Epoxidation Of Cyclohexene Research Articles

Selective Oxidation of Cyclohexene with H2O2 Catalyzed by Resin Supported Peroxo Phosphotungstic Acid Under Mild Conditions

A series of modified chloromethyl polystyrene resins loaded with peroxo phosphotungstic acid catalysts were synthesized for the selective oxidation of cyclohexene. The surface of resin was enriched with high concentration quaternary ammonium salt, and grafted with a large amount of peroxo PW-anion through ion exchange. The novel resin catalyst showed excellent cyclohexene conversion and epoxide selectivity using 30% H2O2 as oxidant at ambient temperature. Furthermore, the resin catalyst exhibited excellent recycling stability, which can be reused by a simple filtration and the peroxo phosphotungstic acid did not leach into the solvent after reaction.

Hydrothermal synthesis of tungsten-tin bimetallic MFI type zeolites and their catalytic properties for cyclohexene epoxidation

Abstract A series of tungsten-tin bimetallic MFI type zeolites (WSn-MFI) with different Sn and W contents were hydrothermally synthesized using tetrapropyl ammonium hydroxide (TPAOH) as a template and polypyrrolidone as a co-surfactant. Tetraethylorthosilicate (TEOS), ammonium tungstate hydrate and tin (IV) chloride pentahydrate were used as the Si, W and Sn sources, respectively. The resultant samples were characterized by various techniques, and were evaluated as catalysts for the epoxidation of cyclohexene with hydrogen peroxide. The results reveal that all the W–Sn bimetallic zeolites have the typical MFI structure, and their relative crystallinities and morphologies change somewhat with the variety of W and Sn contents. Both the isolated framework SnO4 species and the extra-framework SnO2 species could be detected in all WSn-MFI samples, while only trace amount of extra-framework W species are present inside the channels/cages of the bimetallic zeolites. Compared with the monometallic zeolites of W-MFI and Sn-MFI, the bimetallic WSn-MFI zeolites exhibit much higher catalytic activity for the epoxidation of cyclohexene. Of these, the sample named WSn-MFI-a could efficiently convert cyclohexene to the corresponding epoxide with a high yield of 79% under an optimized reaction condition. A synergistic effect between the W and Sn species should play critical role in improving the catalytic activity and the epoxide selectivity of the bimetallic zeolite catalysts.

Tetranuclear molybdenum(vi) hydrazonato epoxidation (pre)catalysts: Is water always the best choice?

Self-assembled tetranuclear molybdenum(vi) complexes with hydrazonato ligands, [MoO2L]4, were tested as (pre)catalysts for cyclooctene and cyclohexene epoxidation without extra organic solvent added. Special attention was addressed to the comparison of oxidizing agents, TBHP in water vs. TBHP in decane. The idea was to test the greenness of the complete process. Density Functional Theory calculations were used to support and explain experimental catalytic result for tetranuclear self-assembled systems.

Bimetallic Aluminum Complexes Bearing Binaphthyl-Based Iminophenolate Ligands as Catalysts for the Synthesis of Polyesters

Two dinuclear aluminum complexes bearing dinaphthalene bridging Schiff bases have been synthesized and investigated as catalysts in ring-opening polymerization (ROP) of cyclic esters such as rac-lactide (rac-LA) and ε-caprolactone (ε-CL) and in the copolymerization (ROCOP) of phthalic anhydride (PA) with cyclohexene oxide (CHO) and limonene oxide (LO). The polymerizations of cyclic esters were living, producing polymers with narrow molar mass distributions. Kinetic studies showed that the polymerizations were first order with respect to the monomers. Cooperative effects between two metal centers, located in proximal positions, are invoked to rationalize the high activities toward both monomers, although the rigid backbone of the complexes enhances the reactivity of less encumbered caprolactone in comparison to lactide. Good activities were achieved also in the copolymerization of phthalic anhydride with cyclohexene epoxide and with the bioderived limonene oxide.

