Partial Oxidation Of Benzyl Alcohol Research Articles

One‐Step Synthesis of Melem‐Based Supramolecular Assemblies and Their Photocatalytic Properties

In this work, melem‐based supramolecular assemblies were obtained in one step by thermal treatment of melamine in an autoclave in the presence of sodium chloride. The detailed analysis showed that the obtained powder consists of two phases: poorly crystalline Na‐PHI flakes and rod‐shaped melem hydrate single crystals (several micrometers long and ~300‐500 nm wide). Melem hydrate crystals absorb light in the visible range (Eg = 2.7 eV) and demonstrate photocatalytic activity in the reaction of partial oxidation of benzyl alcohol to benzaldehyde by air under visible light with high selectivity for the target product. At 60% conversion of benzyl alcohol, the selectivity of benzaldehyde formation is above 95%.

Improved charge carrier mobility in a copper oxide heterostructure enhances the photocatalytic partial oxidation of benzyl alcohol to benzaldehyde

The enhancement of the partial oxidation of an aromatic alcohol to its corresponding aldehyde through the coupling of Cu2O with CuO is comprehensively discussed.

An efficient and green synthesis of 2-phenylquinazolin-4(3H)-ones via t-BuONa-mediated oxidative condensation of 2-aminobenzamides and benzyl alcohols under solvent- and transition metal-free conditions

Abstract Quinazolinone synthesis usually requires employing sensitive substrates, hazardous solvents, large excess oxidants, and expensive catalysts. In this study, an efficient and environmentally benign pathway was developed to synthesize 2-phenylquinazolin-4(3H)-one via oxidative coupling between commercially available and stable chemicals, including 2-aminobenzamide and benzyl alcohol without toxic oxidizing agents and transition-metal catalysts. A high yield of the desired product (up to 84%) was obtained at 120°C for 24 h in the presence of oxygen as a green oxidant and t-BuONa as a base. Importantly, the study scope was expanded toward successfully producing various 2-phenylquinazolin-4(3H)-one derivatives in moderate-to-good yields. Furthermore, control experiments proposed that the conversion involved the initial partial oxidation of benzyl alcohol to the benzaldehyde intermediate under basic conditions, followed by the condensation, intramolecular nucleophilic addition, and oxidative dehydrogenation to 2-phenylquinazolin-4(3H)-one.

Mechanistic and kinetic studies of benzyl alcohol photocatalytic oxidation by nanostructured titanium (hydro)oxides: Do we know the entire story?

Selective upgrade of lignocellulosic biomass-derived aromatic compounds by photocatalytic oxidation is assumed as a prosperous, environmentally friendly, and cost-effective process. We present for the first time the application of various advantageous titanium oxide nano-photocatalysts for the additives-free selective partial oxidation of benzyl alcohol to benzaldehyde at ambient conditions. The two best-performing materials were found titanate nanotubes and nanocores of anatase surrounded by amorphous titanium hydroxide phase. The results obtained by scavenger tests on top of the DFT calculations led us to conclude that various reactions and active species are responsible by a complex way for materials’ photoreactivity. Depending on nanocatalysts’ physicochemical features as well as the light irradiation (ultraviolet vs. royal-blue), different mechanisms/oxidation-pathways are photo-catalyzed. Finally, we show that utilizing organic compounds like benzoquinone as scavenger hides risks due to the interactions with the targeted to be converted organic that results in elevated photolytic decomposition even under royal-blue light.

Support, composition, and ligand effects in partial oxidation of benzyl alcohol using gold–copper clusters

The effect of metallic composition, support, and ligands on catalytic performance using AuCu clusters in benzyl alcohol oxidation is investigated.

Compatibility between Activity and Selectivity in Catalytic Oxidation of Benzyl Alcohol with Au-Pd Nanoparticles through Redox Switching of SnOx.

