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Epoxidation
Kinds of Epoxidation Terms modified by Epoxidation Selected AbstractsSolvent Effects on Catalytic Epoxidation of Alkenes by Tetra- n -butylammonium Periodate and (Tetraarylporphyrinato)manganese(III)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2008Daryoush Mohajer Abstract The epoxidation of cyclooctene and cis -stilbene was performed by tetra- n -butylammonium periodate (nBu4NIO4)in the presence of (tetraarylporphyrinato)manganese(III) [Mn(por)] and imidazole (im) in various CH2Cl2/alcohol solvents (alcohol = CH3OH, C2H5OH, n -C3H7OH, i -C3H7OH, t -C4H9OH). In accord with the coordinating abilities of the alcohols to [Mn(por)], the epoxidation yields increased from CH2Cl2/CH3OH to CH2Cl2/t -C4H9OH. In the epoxidation of cis -stilbene in the presence of (acetato)(tetraphenylporphyrinato)manganese(III) [Mn(tpp)(OAc)], the cis - to trans -stilbene oxide ratio increased consistently with the bulk of the alcohol in CH2Cl2/alcohol solvents. Also, it was found that the interaction of [Mn(tpp)(OAc)] and (acetato)(tetramesitylporphyrinato)manganese(III) [Mn(tmp)(OAc)] with nBu4NIO4 in the presence of imidazole but in the absence of alkenes yields [Mn(tpp)(O)(im)]+ and [Mn(tmp)(O)(im)]+ complexes. The formation of the Mn=O species for the small linear alcohols was faster than that for the larger ones, whereas the stability of the Mn=O complex was greater in the presence of the bulkier alcohols. Attempts were made to explain these effects.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Incorporation of a (Cyclopentadienyl)molybdenum Oxo Complex in MCM-41 and Its Use as a Catalyst for Olefin EpoxidationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2004Marta Abrantes Abstract The tricarbonyl complex [(,5 -C5H4 -COOMe)Mo(CO)3Cl] was prepared from the reaction of sodium (methoxycarbonyl)cyclopentadienide, (C5H4 -CO2Me)Na, with (Bu4N)[Mo(CO)5I]. Heating the ester with 3-(triethoxysilyl)propylamine gave the amide derivative {[,5 -C5H4 -CONH-C3H6Si(OEt)3]Mo(CO)3Cl}. The functionalised tricarbonyl complex was immobilised in the ordered mesoporous silica MCM-41 with a loading of 13 wt.-% Mo (1.4 mmol·g,1) by carrying out a grafting reaction in dichloromethane. Powder X-ray diffraction and nitrogen adsorption,desorption analysis indicated that the structural integrity of the support was preserved during the grafting and that the channels remained accessible, despite significant reductions in surface area, pore volume and pore size. The success of the coupling reaction was confirmed by 29Si and 13C (CP) MAS NMR spectroscopy. A supported dioxo complex of the type [(,5 -C5H4R)MoO2Cl] was subsequently prepared by oxidative decarbonylation of the tethered tricarbonyl complex using tert -butyl hydroperoxide (TBHP). The oxidised material is an active catalyst for the liquid phase epoxidation of cyclooctene with TBHP as the oxygen source. Similar catalytic results were obtained using the tethered tricarbonyl complex directly as a pre-catalyst since fast oxidative decarbonylation occurs under the reaction conditions used. For both systems, the desired epoxide was the only product and the initial activities were about 13 mol·molMo,1·h,1. The solid catalysts were recycled several times. Some activity was lost between the first and second runs but thereafter tended to stabilise. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis of Both Enantiomers of Conduritol C Tetraacetate and of meso -Conduritol D Tetraacetate by Oxidation of Benzoquinone Bis(ethylene acetal)EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2007Martin Lang Abstract Epoxidation of p -benzoquinone bis(ethylene acetal) (1) with m -chloroperbenzoic acid or hydrogen peroxide/benzonitrile afforded corresponding monoepoxide 2, which was converted into p -benzoquinone mono(ethylene acetal) monoepoxide 5 with perchloric acid. Dihydroxylation of 1 with osmium tetroxide or ruthenium trichloride/sodium periodate afforded corresponding cis -diol 6, which was subsequently acetylated to give diacetate 7. One ethyleneacetal moiety in 7 could be selectively hydrolyzed with silica gel/ferric chloride under solvent-free conditions to give ketone 8, which, upon reduction with sodium borohydride and subsequent acetylation of the formed alcohol group, afforded two diastereomeric triacetates 10. Hydrolysis of the