Oxidation Of 1-phenylethanol Research Articles

Solvent-free oxidation of alcohols by a heterogeneous Fe3O4@SiO2-DTPA-Ru nanocatalyst

A novel magnetic heterogeneous ruthenium catalyst (Fe3O4@SiO2-DTPA-Ru) was prepared by using magnetic silicon spheres as support, ethylenediaminepentaacetic acid (DTPA) as functional ligands, ruthenium chloride as catalyst precursor. The results obtained after a series of characterizations showed that the catalyst Fe3O4@SiO2-DTPA-Ru was 5–15 nm in size with a 0.205 nm lattice and contained 0.31 mmol Ru/g catalyst. It also had a good thermal stability under 232°C which was verified by thermal filtration method. Besides, the saturation magnetic intensity was as high as 20.54 emu/g. The catalyst Fe3O4@SiO2-DTPA-Ru was applied for the first time into thirteen oxidation reactions of aromatic alcohols and showed good catalytic activity even the yields of eleven aromatic alcohols were all over 90%. In catalyzing 1-phenylethanol to acetophenone, its TOF and TON were 9677 h−1 and 6991, respectively. The Fe3O4@SiO2-DTPA-Ru catalyst could still maintain good reusability and catalytic performance after 15 cycles of 1-phenylethanol oxidation, which was superior to many reported catalysts and had great potential in future industrial production.

A green and pollution-free heterogeneous ruthenium catalyst anchoring on magnetic nanoparticles with FPBA and DTPA groups for oxidation of aromatic alcohols

Using ruthenium chloride as catalyst precursor, magnetic silicon spheres as support, 4-formylphenylboronic acid and ethylenediaminepentaacetic acid as functional ligands, a magnetic heterogeneous nano-ruthenium catalyst (Fe3O4@SiO2-FPBA-DTPA-Ru) was prepared for the first time. It was nano level with 20.17 emu/g saturation magnetic strength and thermal stability under 249.63 °C. Fe3O4@SiO2-FPBA-DTPA-Ru contained 0.38 mmol/g Ru and was successfully used to catalyze the oxidation reactions of 15 aromatic secondary alcohols. Results proved that Fe3O4@SiO2-FPBA-DTPA-Ru as catalyst had good catalytic activity for the oxidation of secondary aromatic alcohols with yields exceeding 90 % for 12 products and 95 % for 10 products. High TON and TOF values (6386 and 9158 h−1) in 1-phenylethanol oxidation were obtained. All the reactions of aromatic alcohols were carried out in a solvent-free system, so the prepared catalyst had the characteristics of green and pollution-free. It was’nt suitable for oxidation of aromatic primary alcohols. If there was steric hindrance around the hydroxyl group in substrate, the catalysis also may be limited. The Fe3O4@SiO2-FPBA-DTPA-Ru catalyst also exhibited the advantages of energy saving, satisfactory reusability and stability in 9 consecutive runs. It showed great potential for future large-scale industrial production.

Synthesis of Copper-Substituted Polyoxovanadate and Oxidation of 1-Phenyl Ethanol

Dicopper-substituted polyoxovanadate [Cu2V16O44(NO3)]5− (Cu2V16) was synthesized through the reaction of [Cu2V8O24]4− and [V4O12]4− in the presence of nitrate salt. From single crystal X-ray analysis, Cu2V16 exhibited the same helical structure as that of nitrate-incorporated polyoxovanadate, [V18O46(NO3)]5− (V18). Both complexes had the same framework with the same guest anion and are considered to be substituted isomers for each other by replacing two Cu2+ ions and two [VO]2+ ions. The incorporated nitrate showed short and long N–O bond lengths (1.14, 1.26 and 1.30 Å) as in the case of V18 (1.09, 1.16 and 1.28 Å). Reflecting the inequivalent bond lengths of the nitrate, the IR spectrum of V18 shows split peaks at 1359 and 1342 cm−1. But the Cu2V16 spectrum showed a single peak due to the presence of nitrate at 1353 cm−1. When the temperature was lowered, the nitrate peak in Cu2V16 was split into two positions at 1354 and 1345 cm−1 when the temperature reached −140 °C. These results indicate that the nitrate incorporated in Cu2V16 rotates relatively easily in the Cu2V16 cavity at room temperature compared to V18. In addition, the oxidation of 1-phenyl ethanol to acetophenone with Cu2V16 smoothly proceeded in comparison with V18. By taking advantage of the same framework in both catalysts, we can deduce the position of potential active sites in the oxidation reaction. We have concluded that the most active site is not on the peripheral of the vanadate framework, but it is reasonable to suggest that the active site is on the substituted copper atoms rather than the polyoxovanadate framework.

