Epoxidation Of Cyclohexene Research Articles

New mesoporous titanosilicate MCM-36 material synthesized by pillaring layered ERB-1 precursor

New mesoporous Ti-containing MCM-36 materials prepared by pillaring borosilicate ERB-1 precursor with titanosilicate have significantly improved catalytic activities in cyclohexene epoxidation, in comparison with analogous materials prepared from MCM-22.

Synthesis and Catalytic Applications of Chemically Grafted SiH-Functionalized Tripodal Ti-POSS Complexes in Crosslinked Hyperbranched Poly(siloxysilane)

This study investigated the synthesis, activity, epoxide selectivity, H2O2 efficiency, and recyclability of new heterogeneous alkene epoxidation catalysts prepared by chemical grafting of new SiH-functionalized tripodal Ti–polyhedral oligomeric silsesquioxane (Ti-POSS) complexes in hyperbranched poly(siloxysilane) via hydrosilation. Crosslinked hyperbranched poly(siloxysilane)-grafted [{(p-HSiMe2(CH2)2C6H4)(c-C6H11)6Si7O12}Ti(NMe2)] (11) and crosslinked hyperbranched poly(siloxysilane)-grafted [{(HSiMe2(CH2)3)(i-C4H9)6Si7O12}- Ti(NMe2)] (12) displayed high activity, epoxide selectivity (≥98 %), and H2O2 efficiency (≥97 %) in cyclohexene and 1-octene epoxidation with aqueous H2O2. Moreover, these catalysts were highly recyclable with retained activity and durability and proved to be truly heterogeneous. Using chemical grafting for the synthesis of 11 and 12 enhanced their recyclability and durability with retained activity. The high H2O2 efficiency can be attributed to the uniformly non-polar environment provided about Ti in 11 and 12 by the polymer; this results in low water concentrations and higher [alkene] : [H2O2] ratios at the Ti active site than in the rest of the solution. These effects enhance the epoxide selectivity and minimize leaching of titanium.

Preparation and characterization of activated montmorillonite clay supported 11-molybdo-vanado-phosphoric acid for cyclohexene oxidation

Heterogenization of homogenous catalysts consisting of vanadium substituted polyphosphomolybdate with Keggin structure supported on activated bentonite for epoxidation of cyclohexene.

Molybdenum(VI) complex with a tridentate Schiff base ligand immobilized on SBA-15 as effective catalysts in epoxidation of alkenes

Two novel molybdenum(VI) tridentate Schiff base complexes supported onto modified mesoporous SBA-15 were prepared by a covalent grafting method, one of which involved the postsynthesis trimethylsilylation of Mo-FSAP-Cl-SBA-15 to remove the residual surface silanol groups. The prepared complex materials were characterized by FT-IR, XRD, SEM, TEM, 29Si CP–MAS-NMR, TGA, ICP-AES and nitrogen adsorption–desorption. Both two were active in the catalytic epoxidation of cyclohexene at 80°C using tert-butylhydroperoxide (TBHP) as oxidant and 1,2-dichloroethane as solvent. The catalytic activity of the heterogenized organo catalyst can be further enhanced by silylation of the residual Si–OH groups using Me3SiCl, due to the higher content of Mo active sites and better surface hydrophobicity. As a result, using the more efficient catalyst Mo-FSAP-CH3-Cl-SBA-15 for catalytic reaction, the conversion and selectivity were 94.38% and 91.63%, respectively, under the optimized condition. After being used five times, the conversion and selectivity of Mo-FSAP-CH3-Cl-SBA-15 were still above 80.00% and 90.00% indicating the good reusability of Mo-FSAP-CH3-Cl-SBA-15.

An Efficient Catalyst Based on a Metal Metalloporphyrinic Framework for Highly Selective Oxidation

An efficient metal–organic framework catalyst was developed with manganese tetrakis(4-carboxyphenyl)porphyrin as either bridging moiety or catalytically active sites under a hydrothermal condition. Surprisingly, the X-ray diffraction details showed that this porous network, MMPF (MMPF denotes iron-connected metal metalloporphyrinic framework) was successfully constructed with a physically flexible framework and resistance to basic solution. Accordingly, catalytic studies have demonstrated that MMPF can catalyze the selective oxidation of a variety of substrates with PhIO as oxidant in acetonitrile solution under mild temperature. More importantly, the MMPF outperformed the homogeneous Mn-TPP in catalyzing epoxidation of cyclohexene, mainly due to its high efficiency of 3D network-based nanochannel-reactor in MMPF. This gave rise to a structural resistance to formation of catalytically inactive species.

