- Red light-induced reaction of NO2 with 2,3-dimethyl-2-butene in a low-temperature argon matrix
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Red light-induced oxygen atom transfer from NO2 to 2,3-dimethyl-2-butene has been investigated in a low-temperature argon matrix.The IR spectra of a reaction intermediate identified as an alkyl nitrite radical and two final products, tetramethyloxirane and 3,3-dimethyl-2-butanone (pinacolone), were observed.From analysis of the absorbance growth of the IR bands, first-order rate constants were determined by least-square fitting.Based on these results and those of our earlier works on NO2 photoreactions with other alkenes, a reaction mechanism is proposed that involves oxygen atom transfer from NO2 to the C=C bond of 2,3-dimethyl-2-butene to give a short-lived singlet oxirane biradical.Alkyl nitrite radical is produced by a recombination of the transient biradical with NO trapped in the cage of the matrix.Tetramethyloxirane and pinacolone emerge from secondary photolysis of the trapped alkyl nitrite radical.
- Nakata, Munetaka
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- The Oxidation of Organic Compounds with Iodosylbenzene catalysed by Tetra(4-N-methylpyridyl)porphyrinatoiron(III) Pentacation: A Polar Model System for the Cytochrome P450 Dependent Mono-oxygenases
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Replacing the tetraphenylporphyrinatoiron(III) chloride (Fe(III)TPPCl) catalyst, in Groves' model system (Fe(III)TPPCl-PhIO) for cytochrome P450 mono-oxygenases, with tetra(4-N-methylpyridyl)porphyrinatoiron(III) pentacation allows oxidations to be carried out in protic and dipolar aprotic solvents without significantly altering the mechanisms of the reactions.
- Smith, John R. Lindsay,Mortimer, David N.
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- METALLOPORPHYRIN-MEDIATED RADICAL CYCLOADDITIONS OF p-CYANO-N,N-DIMETHYLANILINE
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Tetrahydroquinolines are formed via metalloporphyrin-catalyzed radical cycloadditions of olefins (2,3-dimethyl-2-butene and norbornene) and p-cyano-N,N-dimethylaniline; their synthesis, characterization and a mechanistic rationale of their formation are presented.
- Dicken, C. Michael,Lu, Fu-Lung,Bruice, Thomas C.
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- The reaction of permanganyl chloride with olefins: Intermediates and mechanism as derived from matrix-isolation studies and density functional theory calculations
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Density functional theory (DFT) calculations predict that the [2+3] addition of tetramethylethylene (TME) to the MnO2 moiety of MnO3Cl is thermodynamically favoured over [2+1] addition (epoxidation), while the kinetic barriers for bo
- Wistuba, Tobias,Limberg, Christian
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- Reactions of Superoxide with Peroxides
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The reactions of superoxide with tert-butyl hydroperoxide and 98percent H2O2 have been studied in aprotic solvents.In benzene solvent, the proton-catalyzed disproportionation of superoxide followed by the base-catalyzed disproportionation of H2O2 appear to be the only reactions to occur.In acetonitrile, peroxy anions react with the solvent to form, ultimately, acetamide.Reactions of superoxide with diacyl peroxides are rather complex, but this reacting system produces intermediates capable of epoxidation of a number of olefins.Reactions of superoxide with acid chlorides and anhydrides in the presence of olefins also produce epoxides.Plausible mechanisms for these reactions are discussed.
- Stanley, James P.
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- A Kinetic Study of the Epoxidation 2,3-Dimethyl-2-butene by tert-Butyl Hydroperoxide Catalyzed by Imidazole Ligated (meso-Tetraphenylporphinato)manganese(III)
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A kinetic study of the epoxidation of 2,3-dimethyl-2-butene (TME) by t-BuOOH in the presence of (mesotetraphenylporphinato)manganese(III) chloride (TPP)Mn(III)Cl) and imidazole (ImH) has been carried out (30 deg C, CH2Cl2 solvent).The rates of decrease in and increase in have been determined as a function of the initial concentrations of , , ImH>, and .As found previously, ImH ligation is required for the reaction of the manganese(III) porphyrin with t-BuOOH and thus for the epxidation of TME.Under the condition of i, i, and i >> i, it is found that the rate for disappearance of t-BuOOH is a;ways more than twofold greater than is the rate of epoxide formation regardlessof the ratios of , , and .This requires that in addition to an ImH ligated higher valent manganese oxo porphyrin there is the formation of an additional intermediate species capable of transferring oxygen.This must be so, because the total concentrations of (TPP)Mn(III)Cl is not sufficient to store the oxygen equivalents.Other pertinent observations are as follows: (i) Disappearance of t-BuOOH follows the first-order rate law in the absence of TME while in the presence of TME its disappearance follows two sequential first-order processes; (ii) formation of epoxide is always first-order; (iii) the maximum yield of epoxide is but 60percent; (iv) the percent yield of epoxide increases and then decreases with increase in i; and (v) there is formation of a small percentage of di-tert-butyl peroxide ((t-BuO)2).A proposed reaction sequence which competent in accounting for these observations is presented in Scheme I. the equilibrium constants for ligation of ImH with manganese(III) porphyrin and the rate constants for oxygen transfer from t-BuOOH to both (TPP)Mn(III)(ImH)Cl and (TPP)Mn(III)(ImH)2 were determined individually while the other constants of Scheme I were obtained as the best minimal values by computer simulation of the time dependence for the disappearance of t-BuOOH and the appearence of epoxide and (t-BuO)2.
- Balasubramanian, P. N.,Sinha, Ashoke,Bruice, Thomas C.
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- Porphyrins in aqueous amphiphilic polymers as peroxidase mimics
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Water-insoluble porphyrins dissolve in aqueous solutions of amphiphilic polymers to give systems which mimic the action of peroxidase enzymes.
- Johnstone, Robert A. W.,Simpson, Anthony J.,Stocks, Paul A.
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- Relative Rate Study of the Addition of HO2 Radicals to Ethylene and to Tetramethylethylene
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Studies of the competitive oxidation of ethylene and tetramethylethylene in the presence and absence of tetramethylbutane as a source of HO2 radicals have been carried out between 400 and 500 deg C over a range of mixture composition and total pressure using aged boric-acid-coated Pyrex vessels.From measurements of the initial relative yields of oxirane and tetramethyloxirane, values of log10(A7/A5) = -0.77 +/- 0.09 and E5 - E7 = 36.5 +/- 0.9 kJ mol-1 have been obtained: HO2 + C2H4 -> C2H4O + OH (5), HO2 + (CH3)2C=C(CH3)2 -> (CH3)2C(O)C(CH3)2 + OH (7).Use of the published values of the Arrhenius parameters for reaction (5) gives log10(A7/dm3 mol-1 s-1) = 9.24 +/- 0.29 and E7 = 40.0 +/- 4.5 kJ mol1-.No other values are available in the literature, but the present results are consistent with the very limited data available for the addition of HO2 radicals to ethylene, propene and i-butene.Trends in the variation of the values of the rate constant and of the activation energy for HO2 addition with structure of the alkene are very similar to those observed for the addition of CH3O2 and i-C3H7O2 radicals.The relative rate of addition of i-C3H7O2, CH3O2 and HO2 radicals to any alkene at 130 deg C is ca. 1:4:30.