Tuning Ni-Pyrazolate Frameworks by Post-Synthetic Fe-Incorporation for Oxidase-Mimicking H2 O2 Activation.

The introduction of iron ionic sites by metal exchange of defective homometallic nickel pyrazolate frameworks generates non-precious, Earth-abundant, first-row heterometallic Fe/Ni-pyrazolate frameworks. The Fe incorporation at the Ni nodes of the framework allows to control the hydrogen peroxide activation, minimizing its decomposition and O2 liberation, occurring at the homometallic Ni nodes. The generation of Fe-OH reactive oxygen species at the heterometallic Fe/Ni nodes is demonstrated by the higher activity in the proof-of-concept oxidation of 1-phenylethanol to acetophenone in an aqueous medium.

Solvent-free selective oxidation of benzyl alcohol using Ru loaded ceria-zirconia catalysts

Selective oxidation of alcohols to aldehydes or ketones is a fundamental process in organic chemistry and the development of green and sustainable transformations are strongly required. Herein, we focused on the development of Ru-based catalysts deposited over ceria-zirconia supports (CZRu) for the solvent free oxidation of benzyl alcohol using air as oxidant, which is a cheap and safe process and meets to the atom economy and environment requirements. XPS characterization of the material reveals that the formation of RuO2 on the surface is necessary to achieve higher catalytic activity. The activity is strongly related to the reducibility of the material and to the close interaction between ceria-zirconia and RuO2, with the likely formation of Ru-O-Ce arrangements. The greater mobility of oxygen due to the formation of bridging oxygens in Ru-O-Ce and to the formation of superoxide species (O2−) over Ce3+ sites, significantly boosts the selective oxidation of alcohols. CZRu is a promising material with a remarkable 61% alcohol conversion at 90 °C without solvents; it also exhibits high activity (55% conversion) and complete selectivity (100%) for the selective oxidation of 1-phenylethanol to acetophenone. Overall, the formulation is among the most active reported so far under solvent free conditions and molecular oxygen. In addition, the reaction over CZRu exhibits an environmental factor (E-factor) lower than 1 (0.95) confirming the sustainability of the proposed process.

Heterostructure-Engineered Semiconductor Quantum Dots toward Photocatalyzed-Redox Cooperative Coupling Reaction.

Semiconductor quantum dots have been emerging as one of the most ideal materials for artificial photosynthesis. Here, we report the assembled ZnS-CdS hybrid heterostructure for efficient coupling cooperative redox catalysis toward the oxidation of 1-phenylethanol to acetophenone/2,3-diphenyl-2,3-butanediol (pinacol) integrated with the reduction of protons to H2. The strong interaction and typical type-I band-position alignment between CdS quantum dots and ZnS quantum dots result in efficient separation and transfer of electron-hole pairs, thus distinctly enhancing the coupled photocatalyzed-redox activity and stability. The optimal ZnS-CdS hybrid also delivers a superior performance for various aromatic alcohol coupling photoredox reaction, and the ratio of electrons and holes consumed in such redox reaction is close to 1.0, indicating a high atom economy of cooperative coupling catalysis. In addition, by recycling the scattered light in the near field of a SiO2 sphere, the SiO2-supported ZnS-CdS (denoted as ZnS-CdS/SiO2) catalyst can further achieve a 3.5-fold higher yield than ZnS-CdS hybrid. Mechanistic research clarifies that the oxidation of 1-phenylethanol proceeds through the pivotal radical intermediates of •C(CH3)(OH)Ph. This work is expected to promote the rational design of semiconductor quantum dots-based heterostructured catalysts for coupling photoredox catalysis in organic synthesis and clean fuels production.

Application of gold and palladium nanoparticles supported on polymelamine microspheres in the oxidation of 1-phenylethanol and some other phenyl substituted alcohols

Melamine formaldehyde and melamine resorcinol formaldehyde microspheres were decorated with Au and Pd nanoparticles and applied as heterogeneous catalysts in the oxidation of 1-phenylethanol. The catalysts showed similar activities irrespective of the support employed. Moderate conversion activities of 48–50% were achieved when using acetonitrile as solvent; however, when employing water as solvent, the supported catalysts formed a three-phase, emulsion system which facilitated the catalytic conversion of 1-phenylethanol to acetophenone at much higher conversions of around 83%. The oxidant, TBHP, decomposed rapidly in acetonitrile, whilst it remained stable in aqueous solution, leading to the enhanced activities observed when using water as solvent. These systems also proved to be recyclable for up to five cycles, with only slight loss of activity observed; this can be attributed to the physical loss of catalyst during the workup procedure conducted between each cycle.

