Showing papers on "Benzaldehyde published in 2021"

TiO2/Ti3C2 as an efficient photocatalyst for selective oxidation of benzyl alcohol to benzaldehyde

Abstract: Photocatalytic selective oxidation of alcohols into corresponding aldehydes has received enormous attention. However, it remains a great challenge to explore photocatalysts with high conversion efficiency and selectivity. Herein, we developed a composite consisted of TiO2 and Ti3C2 through a simple calcination of Ti3C2 nanosheets. It was found that Ti3C2 could stabilize the oxygen vacancies and Ti3+ species in the TiO2/Ti3C2 composite, which could subsequent promote the production of active intermediates during the photocatalytic oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). Additionally, the valence band of TiO2 in the composites was found to be up-shifted, which would avoid the further oxidation of BAD and enhance selectivity. As a result, the optimal composite exhibits the BA conversion efficiency of 97 % and BAD selectivity of 98 %, which is 2.8 and 1.2 folds higher than that of pristine TiO2. Our work may provide insights for designing efficient photocatalysts for selective oxidation of alcohols.

Enhanced Selective Oxidation of Benzyl Alcohol via In Situ H2O2 Production over Supported Pd-Based Catalysts

Abstract: Bimetallic Pd-Fe catalysts supported on TiO2 are shown to be highly effective toward the selective oxidation of benzyl alcohol to benzaldehyde via the in situ production of H2O2 from molecular H2 and O2, under conditions where no reaction is observed with molecular O2 alone. The rate of benzyl alcohol oxidation observed over supported Pd-Fe nanoparticles is significantly higher than those of either Pd-Au or Pd-only analogues. This enhanced activity can be attributed to the bifunctionality of the Pd-Fe catalyst to both synthesize H2O2 and catalyze the production of oxygen-based radical specie,s as indicated by an electron paramagnetic resonance analysis. Further studies also reveal the noninnocent nature of the solvent, resulting in the propagation of radical generation pathways.

Recognition of Water-Induced Effects toward Enhanced Interaction between Catalyst and Reactant in Alcohol Oxidation.

Abstract: Pickering emulsion stabilized by solid nanoparticles provides a diverse solvent microenvironment and enables to promote the phase transfer of reaction substrates/products in catalytic reactions, but the intrinsic role of solvent is still not clear. Herein, using benzyl alcohol (BA) as a model reactant, we demonstrate the nature of the water-promoted activity for alcohol oxidation over the Pd/MgAl-LDO catalyst. Depending on the water in the solvent, we observe different reactivities regarding the proportion of the water in the system. Kinetic isotope effects confirm the participation and positive effects of water for oxidation of BA. The water promotion effects are recognized and identified by the water vapor pulse adsorption coupled with temperature program desorption. Moreover, the adsorption behavior of BA or benzaldehyde at the interface of water and Pd/MgAl-LDO is also investigated by quasi-in-situ Raman spectroscopy. In addition, the mechanism of water-promoted alcohol oxidation is rationally proposed based on the Langmuir-Hinshelwood mechanism. The general applicability of the water promotion effects is further demonstrated over different supports and substrates, which well achieves excellent catalytic activity and selectivity in Pickering emulsion compared to that in the pure toluene system.

Cobalt Single Atoms Embedded in Nitrogen-Doped Graphene for Selective Oxidation of Benzyl Alcohol by Activated Peroxymonosulfate.

Abstract: The development of novel single atom catalyst (SAC) is highly desirable in organic synthesis to achieve the maximized atomic efficiency. Here, a Co-based SAC on nitrogen-doped graphene (SACo@NG) with high Co content of 4.1 wt% is reported. Various characterization results suggest that the monodispersed Co atoms are coordinated with N atoms to form robust and highly effective catalytic centers to activate peroxymonosulfate (PMS) for organic selective oxidation. The catalytic performance of the SACo@NG/PMS system is conducted on the selective oxidation of benzyl alcohol (BzOH) showing high efficiency with over 90% conversion and benzaldehyde selectivity within 180 min under mild conditions. Both radical and non-radical processes occurred in the selective oxidation of BzOH, but the non-radical oxidation plays the dominant role which is accomplished by the adsorption of BzOH/PMS on the surface of SACo@NG and the subsequent electron transfer through the carbon matrix. This work provides new insights to the preparation of efficient transition metal-based single atom catalysts and their potential applications in PMS mediated selective oxidation of alcohols.

Hydrogen Bonding Enhances the Electrochemical Hydrogenation of Benzaldehyde in the Aqueous Phase.

