Oxidation Of 1-phenylethanol Research Articles

An anionic d-valine–palladium(ii) complex supported on a hydroxy double salt with a Brønsted basic phosphate anion: application for a heterogeneous catalyst toward aerobic alcohol oxidation

An anionic D-valine–Pd(II) complex intercalated into an anion exchangeable Ni–Zn mixed basic salt (NiZn), which is classified as a layered hydroxy double salt, was synthesised in situ via a simple anion exchange procedure. A Bronsted basic PO43− anion was also intercalated into the NiZn interlayer along with the anionic D-valine–Pd(II) complex. The Bronsted basic clay–Pd(II) nanocomposite catalysed the aerobic oxidation of a wide variety of alcohols to the corresponding aldehydes and ketones. In the aerobic oxidation of 1-phenylethanol, for example, a turnover number (TON) of 2000 based on Pd was achieved. During the aerobic alcohol oxidation, the D-valine–Pd(II) complex in the NiZn interlayer maintained its original monomeric Pd(II) structure due to the strong electrostatic interaction between the NiZn host and the anionic Pd(II) complex. This catalyst could be reused without loss of either catalytic activity or selectivity for the aerobic oxidation of alcohols.

Facile synthesis of hierarchical core–shell Fe3O4@MgAl–LDH@Au as magnetically recyclable catalysts for catalytic oxidation of alcohols

A novel core-shell structural Fe(3)O(4)@MgAl-LDH@Au nanocatalyst was simply synthesized via supporting Au nanoparticles on the MgAl-LDH surface of Fe(3)O(4)@MgAl-LDH nanospheres. The catalyst exhibited excellent activity for the oxidation of 1-phenylethanol, and can be effectively recovered by using an external magnetic field.

Synthesis, Characterization, and Catalytic Properties of Hollow γ-Fe2O3 Spheres toward Liquid-Phase Oxidation Using Hydrogen Peroxide

Abstract Hollow γ-Fe2O3 nanospheres were synthesized using carboxylated polystyrene spheres as a core template by thermal treatment followed by calcination. The obtained material was characterized by FT-IR, N2 adsorption–desorption, TEM, XRD, and Fe K-edge XAFS measurements. The size of the hollow γ-Fe2O3 nanospheres were about 400–500 nm, which was assembled from primary particles with a size of approximately 10–20 nm. The phase transition of the composed particles from magnetite (Fe3O4) to maghemite (γ-Fe2O3) was identified after calcination in the presence of O2 at relatively low temperature. The hollow γ-Fe2O3 acted as an efficient heterogeneous catalyst for the liquid-phase selective oxidation of 1-phenylethanol using hydrogen peroxide (H2O2) as an oxidant. It exhibited enhanced catalytic activity compared to its bulk counterpart and also showed higher selectivity than nanosized γ-Fe2O3. Recovery of the hollow γ-Fe2O3 nanospheres from the reaction mixture could be attained by applying an external permanent magnet, and the spent catalyst could be recycled without any appreciable loss of its inherent catalytic ability.

Oxidation of Reactive Alcohols with Hydrogen Peroxide Catalyzed by Manganese Complexes

Two manganese-containing catalysts have been employed in the oxidation with hydrogen peroxide of two reactive alcohols (1-phenylethanol and glycerol): soluble catalyst [LMn(μ-O)3MnL](PF6)2 (1a) and heterogenized catalyst [LMn(μ-O)3MnL]2[SiW12O40] (1b) (L is 1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN). Oxidation of 1-phenylethanol catalyzed by 1a in acetonitrile solution proceeds at room temperature in the presence of a small amount of oxalic acid; the turnover number attains 15,000 after 3 h. It has been proposed on the basis of the kinetic study that an oxidizing species is a manganyl species containing fragment “Mn=O” rather that hydroxyl radical. This species reacts competitively with the alcohol, acetonitrile and hydrogen peroxide. In the case of 1b dependences of the initial rates of acetophenone accumulation on concentration of the alcohol and amount of 1b have plateau. Both homogeneous and heterogeneous catalysts are efficient in the oxidation of glycerol to produce dihydroxyacetone (DHA) as the main product. The oxidation catalyzed by 1a is one of the first examples of the glycerol oxidation by a catalytic homogeneous system. The yield of valuable products attained 45%. The oxidation of DHA in the absence of glycerol afforded mainly glycolic acid in yield 60% based on the starting DHA. The oxidation on 1b represents the first example of the glycerol transformation catalyzed by a heterogenized metal complex. Under certain conditions yields of products of deeper oxidation (glyceric, glycolic and hydroxypyruvic acids) are somewhat higher than the yield of dihydroxyacetone. Special experiments demonstrated that no leaching of active species occurs from catalyst 1b to the solution and that this catalyst can be re-used at least four times without substantial loss of activity. Manganese-containing complexes are very efficient catalysts in the oxidation of reactive alcohols (1-phenylethanol and glycerol) with H2O2: soluble [LMn(O)3MnL](PF6)2 and heterogenized [LMn(O)3MnL]2[SiW12O40] (L is 1,4,7-trimethyl-1,4,7-triazacyclononane).

