System For Oxidation Of Alcohols Research Articles

Efficient Visible‐Light‐Driven Aromatic Alcohol Oxidation Using PI‐TiO2 Composite Photocatalyst

AbstractSynthesizing fine chemicals and valuable pharmaceutical intermediates through selective catalytic oxidation of alcohols is indispensable and crucial. However, the conventional methods of alcohol oxidation have inevitable drawbacks, including harsh reaction conditions and environmental pollution. Thus, it is imperative to develop efficient catalytic oxidation systems for alcohols. Herein, we successfully synthesized a 15 wt %PI‐TiO2 composite by a one‐step solid‐state heating polymerization technique. This catalyst exhibits excellent responsiveness to visible light and demonstrates remarkable catalytic activity. Furthermore, TEMPO was introduced as a cocatalyst to construct a PI‐TiO2/TEMPO/O2 system for the catalytic oxidation of alcohols. In comparison to the individual effects of PI or TiO2, this system showcases improved catalytic activity and broader substrate applicability. As a result, the conversion efficiency of benzyl alcohol increases by 3.44 times and 2.26 times, respectively. This research not only introduces a novel approach for preparing visible light‐active PI‐TiO2 catalysts but also indicates the significance of establishing an efficient electron transfer process in alcohol catalytic oxidation.

An In‐Situ‐Formed Copper‐Based Perfluorinated Catalytic System for the Aerobic Oxidation of Alcohols

AbstractHerein, we report a new catalytic protocol for the aerobic oxidation of alcohols. The catalytic system is formed in situ, in a straightforward and user‐friendly manner, combining a widely available copper source (Cu2O) with one imidazolium salt precursor bearing perfluorinated moieties. Our protocol uses TEMPO, as additive, and the reaction takes place at the interface of a biphasic solvent system, consisting of anisole and 1‐bromoperfluorooctane. The as‐prepared carbonyl compounds remain in the organic solvent, while the catalytic system remains in the fluorous phase. In this manner, the isolation and purification of the desired products are quite facile. Our protocol uses low catalytic loadings and is more efficient with primary alcohols, affording the desired products in good to excellent yields. The fluorous phase containing the catalytic system can be efficiently recovered and reused for at least six times, without a significant decrease in its catalytic efficiency.

A manganese-based catalyst system for general oxidation of unactivated olefins, alkanes, and alcohols.

Non-noble metal-based catalyst systems consisting of inexpensive manganese salts, picolinic acid and various heterocycles enable epoxidation of the challenging (terminal) unactivated olefins, selective C-H oxidation of unactivated alkanes, and O-H oxidation of secondary alcohols with aqueous hydrogen peroxide. In the presence of the in situ generated optimal manganese catalyst, epoxides are generated with up to 81% yield from alkenes and ketone products with up to 51% yield from unactivated alkanes. This convenient protocol allows the formation of the desired products under ambient conditions (room temperature, 1 bar) by employing only a slight excess of hydrogen peroxide with 2,3-butadione as a sub-stoichiometric additive.

Construction of a g-C3N4-driven photocatalytic system for boosted biomass-derived alcohol oxidation: a promising route towards sustainable biomass valorization

We present feasible regulation strategies of a g-C3N4-based photocatalytic system for selective oxidation of biomass-derived alcohols for better biomass valorization.

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•–.

A Highly Efficient Bismuth Nitrate/Keto-ABNO Catalyst System for Aerobic Oxidation of Alcohols to Carbonyl Compounds under Mild Conditions.

An efficient and practical catalytic system for the oxidation of alcohols to aldehydes/ketones using catalytic amounts of Bi(NO3)3 and Keto-ABNO (9-azabicyclo [3.3.1]nonan-3-one N-oxyl) with air as the environmentally benign oxidant was developed. Various primary and secondary alcohols were smoothly oxidized to the corresponding products under mild conditions, and satisfactory yields were achieved. Moreover, this methodology avoids the use of a ligand and base. The gram-scale reaction was demonstrated for the oxidation of 1-phenyl ethanol, and the product of acetophenone was obtained at an isolated yield of about 94%.

Catalytic behaviour of the Cu(i)/L/TEMPO system for aerobic oxidation of alcohols - a kinetic and predictive model.

