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In order to obtain monomers from vegetable source, the castor oil epoxidation process was investigated. The catalytic system used in this work, H 2 O 2 /alumina/ethyl acetate, can be considered as a green system, free of heavy metals and toxic solvents. These characteristics make the system appropriate for the purpose of this study since they increase the probabilities of obtaining a biomaterial with the desired specifications regarding toxicity. Reaction conditions of castor oil epoxidation were optimized using methyl ricinoleate as a model compound. In order to identify the operating region, it was developed an experimental design 2 3 with 17 assays (6 axial points and central point in triplicate) in which, methyl ricinoleate, hydrogen peroxide and catalyst initial quantities in the reaction mixture were the studied variables. The system showed great efficiency with 100% of selectivity in the methyl ricinoleate epoxide production. In optimized conditions, it showed conversion of 99% in 6 h. It was obtained a conversion of 94%, an epoxidation percentage of 84 and a selectivity of 89% toward the epoxides for the castor oil epoxidation. These results show the efficacy of the catalytic system used in this work. Epoxidized castor oil structure was confirmed by FTIR, Raman and 1 H NMR techniques. [ABSTRACT FROM AUTHOR]

A mechanistic study of ethylene epoxidation by hydrogen peroxide catalyzed by niobium doped in a silica mesopore is reported. Density functional theory calculations at the M06-L/aug-cc-pVDZ level were used to investigate the catalytic pathway. A five-step cycle is proposed. The initial steps are the adsorption of H 2 O 2 to the Nb center followed by coordination of ethylene to the hydrogen peroxide. The rate-limiting step is the subsequent epoxidation of ethylene via transfer of an oxygen atom, which has a calculated enthalpic barrier of 11.6 kcal/mol relative to the preceding intermediate. This is followed by desorption of the ethylene oxide product and dehydration to regenerate the catalyst. The reaction barrier is lower than reported for other catalysts in the literature, consistent with recent experimental reports of the efficacy of Nb-doped mesoporous silica catalysts [ Catal. Sci. Technol., 2014 , 4 , 4433–4439]. The mechanistic details elucidated in the present calculations may aid in the rational design of new epoxidation catalysts and thus the factors influencing the reaction, e.g. , geometry and charge changes, are discussed. [ABSTRACT FROM AUTHOR]

Ag-MCl x /BaCO 3 catalysts with different chloride promoters, prepared by reduction-deposition-impregnation method, were investigated for gas-phase epoxidation of propylene to propylene oxide (PO) by molecular oxygen. Ag-CuCl 2 /BaCO 3 catalyst with 360 ppm of Cu and 400 ppm of Cl exhibits the best initial catalytic performance, in which PO selectivity of 71.2% and propylene conversion of 1.3% are achieved, but only PO selectivity of 13.9% is obtained at propylene conversion of 3.2% after reaction for 500 min. The catalytic reaction mechanism over Ag-CuCl 2 /BaCO 3 catalyst follows Rideal-Eley mechanism, in which propylene in the gas phase reacts with molecular oxygen species adsorbed on the surface of Ag at the interface in close contact with CuCl 2 to produce PO, and with atomic oxygen species adsorbed on the surface of Ag nanoparticles to produce CO 2 and H 2 O. One oxygen atom of molecular oxygen species reacts with propylene to form a PO molecule, and the left insufficient oxygen atoms react with propylene to produce oxygen-containing intermediates and then to form coke deposition which covers the active sites and thus results in the catalyst deactivation. The deactivated Ag-CuCl 2 /BaCO 3 catalyst can be completely regenerated by combustion of coke deposition and then impregnation with appropriate amount of Cl. [ABSTRACT FROM AUTHOR]

Propene oxide is an important chemical intermediate and titanium silicalite (TS-1) has been widely investigated as a promising catalyst for the direct epoxidation of propene with ex-situ or in-situ produced hydrogen peroxide as an oxidant. In order to clarify the effects of the kind of precious metal and treatment process in the catalyst preparation on the propene epoxidation and the hydrogen peroxide decomposition, TS-1 was impregnated with gold and palladium via drying, calcination and reduction and the experiments to check its catalytic performance were conducted in a gas aspirating autoclave reactor in the absence of mass transfer limitations. The presence of precious metals vigorously catalyzed the side reactions and hydrogen peroxide decomposition. Some of the precious metal containing TS-1 catalysts showed high initial rates but there was no catalyst with a propene oxide yield after 5 h reaction time comparable to TS-1 alone because of the enhancement of side reactions by precious metals. The significant decline in the selectivity to propene oxide over the dried precious metal containing TS-1 catalysts was attributed to the leaching of precious metals into the reaction medium. Palladium containing TS-1 showed exceptionally high decomposition of hydrogen peroxide. Reduction and calcination increased the decomposition by forming metallic gold and palladium. Homogeneous dispersion of gold nanoparticles was achieved by a sol immobilization method which led to a decrease of propene oxide selectivity and an increase of hydrogen peroxide decomposition. [ABSTRACT FROM AUTHOR]