A balance between catalytic activity and product selectivity remains a dilemma for the partial oxidation processes because the products are prone to be overoxidized. In this work, we report on the partial oxidation of benzyl alcohol using a modified catalyst consisting of nanosized Au-Pd particles (NPs) with tin oxide (SnOx) deposited on a mesoporous silica support. We found that the SnOx promotes the autogenous reduction of PdO to active Pd0 species on the Au-Pd NP catalyst (SnOx@AP-ox) before H2 reduction, which is due to the high oxophilicity of Sn. The presence of active Pd0 species and the enhancement of oxygen transfer by SnOx led to high catalytic activity. The benzaldehyde selectivity was enhanced with the increase of SnOx content on catalyst SnOx@AP-ox, which is ascribed to the modulated affinity of reactants and products on the catalyst surface through the redox switching of Sn species. After H2 reduction, SnOx was partially reduced and Au-Pd-Sn alloy was formed. The formation of Au-Pd-Sn alloy weakened both the catalytic synergy of Au-Pd alloy NPs and the adsorption of benzyl alcohol on the reduced catalyst, thus leading to low catalytic activity.

Photocatalytic Activity of g-C3N4 in the Partial Oxidation of Benzyl Alcohol Under Visible Light

It is shown that post-synthetic thermal treatment of graphitic carbon nitride (g-C3N4), obtained by pyrolysis of melamine, in molten potassium and lithium salts leads to a sixfold increase in its photocatalytic activity in the selective oxidation of benzyl alcohol by air to benzaldehyde in visible light at room temperature, and this is much higher when oxygen is used as oxidant. The conversion of benzyl alcohol and the selectivity for benzaldehyde under optimal conditions are 81% and 96%, respectively.

Design and development of TiO2 coated microflow reactor for photocatalytic partial oxidation of benzyl alcohol

The synthesis of valuable organic compounds from naturally available and renewable biomass is an open field of research towards adaptation in real-life applications. Photocatalytic valorization is assumed as a potential candidate, although the lower efficiency of the traditional batch photocatalytic reactor sets some drawbacks. Recently, photocatalytic microreactors revealed as a prosperous candidate for various photocatalytic reactions, especially for selective oxidation. This area of research is challenging due to the development of the proper photocatalytic microreactor for the targeted application. Deposition of the catalyst on the internal surface of the microreactor, the sufficient utilization of the irradiation, optimization of the reaction parameters are among the most vital parameters that should be considered upon the design. Although, to obtain the most active material and tune its crucial features to maximize its catalytic performance inside the microreactors is the uppermost important part. This work introduces ultrasound-assisted TiO2 deposition on the inner walls of a perfluoroalkoxyalkane microtube under mild conditions. The deposition experiments were carried out with commercial and sol-gel synthesized TiO2. The materials were characterized by XRD, UV–vis DRS, Scanning Electron Microscopy (SEM), and nitrogen sorption. The photocatalytic activities of the TiO2 nano-engineered fluoropolymer based microreactors were evaluated for the oxidation of benzyl alcohol in flow.

Ecofriendly oxidation of benzyl alcohol to benzaldehyde using Zr-Ni/Natural phosphate as an efficient and recyclable heterogeneous catalyst

The partial oxidation of benzyl alcohol to benzaldehyde is a fundamental synthetic transformation in organic chemistry. However, the conventional oxidation methods pose many environmental problems such as the use of inorganic oxidants (chromates, permanganate and chlorinated oxidants) with high toxicity in organic media and the generation of a large amount of waste.In this work, we report a green approach for the oxidation of benzyl alcohol to benzaldehyde using bimetallic zirconium-nickel loaded on natural phosphate as heterogeneous catalyst with aqueous hydrogen peroxide as green oxidant under solvent-free conditions. The catalyst has been prepared by using a wet impregnation method and characterized by powder XRD and FT-IR studies. Compared to other works in literature, the developed catalyst showed relatively short reaction time (45 min), good yield (93%) and high recyclability without a significant loss in its activity.