- Baldwin, Roy R.,Stout, David R.,Walker, Raymond W.
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- Synthesis and reaction of cyano-substituted 1,2,4-trioxolanes
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Carbonyl oxides, derived from the ozonolyses of vinyl ethers, readily undergo [3 + 2] cycloadditions with acyl cyanides affording the corresponding cyano-substituted 1,2,4-trioxolanes in isolated yields of 34-88%. In competition experiments, a relative order of reactivity of the carbonyl oxide trapping agents was tentatively deduced; trifluoroacetophenone > α,α-diphenyl-N-methylnitrone (N-methyldiphenyl-methylideneamine N-oxide) > benzoyl cyanide > methyl benzoylformate > α,α,N-triphenylimine [N-(diphenylmethylidene)aniline] ? benzaldehyde. As expected from the electron-withdrawing ability of the cyano group, 3-cyano-3-phenyl-1,2,4-trioxolane oxidized not only triphenylphosphine but also methyl p-tolyl sulfide and 2,3-dimethylbut-2-ene very easily.
- Kuwabara, Hajime,Ushigoe, Yoshihiro,Nojima, Masatomo
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- Formation of β-Ga2O3nanorings from metal-organic frameworks and their high catalytic activity for epoxidation of alkenes
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Here we report a novel synthesis of hollow high-quality β-Ga2O3 nanorings based on an interesting structural evolution from concave Ga-MOF nanodisks. The concave low-crystallinity nanodisks were constructed by non-classical crystallization with particle a
- Wang, Wei Ping,Song, Le Xin,Li, Yao,Teng, Yue,Xia, Juan,Wang, Fang,Liu, Nan Ning
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p. 349 - 357
(2021/01/14)
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- A General Regioselective Synthesis of Alcohols by Cobalt-Catalyzed Hydrogenation of Epoxides
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A straightforward methodology for the synthesis of anti-Markovnikov-type alcohols is presented. By using a specific cobalt triphos complex in the presence of Zn(OTf)2 as an additive, the hydrogenation of epoxides proceeds with high yields and selectivities. The described protocol shows a broad substrate scope, including multi-substituted internal and terminal epoxides, as well as a good functional-group tolerance. Various natural-product derivatives, including steroids, terpenoids, and sesquiterpenoids, gave access to the corresponding alcohols in moderate-to-excellent yields.
- Beller, Matthias,Junge, Kathrin,Leischner, Thomas,Li, Wu,Liu, Weiping
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supporting information
p. 11321 - 11324
(2020/05/16)
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- Synthesis, characterization and catalytic epoxidation properties of a new tellurotungstate(iv)-supported rhenium carbonyl derivative
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A monomeric tellurotungstate(iv)-supported rhenium carbonyl derivative: Na2H2[(CH3)4N]6[Te2W20O70{Re(CO)3}2]·20H2O (1) has been successfully isolated and structurally characterized by single crystal X-ray diffraction crystallography, IR and UV-Vis spectroscopy, thermogravimetric analysis, etc. In particular, complex 1 could act as a efficient and reusable heterogeneous catalyst for selective epoxidation of various alkenes including different cycloalkenes, styrene derivatives, internal and long-chain alkenes. For example, cis-cyclooctene undergoes up to 98.2% conversion and >99% selectivity at 75 °C in acetonitrile with 30% H2O2 as an oxidant. Additionally, the electrocatalytic property of 1 for NO2? reduction was also investigated.
- Lu, Jingkun,Ma, Xinyi,Wang, Ping,Feng, Junwei,Ma, Pengtao,Niu, Jingyang,Wang, Jingping
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p. 628 - 634
(2019/01/08)
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- Experimental investigation of the low temperature oxidation of the five isomers of hexane
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The low-temperature oxidation of the five hexane isomers (n-hexane, 2-methyl-pentane, 3-methyl-pentane, 2,2-dimethylbutane, and 2,3-dimethylbutane) was studied in a jet-stirred reactor (JSR) at atmospheric pressure under stoichiometric conditions between 550 and 1000 K. The evolution of reactant and product mole fraction profiles were recorded as a function of the temperature using two analytical methods: gas chromatography and synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Experimental data obtained with both methods were in good agreement for the five fuels. These data were used to compare the reactivity and the nature of the reaction products and their distribution. At low temperature (below 800 K), n-hexane was the most reactive isomer. The two methyl-pentane isomers have about the same reactivity, which was lower than that of n-hexane. 2,2-Dimethylbutane was less reactive than the two methyl-pentane isomers, and 2,3-dimethylbutane was the least reactive isomer. These observations are in good agreement with research octane numbers given in the literature. Cyclic ethers with rings including 3, 4, 5, and 6 atoms have been identified and quantified for the five fuels. While the cyclic ether distribution was notably more detailed than in other literature of JSR studies of branched alkane oxidation, some oxiranes were missing among the cyclic ethers expected from methyl-pentanes. Using SVUV-PIMS, the formation of C 2-C3 monocarboxylic acids, ketohydroperoxides, and species with two carbonyl groups have also been observed, supporting their possible formation from branched reactants. This is in line with what was previously experimentally demonstrated from linear fuels. Possible structures and ways of decomposition of the most probable ketohydroperoxides were discussed. Above 800 K, all five isomers have about the same reactivity, with a larger formation from branched alkanes of some unsaturated species, such as allene and propyne, which are known to be soot precursors.
- Wang, Zhandong,Herbinet, Olivier,Cheng, Zhanjun,Husson, Benoit,Fournet, Rene,Qi, Fei,Battin-Leclerc, Frederique
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p. 5573 - 5594
(2014/08/18)
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- Oxidative bromination of alkenes mediated with nitrite in ionic liquids
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The oxidative bromination of C2-C8 alkenes with HBr-NaNO2-O2 in solutions of BMImBr, HMImBr or BMImBF 4 containing 16-28 wt% H2O was studied using volumetric method, GC-MS analysis, 14N NMR and UV-VIS spectroscopy. The optimal conditions to conduct the reaction at high selectivity for 1,2-dibromoalkanes in BMImBr were determined. The composition of ionic liquid affects the catalytic performance. Although in BMImBF4 the reaction runs with equal rate as in bromide ionic liquid, the fraction of bromohydrin in the reaction products increases to 20 %. Generated from NaNO2, NOx operated as a catalyst in the oxidation of Br- and was oxidized to catalytically inert NO3 - anions when complete conversion of HBr was attained. Graphical Abstract: Oxidative bromination of alkenes [Figure not available: see fulltext.]
- Kuznetsova, Lidia I.,Kuznetsova, Nina I.,Zudin, Vladimir N.,Utkin, Viktor A.,Trebushat, Dmitry V.,Fedotov, Martin A.,Larina, Tatyana V.