Here, we disclose a new copper(i)-Schiff base complex series for selective oxidation of primary alcohols to aldehydes under benign conditions. The catalytic protocol involves 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), N-methylimidazole (NMI), ambient air, acetonitrile, and room temperature. This system provides a straightforward and rapid pathway to a series of Schiff bases, particularly, the copper(i) complexes bearing the substituted (furan-2-yl)imine bases N-(4-fluorophenyl)-1-(furan-2-yl)methanimine (L2) and N-(2-fluoro-4-nitrophenyl)-1-(furan-2-yl)methanimine (L4) have shown excellent yields. Both benzylic and aliphatic alcohols were converted to aldehydes selectively with 99% yield (in 1–2 h) and 96% yield (in 16 h). The mechanistic studies via kinetic analysis of all components demonstrate that the ligand type plays a key role in reaction rate. The basicity of the ligand increases the electron density of the metal center, which leads to higher oxidation reactivity. The Hammett plot shows that the key step does not involve H-abstraction. Additionally, a generalized additive model (GAM, including random effect) showed that it was possible to correlate reaction composition with catalytic activity, ligand structure, and substrate behavior. This can be developed in the form of a predictive model bearing in mind numerous reactions to be performed or in order to produce a massive data-set of this type of oxidation reaction. The predictive model will act as a useful tool towards understanding the key steps in catalytic oxidation through dimensional optimization while reducing the screening of statistically poor active catalysis.

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.

Synergistic catalysis within core-shell Fe3O4@SiO2 functionalized with triethylene glycol (TEG)-imidazolium ionic liquid and tetramethylpiperidine N-oxyl (TEMPO) boosting selective aerobic oxidation of alcohols

HypothesisIt is expected that incorporation of 2, 2, 6, 6-tetra-methyl piperidine-N-oxyl radical (TEMPO) and an imidazolium bromide bearing hydrophilic triethylene glycol (TEG) groups on Fe3O4@SiO2 core–shell may not only result in a novel highly water-dispersible/magnetically separable multi-functional catalyst system for metal-free aerobic oxidation of alcohols, which operates through a synergistic relay pathway, but it could potentially provide a strong platform for simultaneous separation and recycling of all components. ExperimentsThe catalyst was prepared by anchoring TEMPO moieties onto a magnetic core–shell Fe3O4@SiO2 functionalized with an ionic liquid bearing TEG groups. The materials was characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption isotherms, thermal gravimetric analysis, and elemental analysis. The performance of the catalyst was evaluated and quantitatively measured in the aerobic oxidation of alcohols in water. FindingsThe catalyst exhibited excellent and stable colloidal dispersion in water and high performance in the aerobic oxidation of various types of alcohols under metal- and halogen-free reaction conditions. As hypothesized, strong synergistic effect between functionalized components was seen in the described reaction. The catalyst displayed excellent dual-adjustable-selectivity in the oxidation of primary alcohols to either the corresponding aldehydes or carboxylic acids by tuning the reaction solvent and/or reaction time and excellent recycling behavior through a “double-separation-strategy”.

Green, homogeneous oxidation of alcohols by dimeric copper(II) complexes

Three pyrazole derivatives, 3,5-dimethyl-1H-pyrazole (DMPz) (I), 3-methyl-5-phenyl-1H-pyrazole (MPPz) (II), and 3,5-diphenyl-1H-pyrazole (DPPz) (III), were prepared via reacting semicarbazide hydrochloride with the acetylacetone, 1-phenylbutane-1,3-dione, and 1,3-diphenylpropane-1,3-dione, respectively. Complexes 1–3 were isolated by reacting CuCl2·2H2O with I–III, respectively, and characterized by CHNS elemental analyses, FT-IR, UV-Vis, 1H and 13C NMR, EPR spectra, and TGA/DTA. Molecular structures of the pyrazole derivatives I–III and copper(II) complexes 2 and 3 were studied through single-crystal XRD analysis to confirm their molecular structures. Overlapping of hyperfine splitting in the EPR spectra of the dimeric copper(II) complexes 1–3 indicates that both copper centers do not possess the same electronic environment in solution. The copper(II) complexes are dimeric in solid state as well as in solution and catalyze the oxidation of various primary and secondary alcohols selectively. Catalysts 1–3 show more than 92% product selectivity toward ketones during the oxidation of secondary alcohols. Surprisingly primary alcohols, which are relatively difficult to oxidize, produce carboxylic acid as a major product (48%–90% selectivity) irrespective of catalytic systems. The selectivity for carboxylic acid rises with decreasing the carbon chain length of the alcohols. An eco-friendly and affordable catalytic system for oxidation of alcohols is developed by the utilization of H2O2, a green oxidant, and water, a clean and greener solvent, which is a notable aspect of the study.

