Epoxidation Of Cyclooctene Research Articles

Hybrid Materials Based on Keggin Phosphotungstate and Bipyridine with Valuable Hydrophobic and Redox Properties.

A thorough investigation of two novel hybrid materials, namely, (2,2'-Hbpy)3[PW12O40] and (4,4'-H2bpy)1.5[PW12O40]·1.5H2O built from Keggin phosphotungstic acid (PTA) and bipyridine, describes the impact of bipyridine isomers in their formation and physicochemical properties. The hybrids' formation was confirmed by powder X-ray diffraction, while infrared spectroscopy (IR) proved the polyoxometalate (POM) structural preservation. The stoichiometric composition and thermal stability of the hybrids were solved by thermogravimetric analysis-mass spectrometry, which also revealed newly acquired hydrophobic properties. Raman and IR spectroscopies demonstrated that the POM skeleton units in both hybrids were distorted compared to the POM in PTA, which induced a decrease of their reduction potentials as observed by diffuse reflectance ultraviolet-visible spectroscopy (DR-UV-vis). The hybrids' acidity was assessed by ammonia temperature-programmed desorption, which showed no remaining acid sites compared to the strong acidic character of the pristine PTA. The properties of the hybrids were tested in the epoxidation of cyclooctene in the presence of H2O2. The reaction was boosted when the hybrids were pre-activated with H2O2.

Direct Oxygen Transfer from H2 O to Cyclooctene over Electron-Rich RuO2 Nanocrystals for Epoxidation and Hydrogen Evolution.

Production of more than 20 million tons of epoxides per year from olefins suffers from low atom economy due to the use of oxidants and complex catalysts with unsatisfactory selectivity, leading to huge environmental and economic costs. We present a proof-of-concept application of electron-rich RuO2 nanocrystals to boost the highly selective epoxidation of cyclooctene via direct oxygen transfer from water as the sole oxygen source under mild conditions. The enhanced electron enrichment of RuO2 nanocrystals via the Schottky effect with nitrogen-doped carbons largely promotes the capture and activation of cyclooctene to give a high turnover frequency (260 h-1 ) of cyclooctene oxide, far surpassing the reported values (<20 h-1 ) of benchmarked catalysts at room temperature with oxidants. Our electron-rich RuO2 electrocatalysts enable efficient and durable hydrogen production (Faradaic efficiency >90 %) on the cathode without impacting on the selectivity to epoxide (>99 %) on the anode.

Direct Oxygen Transfer from H2O to Cyclooctene over Electron‐Rich RuO2 Nanocrystals for Epoxidation and Hydrogen Evolution

AbstractProduction of more than 20 million tons of epoxides per year from olefins suffers from low atom economy due to the use of oxidants and complex catalysts with unsatisfactory selectivity, leading to huge environmental and economic costs. We present a proof‐of‐concept application of electron‐rich RuO2 nanocrystals to boost the highly selective epoxidation of cyclooctene via direct oxygen transfer from water as the sole oxygen source under mild conditions. The enhanced electron enrichment of RuO2 nanocrystals via the Schottky effect with nitrogen‐doped carbons largely promotes the capture and activation of cyclooctene to give a high turnover frequency (260 h−1) of cyclooctene oxide, far surpassing the reported values (&lt;20 h−1) of benchmarked catalysts at room temperature with oxidants. Our electron‐rich RuO2 electrocatalysts enable efficient and durable hydrogen production (Faradaic efficiency &gt;90 %) on the cathode without impacting on the selectivity to epoxide (&gt;99 %) on the anode.