Highly selective epoxidation of olefins using vanadium (IV) schiff base- amine-tagged graphene oxide composite

Catalysts are of great importance in the petrochemical industry, so the design and synthesis of heterogeneous catalysts for this purpose is the most important field in catalysts. In this context, 3-aminopropyltriethoxysilane was grafted into graphene oxide via the condensation reaction, and then the amine terminal groups were utilized to produce azomethine (–C = N–) group using the 3-formyl 4-hydroxy benzoic acid compound. The post-modification approach was used to fabricate the novel vanadium (IV) Schiff-base complex. Characterization was carried out to achieve chemical composition and physical properties such as Raman spectroscopy, FTIR, XRD, XPS, elementary analysis, TGA, FESEM-EDX, AFM, HRTEM, and nitrogen sorption have been performed to realize the grafting vanadium (IV) Schiff base complex on GO. The value of the prepared material as a catalyst was examined for the epoxidation of cyclohexene, cyclooctene, 1-octene, styrene, allyl bromide, and ally alcohol, and styrene. Also, the impact of pH, time, temperature, and catalyst dose was observed. The results showed that the novel catalyst for the epoxidation reaction showed distinct catalytic efficiency. Besides, owing to the strong interaction between the V(IV) ions and chelating moieties in GO, the novel catalyst showed outstanding recycling effectiveness after being used for six subsequent cycles.

Demonstrating the Critical Role of Solvation in Supported Ti and Nb Epoxidation Catalysts via Vapor-Phase Kinetics

Catalytic oxidation of hydrocarbons with hydrogen peroxide (H2O2) has been of the utmost importance for several decades. The vast majority of studies have been performed in the condensed phase, even though condensed phases introduce complex solvent effects and can promote the leaching of active sites. In response, we have built a custom reactor system to understand H2O2 activation and selective oxidation in the vapor-phase. In this report, we study the epoxidation of cyclohexene with H2O2 over four Lewis-acidic metal oxide catalysts: Ti and Nb grafted on SiO2 and on the Zr based metal–organic framework, NU-1000. The M–SiO2 materials are highly selective to the formation of epoxides and diols, as they can be in the condensed phase, while the NU-1000 based materials are far more prone to overoxidation to CO2, which appears to be connected to their strong reactant adsorption. Apparent activation energies are calculated for all materials when operating in the same kinetic regime, and the heats of cyclohexene adsorption into their pores are then used to directly compare intrinsic enthalpies of activation in the vapor vs condensed phase for the M–SiO2 catalysts. Nb–SiO2 catalysts exhibit similar intrinsic enthalpies of activation in the vapor and condensed phases, whereas the condensed phase transition state in Ti–SiO2 is 24 kJ/mol lower in energy than that of the same material in the vapor phase. These experiments establish another methodology for understanding the various roles of solvent in selective oxidation reactions and studying these reactions under conditions that differ significantly from the thousands of prior studies in the condensed phase.

Enzymatic epoxidation of cyclohexene by peroxidase immobilization on a textile and an adapted reactor design

A textile-based reaction system for new peroxidase reactions in non-native media was implemented. The epoxidation of cyclohexene by the commercial peroxidase MaxiBright® was realized with the textile-immobilized enzyme in an adapted liquid-liquid two-phase reactor. A commercially available polyester felt was used as low-price carrier and functionalized with polyvinyl amine. The covalent immobilization with glutardialdehyde lead to an enzyme loading of 0.10 genzyme/gtextile. The textile-based peroxidase shows a high activity retention in the presence of organic media. This catalyst is shown to enable the epoxidation of cyclohexene in various solvents as well as under neat conditions. A model reactor was produced by 3D printing which places the textile catalyst at the interphase between the liquid reaction phase and the product extracting solvent.

