Showing papers on "Styrene oxide published in 2008"

Enantioselective polymerization of epoxides: a highly active and selective catalyst for the preparation of stereoregular polyethers and enantiopure epoxides.

Abstract: A chiral, bimetallic cobalt catalyst was discovered that is highly active and enantioselective for epoxide polymerization. The enantiomerically pure catalyst system exhibits a stereoselectivity factor (s = kfast/kslow) of 370 for propylene oxide, allowing enantiomerically pure epoxide to be recovered in nearly the maximum theoretical yield. In addition, the racemic catalyst forms highly isotactic poly(propylene oxide) in quantitative yield. The catalyst is active and selective for other epoxides, such as 1-butene oxide, 1-hexene oxide, and styrene oxide.

Mn(III)(salen)-catalyzed synthesis of cyclic organic carbonates from propylene and styrene oxide in “supercritical” CO2

Abstract: Various homogeneous and immobilized manganese-salen complexes were synthesized and tested as catalysts for the formation of cyclic organic carbonates from two liquid epoxides (propylene oxide and styrene oxide) and CO2, which served as reactant and solvent. Reaction rates in terms of turnover frequencies up to 255 molproduct molMn−1 h−1 at 98% selectivity were achieved by optimizing the salen ligand as well as the reaction temperature and CO2 pressure. The reaction rates did not only strongly depend on the kind of salen ligand, the phase behaviour, and the reaction conditions but significant differences were also observed between the epoxide reactants. In addition, two different and simple ways for the immobilization of Mn-salen complexes were examined, among which one led to a highly active, stable and reusable heterogeneized catalyst. In this heterogeneous catalyst the salen ligand was covalently bound to the silica surface and showed low deactivation and almost no leaching of Mn during repetitive use. A coordinatively bound Mn-salen complex resulted in a high loading of the Mn-salen complex on a specially modified silica surface, but was not stable enough. Furthermore, phase behaviour studies and ATR-IR spectroscopic investigations on the product formation are reported that gave further insight into this catalytic reaction taking place at elevated pressure.

Computational study-led organocatalyst design: a novel, highly active urea-based catalyst for addition reactions to epoxides.

Abstract: An in silico study examined the stabilities of hydrogen-bonded complexes between simple thiourea catalysts and three different electrophiles and identified a novel, highly active N-tosyl urea catalyst for the promotion of addition reactions to epoxide electrophiles. Synthesis and evaluation of 6 revealed it to be a powerful catalyst for the addition of 1,2-dimethylindole to styrene oxide under conditions in which simple N,N-bis-aryl ureas and thioureas (including 1) are inactive. Subsequent studies determined 6 to be compatible with a range of indole and epoxide substrates (including (E)-stilbene oxide) and found that relatively poor nucleophiles such as sterically and electronically deactivated anilines, thiophenol, and benzyl alcohol could be efficiently and regioselectively added to oxiranes under mild conditions.

Enantioconvergent bioconversion of p-chlorostyrene oxide to (R)-p-chlorophenyl-1,2-ethandiol by the bacterial epoxide hydrolase of Caulobacter crescentus.

Abstract: The enantioselective hydrolysis of eight racemic styrene oxide derivatives has been investigated by using the recombinant cell containing epoxide hydrolase (EH) of Caulobacter crescentus. Some styrene oxide derivatives were hydrolyzed via enantioconvergent manner so that enantiopure diol products could be prepared with a 100% theoretical yield. The recombinant cell containing C. crescentus EH exhibited an ability to hydrolyze racemic p-chlorostyrene oxide the most enantioconvergently, thus affording the formation of the corresponding (R)-diol with enantiomeric excess (ee) as high as 95% and a 72% yield in preparative-scale (16.8 g/l) bioconversion.

An Exploration of the Coupling Reactions of Epoxides and Carbon Dioxide Catalyzed by Tetramethyltetraazaannulene Chromium(III) Derivatives: Formation of Copolymers versus Cyclic Carbonates

Abstract: The high catalytic activity of a tetramethyltetraazaannulene (tmtaa) chromium complex toward the copolymerization of cyclohexene oxide and carbon dioxide to discriminatively provide poly(cyclohexylene carbonate) has directed further studies into the capabilities of the catalyst system. Various [PPN]X (PPN+ = bis(triphenylphosphoranylidene)ammonium) cocatalysts, where X = Cl, N3, Br, CN, and OBzF5, in the presence of (tmtaa)CrCl were examined for catalytic reactivity and selectivity for polycarbonate formation, achieving turnover frequencies of 1500 h−1 at 80 °C in the case of PPNCl. The catalyst system was examined under varied pressures and found to be active even at 1 bar of CO2 pressure. In addition to cyclohexene oxide, the (tmtaa)CrCl complex was investigated for catalytic activity toward the coupling of carbon dioxide with propylene oxide, isobutylene oxide, 1,2-epoxyhexane, styrene oxide, and 4-vinyl cyclohexene oxide. Activation energies were found for the copolymerization reaction between cyclohe...