remaining acetal functions in the two diastereomers 10, followed by reduction of the second carbonyl group as described above, afforded racemic conduritol C and meso -conduritol D tetraacetates 12 and 13, respectively. Enzymatic resolution of the racemic arabino -configured triacetate 10 with Lipozym failed, while the ribo -configured counterpart reacted smoothly to give enantiomerically pure D - ribo - and L - ribo -configured triacetates 10. The latter pair of enantiomerically pure triacetates were converted into both enantiomers of conduritol C tetraacetate 13 as described for the racemic compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Activation Parameters for the Epoxidation of Substituted cis/trans Pairs of 1,2-Dialkylalkenes by DimethyldioxiraneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2006Brian S. Crow Abstract The first activation parameter data for the reaction of dimethyldioxirane (1) with five cis/trans pairs of alkenes are reported. The epoxidation of cis -1,2-dialkylalkenes (2cis: R1 = Me, R2 = iPr; 3cis: R1 = Me, R2 = tBu; 4cis: R1 = R2 = Et; 5cis: R1 = Et, R2 = iPr; 6cis: R1 = Et, R2 = tBu) and trans -1,2-dialkylalkenes (2trans: R1 = Me, R2 = iPr; 3trans: R1 = Me, R2 = tBu; 4trans: R1 = R2 = Et; 5trans: R1 = Et, R2 = iPr; 6trans: R1 = Et, R2 = tBu) by 1 produced the corresponding epoxides, quantitatively and stereospecifically, as the sole observable products. Activation parameters of the epoxidation of the five pairs of alkenes, 2cis,6cis and 2trans,6trans, by 1 were determined using the Arrhenius method. Enhanced selectivity for cis - vs. trans -alkene epoxidation was observed at lower temperatures. In general, the ,G, terms were larger and showed more variability for the reaction of 1 with trans -alkenes as compared to those for the corresponding cis isomers. The ,H, terms mirrored trends observed in ,G, because ,S, terms for all ten of the compounds were roughly identical. The ,,G, values, a comparison of the trans to the cis isomer data, yielded positive values of 1.2 to 1.8 kcal/mol for the five sets of data and appeared to be dependent on relative steric interactions. The experimental activation parameter data, consistent with predictions from ab initio calculations based on a spiro transition-state model, showed that the lower reactivity of trans -alkenes is due to enthalpy factors. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Kinetics of (Porphyrin)manganese(III)-Catalyzed Olefin Epoxidation with a Soluble Iodosylbenzene DerivativeEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2006James P. Collman Abstract We examined the kinetics of a well-behaved system for homogeneous porphyrin-catalyzed olefin epoxidation with a soluble iodosylbenzene derivative 1 as the terminal oxidant and Mn(TPFPP)Cl (2) as the catalyst. The epoxidation rates were measured by using the initial rate method, and the epoxidation products were determined by gas chromatography. The epoxidation rate was found to be first order with respect to the porphyrin catalyst and zero order on the terminal oxidant. In addition, we found the rate law to be sensitive to the nature and concentration of olefin substrates. Saturation kinetics were observed with all olefin substrates at high olefin concentrations, and the kinetic data are consistent with a Michaelis,Menten kinetic model. According to the observed saturation kinetic results, we propose that there is a complexation between the active oxidant and the substrate, and the rate-determining step is thought to be the breakdown of this putative substrate,oxidant complex that generates the epoxidation products and the resting state porphyrin catalyst. Competitive epoxidations further indicate a reversible complexation of the active oxidant and the olefin substrate. The activation parameters ,H, and ,S, for the oxygen-transfer process (k2) in the cis -cyclooctene epoxidation were determined to be 12.3,±,0.9 kcal,mol,1 and,15.6,±,3.2 cal,mol,1,K,1, respectively. In addition, the Hammett constant ,+ was measured for the epoxidation of para -substituted styrenes, and the value of ,0.27,±,0.04 is too low to be consistent with the involvement of a discrete carbocation in the transition state. We also prepared a (porphyrin)manganese catalyst immobilized on silica support, and found the epoxidation of cis -cyclooctene catalyzed by this heterogeneous catalyst proceeds at