Dual stimuli-responsive silver nanoparticles decorated SBA‒15 hybrid catalyst for selective oxidation of alcohols under ‘mild’ conditions

Herein, we develop an efficient and novel catalytic system, i.e. silver nanoparticles (AgNPs) incorporated mesoporous silica SBA‒15/copolymer hybrid material, for selective oxidation of different alcohols to aldehydes or ketones under ‘mild’ conditions. The copolymer of N,-N -dimethylaminoethyl methacrylate and 2-hydroxyethyl acrylate (p(DMAEMA- co -HEA)) was used to graft the surface-modified SBA‒15 (MS) using free radical polymerization method. Then AgNPs were decorated on the polymer grafted SBA‒15. The dual (thermal and pH) responsive behaviors of the AgNPs/p(DMAEMA- co -HEA)/MS catalyst were investigated using the dynamic light scattering technique. The lower critical solution temperature (LCST) of the copolymer was found to be approximately 30–35 °C. The catalytic activity of AgNPs/p(DMAEMA- co -HEA)/MS was investigated for the selective oxidation of different alcohols to aldehydes or ketones. The conversion of catalytic products and selectivity were calculated using gas chromatographic techniques, whereas the molecular structure of products was determined using 1 H and 13 C nuclear magnetic resonance spectroscopy. The catalyst showed improved catalytic activity toward the oxidation of alcohols to aldehydes in aqueous medium below LCST and pKa value (7–7.5) of the copolymer. The selectivity toward the corresponding aldehyde was found to be significantly high (99%). The main advantages of the hybrid catalyst as compared to existing catalysts include outstanding alcohol conversion (up to 99%), short reaction time (1 h), small necessary amount of catalyst (6 mg), and performing the catalytic conversion at room temperature using water as a solvent, which are highly beneficial for organic conversion under mild reaction conditions. • A catalytic system for selective oxidation of alcohols under ‘mild’ conditions was developed. • The catalyst consists of a temperature and pH-responsive copolymer, SBA-15, and Ag nanoparticles. • The catalyst showed outstanding alcohol conversion (up to 99%) within a short reaction time (1 h). • The catalyst performed the catalytic conversion at room temperature using water as a solvent.

A novel magnetically separable laccase‐mediator catalyst system for the aerobic oxidation of alcohols and 2‐substituted‐2,3‐dihydroquinazolin‐4(1H)‐ones under mild conditions

In this study, a magnetically reusable artificial metalloenzyme has been constructed by co‐immobilization of palladium nanoparticles as a strong oxidizing catalyst and laccase as an oxygen‐activating enzyme into the cavities of magnetic mesocellular foams silica (Pd‐Laccase@MMCF). The combination of Pd‐Laccase@MMCF and hydroquinone (HQ) act as electron‐transfer mediator system and make stepwise electron transfer from substrate to molecular oxygen. This catalyst system was used for the aerobic (i) oxidation of alcohols to the corresponding carbonyl compounds and (ii) dehydrogenation of 2‐substituted‐2,3‐dihydroquinazolin‐4(1H)‐ones in phosphate buffer (0.1 M, pH 4.5, 4 mL)/THF (4%, 1 mL) as solvent under mild conditions. The co‐immobilization of both laccase and Pd onto high surface area mesoporous support, high catalytic activity and magnetically separable and reusable make the present catalyst system superior to other currently available electron‐transfer mediator systems.

Synergistic Catalytic Effect of N-Hydroxyphthalimide/Cobalt Tetraamide Phthalocyanine and Its Application for Aerobic Oxidation of Hydrocarbons and Alcohols

The activation of oxygen for selective oxidation of organic molecules, such as hydrocarbons and alcohols, remains a major catalytic challenge. We have developed a catalytic system combining N-hydroxyphthalimide (NHPI) with cobalt tetraamide phthalocyanine [CoPc(CONH2)4] for the oxidation of hydrocarbons and alcohols at 75 °C under an oxygen atmosphere. CoPc(CONH2)4 was synthesized by trimellitic anhydride-urea method, and its structure was confirmed by FT-IR, UV–Vis and XRD. This catalyst, in synergy with NHPI/O2 system, exhibited excellent catalytic ability and high selectivity in the oxidation of hydrocarbons and alcohols. Based on the experimental results, a reasonable reaction mechanism was proposed for the oxidation of alkanes and alcohols, respectively. Cobalt tetraamide phthalocyanine (CoPc(CONH2)4) was synthesized by a simple solid-thermal method, and the synergistic catalysis oxidation of NHPI and CoPc(CONH2)4 was studied. A synergistic catalysis system for the aerobic oxidation of hydrocarbons and alcohols by N-hydroxyphthalimide combined with cobalt tetraamide phthalocyanine has been developed.