Active epoxidation bipyridine-oxodiperoxotungstate catalysts

Herein, we report the preparation of four compounds obtained by the reaction of H3PW12O40/H3PO4/H2O2 with 2,2’-bpy (a-22) or 4,4’-bpy (a-44) and H3PW12O40/H2O2 with 2,2’-bpy (b-22) or 4,4’-bpy (b-44) for the catalytic epoxidation of cyclooctene with H2O2 under monophasic conditions. The anions of the four compounds are composed of oxodiperoxotungstate WO(O2)2 moieties and their overall anionic structures are less condensed than the pristine [PW12O40]3− polyoxometalate (PW12) precursor (Raman and IR spectroscopies). The peroxo anions and bipyridine interact in a way differing from one bpy isomer to the other. Isomer 4,4’-bpy interacts electrostatically with the peroxo species and 2,2’-bpy in a coordinative mode. Compounds synthesized with isomer 2,2’-bpy (a-22 and b-22) are more epoxidation-active than those containing 4,4’-bpy (a-44 and b-44). Compounds a-22 and b-22 share the same structure (PXRD), but a-22 exhibits substantially better catalytic activity. This superior catalytic efficiency is associated to the presence of phosphatooxoperoxotungstates PWn (n = 1; 2; 3; 4) species with high n value (namely PW4 > PW3 >> PW2) (31P NMR and Raman spectroscopies). The PWn species are produced before reaction with bipyridine as a result of the degradation of PW12 with H2O2 which, under the employed conditions, is complete after 30 min. In the aqueous solution, the PWn species are present in different concentrations and coexist in a fast-dynamic equilibrium. Under the operated catalytic conditions, our materials outperform the homogeneous benchmark catalyst of Venturello ((C6H13)4N+)3[PW4O24]3−) which shows poor activity. The most active a-22 and b-22 catalysts are partially dissolved in the liquid medium, but they precipitate as the epoxide builds in the reaction medium, allowing for potential catalyst separation and reuse. It is revealed that H2O2 is required not only to generate epoxidation activity, but to preserve the structure of the catalyst, since without it, the structural damaged appears irreversible.

Synthesis, characterization, DFT calculations, and catalytic epoxidation of two oxovanadium(IV) Schiff base complexes

The present paper reports the synthesis, characterization, and DFT calculations of two oxovanadium (IV) Schiff base complexes symbolized as VOL1 and VOL2, which prepared by the reaction of bivalent tridentate Schiff base ligands (E)-2-((5-chloro-2-hydroxybenzylidene)amino)acetic acid and (E)-2-((2-hydoxy-5-nitrobenzylidene)amino)acetic acid and VO(acac)2 as vanadium source. The Schiff base ligands and its oxovanadium (IV) complexes were characterized by the elemental analysis (C, H, N), FTIR, 1H NMR and 13C NMR, DFT calculations were performed to derive some of their molecular properties. Schiff base ligands coordinated to vanadium center via nitrogen from the azomethine group and one oxygen from the hydroxyl attached to the benzene ring and one oxygen from hydroxyl of carboxyl group. The catalytic activity of the two complexes were tested against cyclooctene and found that both complexes were highly effective and selective in optimized conditions when used as cyclooctene epoxidation catalysts with the conversion percentage of 91.85% (with VOL1) and 87.40% (with VOL2) at 78 °C within a period of ten hours. To understand the structural properties of the two complexes, the two complexes were well optimized at B3LYP/6-31G(d,p) level of theory, structural parameters such as electron affinity, global electrophilicity, global hardness, electronegativity, ionization potential, and electron chemical potential based on HOMO and LUMO energy values were calculated.

The Fabrication of PMo11Fe Cluster Supporting on SBA-15 and Catalytic Epoxidation of Cyclooctene with H2O2 as Oxidant

The Fabrication of PMo11Fe Cluster Supporting on SBA-15 and Catalytic Epoxidation of Cyclooctene with H2O2 as Oxidant

Multiscale porous single-atom Co catalysts for epoxidation with O2

The single-atom Co anchored on N-doped carbon supports with a multiscale porous structure has been successfully constructed for the epoxidation of cyclooctene with 95% yield of 1,2-epoxycycloheptane at 140 °C and 0.5 MPa O2.

Kinetics of Epoxidation of Cyclooctene with Ionic Liquids Containing Tungstate as Micellar Catalyst

AbstractThe kinetics of cyclooctene epoxidation with H2O2 by micellar catalysis was studied. As catalyst, an ionic liquid (IL) containing the catalytically active tungstate anion was used. The tungstate IL forms micelles in the aqueous H2O2 phase. It is simply formed by dissolving sodium tungstate and 1‐octyl‐3‐methylimidazolium tetrafluoroborate [OMIM][BF4] in aqueous H2O2. For the epoxidation of cyclooctene by micellar catalysis, a power law kinetic model was determined that takes the critical micelle concentration into account. The kinetics of the [OMIM][BF4]/Na2WO4 catalyst is similar to pure [OMIM]2[WO4], which indicates that the active species is formed in situ. Addition of phenylphosphonic acid improves the activity of the tungstate IL. The most effective catalyst was tested in a semi‐continuous and continuous loop reactor.