virtually the same turnover frequency as by the homogeneous porphyrin catalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Selectivity Enhancement for the Jacobsen,Katsuki Epoxidation in Fluorinated SolventsHELVETICA CHIMICA ACTA, Issue 4 2009Nizam Havare Abstract In 1,1,1,2,3,4,4,5,5,5-Decafluoropentane using 2-phenylpyridine N- oxide as donor ligand, the enantioselectivity of the Jacobsen,Katsuki epoxidation is improved up to 10% ee as compared to established protocols. [source] Epoxidation of Polyunsaturated Fatty Acid Double Bonds by Dioxirane Reagent: Regioselectivity and Lipid Supramolecular OrganizationHELVETICA CHIMICA ACTA, Issue 10 2006Stanislav Abstract The use of dimethyldioxirane (DMD) as the epoxidizing agent for polyunsaturated fatty acids was investigated. With fatty acid methyl esters, this is a convenient method for avoiding acidic conditions, using different solvents, and simplifying the isolation procedures, with less contamination due to by-products. The reagent was also tested with free fatty acids in water. In this case, the supramolecular organization of fatty acids influenced the reaction outcome, and the epoxidation showed interesting regioselective features. The CC bonds closest to the aqueous-micelle interface is the most favored for the interaction with dimethyldioxirane. The preferential epoxidation of linoleic acid (=,(9Z,12Z)-octadeca-9,12-dienoic acid) to the 9,10-monoepoxy derivative was achieved, with a high yield and 65% regioselectivity. In case of arachidonic acid (=,(5Z,8Z,11Z,14Z)-eicosa-5,8,11,14-tetraenoic acid) micelles, the regioselective outcome with formation of the four possible monoepoxy isomers was studied under different conditions. It resulted to be a convenient synthesis of ,cis -5,6-epoxyeicosatrienoic acid' (=,3-[(2Z,5Z,8Z)-tetradeca-2,5,8-trienyl]oxiran-2-butanoic acid), whereas in reverse micelles, epoxidation mostly gave ,cis -14,15-epoxyeicosatrienoic acid (=,(5Z,8Z,11Z)-13-(3-pentyloxiran-2-yl)trideca-5,8,11-trienoic acid). [source] Grafting of Molecularly Ordered Mesoporous Phenylene-Silica with Molybdenum Carbonyl Complexes: Efficient Heterogeneous Catalysts for the Epoxidation of OlefinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Abstract Arenetricarbonyl complexes, or the general formula C6H4Mo(CO)3, were incorporated into crystal-like mesoporous phenylene-silica by liquid-phase deposition of molybdenum hexacarbonyl [Mo(CO)6]. By adjusting the reaction conditions, different molybdenum loadings of 1.5 and 5.9,wt% were obtained, which correspond to 3% and 14% of the phenylene contents. The texture properties of the materials as well as the nature of the surface-fixed complexes were characterized by powder X-ray diffraction, transmission electron microscopy (TEM), N2 adsorption, FT-IR, UV-vis and MAS (13C, 29Si) NMR spectroscopy. The derivatized organosilicas were examined as catalyst precursors for the liquid-phase epoxidation of cis -cyclooctene, 1-octene, trans -2-octene and (R)-(+)-limonene at 55,°C, using tert -butyl hydroperoxide as the oxidant. For each olefin the corresponding epoxide was the only product detected. In the case of cyclooctene, the intrinsic reaction rates per surface molybdenum atom were similar for both Mo loadings (TOF,1150 mol,molMo,1,h,1), suggesting that the resultant materials act as single site epoxidation catalysts. Leaching tests and metal analyses of reaction solutions showed that the catalytic activity stemmed from the immobilized species and not from the leaching of active species into solution. The oxidation of limonene gave limonene oxide as the only product in 95% yield at 3,h, which reveals an outstanding regioselectivity to the epoxidation of the endocyclic double bond. [source] Iron-Catalyzed Epoxidation of Aromatic Olefins and 1,3-DienesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Kristin Schröder Abstract The combination of iron(III) chloride, pyridine-2,6-dicarboxylic acid and formamidine ligands allows for the epoxidation of styrenes and conjugated dienes in excellent chemoselectivity and yields. [source] An Efficient and Selective Epoxidation of Olefins with Novel Methyltrioxorhenium/(Fluorous Ponytailed) 2,2,-Bipyridine CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 8 2010Raffaele Saladino Abstract Novel complexes between methyltrioxorhenium (MTO) and bis(fluorous-ponytailed) 2,2,-bipyridines (bpy-Fn) were synthesized and used for the oxidation of alkenes with hydrogen peroxide under fluorous catalysis. High conversions and yields of the corresponding epoxides were obtained. [source] Highly Enantioselective Epoxidation of Unfunctionalized Olefins Catalyzed by Chiral Jacobsen's Catalyst Immobilized on Phenoxy-Modified Zirconium Poly(syrene-phenylvinylphos- phonate)phosphateADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010Xiaochuan Zou Abstract Chiral Jacobsen's catalyst was axially immobilized onto phenoxy-modified zirconium poly(styrene-phenylvinylphosphonate)phosphate (ZPS-PVPA). The immobilized catalysts show comparable ee values for asymmetric epoxidation of styrene and much higher ee values for ,-methylstyrene (73.7% vs. 54.0%) and indene (99.9% vs. 65.0%) than the homogeneous Jacobsen's catalyst. Moreover, the as-synthesized catalysts are relatively stable and can be recycled at least five times without significant loss of activity and enantioselectivity. A point worth emphasizing is that the heterogeneous catalysts afforded remarkable increases of conversion and ee values in the absence of expensive O-coordinating axial bases for the asymmetric epoxidation of olefins, especially for the epoxidation of ,-methylstyrene (conversion: from 24.3% to 99.9%; ee: from 29.4% to 73.7%), which may overcome the last obstacle for the potential industry application of chiral Jacobsen's catalyst. [source] Productive Asymmetric Styrene Epoxidation Based on a Next Generation Electroenzymatic MethodologyADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Reto Ruinatscha Abstract We have established a novel and scalable methodology for the productive coupling of redox enzymes to reductive electrochemical cofactor regeneration relying on efficient mass transfer of the cofactor to the electron-delivering cathode. Proof of concept is provided by styrene monooxygenase (StyA) catalyzing the asymmetric (S)-epoxidation of styrene with high enantiomeric excess, space-time yields, and current efficiencies. Highly porous reticulated vitreous carbon electrodes, maximized in volumetric surface area, were employed in a flow-through mode to rapidly regenerate the consumed FADH2 cofactor required for StyA activity. A systematic investigation of the parameters determining cofactor mass transfer revealed that low FAD concentrations and high flow rates enabled the continuous synthesis of the product (S)-styrene oxide at high rates, while at the same time the accumulation of the side-products acetophenone and phenylacetaldehyde was minimized. At 10,,M FAD and a flow rate of 150,mL,min,1, an average space-time yield of 0.35,g,L,1,h,1 could be achieved during 2,h with a final (S)-styrene oxide yield of 75.2%. At two-fold lower aeration rates, the electroenzymatic reaction could be sustained for 12,h, albeit at the expense of lower (59%) overall space-time yields. Under these conditions, as much as 20.5% of the utilized current could be channeled into (S)-styrene oxide formation. In comparison with state-of-the-art electroenzymatic methodologies for the same conversion, (S)-styrene oxide synthesis could be improved up to 150-fold with respect to both reaction time and space-time yield. These productivities constitute the most efficient reaction reported for asymmetric in vitro epoxidations of styrene. [source] Highly Efficient Asymmetric Epoxidation of Electron-Deficient ,,,-Enones and Related Applications to Organic SynthesisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Changwu Zheng Abstract The asymmetric epoxidation of electron-deficient olefins has been achieved using inexpensive and readily available prolinols as catalysts with good to excellent yields and enantioselectivities. The utility of the resulting chiral epoxides was illustrated by elaboration to several synthetically useful compounds featuring a concise synthesis of (,)-(5R,6S)-balasubramide. [source] Highly Enantioselective Biphasic Iminium-Catalyzed Epoxidation of Alkenes.