Effect of the synthetic method on the catalytic activity of alumina: Epoxidation of cyclohexene

Al2O3 was prepared from different inorganic precursors via the Pechini method and compared with Al2O3 prepared by the sol–gel method. Structural characterization of these materials was carried out by FTIR, X-ray diffraction (XRD), N2 adsorption at −196°C and transmission electron microscopy (TEM). The solids were tested in the epoxidation of cyclohexene and a difference in their catalytic activities was observed. The characterization results indicate that the samples prepared by Pechini have a mixture of γ-alumina and boehmite, a condition favoring catalytic activity, whereas the sol–gel sample is less crystalline due to higher boehmite content. These results indicate that both the nature of the precursor and the method of synthesis strongly affect the catalytic activity of Al2O3.

Preparation of Immobilized Chromium Schiff Base Complexes and their Catalytic Performance for Olefins Epoxidation

A series of transition metal alanine-salicylaldehyde Schiff base chromium (III) complexes immobilized on MCM-41 were prepared and characterized by various physico-chemical measurements such as FIIR, XRD, HRTEM, N2 sorption and elemental analysis. The immobilized complexes were effective and stable catalysts for the epoxidation of styrene and cyclohexene with 30% hydrogen peroxide. Moreover, the metal centers were found to play important roles in the catalytic performance of immobilized complex catalysts.

Bioinspired covalently grafted Cu(II)–C protected amino acid complexes: selective catalysts in the epoxidation of cyclohexene

In this work, the syntheses of covalently grafted C-protected Cu(II)–amino acid (methylesters of l-histidine and l-cystine) uniform and mixed ligand complexes with two different amino acid esters are described using chloropropylated silica gel as the support. The conditions of the syntheses were systematically altered. The structural features of the substances obtained were studied by the Kjeldahl method, ICP-MS, X-ray absorption and mid/far infrared spectroscopies. The superoxide dismutase-like activities of the materials were determined in a biochemical test reaction and these substances were also tested as catalysts in the oxidation of cyclohexene. It was possible to prepare metal ion-amino acid complexes grafted with covalent bonds onto the supports. All the covalently anchored materials displayed superoxide dismutase-like activity and most of them were active in the oxidation of cyclohexene, providing the epoxide with high selectivity.

Effect of fungal and plant metabolites on broomrapes (Orobanche and Phelipanche spp.) seed germination and radicle growth.

Orobanche and Phelipanche species (the broomrapes) are root parasitic plants, some of which cause heavy yield losses on important crops. The development of herbicides based on natural metabolites from microbial and plant origin, targeting early stages on parasitic plant development, might contribute to the reduction of broomrape seed bank in agricultural soils. Therefore, the effect of metabolites belonging to different classes of natural compounds on broomrape seed germination and radicle development was assayed in vitro. Among the metabolites tested, epi-sphaeropsidone, cyclopaldic acid, and those belonging to the sesquiterpene class induced broomrape germination in a species-specific manner. epi-Epoformin, sphaeropsidin A, and cytochalasans inhibited germination of GR24-treated broomrape seeds. The growth of broomrape radicle was strongly inhibited by sphaeropsidin A and compounds belonging to cyclohexene epoxide and cytochalasan classes. Broomrape radicles treated with epi-sphaeropsidone developed a layer of papillae while radicles treated with cytochalasans or with sphaeropsidin A turned necrotic. These findings allow new lead natural herbicides for the management of parasitic weeds to be identified.