Catalytic performance of a wide range of rare-earth titanate pyrochlore (RE2Ti2O7, RE = Sm, Gd, Dy, and Yb) microstructures in the epoxidation of cyclooctene: An electro-structural investigation

A series of rare-earth titanate oxides RE2Ti2O7 (RE =Sm, Gd, Dy and Yb) were synthesized using a solid state method. The pyrochlore structures of these compounds were confirmed by the Rietveld method from X-ray diffraction data (XRD). XRD results showed that RE2Ti2O7 structures had cubic crystal system with the Fd3m space group. Morphology and mean particle sizes of the samples were obtained by the scanning electron microscope (SEM). Chemical characterizations of the samples were confirmed by energy dispersive x-ray spectroscopy (EDX). The specific surface areas were calculated using BET analyses. Fourier transform infrared spectra of the obtained compounds in (400–4000 cm−1) range were also studied. The obtained RE2Ti2O7 pyrochlore materials were used as catalysts for epoxidation of cyclooctene as a model alkene with tert-butyl hydroperoxide. Various parameters including catalyst type and amount, solvent type and amount, oxidant/substrate ratio, and time have been optimized and high catalytic activity and epoxide selectivity have been found. Gd2Ti2O7 showed the best activity and epoxide selectivity.

Dual-template synthesis of hierarchically layered titanosilicate-1 zeolites for catalytic epoxidation of cyclooctene

A one-pot facile route for preparing hierarchically layered titanosilicate-1 (LTS-1) zeolites with stable interlayered mesopores was proposed by integrated using bolaform surfactant (BC ph-12-6-6 ) and tetrapropyl ammonium hydroxide (TPAOH) as dual templates. By tuning the molar ratios of BC ph-12-6-6 /TPAOH from 5/0 to 5/9, the corresponding LTS-1 samples showed continuous transformations in morphology and intensified degrees of intergrowth by TS-1 nanosheets, resulting in an effective interlayer self-pillaring to avoid the excessive collapse after the removal of the occupied templates by calcination. Moreover, the LTS-1 samples by dual-template synthesis manifested enriched contents of mononuclear octahedrally coordinated Ti species (“TiO 6 ”). Benefitted by the highly patulous structure and more accessible Ti active sites predominated with high-performance “TiO 6 ” species, the LTS-1 catalysts by dual-template synthesis exhibited a superior catalytic activity in the epoxidation of cyclooctene compared with the layered TS-1 directed by sole template of BC ph-12-6-6 and the conventional bulk TS-1. It is reasonable to expect that the demonstrated work has important implications for the design and facile synthesis of layered titanosilicate zeolite catalysts with a stably hierarchical structure and tunable catalytic oxidation activities by an optimized distribution of titanium coordination states containing the coordinated “TiO 4 ” and “TiO 6 ” species. • One-pot dual-template synthesis of hierarchically layered titanosilicate-1 (LTS-1). • Effective interlayer self-pillaring by integrated templating of BC ph-12-6-6 and TPAOH. • LTS-1 manifests enriched contents of mononuclear octahedrally coordinated Ti species (“TiO 6 ”). • Improved catalytic epoxidation performances by the highly patulous structure and more accessible Ti active sites.

Implication of oxidant activation on olefin epoxidation catalysed by Molybdenum catalysts with aroylhydrazonato ligands: Experimental and theoretical studies