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%.

Purification and characterisation of (S)-specific alcohol dehydrogenase from Candida parapsilosis ATCC 7330

Alcohol dehydrogenases (ADHs) catalyses reversible reduction of carbonyl group to its corresponding alcohols and have been widely employed as versatile biocatalyst due to its high enantioselectivity to produce chiral alcohols. In this study, the (S) - specific alcohol dehydrogenase (S-ADH) enzyme was purified from Candida parapsilosis ATCC 7330. It asymmetrically reduced acetophenone to (S)-1-phenylethanol with > 99% ee with an effective substrate coupled approach for cofactor recycling. In the reverse reaction, i.e., oxidation of 1-phenylethanol, S-ADH produced (R)-1-phenylethanol with > 99% ee via kinetic resolution. S-ADH is a zinc dependent medium chain dehydrogenase/reductase. It was found to be a tetramer in nature with subunit molecular mass of 40 kDa catalysing oxidation and reduction reactions only using NAD+ and NADH as the cofactors respectively with higher affinity for NAD+. Further biochemical characterisation indicated that His and Cys residues play a crucial role in the enzymatic catalysis and requires a reducing environment at the active site. S-ADH was stable at pH 6.0 in reducing acetophenone and pH 8.0 in oxidising 1-phenylethanol at 45 °C with the t1/2 of 6.8 h and 9.0 h respectively. Therefore, purified S-ADH would be a useful biocatalyst in the synthesis of enantiopure (S)- and (R)-1-phenylethanol which are used in the fragrance preparation.

C-Heterogenized Re Nanoparticles as Effective Catalysts for the Reduction of 4-Nitrophenol and Oxidation of 1-Phenylethanol

Rhenium nanoparticles (Re NPs) supported on Norit (activated carbon—C) and graphene (G) were prepared by a solvothermal method under microwave irradiation (MW). The synthesised heterogeneous catalysts were characterised and tested as reduction and oxidation catalysts, highlighting their dual catalytic behaviour. In the first case, they were used, for the first time, to reduce 4-nitrophenol, in aqueous medium, under MW irradiation. Re catalysts were easily recovered by centrifugation and recycled up to six times without significant activity loss. However, the same Re catalysts in MW-assisted oxidation of 1-phenylethanol with no added solvent experienced a significant loss of activity when recycled. The higher activity of the rhenium nanoparticles supported on graphene (Re/G) catalyst in both reactions was assigned to the higher dispersion and smaller particle size of Re NPs when graphene is the support.

Nano NiFe2O4 supported phenanthroline Cu(II) complex as a retrievable catalyst for selective and environmentally friendly oxidation of benzylic alcohols

A new magnetically recoverable catalyst consisting of phenanthroline Cu(II) complex supported on nickel ferrite nanoparticles was prepared. The synthesized catalyst was characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, transmission and scanning electron microscopes, thermogravimetry, energy dispersive X-ray spectroscopy, vibrating sample magnetometry and inductively coupled plasma. Supported copper complex used for solvent free oxidation of 1- phenyl ethanol as a model. Influence of the reaction parameters (kind of oxidant, amount of the catalyst, reaction time, solvent and reaction temperature) were studied. Because of the immobilized complex has been shown to be an efficient heterogeneous catalyst for the selective oxidation of 1-phenyl ethanol to acetophenone (94% yield) by hydrogen peroxide so this green approach extended to other benzylic alcohols. The catalyst had been reused 10 times with no significant loss of catalytic activity. SEM, EDX, XRD, and ICP analysis of reused catalyst indicated that the catalyst was stable after the reaction.

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.

Catalytic alcohol oxidation using cationic Schiff base manganeseIII complexes with flexible diamino bridge

Four Schiff base manganese(III) complexes with derivatives of [(R,R)-N,N’-bis(salicy1idene)-1,2-cyclohexanediaminato)] including substituents on salicylaldehyde such as 3-methoxy, 3,5-di-tert-butyl and 3,5-chloro were synthesized and characterized using a combination of IR, UV–Vis, and HR ESI-MS techniques. The catalytic activity of these complexes was tested in the oxidation of 1-phenylethanol to acetophenone, revealing very good performances for all of the four manganese complexes. The catalytic reactions were carried out in the presence of tert-butyl hydroperoxide (TBHP) as oxidant and imidazole as co-catalyst. Complex Mn-4, bearing electron withdrawing [(R,R)-N,N’-bis(3,5-di-chloro-salicylidene)-1,2-cyclohexanediaminato)] ligand was found to be the most stable of the tested Mn(III) complexes and was selected for the oxidation of several primary and secondary alcohols.

