Showing papers on "Styrene oxide published in 2010"

Cyclic Carbonate Synthesis Catalysed by Bimetallic Aluminium-Salen Complexes

Abstract: The development of bimetallic aluminium-salen complexes [{A1-(salen)} 2 O] as catalysts for the synthesis of cyclic carbonates (including the commercially important ethylene and propylene carbonates) from a wide range of terminal epoxides in the presence of tetrabutylammonium bromide as a cocatalyst is reported. The bimetallic structure of one complex was confirmed by X-ray crystallography. The bimetallic complexes displayed exceptionally high catalytic activity and in the presence of tetrabutylammonium bromide could catalyse cyclic carbonate synthesis at atmospheric pressure and room temperature. Catalyst-reuse experiments demonstrated that one bimetallic complex was stable for over 60 reactions, though the tetrabutylammonium bromide decomposed in situ by a retro-Menschutkin reaction to form tributylamine and had to be regularly replaced. The mild reaction conditions allowed a full analysis of the reaction kinetics to be carried out and this showed that the reaction was first order in aluminium complex concentration, first order in epoxide concentration, first order in carbon dioxide concentration (except when used in excess) and unexpectedly second order in tetrabutylammonium bromide concentration. Further kinetic experiments demonstrated that the tributylamine formed in situ was involved in the catalysis and that addition of butyl bromide to reconvert the tributylamine into tetrabutylammonium bromide resulted in inhibition of the reaction. The reaction kinetics also indicated that no kinetic resolution of racemic epoxides was possible with this class of catalysts, even when the catalyst was derived from a chiral salen ligand. However, it was shown that if enantiomerically pure styrene oxide was used as substrate, then enantiomerically pure styrene carbonate was formed. On the basis of the kinetic and other experimental data, a catalytic cycle that explains why the bimetallic complexes display such high catalytic activity has been developed.

Metal-organic frameworks as efficient heterogeneous catalysts for the regioselective ring opening of epoxides.

Abstract: An iron-based metal―organic framework, [Fe(BTC)] (BTC: 1,3,5-benzenetricarboxylate) is an efficient catalyst in the ring opening of styrene oxide with alcohols and aniline under mild reaction conditions. Out of the various alcohols tested for ring opening of styrene oxide, methanol was found to be the most reactive in terms of percentage conversion and reactivity. The rate of the ring-opening reaction of styrene oxide decreases as the size of the alcohol is increased, suggesting the location of active sites in micropores. [Fe(BTC)] was a truly heterogeneous catalyst and could be reused without loss of activity. The analogous compound [Cu 3 (BTC) 2 ] was also found to be effective, although with somewhat lower activity than [Fe(BTC)]. The present heterogeneous protocol is compared with a homogeneous catalyst to give an insight into the reaction mechanism.

Heterogenization of functionalized Cu(II) and VO(IV) Schiff base complexes by direct immobilization onto amino-modified SBA-15: Styrene oxidation catalysts with enhanced reactivity

Abstract: Two functionalized copper(II) and oxovanadium(IV) Schiff base complexes of type [M(N 2 O 2 ), M = Cu, VO] bearing chloromethyl groups were respectively synthesized, directly anchored onto amino-modified SBA-15 materials and examined as catalysts for styrene oxidation. The purity of each ligand was confirmed by 1 H NMR, FT-IR and elemental analysis. XRD, N 2 adsorption/desorption and TEM results indicated that the mesoporous structure of SBA-15 remained intact throughout the grafting procedure. FT-IR, UV–vis spectroscopy plus TG–DTA data demonstrated the incorporation of copper(II) and oxovanadium(IV) complexes on amino-modified SBA-15. ICP-AES, SEM-EDX combined with XPS data further showed the different anchorage status of copper(II) and oxovanadium(IV) species on amino-modified SBA-15. The copper(II) Schiff base complex was anchored through the coordination of copper atom with the nitrogen atom of the amino group modified on the SBA-15 external surface. The oxovanadium(IV) Schiff base complex, however, was covalently anchored on SBA-15 via the condensation reaction of the chloromethyl group of the Schiff base with the amino group from the modified SBA-15 matrix. The catalytic properties of supported copper(II) and oxovanadium(IV) complexes in the oxidation of styrene with air or H 2 O 2 as oxidant were investigated and compared with the properties of their homogeneous analogues. It was found that both heterogeneous copper(II) and oxovanadium(IV) catalysts were more active than their homogeneous analogues and that the product selectivity varied in cases of different oxidants. The supported oxovanadium(IV) complex showed high yield of styrene oxide (56.0%) and good recoverability when using air as oxidant.