Resin supported solid acid catalysts have extended the application of conventional solid acid catalysts in the field of selective oxidations. The present work describes selectively catalytic epoxidation of cyclohexene with aqueous 30% H 2 O 2 over powdered anion-resin supported peroxo phosphotungstic acid heterogeneous catalysts prepared through a simple anion-exchange from powdered chloride-form anion resin without any special pre-exchanged treatment. Among these powdered solid catalysts, anion-exchanged resin D201 supported peroxo phosphotungstic acid exhibits the best activity for the titled reaction to obtain 92.4 mol% conversion and 98.1% selectivity of epoxide, for which D201-PWAR(4) behaves as a truly heterogeneous catalyst. Some factors such as various peroxo phosphotungstic acid concentrations, the oxidants, the solvents, the molar ratios of H 2 O 2 /cyclohexene, the catalyst amount, the reaction temperature and time play important roles in controlling the epoxidation. [ABSTRACT FROM AUTHOR]

The photo-assisted oxygen transfer to cyclohexene, cyclooctene and 1-octene was investigated using molecular O 2 as a primary oxidant with a dichloro-dioxo-(4,4′-dicarboxylato-2,2′-bipyridine) molybdenum (VI) complex grafted on the surface of mesoporous TiO 2 supports exhibiting different textural properties. Such mesoporous titania samples were prepared following a hydrothermal treatment (HT) and through an original procedure under supercritical CO 2 (SC) conditions. Non porous TiO 2 Degussa P-25 was also used for comparison purposes. The porosity of the titania supports, as well as the amount and dispersion of the covalently anchored dioxo Mo (VI) complex were shown to strongly influence the resulting photo-catalytic properties. A particular attention was also devoted to the stability of the grafted catalysts by performing long-term epoxidation experiments. The new hybrid Mo (VI) -derivatized mesoporous SC TiO 2 catalyst proved to be the most efficient in the photo-assisted oxygen transfer to various alkenes. Additionally, the high stability of such catalyst was ascertained by recycling studies. [ABSTRACT FROM AUTHOR]

Soluble gallium and aluminum nitrates (simple salts of non-transition metals) are good catalysts for the epoxidation of olefins (cyclooctene, dec-1-ene) including terpenes (carvone, limonene) with hydrogen peroxide in ethyl acetate or tetrahydrofurane (THF). Typically, the gallium salt is more efficient in comparison with the aluminum derivative. Products are formed in yields up to 93%, turnover numbers (TONs) attained 40. Addition of trifluoroacetic acid or pyrazine-2-carboxylic acid (PCA) accelerates the reaction and improves the yield. In striking contrast, added 2,2′-bipyridine or phenanthroline dramatically inhibit the oxidation. [ABSTRACT FROM AUTHOR]

The highly enantioselective epoxidation of several conjugated olefins with H 2 O 2 in the presence of five chiral titanium(IV) salalen (dihydrosalen) complexes has been studied, with focus on the effects of substituents (electronic and steric) on the epoxide yield and enantioselectivity. The introduction of electron acceptors at the ligand’s remote positions enhances the catalytic reactivity, without drastic effect on the stereoselectivity and ultimate catalytic efficiency. In turn, the replacement of Ph substituents of the ligand core with o -MeO-Ph and o -Et-Ph substituents leads to the enhancement in enantioselectivity (up to 99.8% ee ), conversion (up to 100%) and efficiency (up to 125 TN). Kinetic and Hammett data provide evidence in favour of a stepwise epoxidation mechanism on Ti-salalen catalysts. As compared to Ti-salan protagonists, Ti-salalen catalysts exhibit much higher activity and efficiency, and in most cases comparable enantioselectivity. Kinetic peculiarities of epoxidations on Ti-salalen and Ti-salan complexes are considered. [ABSTRACT FROM AUTHOR]

Ti sites grafted on MCM-41, pretreated at different temperatures, have been modified with chiral tartrates, leading to different species. Those solids are active catalyst for the epoxidation of styrene with tert -butyl hydroperoxide, although their efficiency is not optimal, mainly due to the subsequent epoxide rearrangement to phenyl acetaldehyde and further oxidation of it. Styrene oxide is obtained with moderate enantioselectivity, in the range of 55–62% e.e., and the best overall results correspond to the use of MCM-41 calcined at the lowest temperature (550 °C). These results are much better with regard to styrene oxide selectivity than those obtained in homogeneous phase under the same conditions, whereas enantioselectivity is similar. The heterogeneous catalysts are recoverable, but only partially due to a loss in activity, although enantioselectivity is kept at similar levels, demonstrating the stability of the supported Ti-tartrate species. [ABSTRACT FROM AUTHOR]

This contribution introduces a strategy to use Ru(II)-porphyrin complexes as catalysts for the epoxidation of alkenes in water. The design is based on shell cross-linked micelle-based nanoreactors with hydrophobic cores and hydrophilic shells as supports for the Ru(II) porphyrin complexes. The supported complexes are efficient catalysts for oxidation reactions, specifically the selectively oxidation of alkenes to epoxides. The presented strategy is the first system that allows for running Ru-catalyzed epoxidation reactions in water. [ABSTRACT FROM AUTHOR]