Abstract: The hydrogenation of benzaldehyde to benzyl alcohol on carbon-supported metals in water, enabled by an external potential, is markedly promoted by polarization of the functional groups. The presence of polar co-adsorbates, such as substituted phenols, enhances the hydrogenation rate of the aldehyde by two effects, that is, polarizing the carbonyl group and increasing the probability of forming a transition state for H addition. These two effects enable a hydrogenation route, in which phenol acts as a conduit for proton addition, with a higher rate than the direct proton transfer from hydronium ions. The fast hydrogenation enabled by the presence of phenol and applied potential overcompensates for the decrease in coverage of benzaldehyde caused by competitive adsorption. A higher acid strength of the co-adsorbate increases the intensity of interactions and the rates of selective carbonyl reduction.

Selective photoelectrocatalytic tuning of benzyl alcohol to benzaldehyde for enhanced hydrogen production

Abstract: Hydrogen production can be promoted by replacing sluggish oxygen evolution reaction (OER) with a thermodynamically more favorable reaction, the primary oxidation reaction of benzyl alcohol to benzaldehyde. On a Bi2MoO6@TiO2NTA photocathode, the conversion of benzyl alcohol to benzaldehyde is realized with the selectivity of 100 %. This is originated from enhanced adsorption and activation of benzyl alcohol on this photoanode, as confirmed from tested by in situ FTIR techniques. The electrons generated during such a controllable and selective primary oxidation reaction is then utilized as the source for synergistical hydrogen production. The amount of generated hydrogen is then 5.5 times higher than that when OER is used. The efficiency for such hydrogen production is as high as 85 %. The proposed strategy combines solar energy and biomass for the efficient production of the valuable raw material - benzaldehyde as well as green energy source - hydrogen.

Critical role of solvent-modulated hydrogen-binding strength in the catalytic hydrogenation of benzaldehyde on palladium

Abstract: Solvents not only disperse reactants to enhance mass transport in catalytic reactions but also alter the reaction kinetically. Here, we show that the rate of benzaldehyde hydrogenation on palladium differs by up to one order of magnitude in different solvents (dioxane < tetrahydrofuran < water < methanol). However, the reaction pathway does not change; the majority of turnovers occurs by stepwise addition of sorbed hydrogen to sorbed benzaldehyde, first to the carbonyl oxygen and then to the carbon atom of the formyl group, forming benzyl alcohol. An analysis of the solvation energies shows that both ground and transition states are destabilized by the solvents compared to those at the gas–solid interface. The destabilization extent of the reacting organic substrates in both states are similar and, therefore, compensate each other, making the net kinetic effects inconsequential. Instead, the marked reactivity differences arise only from the differences in the solvation of sorbed hydrogen. Solvent effects play major roles in determining the mechanism of catalytic reactions, but their understanding remains often qualitative. Here, the authors provide a quantitative analysis of the effect of solvents on the catalytic hydrogenation of benzaldehyde on palladium, revealing the solvents’ crucial role in modulating the hydrogen-binding strength.

Comprehensive insights into the production of long chain aliphatic aldehydes using a copper-radical alcohol oxidase as biocatalyst

Abstract: The oxidation of alcohols is a cornerstone reaction in chemistry, notably in the flavor and fragrance industry where long-chain aliphatic aldehydes are major odorant compounds. In a context where greener alternatives are sought after, biocatalysis holds many promises. Here, we investigated the ability of the alcohol oxidase from Colletotrichum graminicola (CgrAlcOx)—an organic cofactor-free enzyme belonging to the copper-radical oxidase (CRO) class—to convert industrially relevant long-chain aliphatic alcohols. CgrAlcOx is a competent catalyst for the conversion of octan-1-ol when supported by the accessory enzymes peroxidase and catalase. Detailed examination of the products revealed the occurrence of an overoxidation step leading to the production of carboxylic acid for some aliphatic aldehydes and benzaldehyde derivatives. The partition between aldehyde and acid products varied upon substrate properties (chain length and propensity to form geminal-diols) and enzyme specificity and could be tuned by controlling the reaction conditions. In silico analyses suggested an inhibitory binding mode of long-chain aliphatic geminal-diols and a substrate-induced fit mechanism for a benzyl alcohol derivative. By demonstrating their natural ability to perform long-chain aliphatic alcohol oxidation, the present study establishes the potential of fungal CRO-AlcOx as promising candidates for the green production of flavor and fragrance compounds.