New Ti-incorporated MCM-36 as an efficient epoxidation catalyst prepared by pillaring MCM-22 layers with titanosilicate

A new Ti-incorporated MCM-36 material (shortly termed Si/Ti-MCM-36) with bimodal pore structures was prepared through sequential steps. The hexadecyltrimethylammonium swollen MCM-22 precursor was pillared with titanosilicate formed via hydrolysis of an interlayer mixture of tetraethylorthosilicate (TEOS) and tetrabutylorthotitanate (TBOT). Hydrolyzation of TEOS and TBOT was a key step for intercalation efficiency. The X-ray diffraction (XRD) patterns and N2 sorption isotherm data confirmed the intercalation efficiency and the retention of basal layer MWW structure. A slightly ordered stacking of MWW sheets along c-direction was observed, generating mesopores of ca. 2nm in diameter. Ti(IV) was well dispersed in the matrix of titanosilicate pillars, which expand the MWW layers apart. The Ti coordination environment examined by DR UV–Vis and Ti K-edge X-ray absorption spectroscopies was mainly in tetrahedral coordination. Post-treatment of the Si/Ti-MCM-36 materials with acid resulted in a new Ti-incorporated MCM-36 with good catalytic activities in cyclohexene epoxidation.

Selective Epoxidation of Cyclohexene Catalyzed by New Bidentate Schiff Base Dioxomolybdenum(VI) Complex Immobilized on Crosslinked Polystyrene Microspheres

A new immobilized bidentate Schiff base dioxomolybdenum(VI) complex was prepared with chloromethlated crosslinked polystyrene (CMCPS) microspheres as starting carrier via two stepwise polymer reactions with p-hydroxybenzaldehyde and glycine as reagents, respectively, as well as a coordination reaction with MoO2(acac)2, and the immobilized dioxomolybdenum(VI) complex abbreviated to CPS-[MoO2(ALGL)2] (ALGL refers to the bidentate Schiff base ligand, which comes form aldehyde [AL] group and glycine [GL]) was used in the epoxidation reaction of cyclohexene with tert-butyl hydroperoxide (TBHP) as oxidant. In the epoxidation reaction of cyclohexene, this heterogeneous dioxomolybdenum(VI) complex catalyst has high catalytic activity and excellent catalytic selectivity.

Zirconium phenylphosphonate-anchored methyltrioxorhenium as novel heterogeneous catalyst for epoxidation of cyclohexene

Epoxidation of olefins to epoxides is widely recognized as an important unit process in the manufacture of fine chemicals and intermediates. Developing an environmentally benign heterogeneous catalytic system for olefin epoxidation with high activity and selectivity is still a challenge in this research field. Herein, we report our attempts to synthesize novel zirconium phenylphosphonate-anchored methyltrioxorhenium (MTO/ZrPP) heterogeneous catalysts by a conventional impregnation method and evaluate their catalytic performance for epoxidation of cyclohexene using urea–hydrogen peroxide adduct (UHP) as oxidant without the addition of base ligands. The MTO/ZrPP catalyst samples are characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), inductively coupled plasma emission spectrometry (ICP-ES), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and solid-state 1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR) techniques. Meanwhile, the density functional theory (DFT) calculation is carried out to further understand the structure feature and interactions of the MTO/ZrPP catalyst. It is revealed that MTO is anchored on support surface by the favored hydrogen-bonding interaction between two oxo ligands of MTO and two H atoms from the adjacent phenyls of ZrPP. MTO/ZrPP catalyst displays excellent catalytic activity for cyclohexene epoxidation. Moreover, only cyclohexene oxide production can be obtained under the employed reaction conditions.

Effectiveness of the reversible structural conversion of MWW zeolite for preparation of interlayer-expanded Ti-MWW with high catalytic performance in olefin epoxidation

Interlayer-expanded MWW-type titanosilicate, Ti-IEZ-MWW, has been successfully prepared through the reversible structural conversion (RSC) of the MWW zeolite. First, the layered precursor of the MWW titanosilicates, Ti-MWW(P), was treated in an aqueous solution of HNO3 to remove octahedrally-coordinated Ti species in Ti-MWW(P) (Ti-MWW(P)-AT). This acid-treatment led to the partial removal of piperidine molecules, which served as pillaring species between the MWW layers as well as the structure-directing agent for the MWW-type zeolite, resulting in the condensation of silanol on the layer surface and formation of the three-dimensional (3D) MWW structure. Next, to promote the structural rearrangement from the 3D MWW structure to the original layered precursor, Ti-MWW(P)-AT was hydrothermally treated in the aqueous solution containing piperidine, forming a layered material (Ti-MWW(P)-RSC), which has almost the same structure as Ti-MWW(P). Finally, the interlayer silylation of Ti-MWW(P)-RSC was performed using diethoxydimethylsilane under acidic conditions. Thus prepared material, Ti-IEZ-MWW-RSC, contained unique framework Ti species and showed a higher catalytic activity in the epoxidation of cyclohexene with H2O2 compared to Ti-IEZ-MWW directly prepared from Ti-MWW(P) as well as the conventional 3D Ti-MWW.