Oxidation of benzyl alcohol and styrene using H2O2 catalyzed by tetraazamacrocycle complexes of Cu(II) and Ni(II) encapsulated in zeolite-Y

Abstract: Encapsulation of 7,16-diacetyl[M{Me4(Bzo)2[14]tetraeneN4}], {M = Cu(II) and Ni(II)} tetraazamacrocycle complexes in the cavity of Zeolite-Y by the template synthesis method has been described. These complexes have been characterized using various physico-chemical techniques viz., spectroscopic (electronic and IR) studies, thermal analysis, metal analysis, field emission scanning electron micrographs and X-ray powder diffraction patterns. These encapsulated tetraazamacrocycle complexes have been used as a heterogeneous catalyst for the oxidation of styrene and for the solvent free oxidation of benzyl alcohol using hydrogen peroxide as oxidant. The solvent free catalyzed oxidation of benzyl alcohol catalyzed by 7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY gives benzaldehyde as the major product, while that of styrene gives benzaldehyde and styrene oxide as major oxidation products when 7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY is used as catalyst.

Structure and ligand binding properties of the epoxidase component of styrene monooxygenase

Abstract: Styrene monooxygenase (SMO) is a two-component flavoprotein monooxygenase that transforms styrene to styrene oxide in the first step of the styrene catabolic and detoxification pathway of Pseudomon...

Access to enantiopure aromatic epoxides and diols using epoxide hydrolases derived from total biofilter DNA

Abstract: Metagenomic DNA is a rich source of genes encoding novel epoxide hydrolases (EHs). We retrieved two genes encoding functional EHs from total DNA isolated from biofilter-derived biomass, using PCR with EH-specific degenerate primers followed by genome-walking PCR. The degenerate primers were based on two EH-specific consensus sequences: HGWP and GHDWG. The resulting recombinant EHs, Kau2 and Kau8, were expressed in Escherichia coli , and their enantioselectivity and regioselectivity were determined using 13 different epoxide substrates. The EH Kau2 had broad substrate specificity and preferentially hydrolyzed epoxides with S -configuration. It showed high enantioselectivity towards aromatic epoxides such as styrene oxide, p -nitrostyrene oxide, and trans -1-phenyl-1,2-epoxypropane. In addition, Kau2 showed enantioconvergent hydrolysis activity. The EH Kau8 also showed broad substrate specificity and preferentially hydrolyzed epoxides with R -configuration. High enantioselectivity was observed for p -nitrostyrene oxide, and the hydrolysis activity of Kau8 was less enantioconvergent than that of Kau2. To determine the usefulness of Kau2 for synthetic applications, preparative-scale biohydrolysis reactions were performed. Specifically, two kinetic resolutions were carried out with 80 g/L of racemic trans -1-phenyl-1,2-epoxypropane, affording both (1 R ,2 R )-epoxide and the corresponding (1 R ,2 S )-diol in high enantiomeric excess (>99%) and good yield (>45%). In addition, a process based on enantioconvergent hydrolysis by the EH Kau2 was established for racemic cis -1-phenyl-1,2-epoxypropane at a concentration of 13 g/L, resulting in the formation of the corresponding (1 R ,2 R )-diol with a 97% yield and an enantiomeric excess exceeding 98%.

