Efficient Oxidation Of Alcohols Research Articles

Oxidation by Reduction: Efficient and Selective Oxidation of Alcohols by the Electrocatalytic Reduction of Peroxydisulfate.

Alcohol oxidation is an important class of reaction that is traditionally performed under harsh conditions and most often requires the use of organometallic compounds or transition metal complexes as catalysts. Here, we introduce a new electrochemical synthetic method, referred to as reductive oxidation, in which alcohol oxidation is initiated by the redox-mediated electrocatalytic reduction of peroxydisulfate to generate the highly oxidizing sulfate radical anion. Thus, and counter-intuitively, alcohol oxidation occurs as a result of an electrochemical reduction reaction. This approach provides a selective synthetic route for the oxidation of alcohols carried out under mild conditions to aldehydes, ketones, and carboxylic acids with up to 99% conversion yields. First-principles density functional theory calculations, ab initio molecular dynamics simulations, cyclic voltammetry, and finite difference simulations are presented that support and provide additional insights into the S2O82--mediated oxidation of benzyl alcohol to benzaldehyde.

Direct activation of PMS by highly dispersed amorphous CoOx clusters in anatase TiO2 nanosheets for efficient oxidation of biomass-derived alcohols

Developing a green and cost-effective catalytic system for the selective oxidation of biomass-derived alcohols is vital for the sustainable synthesis of fine chemicals. Herein, highly dispersed subnanometric amorphous CoOx clusters in anatase TiO2 nanosheets (Co-TiO2) fabricated by green solvent CO2-assisted approach could directly activate peroxymonosulfate (PMS) for the highly selective oxidation of various biomass-derived alcohols. Advanced characterizations (e.g., EXAFS, EPR, AC HAADF-STEM) reveal that a strong interaction of CoOx clusters and the anatase TiO2 support exist in Co-TiO2 and Co atom in Co-TiO2 is mainly consisted of Co2+ and Co3+. The Co-TiO2 catalyst offers superior catalytic performance in the conversion of six types of alcohols (e.g., benzyl alcohol (BAL), 5-hydroxymethylfurfural (HMF)) with high selectivity to produce corresponding aldehydes. Highly dispersed CoOx clusters and the interaction between CoOx clusters and TiO2 support contribute to the superior performance. Mechanism studies show that SO4•− radicals play the dominant role in the selective oxidation of model reactant BAL and 1O2 participates in the non-radical pathway. DFT calculations are well matched with experiment and decipher that the strong interaction between CoOx clusters and TiO2 support promotes the formation of SO4•– and SO5•–.

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.

Accelerated Decomposition of Potassium Permanganate in Ferrocenium Ion as Ferrocenium-Doped Manganese(IV) Oxide for Selective Oxidation of Alcohols

AbstractFerrocenium-doped manganese(IV) oxide (Fc+/MnO2) was synthesized through accelerated decomposition of KMnO4 in the presence of ferrocenium ion (Fc+) generated by concentrated sulfuric acid. The corresponding catalysts enabled highly efficient oxidation of alcohols with aldehyde or ketone.

Facile Synthesis of Single Iron Atoms over MoS2 Nanosheets via Spontaneous Reduction for Highly Efficient Selective Oxidation of Alcohols.

The facile creation of high-performance single-atom catalysts (SACs) is intriguing in heterogeneous catalysis, especially on 2D transition-metal dichalcogenides. An efficient spontaneous reduction approach to access atomically dispersed iron atoms supported over defect-containing MoS2 nanosheets is herein reported. Advanced characterization methods demonstrate that the isolated iron atoms situate atop of molybdenum atoms and coordinate with three neighboring sulfur atoms. This Fe SAC delivers exceptional catalytic efficiency (1 atm O2 @ 120°C) in the selective oxidation of benzyl alcohol to benzaldehyde, with 99% selectivity under almost 100% conversion. The turnover frequency is calculated to be as high as 2105 h-1 . Moreover, it shows admirable recyclability, storage stability, and substrate tolerance. Density functional theory calculations reveal that the high catalytic activity stems from the optimized electronic structure of single iron atoms over the MoS2 support.