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p. 1499 - 1506,8
(2014/11/08)
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- EFFICIENT PROCESS FOR PRODUCING EPOXIDES BY OXIDATION OF OLEFINS IN THE HOMOGENEOUS GAS PHASE
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An economical one-step process is provided for the preparation of epoxides by oxidation of olefins in a homogeneous gas phase reaction, wherein the olefin is reacted in a flow reactor with a gas mixture of ozone and NO2 and/or NO as oxidants without use of a catalyst, and wherein ozone and NO2 and/or NO are mixed in a mixing chamber connected upstream to the flow reactor. The process is characterized in that the olefin in the reaction zone of the flow reactor is reacted at a reaction temperature of approximately 150° C. to approximately 450° C. and a pressure of 250 mbar to 10 bar with the gas mixture of the oxidant, that the carrier gas flow containing the olefin is heated in a preheating zone of the flow reactor to a temperature of 250° C. to 650° C., and that the gas mixture of the oxidant from the mixing chamber, having ambient temperature, is turbulently mixed with the olefin in the reaction zone of the flow reactor, so that the reaction temperature is reached during the mixing and the ratio of olefin-gas flow and gas flow of the oxidant is 5:1 to 1:1.
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(2011/06/26)
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- Investigation of the thermal and photochemical reactions of ozone with 2,3-dimethyl-2-butene
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The matrix isolation technique, combined with infrared spectroscopy and twin jet codeposition, has been used to characterize intermediates formed during the ozonolysis of 2,3-dimethyl-2-butene (DMB). Absorptions of early intermediates in the twin jet experiments grew up to 200% upon annealing to 35 K. A number of these absorptions have been assigned to the elusive Criegee intermediate (CI) and secondary ozonide (SOZ) of DMB, transient species not previously observed for this system. Also observed was the primary ozonide (POZ), in agreement with earlier studies. The wavelength dependence of the photodestruction of these product bands was explored with irradiation from λ ≥ 220 to ≥580 nm. Merged jet (flow reactor) experiments generated "late" stable oxidation products of DMB. A recently developed concentric jet method was also utilized to increase yields and monitor the concentration of intermediates and products formed at different times by varying the length of mixing distance (d = 0 to -11 cm) before reaching the cold cell for spectroscopic detection. Identification of intermediates formed during the ozonolysis of DMB was further supported by 18O and scrambled 16,18O isotopic labeling experiments as well as theoretical density functional calculations at the B3LYP/6-311++G(d,2p) level.
- Coleman, Bridgett E.,Ault, Bruce S.
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experimental part
p. 12667 - 12674
(2011/02/27)
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- Activation of molecular oxygen by a dioxygenase pathway by a ruthenium bis-bipyridine compound with a proximal selenium site
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A ruthenium(II) bipyridine complex with proximal phenylselenium tethers, [Ru](H2O)2, reacted intramolecularly with O2 in a protic slightly acidic solvent, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), to yield an O-O bond cleaved product, [Ru](O)2, with formation of two Ru-O-Se moieties. This stable compound was isolated, and its structure was determined by X-ray diffraction. The identification of the compound in solution was confirmed by ESI-MS and the 1H NMR with the associated Curie plot that showed that [Ru](O)2 was paramagnetic. The magnetic susceptibility was 2.8 μB by Evan's method suggesting a ground state triplet or biradical. DFT calculations, however, predicted a ground state singlet and an oxidized Se atom. Further it was shown that [Ru](O)2 is a potent oxygen transfer species of both O2-derived atoms to triphenylphosphine and a nucleophilic alkene such as 2,3-dimethyl-2-butene in both HFIP and acetonitrile. UV-vis spectroscopy combined with the measured stoichiometry of PPh3:O2 = 2 in a catalytic oxidation of PPh3 suggests a dioxygenase type activation of O 2 with structural identification of the O-O bond cleavage reaction step, formation of [Ru](O)2 as an intermediate, and the proof that [Ru](O)2 is a donor of both oxygen atoms.
- Laskavy, Alexander,Shimon, Linda J. W.,Konstantinovski, Leonid,Iron, Mark A.,Neumann, Ronny
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body text
p. 517 - 523
(2010/03/25)
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- The unexpected role of pyridine-2-carboxylic acid in manganese based oxidation catalysis with pyridin-2-yl based ligands
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A number of manganese-based catalysts employing ligands whose structures incorporate pyridyl groups have been reported previously to achieve both high turnover numbers and selectivity in the oxidation of alkenes and alcohols, using H2O2 as terminal oxidant. Here we report our recent finding that these ligands decompose in situ to pyridine-2-carboxylic acid and its derivatives, in the presence of a manganese source, H2O 2 and a base. Importantly, the decomposition occurs prior to the onset of catalysed oxidation of organic substrates. It is found that the pyridine-2-carboxylic acid formed, together with a manganese source, provides for the observed catalytic activity. The degradation of this series of pyridyl ligands to pyridine-2-carboxylic acid under reaction conditions is demonstrated by 1H NMR spectroscopy. In all cases the activity and selectivity of the manganese/pyridyl containing ligand systems are identical to that observed with the corresponding number of equivalents of pyridine-2-carboxylic acid; except that, when pyridine-2-carboxylic acid is used directly, a lag phase is not observed and the efficiency in terms of the number of equivalents of H 2O2 required decreases from 6-8 equiv. with the pyridin-2-yl based ligands to 1-1.5 equiv. with pyridine-2-carboxylic acid.
- Pijper, Dirk,Saisaha, Pattama,De Boer, Johannes W.,Hoen, Rob,Smit, Christian,Meetsma, Auke,Hage, Ronald,Van Summeren, Ruben P.,Alsters, Paul L.,Feringa, Ben L.,Browne, Wesley R.
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supporting information; experimental part
p. 10375 - 10381
(2011/01/09)
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- DEHYDRATION OF ALCOHOLS TO GIVE ALKENES OR ETHERS
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The present invention relates to a process for the dehydration of alcohols, polyalcohols or alcoholates having at least one CH group in the α-position to the alcoholate or alcohol function to give alcenes or ethers, where the dehydration is carried out in ionic liquids of the general formula K+A?.
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Page/Page column 9
(2009/04/24)
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- Generation of mono- and bis-dioxiranes from 2,3-butanedione
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Biacetyl reacts with oxone to give bis-dioxirane [3,3′-dimethyl-3, 3′-bidioxirane, 3B] and mono-dioxirane [1-(3-methyl-dioxiran-3-yl) ethanone, 3A)]. Bis-dioxirane 3B is formed when two oxygens are incorporated into biacetyl, while mono-dioxirane 3A incorporated only one. A greater stability is observed in 3B compared to 3A, which is attributed to an α-dioxiranyl (anomeric) effect in the former. In contrast, 3A suffers from a destabilizing π-electron withdrawing effect from the adjacent carbonyl group.
- Sawwan, Nahed,Greer, Alexander
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p. 5796 - 5799
(2007/10/03)
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- WO3 Nanoparticles on MCM-48 as a Highly Selective and Versatile Heterogeneous Catalyst for the Oxidation of Olefins, Sulfides, and Cyclic Ketones
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It is shown that nanosized WO3 particles supported on MCM-48 work as a highly efficient and selective heterogeneous catalyst for the oxidation of olefins, sulfides, and cyclic ketones using hydrogen peroxide or peracetic acid. The catalytic activity of the supported tungstate was dependent on the nature of the supporting materials and particle size. The catalyst system employs environmentally benign oxidants in halide-free solvents, and it does not require phase-transfer agents and pH control.
