Showing papers on "Styrene oxide published in 2004"

Styrene oxidation with H2O2 over Ti-containing molecular sieves with MFI, BEA and MCM-41 topologies

Abstract: A comparative study concerning the use of Ti-containing molecular sieves with MFI (TS-1), BEA (Ti-beta) and MCM-41 (TiMCM-41) topologies for the styrene oxidation in liquid phase by hydrogen peroxide was performed. The major reactions were epoxidation of styrene, the isomerization of styrene oxide into phenylacetaldehyde (PhAA) as well as its oxidative cleavage into benzaldehyde (BzA) and formaldehyde. A high selectivity to PhAA was observed over TS-1, whereas the BzA formation is predominant on Ti-beta and TiMCM-41. Also, the influence of the reaction time and the nature of solvent on the styrene conversion, the selectivity of hydrogen peroxide consumption and on the product distribution were studied.

Donor Ligand Effect on the Nature of the Oxygenating Species in MnIII(salen)-Catalyzed Epoxidation of Olefins: Experimental Evidence for Multiple Active Oxidants

Abstract: The stereoselectivity of olefin epoxidation catalyzed by MnIII(salen)X (1a, X = Cl-; 1b, X = BF4-) complexes is examined in the presence of neutral donor ligands, employing various iodosylarenes (ArIO: PhIO, C6F5IO, and MesIO) as the oxygen atom source. The cis/trans ratios of stilbene oxides and the enantiomeric excesses of styrene oxide and 1,2-dihydronaphthalene oxide are found to be strongly dependent on the nature of the iodosylarenes under certain conditions. In other cases, olefin epoxidation is shown to proceed with essentially identical diastereoselectivities or enantioselectivities, regardless of the oxygen atom source used. We propose that a MnV(salen)-oxo intermediate and a complex between the catalyst and the terminal oxidant competitively effect the epoxidation when the stereoselectivities are markedly dependent on the oxygen atom source. A single MnV(salen)-oxo species is considered to be the sole oxygenating intermediate when the terminal oxidants do not exert a notable influence on the p...

Shape-controlled preparation and catalytic activity of metal nanoparticles for hydrogenation of 2-butyne-1,4-diol and styrene oxide

Abstract: Stable nanocluster catalysts prepared by chemical and γ-radiolytic reduction methods were found to give very high turn-over frequency numbers in hydrogenation of styrene oxide and 2-butyne-1,4-diol (B3D) as compared to the conventional catalysts. A systematic study was carried out on the effects of different transition metals, their reduction methods, types of polymer used as a capping agent, and the concentration and composition of solvent used during catalyst preparation on the size and shape of nanoparticles. The reduction method of metal precursor directly influenced the morphology of the nanoparticles, affecting the catalyst activity considerably. The cubic-shaped nanoparticles (5–7 nm) were obtained in chemical reduction, while radiolytic reduction method gave spherical nanoparticles (1–7 nm).

An efficient synthesis of 2-amino alcohols by silica gel catalysed opening of epoxide rings by amines

Abstract: Silica gel (60–120 mesh) efficiently catalyses the opening of epoxide rings by amines at rt under solvent-free conditions providing an easy method for the synthesis of 2-amino alcohols. Aromatic and aliphatic amines react with cyclohexene oxide with exclusive formation of the trans-2-aryl/alkylaminocyclohexanols in high yields. A complementary regioselectivity is exhibited by aromatic and aliphatic amines during the reaction with styrene oxide. The epoxide ring of non-styrenoidal unsymmetrical alkene oxide undergoes selective nucleophilic attack at the sterically less hindered carbon by aniline.

Enzymatic transformations. Part 58: Enantioconvergent biohydrolysis of styrene oxide derivatives catalysed by the Solanum tuberosum epoxide hydrolase

Abstract: The biohydrolysis of four racemic styrene oxide derivatives has been explored, using the (recombinant) Solanum tuberosum epoxide hydrolase. Interestingly, this enzyme showed a marked tendency to operate a so-called enantioconvergent process, thus affording the corresponding (R)-diol in a nearly quantitative yield and good to excellent ee. We have demonstrated that this is due to the fact that the (S)-enantiomer of these epoxides was preferably attacked at the (benzylic) more substituted carbon atom, whereas the (R)-epoxide was attacked at the (terminal) less substituted carbon atom. The thus obtained meta- and para-chlorostyrene diol derivatives are important building blocks in the synthesis of various biologically active molecules. A nine cycles repeated batch reactor was performed starting from racemic meta-chlorostyrene oxide and afforded a 100% analytical yield (88% preparative) of the corresponding diol, obtained with ees as high as 97%.