Epoxidation of styrene to styrene oxide using carbon dioxide and hydrogen peroxide in ionic liquids

Abstract: The epoxidation of styrene using hydrogen peroxide and compressed CO 2 was conducted in 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4 ]), 1-butyl-3-methylimidazolium hexafluoroborate ([bmim][PF 6 ]), 1-butyl-3-methylimidazolium chloride ([bmim]Cl), 1,1,3,3-tetramethylguanidinium lactate [TMG][Lac], 1,1,3,3-tetramethylguanidinium trifluoroacetate [TMG][CF 3 COO], ethanol, and acetonitrile. It was demonstrated that the reaction could be carried out effectively in [bmim][BF 4 ] or [bmim]Cl without any metallic catalysts. HCO 4 − produced from CO 2 and H 2 O 2 acted as the catalyst. The conversion of styrene and the yield of styrene oxide could reach 95% and 69%, respectively.

Double Metal Cyanides as Efficient Solid Acid Catalysts for Synthesis of β-Amino Alcohols Under Solvent-Free Conditions

Abstract: A novel application of Fe–Zn double metal cyanide complexes as solid, acid catalysts for regioselective synthesis of β-amino alcohols under solvent-free conditions via ring-opening of epoxides with amines is reported for the first time. The conversion of epoxides to β-amino alcohols is nearly 100%. In the reaction with styrene oxide, regioselective β-amino alcohol formation is higher with aromatic than with aliphatic amines. Strong Lewis acidic Zn2+ ions in the catalyst are probably the active sites in this reaction.

Enantioselective resolution of racemic styrene oxide at high concentration using recombinant Pichia pastoris expressing epoxide hydrolase of Rhodotorula glutinis in the presence of surfactant and glycerol.

Abstract: The reaction medium was optimized to accomplish epoxide hydrolase-catalyzed, batch enantioselective hydrolysis of racemic styrene oxide at high initial substrate concentrations. The recombinant Pichia pastoris containing the epoxide hydrolase gene of Rhodotorula glutinis was used as the biocatalyst. Enantiopure (S)-styrene oxide with 98% ee was obtained with 41% yield (maximum yield = 50%) from 1.8 M racemic styrene oxide at pH 8.0, 4°C in the presence of 40% (v/v) Tween 20 and 5% (v/v) glycerol.

Substrate‐dependent hysteretic behavior in StEH1‐catalyzed hydrolysis of styrene oxide derivatives

Abstract: The substrate selectivity and enantioselectivity of Solanum tuberosum epoxide hydrolase 1 (StEH1) have been explored by steady-state and pre-steady-state measurements on a series of styrene oxide derivatives. A preference for the (S)- or (S,S)-enantiomers of styrene oxide, 2-methylstyrene oxide and trans-stilbene oxide was established, with E-values of 43, 160 and 2.9, respectively. Monitoring of the pre-steady-state phase of the reaction with (S,S)-2-methylstyrene oxide revealed two observed rates for alkylenzyme formation. The slower of these rates showed a negative substrate concentration dependence, as did the rate of alkylenzyme formation in the reaction with the (R,R)-enantiomer. Such kinetic behavior is indicative of an additional, off-pathway step in the mechanism, referred to as hysteresis. On the basis of these data, a kinetic mechanism that explains the kinetic behavior with all tested substrates transformed by this enzyme is proposed. Regioselectivity of StEH1 in the catalyzed hydrolysis of 2-methylstyrene oxide was determined by 13C-NMR spectroscopy of 18O-labeled diol products. The (S,S)-enantiomer is attacked exclusively at the C-1 epoxide carbon, whereas the (R,R)-enantiomer is attacked at either position at a ratio of 65 : 35 in favor of the C-1 carbon. On the basis of the results, we conclude that differences in efficiency in stabilization of the alkylenzyme intermediates by StEH1 are important for enantioselectivity with styrene oxide or trans-stilbene oxide as substrate. With 2-methylstyrene oxide, slow conformational changes in the enzyme also influence the catalytic efficiency.

Applications of Calixarenes in Polymer Synthesis

Abstract: The applications of calixarenes in polymer synthesis have been reviewed. Calixarenes have been used as ligands to prepare rare earth calixarene complexes. A series of rare earth calixarene complexes have been synthesized and employed as efficient catalysts for the polymerization of ethylene, styrene, butadiene, propylene oxide, styrene oxide, trimethylene carbonate, and 5,5-dimethyl trimethylene carbonate. On the other hand, the synthesis and characterization of star-shaped polymers with calixarene as core molecules are also described.

Synthesis of Fe‐MCM‐41 from silatrane and FeCl3 via sol–gel process and its epoxidation acivity

Abstract: An iron-containing mesoporous molecular sieve, or Fe-MCM-41, was successfully synthesized the via sol–gel technique using silatrane and FeCl3 as the silicon and iron sources, and was characterized using various techniques. Many factors were investigated, namely, reaction temperature and time, calcination rate, and iron amount in the reaction mixture. It was found that the optimum conditions in which to synthesize Fe-MCM-41 was to carry out the reaction at 60 °C for 7 h using a 1 °C min−1 calcination rate and a 550 °C calcination temperature. The catalytic activity and selectivity of styrene epoxidation using hydrogen peroxide showed that the selectivity of the styrene oxide reached 65% at a styrene conversion of 22% over the 1%wt catalyst. Copyright © 2008 John Wiley & Sons, Ltd.