Self-assembled dicopper(ii) diethanolaminate cores for mild aerobic and peroxidative oxidation of alcohols

The new dicopper(ii) complexes [Cu(2)(μ-Hmdea)(2)(NCS)(2)] (1) and [Cu(2)(μ-Hedea)(2)(N(3))(2)]·(H(2)O)(0.25) (2) with the {Cu(2)(μ-O)(2)} diethanolaminate cores have been easily generated by aqueous medium self-assembly reactions of copper(ii) nitrate with N-methyl- or N-ethyldiethanolamine (H(2)mdea or H(2)edea, respectively), in the presence of sodium thiocyanate (for 1) or sodium azide (for 2) as ancillary ligands sources. They have been isolated as air-stable crystalline solids and fully characterized by IR and UV-vis spectroscopies, ESI-MS(+), elemental and single-crystal X-ray diffraction analyses. The latter complex also features a fourfold linkage of neighbouring dimeric units via strong intermolecular O-HO hydrogen bonds, giving rise to the formation of tetracopper aggregates. The catalytic activity of compounds 1 and 2 has been studied for the mild (50-80 °C) and selective oxidations of alcohols, namely for (i) the aerobic aqueous medium oxidation of benzyl alcohols to benzaldehydes, mediated by TEMPO radical, and for (ii) the solvent-free oxidation of secondary alcohols to ketones by t-BuOOH under microwave (MW) irradiation. Complex 2 shows the highest efficiency in both oxidation systems, resulting in up to 99% molar yields (based on the alcohol substrate) of products. In addition, remarkably high values of TON (1020) and TOF (4080 h(-1)) have been achieved in the MW-assisted peroxidative oxidation of 1-phenylethanol to acetophenone (model reaction). Attractive green features of these catalytic systems include the operation in aqueous or solvent-free reaction medium, under mild conditions and with high yields and selectivities, using Cu catalyst precursors that are readily available by self-assembly in water of simple chemicals.

Environmentally benign aqueous oxidative catalysis using AuPd/TiO2 colloidal nanoparticle system stabilized in absence of organic ligands

The use of nanoparticles (NPs) for efficient, environmentally benign catalysis is receiving increasing attention, with gold and palladium NPs being an important area of research. Herein we present a simple, reliable and cost-effective preparation of a catalytically active gold-palladium NP system that is stabilized by an aqueous titania dispersion (AuPd/TiO2) in the absence of organic ligands. The major advantages of this system are that it is catalytically active in the as-prepared colloidal state, eliminating the need for drying and sintering before use and is colloidally stable in oxidative conditions. The AuPd/TiO2 system exhibits efficient oxidative catalysis in both the presence of hydrogen peroxide and atmospheric oxygen, even at ambient temperatures for our model aqueous phase reaction of 1-phenylethanol oxidation. The preparation and characterization of the AuPd/TiO2 system is described with respect to the effects of colloidal stability, particle size and morphology on aqueous oxidative catalysis. The major finding is that NPs with a gold core and thin palladium shell (70 mol% gold, 30 mol% palladium, Au70Pd30/TiO2) provides the most catalytically active system. The ability of the catalyst to use atmospheric oxygen at ambient temperatures in aqueous media highlights the strong potential of the developed catalytic system for green oxidative processes. The presented approach provides a new platform of all-inorganic colloidal nanoparticle systems for future development of industrially viable, environmentally friendly catalysts.

Kinetics and mechanism of 1-phenylethanol oxidation by the system hydrogen peroxide-manganese(IV) binuclear complex-oxalic acid

Hydrogen peroxide was found to oxidize 1-phenylethanol to acetophenone in acetonitrile homogeneous solution efficiently at room temperature in the presence of a dimeric complex of manganese (IV) [LMn(O)3MnL](PF6)2(where L = 1,4,7-trimethyl-1,4,7-triazacyclononane) as the catalyst and oxalic acid as a co-catalyst. The number of catalytic cycles was 15 000 3 h after the onset of the reaction. The dependences of the initial rate of acetophenone accumulation on the initial concentrations of the reagents were studied. Based on an analysis of the kinetic data, we conclude that phenylethanol is oxidized by a manganyl particle containing an Mn = O fragment that interacts competitively with hydrogen peroxide.