Bolaform surfactant-directed synthesis of TS-1 zeolite nanosheets for catalytic epoxidation of bulky cyclic olefins

Hierarchical TS-1 nanosheets were hydrothermally synthesized by using a bolaform surfactant as the structure-directing agent and exhibited improved catalytic performance and superior recyclability in the epoxidation of cyclohexene and cyclooctene.

Cyclohexene epoxidation with H2O2 in the vapor and liquid phases over a vanadium-based metal–organic framework

A V-containing metal–organic framework exhibits significantly different catalytic mechanisms between liquid-phase and gas-phase cyclohexene oxidations.

Fast synthesis of hierarchical Al-free Ti-BEA plate-like nanocrystals from low-templated dry gel via a steam-assisted conversion method

A hierarchical nanosized Ti-BEA zeolite prepared via a green steam-assisted conversion (SAC) method.

Nickel(ii)dibenzotetramethyltetraaza[14]annulene complex immobilized on amino-functionalized TUD-1: an efficient catalyst for immediate and quantitative epoxidation of cyclohexene under ambient conditions

Nickel(ii)dibenzotetramethyltetraaza[14]annulene complex immobilized on amino-functionalized TUD-1 as a new nanocatalyst for spontaneous and quantitative epoxidation of cyclohexene under ambient conditions.

Organic Solvent-Free Olefins and Alcohols (ep)oxidation Using Recoverable Catalysts Based on [PM12O40]3- (M = Mo or W) Ionically Grafted on Amino Functionalized Silica Nanobeads.

Catalyzed organic solvent-free (ep)oxidation were achieved using H3PM12O40 (M = Mo or W) complexes ionically grafted on APTES-functionalized nano-silica beads obtained from straightforward method (APTES = aminopropyltriethoxysilane). Those catalysts have been extensively analyzed through morphological studies (Dynamic Light Scattering (DLS), TEM) and several spectroscopic qualitative (IR, multinuclear solid-state NMR) and quantitative (1H and 31P solution NMR) methods. Interesting catalytic results were obtained for the epoxidation of cyclooctene, cyclohexene, limonene and oxidation of cyclohexanol with a lower [POM]/olefin ratio. The catalysts were found to be recyclable and reused during three runs with similar catalytic performances.

Epoxidation of cyclohexene with H2O2 over efficient water‐tolerant heterogeneous catalysts composed of mono‐substituted phosphotungstic acid on co‐functionalized SBA‐15

A series of Keggin‐type heteropolyacid‐based heterogeneous catalysts (Co‐/Fe‐/Cu‐POM‐octyl‐NH3‐SBA‐15) were synthesized via immobilized transition metal mono‐ substituted phosphotungstic acids (Co‐/Fe‐/Cu‐POM) on octyl‐amino‐co‐functionalized mesoporous silica SBA‐15 (octyl‐NH2‐SBA‐15). Characterization results indicated that Co‐/Fe‐/Cu‐POM units were highly dispersed in mesochannels of SBA‐15, and both types of Brønsted and Lewis acid sites existed in Co‐/Fe‐/Cu‐POM‐octyl‐NH3‐SBA‐15 catalysts. Co‐POM‐octyl‐NH3‐SBA‐15 catalyst showed excellent catalytic performance in H2O2‐mediated cyclohexene epoxidation with 83.8% of cyclohexene conversion, 92.8% of cyclohexene oxide selectivity, and 98/2 of epoxidation/allylic oxidation selectivity. The order of catalytic activity was Co‐POM‐octyl‐NH3‐SBA‐15 > Fe‐POM‐octyl‐NH3‐SBA‐15 > Cu‐POM‐octyl‐NH3‐SBA‐15. In order to obtain insights into the role of ‐octyl moieties during catalysis, an octyl‐free catalyst (Co‐POM‐NH3‐SBA‐15) was also synthesized. In comparison with Co‐POM‐NH3‐SBA‐15, Co‐POM‐octyl‐NH3‐SBA‐15 showed enhanced catalytic properties (viz. activity and selectivity) in cyclohexene epoxidation. Strong chemical bonding between ‐NH3+ anchored on the surface of SBA‐15 and heteropolyanions resulted in excellent stability of Co‐POM‐octyl‐NH3‐SBA‐15 catalyst, and it could be reused six times without considerable loss of activity.