- Koo, Dong Hyun,Kim, Min,Chang, Sukbok
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p. 5015 - 5018
(2007/10/03)
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- Asymmetric alkene epoxidation catalysed by a novel family of chiral metalloporphyrins: Effect of structure on catalyst activity, stability and enantioselectivity
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A selection of alkenes has been epoxidised with iodosylbenzene, catalysed by three related iron(III) tetraarylporphyrins: 1*, 2* and 3* with four 2,6-di(1-phenylbutoxy)phenyl groups, with one pentafluorophenyl and three 2,6-di(1-phenylbutoxy)phenyl groups and with two pentafluorophenyl and two 2,6-di(1-phenylbutoxy)phenyl groups, respectively. 1* is very sterically hindered and prone to self-oxidation which makes it a relatively poor epoxidation catalyst. Introducing the smaller pentafluorophenyl groups, in place of 2,6-di(1-phenylbutoxy)phenyl, increases catalyst reactivity, stability and selectivity. This change allows easier access of the substrates to the active oxidant and also, by decreasing the electron density on the porphyrin ligand, increases the reactivity of the oxoiron intermediate and its stability towards self-oxidation. A family of five homochiral catalysts, 1, 2 and 3, [the analogues of 1*, 2* and 3*, prepared from (R,R)-2,6-di(1-phenylbutoxy)benzaldehyde] and catalyst 4 with three pentafluorophenyl and one (R,R)-2,6-di(1-phenylbutoxy)phenyl group and 5 the manganese(III) analogueof 3 have been used to epoxidise three prochiral alkenes. All the reactions give low enantioselectivities. Using styrene as the substrate, (S)-styrene epoxide is the major enantiomer obtained with all the catalysts except 1 which leads to the (R)-styrene epoxide being preferred. In contrast cis-hept-2-ene and 2-methylbut-2-ene give the same major epoxide enantiomer with all the catalysts. The dependence of the ee values on catalyst and substrate structure, temperature and solvent is examined and discussed.
- Lindsay Smith, John R.,Reginato, Gloriana
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p. 2543 - 2549
(2007/10/03)
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- Activation of hydrogen peroxide through hydrogen-bonding interaction with acidic alcohols: Epoxidation of alkenes in phenol
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(Matrix presented) Electrophilic activation of hydrogen peroxide can be achieved in acidic alcohol solvents without the need for a metal catalyst. This concept is illustrated by the epoxidation of alkenes with H2O 2 employing phenol as a solvent. It is proposed that intermolecular hydrogen bonding between H2O2 and phenol activates H 2O2 for oxygen-atom transfer. In this interaction, the role of phenol is purely catalytic.
- Wahlen, Joos,De Vos, Dirk E.,Jacobs, Pierre A.
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p. 1777 - 1780
(2007/10/03)
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- A Simple and Convenient Method for Epoxidation of Olefins without Metal Catalysts
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An easy method for epoxidation of olefins using bleach (sodium hypochlorite) and either a stoichiometric or catalytic amount of bromide ion has been developed. Without any transition metal catalyst a variety of non-activated olefins give epoxides in high yields and good selectivity at ambient conditions.
- Klawonn, Markus,Bhor, Santosh,Mehltretter, Gerald,Doebler, Christian,Fischer, Christine,Beller, Matthias
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p. 389 - 392
(2007/10/03)
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- Manganese-catalyzed epoxidations of alkenes in bicarbonate solutions
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This paper describes a method, discovered and refined by parallel screening, for the epoxidation of alkenes. It uses hydrogen peroxide as the terminal oxidant, is promoted by catalytic amounts (1.0-0.1 mol %) of manganese(2+) salts, and must be performed using at least catalytic amounts of bicarbonate buffer. Peroxymonocarbonate, HCO4-, forms in the reaction, but without manganese, minimal epoxidation activity is observed in the solvents used for this research, that is, DMF and tBUOH. More than 30 d-block and f-block transition metal salts were screened for epoxidation activity under similar conditions, but the best catalyst found was MnSO4. EPR studies show that Mn2+ is initially consumed in the catalytic reaction but is regenerated toward the end of the process when presumably the hydrogen peroxide is spent. A variety of aryl-substituted, cyclic, and trialkyl-substituted alkenes were epoxidized under these conditions using 10 equiv of hydrogen peroxide, but monoalkyl-alkenes were not. To improve the substrate scope, and to increase the efficiency of hydrogen peroxide consumption, 68 diverse compounds were screened to find additives that would enhance the rate of the epoxidation reaction relative to a competing disproportionation of hydrogen peroxide. Successful additives were 6 mol % sodium acetate in the tBUOH system and 4 mol % salicylic acid in the DMF system. These additives enhanced the rate of the desired epoxidation reaction by 2-3 times. Reactions performed in the presence of these additives require less hydrogen peroxide and shorter reaction times, and they enhance the yields obtained from less reactive alkene substrates. Possible mechanisms for the reaction are discussed.
- Lane, Benjamin S.,Vogt, Matthew,DeRose, Victoria J.,Burgess, Kevin
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p. 11946 - 11954
(2007/10/03)
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- Processes for preparation of 3-keto-7alpha-alkoxycarbonyl-delta-4,5- steroids and intermediates useful therein
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Multiple novel reaction schemes, novel process steps and novel intermediates are provided for the synthesis of epoxymexrenone and other compounds of Formula I wherein:-A-A- represents the group -CHR4-CHR5- or -CR4=CR5- R3, R4 and R5 are independently selected from the group consisting of hydrogen, halo, hydroxy, lower alkyl, lower alkoxy, hydroxyalkyl, alkoxyalkyl, hydroxycarbonyl, cyano, varyloxy;R1 represents an alpha-oriented lower alkoxycarbonyl or hydroxyalkyl radical;-B-B- represents the group -CHR6-CHR7- or an alpha- or beta- oriented group: where R6 and R7 are independently selected from the group consisting of hydrogen, halo, lower alkoxy, acyl, hydroxyalkyl, alkoxyalkyl, hydroxycarbonyl, alkyl, alkoxycarbonyl, acyloxyalkyl, cyano and aryloxy; andR8 and R9 are independently selected from the group consisting of hydrogen, hydroxy, halo, lower alkoxy, acyl, hydroxyalkyl, alkoxyalkyl, hydroxycarbonyl, alkyl, alkoxycarbonyl, acyloxyalkyl, cyano and aryloxy, or R8 and R9 together comprise a carbocyclic or heterocyclic ring structure, or R8 or R9 together with R6 or R7 comprise a carbocyclic or heterocyclic ring structure fused to the pentacyclic D ring.
