Showing papers on "Styrene oxide published in 2022"

High-Performance Styrene Epoxidation with Vacancy-Defect Cobalt Single-Atom Catalysts.

Abstract: Exploring highly active and cost-effective catalysts for styrene epoxidation is of great significance, but it remains challenging to simultaneously achieve excellent conversion and selectivity toward styrene oxide. In this work, the structures and performance of Co, Fe, and Cu single-atom catalysts (SACs) in styrene epoxidation with tert-butyl hydroperoxide (TBHP) are predicted using density functional theory (DFT) calculations. The results reveal that the Co-N structure prefers that of styrene oxide over Fe-N and Cu-N structures. This predicted result is verified via catalytic evaluations, where the Co SACs displayed significantly higher styrene oxide selectivity than Fe and Cu SACs. Moreover, the activity of Co SAC can be further improved by the construction of unsaturated vacancy-defect cobalt single sites. As a result, excellent performance with styrene conversion of 99.9% and styrene oxide selectivity of 71% is achieved after a reaction time of 8 h on the optimal Co SAC.

Highly Selective Oxidation of Styrene to Styrene Oxide over a Tetraphenylporphyrin-Bridged Silsesquioxane-Based Hybrid Porous Polymer

Abstract: Two silsesquioxane-based hybrid porous polymers (PcsM and PcsH) were easily synthesized by the Friedel–Crafts reaction of tetraphenylporphyrin derivative (HTPP and MnTPP) with octavinylsilsesquioxane (OVS) applying AlCl3 as catalyst. A series of characterization results demonstrate that the materials have been successfully prepared. PcsM and PcsH act as effective catalysts to selectively oxidize styrene to styrene oxide with oxygen as a green and economical oxidant. The effects of reaction conditions on the reaction activity, such as reaction energy, reaction time, solvent type, catalyst dosage, etc., were systematically discussed. Under optimized conditions, the conversion rate of styrene was 99.9%, and the yield of styrene oxide could reach 80.6%. Moreover, the reaction mechanism of selective oxidation of styrene to styrene oxide using PcsM as a catalyst is reasonably proposed. Importantly, PcsM shows an excellent recyclable performance.

Copper-complexed dipyridyl-pyridazine functionalized periodic mesoporous organosilica as a heterogeneous catalyst for styrene epoxidation.

Abstract: A new heterogeneous catalyst has been synthesized by immobilization of a copper complex on dipyridyl-pyridazine functionalized periodic mesoporous organosilica (dppz-vPMO). This ordered support was first prepared by a co-condensation reaction between vinyltriethoxysilane and 1,2-bis(trimethoxysilyl)ethane and further post-functionalized through a hetero Diels-Alder reaction with 3,6-di-2-pyridyl-1,2,4,5-tetrazine. Techniques such as XRD, N2 isotherms, TEM, 13C NMR, XPS and DRIFT, among others, were employed to characterize the surface functionalized materials. These results have proven the ordered mesostructure of the materials as well as the presence of novel nitrogen-chelating heterocyclic compounds on the pore surface after the post-modification process. Additionally, the successful anchoring of a copper complex on the dipyridyl-pyridazine (dppz) ligands has been confirmed. The resulting material was evaluated as a heterogeneous catalyst in the epoxidation of styrene using tert-butylhydroperoxide (TBHP) as an oxidant. Under the optimized reaction conditions, Cu@dppz-vPMO showed a high styrene conversion (86.0%) and a remarkable selectivity to styrene oxide (41.9%). Indeed, this catalyst provided excellent catalytic results in terms of stability, reaction rate, conversion and selectivity compared to other bipyridine-like copper catalysts.

Alumina-Based Bifunctional Catalyst for Efficient CO2 Fixation into Epoxides at Atmospheric Pressure.