Wells-Dawson structured heteropoly acid (H 6 P 2 W 18 O 64 ) was immobilized into the SBA-16 mesoporous material by ship-in-a-bottle method. The obtained material was characterized by Fourier transform infrared (FT-IR) and inductively coupled plasma-atomic emission (ICP-AES) spectroscopies, X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption–desorption analysis, and thermogravimetric analyses (TGA-DTA). The results indicated that the surface area of SBA-16 support decreased after immobilization of the heteropoly acid and next modification with silylating agent. The prepared material exhibited excellent catalytic performance in the epoxidation of olefins and allylic alcohols in the presence of hydrogen peroxide as green oxidant. The catalyst showed all of the expected advantages of the heterogeneous systems and was shown to be recoverable and reusable several times without major loss of activity. [ABSTRACT FROM AUTHOR]

Molybdenum complexes with ONO tridentate Schiff base ligands based on salicylideneaminophenolato (SAP) backbone with OH substitution on the salicyl arene ring have been synthesized and characterized. The molecular structures of the full series of OH substituted molybdenum complexes were determined by X-ray crystallography as monomers stabilized by one solvent molecule, [MoO 2 L(D)]. All dimeric complexes [MoO 2 L] 2 were tested for the epoxidation of cyclooctene and cyclohexene under organic solvent-free conditions using aqueous TBHP as oxidant. The position of the OH on the SAP-modified ligand influenced the catalytic activity of the respective complexes. DFT calculations for the catalytic cycle yield energy spans in agreement with the experimentally observed activity trend. [ABSTRACT FROM AUTHOR]

[Mn(3,5-dtSALEN)Cl] (I) and [Mn(3,5-dtSALHD)Cl] (II) complexes (3,5-dtSALEN = N,N′ -bis(3,5-di-tert-butylsalicylaldehyde)ethylenediamine; 3,5-dtSALHD = N′N -bis-(3,5-di-tert-butylsalicylaldehyde)-1,2-cyclohexanediamine) were successfully encapsulated within a natural bentonite by using three preparative approaches: (A) direct adsorption of every metal complex on the previously Al-pillared bentonite, Al-PILC; (B) two-step liquid phase methodology: (i) cationic adsorption of Mn 2+ in Al-PILC by substituting its residual cationic exchange capacity (CEC), followed by (ii) diffusion of either 3,5-dtSALEN or 3,5-dtSALHD ligands, for in-situ generation of the corresponding interlayered metal complexes; and (C) simultaneous pillaring/encapsulation of the complexes on the raw starting clay. The materials were characterized by cationic exchange capacity, X-ray diffraction, atomic absorption, FT-Infrared and UV–vis spectroscopies, and N 2 adsorption at 77 K. The physical encapsulation of the complexes into final materials was proven by spectroscopic analyses. Method C yielded both highest metal incorporation and enhanced basal space on the modified clay. All materials showed to be active catalysts in cyclohexene epoxidation with hydrogen peroxide using acetonitrile as solvent (0.79 atm, 293 K). Addition of sodium bicarbonate as co-catalyst led to enhanced conversion (100%) and selectivity (70%) towards the epoxide in the presence of such a kind of heterogeneized metal-complex catalysts. The catalysts were stable and reusable along at least two catalytic cycles. [ABSTRACT FROM AUTHOR]

The development of new functional catalytic materials prepared via appropriate chemical modification of mesoporous silica SBA-15, MCM-41 or carbon nanomaterials CMK-3, are presented. Their synthesis has been carried out via two synthetic approaches: (a) a two steps procedure which includes grafting of the Schiff base ligand 1,3-bis[3-aza-3-(1-methyl-3-oxobut-1-enyl)-prop-3-en-1-yl]-2-(4-hydroxy-phenyl)-1,3-imidazolidine (L) onto the suppors and subsequent metalation of the so-formed hybrid material, and (b) an one step procedure which allows covalent grafting of the entire [Mn II -Schiff base] catalyst onto the carbonaceous support. The resulting single-site heterogeneous catalysts were characterized and evaluated for alkene epoxidation with H 2 O 2 in the presence of CH 3 COONH 4 as additive. They are efficient and selective towards formation of epoxides. The highest TONs have been achieved by L@MCM-41-Mn II and Mn II -L@CMK-3 . Moreover, Mn II -L@CMK-3 is operative for a second use and kinetically very fast, demonstrating remarkably high TOFs 65–634 h −1 that is correlated to its practically zero porosity. Based on the present data, the textural features of the obtained catalysts are discussed in correlation with their catalytic performance. [ABSTRACT FROM AUTHOR]

A new type of bis-quaternary ammonium bromide as chiral multifunctional phase transfer catalysts derived from readily available inexpensive cinchona alkaloids has been developed and evaluated for the enantioselective asymmetric epoxidation of various chalcones in the presence of lower concentrations of various oxidants, bases, solvents and ambient temperature conditions. Under optimized reaction conditions, highest chemical yields of up to 98% along with the excellent enantioselectivities of about 99% were obtained by using the cinchona based chiral multifunctional phase transfer catalysts. [ABSTRACT FROM AUTHOR]

