Selective aerobic oxidation in supercritical carbon dioxide catalyzed by the H5PV2Mo10O40 polyoxometalate

Selective aerobic oxidation of benzylic alcohols and of activated aromatic hydrocarbons occurs in supercritical CO2 as reaction medium using H5PV2Mo10O40 as a quasi-heterogeneous catalyst without further additives or co-solvents; efficient recycling is possible and no metal leaching is detectable in the product stream.     

Direct aerobic epoxidation of alkenes catalyzed by metal nanoparticles stabilized by the H5PV2Mo10O40 polyoxometalate

Ag and Ru nanoparticles stabilized by H5PV2Mo10O40, prepared by a sequence of redox reactions and supported on alpha-alumina, were effective catalysts for the direct aerobic epoxidation of alkenes in the liquid phase.     

An efficient, catalytic, aerobic, oxidative iodination of arenes using the H5PV2Mo10O40 polyoxometalate as catalyst

Iodination of arenes was carried out by reacting 1 equiv of arene substrate with 0.5 equiv of iodine under an oxygen atmosphere with H5PV2Mo10O40 as oxidation catalyst. The synthesis is an inherently waste-free method for the preparation of iodoarenes.     

Oxidative C-C bond cleavage of primary alcohols and vicinal diols catalyzed by H5PV2Mo10O40 by an electron transfer and oxygen transfer reaction mechanism

Primary alcohols such as 1-butanol were oxidized by the H5PV2Mo10O40 polyoxometalate in an atypical manner. Instead of C-H bond activation leading to the formation of butanal and butanoic acid, C-C bond cleavage took place leading to the formation of propanal and formaldehyde as initial products. The latter reacted with the excess 1-butanol present to yield butylformate and butylpropanate in additional oxidative transformations. Kinetic studies including measurement of kinetic isotope effects, labeling studies with 18O labeled H5PV2Mo10O40, and observation of a prerate determining step intermediate by 13C NMR leads to the formulation of a reaction mechanism based on electron transfer from the substrate to the polyoxometalate and oxygen transfer from the reduced polyoxometalate to the organic substrate. It was also shown that vicinal diols such as 1,2-ethanediol apparently react by a similar reaction mechanism.     

Electron and oxygen transfer in polyoxometalate, H(5)PV(2)Mo(10)O(40), catalyzed oxidation of aromatic and alkyl aromatic compounds: evidence for aerobic Mars-van Krevelen-type reactions in the liquid homogeneous phase

The mechanism of aerobic oxidation of aromatic and alkyl aromatic compounds using anthracene and xanthene, respectively, as a model compound was investigated using a phosphovanadomolybdate polyoxometalate, H(5)PV(2)Mo(10)O(40), as catalyst under mild, liquid-phase conditions. The polyoxometalate is a soluble analogue of insoluble mixed-metal oxides often used for high-temperature gas-phase heterogeneous oxidation which proceed by a Mars-van Krevelen mechanism. The general purpose of the present investigation was to prove that a Mars-van Krevelen mechanism is possible also in liquid-phase, homogeneous oxidation reactions. First, the oxygen transfer from H(5)PV(2)Mo(10)O(40) to the hydrocarbons was studied using various techniques to show that commonly observed liquid-phase oxidation mechanisms, autoxidation, and oxidative nucleophilic substitution were not occurring in this case. Techniques used included (a) use of (18)O-labeled molecular oxygen, polyoxometalate, and water; (b) carrying out reactions under anaerobic conditions; (c) performing the reaction with an alternative nucleophile (acetate) or under anhydrous conditions; and (d) determination of the reaction stoichiometry. All of the experiments pointed against autoxidation and oxidative nucleophilic substitution and toward a Mars-van Krevelen mechanism. Second, the mode of activation of the hydrocarbon was determined to be by electron transfer, as opposed to hydrogen atom transfer from the hydrocarbon to the polyoxometalate. Kinetic studies showed that an outer-sphere electron transfer was probable with formation of a donor-acceptor complex. Further studies enabled the isolation and observation of intermediates by ESR and NMR spectroscopy. For anthracene, the immediate result of electron transfer, that is formation of an anthracene radical cation and reduced polyoxometalate, was observed by ESR spectroscopy. The ESR spectrum, together with kinetics experiments, including kinetic isotope experiments and (1)H NMR, support a Mars-van Krevelen mechanism in which the rate-determining step is the oxygen-transfer reaction between the polyoxometalate and the intermediate radical cation. Anthraquinone is the only observable reaction product. For xanthene, the radical cation could not be observed. Instead, the initial radical cation undergoes fast additional proton and electron transfer (or hydrogen atom transfer) to yield a stable benzylic cation observable by (1)H NMR. Again, kinetics experiments support the notion of an oxygen-transfer rate-determining step between the xanthenyl cation and the polyoxometalate, with formation of xanthen-9-one as the only product. Schemes summarizing the proposed reaction mechanisms are presented.     