Atomically dispersed Feδ+ anchored on nitrogen-rich carbon for enhancing benzyl alcohol oxidation through Mott-Schottky effect

Abstract: Active and stable supported metal catalysts, with low metal loading amount and easy access if possible, are preferentially considered and synthesized This study reports a novel synthesis strategy to prepare Mott-Schottky type nitrogen-doped carbon supported single-atom iron SA-Fe/Nx-C catalysts by ligand-coordinated metallic method together with carbon nitride as template agent and nitrogen source for selective oxidation of benzyl alcohol to benzaldehyde The SA-Fe/Nx-C catalysts exhibited excellent catalytic performance in benzyl alcohol oxidation compared to that of Fe nanoparticle-based catalyst The reason for high catalytic activity was attributed to the formed tetra-coordinated FeN4 structure on which electron transfer occurred from metallic Fe to N atoms in the interface of Mott-Schottky contact Moreover, by tuning the ratio of carbon nitride in preparation of catalysts, the N content doped into carbon could be regulated, accomplishing controllable adjustment of electron transfer of metallic Fe and thus improving the selective benzyl alcohol oxidation

Dye-Sensitized Photoelectrosynthesis Cells for Benzyl Alcohol Oxidation Using a Zinc Porphyrin Sensitizer and TEMPO Catalyst

Abstract: Exploring a catalytic reaction other than water oxidation at the photoanode of a photoelectrochemical cell is probably a key feature to more efficiently generate the electrons needed to produce solar fuels. In this framework, we describe herein the fabrication of a TiO2-based dye-sensitized photo-electrosynthesis cell (DSPEC) using a zinc porphyrin (ZnP) sensitizer and a 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) organo-catalyst that quite efficiently catalyzes light-driven oxidation of methoxybenzyl alcohol into aldehyde. Two dyads ZnP–TEMPO, differing by the anchoring group (carboxylic acid and hydroxamic acid) on ZnP, were prepared and their electrochemical, absorption, and emission properties were recorded and quantum chemical modeling was realized. The photovoltaic performances in dye-sensitized solar cells were first examined in order to optimize the dyeing conditions and compare the relative efficiencies of the compounds. The dyads substituted with TEMPO outperform the reference zinc porphyrin lacking TEMPO with a much higher Jsc and Voc. The photocatalytic properties after immobilization on TiO2 nanocrystalline films toward para-methoxy benzyl alcohol oxidation were explored in borate buffer and in an acetonitrile electrolyte. In borate buffer, the optimal pH was 8 and using dyad ZnP–TEMPO anchored with hydroxamic acid, para-methoxy benzaldehyde was selectively produced with an average photocurrent density of 200 μA/cm2, a Faradaic efficiency of 82%, a turnover number (TON) of 26, and a turnover frequency (TOF) of 47 h–1. In acetonitrile, in the presence of 0.1 M N-methyl-imidazole, the same dyad gives an average photocurrent density of about 100 μA/cm2, a Faradaic efficiency of 76%, a TON of 13, and a TOF of 24 h–1. The stability of the anchor is crucial in the acetonitrile electrolyte, where the dyad is quite soluble since only the dyad functionalized with hydroxamic acid is compatible with these organic solvent conditions. Overall, this study paves the way to the development of more efficient and probably more stable TiO2-based DSPECs for alcohol oxidation that could advantageously complement those devoted to water oxidation.

Straightforward synthesis of a porous chromium-based porphyrinic metal-organic framework for visible-light triggered selective aerobic oxidation of benzyl alcohol to benzaldehyde

Abstract: Among MOFs, chromium-based metal–organic frameworks (Cr-MOFs) represent attractive scaffolds for variety of potential applications due to their high porosity and stability. Nevertheless, Cr-MOFs are not very common due to complicate synthesis. Cr-MOFs of large linkers are one clear example of synthetic limitations, since their preparation takes place by post-synthetic routes, commonly starting from Fe-MOFs as precursors. Hence, in this work, the direct synthesis of a phorphyrinic chromium-based MOF, Cr-PCN-600 (PCN stands for Porous Coordination Network) under solvothermal conditions is reported. The resulting Cr-MOF exhibits high surface area, permanent porosity, and broad light absorption wavelength range. Interestingly, this Cr-MOF is a highly effective heterogeneous photocatalyst for the selective aerobic oxidation of benzyl alcohol to benzaldehyde under visible light irradiation without any additive. Importantly, the Cr-MOF showed good recyclability maintaining its activity for three runs. The present results lay the foundation for both synthesis and applications of Cr-MOFs as robust photocatalysts in advanced organic transformations. Notably, quenching studies confirmed the generation of superoxide radical anion (O2 −) and singlet oxygen (1O2) (mostly) as reactive species under the reaction conditions.