Jacobsen’s complexes are famous for their usability for enantioselective epoxidations. However, the applicability of this catalytic system has been severely limited by several practical problems such as deactivation and separation after reaction. Grafting of Jacobsen-type complexes on solid supports is an attractive way to overcome these problems but led to a decrease in selectivity. A combined theoretical and experimental approach is presented to unravel the factors governing enantioselectivity. The importance of different substituents was determined by analyzing the transition state for the oxygen transfer using the full system as a model. An analysis of the asymmetric complex has shown an inherent tendency for a decreased selectivity due to the lack of specific bulky groups. Experimentally an immobilized Jacobsen catalyst on a metal organic framework (MIL-101) was synthesized which confirms the computational tendencies but the decrease in selectivity is limited, indicating that the MIL-101(Cr) is a suitable carrier for this complex. [ABSTRACT FROM AUTHOR]

A series of dinuclear and mononuclear oxovanadium(V) complexes containing tridentate Schiff base ligands derived from pyridoxal and appropriate thiosemicarbazide or hydrazide are reported. The compounds were characterised by elemental analysis, thermogravimetric analysis, IR and NMR spectroscopy. The molecular structure of the dioxido-vanadium(V) complex [VO 2 (HL 5 )]·MeOH·H 2 O (H 2 L 5 = pyridoxal benzhydrazido ligand), determined by X-ray crystallography, reveals an unexpected distorted trigonal bipyramidal arrangement of the VO 2 moiety. A DFT study of this molecule and of the related [VO 2 (H 2 L 5 )] complex of V IV reveals a moderate effect of the oxidation state change on the bond distances and angles, pointing to solvation as the cause of the structural distortion. All complexes were tested as (pre) catalysts for olefin epoxidation by aqueous tert -butylhydroxyperoxide (TBHP) under solvent-free conditions. Low vanadium loadings (0.05% vs . olefin) resulted in good cyclooctene conversions and TOFs. The lifetime of one catalyst was explored through repeated runs with recovery/recycling. DFT calculations have also addressed the olefin epoxidation mechanism, which reveals the possible direct O atom transfer from the activated tert -butoxido ( t BuOO – ) ligand, without the need to generate a peroxido (O 2 2– ) ligand. [ABSTRACT FROM AUTHOR]

Twelve bi-/tridentate Schiff-base ligands ( L 1 – L 12 ) have been designed, synthesized and coordinated with ion-exchanged Co–MOR (Mordenite) forming a series of Co–MOR( L ) composite catalysts, for which various analyzes and characterizations are conducted. Selectively catalytic epoxidation of α -pinene with dry air over Co–MOR( L ) catalysts has been carried out, where uses TBHP in small amounts as the initiator. Among these Co–MOR( L ) catalysts, Co–MOR( L 8 ) exhibits the best activity for the titled reaction to obtain 85.8 mol% conversion and 90.8% selectivity of epoxide. Some factors such as the structure of ligands, the oxidants, the solvents, the catalyst amount, the reaction temperature and time play important roles in controlling the epoxidation. The recyclable stability of the Co–MOR( L 8 ) catalyst is confirmed. The studies on the electrochemical behaviors of Co species in Co–MOR( L 8 ) reveal the importance of reversible change between Co oxidation states for the epoxidation. [ABSTRACT FROM AUTHOR]

In the present work, nanoporous Cu 3 (BTC) 2 (abbreviated as CuBTC and BTC = benzene-1,3,5-tricarboxylate) metal-organic framework (MOF) was modified in a two-step post-synthetic reaction by covalent attachment of aminopyridine groups followed by the reaction with bis(acetylacetonato) dioxomolybdenum(VI). The prepared molybdenum containing MOF was utilized as a heterogeneous catalyst in the epoxidation of olefins and allylic alcohols. Characterization of the prepared catalyst was performed using Fourier transform infrared, atomic absorption spectroscopies, CHN elemental analysis, powder X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and nitrogen adsorption/desorption techniques. The resulting catalyst showed high selectivity and catalytic activity toward the epoxidation reaction. Moreover, the catalyst demonstrated size-selective properties suggested the reaction occurred inside the pores. [ABSTRACT FROM AUTHOR]

The clean synthesis of 6-cyano-2,2-dimethyl-2- H -1-benzopyran epoxide starting from 3-methyl-2-butenal is reported using recyclable catalysts. H 4 PMo 11 VO 40 (PMo 11 V) and (PyH) 3 HPMo 11 VO 40 (Py 3 –PMo 11 V) Keggin-type heteropolyacids were used to synthesize 6-cyano-2,2-dimethyl-2- H -1-benzopyran in two steps with 35% yield. This is an alternative procedure to the traditional methodology with pyridine or picoline as catalyst, where 6-cyano-2,2-dimethyl-2- H -1-benzopyran is obtained by condensation of 4-cyanophenol with 1,1-diethoxy-3-methyl-2-butene. The 6-cyano-2,2-dimethyl-2- H -1-benzopyran epoxide was obtained using Jacobsen-type catalysts, and in situ generated dimethyldioxirane (DMD) as oxidizing agent, that in comparison to m -CPBA/4-NMO and NaOCl/4-PPNO did not degrade the catalyst. In presence of 4-phenylpyridine N -oxide (4-PPNO) at 4 °C, enantioselectivities of 87% for 3S,4S-epoxide and 68% for 3R,4R-epoxide were obtained with the S,S- and R,R-Jacobsen catalysts, respectively. Overall yield was approximately 17% for 3S,4S-epoxide. [ABSTRACT FROM AUTHOR]