Nitrogen-Dopped Ordered Mesoporous Carbon Anchored Pd Nanoparticles for Solvent Free Selective Oxidation of Benzyl Alcohol to Benzaldehyde by Using O2.

Introducing electron-rich nitrogen atoms to ordered mesoporous carbons (OMC) as supports for noble metal catalysts, not only improves the hydrophilic properties of a mesoporous carbon surface, but also enhances the coordination and binding abilities of metal ion. In the present work, nitrogen-doped ordered mesoporous carbons (NOMCs) were successfully fabricated via a facile hydrothermal self-assembly. The prepared NOMCs were characterized through powder X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption-desorption isotherm. The analyses demonstrated that the NOMCs prepared at a pyrolysis temperature of 750°C possessed an ordered 2D hexagonal mesoporous structure, a high graphitization degree, large surface area, and a well-distributed pore size. In particular, NOMCs could anchor Pd nanoparticles uniformly because of the introducing N atoms with strong electronegativity, which were selected as efficient catalysts for the partial oxidation of benzyl alcohol to benzaldehyde. Approximately 24.63% conversion with 85.71% selectivity to benzaldehyde was obtained without using any solvent by molecular O2 oxidation. Most importantly, the TOF value of the catalyst in the reaction system was up to 8698 h−1. After five runs reaction, TOF and selectivity of the catalyst remained essentially same. Hence, the proposed catalyst has a potential engineering application value.

Evaluation of catalytic activity of MeOx/sepiolite in benzyl alcohol oxidation

Abstract A series of MeOx/sepiolite (Me = Cu, Cr, Mn, Co, Ni) catalysts was prepared through the deposition–precipitation and characterized by means of XRD, EDS, SEM, BET, and H2-TPR. The structural characterization showed a fine distribution of MeOx metal oxides on magnesium silicate nanobars. The sepiolite-loaded-metal oxide catalysts have been screened for the partial oxidation of benzyl alcohol and shown a good conversion and a very high selectivity to benzaldehyde at mild conditions. Under similar experiments, the catalytic activity of the transition metal oxides on sepiolite decreased in the order of Cr > Co > Cu > Mn > Ni. The productivity of benzaldehyde was associated with the behavior of transition metal ions and reaction temperatures.

Spinel‐Type Mixed Oxides for Stable and Selective Partial Oxidation of Benzyl Alcohol

AbstractBenzaldehyde is an important chemical intermediate, which need to be prepared through an eco‐friendly process. Manganese oxides are active as catalysts for its preparation through partial oxidation of benzyl alcohol. In this study, Cu, Co and Mn containing spinel based mixed oxides (CuxMn3−xO4) were prepared and tested for partial oxidation of benzyl alcohol to get benzaldehyde with high selectivity. The catalytic activity strongly depended on chemical composition, acid‐base properties and oxygen uptake. The influence of chemical composition, reaction temperature, oxygen partial pressure and the weight hourly space velocity (WHSV) were investigated to optimize benzaldehyde yield and to stabilize the catalyst activity. A high benzaldehyde selectivity of 98%, accompanied with benzyl alcohol conversion of 84.5% was obtained over Cu0.25Mn2.75O4 catalyst at 300 °C. It was evident from temperature programmed desorption (TPD) of CO2 that this catalyst was found to have optimum basicity and high oxygen uptake, thus imparting high activity and stability. Activity and catalyst life could be attributed to appropriate acid‐base properties.