Abstract: The quest toward sustainability and decarbonization demands the development of methods for efficient carbon dioxide capture and utilization. The nonreductive CO2 fixation into epoxides to prepare cyclic carbonates has gained attention in recent years. In this work, we report the development of guanidine hydrochloride-functionalized γ alumina (γ-Al2O3), prepared using green solvents, as an efficient bifunctional catalyst for CO2 fixation. The resulting guanidine-grafted γ-Al2O3 (Al-Gh) proved to be an excellent catalyst to prepare cyclic carbonates from epoxides and CO2 with high selectivity. The nitrogen-rich Al-Gh shows increased CO2 adsorption capacity compared to that of γ-Al2O3. The as-prepared catalyst was able to carry out CO2 fixation at 85 °C under atmospheric pressure in the absence of solvents and external additives (e.g., TBAI or KI). The material showed negligible loss of catalytic activity even after five cycles of catalysis. The catalyst successfully converted many epoxides into their respective cyclic carbonates under the optimized conditions. The gram-scale synthesis of commercially important styrene carbonates from styrene oxide and CO2 using Al-Gh was also achieved. Density functional theory (DFT) calculations revealed the role of alumina in activating the epoxide. This activation facilitated the chloride ion to open the ring to react with CO2. The DFT studies also validated the role of alumina in stabilizing the electron-rich intermediates during the course of the reaction.

Experimental and theoretical insight into the mechanism of CO2 cycloaddition to epoxides catalyzed by ammonium ferrates

Abstract: Soluble tetrabutylammonium ferrates, [TBA][FeX3Y] (TBA = nBu4N) were synthetized by treating ferric salts (FeX3) with tetrabuthylammoniom halides. Their activity as a stand-alone catalyst in CO2 cycloaddition reactions to epoxides was assessed under solvent free and quite mild reaction conditions (CO2 pressures between 0.4 and 0.8 MPa) and TOF up to 428 h-1 (T = 150 °C) were observed. Good yields of cyclic organic carbonates were obtained, especially with terminal epoxides, without the need of any Lewis base as co-catalyst, with a broad reaction scope. A scale-up reaction on 5 mL of styrene oxide was performed and the robustness of the catalyst was proved up to three recycles in the case of propylene oxide (TON = 594). To shed light on the reaction mechanism, an extensive set of theoretical calculations has been carried out. Iron salts almost annihilate the barrier for the epoxide ring opening and stabilize the first reaction intermediate. Along the same reaction path, chloride proved to be more effective as nucleophile than bromide, and preferentially attacks on the more hindered carbon atom. On the other hand, when no Lewis acid (LA) is present, the rate determining step of the reaction becomes the ring opening of the epoxide. A tight correlation with experimental results was observed.

Ag nanoparticles immobilized over highly porous crystalline organosilica for epoxidation of styrene using CO2 as oxidant

Abstract: Selective epoxidation of olefins is a very important reaction as epoxides are widely been used as platform chemical in polymer and pharmaceutical industries. Unlike conventional oxidants like molecular O2 or peroxides, the use of CO2 as a soft oxidant for the oxidation of olefins is very challenging as it offers the utilization of waste and plentiful CO2 together with the potential for the mitigation of its harmful environmental effect. Thus, this process is cost effective and environmentally challenging. Herein, we report the synthesis of a new crystalline porous organosilica material TSOS-1 with orthorhombic crystal structure by using a tailor made bridging organoslilane precursor prepared through the Schiff base condensation of p-terphenyl-4,4′'-dialdehyde and 3-aminopropyl-trimethoxysilane. This novel crystalline material TSOS-1 has been synthesized hydrothermally in the absence of any structure-directing agent and it showed high BET surface area (220 m2 g−1) and nanoscale porosity. TSOS-1 is used as a support for stabilizing tiny AgNPs to obtain a robust nanocatalyst [email protected], which efficiently catalyses the conversion of styrene into predominantly styrene oxide (SO) using CO2 as a soft oxidant in an autoclave reactor under mild reaction conditions.

Electrochemically Assisted Cycloaddition of Carbon Dioxide to Styrene Oxide on Copper/carbon Hybrid Electrodes: Active Species and Reaction Mechanism.