Liquid phase cyclohexene oxidation over vanadia based catalysts with tert-butyl hydroperoxide: Epoxidation versus allylic oxidation

VO2–SiO2 based catalysts with V contents between 5 and 20wt.% were prepared from inorganic precursors via the sol–gel process and subsequently dried, calcined and reduced at 673K. Structural characterization of these materials was carried out with X-rays diffraction (XRD), ICP, N2 adsorption–desorption at 77K, UV–vis diffused reflectance spectroscopy (DR UV–vis), FTIR and pyridine adsorption followed by FTIR. Their catalytic activities in the cyclohexene epoxidation with TBHP as oxidant and heptane as solvent were also examined. Results of XRD and DR UV–visible spectroscopy revealed that VO2 species are well dispersed on silica. BET analysis showed that the surface area decreases from 390 to 22m2g−1 with V content. The results of pyridine adsorption followed by FTIR indicated that the 5wt.% VO2–SiO2 catalyst displays low acid densities. Experimental results pointed out that the 5wt.% VO2–SiO2 catalysts offer excellent activity. The obtained cyclohexene conversion and selectivity toward epoxide are 21% and 84% respectively. A reaction mechanism explaining clearly epoxidation versus allylic oxidation is proposed.

Photoactivation of Molecular Oxygen by an Iron(III) Porphyrin with a Magnesium Aluminum Layered Double Hydroxide for the Aerobic Epoxidation of Cyclohexene

AbstractThe photocatalytic aerobic epoxidation of cyclohexene proceeded under visible‐light irradiation only if 5,10,15,20tetrakis(pentafluorophenyl)porphyrin iron(III) chloride ([FeIII(TPFPP)Cl]) was combined with Mg‐Al layered double hydroxide (Mg‐Al LDH) as a solid base in chloroform. The OH groups in the Mg‐Al LDH exchanged with the axial Cl ligands in [FeIII(TPFPP)Cl] to afford [FeIII(TPFPP)OH], which functioned photocatalytically in the presence of Mg‐Al LDH but was inactive in its absence. The band in the action spectrum agreed well with the Soret band in the UV/Vis absorption spectrum of [FeIII(TPFPP)OH]. The spectral changes indicated the reduction of [FeIII(TPFPP)OH] to [FeII(TPFPP)] under visible‐light irradiation, which in turn activates O2 that could be used for the epoxidation of cyclohexene.

Titanosilicate composite with zeolite-large-crystal core and mesoporous shell structures: One-step synthesis and application in catalytic oxidations

Porous titanosilicate composite with a core/shell structure and tetrahedral Ti species was synthesized by one-step process in fluoride medium, in which a mixture of small organic ammonium salt and cationic polymer was used as template. The composite displayed higher activity than the TS-1 large crystals prepared without cationic polymer in the epoxidation of cyclohexene with aqueous H2O2 and tert-butyl hydroperoxide, mainly ascribed to the improved accessibility of reactants to the active sites via the mesopores in the shell. Notably, the composite can be easily separated from the reaction solution thanks to its large crystal format.

A MoVI grafted Metal Organic Framework: Synthesis, characterization and catalytic investigations

We present the post-modification of a gallium based Metal Organic Framework, COMOC-4, with a Mo-complex. The resulting Mo@COMOC-4 was characterized by means of N2 sorption, XRPD, DRIFT, TGA, XRF, XPS and TEM analysis. The results demonstrate that even at high Mo-complex loadings on the framework, no aggregation or any Mo or Mo oxide species are formed. Moreover, the Mo@COMOC-4 was evaluated as a catalyst in the epoxidation of cyclohexene, cyclooctene and cyclododecene employing TBHP in decane as oxidant. The post-modified COMOC-4 exhibits a very high selectivity toward the epoxide (up to 100%). Regenerability and stability tests have been carried out demonstrating that the catalyst can be recycled without leaching of Mo or loss of crystallinity.