The mild epoxidation of strained alkenes using (DMPO) 2 MnCl catalyst (DMPO = 1,2-dimethyl-4(1H)-pyridinone-3-olate) in the presence of various oxidants was studied. Hydrogen peroxide and monopersulfate were found to be the best oxidants when used with imidazole in acetonitrile at 4 °C, with up to 94% conversion. Dismutation of hydrogen peroxide was also observed when used as an oxidant. The epoxidation using hydrogen peroxide or monoperoxysulfate appears to be mild and very selective for strained alkenes. A mechanism is proposed where imidazole is required for activation of the oxidant and where a detected Mn V = O species is proposed as the active species. Competitive reaction between H 2 O 2 and the substrate for the active species is proposed and homolytic vs heterolytic scissions of the O O bond of the oxidant are discussed. [ABSTRACT FROM AUTHOR]

As a new heterogeneous catalyst, Fe 3 O 4 nanoparticles were prepared and modified with sodium silicate and (3-aminopropyl) trimethoxysilane (APTMS) followed by complexation with V-MIL-101 and designated as Fe 3 O 4 @SiO 2 @APTMS@VMIL-101. It was characterized using FTIR, TEM, and VSM techniques. The Fe 3 O 4 @SiO 2 @APTMS@VMIL-101 was found to successfully catalyze the epoxidation of allyl alcohols and alkenes with tert -butylhydroperoxide (TBHP) in moderate to high yields. The epoxidation of trans -stilbene, norbornen, cyclooctene, geraniol, trans -2-hexene-1ol and 1-octene-3-ol with 100% selectivity is promising. Investigation of the stability and reusability of Fe 3 O 4 @SiO 2 @APTMS@V-MIL-101 revealed the heterogeneity character of the catalyst with no desorption during the course of epoxidation reactions. High yields, clean reactions, ease of catalyst separation and recyclability of the solid catalyst are some advantages of this method. [ABSTRACT FROM AUTHOR]

Novel mesostructured hybrid materials containing a molybdenum Schiff base complex grafted on the internal surface of SBA-15 pores were prepared by introducing MoO 2 (acac) 2 into a mesoporous silica functionalized with Schiff base ligands. The SBA-15 supports modified by an amine or salicylaldehyde were obtained by co-condensation of tetraethylorthosilicate and the corresponding organosilane in the presence of Pluronic P123 surfactant as a structure directing agent using bis[3-(trimethoxysilyl)propyl]amine or 5-chloromethylsalicylaldehyde coupled with bis[3-(trimethoxysilyl)propyl]amine as precursor. The molybdenum (VI) complexes immobilized on the internal surface of SBA-15 pores were employed as catalyst in the epoxidation of various alkenes using tert-butylhydroperoxide as oxidant. These immobilized molybdenum complexes are highly active and selective catalysts in liquid phase olefin epoxidation in dichloroethane at 84 °C. Leaching tests and metal analysis of reaction solutions showed that the kinetically competent catalyst is the molybdenum complex immobilized on the internal surface of SBA-15 pores and there is no molybdenum species in the solution. [ABSTRACT FROM AUTHOR]

The homogeneous epoxidation of cis -cyclooctene with H 2 O 2 , catalyzed by various Zr/Hf-containing Keggin sandwich polyoxometalates (POMs), i.e., the 1:2 complexes [M(α-PW 11 O 39 ) 2 ] 10− (M = Zr, 1 and M = Hf, 2 ), the 4:2 complexes [[{M(H 2 O)} 2 {M(H 2 O) 2 } 2 (μ-OH) 3 (μ-OH) 2 ](α-1,2-PW 10 O 37 ) 2 ] 7− (M = Zr, 3 and M = Hf, 4 ), the 2:2 complexes [{M(μ-OH)(H 2 O)} 2 (α-PW 11 O 39 ) 2 ] 8− (M = Zr, 5 and M = Hf, 6 ), and the 3:2 complex [Zr 3 (μ 2 -OH) 3 (A-α-PW 9 O 34 ) 2 ] 9− ( 7 ), was examined. At least two different reaction types exist: (1) one brought about by the highly catalytically active Venturello complex [PO 4 {WO(O 2 ) 2 } 4 ] 3− , which was generated by reactions of the Zr/Hf-containing POMs with hydrogen peroxide, and (2) the reaction with active species formed on Zr/Hf clusters in the POMs. In the first type, the original sandwich structures are not maintained during the reactions (as shown in 1 , 2 , 3 , and 4 ), but in the second type, the sandwich structures are maintained (as seen in 5 and 6 ). 7 was inactive. The reaction, ( 5 + cis -cyclooctene) + H 2 O 2 , was explicitly influenced by changing the reaction time of 5 and olefin, before addition of H 2 O 2 , indicating a significant interaction between 5 and olefin, such as coordination of olefin to the POM. Thus, for homogeneous olefin epoxidation by hydrogen peroxide catalyzed by di-Zr/Hf clusters, a new mechanism is proposed through olefin-coordinated species to di-Zr/Hf centers. [ABSTRACT FROM AUTHOR]