• Dinuclear and mononuclear molybdenum(VI) complexes with aroylhydrazonato ligands were tested as catalysts for cyclooctene and oct-1-ene epoxidation. • TBHP in decane provided outstanding results in terms of cyclooctene epoxidation: TOF 2.5 min >9000 with 0.25 mol % [Mo] loading. • DFT calculations confirmed the relationship between the ligand nature and reactivity with TBHP and H 2 O 2 as oxidant agents. Dinuclear and mononuclear molybdenum(VI) complexes with aroylhydrazonato ligands were studied as catalysts for cyclooctene and oct-1-ene epoxidation. Different isomers of the OH and NH 2 functionalised aroylhydrazones led to four specific [MoO 2 L] units showing different catalytic activity. Three oxidants have been investigated: tert -butylhydroperoxide (TBHP) in water or in decane, and hydrogen peroxide (H 2 O 2 ). Catalytic processes with TBHP in decane provided outstanding results in the case of cyclooctene epoxidation: TOF 2.5 min > 9000 with 0.25 mol % [Mo] loading. DFT calculations confirmed the relationship between the ligand nature and reactivity with TBHP and H 2 O 2 as oxidant agents. In the case of TBHP as oxidant, calculations considered the solvent in which the oxidant is delivered to the olefin. A plausible mechanism with H 2 O 2 has been proposed after considering various pathways.

PH Changes That Induce an Axial Ligand Effect on Nonheme Iron(IV) Oxo Complexes with an Appended Aminopropyl Functionality

Nonheme iron enzymes often utilize a high-valent iron(IV) oxo species for the biosynthesis of natural products, but their high reactivity often precludes structural and functional studies of these complexes. In this work, a combined experimental and computational study is presented on a biomimetic nonheme iron(IV) oxo complex bearing an aminopyridine macrocyclic ligand and its reactivity toward olefin epoxidation upon changes in the identity and coordination ability of the axial ligand. Herein, we show a dramatic effect of the pH on the oxygen-atom-transfer (OAT) reaction with substrates. In particular, these changes have occurred because of protonation of the axial-bound pendant amine group, where its coordination to iron is replaced by a solvent molecule or anionic ligand. This axial ligand effect influences the catalysis, and we observe enhanced cyclooctene epoxidation yields and turnover numbers in the presence of the unbound protonated pendant amine group. Density functional theory studies were performed to support the experiments and highlight that replacement of the pendant amine with a neutral or anionic ligand dramatically lowers the rate-determining barriers of cyclooctene epoxidation. The computational work further establishes that the change in OAT is due to electrostatic interactions of the pendant amine cation that favorably affect the barrier heights.

Molybdate Stabilized Magnesium‐Iron Hydrotalcite Materials: Potential Catalysts for Isoeugenol to Vanillin and Olefin Epoxidation

A series of molybdate-intercalated and stabilized magnesium‐iron hydrotalcite (HMFeMo) materials with different molybdate loadings were successfully prepared by an in-situ hydrothermal method. The prepared HMFeMo materials were systematically characterized using Fourier-transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), Ultraviolet-visible spectroscopy, scanning electron microscopy, thermo-gravimetric analysis, nitrogen adsorption-desorption and X-ray photoelectron spectroscopy (XPS) experiments. The XRD results demonstrated the successful intercalation of molybdate ions in the interlayer space of magnesium-iron hydrotalcite and the stabilization of the layered structure. In addition, the XPS spectra of the HMFeMo materials revealed the presence of molybdenum in a higher-valent oxidation state. The calcination of HMFeMo materials led to the formation of solid solution of mixed metal oxides. Both the as-prepared and calcined HMFeMo catalysts showed promising activity for the epoxidation of cyclooctene, as a model reaction. Furthermore, the performance of the as-prepared and calcined HMFeMo catalysts for the oxidation of a biomass model compound, namely isoeugenol to vanillin, was evaluated. The isoeugenol conversion over the as-prepared HMFeMo catalysts under solvent-free conditions and using tertiary-butyl hydroperoxide in decane as the oxidant was good. Moreover, the isoeugenol conversion and selectivity toward vanillin of HMFeMo0.1, with a molybdate loading of 0.1 mol %, were the highest (86.2% and 83.1%, respectively) of all HMFeMo catalysts in this study at 80 °C for 5 hr. HMFeMo0.1 presented the best catalytic activity for both the epoxidation of cyclooctene and oxidation of isoeugenol to vanillin, and its activity remained unchanged after several runs.