Efficient utilization of photogenerated electrons and holes for photocatalytic redox reactions using visible light-driven Au/ZnIn2S4 hybrid.

In this study, a new photocatalytic reaction system for simultaneous selective oxidation of aromatic alcohols to corresponding aldehydes and reduction of protons to H2 has been developed. The results reveal that compared with pure ZnIn2S4, the ZnIn2S4 photocatalysts modified with noble metal gold (Au/ZnIn2S4) significantly promote the photocatalytic performance. Among them, the 0.5% Au/ZnIn2S4 nanosheets shows the highest photocatalytic activity for selective oxidation of benzyl alcohol to benzaldehyde and hydrogen production, and the yields of H2 and benzaldehyde are 326.68 and 352.04 μmol under visible light irradiation for 4 h, respectively. Those are about 4.4 and 3.6 times higher than those of pure ZnIn2S4 sample (74.0 μmol H2 and 98.04 μmol benzaldehyde), respectively. The utilization ratio of photogenerated electrons to holes can achieve 92.8%. Additionally, the control experiments demonstrate that the photogenerated electrons and holes play significant roles during the reaction process. It is hoped that the current work can offer an avenue to utilize the photogenerated carriers more efficiently and to develop other photocatalytic reaction systems, such as nitrogen fixation and reduction of carbon dioxide.

Synthesis of high surface area magnesia by using walnut shell as a template

Abstract In the present study, high surface area amorphous magnesia was synthesized using walnut shell as a template. This green, simple and useful synthetic protocol was based on the precipitation of magnesium nitrate on biomass in an aqueous phase, followed by calcination. Materials were characterized using X-ray diffraction, scanning electron microscopy (SEM) and N2 adsorption/desorption porosimetry, and the results exhibited high surface area for magnesium oxide. Furthermore, the pore size and surface area of these mesoporous materials can be adjusted by varying the biomass/magnesium nitrate ratio. In addition, magnesium oxide was studied as the support of palladium nanoparticles for the aerobic oxidation of alcohols. We have found out that the resulting Pd-loaded material acts as an effective catalytic system for the aerobic oxidation of benzylic and aliphatic alcohols. The catalyst can be recovered and reused three times without loss of activity. Also, to test the catalytic activity of magnesium oxides as a solid catalyst, we selected Meerwein-Ponndorf-Verley reduction of cyclohexanone with 2-propanol over different magnesium oxides.

LaoABCR, a Novel System for Oxidation of Long-Chain Alcohols Derived from SDS and Alkane Degradation in Pseudomonas aeruginosa.

The opportunistic pathogen Pseudomonas aeruginosa strain PAO1 is able to use a variety of organic pollutants as growth substrates, including the anionic detergent sodium dodecyl sulfate (SDS) and long-chain alkanes. While the enzymes initiating SDS and alkane degradation are well known, the subsequent enzymatic steps for degradation of the derived primary long-chain alcohols have not yet been identified. By evaluating genes specifically induced during growth with SDS, a gene cluster encoding a putative alcohol dehydrogenase (PA0364/LaoA), a probable inner membrane protein (PA0365/LaoB), and a presumable aldehyde dehydrogenase (PA0366/LaoC) was identified and designated the Lao (long-chain-alcohol/aldehyde-oxidation) system. Growth experiments with deletion mutants with SDS, 1-dodecanol, and alkanes revealed that LaoA and LaoB are involved in the degradation of primary long-chain alcohols. Moreover, detection of 1-dodecanol oxidation in cell extracts by activity staining revealed an interdependency of LaoA and LaoB for efficient 1-dodecanol oxidation. An in silico analysis yielded no well-characterized homologue proteins for LaoA and LaoB. Furthermore, a gene adjacent to the lao gene cluster encodes a putative transcriptional regulator (PA0367/LaoR). A laoR deletion mutant exhibited constitutive expression of LaoA and LaoB, indicating that LaoR is a repressor for the expression of laoABC Taken together, these results showed that the proteins LaoA and LaoB constitute a novel oxidation system for long-chain alcohols derived from pollutants.IMPORTANCE The versatile and highly adaptive bacterium Pseudomonas aeruginosa is able to colonize a variety of habitats, including anthropogenic environments, where it is often challenged with toxic compounds. Its ability to degrade such compounds and to use them as growth substrates can significantly enhance spreading of this opportunistic pathogen in hygienic settings, such as clinics or water distribution systems. Thus, knowledge about the metabolism of P. aeruginosa can contribute to novel approaches for preventing its growth and reducing nosocomial infections. As the Lao system is important for the degradation of two different classes of pollutants, the identification of these novel enzymes can be a useful contribution for developing effective antibacterial strategies.