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- Direct formation of pinacols from olefins over various titano-silicates
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The epoxidation and successive pinacol formation of tri- and tetraalkyl-substituted olefins using Ti-β/H2O2/H2O as the catalytic system has been investigated. Aluminum-free Ti-β exhibits better activity and pinacol selectivity than TS-1, TS-2, Ti-MCM-22, and mesoporous Ti-MCM-41. Pinacol (vic-diol) is obtained as the major product with small amounts of the side products pinacolone, alcohol (via hydration), and oligomers. The conversion and pinacol selectivity increase with an increase in reaction temperature and time. The change in product distribution with reaction time over Ti-β shows that the epoxide is the initial product which undergoes a secondary reaction to give pinacol as the major product. The conversion and H2O2 selectivity decrease with the bulkiness of the substituents at the C=C bond but the selectivity of pinacol is not significantly affected. The reactivity of cyclic 1-methyl-1-cyclohexene is considerably lower than that of the corresponding open-chain analogue 2-methyl-2-butene. The symmetrical tetramethyl-substituted 2,3-dimethyl-2-butene led to the formation of small amount of dimers over medium-pore titanium silicates TS-1, TS-2, and Ti-MCM-22. The epoxidation of these substituted olefins proceeded more rapidly when using acetonitrile as a cosolvent than under triphase conditions. Mechanistically, the primary epoxide product undergoes acid-catalyzed nucleophilic ring opening by H2O molecules to give pinacol.
- Sasidharan,Wu, Peng,Tatsumi, Takashi
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p. 260 - 265
(2007/10/03)
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- Photoinitiated olefin epoxidation with molecular oxygen, sensitized by free base porphyrins and promoted by hexacarbonylmolybdenum in homogeneous solution
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The photooxidation of various olefins in homogeneous solution under an oxygen atmosphere, by use of visible light, a dye sensitizer, and an oxygen-transfer catalyst, has been investigated. The oxygen transfer from molecular oxygen to olefin involves the following steps: i) photoinduced singlet-oxygen formation, ii) alkyl hydroperoxide formation through the ene reaction, iii) the intermediacy of a reactive molybdenum peroxide, and iv) olefin epoxidation of the remaining substrate or of a second olefin. Among the various sensitizers and catalysts tested, the electron- deficient free base porphyrin 5,10,15,20-tetrakis(2′,6′-dichlorophenyl) -β-octabromoporphyrin and hexacarbonylmolybdenum showed the best performances in terms of robustness and activity. Under suitable conditions, complete olefin conversion may be obtained by adoption of molar ratios of sensitizer/catalyst/substrate of 1:50:2000, with the formation of the corresponding epoxide in up to 38% yield, which corresponds to 77% of the theoretical maximum. Quite interestingly, olefins reluctant to undergo ene reactions may be epoxidized in the presence of a second sacrificial olefin, yielding the corresponding epoxides with up to 80% total selectivity. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Campestrini, Sandro,Tonellato, Umberto
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p. 3827 - 3832
(2007/10/03)
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- A new non-metal heterogeneous catalyst for the activation of hydrogen peroxide: A perfluorinated ketone attached to silica for oxidation of aromatic amines and alkenes
-
A silane functionalized by octafluoroacetophenone was polymerized by the sol-gel method to form an insoluble silicate with perfluoroketone pendants; the silicate was used as a heterogeneous catalyst for the activation of aqueous hydrogen peroxide and the oxidation of aromatic amines and alkenes.
- Neimann,Neumann
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p. 487 - 488
(2007/10/03)
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- Selective epoxidation of olefins by hydrogen peroxide in water using a polyoxometalate catalyst supported on chemically modified hydrophobic mesoporous silica gel
-
A new heterogeneous catalyst prepared by immobilisation of polyoxometalates on chemically modified hydrophobic mesoporous silica gel has been successfully applied to the selective epoxidation of olefins with 15% aqueous H2O2 without the use of organic solvent. (C) 2000 Elsevier Science Ltd.
- Sakamoto,Pac
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p. 10009 - 10012
(2007/10/03)
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- Aerobic epoxidation of alkenes catalysed by cobalt(II) 1,1,1,5,5,5-hexafluoroacetylacetonate or cobalt(II) benzoylacetonate
-
The aerobic epoxidation of terminal or electron deficient alkenes with an aldehyde does not proceed with cobalt(II) acetylacetonate but goes to completion with the cobalt(II) benzoylacetonate and cobalt(II) 1,1,1,5,5,5-hexafluoroacetylacetonate complexes.
- Hunter,Turner,Rimmer
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p. 4461 - 4466
(2007/10/03)
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- Electrophilic activation of hydrogen peroxide: Selective oxidation reactions in perfluorinated alcohol solvents
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The catalytic electrophilic activation of hydrogen peroxide with transition metal compounds toward reaction with nucleophiles is a matter of very significant research and practical interest. We have now found that use of perfluorinated alcoholic solvents such as 1,1,1,3,3,3-hexafluoro-2-propanol in the absence of catalysts allowed electrophilic activation of hydrogen peroxide toward epoxidation of alkenes and the Baeyer-Villiger oxidation of ketones.
- Neimann, Karine,Neumann, Ronny
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p. 2861 - 2863
(2007/10/03)
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- NaY zeolite as host for the selective heterogeneous oxidation of silanes and olefins with hydrogen peroxide catalyzed by methyltrioxorhenium
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The methyltrioxorhenium(MTO)-catalyzed oxidation of silanes to silanols and the epoxidation of various olefins by aqueous 85% H2O2 proceed in high yields and excellent product selectivities (no disiloxanes, diols) in the presence of the zeolite NaY. The oxidative species is located inside the 12- A supercages. This prevents the bimolecular condensation of the silanol to disiloxane by steric means and the Lewis-acid assisted hydrolysis of the epoxide to the diol.
- Adam, Waldemar,Saha-Moeller, Chantu R.,Weichold, Oliver
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p. 2897 - 2899
(2007/10/03)
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- Experimental investigation of the primary and secondary deuterium kinetic isotope effects for epoxidation of alkenes and ethylene with m- chloroperoxybenzoic acid
-
The secondary deuterium kinetic isotope effect (DKIE) for the epoxidation of ethylene and d4-ethylene by m-chloroperoxybenzoic acid (MCPBA) is determined to be 0.83, or 0.95/α-H. The second-order rate constants for MCPBA and MCPBA-O-D epoxidation of a variety of alkenes that differ in the steric access to the double bond (anti-sesquinorbornene (2), tetramethylethylene (3), adamantylideneadamantane (4), 7-norbornylidene-7'- norbornane (5), bis(bicyclo[3.3.1.]non-9-ylidene) (6), bis(homoadamantane) (7), cyclohexene (8), 1-octene (9), trans-5-decene (10) and 2-methyl-1- pentene (11)) have been determined in dichloroethane at 25°C using UV kinetics, and the primary DKIE, k(OH)/k(OD), is 1.05 ± 0.05 in all eases. By comparison of the rates of epoxidation of sterically encumbered alkenes, it is suggested that the spiro epoxidation transition state is favored over a planar one. The products of the epoxidation of anti-sesquinorbornene are determined to be the epoxide and a cis-hydroxy ester, the latter most probably being formed by acid-catalyzed ring opening of the epoxide by in situ-produced m-chlorobenzoic acid produced in situ to form a β-hydroxy carbocation and carboxylate ion pair that collapses to product.