Olefin epoxidation with hydrogen peroxide catalyzed by lacunary polyoxometalate [gamma-SiW10O34H2O2]4-

The tetra-n-butylammonium (TBA) salt of the divacant Keggin-type polyoxometalate [TBA](4)[gamma-SiW(10)O(34)(H(2)O)(2)] (I) catalyzes the oxygen-transfer reactions of olefins, allylic alcohols, and sulfides with 30 % aqueous hydrogen peroxide. The negative Hammett rho(+) (-0.99) for the competitive oxidation of p-substituted styrenes and the low value of (nucleophilic oxidation)/(total oxidation), X(SO)=0.04, for I-catalyzed oxidation of thianthrene 5-oxide (SSO) reveals that a strongly electrophilic oxidant species is formed on I. The preferential formation of trans-epoxide during epoxidation of 3-methyl-1-cyclohexene demonstrates the steric constraints of the active site of I. The I-catalyzed epoxidation proceeds with an induction period that disappears upon treatment of I with hydrogen peroxide. (29)Si and (183)W NMR spectroscopy and CSI mass spectrometry show that reaction of I with excess hydrogen peroxide leads to fast formation of a diperoxo species, [TBA](4)[gamma-SiW(10)O(32)(O(2))(2)] (II), with retention of a gamma-Keggin type structure. Whereas the isolated compound II is inactive for stoichiometric epoxidation of cyclooctene, epoxidation with II does proceed in the presence of hydrogen peroxide. The reaction of II with hydrogen peroxide would form a reactive species (III), and this step corresponds to the induction period observed in the catalytic epoxidation. The steric and electronic characters of III are the same as those for the catalytic epoxidation by I. Kinetic, spectroscopic, and mechanistic investigations show that the present epoxidation proceeds via III.     

纳米钼钒砷杂多酸盐催化苯羟化合成苯酚的研究

过氧化氢作为一种清洁氧化剂,在苯的直接羟化的研究中受到重视。催化剂主要有含钛催化剂系列、含铁催化剂系列和含铜催化剂系列、含钒催化剂系列和其它杂原子催化剂。杂多化合物是一类酸性和氧化性较强的双功能催化剂,但由于受其低比表面积的限制,导致杂多化合物固有的高催化活性在苯的过氧化氢羟化反应中难以充分发挥。本文对所制得的4种过渡金属钼钒砷杂多酸盐纳米催化剂应用于苯的过氧化氢直接羟化合成苯酚的反应,取得了苯酚收率〉50％,选择性〉98％的结果。     

Selective oxidation of ethylbenzene catalyzed by fluorinated metalloporphyrins with molecular oxygen

This paper reported the oxidation of ethylbenzene catalyzed by fluorinated metalloporphyrins under mild conditions without any additives.The results showed that the cobalt(Ⅱ)(5,10,15,20-tetrakis(pentafluorophenyl))porphyrin was the best catalyst among the fluorinated metalloporphyrins.The conversion of ethylbenzene reached 38.6%,the selectivity to acetophenone reached 94.0%,and the turnover number is 2719 under the optimal conditions.     