In-situ construction of Bi24O31Br10-decorated self-supported BiOBr microspheres for efficient and selective photocatalytic oxidation of aromatic alcohols to aldehydes under blue LED irradiation

The efficient and selective oxidation of aromatic alcohols into corresponding aldehydes under mild conditions is an encouraging but challenging topic in catalysis chemistry and the chemical industry. Herein, a novel Bi24O31Br10-decorated BiOBr composite was synthesized by an in-situ phase transformation route, in which BiOBr microspheres used as 3D self-supported carriers, and Bi24O31Br10 nanosheets are highly dispersed and anchored on the surface of BiOBr microspheres. The as-synthesized composite photocatalysts showed superior selectivity and conversion efficiency for the photocatalytic oxidation of aromatic alcohols under blue LED irradiation. The excellent catalytic performance of Bi24O31Br10-decorated BiOBr is ascribed to its structural relationship between the two components and the dense heterojunction interface, which exposes more active sites and accelerate the spatial charge carriers’ separation. Based on the identification of reactive species (RS) and density functional theory (DFT) calculations, a two-step oxidation mechanism of aromatic alcohols was proposed. In particular, the respective roles of the reactive species, the reason for the first hydrogen loss of aromatic alcohols, and the effects of different substituents on their selectivity were clarified at the molecular level. It is hoped that this work can provide a feasible paradigm for the spatial structure design of different components in heterojunction catalysts to improve the efficiency and selectivity of photocatalytic reactions.

Porous organic polymer-supported manganese catalysts with tunable wettability for efficient oxidation of secondary alcohols

Porous organic polymers (POPs) feature high surface areas, tunable components, and designable hierarchical pores, thus showing versatile applications including catalysis, separation, gas storage and so on. However, the inherently hydrophobic property may be unfavorable for the catalytic reaction that involves hydrophilic reactants. By using the hydrophilic principle of the amide bond, R-NH-CO-R can be constructed in the porous frameworks to regulate the wettability. Herein, we report the construction of an amphiphilic and hierarchical porous Mn-N4 catalyst via the solvothermal copolymerization, in which N,N-methylenebisacrylamide is used as a hydrophilic monomer. This POP-based manganese catalyst can effectively promote the oxidation of secondary alcohol to produce the ketone using aqueous hydrogen peroxide as the oxidant under mild conditions. Note that this amphiphilic catalyst displays high catalytic activity as its homogeneous counterpart in the selective oxidation of alcohols. The present work has provided a successful approach for improving the catalytic activity by tuning the wettability of POP-based heterogeneous catalysts.

A host-guest interaction activated Bobbitt oxidant for highly efficient oxidation of alcohols.

Host-guest complexation using hydrogen-bonded macrocycles was found to enable activation of the Bobbitt oxidant reagent, which greatly facilitates the highly efficient oxidation of unactivated primary alcohols. This work provides a complementary approach to the activation of Bobbitt's salt with shape-persistent macrocycles in supramolecular catalysis.

Reusable homogeneous metal- and additive-free photocatalyst for high-performance aerobic oxidation of alcohols to carboxylic acids

How to realize the recycling of homogeneous catalysts has been a great challenge for chemists. In this background, a new pyridinium compound was synthesized and applied in selective photocatalytic oxidation. This photocatalytic system is advantageous in accelerating the transformation of alcohols into acids by two consecutive routes, including (1) photocatalytic oxidation of alcohols to aldehydes; (2) photocatalytic oxidation and autoxidation of aldehydes to acids. By activating molecular oxygen into •O2− and 1O2, the system displays advantages of high efficiency and simplicity, as well as environment-friendly nature without metals or additives. Attractively, this compound as a homogeneous catalyst can be reused by direct filtration of products profiting from its high performance and stability. The present work develops a new approach to achieve an efficient and recyclable aerobic oxidation of alcohols into acids by using pyridinium-based photocatalysts and provides a valuable insight into the separation and recycling of homogeneous catalysts for economic compatibility and industrial application.