VO 2 –SiO 2 based catalysts with V contents between 5 and 20 wt.% were prepared from inorganic precursors via the sol–gel process and subsequently dried, calcined and reduced at 673 K. Structural characterization of these materials was carried out with X-rays diffraction (XRD), ICP, N 2 adsorption–desorption at 77 K, 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 VO 2 species are well dispersed on silica. BET analysis showed that the surface area decreases from 390 to 22 m 2 g −1 with V content. The results of pyridine adsorption followed by FTIR indicated that the 5 wt.% VO 2 –SiO 2 catalyst displays low acid densities. Experimental results pointed out that the 5 wt.% VO 2 –SiO 2 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. [ABSTRACT FROM AUTHOR]

A metal-template/metal-exchange method was used to imprint covalently attached bis(8-quinolinolato)dioxomolybdenum(VI) and dioxotungsten(VI) complexes onto large surface-area, mesoporous SBA-15 silica to obtain discrete MoO2VIT and WO2VIT catalysts bearing different metal loadings, respectively. Homogeneous counterparts, MoO2VIN and WO2VIN, as well as randomly ligand-grafted heterogeneous analogues, MoO2VIG and WO2VIG, were also prepared for comparison. X-ray absorption fine structure (XAFS), pair distribution function (PDF) and UV-vis data demonstrate that MoO2VIT and WO2VIT adopt a more solution-like bis(8-quinolinol) coordination environment than MoO2VIG and WO2VIG, respectively. Correspondingly, the templated MoVI and WVI catalysts show superior performances to their randomly grafted counterparts and neat analogues in the epoxidation of cyclooctene. It is found that the representative MoO2VIT-10% catalyst can be recycled up to five times without significant loss of reactivity, and heterogeneity test confirms the high stability of MoO2VIT-10% catalyst against leaching of active species into solution. The homogeneity of the discrete bis(8-quinolinol) metal spheres templated on SBA-15 should be responsible for the superior performances. [ABSTRACT FROM AUTHOR]

Highlights: [•] Well dispersed molybdenum atoms onto MCM-41through oxidative decomposition were obtained. [•] The catalyst was characterized with FT-IR, XPS and EPR techniques. [•] Cyclic and linear alkenes were efficiently epoxidized with good to excellent yields. [•] The grafted catalyst can be reused several times in the model epoxidation reaction. [ABSTRACT FROM AUTHOR]

Highlights: [•] The 0.32wt.% Sn–1.39wt.% Cu–17.16wt.% Ag/SrTiO3 provided the highest EO selectivity. [•] The best diluent gas was found to be 35%CH4/53% He over all studied catalysts. [•] CH4 enhanced C2H4 conversion while He provided both high EO selectivity and yield. [•] The 35% CH4/53% He produced the lowest coke formation and highest long term stability. [ABSTRACT FROM AUTHOR]

Highlights: [•] Straightforward, three step synthesis of Mo-complexes. [•] Catalysts are easy to handle in normal atmosphere. [•] Highly active epoxidation catalysts (TON up to 5000). [•] Highly selective epoxidation catalyst also with challenging substrates. [•] Broad substrate scope. [Copyright &y& Elsevier]

Highlights: [•] A new heterogeneous molybdenum catalyst was synthesized for oxidation of olefins. [•] High activity and selectivity were obtained for the formation of the epoxides. [•] The catalytic activity is influenced by the amount of adsorbed Mo on the polymer. [•] Adsorption of the Mo is related to ratio of Zr/Si and S/Zr. [•] Amount of adsorbed Mo plays a crucial role in the particle size and morphology. [Copyright &y& Elsevier]

Highlights: [•] The combination of zwitterion and phosphotungstate constructed a catalyst. [•] The combined catalyst exhibited high TON and TOF values for expoxidation. [•] The epoxidation can be performed under solventless and ice bath conditions. [•] Strong cooperative effect existed between zwitterions and phosphotungstate. [•] The formation of W/O emulsion by the zwitterion facilitated the reaction. [ABSTRACT FROM AUTHOR]

Highlights: [•] Cd modified TS-1 were used as catalysts for butadiene epoxidation. [•] The addition of Cd significantly promoted vinyloxirane yield and H2O2 utilization. [•] Quantum chemical calculations were used to explore detailed Cd roles in TS-1. [•] Five-membered cyclic intermediate formation was facilitated for Cd modification. [•] Active O eletrophilicity in H2O2 was promoted for Cd modification. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis of novel Fe3O4/P4VP nanospheres via an miniemulsion polymerization. [•] Composite nanospheres with multiple Fe3O4 cores embedded in P4VP shell. [•] High catalytic efficiency of Fe3O4@P4VP@MoO2(acac)2 for the green epoxidation. [•] Facile magnetic recyclability of Fe3O4@P4VP@MoO2(acac)2 nanocatalyst. [ABSTRACT FROM AUTHOR]