Abstract: A novel electrochemically assisted cycloaddition reaction process was proposed, in which highly efficient coupling of CO 2 with styrene oxide (SO) can be achieved forming styrene carbonate (SC) as high value-added product. A series of Cu catalysts with different morphologies and chemical states were fabricated on carbon paper using the in-situ electrodeposition method, and the sample with nano-dendrimer structure exhibited relatively high activity of 74.8% SC yield with 92.7% SO conversion under gentle reaction conditions, showing its potential for practical applications. The relatively high electrochemical active surface area and charge transfer ability of dendrimer-like Cu benefited the electrochemical reaction. Especially the Cu 2+ species those were in-situ formed during the reaction played a vital role in enhancing the activity and selectivity of the proposed copper/carbon paper (Cu/CP) hybrid catalyst. Cu 2+ served as the active sites, that can not only electrochemically activate CO 2 but also facilitate the ring-opening process of SO. Mechanistic analysis suggested that the reaction followed the electrochemical and liquid phase heterogeneous paths, respectively, which provided a new green and sustainable route for efficient utilization of CO 2 resources for fine chemical electro-synthesis.

Styrene Cytotoxicity in Testicular Leydig Cells In Vitro

Abstract: Styrene is the precursor of polystyrene. Human exposure to styrene could occur in occupational and residential settings and via food intake. Styrene is metabolized to styrene-7,8-oxide by cytochrome P450 enzyme. In the present study, we investigated the cytotoxicity mediated by styrene and styrene-7,8-oxide in TM3 testicular Leydig cells in vitro. We first monitored the nuclear fragmentation in Leydig cells after exposure to styrene or styrene-7,8-oxide. Hoechst 33258 cell staining showed that styrene exposure in TM3 Leydig cells did not exhibit nuclear fragmentation at any concentration. In contrast, nuclear fragmentation was seen in styrene-7,8-oxide-exposed cells. These results indicate that cytotoxicity-mediated cell death in Leydig cells is more susceptible to styrene-7,8-oxide than to styrene. Following styrene treatment, procaspase-3 and XIAP protein levels did not show significant changes, and cleaved (active) forms of caspase-3 were not detected. Consistent with the western blot results, the active forms of caspase-3 and XIAP proteins were not prominently altered in the cytoplasm of cells treated with styrene. In contrast to styrene, styrene-7,8-oxide induced cell death in an apoptotic fashion, as seen in caspase-3 activation and increased the expression of XIAP proteins. Taken together, the results obtained in this study demonstrate a fundamental idea that Leydig cells are capable of protecting themselves from cytotoxicity-mediated apoptosis as a result of styrene exposure in vitro. It remains unclear whether the steroid-producing function, i.e., steroidogenesis, of Leydig cells is also unaffected by exposure to styrene. Therefore, further studies are needed to elucidate the endocrine disrupting potential of styrene in Leydig cells.

Synthesis of nanoscale CuO via precursor method and its application in the catalytic epoxidation of styrene

Abstract: Nanoscale CuO with diameters in the range of 7–8 nm has been synthesized via a two-step precipitation–calcination method using copper(ii) isonicotinate tetrahydrate as the precursor. The first step involves the room temperature stirring of an alkaline ethanolic solution of the precursor which gives a non-crystalline CuO species, while the second step involves the calcination of the product of the first step at 180 °C to form nanocrystalline CuO which has been characterized by PXRD, TEM, SEM, H2-TPR and Raman spectroscopy, etc. The CuO material has shown excellent catalytic activity in the oxidation of styrene using TBHP as the oxidizing agent leading to complete styrene conversion with more than 95% styrene oxide selectivity at the end of 6 h. The oxide catalyst can be reused for at least 6 successive runs without significant loss in activity.