Triphasic Continuous‐Flow Oxidation System for Alcohols Utilizing Graft‐Polymer‐Supported TEMPO

AbstractWe developed a triphasic (solid–organic–aqueous) continuous‐flow reaction system for the chemoselective oxidation of primary and secondary alcohols, using 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) immobilized on polyethylene‐g‐polyacrylic acid graft polymer (g‐TEMPO). g‐TEMPO exhibited higher contact efficiency than TEMPO supported on silica or cross‐linked polystyrene under immiscible‐flow conditions, and maintained excellent conversion for at least 9 days with no loss of catalytic activity.

A silver NP-dispersed water extract of fly ash as a green and efficient medium for oxidant-free dehydrogenation of benzyl alcohols.

Herein, a green, efficient, and new catalytic system for dehydrogenative oxidation of benzyl alcohols using Ag nanoparticles (NPs) dispersed in water extract of fly ash (WEFA) has been developed. Various characterization techniques were performed to authenticate the formation of Ag@WEFA. The as-prepared Ag NPs (10–20 nm) were found to be dispersed in WEFA, as indicated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images. With Ag@WEFA, a variety of substituted benzyl alcohols were efficiently converted to carbonyl compounds in high yields. All the reactions were deliberately carried out without using any ligand or hazardous organic solvent. This catalytic system involving WEFA is a genuinely new concept. It is, therefore, expected to attract attention from researchers working in the areas of sustainable chemistry.

Organocatalyzed oxidation of benzyl alcohols by a tetrazole-amino-saccharin: A combined experimental and theoretical (DFT) study

A new catalytic system for the anaerobic oxidation of benzyl alcohols using a tetrazole-amino-saccharin organocatalyst has been established. In a solvent-free and microwave assisted process comprising aqueous tert-butyl hydroperoxide (TBHP) as oxidant, a variety of benzyl alcohols has been efficiently converted to aldehydes under mild conditions. Most reactions are complete within 30min and the catalyst exhibits varied functional group compatibility. A catalytic cycle for the oxidation of the alcohols promoted by the tetrazole-amino-saccharin derivative is outlined involving radical species. DFT calculations performed for the oxidation of benzyl alcohol with and without organocatalyst show that the rate limiting step of the whole reaction is the cleavage of the OO bond in TBHP with the subsequent hydrogen abstraction from the alcohol. The tetrazole-amino-saccharin organocatalyst assists the H-abstraction from benzyl alcohol by the bound HO radical. The simplicity, selectivity and softness of reaction conditions of the studied organocatalytic protocol suggest a great potential for extensive use in synthetic chemistry.

Practical Aerobic Oxidation of Alcohols: A Ligand‐Enhanced 2,2,6,6‐Tetramethylpiperidine‐1‐oxy/Manganese Nitrate Catalyst System

AbstractA highly efficient, ligand‐enhanced 2,2,6,6‐tetramethylpiperidine‐1‐oxy (TEMPO)/Mn(NO3)2 catalyst system for the aerobic oxidation of alcohols is described. From the series of coordinating ligands studied herein, 2‐picolinic acid (PyCOOH) improves the catalytic activity of TEMPO/Mn(NO3)2 remarkably. Under ambient air at room temperature in acetic acid, the ligand‐enhanced catalyst converts aliphatic and benzylic primary alcohols that bear various functional groups into their respective aldehydes with near quantitative conversions. The applicability of the catalyst for convenient preparative synthesis was demonstrated by conducting oxidations on a gram scale. A change of TEMPO to the sterically less demanding 9‐azabicyclo[3.3.1]nonane N‐oxyl results in a Mn catalyst that is also able to oxidize secondary alcohols to ketones. Mechanistic studies showed that alcohols are oxidized by the oxoammonium cation derived from the nitroxyl radical. The active oxidant is regenerated by Mn(NO3)2, and this process is greatly promoted by the coordination of PyCOOH to Mn.