-modified chitosan beads were used to coordinate with Au(III) ions and act as stabilizing agents, and S. argel leaf extract was used as a cost-effective phyto-reducing agent to reduce gold ions to elemental Au nanoparticles. The successful cross-linking of chitosan with glutaraldehyde, the coordination of Au(III) ions into the chitosan matrix, and the phytochemical reduction of Au(III) to Au nanoparticles were investigated via FT-IR spectroscopy. The obtained Au nanoparticles have a uniform spherical shape and size <10 nm, as confirmed by both X-ray diffraction (XRD) (~8.8 nm) and TEM (6.0 ± 3 nm). The uniformity of the AuNPs’ size was confirmed by Scanning Electron Microscopy (SEM) and Transition Electron Microscopy (TEM). The powder X-ray diffraction technique showed crystalline AuNPs with a face-centered cubic structure. The elemental analysis and the Energy Dispersive Spectroscopy (EDS) analysis both confirmed the successful integration of Au nanoparticles with the chitosan network. The catalytic activity of this highly stable nanocomposite was systematically investigated via the selective oxidation of benzyl alcohol to benzaldehyde. Results showed a remarkable conversion (97%) and excellent selectivity (99%) in the formation of benzaldehyde over other side products.

Transforming Waste Clamshell into Highly Selective Nanostructured Catalysts for Solvent Free Liquid Phase Oxidation of Benzyl Alcohol

High yield production of benzaldehyde in the solvent-free oxidation of benzyl alcohol by using green catalysts is highly desirable. In this work, calcium hydroxide derived from waste clamshell was used as low-cost and environmentally friendly catalyst support (CaSUP) for Pd and V nanoparticles. The physicochemical properties of the catalysts were analyzed using X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) technique, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The catalytic oxidation of benzyl alcohol to benzaldehyde was studied in a liquid phase reaction by using H2O2 as an oxidizing agent. The effects of catalyst loading, the molar ratio of hydrogen peroxide to benzyl alcohol, temperature and reaction duration were investigated. In the optimized conditions, Pd nanoparticles supported on clamshell-derived supports displayed excellent catalytic conversion (88%) and selectivity to benzaldehyde (89%). Furthermore, the catalyst can be effectively reused without a significant loss in its activity and selectivity. The high yield and stability can be related to the structural and basic properties of the catalyst. These results provide important insights into the benzyl alcohol oxidation process for industrial applications.

Transition Metal‐Free Aerobic Oxidation of Aryl Secondary and Primary Alcohols to Carbonyl Compounds in Open Air

AbstractThe ketones and benzoic acids are very useful chemicals as the precursors and intermediates in both laboratory and synthetic industrial applications, which are usually obtained by selective catalytic oxidation of alcohols using a amount of certain expensive oxidants or metal catalysts. Here, an efficient and practical oxidation the aryl secondary and primary alcohols to corresponding carbonyl compounds using NaOtBu in open air at room temperature has been developed. And utilizing NaOtBu/air/ toluene, a series of ketones or benzoic acids were obtained from secondary and primary alcohols in high yields, respectively. More importantly, most of the substrates with electron‐withdrawing or electron‐donating groups could be converted to the corresponding products in high to excellent yields. Furthermore, the practicality of the reaction was demonstrated through 1.0 gram‐scale reaction with excellent yield.

Synthesis, and Characterization of Merrifield Resin-Supported Vanadium Complexes for the Catalytic Oxidation of Straight-Chain Aliphatic Alcohols

Synthesis, and Characterization of Merrifield Resin-Supported Vanadium Complexes for the Catalytic Oxidation of Straight-Chain Aliphatic Alcohols