Selective and efficient aerobic oxidation of benzyl alcohols using plasmonic Au-TiO2: Influence of phase transformation on photocatalytic activity

Chemical processes using heterogeneous photocatalytic systems are widely used for the synthesis of valuable fine chemicals. To improve these chemical processes both environmental and energy aspects must be kept in mind for favorable reaction conditions, such as optimum temperature and atmospheric pressure. In this study, plasmonic Au nanoparticles (Au NP) dispersed over TiO2 photocatalyst with different phases of TiO2 (amorphous, anatase and rutile) have been synthesized by using a facile sol–gel method followed by calcination for the photocatalytic oxidation of benzyl alcohol (BnOH) to benzaldehyde (BzH) under visible light irradiation at ambient conditions. The best photocatalyst exhibits high surface area and excellent catalytic conversion efficiency (96%) for the oxidation of BnOH to BzH in less reaction time using a green solvent, acetonitrile at room temperature. The detailed optimization of reaction parameters was performed for alcohol conversion. In addition the corresponding green metrics parameters were also calculated. The photocatalyst also shows excellent stability and reusability for multiple cycles. This work suggests that the Au-TiO2 catalyst provides a novel green and sustainable approach for the selective and efficient aerobic oxidation of BnOH to BzH under visible light irradiation. Furthermore, the impact of different phases of TiO2 on the photocatalytic activity has also been discussed.

Oxidation of alcohols to aldehydes with bromoisobutyrate and dimethyl sulfoxide

We have developed an efficient oxidation of primary alcohols to aldehydes with ethyl bromoisobutyrate and dimethyl sulfoxide. Diaryl ketone can also be prepared under this reaction system.

Magneto-structural properties and reliability of (Mn/Ni/Zn) substituted cobalt-copper ferrite heterogeneous catalyst for selective and efficient oxidation of aryl alcohols

Herein, M2+ substituted CoCuFe2O4 (M2+ = Mn, Zn, Ni) ferrites have been synthesized using the sol-gel auto combustion method. The structural, morphological and magnetic studies confirm the phase formation of pure magnetic cubic spinel MCoCuFe2O4 (M2+ = Mn, Zn, Ni) ferrites. The substitution with Mn, Ni and Zn does not show large variation in binding energies obtained from XPS of Cu (2p) that specifies identical copper concentration (Cu0.5) and substitution of only cobalt (Co2+) in Mn-F, Ni-F and Zn-F catalysts. Interestingly, MCoCuFe2O4 magnetic catalysts were explored for selective oxidation of a series of substituted benzyl alcohols. Catalyst Mn-F showed 93% conversion of benzyl alcohol while, Ni-F showed 95% conversion of 4-nitrobenzyl alcohol. Whereas, the catalyst Zn-F was showed 96% conversion for 4-methoxybenzyl alcohol. Additionally the results also indicate an efficient separation and recovery of the magnetic catalysts after four successive reuses without any considerable loss in its catalytic activity.

G-C3N4-Stabilised Organic–Inorganic Halide Perovskites for Efficient Photocatalytic Selective Oxidation of Benzyl Alcohol

The outstanding optoelectronic performance and facile synthetic approach of metal halide perovskites has inspired additional applications well beyond efficient solar cells and light emitting diodes (LEDs). Herein, we present an alternative option available for the optimisation of selective and efficient oxidation of benzylic alcohols through photocatalysis. The materials engineering of hybrids based on formamidine lead bromide (FAPbBr3) and graphic carbon nitride (g-C3N4) is achieved via facile anti-solvent approach. The photocatalytic performance of the hybrids is highly reliant on weight ratio between FAPbBr3 and g-C3N4. Besides, the presence of g-C3N4 dramatically enhances the long-term stability of the hybrids, compared to metal oxides hybrids. Detailed optical, electrical and thermal studies reveal the proposed novel photocatalytic and stability behaviours arising in FAPbBr3 and g-C3N4 hybrid materials.

Synergistic effect of iodine doped TiO2 nanoparticle/g-C3N4 nanosheets with upgraded visible-light-sensitive performance toward highly efficient and selective photocatalytic oxidation of aromatic alcohols under blue LED irradiation