Epoxidation of styrene by anhydrous t-butyl hydroperoxide over gold supported on Al2O3, Ga2O3, In2O3 and Tl2O3

Abstract: Group IIIa metal (viz. Al, Ga, In and Tl) oxide-supported gold nanoparticles, prepared by deposition–precipitation (DP) using NaOH and by homogeneous deposition–precipitation (HDP) using urea, were employed as highly active/selective and reusable catalysts for the epoxidation of styrene (at 82 °C) by anhydrous t -butyl hydroperoxide (TBHP). The loading and average particle size of gold, when it was deposited on the Gr. IIIa metal oxides by the HDP, was found to increase in the following order: Al 2 O 3 (6.36 wt.%, 4.1 ± 2.3 nm) 2 O 3 (6.43 wt.%, 6.67 ± 3.7 nm) 2 O 3 (6.81 wt.%, 15.6 ± 6.3 nm) 2 O 3 (8.00 wt.%, 24.4 ± 13.1 nm). Both the activity and the epoxide selectivity of the supported gold catalysts are in the following order: Au/Al 2 O 3 2 O 3 2 O 3 2 O 3 . Using the DP method, the Au loading on Al 2 O 3 and Tl 2 O 3 was found to be 2.10 and 5.42 wt.%, respectively, such values are much lower than those achieved by the HDP method. The Al 2 O 3 , Ga 2 O 3 and In 2 O 3 supports alone showed little or no epoxidation activity/selectivity. However, the Tl 2 O 3 support alone showed the activity and epoxide selectivity comparable to that of the Au/Tl 2 O 3 catalysts. The surface species on the Au/Al 2 O 3 were found to be only metallic gold (Au 0 ) ones and Al in single oxidation state (Al 3+ ). However, the surface species on the Au/In 2 O 3 were both the metallic and ionic gold (Au 0 and Au 3+ ) and the indium in two oxidation states (In 3+ and In 2+ or In 1+ ). The gold loading and both the epoxidation activity and selectivity are increased with increasing the basicity and/or reduction potential of the support used in the supported Au catalysts.

Colorimetric High-Throughput Assay for Alkene Epoxidation Catalyzed by Cytochrome P450 BM-3 Variant 139-3

Abstract: Cytochrome P450 BM-3 variant 139-3 is highly active in the hydroxylation of alkanes and fatty acids (AGlieder, ET Farinas, and FH Arnold, Nature Biotech 2002;20:1135-1139); it also epoxidizes various alkenes, including styrene. Here the authors describe a colorimetric, high-throughput assay suitable for optimizing this latter activity by directed evolution. The product of styrene oxidation by 139-3, styrene oxide, reacts with the nucleophile γ-(4-nitrobenzyl)pyridine (NBP) to form a purple-colored precursor dye, which can be monitored spectrophotometrically in cell lysates. The sensitivity limit of this assay is 50-100 μ Mof product, and the detection limit for P450 BM-3 139-3 is ~0.2 μ Mof enzyme. To validate the assay, activities in a small library of random mutants were compared to those determined using an NADPH depletion assay for initial turnover rates. (Journal of Biomolecular Screening 2004:141-146)

Epoxidation of Styrene by Anhydrous t-Butyl Hydroperoxide over Au/TiO2 Catalysts

Abstract: Nanosize gold deposited on TiO2, by homogeneous deposition-precipitation (HDP) using urea as the precipitation agent is an active/selective and reusable catalyst for the epoxidation of styrene (at 82°C) by anhydrous t-butyl hydroperoxide (TBHP) The activity and epoxide selectivity of the Au/TiO2 catalyst in the epoxidation is increased with increasing the Au loading on the TiO2 support The Au/TiO2catalyst prepared by the deposition precipitation using sodium hydroxide as the precipitation agent (DP method) has much lower gold loading and also lower Au dispersion and consequently possesses lower epoxidation activity as compared to that prepared by the HDP method The styrene oxide selectivity is not influenced very significantly by the catalyst preparation method or by the Au loading (except at the very low Au loading) In the Au/TiO2 catalysts prepared by both the methods, Au is found to exist in both the metallic (Au°) and cationic (Au3+) forms

Epoxidation of styrene by t-butyl hydroperoxide over gold supported on Yb2O3 and other rare earth oxides

Abstract: Gold nanoparticles deposited [by homogeneous deposition-precipitation (HDP) using urea] on Yb 2 O 3 and other rare-earth oxides (viz. Sm 2 O 3 , Eu 2 O 3 , and Tb 2 O 3 ) are novel highly active/selective and reusable catalysts for the selective epoxidation of styrene to styrene oxide by anhydrous or aqueous t-butyl hydroperoxide and no problems are foreseen for a large scale operation of this green process.