Highlights: [•] Heterocycle-modified PWA was adopted as catalysts for epoxidation of propylene. [•] Imidazole and 1,2,4-triazole was represented as the excellent modifier. [•] Modified PWA catalyst exhibited the high selectivity to propylene oxide. [•] Modification of heterocycles increased thermal stability of the catalysts. [•] The modified PWA can be recycled, preventing significant loss of catalyst. [ABSTRACT FROM AUTHOR]

Highlights: [•] First report of metallocorroles catalyzed epoxidation in ionic liquid medium. [•] Catalytic alkene epoxidation at room temperature by iron (IV) and manganese (III) corrole. [•] Tuning of selectivity by ionic liquid. [•] Use of NaOCl as terminal oxidant for epoxidation by metallocorroles for the first time. [•] Selective and recyclable epoxidation system based on metallocorroles. [ABSTRACT FROM AUTHOR]

Highlights: [•] Unsymmetric chiral Mn(III) salen complexes were immobilized on mesoporous silica. [•] Great difference in reactivity was observed with different oxidants. [•] UV–vis spectra and reaction kinetics were employed to analyze the difference. [ABSTRACT FROM AUTHOR]

Highlights: [•] Functionalized imidazolate mesoporous supports were prepared by co-condensation. [•] Immobilized chiral Mn(III) salen catalysts showed excellent catalytic performance. [•] Notably high TOF values (up to 165h−1) were obtained for olefin epoxidation. [•] Co-condensed supports were better than the post-functionalized materials. [•] Bigger support pore sizes gave better catalytic performance. [ABSTRACT FROM AUTHOR]

Highlights: [•] Encapsulation of ruthenium salophen on dealuminated zeolite Y. [•] A heterogeneous catalyst was prepared. [•] The catalyst was used for size selective epoxidation of alkenes. [•] The catalyst was reusable. [ABSTRACT FROM AUTHOR]

Highlights: [•] The secondary amine N,N-dioxo-radical is the direct oxidant of the epoxidation. [•] Secondary amine N,N-dioxo radicals were observed by ESI-MS. [•] The N,N-dioxo-radical structure can lead to the enantioselectivity of epoxidation. [•] Protonated N,N-dioxo-radical can oxidize olefin into diol. [•] Pyridine can suppress the protonation of N,N-dioxo-radical. [Copyright &y& Elsevier]

Abstract: The molybdenum tricarbonyl complexes [Mo(CO)3(HC(3,5-Me2pz)3)] (1) and [Mo(CO)3(HC(pz)3)] (2) (HC(3,5-Me2pz)3 =tris(3,5-dimethyl-1-pyrazolyl)methane, HC(pz)3 =tris(1-pyrazolyl)methane) were obtained in good yields by the microwave-assisted reaction of Mo(CO)6 with the respective organic ligand. Complete oxidative decarbonylation of 1 and 2 was achieved by reaction with excess tert-butylhydroperoxide (TBHP) in 1,2-dichloroethane at 55°C. For complex 1, the (μ2-oxo)bis[dioxomolybdenum(VI)] hexamolybdate of composition [{MoO2(HC(3,5-Me2pz)3)}2(μ2-O)][Mo6O19] (3) was obtained in good yield, and its structure was determined by single crystal X-ray diffraction. The compound (4) obtained by oxidative decarbonylation of 2 was not unambiguously identified, but may be chemically analogous to 3. Compounds 1–4 were examined for the first time as homogeneous (pre)catalysts for the epoxidation of olefins with TBHP, using different types of cosolvents at 55°C. During the catalytic reactions 1 and 2 transform in situ into 3 and 4, respectively, and the latter two are fairly stable catalysts. Catalytic tests and characterization studies of the recovered catalysts were carried out in an attempt to understand the kinetic differences observed between the compounds prepared in situ during the catalytic reaction and those prepared prior to the catalytic reaction, from the same precursor complex. [Copyright &y& Elsevier]

Abstract: This work presents the epoxidation of camphene employing methyltrioxorhenium(VII) (MTO) as catalyst. The effect of different factors on the formation of camphene oxide with respect to high yield and selectivity was investigated. First, the ratio camphene:MTO:pyrazole:H2O2 was studied in dichloromethane as solvent in order to determine the optimal condition. Moreover, the influence of the Lewis base adduct (tert-butylpyridine, 4,4′-dimethyl-2,2′-bypridine, imidazole or pyrazole) was investigated. The effect of an aqueous oxidant, namely H2O2 and a solid oxidant, namely urea hydrogen peroxide (UHP) was also examined. Finally, the solvent was varied from dichloromethane to chloroform, toluene and nitromethane. Based on the results the optimal conditions for the epoxidation of camphene using MTO as catalyst were determined. The molar ratio camphene:MTO:pyrazole:H2O2 of 100:0.5:10:110 in dichloromethane at room temperature leads after 3h to 97% yield and 98% selectivity toward camphene oxide at 99% conversion. [Copyright &y& Elsevier]

