Epoxidation Of Olefins Research Articles

Zeolite structure descriptor for guiding the synthesis of efficient titanosilicalites through matching Ti sites and framework topologies for 1-Hexene epoxidation

Rational design of metal-containing zeolites with different framework topologies can boost catalytic performance, but the successful synthesis of metal-containing zeolites typically requires selection of suitable zeolite scaffolds. Herein, a zeolite structure descriptor (i.e., the local framework disturbance index, LFDI) is proposed to guide the design of Ti-containing zeolites by matching Ti sites and different framework topologies to enhance olefin epoxidation performance. Theoretical calculations of the incorporation of Ti metal atoms into different crystallographic T sites indicate that the BEA framework exhibits the more negative average substitution energy (-0.50 eV) than MFI and MEL frameworks due to the lowest average LFDI (3.14). As expected, the BEA framework showed the highest capacity of framework Ti species than MFI and MEL frameworks by atom-planting method. This high framework Ti content demonstrated outstanding 1-hexene epoxidation performances (TON: 1827.5). This work paves the way to rationally design Ti-containing zeolites by atom-planting method for epoxidation reactions.

Tracking Coordination Environment and Reaction Intermediates in Homogeneous and Heterogeneous Epoxidation Catalysts via Ti L2,3-Edge Near-Edge X-ray Absorption Fine Structures.

Ti-based molecules and materials are ubiquitous and play a major role in both homogeneous and heterogeneous catalytic processes. Understanding the electronic structures of their active sites (oxidation state, local symmetry, and ligand environment) is key to developing molecular-level structure-property relationships. In that context, X-ray absorption spectroscopy (XAS) offers a unique combination of elemental selectivity and sensitivity to local symmetry. Commonly, for early transition metals such as Ti, K-edge XAS is applied for in situ characterization and subsequent structural analysis with high sensitivity toward tetrahedral species. Ti L2,3-edge spectroscopy is in principle complementary and offers specific opportunities to interrogate the electronic structure of five-and six-coordinated species. It is, however, much more rarely implemented because the use of soft X-rays implies ultrahigh vacuum conditions. Furthermore, the interpretation of the data can be challenging. Here, we show how Ti L2,3-edge spectroscopy can help to obtain unique information about both homogeneous and heterogeneous epoxidation catalysts and develop a molecular-level relationship between spectroscopic signatures and electronic structures. Toward this goal, we first establish a spectral library of molecular Ti reference compounds, comprising various coordination environments with mono- and dimeric Ti species having O, N, and Cl ligands. We next implemented a computational methodology based on multiplet ligand field theory and maximally localized Wannier orbitals benchmarked on our library to understand Ti L2,3-edge spectroscopic signatures. We finally used this approach to track and predict the spectra of catalytically relevant intermediates, focusing on Ti-based olefin epoxidation catalysts.

Synthesis of pyrogallol triglycidyl ether: A bio-based epoxy resin monomer with low viscosity, high activity, and good thermomechanical properties

With increasing development of chip and circuit integration, the requirements regarding the viscosity, activity, and thermomechanical properties of underfill are becoming increasingly stringent. However, common low-viscosity resins are often obtained with poor thermal and thermomechanical properties. In this study, natural renewable pyrogallol was used as a raw material and preparedto prepare a high-performance polyphenol epoxy resin monomer named E3PG (pyrogallol triglycidyl ether) through employing a combination of epichlorohydrin and olefin epoxidation methods for the first time. At 25°C, the viscosity of E3PG was only 210 cps, indicating excellent processability. Compared with traditional epoxy resin (E51), E3PG has a lower activation energy, and more importantly, exhibits excellent thermomechanical properties after curing; its glass transition temperature (Tg) reaches 164°C, and its storage modulus (E′) reaches 3500 MPa at 25°C. In this study, an epoxy resin monomer with excellent properties was successfully prepared using renewable polyphenols as raw materials, providing a unique and novel approach for the synthesis of epoxy resin monomers.