Selective oxidation of alcohols via photocatalytic processes by O2 molecules as a green oxidant and visible light has a great potential to dissolve the environmental crisis and worldwide energy. Herein, I-TiO2 Nanoparticle/g-C3N4 Nanosheets (I-TiO2/CNNSs) heterostructured composite with different contents of graphitic carbon nitride nanosheets has been successfully prepared via a facile and simple procedure. The structure of the I-TiO2/CNNSs nanocomposite was analyzed by FT-IR, XRD, EDX, BET, TGA, FESEM, DRS, and PL techniques. The resultant nanocomposite (I-TiO2/(20 wt%)CNNSs) exhibits superior photocatalytic efficiency than its pristine g-C3N4 and iodine doped TiO2 for the oxidation of benzyl alcohols under the illumination of visible light (λ ≥ 400 nm). Introduction of the I-TiO2 on the surface of CNNSs can improve the absorption ability in the visible region and separation efficiency of charge carriers during the photocatalytic oxidation. Hence, these obtained results show that the I-TiO2/(20 wt%)CNNSs nanocomposite possess high photocatalytic performance and excellent reusability in oxidation reactions and other sustainable energy-related applications.

Au-catalyzed electrochemical oxidation of alcohols using an electrochemical column flow cell

A novel green system for the electrochemical oxidation of alcohols is demonstrated using a column flow cell. Voltammetric analysis revealed that the oxidation of 1-phenylethanol and benzaldehyde are promoted by using both an Au-electrode and an alkaline medium. To conduct such reaction with a column flow cell, we developed a method to modify a carbon-fiber thread with Au nanoparticles. The column carbon-fiber thread electrode modified with Au nanoparticles showed a high surface area, enabling the efficient electrochemical oxidation of various alcohols.

Boosting activity of molecular oxygen by pyridinium-based photocatalysts for metal-free alcohol oxidation

Pyridinium molecules are developed as electron- and energy-transfer mediators to boost the activity of air oxygen and thus achieve highly efficient photocatalytic oxidation of alcohols without any noble metal and additional co-catalysts/additives under mild conditions.

A new porous Co(ii)-metal–organic framework for high sorption selectivity and affinity to CO2 and efficient catalytic oxidation of benzyl alcohols to benzaldehydes

A new porous Co(ii)-MOF I has been prepared. Gas sorption and catalytic experiments show that the guest-free sample I′ shows the high capacity and selectivity to CO2 over CH4 and catalytically oxidize benzyl alcohols efficiently into benzaldehydes.

Efficient Photocatalytic Oxidation of Aromatic Alcohols over Thiophene‐based Covalent Triazine Frameworks with A Narrow Band Gap

AbstractPhotocatalytic selective oxidation of aromatic alcohols by covalent organic frameworks (COFs) is a sustainable strategy to replace present metal‐based heterogeneous catalytic oxidation systems. Covalent triazine‐based frameworks (CTFs), a subgroup of COFs, possess promising properties as efficient catalysts for photocatalytic oxidation. Sulfur‐containing metal‐free CTFs exhibit a good performance in photocatalysis due to their narrowed band gap, and the fast generated photoelectrons/holes separation and transfer. Here, we report the synthesis of thiophene‐based CTFs under mild conditions for photocatalytic oxidation of aromatic alcohols to the corresponding benzaldehydes using pure oxygen as the oxidant. Full conversion and a selectivity as high as 90 % to benzaldehyde were obtained paving the way for a potential application of these metal‐free photocatalysts in fine chemicals synthesis.

Efficient aerobic oxidation of alcohols to esters by acidified carbon nitride photocatalysts

Photocatalytic aerobic oxidation of alcohols for the direct synthesis of esters has received significant attention in recent years, but the relatively low efficiency and selectivity under visible light irradiation is the main challenge for their practical applications. Here, surface acidic sites were imparted onto metal-free heterogeneous photocatalysts by the protonation of carbon nitride (HMCN) to promote the activity for the esterification reaction through further adsorption and activation of the intermediate aldehyde. The activation of the substrate could be remarkably modulated through tuning the acidic sites on the surface of the photocatalyst, leading to a controllable reactivity of the catalytic reaction. The one-pot process for the direct aerobic oxidative esterification of alcohol exhibits high efficiency and selectivity under mild and additive-free conditions and the apparent quantum yield (AQY) of the photocatalytic esterification reaction is 0.41% at 420 nm. Moreover, a scalable photocatalytic process by the merging of a continuous flow system with the heterogeneous HMCN photocatalyst is demonstrated, combining high catalytic efficiency and stability at ambient temperatures and being promising for larger-scale applications.