In vitro evolution of styrene monooxygenase from Pseudomonas putida CA-3 for improved epoxide synthesis

Abstract: The styAB genes from Pseudomonas putida CA-3, which encode styrene monooxygenase, were subjected to three rounds of in vitro evolution using error-prone polymerase chain reaction with a view to improving the rate of styrene oxide and indene oxide formation. Improvements in styrene monooxygenase activity were monitored using an indole to indigo conversion assay. Each round of random mutagenesis generated variants improved in indigo formation with third round variants improved nine- to 12-fold over the wild type enzyme. Each round of in vitro evolution resulted in two to three amino acid substitutions in styrene monooxygenase. While the majority of mutations occurred in styA (oxygenase), mutations were also observed in styB (reductase). A mutation resulting in the substitution of valine with isoleucine at amino acid residue 303 occurred near the styrene and flavin adenine dinucleotide binding site of styrene monooxygenase. One mutation caused a shift in the reading frame in styA and resulted in a StyA variant that is 19 amino acids longer than the wild-type protein. Whole cells expressing the best styrene monooxygenase variants (round 3) exhibited eight- and 12-fold improvements in styrene and indene oxidation rates compared to the wild-type enzyme. In all cases, a single enantiomer, (S)-styrene oxide, was formed from styrene while (1S,2R)-indene oxide was the predominant enantiomer (e.e. 97%) formed from indene. The average yield of styrene oxide and indene oxide from their respective alkene substrates was 65% and 90%, respectively.

Isomerization of styrene oxide to phenylacetaldehyde over supported phosphotungstic heteropoly acid.

Abstract: Silica-supported H3PW12O40 (PW), the strongest heteropoly acid in the Keggin series, is an efficient, environmentally friendly heterogeneous catalyst for the liquid-phase isomerization of styrene oxide into phenylacetaldehyde, an industrially important intermediate for fine chemical synthesis The reaction occurs in cyclohexane as a solvent under mild conditions at 25–70 °C with low catalyst loadings and without PW leaching in solution At 60 °C, the yield of phenylacetaldehyde reaches 92% at 97% styrene oxide conversion, with a catalyst turnover number of 19 600 The catalyst can be recovered and reused

Synthesis of Styrene Carbonate from Carbon Dioxide and Styrene Oxide with Various Zinc Halide-Based Ionic Liquids

Abstract: Various zinc halide-based ionic liquids were prepared from zinc halides and onium halides as catalysts for the synthesis of styrene carbonate (SC) from styrene oxide and carbon dioxide. The effects of the ionic liquid catalyst composition (types of onium cation and halide, onium cation/zinc ratio) and CO2 pressure on the reaction were investigated. The effectiveness of the onium cation as the active catalyst component was in the order of tetrabutylammonium > 1-butylpyridinium > 1-butyl-3-methylimidazolium ≫ choline. The type of halide atom originating from the zinc salt affected the catalytic activity of the ionic liquid more significantly than that of the one originating from the onium salt. The onium cation/zinc ratio also affected the SC yield, but its manner was different depending on the type of onium cation. Influence of CO2 pressure was not significant. Various zinc halide-based ionic liquids were prepared from zinc halides and onium halides as catalysts for the synthesis of styrene carbonate from styrene oxide and CO2. Effects of types of onium cations and halides, the molar ratio of onium cation to zinc, and CO2 pressure on the carbonate yield were investigated.

Asymmetric alcoholytic kinetic resolution of styrene oxide catalysed by chiral metal–organic framework crystals

Abstract: The methanolytic kinetic resolution of styrene oxide catalyzed by chiral metal–organic framework crystals afforded both 2-methoxy-2-phenylethanol and unreacted styrene oxide in good enantiomeric excesses.

A highly efficient polymer‐anchored palladium(II) complex catalyst for hydrogenation, Heck cross‐coupling and cyanation reactions

Abstract: BACKGROUND: Precise architectures of steric and electronic properties of palladium species play a crucial role in designing highly functionalized catalyst systems responsible for target organic transformations. Pd catalysts supported on polymer materials have been employed extensively as catalysts not only for hydrogenation but also for coupling reactions in the production of fine chemicals. RESULTS: A new polymer-anchored Pd(II) complex has been synthesized and characterized. The catalyst shows high catalytic activity in the hydrogenation of styrene oxide, Heck cross-coupling and cyanation reactions of aryl halides. The effect of various reaction parameters were investigated to optimize reaction conditions. The catalytic system shows good activity in the hydrogenation of styrene oxide (conversion 98%) with a selectivity to 2-phenylethanol (93%) which is higher than its homogeneous analogues. The catalyst also exhibits excellent catalytic activity for the Heck cross-coupling and cyanation reactions of various substituted and non-substituted aryl halides. CONCLUSIONS: Results demonstrate that the catalyst is robust and stable and can be recovered quantitatively by simple filtration and reused several times without loss of activity. Copyright © 2010 Society of Chemical Industry