V@CN催化的芳烃的氧气羟基化反应

制备了V@CN催化剂,并用于氧气条件下芳烃的直接羟基化反应。结果表明,在V@CN催化剂作用下,带有不同吸电子基团(CN, NO2, COOH, CF3和COCH3)的芳烃均可被O2氧化得到相应的酚,产率中等。含有卤素(F, Cl和Br)的芳烃也可在该催化体系作用下转化为相应的酚。     

Efficient hydroxylation of aromatic compounds catalyzed by an iron(II) complex with H2O2

A mononuclear iron(II) complex, Et₄N[Fe(C₁₀H₆NO₂)₃], coordinated by three 1‐nitroso‐2‐naphtholate ligands in a fac‐N₃O₃ geometry, was initiated to catalyze the direct hydroxylation of aromatic compounds to phenols in the presence of H₂O₂ under mild conditions. Various reaction parameters, including the catalyst dosage, temperature, mole ratio of H₂O₂ to benzene, reaction time and solvents which could affect the hydroxylation activity of the catalyst, were investigated systematically for benzene hydroxylation to obtain ideal benzene conversion and high phenol distribution. Under the optimum conditions, the benzene conversion was 10.2% and only phenol was detected. The catalyst was also found to be active towards hydroxylation of other aromatic compounds with high substrate conversions. The hydroxyl radical formed due to the reaction of the catalyst and H₂O₂ was determined to be the crucial active intermediate in the hydroxylation. A rational pathway for the formation of the hydroxyl radical was proposed and justified by the density functional theory calculations. Copyright © 2014 John Wiley & Sons, Ltd.     

Pyridine-H_5PMo_(10)V_2O_(40) hybrid catalysts for liquid-phase hydroxylation of benzene to phenol with molecular oxygen

Pyridine(Py)-modified Keggin-type vanadium-substituted heteropoly acids(PynPMo10V2O40,n=1 to 5) were prepared by a precipitation method as organic/inorganic hybrid catalysts for direct hydroxylation of benzene to phenol in a pressured batch reactor and their structures were detected by FT-IR.Among various catalysts,Py3PMo10V2O40 exhibits the highest catalytic activity(yield of phenol,11.5%),without observing the formation of catechol,hydroquinone and benzoquinone in the reaction with 80 vol% aqueous acetic ...     

Selective oxidation of tetrahydrofuran with molecular oxygen catalyzed by polyalumazane–platinum complexes

Tetrahydrofuran (THF) was oxidized selectively with molecular oxygen catalyzed by magnesium oxide-based polyalumazane-supported platinum complexes under mild conditions. The selective oxidation of C–H bond α to the oxygen atom of ether and the oxidative path to ester other than ring cleavage to carboxylic acid were controlled by carrying out the reaction at 60°C with nitroethane as solvent. The platinum loading and the reaction time greatly affected the yield of γ-butyrolactone whereas the selectivity always remained at 100%. 76.92% γ-butyrolactone was obtained with 0.2811 mmol platinum loading per gram support within 12 hr. The single product of the THF oxidation was confirmed by ¹H-nuclear magnetic resonance. X-ray photoelectron spectroscopy data also confirmed the more recent report on the activation of the C–H bond by the null valent platinum from the viewpoint of supported platinum catalyst. The oxidation path was also suggested.     

Selective oxygenation of 4,4'-dimethylbiphenyl with molecular oxygen, catalyzed by 9-phenyl-10-methylacridinium ion via photoinduced electron transfer

Photooxygenation of 4,4'-dimethybiphenyl with oxygen occurs efficiently in the presence of 9-phenyl-10-methylacridinium perchlorate (AcrPh(+)ClO(4)(-)) under visible light irradiation in O(2)-saturated chloroform (CHCl(3)) to yield 4-(4'-methylphenyl)benzaldehyde as a main oxygenated product. Prolonged photoirradiation afforded the further oxygenated product, 4,4'-diformylbiphenyl. The reactive radical intermediates involved in the photocatalytic cycle have successfully been detected by laser flash photolysis and electron spin resonance (ESR) measurements. The photocatalytic mechanism for the oxygenation of 4,4'-dimethybiphenyl via photoinduced electron transfer from 4,4'-dimethybiphenyl to the singlet excited state of AcrPh(+) is clarified based on the dependence of quantum yields on concentrations of substrates and the detected radical intermediates.     