Morphological Control of Carbon Carrier in Pt–Carbon Nanocomposites Derived from Photocatalytic Reactions on Titanium(IV) Oxide Powders

Photodeposition of Pt nanoparticle and phenolic polymer on TiO2 in a deaerated aqueous system containing hexachloroplatinic acid and phenol were investigated. We observed that reductive deposition of Pt nanoparticles with electrons proceeded rapidly, while the oxidative deposition of a phenolic polymer with positive holes was relatively slow. The difference ensured the encapsulation of Pt nanoparticles between the polymer layer and TiO2. Carbonization of the polymer components followed by removing TiO2 resulted in the formation of two types of Pt–carbon nanocomposites with different morphologies of carbons, depending on photoirradiation duration. These composites exhibited high levels of catalytic activity and reusability for aqueous oxidation of 1-phenylethanol with molecular oxygen.

Palladium-loaded oxidized diamond catalysis for the selective oxidation of alcohols

Oxidation of alcohols (benzyl alcohol, 1-phenylethanol and cinnamyl alcohol) using oxidized diamond (O-Dia) supported Pd catalyst was studied. The O-Dia supported catalyst exhibited a high catalytic activity among the support materials of Pd-loaded catalysts in the oxidation of benzyl alcohol at 85°C, showing TOFs of 850h−1. The addition of small amount of CeO2 to O-Dia supports further improved catalytic activity in the oxidation of 1-phenylethanol with molecular oxygen. The promotion effect of CeO2 was the suppression of acidic properties of the Pd/O-Dia, leading to dehydration and hydrogenolysis reactions of 1-phenylethanol. In addition, the Pd/CeO2/O-Dia catalyst showed a higher catalytic activity in the oxidation of various alcohols than that of Pd/O-Dia. Moreover, the basic metal oxide-promoted catalysts exhibited high catalytic activity in the dehydrogenation of 1-phenylethanol without molecular oxygen at 120°C.

Kinetics of the oxidation of 1-phenyl ethanols with phase-transferred monochromate in organic solvents

Kinetic studies on the oxidation of 1-phenyl ethanol and its para-methyl, para-methoxy and para chloro derivatives have been carried out using phase transferred chromate as oxidant in pure organic solvents. The inorganic oxidant was transferred to the non polar media using the phase transfer catalyst, tetrabutyl phosphonium bromide (TB PB). The electronic effects of the substituents, effect of varying the temperature on the rate, as well as the effect of varying the dielectric constant of the medium on the rate have been investigated. The rate data fitted well with the Hammett equation.

Au/PCPs-Catalyzed Aerobic Oxidation of Alcohols

The aerobic oxidation of alcohols was performed with deposited gold clusters on porous coordination polymers (PCPs) such as MOF-5, Al-MIL53, CPL-1, CPL-2 and Cu-BTC in MeOH. Thus, the oxidation of benzyl alcohol (1) was carried out in methanol with Au/MOF-5 and K2CO3 under O2 to give methyl benzoate (2) in 91% yield. The oxidation of 1-phenylethanol (3) with Au/MOF-5 under similar conditions gave aceto­phenone (4) in 79% yield.

Oxidation of Alcohols Catalyzed by Au(0)-Pd(0)/PI Membrane

A polyvinylpyrrolidone (PVP) protected Au(0)-Pd(0) (8:2) nano-composite in porous polyimide (PI) membrane (Au(0)-Pd(0)/PI) was prepared by casting a mixed solution of Au(0)/Pd(0) and Pl on the glass plate, followed by cross-linking with p-xylyenediamine. The oxidation of various alcohols 1 catalyzed by Au(0)-Pd(0)/PI was carried out under O2 to give the corresponding carbonyl compounds 2. The oxidation rate over the Au(0)-Pd(0)/PI decreased in order benzylic > allylic > aliphatic. The Au(0)-Pd(0)/PI was also applied in solvent-free conditions for the oxidation of 1-phenylethanol.