Synthesis and Crystal Structure of a Dioxomolybdenum(VI) Complex Derived from 2-Bromo-N'-(3,5-dichloro-2-hydroxybenzylidene)benzohydrazide with Catalytic Epoxidation Property

A dioxomolybdenum(VI) complex [MoO2L(EtOH)] (I), derived from the hydrazone ligand 2‑bromo-N'-(3,5-dichloro-2-hydroxybenzylidene)benzohydrazide has been prepared and characterized by physico-chemical and spectroscopic methods, as well as single crystal X-ray diffraction (CIF file CCDC no. 1840671). The hydrazone ligand coordinates to the Mo atom through the phenolate oxygen, imino nitrogen, and enolic oxygen. The Mo atom is six-coordinate in an octahedral geometry. Complex I shows high catalytic activity and selectivity in the epoxidation of cyclohexene with tert-butylhydroperoxide as primary oxidant.

Regulation of framework titanium siting in MWW-type titanosilicates by boron and aluminum incorporation and its effect on the catalytic performance

Abstract The exploration of efficient catalysts with more accessible active titanium species based on the titanosilicate zeolites is in incremental demands for the construction of the high utilization active centers to the various reactions. Here, we report an active oxidation catalyst MWW-type titanosilicate (Al-Ti-MWW) with more “Ti” active species distributed on the zeolite surface obtained through the implantation of the heteroatom aluminum to the conventional Ti-MWW synthesis. Combined with the overall measurements, it was deduced that more “Ti” species were regulated to evenly distributed in the zeolite crystal, which was due to the competitive occupancy of the heteroatom Al, B and Ti over T locations. Consequently, the bulky-substrate reaction results such as the cyclohexene epoxidation reaction and cyclohexanone ammoximation reaction showed that the Al-Ti-MWW catalyst had a superior catalytic oxidation activity than that of conventional Ti-MWW. It is believed that the application of the convenient treatment method could provide an effective strategy for designing high-performance titanosilicate catalysts.

A Facile Synthesis of Molybdenum‐Promoted Reduced Graphene Oxide as Catalyst towards Epoxidation of Cyclohexene

AbstractA facile method by incipient wetness impregnation for synthesis of materials with different ratios of molybdenum (5/100), (10/100) and (15/100) promoted on reduced graphene oxide (RGO) is reported. Catalytic activity of the prepared materials towards liquid phase epoxidation of cyclohexene was investigated. The catalyst materials were fully characterized by varied techniques including XRD, FT‐IR, Raman spectra, and SEM analysis. The (10/100) metal to substrate ratio catalyst (Mo‐RGO‐2) showed excellent efficiency with 100% conversion of cyclohexene with 93% selectivity towards cyclohexene oxide. The catalyst exhibited good stability during recycling tests.

Cobalt imine–pyridine–carbonyl complex functionalized metal–organic frameworks as catalysts for alkene epoxidation

Aerobic epoxidation of alkene is a green and economical route to produce epoxides. For such reaction, transition metal complexes exhibit favorable catalytic activity. In this work, NH2-MIL-101, a stable metal–organic framework (MOF) material with large surface area and high pore volume, was functionalized with pyridine-2,6-dicarbaldehyde and Co(NO3)2, to realize the immobilization of Co(II) via imine–pyridine–carbonyl (N,N,O) tridentate ligands bonding to MOF skeleton. The modified materials were applied as heterogeneous catalysts for the aerobic epoxidation of cyclohexene at ambient temperature, and multiple factors were studied to explore their influences on catalytic effects. Under the optimal reaction conditions, satisfactory substrate conversion and epoxide selectivity were reached. In addition, this catalytic system is suitable for a variety of alkene substrates. Furthermore, recycle experiments and infrared spectroscopy characterization illustrated that the coordination surroundings of Co are altering smoothly during the reaction process, thus having an impact on the performance of catalyst.