Enantioselective Hydrolytic Kinetic Resolution of Epoxides Catalyzed by Chiral Co(III) Salen Complexes Immobilized in the Membrane Reactor

Abstract: The supported ZSM-5 film was synthesized hydrothermally on the porous supports such as Anodisc and alumina tube. The enantioselective hydrolytic resolution of racemic epoxides was performed in the ZSM-5/Anodisc membrane reactor containing chiral salen complexes. The chiral (Co-salen)+PF6- and (Co-salen)+BF4- complexes immobilized on the membrane showed a very high enantioselectivity and recyclability in the hydrolysis of epichlorohydrine, 1,2-epoxybutane, 1,2-epoxyhexane and styrene oxide. It was easy to separate the products, and the catalysts could be recycled without observable loss in activity and enantioselectivity using the batch-type and continuous-type membrane reactor. The obtained epoxide product remained in the organic phase and the hydrophilic water-soluble diols diffused into the aqueous phase through the ZSM-5 film layer.

Gelation of concentrated micellar solutions of a triblock copolymer of ethylene oxide and styrene oxide, S5E45S5.

Abstract: Triblock copolymer S5E45S5 was synthesized by oxyanionic polymerization of styrene oxide initiated by a preformed difunctional polyethylene glycol. Here E denotes OCH2CH2, S denotes OCH2CH(C6H5), and the subscripts denote number-average block lengths in repeat units. Previous work on the closely related copolymer S4E45S4 indicated that micelles would form in aqueous solutions of copolymer S5E45S5, and that they would undergo transient intermicellar bridging. Dynamic light scattering was used to confirm this. Rheometry and small-angle X-ray scattering were used to explore gel boundaries, structures, and properties. At moderate copolymer concentrations (14 and 20 wt %) measurements of the dynamic shear moduli indicated the formation of low-modulus soft gels attributed to spherical micelles forming transient networks. A region of low storage modulus at c approximately 30 wt % preceded a change to hard gel. A 40 wt % hard gel was disordered, while at higher concentrations (49 and 60 wt %) the micelles packed into hexagonal structures with high values of the storage modulus (G' approximately 10 kPa at 25 degrees C and 1 Hz).

Functionalization of Poly(styryl)lithium with Styrene Oxide

Abstract: The functionalization of poly(styryl)lithium with styrene oxide as a route to functional polymers was investigated. When the reaction was performed in benzene at room temperature, analysis of the products by SEC and column chromatography indicated the presence of functional polymer (83.5 wt %), along with unfunctionalized polymer (9.0 wt %), dimeric product (5.6 wt %), and trimeric product (0.1 wt %). The structure of the dimeric product was determined to be head-to-head dimer from both 13C NMR analysis and MALDI−TOF MS and was proposed to result from an electron-transfer mechanism. The dimeric product was eliminated when the functionalization was effected in the presence of tetrahydrofuran (>15 mol equiv). Under these conditions >99 wt % functionalized polymer was obtained as determined by column chromatography and MALDI−TOF MS. Addition of PSLi to the epoxide can occur by addition to the least hindered carbon or by addition to the most hindered carbon. Analysis of the regiochemistry of the chain end was...

Influence of selected inhibitors on the metabolism of the styrene metabolite 4-vinylphenol in wild-type and CYP2E1 knockout mice.

Abstract: 4-Vinylphenol (4-VP), a minor metabolite of styrene, is a more potent hepato- and pneumotoxicant than either styrene or styrene oxide. In CD-1 mice 4-VP is metabolized primarily by cytochrome P-450 (CYP) 2E1 and CYP2F2. However, there is no difference in the rate of metabolism of 4-VP between wild-type and CYP2E1 knockout mice, indicating that other cytochromes P-450 play an important role. To understand the role of various cytochromes P-450, the in vitro metabolism of 4-VP was measured in the presence of selected inhibitors. Chemical inhibitors used to ascertain the contributions made by various cytochromes P450 were imipramine for CYP2C, alpha-methylbenzylaminobenzotriazole (MBA) for CYP2B, alpha-naphthoflavone (ANF) for CYP1A, 5-phenyl-1-pentyne (5P1P) for CYP2F2, and diethyldithiocarbamate (DTTC) for CYP2E1. Imipramine, MBA, and ANF produced significant inhibition in both the wild-type and CYP2E1 knockout mouse liver with minimal effects in lung. 5P1P significantly inhibited enzymic activity in both tissues, but to a greater extent in lung. The greatest inhibition was observed with DDTC even in the knockout mice, suggesting that it must also inhibit cytochromes P-450 in addition to CYP2E1. The results show little difference between the wild-type and knockout mice with respect to the contributions made by the cytochromes P-450 in the metabolism of 4-VP.