Gold supported on Mg, Al and Cu containing mixed oxides: Relation between surface properties and behavior in catalytic aerobic oxidation of 1-phenylethanol

Aerobic oxidation of 1-phenylethanol was investigated over Au deposited on flame-derived Mg–Al and Cu–Mg–Al mixed oxides with different metal ratios. A maximum in acetophenone (1-phenyl-ethanone) yield was observed for catalysts based on both Cu–Mg–Al and Mg–Al mixed oxides depending on their composition. Special attention was given to the elucidation of the role of surface basicity and the influence of the preparation route on the particle size of Au. Adsorption of CO 2 from the liquid phase combined with in situ ATR-IR and modulation excitation spectroscopy (MES) was applied to investigate differences in the surface properties of the mixed oxides as a function of the composition. Monodentate and bidentate carbonates were identified, the former being dominant on supports with high Cu contents. In order to obtain a rough quantification of the surface basicity, the retroaldolisation of 4-hydroxy-4-methyl-2-pentanone (diacetone alcohol, DAA) was chosen as a probe reaction indicating that a ratio Mg/Al = 3 results in optimal surface basicity. Moreover, the addition of Cu only lead to a partial loss in retroaldolisation activity, indicating that also the copper sites form basic centers on the surface, however, slightly weaker ones than the corresponding Mg sites. The preparation routes applied (adsorption of colloid, deposition precipitation, and impregnation) lead to different gold particle sizes characterized by mean diameters of ≈2, ≈9 and ≈30 nm, respectively. Catalytic tests using Au/Cu 1Mg 2Al 1O x catalysts with different mean gold particle size hint towards a particle size dependence of the aerobic oxidation of 1-phenylethanol, showing higher activity for the catalyst containing gold particles of ca. 9 nm compared to those with 2 and 30 nm particles, respectively.

Oxidation of Alcohols Using Hydrotalcite-Supported Silver Nanoparticles

Hydrotalcite (HT) reacted with 5.0 mM aqueous solution of AgNO3 at 3 °C for 1 h to afford HT-supported Ag(I). The Ag(I) ions were reduced with hydrogen to give the Ag/HT catalyst (eq. 1). The oxidation (dehydrogenation) of various alcohols 1 without oxidant took place under Ar atmosphere in the presence of the Ag/HT catalyst to give the corresponding carbonyl compounds 2 with up to 99% conversion and chemo­selectivity (eq. 2). This catalyst was reused four times in the oxidation of 1-phenylethanol with no significant loss of activity and chemoselectivity.

Gold supported on Cu–Mg–Al and Cu–Ce mixed oxides: An in situ XANES study on the state of Au during aerobic alcohol oxidation

Liquid-phase in situ XANES experiments were used to elucidate the oxidation state of differently supported Au catalysts during the selective oxidation of 1-phenylethanol with molecular oxygen. The catalysts investigated included (i) Au(0.6 wt%)/Cu 3Mg 3Al 2O x , (ii) Au(0.6 wt%)/Mg 3AlO x , (iii) Au(2.9 wt%)/CeO 2, and (iv) a copper-doped analog, Au(0.6 wt%)/CuO–CeO 2 (20 wt% CuO). The XANES and EXAFS data were collected mainly in the fluorescence mode. Simultaneous determination of the structure (XANES) and the activity of the catalysts in the continuous-flow microreactor was achieved by following the oxidation state using XANES and the characteristic carbonyl vibration of the desired reaction product acetophenone using an IR spectrometer equipped with a transmission cell. Au/Cu 3Mg 3Al 2O x showed a small increase of conversion with time on stream accompanied by a slight reduction of the gold component. With Au/Mg 3AlO x and Au/CuO–CeO 2, a stronger reduction accompanied by increased catalytic activity was observed. The results of these mixed oxide-supported Au catalysts demonstrate that metallic gold is the main active species in catalytic aerobic alcohol oxidation. In contrast, a decrease in the product formation rate was observed for Au/CeO 2 with ongoing reduction. Results obtained from factor analysis indicate that the decrease in activity of the Au/CeO 2 with time on stream does not correlate with the much faster reduction of the catalyst and thus cannot be attributed to the increasing fraction of Au 0 species. This finding corroborates the importance of recording XANES spectra for structural identification simultaneously with online determination of the catalytic performance.