Epoxidation of styrene with molecular O2 over sulfated Y–ZrO2 based solid catalysts

Abstract: Liquid phase epoxidation of styrene was studied over non-sulfated and sulfated yttria–zirconia (Y–ZrO 2 ) based solid catalysts using molecular O 2 in the presence of DMF solvent. All catalysts yielded styrene oxide and benzaldehyde as two major products. Among all the catalysts studied, sulfated Co–Y–ZrO 2 catalyst resulted in the maximum (61%) styrene conversion with 80% styrene oxide selectivity. Reactions studied in the absence of DMF solvent or in the presence of a small amount of water favored benzaldehyde formation predominantly. Thermally regenerated catalysts showed slight lower conversion (54%) without affecting the selectivity through three reaction cycles.

Synthesis, characterization and catalytic properties of heterogeneous iron(III) tetradentate Schiff base complexes for the aerobic epoxidation of styrene

Abstract: A series of hybrid mesoporous SBA-15 materials containing four iron(III) Schiff base complexes of the type [FeL x (NO3)] (x = 4–7, L = N,N′-bis(salicylidene)ethylenediamine, N,N′-bis(salicylidene)diethylenetriamine, N,N′-bis(salicylidene)o-phenylenediamine, N,N′-bis(3-nitro-salicylidene)ethylenediamine) was synthesized by a post-grafting route. The XRD, N2 adsorption/desorption and TEM measurements confirmed the structural integrity of the mesoporous hosts, and the spectroscopic characterization techniques (FT-IR, UV–vis spectroscopy, 1H NMR) confirmed the ligands and the successful anchoring of iron(III) Schiff base complexes over the modified mesoporous support. Quantification of the supported ligand and metal was carried out by TG/DSC and ICP-AES techniques. The catalyst FeL7-SBA resulting from N,N′-bis(3-nitro-salicylidene)ethylenediamine) ligand was considerably active for the aerobic epoxidation of styrene, in which the highest conversion of styrene reached 83.6%, and the selectivity to styrene oxide was 83.0%. Moreover, it was also found that the catalytic activity increases with the decrease in the electron-donating ability of the Schiff bases, and the selectivity varies according to the types of substituents in the ligands.

Cesium Promotion in Styrene Epoxidation on Silver Catalysts

Abstract: The adsorption of a small amount of cesium on Ag(110) redirects the partial oxidation products of styrene from phenylacetaldehyde and phenylketene to styrene oxide. The cesium stabilizes the oxametallacycle intermediate and hinders its transformation to the intermediate that leads to the other products. Cesium does not appear to create any electronic effects on the bonding of the intermediates. Low coverages of cesium induce a (1 × 2) missing-row reconstruction of the entire clean Ag(110) surface and a (3 × 5) surface oxide structure on the cesium-reconstructed Ag(110) surface. This (3 × 5)-ordered surface oxide is superimposed on the Ag(111) microfacets produced by the cesium-induced reconstruction, which leads to selectivity and reactivity very similar to those of the extended (111) surface. These studies provide insight into the microscopic origins of the structural effects of cesium in styrene epoxidation on silver catalysts.

Surface properties of monolayers of amphiphilic poly(ethylene oxide)-poly(styrene oxide) block copolymers

Abstract: The surface properties of poly(styrene oxide)-poly(ethylene oxide) block copolymers EO12SO10, EO10SO10EO10, and EO137SO18EO137 at the air−water (a/w) and chloroform−water (c/w) interfaces have been analyzed by Tracker drop tensiometry, Langmuir film balance, and atomic force microscopy (AFM). The kinetic adsorptions for the block copolymer solutions at both interfaces were determined by the pendant drop technique. At the a/w, the polymer adsorption is reduced as the polymer hydrophobicity increases. Measurements of the interfacial rheological behavior of the copolymers showed that the adsorption layers at the a/w interface manifest obvious solid-like properties in the whole accessible frequency range, whereas a viscous fluid-like behavior is displayed at the c/w interface. The differences observed in the monolayer isotherms obtained for the three copolymers arose from their different hydrophobic/hydrophilic block ratios and block lengths. In this regard, copolymer EO137SO18EO137 displays an adsorption iso...