Efficient Molybdenum Hydrazonato Epoxidation Catalysts Operating under Green Chemistry Conditions: Water vs. Decane Competition

Molybdenum compounds containing benzaldehyde-based hydrazones were obtained. The reaction in MeOH resulted with monomeric Mo complexes, [MoO2(L)(MeOH)], while the reaction in dichloromethane (DCM) provided oligomeric complexes, [MoO2(L)]n. The solid-state structures of the obtained compounds were investigated through Infrared Spectroscopy - Attenuated Total Reflection (IR-ATR), Thermogravimetric analysis (TGA), and via X-ray diffraction. The prepared molybdenum species were employed as cyclooctene epoxidation catalysts. TBHP (tert-butylhydroperoxide) in water and TBHP in decane were employed and compared as oxidants, with 0.25 mol% [Mo]. The catalyst activity and selectivity towards epoxide is &gt;90% for all the reactions. The results have been linked to theoretical calculations, showing the importance of the first step, i.e., the transformation of [MoO2(L)(MeOH)] into the pentacoordinate [MoO2(L)].

Mesoporous Methyl-Functionalized Titanosilicate Produced by Aerosol Process for the Catalytic Epoxidation of Olefins

Titanosilicates (Ti-SiO2) are well-known catalysts for the epoxidation of olefins. Isolated Ti inserted in the silica framework in tetrahedral coordination are the active species. Recently, adjusting the hydrophobic/hydrophilic balance of such catalysts’ surfaces has appeared as a promising tool to further boost their performance. However, adjusting the hydrophobic/hydrophilic balance via a one-pot classical sol-gel generally leads to a decrease in the Ti dispersion and/or collapse of the pore network. To overcome this limitation, hydrophobic mesoporous Ti-SiO2 were here synthesized by aerosol-assisted one-pot sol–gel, which allowed the simultaneous control of their Ti loading, degree of methyl-functionalization, and textural properties. Methyl-functionalization was achieved by a partial substitution of tetraethoxy silane (TEOS) by methyltriethoxy silane (MTES) in different ratios. Solid-state 29Si-NMR, FTIR, TGA, and vapor-phase water adsorption showed that methyl moieties were effectively incorporated, conferring a hydrophobic property to the Ti-SiO2 catalysts. ICP-AES, DRUV, XPS, and N2 physisorption demonstrated that Ti dispersion and textural properties were both successfully preserved upon the incorporation of the methyl moieties. In the epoxidation of cyclooctene with tert-butyl hydroperoxide as oxidant, the hydrophobic Ti-SiO2 showed higher catalytic performance than pristine Ti-SiO2 prepared without MTES. In addition to disentangling the positive effect of adjusting the hydrophobic/hydrophilic balance of epoxidation catalysts on their performance, this contribution highlights the advantages of the aerosol procedure to synthesize mesoporous functionalized catalysts with very high dispersion of active sites.

High-dispersed MoO3 nanoparticles in 3D-dendritic mesoporous silica nanospheres: heterogeneous catalysts for the epoxidation of olefins

Highly dispersed molybdenum trioxide were loaded in three-dimensional dendritic mesoporous silica nanospheres (MoO3@3D-DMSNs) by one-pot method. The mesoporous silica nanospheres with central radical channels were obtained through the interaction of bisurfactant and molybdenum source and the as-synthesized MoO3@3D-DMSNs were characterized by specific tests. As a result, the as-prepared MoO3@3D-DMSNs exhibited better catalytic performance for epoxidation of olefins. When the molar ratio value of Mo and Si is 5%, the specific surface area (SBET = 185.8 m2/g) and pore volume (Vp = 0.46 cm3/g) of MoO3@3D-DMSNs reach a maximum, and the catalytic activity is the best for the epoxidation of cyclooctene. The conversion could reach 84% with a selectivity above 98% after 6 h. The better catalytic performance can be maintained after five reaction-regeneration cycles. The dendritic mesoporous structure can be well preserved after recycling. Additionally, olefins with electron-absorbing group exhibit better catalytic activity with MoO3@3D-DMSNs-5 as catalyst. Hence, MoO3@3D-DMSNs catalysts with the center-radial oriented channel exhibit good activity and stability. The central radial channel can effectively disperse the active center MoO3 and play a key role in the transmission and accessibility of substrates, and it would have a good application prospect in the catalytic reactions.