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009On the Importance of the Counterion, of N(sp2)C(sp3) Rotamers Abstract Diastereomeric biaryliminium cations made of an (Ra)-5,5,,6,6,,7,7,,8,8,-octahydrobinaphthyl core and exocyclic appendages derived from (S)- or (R)-3,3-dimethylbutan-2-amine are effective asymmetric epoxidation catalysts for unfunctionalized alkenes. Herein, we report that the negative counterion of the iminium salts has to be chosen wisely. While the hexafluoroantimonate anion [SbF6,] is optimal for reliable results, one has to be careful about other anions and tetraphenylborate [BPh4,] in particular. We also detail that the so far unexplained "lack" of stereochemical control from the chiral exocyclic appendage in this type of catalysts is due to the existence of atropisomers around the N(sp2)C(sp3) bond that links the azepinium core to the exocyclic stereocenter. Finally, we develop a general model to predict with certainty the high selectivity in the formation of non-racemic epoxides of defined absolute configuration. [source] Iminium Salt-Catalysed Asymmetric Epoxidation using Hydrogen Peroxide as Stoichiometric OxidantADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2008Philip C. Bulman Page Abstract Iminium salt organocatalysts can provide high selectivity and high efficiency in catalytic asymmetric epoxidation. They are normally used in conjunction with Oxone as the stoichiometric oxidant. Oxone, however, has limited stability and is insoluble in most organic solvents; we report here for the first time the development of a reaction system driven by hydrogen peroxide as the stoichiometric oxidant, involving an unusual double catalytic cycle. [source] Amine-Catalyzed Asymmetric Epoxidation of ,,,-Unsaturated AldehydesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2007Gui-Ling Zhao Abstract The direct organocatalytic enantioselective epoxidation of ,,,-unsaturated aldehydes with different peroxides is presented. Proline, chiral pyrrolidine derivatives, and amino acid-derived imidazolidinones catalyze the asymmetric epoxidation of ,,,-unsaturated aldehydes. In particular, protected commercially available ,,,-diphenyl- and ,,,-di(,-naphthyl)-2-prolinols catalyze the asymmetric epoxidation reactions of ,,,-unsaturated aldehydes with high diastereo- and enantioselectivities to furnish the corresponding 2-epoxy aldehydes in high yield with up to 97:3 dr and 98,% ee. The use of non-toxic catalysts, water and hydrogen peroxide, urea hydroperoxide or sodium percarbonate as the oxygen sources could make this reaction environmentally benign. In addition, one-pot direct organocatalytic asymmetric tandem epoxidation-Wittig reactions are described. The reactions were highly diastereo- and enantioselective and provide a rapid access to 2,4-diepoxy aldehydes. Moreover, a highly stereoselective one-pot organocatalytic asymmetric cascade epoxidation-Mannich reaction, which proceeds via the combination of iminium and enamine activation, is presented. The mechanism and stereochemistry of the amino acid- and chiral pyrrolidine-catalyzed direct asymmetric epoxidation of ,,,-unsaturated aldehydes are also discussed. [source] Asymmetric Epoxidation of Olefins by Manganese(III) Complexes Stabilised on Nanocrystalline Magnesium OxideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2006M. Choudary Abstract The asymmetric epoxidation of unfunctionalised olefins to epoxides is realised by using manganese(III) complexes stabilised on nanocrystalline magnesium oxide in the presence (1R,2R)-(,)-diaminocyclohexane as a chiral ligand in good yields and up to 91,% enantiomeric excess. [source] A Simple and Convenient Method for Epoxidation of Olefins without Metal CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2003Markus Klawonn Abstract 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. [source] Epoxidation of allyl alcohol with hydrogen peroxide over titanium silicalite TS-2 catalystJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2007Agnieszka Wróblewska Abstract The influence of the technological parameters on the course of the epoxidation of allyl alcohol with 30% H2O2 in the presence of titanium silicalite TS-2 catalyst and methanol as a solvent was studied. The process was performed in an autoclave at the autogenic pressure. The influence of temperature in the range 20,120 °C, molar ratio of allyl alcohol/H2O2 (1:1,10:1), methanol concentration in the reaction mixture (10,80% w/w), catalyst TS-2 concentration (0.1,2.0% w/w) and reaction time (1,8 h) were investigated. The functions describing the process were: selectivity of transformation to glycidocidol in relation to allyl alcohol consumed, selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed, conversions of allyl alcohol and