- Koerner, Terry,Slebocka-Tilk,Brown
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p. 196 - 201
(2007/10/03)
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- Iodomethane oxidation by dimethyldioxirane: A new route to hypoiodous acid and iodohydrines
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matrix presented The oxidation of iodomethane with dimethyldioxirane allows the generation of stable neutral solutions of hypoiodous acid in the absence of any trapping agent for iodide anion. Hypoiodous acid is trapped in situ by addition to representative olefins to give iodohydrines in good yields. The stereochemical study of the products shows the anti-stereospecific nature of the iodohydroxylation reaction.
- Asensio, Gregorio,Andreu, Cecilia,Boix-Bernardini, Carmen,Mello, Rossella,Gonzalez-Nunez, Maria Elena
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p. 2125 - 2128
(2008/02/09)
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- 5-Hydroperoxycarbonylphthalimide: A new reagent for epoxidation
-
Peroxycarboxylic acids, widely used for epoxidation in industry and general research, have various drawbacks, such as difficulty of preparation in a pure state, cost and the possibly ring-opening of the product epoxides due to acid-catalysed reactions; a new reagent, 5-hydroperoxycarbonylphthalimide, overcomes these problems.
- James, Alun P.,Johnstone, Robert A.W.,McCarron, Moya,Sankey, J. Phillip,Trenbirth, Brian
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p. 429 - 430
(2007/10/03)
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- Alkane oxidation with manganese substituted polyoxometalates in aqueous media with ozone and the intermediacy of manganese ozonide species
-
Manganese substituted polyoxometalates (POMs), such as Li12[MnII2ZnW(ZnW9O 34)2] were effective catalysts for the oxidation of alkanes to ketones with ozone in an aqueous reaction medium; a green intermediate compound observable by UV-VIS and ESR at -78 °C was postulated to be a reactive manganese ozonide species.
- Neumann, Ronny,Khenkin, Alexander M.
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p. 1967 - 1968
(2007/10/03)
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- Hydrolysis of genotoxic methyl-substituted oxiranes: Experimental kinetic and semiempirical studies
-
The kinetics of acid-catalyzed hydrolysis of seven methylated aliphatic epoxides - R1R2C(O)CR3R4 (A: R1=R2=R3=R4=H; B: R1=R2=R3=H, R4=Me; C: R1=R2=H, R3=R4=Me; D: R1=R3=H, R2=R4=Me(trans); E: R1=R3=H, R2=R4=Me(cis); F: R1=R3=R4=Me, R2=H; G: R1=R2=R3=R4=Me) - has been studied at 36 ± 1.5°C. Compounds with two methyl groups at the same carbon atom of the oxirane ring exhibit highest rate constants (k(eff) in reciprocal molar concentration per second: 11.0 ± 1.3 for C, 10.7 ± 2.1 for F, and 8.7 ± 0.7 for G as opposed to 0.124 ± 0.003 for B, 0.305 ± 0.003 for D, and 0.635 ± 0.036 for E). Ethylene oxide (A) displays the lowest rate of hydrolysis (0.027 M-1 s-1). The results are consistent with literature data available for compounds A, B, and C. To model the reactivities we have employed quantum chemical calculations (MNDO, AM1, PM3, and MINDO/3) of the main reaction species. There is a correlation of the logarithm k(eff) with the total energy of epoxide ring opening. The best correlation coefficients (r) were obtained using the AM1 and MNDO methods (0.966 and 0.957, respectively). However, unlike MNDO, AM1 predicts approximately zero energy barriers for the oxirane ring opening of compounds B, C, E and G, which is not consistent with published kinetic data. Thus, the MNDO method provides a preferential means of modeling the acidic hydrolysis of the series of methylated oxiranes. The general ranking of mutagenicity in vitro, A > B > C, is in line with the concept that this sequence also gradually leaves the expoxide reactivity optimal for genotoxicity toward reactivities leading to higher biological detoxifications.
- Kirkovsky, Leonid I.,Lermontov, Sergei A.,Zavorin, Sergei I.,Sukhozhenko, Ivan I.,Zavelsky, Vladimir I.,Thier, Ricarda,Bolt, Hermann M.
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p. 2141 - 2147
(2007/10/03)
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- Reactions of Microwave-Generated O(3P) Atoms with Unsaturated Hydrocarbons
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The reactions of neat olefins or solutions of olefins in acetone at low temperature with oxygen atoms were examined. O(3P) atoms were produced by microwave irradiation of He/O2 mixtures, followed by contact of the plasma with the fluid at low pressure and temperature. Addition of oxygen atoms to olefins results in skeletal rearrangements involving hydrogen and alkyl migration reactions and ring rearrangements of the intermediate oxygen adducts in competition with epoxide formation. While epoxide formation predominates for simple olefins such as 1- and 4-octene with minor yields of rearrangement products, for highly substituted or strained olefins, such as norbornadiene, skeletal rearrangement dominates following oxygen atom addition. When oxidation of norbornadiene is carried out in the presence of a radical inhibitor to suppress secondary oxidation leading to benzene, the novel ring-rearrangement product, bicyclo[3.2,31.0]hex- 3-ene-endo-6-carboxaldehyde, is produced from norbornadiene in significant yields.
- Tanner,Kandanarachchi,Das,Brausen,Vo,Camaioni,Franz
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p. 4587 - 4593
(2007/10/03)
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- Metal silicates by a molecular route as catalysts for epoxidation of alkenes with tert-butyl hydroperoxide
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Macroporous, site isolated metal silicates are synthesized by a molecular route; the molybdenum silicate is especially active for the selective epoxidation of alkenes with tert-butyl hydroperoxide.
- Juwiler, David,Blum, Jochanan,Neumann, Ronny
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p. 1123 - 1124
(2007/10/03)
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- Heterogeneous molybdate catalysts for the generation of singlet molecular oxygen (1Δg) from H2O2
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The immobilisation of molybdate on Mg,Al-LDH leads to an active, heterogeneous catalyst that generates singlet molecular oxygen from hydrogen peroxide in the absence of soluble base.
- Laar, F. van,Vos, D. De,Vanoppen, D.,Sels, B.,Jacobs, P. A.,et al.
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p. 267 - 268
(2007/10/03)
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- Oxygen transfer reactions from an oxaziridinium tetrafluoroborate salt to olefins
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Oxaziridinium 5 efficiently epoxidises olefins. It reacts as an electrophilic reagent and does not transfer its oxygen to deactivated double-bonds or carbonyl functions. Epoxidation of cyclic allylic acetates shows a remarkable diastereoselectivity leading to the syn isomer. We propose that the epoxidation reaction proceeds through a one-step process.
- Lusinchi, Xavier,Hanquet, Gilles
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p. 13727 - 13738
(2007/10/03)
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- Intrazeolite assembly of a chiral manganese salen epoxidation catalyst
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Asymmetric manganese salen epoxidation catalysts are assembled and trapped in a multistep synthesis in the cages of zeolite EMT; these heterogeneous catalysts produce high enantiomeric excess in the epoxidation of aromatic alkenes with NaOCl.