Room-temperature olefin epoxidation reaction by two 2D cobalt metal-organic complexes under O2 atmosphere: coordination and structural regulation

Room-temperature olefin epoxidation reaction by two 2D cobalt metal-organic complexes under O2 atmosphere: coordination and structural regulation

Design a new unsymmetrical Schiff base chiral Co-complex containing ionic liquid groups as a reusable green catalyst in the epoxidation of alkenes

Design a new unsymmetrical Schiff base chiral Co-complex containing ionic liquid groups as a reusable green catalyst in the epoxidation of alkenes

Exploiting Hydroxamic Acids as Organocatalysts for the Epoxidation of Alkenes with Hydrogen Peroxide as the Oxidant

AbstractThe epoxidation of alkenes has altered and reshaped the way scientists think in modern organic synthesis. Herein, a novel, sustainable and eco‐friendly protocol for the epoxidation of alkenes is reported, utilizing hydrogen peroxide as the green oxidant and, for the first time, hydroxamic acid derivatives as the organocatalyst. The presented methodology is very effective, leading to good to high yields for the oxidation of a variety of olefins, while various functional groups are well tolerated. Mechanistic studies utilizing direct infusion high resolution mass spectrometry (DI‐HRMS) provide strong evidence for the mechanism of the organocatalytic oxidation.

Mechanistic Insights into Ru‐catalyzed Alkene Epoxidation with Nitrous Oxide as a Terminal Oxidant

AbstractNitrous oxide (N2O) is a greenhouse gas produced in the manufacture of 6,6‐nylon and nitric acid. While an attractive oxidant that releases only N2 as a by‐product, the kinetic stability of N2O typically requires high temperatures and pressures for activation. This work describes initial kinetics of oxygen transfer in the epoxidation of cholesteryl acetate with N2O catalysed by D4‐Ru(VI)(por)(O)2 complexes in efforts to provide a better mechanistic understanding of this chemistry. Insights include a need for low concentrations of the alkene to avoid competitive binding to the metal, possible saturation behavior at high N2O pressures, transfer of only one oxygen of RuVI(O)2 to substrate and a possible catalyst turnover involving disproportionation of RuIV(O) and RuIV(O)(N2O) to active RuVI(O)2, RuIV(O) and N2. These insights will be used in future designs of improved catalysts and reaction protocols that may operate efficiently at low pressures of N2O and ambident temperature.

Practical Epoxidation of Olefins Using Air and Ubiquitous Iron-Based Fluorous Salen Complex.

The epoxidation of olefins by substituting "air" for potentially harmful oxidants was achieved using an oxidation method that integrated a fluorous iron(III) salen catalyst derived from common metals and pivalaldehyde. Several aromatic disubstituted olefins were converted into their corresponding epoxides with high efficiency and quantitative yields. This reaction represents an environmentally friendly oxidation process that utilizes an abundant source of air and employs a readily available metal, iron, in the form of salen complexes, making it an environmentally conscious oxidation reaction.

Synthesis, Structural and Redox Properties of Vanadyl β‐Cyanoporphyrin and its Utilization as Efficient Catalyst for Epoxidation of Olefins and Oxidative Bromination of Phenols