hydrogen peroxide. Copyright © 2007 Society of Chemical Industry [source] Epoxidation of allyl chloride and hydrogen peroxide over titanium silicalite-1 film on SiO2 pellet supportJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2007Li Wang Abstract Titanium silicalite-1 (TS-1) films were prepared on SiO2 pellet supports via an in situ hydrothermal synthesis method and were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and 29Si magic angle spinning nuclear magnetic resonance (Si MAS NMR). The growth time of TS-1 film had a strong effect on its morphology and the thickness and size of the crystals. The uniformity and thickness of TS-1 films increased with increase of growth times. The epoxidation of allyl chloride (ACH) with dilute hydrogen peroxide to form epichlorohydrin (ECH) over the TS-1 films was carried out in a fixed bed reactor. The conversion of ACH and the selectivity to ECH over the TS-1 films of the second growth were higher than that of the first growth, the third and the fourth growth. And the conversion and selectivity as a function of time-on-stream gave a good stable performance in an extended test up to at least 19 h. The final steady-state conversion and selectivity were approximately 86% and 55%, respectively. Copyright © 2007 Society of Chemical Industry [source] New functionalized polyesters to achieve controlled architecturesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2004Anna Finne Abstract Following our continued interest in the production of bioerodible and biodegradable functional polymers for biomedical applications, we synthesized and characterized new unsaturated polyesters. The presence of functional groups in the polymer backbone provided sites for chemical modification, and through a variation in the structure, the physical properties, such as the hydrophilicity and solubility, could be affected. With 1,1-di- n -butyl-stanna-2,7-dioxacyclo-4-heptene as the initiator in the ring-opening polymerization of polyesters, a new set of functionalized polyesters was created. The polymerization of ,-caprolactone resulted in poly(,-caprolactone) with a double bond incorporated into the structure. The polymers were obtained in a controlled manner with low molecular dispersities. The double bond was previously incorporated into L -lactide polymers, and the two reactions were compared in this study. The conversion of ,-caprolactone, with a degree of polymerization of 50, was completed within 140 min, whereas for L -lactide, only a 45% conversion took place in the same period of time. The dispersities were somewhat higher with ,-caprolactone because of the higher reaction rate and, therefore, lower selectivity. The incorporated CC double bond in the polyesters provided a variety of opportunities for further modifications. In this case, the double bond of the L -lactide macromonomers was oxidized into epoxides. Epoxidation was carried out with m -chloroperoxybenzoic acid as a chemical reagent. The conversion of the double bonds into epoxides was completed, and the obtained yields were good (>95%). As a result of the mild reaction conditions, the epoxidation of the double bond was carried out quantitatively without any side reactions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 444,452, 2004 [source] Metabolism of the major Echinacea alkylamide N -isobutyldodeca-2E,4E,8Z,10Z -tetraenamide by human recombinant cytochrome P450 enzymes and human liver microsomesPHYTOTHERAPY RESEARCH, Issue 8 2010F. Toselli Abstract Echinacea preparations are used for the treatment and prevention of upper respiratory tract infections. The phytochemicals believed responsible for the immunomodulatory properties are the alkylamides found in ethanolic extracts, with one of the most abundant being the N -isobutyldodeca-2E,4E,8Z,10Z -tetraenamide (1). In this study, we evaluated the human cytochrome P450 enzymes involved in the metabolism of this alkylamide using recombinant P450s, human liver microsomes and pure synthetic compound. Epoxidation, N -dealkylation and hydroxylation products were detected, with different relative amounts produced by recombinant P450s and microsomes. The major forms showing activity toward the metabolism of 1 were CYP1A1, CYP1A2 (both producing the same epoxide and N -dealkylation product), CYP2A13 (producing two epoxides), and CYP2D6 (producing two epoxides and an hydroxylated