- Ogunwumi, Steven B.,Bein, Thomas
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p. 901 - 902
(2007/10/03)
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- Reactions of pinacols with one-electron oxidants
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Oxidation of the tetraarylpinacols (Ar2COH)2, 1a-e, in which Ar = C6H5 (1a), 4-ClC6H4 (1b), 4-MeC6H4 (1c), 4-MeOC6H4 (1d) and 4-Me2NC6H4 (1e), by thianthrene cation radical (Th?+) in CH3-CN and in CH2Cl2 led quantitatively to the corresponding diaryl ketones Ar2C=O (2a-e), provided a sufficient amount of base, 2,6-di-tert-butyl-4-methylpyridine (DTBMP), was present to prevent presumed acid-catalyzed rearrangement. In the case of 1e, continued oxidation of 2e was also observed. Oxidation of 1a by (4-BrC6H4)3N?+SbCl 6- and (4-BrC6H4)3N?+SbF 6- (Ar3N?+) occurred analogously. Evidence for the catalytic, cation-radical rearrangement of 1a by Ar3N?+ (reported in earlier literature) and by Th?+ could not be found. Quantitative oxidation of 1a to 2a and of 1d to 2d was obtained also with NOBF4, again provided that sufficient DTBMP was present to prevent acid-catalyzed rearrangement. Catalytic, oxidative rearrangement of 1d at room temperature and (as reported in earlier literature) at -5 °C was not observed. Oxidation was also observed of 2,3-diphenyl-2,3-butanediol (3) to acetophenone (9) and of 1,1-dimethyl-2,2-diphenylethanediol (4) to 2a and acetone by Th?+. Oxidation of 2,3-dimethyl-2,3-butanediol (5) by Th?+ was not observed. Instead, even in the presence of DTBMP, pinacolone (10) and tetramethyloxirane (11) were formed, through, it is proposed, a mechanism involving complexation with Th?+.
- Han, Dong Sul,Shine, Henry J.
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p. 3977 - 3982
(2007/10/03)
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- Selective epoxidations involving anionic peroxotungsten compounds generated in situ on layered double hydroxides with various polarities
-
WO42-exchanged LDH catalyses the epoxidation of simple olefins and allylic alcohols. Substrate reactivity, chemo- and regioselectivity vary markedly with the polarity of the peroxotungstate environment.
- Sels, Bert F.,De Vos, Dirk E.,Jacobs, Pierre A.
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p. 8557 - 8560
(2007/10/03)
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- Steric and stereoelectronic control of the mode selectivity as a function of alkene structure in the reaction with dimethyl α-peroxy lactone: Cycloadducts and ene products versus epoxides
-
The oxidation of di-, tri-, and tetrasubstituted alkenes 2 by dimethyl α-peroxy lactone (1) affords the cycloaddition, ene, and epoxidation products 3-6. In the presence of methanol, additionally the trapping products 7 are obtained. The observed dichotomy in the product distribution requires two different paths for this reaction, namely a path via an open, stretched 1,6 dipole and another path for epoxidation. Both paths arise from an SN2 attack of the double bond of the alkene 2 on the peroxide bond of the α-peroxy lactone 1, the first unsymmetrical (end-on attack), leading to the 1,6 dipole A, and the second symmetrical (central attack) with respect to the approach of the double bond, leading to epoxidation. The 1,6 dipole is postulated to afford the cycloadducts, of which the thermodynamically favored diastereomers are obtained, and the ene products. In the epoxidation, the α-lactone released after oxygen transfer oligomerizes to the polyester 8 or in the presence of methanol is trapped as α-methoxy acid 9. The reaction is regioselective both with respect to the attacked oxygen atom of the α-peroxy lactone 1, as revealed by the trapping products 7, as well as with respect to the attacking carbon atom for unsymmetrical alkenes 2c,d, as displayed by the ene products 5 and 6. The former regioselectivity is dictated by the inherent polarization of the peroxide bond through the carbonyl group which makes the alkoxy oxygen the more electrophilic one toward nucleophilic attack, while for the latter the incipient positive charge of the open 1,6 dipole is better stabilized by the more substituted carbon atom of the end-on attacking unsymmetrical alkene. The preferred reaction mode has been found to be sensitive to the structure of the alkene and the difference in reactivity has been explained in terms of steric and stereoelectronic factors. Thus, for the sterically less hindered cis-di- and trisubstitued alkenes the path along the open 1,6 dipole is favored (stereoelectronic control), while the more sterically demanding trans-di- and tetrasubstituted alkenes react by the epoxidation mode (steric control).
- Adam, Waldemar,Blancafort, Lluis
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p. 4778 - 4787
(2007/10/03)
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- Kinetics and mechanism of the epoxidation of alkyl-substituted alkenes by hydrogen peroxide, catalyzed by methylrhenium trioxide
-
Epoxidations of alkyl-substituted alkenes, with hydrogen peroxide as the oxygen source, are catalyzed by CH3ReO3 (MTO). The kinetics of 28 such reactions were studied in 1:1 CH3CN-H2O at pH 1 and in methanol. To accommodate the different requirements of these reactions, 1H-NMR, spectrophotometric, and thermometric techniques were used to acquire kinetic data. High concentrations of hydrogen peroxide were used, so that diperoxorhenium complex CH3Re(O)(η2-O2)2(H 2O), B, was the only predominant and reactive form of the catalyst. The reactions between B and the alkenes are about 1 order of magnitude more rapid in the semiaqueous solvent than in methanol. The various trends in reactivity are medium-independent. The rate constants for B with the aliphatic alkenes correlate closely with the number of alkyl groups on the olefinic carbons. The reactions become markedly slower when electron-attracting groups, such as halo, hydroxy, cyano, and carbonyl, are present. The rate constants for catalytic epoxidations with B and those reported for the stoichiometric reactions of dimethyldioxirane show very similar trends in reactivity. These findings suggest a concerted mechanism in which the electron-rich double bond of the alkene attacks a peroxidic oxygen of B. These data, combined with those reported for the epoxidation of styrene (a term intended to include related molecules with ring and/or aliphatic substituents) by B and by the monoperoxo derivative of MTO, suggest that all of the rhenium-catalyzed epoxidations occur by a common mechanism. The geometry of the system at the transition state can be inferred from these data, which suggest a spiro arrangement.
- Al-Ajlouni, Ahmad M.,Espenson, James H.
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p. 3969 - 3976
(2007/10/03)
-
- Synthesis and oxygen-atom transfer reactions of 3-hydroperoxy-3,4,4,5,5-pentasubstituted-1,2-dioxolanes
-
A series of 3-hydroperoxy-3,4,4,5,5-pentasubstituted-1,2-dioxolanes 2a-d were synthesized in good yield from the corresponding 3-hydroxy-1,2-dioxolanes by reaction with concentrated hydrogen peroxide in acetonitrile with p-toluenesulfonic acid as catalyst. The 3-hydroperoxy-1,2-dioxolanes were effective oxygen-atom transfer reagents for the oxidation of thioanisole, triethylamine and 2,3-dimethyl-2-butene to the sulfoxide, N-oxide and epoxide, respectively. The reactions occurred under mild conditions and were found to be of the second order overall. The second order rate constants (k2) were determined for oxidation of thioanisole by 2a-d in deuteriochloroform. For 2a, k2 values for N-oxidation and epoxidation were also measured. The 3-hydroperoxy-1,2-dioxolanes were found to be less reactive than the structurally similar cyclic α-azohydroperoxides but much more reactive than simple hydroperoxides. The mechanism of oxygen-atom transfer is postulated to occur via nucleophilic attack of the substrate on the terminal oxygen of the hydroperoxide. Intramolecular hydrogen bonding of the hydroperoxy proton to a dioxolane oxygen appears to account for the reaction order in aprotic media.