Liquid phase oxidation of benzyl alcohol to benzaldehyde over sepiolite loaded chromium oxide catalysts

Abstract Sepiolite loaded chromium oxide catalysts were prepared through the precipitation and characterized by physical techniques such as XRD, SEM, TEM BET, EDS, FT-IR, UV–vis, XPS, H2-TPR… The experimental results indicated that Cr2O3 are major Cr-species finely distributed on the sepiolite nanofibers in addition to small amount of Cr(VI) on the catalyst surface. All catalysts have large surface area, high porosity, and good dispersion of Cr2O3 nanoxides on the support. The sepiolite-loaded-Cr catalysts have been tested for the partial oxidation of benzyl alcohol without any base or organic solvent and shown good conversion and very high selectivity to benzaldehyde at mild conditions. The catalytic activity was found to be related to the amount of transition metal oxide content, distribution of Cr(III) sites, oxidant behavior, and reaction variables… An increased calcination temperature of the catalysts leads to the distortion of sepiolite fibers, the interaction between Cr(III) and support, and the enhanced reusability of the catalysts.

Anchoring Tri(8-Quinolinolato)Iron Onto Sba-15 for Partial Oxidation of Benzyl Alcohol Using Water as the Solvent

Abstract Tri(8-quinolinolato)iron complex immobilized onto SBA-15 catalyst has been synthesized through a stepwise procedure. The characterization results indicated that the BET surface area, total pore volume and average pore width decrease after stepwise modification of SBA-15, while the structure keeps intact. Catalytic tests showed that FeQ3-SBA-15 catalyzes the oxidation reaction well with 34.8% conversion of benzyl alcohol and 74.7% selectivity to benzaldehyde when water is used as the solvent after 1 h reaction. In addition, homogeneous catalyst tri(8-quinolinolato)iron exhibits very bad catalytic behavior using water as the solvent.

Immobilization of Cu-chelate onto SBA-15 for partial oxidation of benzyl alcohol using water as the solvent

Bis(8-quinolinolato)copper(II) complex immobilized onto SBA-15 catalyst has been synthesized through a stepwise procedure. The characterization results indicated that the BET surface area, total pore volume, and average pore width decrease after stepwise modification of SBA-15, while the structure stays intact. Catalytic tests showed that CuQ2–SBA-15 catalyzes the oxidation reaction well with 32.5 % conversion of benzyl alcohol and 81.8 % selectivity to benzaldehyde when water is used as the solvent. In addition, homogeneous catalyst bis(8-quinolinolato)copper(II) exhibits very bad catalytic behavior using water as the solvent.

Kinetic modeling of partial oxidation of benzyl alcohol in water by means of Fe(III)/O2/UV–solar simulated process

Abstract The mechanism of selective oxidation of benzyl alcohol to benzaldehyde and of benzaldehyde to benzoic acid by means of ferric ions in water under simulated UV–solar radiation is investigated through the development of a new kinetic model, also based on the results of Electron Spin Resonance (ESR) experiments, not previously reported in the literature. A value of pH = 0.5 is chosen with the aim to minimize the contribution of the undesired hydroxylation reactions. The mathematical model is constituted by of a set of mass balance equations for the chemical species involved in the homogeneous photocatalytic oxidation process. The experimental concentration–time profiles, collected at different starting substrates concentrations, are satisfactorily predicted by the model under deaerated and aerated conditions. The values of different rate constants of the reactions, taken into account for the adopted mechanism, not available in the literature, are estimated by a proper optimizing procedure. The model may be used for the prediction of the performance of the homogeneous Fe(III)-photo-catalytic partial conversion of aromatic alcohols to the corresponding aldehydes in water at room temperature and very acidic pH.

Fe(iii)-photocatalytic partial oxidation of benzyl alcohol to benzaldehyde under UV-solar simulated radiation

A great deal of interest is recorded among researchers in the identification of new catalytic systems that make possible the selective oxidation of organic species in the presence of non-toxic solvents, primarily water, through the use of inexpensive catalysts. The possibility to selectively oxidize benzyl alcohol to benzaldehyde is studied in the present work by using ferric ions as homogeneous catalysts and oxygen as an oxidant under UV-solar simulated radiation. Due to the possibility that Fe(III) aquo-complex photolysis could generate undesired reactive OH radicals with the consequent occurrence of side reactions, most of the runs are carried out at pH = 0.5 at which these events have a reduced incidence. The results indicate that benzyl alcohol can be partially converted into benzaldehyde with yield and selectivity values higher than 40% and 80% respectively for the conditions adopted, with a minor occurrence of benzoic acid formation. Reaction schemes to account for the experimental observations are provided.