Gold supported on Cu–Mg–Al-mixed oxides: Strong enhancement of activity in aerobic alcohol oxidation by concerted effect of copper and magnesium

Gold nanoparticles were deposited on mixed oxides containing Cu, Mg, and Al in different ratios. The mixed-oxide supports were prepared by flame spray pyrolysis (FSP), resulting in agglomerated primary nanoparticles in the 10–15 nm range, onto which 6- to 9-nm gold particles were deposited by means of deposition–precipitation. The mixed-oxide-supported Au catalysts with noble metal loading of 0.6 ± 0.17 wt% were investigated concerning their structural properties and tested in the aerobic liquid-phase oxidation of 1-phenylethanol to phenyl–methyl ketone affording TOFs up to 1300 h −1. The catalytic tests showed that the activity of these catalysts depends strongly on the composition of the support, with Cu and Mg being crucial components. Strongly enhanced catalytic activity was observed for gold supported on a ternary mixed oxide containing Cu, Mg, and Al at the molar ratio of 5:1:2. Extension of the catalytic tests to various structurally different alcohols indicated that the ternary mixed-oxide-supported gold catalyst has excellent catalytic properties in the aerobic oxidation of a broad range of structurally different alcohols, affording selectivities ⩾ 98 % . XANES revealed both reduced and oxidized Au species on the ternary mixed-oxide supports before and after the reaction. CO 2 adsorption from the liquid phase combined with in situ ATR-IR and modulation excitation spectroscopy was applied to investigate differences in the basic surface properties of the mixed oxides. Monodentate and bidentate carbonates were identified, the former being dominant on ternary Cu-containing supports.

Unexpected Performance of Solid Alkaline Metal Hydroxides in Liquid Phase Oxidation of 1-Phenylethanol

Solis alkaline metal hydroxides displayed activity in alcohol oxidation in non-polar medium. Both organic molecules and molecular oxygen were employed as oxidants. The activity was in order KOH > NaOH LiOH.

Comparison of TEMPO and its derivatives as mediators in laccase catalysed oxidation of alcohols

Abstract A series of TEMPO (2,2′,6,6′-tetramethylpiperidinyl-1-oxy) derivatives were studied as mediators of laccase (from Trametes versicolor) in the oxidation of benzyl alcohol and 1-phenylethyl alcohol. TEMPO (1), 4-hydroxy-TEMPO (2) and 4-acetylamino-TEMPO (4) turned out to be the most active mediators for laccase. In addition, 4-acetylamino-TEMPO and 4-hydroxy-TEMPO were more active in the oxidation of 1-phenylethanol compared to TEMPO. For these mediators kinetic isotope effects in the range of 2.1–3.2 were observed for α-monodeutero-p-methylbenzyl alcohol oxidation. These values are consistent with a mechanism involving oxoammonium intermediacy. Competition experiments between benzyl alcohol and 1-phenylethanol showed that TEMPO and its derivatives react faster with primary alcohols than with secondary alcohols, also in line with the proposed mechanism.

Cp*Ir Complex‐Catalyzed Hydrogen Transfer Reactions Directed Toward Environmentally Benign Organic Synthesis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of New Cationic Cp*Ir N-Heterocyclic Carbene Complexes and Their High Catalytic Activities in the Oppenauer-Type Oxidation of Primary and Secondary Alcohols

Several new cationic Cp*Ir N-heterocyclic complexes have been synthesized and their catalytic activities in the Oppenauer-type oxidation have been investigated in order to improve the catalytic activity of [Cp*IrCl(μ-Cl)]2. The reactions of [Cp*IrCl(μ-Cl)]2 (1) with N-heterocyclic carbene ligands afforded Cp*Ir(L)Cl2 (3a−d; L = N-heterocyclic carbene ligands). The cationic complexes [Cp*Ir(L)(MeCN)2]2+ (5a−d) were obtained by the treatment of 3a−d with 2 equiv of AgOTf followed by addition of CH3CN. Structures of complexes 3a−d and 5a−d were determined by X-ray crystallographic studies. Complex 5a (L = 1,3,4,5-tetramethylimidazol-2-ylidene) catalyzed the Oppenauer-type oxidation of primary and secondary alcohols very selectively under mild conditions. In the oxidation of 1-phenylethanol and cyclopentanol using 5a as a catalyst, turnover numbers reached 3200 and 6640, respectively. These results demonstrate that, to the best of our knowledge, the cationic carbene complex 5a is the most effective catalyst in homogeneous oxidation of alcohols in terms of its high catalytic activity and wide applicability to the oxidation of primary and secondary alcohols. In this catalytic system, the stronger electron-donating ability of the N-heterocyclic carbene ligand than the phosphine ligand is more favorable for acceleration of the hydride transfer to acetone as a hydrogen acceptor. Additionally, dihydrido carbene complex Cp*Ir(L)(H)2 (6) and dinuclear iridium carbene complex [Cp*Ir(L)(μ-H)]22+ (7) were prepared to investigate the catalytically active species and fate of the catalyst. Thus, it is highly probable that an iridium-monohydride complex is the catalytically active species and that 7, which could be generated by dimerization of the iridium-monohydride complex in the catalytic system, is inactive.