An improved catalytic process for the preparation of epoxides from alkenes

Abstract: An improved catalytic process for the preparation of epoxides from alkenes using a combination of transition metal salt, an inorganic promoter and an organic additive in absence of solvent or in the presence of a solvent with commercially available hydrogen per oxide has been disclosed. Thus, styrene oxide was prepared at a kilogram scale in 86% isolated yield with purity >95 %.

Mesoporous nickelsilicate membranes on porous alumina supports. II. Catalytic reactor for oxidation of aromatic hydrocarbons

Abstract: After successful synthesis and gas permeation study of ordered mesoporous nickelsilicate membranes on porous Al2O3 substrates, their catalytic properties have been evaluated in the reaction of styrene and benzene with H2O2. Nickelsilicate membranes have active properties for oxidation of styrene and benzene between 297 and 343 K. The effect of permeance of oxidant agent on the catalytic activity of membranes has been studied. Comparative experiments of the membrane reactor and batch reactor with the same catalyst (Ni-MCM-41) in power form revealed quite interesting observation that the oxidation of styrene with membrane reactor conducts to the formation of epoxy ethyl benzene (styrene oxide) while the conventional batch reactor with powdery catalyst gives selectively benzaldehyde. The activity and selectivity of nickelsilicate membrane catalysts have been correlated with their mesoporous structure, permeation properties and characteristics inherent to membrane reactor. It was found that the control of the oxygen peroxide feed and short residence and contact time of reactants and oxidant in membrane reactor result in the selectivity of styrene oxidation to styrene oxide instead of benzaldehyde, a deeper oxidation product, observed in batch reactor. The present paper supplies important information on designing highly efficient and selective catalytic membrane processes.

Metabolism and Toxicity of the Styrene Metabolite 4-Vinylphenol in CYP2E1 Knockout Mice

Abstract: 4-Vinylphenol (4-VP) is a minor metabolite of styrene and is several times more potent as a hepatotoxicant and pneumotoxicant than is either the parent compound or the major metabolite of styrene, styrene oxide 4-VP is metabolized primarily by CYP2E1 and CYP2F2 To further elucidate the possible role of 4-VP in styrene-induced toxicity and the importance of its metabolism by CYP2E1, the metabolism of 4-VP and its hepatotoxicity and pneumotoxicity were compared in wild-type and CYP2E1 knockout mice There were no marked differences between the wild-type and knockout mice in the rates of microsomal metabolism of 4-VP in either liver or lung This unexpected result mimics previous findings with styrene metabolism in wild-type and knockout mice When mice were administered 100 mg/kg 4-VP ip, the knockout mice were more susceptible to hepatotoxicity, as measured by increases in serum sorbitol dehydrogenase activity, than were the wild-type mice There was no significant difference in the pneumotoxicity betwee

Synthesis of polycarbonate monomers by CO2 insertion in epoxides over zeolite-based catalysts

Abstract: A novel application of molecular sieves in the synthesis of cyclic carbonate monomers of polycarbonates is reported. Titanosilicate molecular sieves (TS-1 and TiMCM-41) and zeolite-Y-encapsulated metal phthalocyanines (MPc-Y; M = Al, Cu, Co and Ni) are highly active in the coupling reaction of CO 2 with epoxides, like epichlorohydrin, propylene oxide and styrene oxide, to yield cyclic carbonates at low temperatures and pressures. The cyclic carbonates can also be prepared from the olefins in the same reactor by reacting the olefins with a mixture of an epoxidizing agent (like H 2 O 2 , tert -butyydroperoxide and dioxygen) and CO 2 over titanosilicate molecular sieves or zeolite-Y-encapsulated metal phthalocyanines. A novel transesteriflcation of the cyclic carbonates with methanol and phenol over TiMCM-41 yielded the corresponding dimethyl and diphenyl carbonate monomers, thereby opening a “clean technology“ route for polycarbonates avoiding currently used toxic and hazardous chemicals, like phosgene or carbon monoxide.