Iron-Catalyzed Oxidation of 1-Phenylethanol and Glycerol With Hydrogen Peroxide in Water Medium: Effect of the Nitrogen Ligand on Catalytic Activity and Selectivity.

The iron(II) complexes [Fe(bpy)3](OTf)2 (bpy = 2,2'-bipyridine; OTf = CF3SO3) (1) and [Fe(bpydeg)3](OTf)2 (bpydeg = N4,N4-bis(2-(2-methoxyethoxy)ethyl) [2,2'-bipyridine]-4,4'-dicarboxamide) (2), the latter being a newly synthesized ligand, were employed as catalyst precursors for the oxidation of 1-phenylethanol with hydrogen peroxide in water, using either microwave or conventional heating. With the same oxidant and medium the oxidation of glycerol was also explored in the presence of 1 and 2, as well as of two similar iron(II) complexes bearing tridentate ligands, i.e., [Fe(terpy)2](OTf)2 (terpy = 2, 6-di(2-pyridyl)pyridine) (3) and [Fe(bpa)2](OTf)2 (bpa = bis(2-pyridinylmethyl)amine) (4): in most reactions the major product formed was formic acid, although with careful tuning of the experimental conditions significant amounts of dihydroxyacetone were obtained. Addition of heterocyclic amino acids (e.g., picolinic acid) increased the reaction yields of most catalytic reactions. The effect of such additives on the evolution of the catalyst precursors was studied by spectroscopic (NMR, UV-visible) and ESI-MS techniques.

Ultrasound and Radiation-Induced Catalytic Oxidation of 1-Phenylethanol to Acetophenone with Iron-Containing Particulate Catalysts.

Iron-containing particulate catalysts of 0.1–1 µm size were prepared by wet and ball-milling procedures from common salts and characterized by FTIR, TGA, UV-Vis, PXRD, FEG-SEM, and XPS analyses. It was found that when the wet method was used, semi-spherical magnetic nanoparticles were formed, whereas the mechanochemical method resulted in the formation of nonmagnetic microscale needles and rectangles. Catalytic activity of the prepared materials in the oxidation of 1-phenylethanol to acetophenone was assessed under conventional heating, microwave (MW) irradiation, ultrasound (US), and oscillating magnetic field of high frequency (induction heating). In general, the catalysts obtained by wet methods exhibit lower activities, whereas the materials prepared by ball milling afford better acetophenone yields (up to 83%). A significant increase in yield (up to 4 times) was observed under the induction heating if compared to conventional heating. The study demonstrated that MW, US irradiations, and induction heating may have great potential as alternative ways to activate the catalytic system for alcohol oxidation. The possibility of the synthesized material to be magnetically recoverable has been also verified.

Supported Gold Nanoparticles as Catalysts in Peroxidative and Aerobic Oxidation of 1-Phenylethanol under Mild Conditions.

The efficiency of Au/TiO2 based catalysts in 1-phenylethanol oxidation was investigated. The role of support modifiers (La2O3 or CeO2), influence of gold loading (0.5% or 4%) and redox pretreatment atmosphere, catalyst recyclability, effect of oxidant: tert-butyl hydroperoxide (TBHP) or O2, as well as the optimization of experimental parameters of the reaction conditions in the oxidation of this alcohol were studied and compared with previous studies on 1-octanol oxidation. Samples were characterized by temperature-programmed oxygen desorption (O2-TPD) method. X-ray photoelectron spectroscopy (XPS) measurements were carried out for used catalysts to find out the reason for deactivation in 1-phenylethanol oxidation. The best catalytic characteristics were shown by catalysts modified with La2O3, regardless of the alcohol and the type of oxidant. When O2 was used, the catalysts with 0.5% Au, after oxidative pretreatment, showed the highest activity in both reactions. The most active catalysts in 1-phenylethanol oxidation with TBHP were those with 4% Au and the H2 treatment, while under the same reaction conditions, 0.5% Au and O2 treatment were beneficial in 1-octanol oxidation. Despite the different chemical nature of the substrates, it seems likely that Au+(Auδ+) act as the active sites in both oxidative reactions. Density functional theory (DFT) simulations confirmed that the gold cationic sites play an essential role in 1-phenylethanol adsorption.