Recovery and Recycling of Ti Supported Bimodal Mesoporous Catalysts Prepared via Ship-in-a-bottle Method in the Epoxidation of Cyclohexene

Ti/BMMs (Ti supported bimodal mesoporous silica) catalysts have been prepared via self-assembly route combined with ship-in-a-bottle method. The recovery and recycling performances of Ti/BMMs were investigated in the epoxidation of cyclohexene. In order to the evaluate the regeneration methods and to examine the deactivation behaviors, the deactivated Ti/BMMs catalysts were washed in chloroform or calcinated at 450°C for 6h and then activity of the recovery catalysts were examined. Meanwhile, the structure features and surface properties of the regenerated catalysts were characterized by X-ray diffraction, N2-sorption analysis, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, UV visible spectroscopy and X-ray photoelectron spectroscopy. The results showed that the typical bimodal mesoporous structure of recycled Ti/BMMs catalysts was still maintained, and the phenomenon of Ti leaching during the catalytic process and recovery was negligible. In particular, spectroscopic observations indicated that the effects of the regeneration methods on the tetrahedrally-coordinated Ti species and catalytic deactivation were remarkable. The main reasons were related to the polarities of used solvents during recovery tests, the environment medium of adsorbed water inside mesopore channels and the deposition of bulky molecules of by-products on the mesoporous surface.

Catalytic Performance of Vanadium MIL‐47 and Linker‐Substituted Variants in the Oxidation of Cyclohexene: A Combined Theoretical and Experimental Approach

AbstractThe epoxidation of cyclohexene has been investigated on a metal–organic framework MIL‐47 containing saturated V+IV sites linked with functionalized terephthalate linkers (MIL‐47‐X, X=OH, F, Cl, Br, CH3, NH2). Experimental catalytic tests have been performed on the MIL‐47‐X materials to elucidate the effect of linker substitution on the conversion. Notwithstanding the fact that these substituted materials are prone to leaching in the performed catalytic tests, the initial catalytic activity of these materials correlates with the Hammett substituent constants. In general, substituents led to an increased activity relative to the parent MIL‐47. To rationalize the experimental findings, first‐principles kinetic calculations were performed on periodic models of MIL‐47 to determine the most important active sites by creating defect structures in the interior of the crystalline material. In a next step these defect structures were used to propose extended cluster models, which are able to reproduce in an adequate way the direct environment of the active metal site. An alkylperoxo species V+VO(OOtBu) was identified as the most abundant and therefore the most active epoxidation site. The structure of the most active site was a starting basis for the construction of extended cluster models including substituents. They were used for quantifying the effect of functionalization of the linkers on the catalytic performance of the heterogeneous catalyst MIL‐47‐X. Electron‐withdrawing as well as electron‐donating groups have been considered. The epoxidation activity of the functionalized models has been compared with the measured experimental conversion of cyclohexene. The agreement is fairly good. This combined experimental–theoretical study makes it possible to elucidate the structure of the most active site and to quantify the electronic modulating effects of linker substituents on the catalytic activity.

Epoxidation of cyclohexene with molecular oxygen by electrolysis combined with chemical catalysis

This paper describes an electrochemical coupling epoxidation of cyclohexene by molecular oxygen (O2) under mild reaction conditions. Herein, the electroreduction of O2 to hydrogen peroxide (H2O2) efficiently proceeds in a relatively environmentally friendly acetone/water medium containing electrolytes at 25–30 °C on a self-assembled H type of electrolysis cell with tree electrodes system, providing ca. 44.3 mM concentration of H2O2 under the optimal electrolysis conditions. The epoxidation of cyclohexene with in situ generated H2O2 simultaneously occurs upon catalysis by metal complexes, giving ca. 19.8 % of cyclohexene conversion with 78 % of epoxidative selectivity over the best catalyst 5-Cl-7-I-8-quinolinolato manganese(III) complex (Q3MnIII (e)). The present electrochemical coupling epoxidation result is nearly equivalent to the epoxidation of cyclohexene with adscititious H2O2 catalyzed by the Q3MnIII (e).