Fabrication of Amphiphilic Graphene Oxide—Polyoxometalate with Temperature Response for Epoxidation of Olefin in Water

Here, amphiphilic graphene oxide–polyoxometalate (GO-POM) was fabricated using a new strategy involving control of the stacking of GO lamellae through phosphoric acid and exfoliation by H2O2. The additions of H3PO4 and H2O2 were essential for the formation of the catalytic center of peroxo-POMs. The GO-POM hybrid had one side with hydrophilic properties and another side with hydrophobic properties, which conferred temperature-responding properties. GO-POM could catalyze the epoxidation of cyclooctene with complete conversion and 98% selectivity for epoxide at 50 °C for 12 h in water. Meanwhile, the catalyst could be easily recycled because of its thermosensitive property.

Local environment and catalytic property of External Lewis acid sites in hierarchical lamellar titanium Silicalite-1 zeolites

Abstract Hierarchical two-dimensional (2D) lamellar zeolites represent a young emerging field and a novel expression of the zeolite frameworks. Accompanied with synthesis and catalytic performance investigation, assessment on the local environment and catalytic behavior of acid sites in 2D zeolites are needed. Here, we described the local environment of Lewis acid sites and evaluated catalytic activities of external acid sites (i.e. sites on external surface and in mesopores) in 2D lamellar titanium silicalite-1 (TS-1) zeolites. For comparison purpose, four TS-1 zeolites, including 3D TS-1, multilamellar 2D TS-1 without pillarization and with pillarization by silica and silica/titania, respectively, were prepared. The local environment of Ti-sites, including coordination status of Ti-atom, speciation of hydroxyl (-OH) group that hints degree of confinement, acid site strength and accessibility, was collectively assessed by spectroscopic and organic base titration measurements. Kinetic studies of cyclooctene (C8H14) epoxidation with hydrogen peroxide (H2O2) discerned catalytic activity of external Ti-sites that decreased with increasing mesoporosity due to decrease in site confinement.

Synergistic catalysis by Mn promoted ceria for molecular oxygen assisted epoxidation

Mesoporous manganese doped cerium oxide catalysts were prepared by an inverse micelle method with different manganese loadings. These materials exhibited superior activity for epoxidation of alkenes with molecular oxygen. Highest active 10MnCe material showed an activity of 80 % conversion and >99 % selectivity for cyclooctene epoxidation. The fluorite crystal structure which facilitates the high oxygen mobility, low temperature reducibility, homogeneous distribution of manganese on ceria, nanoparticle nature, higher number of oxygen vacancies, low valent states of manganese and cerium, and the ability to generate reactive oxygen species of the manganese doped cerium oxide could be correlated to the high catalytic activity. The reaction followed first order kinetics with a rate constant of 0.31 h−1 at 100 °C, and the activation energy turned out to be 10.5 kJ/mol. The mechanistic study revealed that the reaction proceeds via a unique mechanism which involves in situ generated superoxide and singlet oxygen species.

Catalytic and photocatalytic epoxidation over microporous titanosilicates with nanosheet or layered structure

Bulky epoxides are industrially produced by organic synthesis in multistep procedures, generating significant amounts of waste products in the process. Efficient catalyst in combination with a simple oxidant (H2O2 or O2) would significantly reduce the waste production. Four types of microporous titanosilicates with extra-large pores (Ti-UTL), and shortened diffusion pathways (L-TS, Ti-MCM-22, and Ti-SPP) were prepared and investigated in the epoxidation of cyclooctene with H2O2 and photocatalytic oxidation using O2. Ti-UTL is a zeolite possessing 14−12-ring channel system. l-TS-1 and Ti-MCM-22 are composed of aggregates of titanosilicate nanosheets with the thickness of ca. 2 nm and hexagonal thin platelets, respectively. Ti-SPP is composed of olive-like aggregates with approximately length of 0.88–1.12 μm and width of 0.44−0.68 μm consisting of intergrown (self-pillared) nanosheets having 13−70 nm in size. In the epoxidation with H2O2 as an oxidant, Ti-MCM-22 showed the highest catalytic activity due to the wide interlayer space, which enhanced the accessibility of cyclooctene to active titanium site. While, in the photocatalytic epoxidation in the presence of O2 instead of H2O2, Ti-UTL showed the highest activity. The incorporated germanium atoms, which is indispensable component for the construction of extra-large pores, may affect the electronic properties of active titanium species, leading to high photocatalytic activity.