Synthesis of γ-Hydroxy-α-amino Acid Derivatives by Enzymatic Tandem Aldol Addition–Transamination Reactions

Abstract: Three enzymatic routes toward γ-hydroxy-α-amino acids by tandem aldol addition-transamination one-pot two-step reactions are reported The approaches feature an enantioselective aldol addition of pyruvate to various nonaromatic aldehydes catalyzed by trans-o-hydroxybenzylidene pyruvate hydratase-aldolase (HBPA) from Pseudomonas putida This affords chiral 4-hydroxy-2-oxo acids, which were subsequently enantioselectively aminated using S-selective transaminases Three transamination processes were investigated involving different amine donors and transaminases: (i) l-Ala as an amine donor with pyruvate recycling, (ii) a benzylamine donor using benzaldehyde lyase from Pseudomonas fluorescens Biovar I (BAL) to transform the benzaldehyde formed into benzoin, minimizing equilibrium limitations, and (iii) l-Glu as an amine donor with a double cascade comprising branched-chain α-amino acid aminotransferase (BCAT) and aspartate amino transferase (AspAT), both from E coli, using l-Asp as a substrate to regenerate l-Glu The γ-hydroxy-α-amino acids thus obtained were transformed into chiral α-amino-γ-butyrolactones, structural motifs found in many biologically active compounds and valuable intermediates for the synthesis of pharmaceutical agents

Dual-Channel Charge Carrier Transfer in CsPbX3 Perovskite/W18O49 Composites for Selective Photocatalytic Benzyl Alcohol Oxidation

Abstract: The selective oxidation of benzyl alcohol to benzaldehyde using oxygen (O2) as the oxidant is a reaction of critical importance in the organic industry. In this study, CsPbX3/W18O49 composites with...

Tunable synthesis of imines and secondary-amines from tandem hydrogenation-coupling of aromatic nitro and aldehyde over NiCo5 bi-metallic catalyst

Abstract: A green process for production of imine and secondary-amine with high selectivity is desirable and challenging. Here, selective production of these nitrogen-containing compounds in one-pot was effectively realized in a hydrogenation-coupling tandem reaction system catalyzed by bi-metallic NiCo catalyst. The investigation of Co/Ni composition vs activity showed a composition-dependence catalysis and the optimal bi-metallic catalyst was NiCo5 (Ni and Co molar ratio 1:5). Nitrobenzene (NB) could almost completely transform toward imine at 70 °C and secondary-amine at 90 °C, respectively. The adsorption configurations of reactant on catalyst surface were analyzed by DFT calculation to probe the reaction mechanism. And the reaction dynamics were also investigated deeply, suggesting that hydrogenation of NB should be promoted but hydrogenation of benzaldehyde (BA) need inhibiting. Additionally, the catalytic system under moderate reaction conditions could also be applied to a variety of substituted aromatic nitro and aldehyde compounds, showing high yields of corresponding imines.

Simultaneous electrocatalytic hydrogenation of aldehydes and phenol over carbon-supported metals

Abstract: Electrocatalytic hydrogenation of furfural, benzaldehyde, and phenol was studied on carbon-supported Rh, Ru, Pd, and Cu catalysts. All metals were active for hydrogenation of the carbonyl group in furfural and benzaldehyde, but only Rh/C was active for phenol hydrogenation. The intrinsic activities for furfural and benzaldehyde conversion were Pd/C < Ru/C ≤ Rh/C < Cu/C and Ru/C < Rh/C < Pd/C < Cu/C, respectively. While the trend in furfural hydrogenation remained the same in the presence of phenol, the trend in benzaldehyde hydrogenation in the presence of phenol changed to Rh/C < Ru/C < Pd/C < Cu/C. The Faradaic efficiencies for hydrogenation of both furfural (in the 10–40% range) and benzaldehyde (in the 45–100% range) followed the trend: Cu/C < Rh/C < Ru/C < Pd/C. When phenol and an aldehyde were present in the reactant solution, phenol hydrogenation was suppressed. In contrast, enhancements in the rates of carbonyl reduction were observed for both aldehydes in presence of phenol. Such enhancements depend on both the aldehyde and the metal catalyst. The enhancing factors for hydrogenation of furfural and benzaldehyde were in the 1.5–2 and 2–4 ranges, respectively. We conclude that intermolecular interactions between adsorbed phenol and the aldehydes is a general phenomenon that can potentially enhance the rates of carbonyl hydrogenation. This work highlights co-adsorption effects that pose both challenges and advantages for electrocatalytic reduction of organic compounds.