Cu(II) and Fe(III) Complexes Derived from N-Acetylpyrazine-2-Carbohydrazide as Efficient Catalysts Towards Neat Microwave Assisted Oxidation of Alcohols

The mononuclear Cu(II) complex [Cu((kNN′O-HL)(H2O)2] (1) was synthesized using N-acetylpyrazine-2-carbohydrazide (H2L) and characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray crystallography. Two Fe(III) complexes derived from the same ligand viz, mononuclear [Fe((kNN′O-HL)Cl2] (2) and the binuclear [Fe(kNN′O-HL)Cl(μ-OMe)]2 (3) (synthesized as reported earlier), were also used in this study. The catalytic activity of these three complexes (1–3) was examined towards the oxidation of alcohols using tert-butyl hydroperoxide (TBHP) as oxidising agent under solvent-free microwave irradiation conditions. Primary and secondary benzyl alcohols (benzyl alcohol and 1-phenylethanol), and secondary aliphatic alcohols (cyclohexanol) were used as model substrates for this study. A comparison of their catalytic efficiency was performed. Complex 1 exhibited the highest activity in the presence of TEMPO as promoter for the oxidation of 1-phenylethanol with a maximum yield of 91.3% of acetophenone.

The catalytic oxidation of 1-phenylethanol over SiO2 supported manganese oxide nanocluster prepared by PVP stabilized colloidal Mn as precursor

• Supported manganese oxide nanoclusters catalyst was prepared by using PVP-stabilized colloidal Mn as precursor. • Manganese oxide nanocluster catalyst was active for the oxidation of 1-phenylethanol using O2 molecules without additives. • XAFS and TEM measurements revealed that the cluster size and chemical state of manganese oxide can be controlled. • XANES analysis showed that the chemical species of Mn was able to be controlled by changing the Mn loading. Supported MnOx nanocluster was prepared by PVP-stabilized Mn colloid as a precursor. Obtained catalysts were applied for 1-phenylethanol oxidation to produce acetophenone. Consequently, prepared catalysts were active for the oxidation of 1-phenylethanol using molecular oxygen without any additives such as base reagents. XAFS and TEM measurements revealed that the valence of manganese oxide and cluster size of manganese oxide on prepared catalysts can be controlled. In addition, the chemical state of Mn species varied with the loading amount of Mn.

Enhanced Selective Production of Carbonyl Products for Aerobic Oxidation of Benzylic Alcohols over Mesoporous Fe2O3 Supported Gold Nanoparticles

Ordered mesoporous Fe2O3 supported gold nanoparticles with a desired specific surface area and porous structure (Au/meso-Fe2O3) was successfully fabricated with a hard templating method by using KIT-6 as the template. The morphology and physico-chemical properties of Au/meso-Fe2O3 were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), etc. The gold nanoparticles are highly dispersed on the surface of the mesoporous Fe2O3. The catalytic performance of the synthesized catalyst was studied for the aerobic oxidation of benzylic alcohols in β–O–4 linked lignin model dimers to the corresponding carbonyl products under atmosphere pressure. Au/meso-Fe2O3 shows an enhanced activity for the aerobic oxidation of 1-phenylethanol in comparison with that of Au/bulk-Fe2O3. The promoted catalytic activity is related to the confined porous structure of mesoporous Fe2O3 and more boundaries contact between gold and meso-Fe2O3, which shows that the porous structure of the support has a significant influence on the activity of gold catalysts.

Solvent-free oxidation of 1-phenylethanol catalysed by gold nanoparticles supported on carbon powder materials

Gold (1 wt.%) was loaded on several carbon materials, namely, polymer based carbon xerogel, activated carbon, microdiamonds, nanodiamonds, graphite and silicon carbide by double impregnation and sol immobilisation. The obtained catalysts were characterised by N2 adsorption at -196 ºC, high-resolution transmission electron microscopy, high-angle annular dark-field imaging (Z-contrast), temperature programmed desorption, atomic absorption spectroscopy and X-ray photoelectron spectroscopy. The obtained materials were tested on the microwave-assisted solvent-free oxidation of 1-phenylethanol by tert-butyl hydroperoxide (TBHP) to produce acetophenone. The results showed that the catalytic activity was influenced by several factors, namely, the nature of the support, reaction time and temperature, amount of catalyst, presence of additives, among others. The best values for acetophenone yield (99.9%) were obtained with Au deposited on microdiamonds by the colloidal method. Catalyst recyclability was tested up to six consecutive cycles at the optimized conditions for each catalyst, and it was found that Au on microdiamonds, prepared by the colloidal method, also maintained higher activity after several reaction cycles as compared to the other carbon supports.