Abstract2‐Cyano‐5,10,15,20‐tetraphenylporphyrin [H2TPPCN] (1) having cyano group at one of β‐pyrrolic positions using nucleophilic substitution reaction of tetrabutylammonium cyanide (TBACN) on free‐base 2‐nitro‐5,10,15,20‐tetraphenylporphyrin, and its oxidovanadium(IV) complex [VIVOTPPCN] (2) were synthesized in good yields. Both the porphyrins 1 and 2 have been characterized by UV‐Vis spectroscopy, mass spectrometry, and cyclic voltammetric techniques. Single crystal X‐Ray crystallography revealed quasi‐planar geometry for 1. Compounds 1 and 2 exhibited a red shift (λmax=7–9 nm) in the Soret band relative to [MTPP], where M=2H, VIVO owing to the electron‐withdrawing effect of the cyano group at the β‐position. The first oxidation (ΔE1/2=110–140 mV) and reduction potentials (ΔE1/2=220–260 mV) of 1 and 2 are anodically shifted relative to [MTPP] where M=2H, VIVO. Porphyrin 2 has been utilized as a catalyst for two reactions: epoxidation of olefins and bromination of phenols. The bromination of phenol using KBr/H2O2/HClO4 in water resulted in 100 % conversion with a TOF value as high as 19.6 s−1 in 0.5 h. Using H2O2/NaHCO3 in a CH3CN/H2O solvent mixture at 60 °C, epoxidation was carried out, and the highest conversion rate with a turnover frequency of 1.9 s−1 was achieved in the case of cyclohexene. Catalyst 2 was recovered successfully at the end of the reaction up to 5 cycles and had good thermal stability, indicating its industrial viability and applicability. Moreover, these cyano‐functionalized porphyrins could be further utilized for the generation of molecular self‐assemblies, post‐functionalization of porphyrin core and various applications. The current findings in this work present insights for a facile approach for the synthesis of β‐cyano functionalized porphyrin 1 and further shed light on the utility of its vanadyl complex 2 as an efficient catalyst for olefin epoxidation and phenol bromination reactions.

Electrocatalytic Epoxidation of Cyclooctene on Surface Modified Ni Foam Using Water as Oxygen Source.

Electrochemical epoxidation of olefins using water as an oxygen atom source is emerging as an alternative approach for an atom economic and sustainable method towards a highly selective synthesis of epoxides. We report an electrochemical procedure for epoxidation of cyclooctene using water as the sole oxygen atom source over a sodium dodecyl sulfonate (SDS) modified nickel hydroxide Ni(OH)2 catalyst directly grown on Ni foam. The SDS modification facilitates the mass transfer of cyclooctene towards the anode, thus achieving a 2.5-fold higher conversion with more than 90 % selectivity towards the corresponding epoxide compared with pure Ni(OH)2 catalyst.

Hydrophilic Ti-MWW for catalyzing epoxidation of allyl alcohol

Titanosilicates are widely applied in the alkene epoxidation reactions with high reaction rate and selectivity to desired products. Their catalytic performance depends on the structure topology, the micro-environment of Ti active sites, and the hydrophobicity/hydrophilicity of zeolite framework. Herein, we focus on a hydrophilic substrate of allyl alcohol (AAL) and investigated catalytic performance of four titanosilicates (TS-1, Ti-MOR, Ti-MWW, and Re-Ti-MWW) in the AAL epoxidation reaction with hydrogen peroxide as the oxidant. Among them, Re-Ti-MWW, synthesized via the post-modification of Ti-MWW with piperidine, exhibited the highest activity. Moreover, the preferred solvent changed from MeCN for Ti-MWW to H2O for Re-Ti-MWW. The relative diffusion rate of AAL over Re-Ti-MWW was up to 466 × 10-7 s-1, much larger than those of other zeolites. The higher diffusion rate of Re-Ti-MWW was probably derived from the higher framework hydrophilicity as revealed by the smaller water contact angle of Re-Ti-MWW compared to the other zeolites, which contributed to the high activity in AAL epoxidation. In the continuous slurry reactor, Re-Ti-MWW achieved a high catalytic lifetime of 163 h, with the selectivity of desirable glycidol product maintained at > 97% in the H2O solvent system, showing high potential as an industrial catalyst for the AAL epoxidation reaction.