Oxidation of Styrene and Phenylacetaldehyde on Ag(111): Evidence for Transformation of Surface Oxametallacycle

Abstract: The oxidation of phenylacetaldehyde has been used to help identify intermediates involved in the secondary oxidation reactions of styrene. Besides the epoxidation reaction found for styrene, styrene and phenylacetaldehyde undergo the same secondary oxidation reactions on oxygen-covered Ag(111) to produce CO2, H2O, benzoic acid, benzene, phenyl, biphenyl, and a small amount of benzeneacetic acid. In addition to oxametallacycle and benzoate intermediates, a stable combustion intermediate is identified in the oxidation of styrene on Ag(111). The oxametallacycle and the combustion intermediate evolve into styrene oxide or into other secondary oxidation products, respectively. Isotopic labeling and X-ray photoelectron studies show that the transformation of surface oxametallacycle to the combustion intermediate is kinetically important in determining the selectivity of styrene epoxidation.

One-pot biotransformation of racemic styrene oxide into (R)-1,2-phenylethandiol by two recombinant microbial epoxide hydrolases

Abstract: An enantioconvergent biotransformation of racemic styrene oxide by using two recombinant microbial epoxide hydrolases (EHs) in one pot has been investigated to prepare enantiopure vicinal diols The recombinant whole cell possessing EH gene from Aspergillus niger LK or Rhodotorula glutinis exhibited a complementary enantioselectivity and regioselectivity, compared to the recombinant cell containing Caulobacter crescentus EH gene When two recombinant microbial EHs were used in combination, 13 g of enantiopure (R)-1,2-phenylethandiol with more than 90% enantiopurity and 95% overall yield was obtained from 12 g of racemic styrene oxide in a preparative-scale batch enantioconvergent biotransformation

Reductions of Benzene Derivatives Whose Benzylic Positions Bear Oxygen Atoms under Mild Conditions

Abstract: Reductions of compounds whose benzylic positions bear O-atoms, such as benzyl alcohol, dibenzyl ether, styrene oxide, benzaldehyde, acetophenone, and benzophenone, to the corresponding non-conjugated dienes were performed by using t-BuOH, Li, and gaseous NH3 in THF at room temperature. In these reductions, it was observed that the functional groups at benzylic positions were reduced first.

A cold-adapted epoxide hydrolase from a strict marine bacterium, Sphingophyxis alaskensis.

Abstract: An open reading frame (ORF) encoding a putative epoxide hydrolase (EHase) was identified by analyzing the genome sequence of Sphingophyxis alaskensis. The EHase gene (seh) was cloned and expressed in E. coli. To facilitate purification, the gene was fused in-frame to 6x histidine at the C-terminus. The recombinant EHase (rSEH) was highly soluble and could be purified to apparent homogeneity by one step of metal affinity chromatography. The purified SEH displayed hydrolyzing activities toward various epoxides such as styrene oxide, glycidyl phenyl ether, epoxyhexane, epoxybutane, epichlorohydrin, and epifluorohydrin. The optimum activity toward styrene oxide was observed at pH 6.5 and 35 degrees . The purified SEH showed a cold-adapted property, displaying more than 40% of activity at low temperature of 10 degrees compared with the optimum activity. Despite the catalytic efficiency, the purified SEH did not hydrolyze various epoxides enantioselectively. Km and kcat of SEH toward (R)-styrene oxide were calculated as 4+/-0.3 mM and 7.42 s(-1), respectively, whereas Km and kcat of SEH toward (S)-styrene oxide were 5.25+/-0.3 mM and 10.08 s(-1), respectively.

Control of the Basicity in Ni–MgO Systems: Influence in the Hydrogenation of Styrene Oxide

Abstract: The addition of basic solutions to the reaction medium in the catalytic hydrogenation of styrene oxide improves the selectivity to 2-phenylethanol (used in perfumery) but also can favour condensation reactions. To study the influence of different basic sites on the reaction products, we prepared several catalysts by mixing a commercial magnesia (MgO), and other previously rehydrated (MgOr), with different amounts of NiO followed by reduction (NiMgO, 4NiMgO, NiMgOr, 4NiMgOr), and by mixing directly MgO with Ni (NiMgOa, 4NiMgOa). Ni–MgO catalysts showed the best conversion and selectivity to 2-phenylethanol values, arriving to 100% when increasing the MgO content. Interestingly, CO2-TPD study of catalyst NiMgO indicates that metallic nickel covers the weakest basic sites of magnesia. On the other hand, CO2-TPD profiles of Ni–MgOr and Ni–MgOa catalysts, which present low catalytic activity, showed an important amount of available basic sites that favour the formation of higher amounts of condensation products, which are responsible for the catalyst deactivation.