- Baumstark,Chen,Rodriguez
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p. 1399 - 1402
(2007/10/03)
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- A Novel Hexanuclear Heteropolyperoxo Oxidation Catalyst: Preparation, X-Ray Crystal Structure and Reactions of 3W6O13(O2)4(OH)2(OH2)>*4H2O
-
The crystal structure of the title compound, 1, reveals the presence of two distinct types of tungsten atom in which the four bearing peroxo groups have distorted pentagonal-bipyramidal geometries and the remaining two are octahedral; 1 is an effective catalyst for monoalkene epoxidation, and the oxidation of primary and secondary alcohols, with H2O2 as co-oxidant.
- Griffith, William P.,Parkin, Bernardeta C.,White, Andrew J. P.,Williams, David J.
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p. 2183 - 2184
(2007/10/02)
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- Oxo Complexes of Ruthenium with N,N'-Donors as Oxidation Catalysts for Alkenes, Alkanes and Alcohols, and their Osmium Analogues
-
Catalysis of the epoxidation of alkenes and oxidation of alkanes and alcohols by a variety of bis-bipy (2,2'-bipyridyl) and bis-phen (1,10-phenanthroline) ruthenium complexes with NaIO4 or IO4 as co-oxidants has been investigated together with similar oxidations with >*1.5H2O.The new complexes > and > (L-L = bipy, phen or 2,2'-dipyridylamine) have been prepared and characterised.
- Bailey, Alan J.,Griffith, William P.,Savage, Paul D.
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p. 3537 - 3542
(2007/10/03)
-
- A New Epoxidation Catalyst: the Reactivity and X-Ray Crystal Structure of >*1.5H2O (bipy = 2,2'-bipyridine)
-
The crystal structure of >*1.5H2O 1 is reported: with NaIO4 or NBun4IO4 as cooxidant it is an efficient catalyst for alkene epoxidations under mild conditions; it also oxidises primary alcohols to aldehydes and secondary alcohols to ketones.
- Bailey, Alan J.,Griffith, William P.,White, Andrew J. P.,Williams, David J.
-
p. 1833 - 1834
(2007/10/02)
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- Epoxide formation in the reactions of the nitrate radical with 2,3-dimethyl-2-butene, cis- and trans-2-butene and isoprene
-
Epoxide formation in the nighttime reaction of NO3 with 2,3-dimethyl-2-butene, cis- or trans-2-butene or isoprene was studied in a 480 l reaction chamber with in situ FTIR spectroscopy as analytical technique. Most experiments were carried out at either 20 Torr in argon or at 740 Torr in synthetic air. In the case of 2,3-dimethyl-2-butene the epoxide formation was studied in the range 20-740 Torr using either argon or air as diluent gas and its O2 dependence was studied in N2/O2 mixtures with O2 concentrations in the range 1.7 x 1015-4.9 x 1018 molec cm-3, at a total pressure of 740 Torr. In the experiments performed at 20 Torr in argon, epoxides were found in all reactions as main products. The measured molar yields were 95.3% for 2,3-dimethyl-2-butene, 50% for cis- and trans-2-butene and 20% for isoprene. In the experiments performed at 740 Torr air, epoxides were below the detection limit in the case of cis- and trans-2-butene and isoprene, whereas a yield of 17.4% of the epoxide was measured in the 2,3-dimethyl-2-butene experiments. Possible reaction mechanisms explaining the experimental results are discussed. Epoxide formation in the nighttime reaction of NO3 with 2,3-dimethyl-2-butene, cis- or trans-2-butene or isoprene was studied in a 480 l reaction chamber with in situ FTIR spectroscopy as analytical technique. Most experiments were carried out at either 20 Torr in argon or at 740 Torr in synthetic air. In the case of 2,3-dimethyl-2-butene the epoxide formation was studied in the range 20-740 Torr using either argon or air as diluent gas and its O2 dependence was studied in N2/O2 mixtures with O2 concentrations in the range 1.7 × 1015-4.9 × 1018 molec cm-3, at a total pressure of 740 Torr. In the experiments performed at 20 Torr in argon, epoxides were found in all reactions as main products. The measured molar yields were 95.3% for 2,3-dimethyl-2-butene, 50% for cis- and trans-2-butene and 20% for isoprene. In the experiments performed at 740 Torr air, epoxides were below the detection limit in the case of cis- and trans-2-butene and isoprene, whereas a yield of 17.4% of the epoxide was measured in the 2,3-dimethyl-2-butene experiments. Possible reaction mechanisms explaining the experimental results are discussed.
- Skov,Benter Th.,Schindler,Hjorth,Restelli
-
p. 1583 - 1592
(2007/10/03)
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- REMPI-MS and FTIR Study of NO2 and Oxirane Formation in the Reactions of Unsaturated Hydrocarbons with NO3 Radicals
-
The yields of NO2 and oxirane have been studied as a function of pressure in the reactions of NO3 with selected unsaturated hydrocarbons.NO2 yields were determined using a flow system with double resonance REMPI-MS technique in the range 1-30 mbar, argon being the buffer gas.The yields of oxiranes were studied using in situ FTIR technique in a static system in the pressure range 30-1000 mbar.With styrene, oxirane formation was also determined by REMPI-MS.The experiments revealed that the NO2 yields decreased strongly with pressure in the case of aliphatic dienes and styrene, whereas only a negligible pressure dependence of NO2 formation was observed with alkenes or cyclic dienes.These results were confirmed for 2,3-dimethyl-2-butene and for isoprene in the FTIR experiments in which the corresponding oxirane yields were measured at up to 1000 mbar of argon.Air as buffer gas reduced oxirane formation.In the reaction of cis-2-butene and trans-2-butene with NO3 similar yields of trans-2,3-dimethyloxirane were obtained.This finding is taken as the most direct evidence for the NO3 radical addition to the carbon double bond in alkenes in the primary reaction step in agreement with previous assumptions.
- Benter, Th.,Liesner, M.,Schindler, R. N.,Skov, H.,Hjorth, J.,Restelli, G.
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p. 10492 - 10496
(2007/10/02)
-
- Kinetics of oxirane formation in the reaction of nitrate radicals with tetramethylethylene
-
The kinetics of oxirane formation in the reaction of nitrate radicals with tetramethylethylene was investigated in a flow system at room temperature. Total pressure ranged from 5 to 1000 mbar. Using inert gas (He, N2) tetramethyloxirane only was detected as reaction product. In the case of synthetic air acetone also is formed in dependence of the system pressure. With increasing pressure the oxirane yield decreases and the acetone yield increases. Under tropospheric conditions 20% tetramethyloxirane was found. It is concluded that the oxirane observed results from the excited adduct formed in the electrophilic addition of the nitrate radical to the double bond. In the absence of O2 the quenched adduct radical formes oxirane in a thermal reaction also.
- Berndt,Boge
-
p. 869 - 871
(2007/10/02)
-