metabolite). Several other forms showed less activity. In incubations with human liver microsomes and selective inhibitors, CYP2E1 was found to be principally responsible for producing the dominant, hydroxylation product, whereas CYP2C9 was the principal source of the epoxides and CYP1A2 was responsible for the dealkylation product. In summary, in this study the relative impacts of the main human xenobiotic-metabolizing cytochrome P450s on the metabolism of a major Echinacea alkylamide have been established and the metabolites formed have been identified. Copyright © 2010 John Wiley & Sons, Ltd. [source] High-Resolution Single-Turnover Mapping Reveals Intraparticle Diffusion Limitation in Ti-MCM-41-Catalyzed Epoxidation,ANGEWANDTE CHEMIE, Issue 5 2010Cremer, Gert De Katalyse in neuem Licht: Mithilfe hochauflösender Fluoreszenzmikroskopie gelang es erstmals, Transportphänomene und deren Rolle in der Katalyse auf Einzelpartikelebene zu kartieren. Der Thiele-Modul konnte partikelweise in nur einem einzigen Experiment gemessen werden, und er beweist das Vorliegen von Diffusionsbeschränkungen bei der Ti-MCM-41-katalysierten Epoxidierung eines fluoreszierenden Reportermoleküls (siehe Bild; TBHP=tert -Butylhydroperoxid). [source] Propene Epoxidation with Dioxygen Catalyzed by Gold Clusters,ANGEWANDTE CHEMIE, Issue 42 2009Jiahui Huang Dr. Weniger als 2.0,nm große Goldcluster , aber keine Goldnanopartikel , auf alkalisiertem Titansilicalit-1 können aus O2 und H2O Hydroperoxid (-OOH) erzeugen. Dieses wird auf benachbarte Ti-Zentren übertragen, wobei Ti-OOH-Gruppen entstehen (siehe Schema), die Propen in Propenepoxid (PO) umwandeln können. [source] Highly Enantioselective Epoxidation of Styrenes Catalyzed by Proline-Derived C1 -Symmetric Titanium(Salan) Complexes,ANGEWANDTE CHEMIE, Issue 40 2009Kazuhiro Matsumoto Dr. Titanhart! Mit neuartigen, von Prolin abgeleiteten C1 -symmetrischen Titan(salan)-Komplexen gelingt die Epoxidierung von Styrolderivaten mit wässrigem Wasserstoffperoxid als Oxidationsmittel mit Enantiomerenüberschüssen zwischen 96 und 98,% (siehe Schema). [source] Epoxidation of Jatropha (Jatropha curcas) oil by peroxyacidsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010Vaibhav V. Goud Abstract Jatropha (Jatropha curcas) oil with iodine value 104 g I2/100 g, and containing 44.7% oleic acid and 31.4% linoleic acid, was epoxidised in situ with hydrogen peroxide (30%) and acetic/formic acid in the presence of catalytic amounts of sulphuric acid. We have compared the kinetics of epoxidation of jatropha oil (JO) by peroxyacetic and peroxyformic acids, in or without toluene at 30, 50, 70, and 85 °C. The effects of temperature and various mole ratios on epoxidation rate, oxirane ring stability, and iodine value of the epoxidised oil were studied, and optimum conditions were established. The rate constants for epoxidation of JO were found to be in the range 0.22,69.4 × 10,6 l.mol,1.s,1 and activation energies were found to be 64.46 KJ.mol,1, 72 KJ.mol,1, 59 KJ.mol,1, 68.24 KJ.mol,1, for peroxyacetic and peroxyformic acids in or without toluene, respectively. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Corrigendum: Cloning and Characterization of the Biosynthetic Gene Cluster of 16-Membered Macrolide Antibiotic FD-891: Involvement of a Dual Functional Cytochrome P450 Monooxygenase Catalyzing Epoxidation and HydroxylationCHEMBIOCHEM, Issue 13 2010Fumitaka Kudo Dr. No abstract is available for this article. [source] ChemInform Abstract: Asymmetric Epoxidation of 2-Arylidene-1,3-diketones: Facile Access to Synthetically Useful Epoxides.CHEMINFORM, Issue 43 2010Alessio Russo Abstract The first asymmetric epoxidation of title arylidenediketones, e.g. (I), (IV) or (VI), is presented. [source] ChemInform Abstract: Synthesis of Salan (Salalen) Ligands Derived from Binaphthol for Titanium-Catalyzed Asymmetric Epoxidation of Olefins with Aqueous H2O2.CHEMINFORM, Issue 34 2010Donglu Xiong Abstract A variety of olefins is efficiently transformed to the corresponding epoxides by Ti-catalyzed asymmetric reaction using novel salan/salalen ligands, e.g. (I) or (II). [source] ChemInform Abstract: One-Pot Synthesis of ,,,-Epoxy Ketones by Palladium-Catalyzed Epoxidation,Oxidation of Terminal Allylic Alcohols.CHEMINFORM, Issue 28 2010Fateh V. Singh Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] | ||||||||||||||||||||||||||||||||||