Development of a continuous flow reactor for pharmaceuticals using catalytic monoliths: Pt/C selective oxidation of benzyl alcohol

A novel design of pilot-scale continuous flow pharmaceutical fixed-bed catalytic reactor has been developed. This incorporates in a structured manner the use of multiple catalytic monoliths (o.d.=20mm; L=50mm). O2 was used as the oxidant (O2/N2 mixture) for the partial oxidation of benzyl alcohol to benzaldehyde, using Pt impregnated (2.5 and 2.7wt%) carbon monoliths. Reactions were performed e.g. at liquid flow=1dm3h−1; benzyl alcohol concentration=1kmolm−3; T=110°C; P=12bar(g). A major breakthrough was the demonstration of the viability of this design at pilot-scale.

Origin of the selectivity in the gold-mediated oxidation of benzyl alcohol

Benzyl alcohol has received substantial attention as a probe molecule to test the selectivity and efficiency of novel metallic gold catalysts. Herein, the mechanisms of benzyl alcohol oxidation on a gold surface covered with atomic oxygen are elucidated; the results show direct correspondence to the reaction on gold-based catalysts. The selective, partial oxidation of benzyl alcohol to benzaldehyde is achieved with low oxygen surface concentrations and takes place through dehydrogenation of the alcohol to form benzaldehyde via a benzyloxy (C6H5–CH2O) intermediate. While in this case atomic oxygen plays solely a dehydrogenating role, at higher concentrations it leads to the formation of intermediates from benzaldehyde, producing benzoic acid and CO2. Facile ester (benzyl benzoate) formation also occurs at low oxygen concentrations, which indicates that benzoic acid is not a precursor of further oxidation of the ester; instead, the ester is produced by the coupling of adsorbed benzyloxy and benzaldehyde. Key to the high selectivity seen at low oxygen concentrations is the fact that the production of the aldehyde (and esters) is kinetically favored over the production of benzoic acid.

Octahedral molecular sieves of the type K-OMS-2 with different particle sizes and morphologies: Impact on the catalytic properties in the aerobic partial oxidation of benzyl alcohol

Abstract Manganese-based octahedral molecular sieves of the type K-OMS-2 (cryptomelane structure) with different morphologies and specific surface areas in the range of 20–135 m2 g−1 were prepared via synproportionation of KMnO4 and Mn2+ salts, either in acidic aqueous suspension (reflux method) or by a solid-state reaction, and via oxidation of MnSO4 either by K2Cr2O7 or by molecular oxygen in aqueous solution. For the reflux method, the influence of K+ cations for the formation of the OMS-2 structure was proven. When KMnO4 is replaced by Ba(MnO4)2, the anion in the Mn2+ salt exerts a strong influence on the synthesis product. All materials were characterized by elemental analysis (ICP-OES), XRD, nitrogen sorption, scanning electron microscopy and TGA. For the oxidation of benzyl alcohol with molecular oxygen in liquid toluene at 110 °C, the catalytic activity of the K-OMS-2 materials is directly correlated to their specific surface area ABET. Since ABET increases with decreasing average crystallite diameter, the catalytic conversion presumably occurs at the outer crystallite surface. These relations are independent of morphology or synthesis procedure. The K-OMS-2 materials are more active than crystalline manganese oxides (MnO, Mn2O3, Mn3O4, β-MnO2), but less active than amorphous MnO2. Regeneration of deactivated K-OMS-2 catalysts can be achieved by calcining at 300 °C in air, partly due to the reversible desorption of water.