Sequence-guided stereo-enhancing and -inverting of (R)-styrene monooxygenases for highly enantioselective epoxidation

Abstract: To improve the enantioselectivity of newly identified (R)-selective styrene monooxygenases, a concise sequence-guided approach was exploited to efficiently identify candidate mutations in SeStyA (from Streptomyces exfoliates). Positions 86 and 219 of SeStyA were experimentally confirmed to be critical for stereo-control, and subsequent saturation mutagenesis revealed multiple beneficial mutations that could enhance or invert the enantioselectivity. In the epoxidation of a panel of styrene derivatives, mutant W86A yielded (R)-oxides with 95–99% ee, a significant increase from the wild-type (83–96% ee); and mutant A219H showed drastic inversion of stereoselectivity, yielding (S)-oxides with 92–99% ee. Such mutational effects could be extended to other (R)-SMOs. Corresponding mutants of NaStyA, AaStyA, and StStyA contributed to an increase from 91–94% ee to 98–99% ee for (R)-styrene oxide, as well as to the formation of (S)-styrene oxide with up to 92% ee.

Brønsted Acid-Catalysed Epoxide Ring-Opening Using Amine Nucleophiles: A facile access to β-amino alcohols.

Abstract: A mild, efficient, and metal-free synthetic protocol for the synthesis of β-amino alcohols is reported. The reaction proceeds at room temperature with only 0.5 mol% catalyst loading and affords β-amino alcohol derivatives in excellent yield. This protocol is well-tolerated by a wide range of styrene oxide and aniline derivatives. A notably efficacious gram-scale synthesis is also reported with a high TON = 842. Further, the Hammett correlation study was also performed to identify the rate-determining step.

Ammonium zincates as suitable catalyst for the room temperature cycloaddition of CO2 to epoxides

Abstract: We have recently shown that simple ammonium ferrates are competent catalyst for the cycloaddition reaction of CO2 to epoxides under moderate reaction conditions (T = 100°C, P(CO2) = 0.8 MPa). We report here that ammonium zincates of general formulae [TBA]2 [ZnX4] (TBA = tetrabutylammonium), simply obtained by treating an ethanolic solution of an appropriate zinc(II) salt with two equivalents of tetrabutylammonium halides, outperform ammonium ferrates in the synthesis of cyclic carbonates under milder reaction conditions (room temperature and atmospheric CO2 pressure). Using [TBA] 2 [ZnBr 4 ] complex as homogeneous catalyst at 100°C and P(CO2) = 0.8 MPa a 52% conversion of styrene oxide with complete selectivity in styrene carbonate in just 15 min was observed, corresponding to a Turnover frequency (TOF) of 416 h−1. The same catalyst proved to be very active even at room temperature and atmospheric or very moderate CO2 pressures (0.2 MPa), with a quite broad range of substrates, especially in the case of terminal epoxides, with high selectivity towards cyclic carbonate products. The difference in reactivity of terminal and internal epoxides could be exploited using 4-vinylcyclohexene dioxide, where the endocyclic epoxide remained untouched when reacted at room temperature and the formation of the di-carbonate product was observed only at harsher conditions. A multigram scale conversion of propylene oxide was achieved (46 mmol) and the catalyst also proved to be recyclable (3 cycles) by distillation of the product and subsequent addition of fresh reagent, maintaining high conversion values and complete selectivity for propylene carbonate. This simple zinc-based catalytic system, which outperform the recently reported iron-based one by working at much milder conditions, could represent a valuable prospect in both laboratory and industrial scale, combining an inherent cheapness and synthetic easiness that should be deeply considered when the goal is to give value to a waste product as CO2.

Enantioconvergent hydrolysis of racemic epoxides at elevated concentrations in Tween-20/phosphate buffer by the corresponding epoxide hydrolases

Abstract: For effectively actualizing the gram-scale preparation of (R)-phenyl-1,2-ethanediol (PED) via the enantioconvergent hydrolysis of racemic (rac-) styrene oxide (SO) at elevated concentration using whole-cell of E. coli/sleh2, the reaction media were constructed by adding non-ionic surfactants, organic solvents, and deep eutectic solvents into phosphate buffer, respectively. After screening, using conversion ratio (c) of rac-SO as the main criterion, the most suitable reaction medium, 30% (v/v) Tween-20/phosphate buffer (50 mM, pH 7.0), was identified, where the c of 400 mM rac-SO was elevated to > 99% from 62.1% in phosphate buffer. The scale-up enantioconvergent hydrolysis of 400 mM rac-SO was carried out in 50 mL Tween-20/aqueous buffer using 200 mg/mL wet cells of E. coli/sleh2 at 20 °C for 8 h, affording (R)-PED with 96.2% eep and 97.2% yield. The experimental results demonstrated that the identified medium can alleviate the inhibition of (R)-PED on the EH activity of E. coli/sleh2. Furthermore, this medium was also applied to the hydrolytic reactions of 300 mM rac-m-nitrostyrene oxide (mNSO) and m-chlorostyrene oxide (mCSO) using the corresponding E. coli/rpehL360C and /pveh1Z6, respectively. The c values of rac-mNSO and mCSO were increased to over 99% from 72.4% and 52.1% in phosphate buffer.