Dynamic Reorganization and Confinement of TiIV Active Sites Controls Olefin Epoxidation Catalysis on Two-Dimensional Zeotypes.

The effect of dynamic reorganization and confinement of isolated TiIV catalytic centers supported on silicates is investigated for olefin epoxidation. Active sites consist of grafted single-site calix[4]arene-TiIV centers or their calcined counterparts. Their location is synthetically controlled to be either unconfined at terminal T-atom positions (denoted as type-(i)) or within confining 12-MR pockets (denoted as type-(ii); diameter ∼7 Å, volume ∼185 Å3) composed of hemispherical cavities on the external surface of zeotypes with *-SVY topology. Electronic structure calculations (density functional theory) indicate that active sites consist of cooperative assemblies of TiIV centers and silanols. When active sites are located at unconfined type-(i) environments, the rate constants for cyclohexene epoxidation (323 K, 0.05 mM TiIV, 160 mM cyclohexene, 24 mM tert-butyl hydroperoxide) are 9 ± 2 M-2 s-1; whereas within confining type-(ii) 12-MR pockets, there is a ∼5-fold enhancement to 48 ± 8 M-2 s-1. When a mixture of both environments is initially present in the catalyst resting state, the rate constants reflect confining environments exclusively (40 ± 11 M-2 s-1), indicating that dynamic reorganization processes lead to the preferential location of active sites within 12-MR pockets. While activation enthalpies are Δ H‡app = 43 ± 1 kJ mol-1 irrespective of active site location, confining environments exhibit diminished entropic barriers (Δ S‡app = -68 J mol-1 K-1 for unconfined type-(i) vs -56 J mol-1 K-1 for confining type-(ii)), indicating that confinement leads to more facile association of reactants at active sites to form transition state structures (volume ∼ 225 Å3). These results open new opportunities for controlling reactivity on surfaces through partial confinement on shallow external-surface pockets, which are accessible to molecules that are too bulky to benefit from traditional confinement within micropores.

Cyclohexene Oxidation with H2O2 over Metal-Organic Framework MIL-125(Ti): The Effect of Protons on Reactivity

The catalytic performance of the titanium-based metal–organic framework MIL-125 was evaluated in the selective oxidation of cyclohexene (CyH) with environmentally friendly oxidants, H2O2 and tBuOOH. The catalytic activity of MIL-125 as well as the oxidant utilization efficiency and selectivity toward epoxide and epoxide-derived products can be greatly improved by acid additives (HClO4 or CF3SO3H). In the presence of 1 molar equivalent (relative to Ti) of a proton source, the total selectivity toward CyH epoxide and trans-cyclohexane-1,2-diol reached 75–80% at 38–43% alkene conversion after 45 min of reaction with 1 equivalent of 30% H2O2 at 50 °C. With 50% H2O2 as the oxidant, the total selectivity toward heterolytic oxidation products increased up to 92% at the same level of alkene conversion. N2 adsorption, powder X-ray diffraction (PXRD), and infrared (IR) spectroscopy studies before and after the catalytic oxidations confirmed the absence of structural changes in the Metal–organic framework (MOF) structure. MIL-125 was stable toward titanium leaching, behaved as a truly heterogeneous catalyst, and could easily be recovered and reused several times without any loss of the catalytic properties.

Fabrication of Super-Hydrophobic Titanosilicate Sub-micro Sphere with Enhanced Epoxidation Catalytic Activity

A super-hydrophobic titanosilicate sub-micro sphere was synthesized via coating a layered organo-titanosilicate onto a hydrophobic silica sphere. The obtained materials exhibit enhanced catalytic activity in cyclohexene epoxidation at 30 °C using 30% H2O2 aqueous solution as oxidant.