Mechanistic Insights into Enantiocontrolling of Styrene Monooxygenase-Catalyzed Epoxidation of Olefins

Mechanistic Insights into Enantiocontrolling of Styrene Monooxygenase-Catalyzed Epoxidation of Olefins

Epoxidation of Olefins Catalyzed by Sulfate‐based Supramolecular Ion Pairs

AbstractThe development of inexpensive and effective catalysts for the epoxidation of olefins to epoxides, which are key commodities for the chemical industry, is a continuing challenge. In this context, we present a supramolecular solution with the development of new host‐guest assemblies of sulfate ions and amidoammonium receptor cations that, for the first time, are shown to act as catalysts for olefin epoxidation by hydrogen peroxide under biphasic conditions. Analysis of the reaction mechanism shows that the reactive and oxidizing peroxymonosulfate is formed in the organic phase. Furthermore, a variety of readily available precursors may be used to form the supramolecular ion pairs (SIPs), which is enabling a large‐scale synthesis of the catalysts while maintaining catalytic control and effectiveness.

HClO‐Mediated Photoelectrochemical Epoxidation of Alkenes with Near 100 % Conversion Rate and Selectivity by Regulating Lattice Chlorine Cycle

AbstractDirectional organic transformation via a green, sustainable catalytic reaction has attracted a lot of attention. Herein, we report a photoelectrochemical approach for highly selective epoxidation of alkenes in a salt solution using Co2(OH)3Cl (CoOCl) as a bridge of photo‐generated charge, where the lattice Cl− of CoOCl can be oxidized to generate HClO by the photo‐generated holes of BiVO4 photoanode and be spontaneously recovered by Cl− of a salt solution, which then oxidizes the alkenes into the corresponding epoxides. As a result, a series of water‐soluble alkenes, including 4‐vinylbenzenesulfonic acid sodium, 2‐methyl‐2‐propene‐1‐sulfonic acid sodium, and 3‐methyl‐3‐buten‐1‐ol can be epoxidized with near 100 % conversion rate and selectivity. Through further inserting a MoOx protection layer between BiVO4 and CoOCl, the stability of CoOCl−MoOx/BiVO4 can be maintained for at least 120 hours. This work opens an avenue for solar‐driven organic epoxidation with a possibility of on‐site reaction around the abundant ocean.

HClO-Mediated Photoelectrochemical Epoxidation of Alkenes with Near 100 % Conversion Rate and Selectivity by Regulating Lattice Chlorine Cycle.

Directional organic transformation via a green, sustainable catalytic reaction has attracted a lot of attention. Herein, we report a photoelectrochemical approach for highly selective epoxidation of alkenes in a salt solution using Co2 (OH)3 Cl (CoOCl) as a bridge of photo-generated charge, where the lattice Cl- of CoOCl can be oxidized to generate HClO by the photo-generated holes of BiVO4 photoanode and be spontaneously recovered by Cl- of a salt solution, which then oxidizes the alkenes into the corresponding epoxides. As a result, a series of water-soluble alkenes, including 4-vinylbenzenesulfonic acid sodium, 2-methyl-2-propene-1-sulfonic acid sodium, and 3-methyl-3-buten-1-ol can be epoxidized with near 100 % conversion rate and selectivity. Through further inserting a MoOx protection layer between BiVO4 and CoOCl, the stability of CoOCl-MoOx /BiVO4 can be maintained for at least 120 hours. This work opens an avenue for solar-driven organic epoxidation with a possibility of on-site reaction around the abundant ocean.

Construction of a highly stable natural silicate-supported molybdenum catalyst for efficient epoxidation of olefins