Tuning the Properties of Ester-Based Degradable Polymers by Inserting Epoxides into Poly(ϵ-caprolactone).

Abstract: A series of ester-ether copolymers were obtained via the reaction between α,ω-dihydroxyl poly(ϵ-caprolactone) (PCL) and ethylene oxide (EO) or monosubstituted epoxides catalyzed by strong phosphazene bases. The two types of monomeric units were distributed in highly random manners due to the concurrence of epoxide ring-opening and fast transesterification reactions. The substituent of epoxide showed an interesting bidirectional effect on the enzymatic degradability of the copolymer. Compared with PCL, copolymers derived from EO exhibited enhanced hydrophilicity and decreased crystallinity which then resulted in higher degradability. For the copolymers derived from propylene oxide and 1,2-butylene oxide, the hydrophobic alkyl pendant groups also allowed lower crystallinity of the copolymers thus higher degradation rates. However, further enlarging the pendant groups by using styrene oxide or 2-ethylhexyl glycidyl ether caused a decrease in the degradation rate, which might be ascribed to the higher bulkiness hindering the contact of ester groups with lipase.

A bioinspired approach toward efficient supramolecular catalysts for CO2 conversion

Abstract: Nature uses enzymes for affording astonishingly efficient chemical transformations with high chemo-, regio-, and stereoselectivity (e.g., carbonic anhydrase for CO2 conversion). Such sophisticated biomolecules lead to excellent catalytic activities as a result of harmonized supramolecular interactions with the substrates/intermediates of the reactions. Based on this approach, different Zn2+ complexes of pseudopeptidic macrocycles with a high level of preorganization were synthesized and tested as catalysts for cycloaddition of CO2 to epoxides. These bioinspired systems promoted remarkable activities even under mild conditions without the need for any auxiliary co-catalysts. The whole catalytic cycle was dominated by cooperative non-covalent forces involving multiple functional sites, displaying enzyme-like catalytic behavior. The chiral environment associated with the amino acid side chains in the preorganized catalytic system provided recognition sites for efficient kinetic resolution of epoxides. In the case of the sluggish styrene oxide substrate, the highest selectivity factor reported to date was attained.

Facile synthesis of 2-hydroxyacetophenone from racemic styrene oxide catalyzed by engineered enzymes

Abstract: We describe a system that allows for biocatalyzed in vivo synthesis of α-hydroxy ketones from racemic epoxide starting material by in vivo co-expression of native and engineered epoxide hydrolase and alcohol dehydrogenases. The constructed expression system exploits the host cell metabolism for supply and regeneration of precious nicotinamide dinucleotide coenzyme. Racemic styrene oxide added to growth medium passively enters the cells and is hydrolyzed into (1R)-phenylethane-1,2-diol, which is subsequently oxidized to the acyloin 2-hydroxyacetophenone. Produced 2-hydroxyacetophenone escapes the cells via passive diffusion into the growth medium. Thus, co-expression of potato epoxide hydrolase and engineered alcohol dehydrogenase variants can be employed for robust and facile production of 2-hydroxyacetophenone from racemic styrene oxide.