Soluble monometallic salen complexes derived from O-functionalised diamines as metalloligands for the synthesis of heterobimetallic complexes

Abstract: O-Functionalised salen ligands were employed as bridging ligands in the synthesis of homo- and heterometallic salen complexes with early and late transition metals (H2salen: N,N′-bis(salicylidene)ethylenediamine, systematic name: 2,2′-{ethane-1,2-diylbis(nitrilomethylidine)}diphenol). A new type of O-functionalised salen ligand was synthesised, which contains alkyl groups to enhance the solubility in organic solvents as well as carboxyl groups to allow introduction of an early transition metal. Two new salen ligands derived from O-functionalised diamines were synthesised from 3,5-di-tert-butylsalicylaldehyde (bsal) and 3,4-diaminobenzoic acid (4cpn) or (R)-2,3-diaminopropionic acid (cen). By using the aryl diamines, a conjugated backbone is obtained, and the alkyl diamines can be used to introduce a chiral centre. The salen ligand derived from 3,4-diaminobenzoic acid was accessible only via a zinc(II)-mediated template reaction. Monometallic salen complexes could be obtained by template synthesis with nickel(II) and copper(II). The analogous chromium(III), manganese(III) and molybdenum(IV) salen complexes were synthesised directly from the salen ligands. The crystal structures of the molybdenum(IV) salen complex and a decomposition product thereof gave insight into the stability of this compound. Starting from (R)-2,3-diaminopropionic acid the corresponding nickel(II), chromium(III), manganese(III) and molybdenum(IV) salen complexes were obtained. Reactions of the conjugated nickel(II) salen complex with metallocene derivatives resulted in the formation of soluble di- and trinuclear heterobimetallic complexes, depending on the stoichiometry used. The compounds were characterised by NMR, IR and EPR spectroscopy, mass spectrometry and, for selected complexes, by X-ray crystallography. For selected mono- and bimetallic salen complexes the catalytic activity in the epoxidation of styrene was tested under different reaction conditions and with different oxidising agents. The highest values (up to 24%) for the conversion of styrene to styrene oxide were obtained with manganese(III) salen complexes.

Mechanistic insights into selectivity control for heterogeneous olefin oxidation: styrene oxidation on Au(111).

Abstract: We demonstrate that intermolecular interactions, controlled by both oxygen and styrene coverage, alter reaction selectivity for styrene oxidation on oxygen-covered Au(111). Several partial oxidation products are formed--styrene oxide, acetophenone, benzoic acid, benzeneacetic acid, and phenylketene--in competition with combustion. The maximum ratio of the yields of styrene oxide to the total CO(2) produced is obtained for the maximum styrene coverage for the first two layers (0.28 ML) adsorbed on Au(111) precovered with 0.2 ML of O. Furthermore, our reactivity and infrared studies support a mechanism whereby styrene oxidation proceeds via two oxametallacycle intermediates which, under oxygen-lean conditions, lead to the formation of styrene oxide, acetophenone, and phenylketene. Benzoate, identified on the basis of infrared reflection absorption spectroscopy, is converted into benzoic acid during temperature-programmed reaction. These results demonstrate the ability to tune the epoxidation selectivity using reactant coverages and provide important mechanistic insight into styrene oxidation reactions.

Facile Conversion of Epoxides to Thiiranes with Ammonium Thiocyanate Catalyzed with Etidronic Acid

Abstract: have also been applied to the conversion of oxiranes into thiiranes. Nevertheless, most of these methods suffer one or more of the following draw-backs: unsatisfactory yield, long reaction time, critical product isolation procedures, the use of expensive and detrimental metal precursors, harsh reaction conditions, and no agreement with the green chemistry protocols, which limit their use.Etidronic acid (Figure 1) is a phosphonic acid with mild aci-dity, is non-volatile and non-corrosive, and is soluble in common organic solvents. It is a white crystalline solid with outstanding physical and chemical properties and is a commercially avail-able cheap chemical. Its applications as a reaction catalyst in organic syntheses have not yet been fully explored. In this paper,we report a simple and efficient synthesis of thiiranes in THFusing etidronic acid as a catalyst (Scheme 1).Initially, we carried out the reaction of styrene oxide with ammonium thiocyanate in THF in the presence of different amounts of etidronic acid at reflux temperature. It was found that the best result was obtained with 10 mol % of etidronic acid.It is worthy to note that in the absence of etidronic acid, the reaction did not yield any product at reflux temperature even after a long reaction time. To select the best solvent for the reaction, the synthesis of thiirane