Epoxides are important bulk chemicals, playing irreplaceable role in the chemical industry, but facing serious pollution and low productivity in the production process. Therefore, the development of green and efficient epoxidation of olefins by stable catalysts with low prices is of great significance. In this study, a Mo-MATP catalyst was prepared by modifying Mo(CO)₆ on attapulgite through Si-O bonding. Mo-MATP exhibits excellent performance (99% yield of cyclooctane oxide, CYCO) and stability (80% selectivity of CYCO after 17 cycles), highly tert-butyl hydroperoxide (TBHP) utilization, and extensive substrate scalability. Furthermore, the in-situ Fourier Transform Infrared Spectroscopy (FT-IR), Electron Spin-resonance Spectroscopy (ESR) and High Resolution Mass Spectrometry (HRMS) spectra suggest that TBHP would be activated by Mo-MATP to generate peroxyl radicals, which then oxidize alkenes to their corresponding epoxides. In this study, the stable loading of Mo would largely solve the problem of Mo loss during the catalytic process, thus providing a stable and dispersed Mo active center, enabling the catalyst to possess high catalytic performance and recycling stability.

Trifluoromethyl Ketone Galactose Catalyst for Asymmetric Epoxidation: Experimental and Theoretical Model

AbstractSince the introduction of the Shi catalyst, the organocatalytic epoxidation of olefins has become an area of continued research interest. To explore the possibility of enhancing the efficiency and stability of the catalyst, the synthesis of a galactose‐derived trifluoromethyl ketone, and its use for stereoselective epoxidation reaction that exploits a transitory dioxirane as active species are herein reported. The trifluoromethyl ketone was built on the C6 of a protected d‐galactopyranose. The organocatalyst was obtained smoothly in a few steps, and when utilized for stereoselective epoxidation exhibited excellent stability as no chemical alterations were observed during the reaction. The stereoselectivity, although sometimes moderate, appears surprisingly high considering the conformational freedom of the trifluoromethyl ketone moiety.DFT calculations were performed to investigate the interactions involved in regulating the observed selectivities. Moreover, a new mnemonic model has been developed to serve as a fast‐predicting tool for epoxidation of new substrates.

Switching Product Selectivity in Immobilized Tungstate Catalysts by Control of Hydrophobicity of Mesoporous Silicate Supports

AbstractNovel mesoporous silicates modified with imidazolium cation were applied as the support for peroxotungstate. Stepwise introduction of multiple functional groups to SBA‐15 was achieved by the combination of the direct and post‐synthesis procedures. The co‐condensation of tetraethoxysilane and 3‐(imidazolyl‐1‐yl)‐propyltriethoxysilane in the presence of the micelles of an amphiphilic surfactant yields the hydrophilic SBA‐15 type silicate support with the imidazole modifier locating into the mesopores. The hydrophobic environment of the supports was imparted by capping the residual silanols on the silicate surface with trimethylsilyl groups. The fluoroalkyl‐ or alkyl‐imidazolium cation‐anchored supports were derived from the corresponding imidazole‐functionalized precursors. The anion‐exchanging reaction between peroxytungstate and the imidazolium cation‐anchored supports yielded the corresponding tungstate‐immobilized catalysts. The hydrophilic catalyst with the fluoroalkyl‐imidazolium mediated alkene epoxidation with H2O2 in less polar solvents. The hydrophobic one, in contrast, produced diol through the epoxidation and following hydration in an aqueous solvent by the action of the highly Lewis acidic tungsten. The hydrophobic catalysts had the advantage of being more tolerant than hydrophilic catalysts, as evidenced by reusability tests. The activities of the alkyl‐imidazolium catalysts were lower than those of the corresponding fluoroalkyl‐imidazolium catalysts, indicating that the local structures surrounding the tungstate site affected the catalytic performance.

Mechanistic insights on the epoxidation of alkenes by high-valent non-heme Fe(iv) and Fe(v) oxidants: a comparative theoretical study

This work is based on the screening of better high-valent oxidants, and also includes a mechanistic study during oxygen atom transfer reactions.

Bulky olefin epoxidation under mild conditions over Mo-based oxide catalysts

Epoxidation of bulky olefins, such as biobased fatty acid methyl esters (FAMEs), with tert-butylhydroperoxide (TBHP), under mild conditions, was promoted by nanocatalysts possessing Mo and M = Ta, Nb or W, prepared via simple, versatile methodology.