Styrene epoxidation catalyzed by polyoxometalate/quaternary ammonium phase transfer catalysts: the effect of cation size and catalyst deactivation mechanism

Abstract: Catalytic epoxidation of alkenes is an important type of organic reaction in chemical industry, and the deep insight into catalyst deactivation will help to develop new epoxidation process. In this work, series of quaternary ammoniums bearing different cationic sizes, i.e. MTOA+ (methyltrioctylammonium, [(C8H17)3CH3N]+), HTMA+(hexadecyltrimethylammonium, [(C16H33)(CH3)3N]+) and DMDOA+ (dimethyldioctadecylammonium, [(C18H37)2(CH3)2N]+) were incorporated with polyoxometalate (POM) anions to prepare phase transfer catalysts (PTCs), which were used in the styrene epoxidations. Among them, (MTOA)3PW4O24 exhibits the best catalytic performance judged from the highest styrene conversion rate (52%) and styrene oxide selectivity (93%), during which the styrene epoxidation conditions were optimized. Meanwhile, the deactivation mechanism of this kind of PTCs was proposed firstly, i.e. in the case of low H2O2 content, the oxidant can only be used in the styrene epoxidation, in which the catalyst can transform into stable Keggin-type POM. But when the content of H2O2 is higher, the excess H2O2 can re-activate the Keggin-type POM into active (PW4O24)3− anions, which can trigger the ring-opening polymerization of styrene oxide. Consequently, the catalyst is deactivated by adhered poly(styrene oxide) irreversibly, which was determined by NMR spectra. In this situation, the active moiety {PO4[WO(O2)2]4}3− in phase-transfer catalytic system can break into some unidentified species with low W/P ratio with the presence of epoxides. This work will be beneficial for the design of new PTCs in alkene epoxidation in fine chemical industry.

Hydroxyl-Imidazolium Ionic Liquid-Functionalized MIL-101(Cr): A Bifunctional and Highly Efficient Catalyst for the Conversion of CO2 to Styrene Carbonate.

Abstract: Considerable attention has been focused on the development of catalysts for the coupling reaction of carbon dioxide (CO2) and epoxides due to the distinct advantages and importance of this reaction. To develop high-performance and easy-to-recycle catalyst is still a hot topic, especially for candidates with excellent activity under moderate conditions. A new heterogeneous catalyst, MIL-101-ImEtOH, is reported by post-synthesis modification, in which 2-(1-imidazol-1-yl) ethanol (Im-EtOH) is immobilized on MIL-101(Cr). In the absence of solvent and co-catalyst, MIL-101-ImEtOH exhibits high activity for the cycloaddition of CO2 and styrene oxide. A 95.6% yield is achieved under 0.5 MPa CO2 pressure and 90 °C by utilization of 50 mg of catalyst for 3 h. Moreover, MIL-101-ImEtOH is easily separated from the catalytic system by simple filtration. To elucidate the influence of hydroxyl group and porous structure on catalysis, other two supported ionic liquids, MIL-101-EtIm and PS-ImEtOH, are prepared and used to catalyze the title reaction under the same conditions. The contribution of each active component is determined by density functional theory along with noncovalent interaction analysis.

CO 2 Cycloaddition to Styrene Oxide Catalysed by ZnBr 2 Impregnated Rice Husk Ash Silica: Structural and Kinetics Studies

Abstract: A series of ZnBr2 impregnated on rice husk ash silica catalysts were synthesised via the wet impregnation method for the CO2 cycloaddition to styrene oxide reaction. The X-ray diffraction (XRD) analysis indicates that the impregnation resulted in the deterioration of the silica's pore channels. Catalyst with 0.5 w/w% of Zn (0.5 wt %ZnBr2-SiO2) was highly active in the CO2 cycloaddition to styrene oxide. The conversion of styrene oxide (StO) was 89.1 %, with the styrene carbonate (SC) selectivity of 92.1 % under the optimum conditions (130 °C, 60 bar, 3 h and solventless). Additionally, the universality of 0.5 wt %ZnBr2-SiO2 was also studied with other epoxides, and it shows good to excellent activity. The catalytic performance of the 0.5 wt %ZnBr2-SiO2 remains constant after being reused three consecutive times. The activation energy of the reaction was determined to be 89.06 kJ/mol.