A Tripodal Peptidic Titanium Phosphonate as a Homochiral Porous Solid Medium for the Heterogeneous Enantioselective Hydration of Epoxides

Abstract: A porous, homochiral titanium-phosphonate material based on a tripodal peptide scaffold was used as a heterogeneous reaction medium for the enantioselective hydration (> 99%) of styrene oxide. This titanium-phosphonate material, which was shown to contain confined chiral spaces, was prepared by polymerization of L -leucine onto a tris(2-aminoethyl)amine initiator, followed by capping with phosphonate groups and completed by non-aqueous condensation with titanium isopropoxide. Circular dichroism confirmed that the peptide tethers yielded a secondary structure. X-ray powder diffraction and transmission electron microscopy supported by a semi-empirical model showed the likely formation of a porous, lamellar material that was quantified by nitrogen adsorption.

Functional expression and magnetic nanoparticle-based Immobilization of a protein-engineered marine fish epoxide hydrolase of Mugil cephalus for enantioselective hydrolysis of racemic styrene oxide

Abstract: A triple-point mutated fish microsomal epoxide hydrolase (mEH) gene from Mugil cephalus was expressed in Escherichia coli in the presence of various chaperones to prevent protein aggregations. The enantioselective hydrolytic activity was more than doubled by co-expressing the EH mutant gene with pGro7 plasmid. The highly active EH mutant with a his-tag was immobilized onto magnetic silica assembled with NiO nanoparticles. The immobilized mEH mutant was re-used more than 10 times with less than 10% activity loss. (S)-Styrene oxide with 98% enantiopurity was repeatedly obtained with over 50% of the theoretical yield by the magnetically separable high-performance mEH mutant.

Metabolism and Toxicity of Styrene in Microsomal Epoxide Hydrolase-Deficient Mice

Abstract: Styrene, which is widely used in manufacturing, is both acutely and chronically toxic to mice. Styrene is metabolized by cytochromes P-450 to the toxic metabolite styrene oxide, which is detoxified via hydrolysis with microsomal epoxide hydrolase (mEH) playing a major role. The purpose of these studies was to characterize the importance of this pathway by determining the hepatotoxicity and pneumotoxicity of styrene in wild-type and mEH-deficient (mEH−/−) mice. While the mEH−/− mice metabolized styrene to styrene oxide at the same rate as the wild-type mice, as expected there was minimal metabolism of styrene oxide to glycol. mEH−/− mice were more susceptible to the lethal effects of styrene. Twenty-four hours following the administration of 200 mg/kg ip styrene, mice demonstrated a greater hepatotoxic response due to styrene, as measured by increased serum sorbitol dehydrogenase activity and greater pneumotoxicity as shown by increased protein levels, cell numbers, and lactate dehydrogenase activity in br...

A novel copper(II) complex bearing salicylaldimine immobilized on SBA-15 and its catalytic performances in styrene oxidation by hydrogen peroxide

Abstract: Salicylaldimine functionalized SBA-15 hybrid mesoporous material was synthesized by post-grafting of salicylaldehyde modified 3-aminopropyltriethoxysilane and followed by introducing Cu(II) ions into the hybrid material via a ligand exchange reaction The prepared catalyst was characterized by means of XRD, N2 adsorption/desorption, SEM, FT-IR, UV–vis spectroscopy, EPR and XPS techniques as well as ICP-AES and elemental analysis measurements The solid catalyst was evaluated in the oxidation of styrene with H2O2 as the oxidant under mild conditions, and the reaction parameters (the molar ratio of styrene/H2O2, amount of catalyst, temperatures, solvents, alkaline additive) were investigated and optimized for the oxidation of styrene The optimal conversion (771%) and yield of styrene oxide (600%) were obtained at 80 °C using CH3CN as the solvent under basic conditions Moreover, the covalently anchored Cu(II) salicylaldimine complex showed good recoverability and high stability against leaching of active copper(II) species