Magnetically separable polyoxometalate catalyst for the oxidation of dibenzothiophene with H2O2

Two types of polyoxometalate-functionalized magnetic nanoparticles catalysts consisting of H(3)PW(12)O(40) supported on surface-modified Fe(3)O(4) magnetite nanoparticles were prepared using an easy synthetic route and successfully applied for the oxidation of dibenzothiophene. The magnetic catalysts showed a catalytic performance in the oxidation of dibenzothiophene in acetonitrile with hydrogen peroxide, and high conversions were obtained. The catalysts could be easily separated from the reaction solution by applying an external magnetic field and recycled several times.     

复合光催化材料H3PW122O40/Ta2O5光催化降解染料的研究

采用溶胶-凝胶法制备了半导体型金属氧化物Ta2O5,并通过浸渍法与杂多酸H,PW12O40复合,获得了纳米复合光催化材料H3PW12O40/Ta2O5.通过1CP-AES、FT-lR、N2吸附、Tc等手段对其组成、结构及其表面物理化学性质进行了表征,并在可见光下考察了该复合材料对可溶性染料罗丹明B和亚甲基蓝的光催化活性.实验结果表明,该复合材料存可见光下有较好的光催化活性,其中,H3PW12O40/Ta2O5在180min内对亚甲基蓝的光催化降解转化率达到78%.     

H_3PW_(12)O_(40)在离子液体中催化β-萘甲醚乙酰化反应

利用吡啶和正溴丁烷合成离子液体中间体[BPy]Br,再由[BPy]Br和NaBF4合成了离子液体[BPy]BF4,对其进行了FT-IR,1 H NMR和TG-DTA表征.将合成的离子液体作为溶剂,磷钨酸为催化剂,催化β-萘甲醚(MM)和乙酸酐(AA)的乙酰化反应.结果表明,该反应的主要产物是2-甲氧基-1-萘乙酮.反应的较佳工艺条件为:β-萘甲醚0.01mol,β-萘甲醚与乙酸酐的摩尔比为1∶1.5,磷钨酸0.05g,100℃下反应4h,反应物β-萘甲醚的转化率达到57.04%,最高选择性可达99.04%.通过萃取分离实现回收磷钨酸-离子液体的催化体系,并可循环使用5次,催化活性无下降.     

Pyridine-H5PMo10V2O40 hybrid catalysts for liquid-phase hydroxylation of benzene to phenol with molecular oxygen

Pyridine(Py)-modified Keggin-type vanadium-substituted heteropoly acids (Py _n PMo₁₀V₂O₄₀, n=1 to 5) were prepared by a precipitation method as organic/inorganic hybrid catalysts for direct hydroxylation of benzene to phenol in a pressured batch reactor and their structures were detected by FT-IR. Among various catalysts, Py₃PMo₁₀V₂O₄₀ exhibits the highest catalytic activity (yield of phenol, 11.5%), without observing the formation of catechol, hydroquinone and benzoquinone in the reaction with 80 vol% aqueous acetic acid, molecular oxygen and ascorbic acid used as the solvent, oxidant and reducing reagent, respectively. Influences of reaction temperature, reaction time, oxygen pressure, amount of ascorbic acid and catalyst on yield of phenol were investigated to obtain the optimal reaction conditions for phenol formation. Pyridine can greatly promote the catalytic activity of the Py-free catalyst (H₅PMo₁₀V₂O₄₀), mostly because the organic π electrons in the hybrid catalyst may extend their conjugation to the inorganic framework of heteropoly acid and dramatically modify the redox properties, at the same time, pyridine adsorbed on heteropoly acids can promote the effect of “pseudo-liquid phase”, thus accounting for the enhancement of phenol yield. Supported by the National Natural Science Foundation of China (Grant Nos. 20476046 and 20776069) and the “Qinglan” Project of Jiangsu Province for Young Researchers     

The study of cyclooctene oxidation with molecular oxygen catalyzed by VSi2

The catalytic effect of VSi₂ on initial stages of the liquid-phase oxidation of cyclooctene by molecular oxygen was studied. The vanadium disilicide influences on the oxidation process in the presence of hydroperoxide. VSi₂ takes part in a radical formation stage by catalysis of hydroperoxide decomposition reaction. The catalyst was investigated before and after reaction using FTIR spectroscopy. From the data obtained, the kinetic model of the catalytic oxidation process was proposed and the equation for the reaction rate was derived. The equation has described all observed dependences of reaction rate on the concentration of reactants and content of catalyst.