Abstract: Organic carbonates, e.g., dimethyl carbonate and propylene carbonate were used as reaction media in enantioselective epoxidation of non-functionalized alkenes by using a series of chiral macrocyclic Mn(III) salen complexes (5mol%) as catalyst with pyridine N-oxide as an axial base. This protocol worked effectively with urea hydrogen peroxide, as well as sodium hypochlorite as oxidants to give respective epoxides in high yields and ee (up to >91% in selected cases). Furthermore kinetic studies of the catalytic epoxidation reaction in dimethyl carbonate:methanol (optimized solvent mixture) with urea hydrogen peroxide as an oxidant showed first order dependence on catalyst and oxidant whereas it is zero order for the substrate, styrene. [Copyright &y& Elsevier]

Abstract: Four ionic liquids (ILs) with both a pyridine N-oxide moiety and an imidazolium moiety combined by an amide spacer were synthesized through a series of reactions including amidation, peroxidation, quaterization and anion exchange reaction. Their structures were fully characterized by 1H NMR, FT-IR, UV–vis and HR–MS. The ionic liquids were used respectively as additives in the methyltrioxorhenium (MTO) catalyzed epoxidation of olefins with 30% H2O2 as an oxidant. The catalytic results displayed that the ILs had excellent performances in suppressing epoxide ring-opening reaction, which led to the significant improvement of the selectivity of the MTO-catalyzed epoxidation with low loadings compared to other substances as additives. The coexistence of the pyridine N-oxide and imidazolium moieties in the structures of ILs is necessary in improving the MTO-catalyzed epoxidation reaction. It was also displayed that the improvement degree on the selectivity of epoxidation depended on the type of anion of the ILs, but not the position of the substituent with imidazolium moiety in the ring of pyridine N-oxide. Meanwhile, the results also showed that the introduction of the ILs caused the decrease of the epoxidation rate, but this side effect was small compared to those of other substances used as additives. [Copyright &y& Elsevier]

Abstract: This article reports our study on asymmetric epoxidation of unfunctionalized alkenes and asymmetric oxidation of sulfides catalyzed by a new triply immobilized (salen)Mn(III) system, when commercial sodium hypochlorite and hydrogen peroxide were loaded as terminal oxidant, respectively. A chiral sulfonato-(salen)Mn(III) complex was grafted onto a novel polysiloxane, then axially coordinated by 3-aminopropyl functionalized silica gel (40–63μm, 1mmolg−1 NH2 loading) as a secondary anchoring mode, and eventually dispersed into ionic liquid BMImX (BMIm+ =1-n-butyl-3-methylimidazolium; X− =PF6 −, BF4 −, NO3 −) for purpose of catalyst recycling. Catalysts were fully characterized by 1H NMR, FT-IR, molar conductivity, elemental analysis, nitrogen adsorption, aqueous particle size and zeta potential analysis, along with XRD. Interestingly, lateral immobilization led to a novel catalyst structure featuring parallel stacking of one-dimensional planers, whereas the lateral together with axial immobilization made supported complex nano-sized crystallite particles (diameter 24.2nm). After stepwise screening, doubly-immobilized catalyst and BMImBF4, in combination, showed best enantiomeric excess (e.e.) values and most stable recycling behavior in two kinds of catalysis, but generally sulfoxidation had better turnover frequencies than epoxidation reaction. [Copyright &y& Elsevier]

Abstract: Monomeric organomolybdenum carbonyl complexes of general formula [(η5-C5R5)Mo(CO)3X] (R=H, CH3, CH2Ph; X=alkyl, halide) are known to be pre-catalysts for olefin epoxidation. In this work, the application of a fluorinated complex, [CpMo(CO)3CF3] (Cp=η5-C5H5), is reported. With hexafluoroisopropanol as a solvent, a turnover frequency (TOF) of >6300h−1 was achieved in the epoxidation of cyclooctene with tert-butyl hydroperoxide (TBHP) as oxidant. So far, only ansa compounds of formula [Mo(η5-C5H4(CH(CH2) n )-η1-CH)(CO)3] are known to deliver better performances in catalytic epoxidation reactions at room temperature. [CpMo(CO)3CF3] was also applied in 2-phase catalytic epoxidation reactions. The high stability of the oxidised species allows catalyst recycling for multiple catalytic runs without significant loss of activity. Besides, the fluorinated complex enables – at this stage preliminary – mechanistic 19F NMR studies, indicating the nature of the catalytically active Mo-species, which has been an unresolved subject for some time. [Copyright &y& Elsevier]

Abstract: Propylene epoxidation is an important reaction as propylene epoxide (PO) has a versatile application for synthesizing various industrially important compounds. Despite of high catalyst activity of Au/Ti–SiO2 catalyst after silylation, the catalyst deactivation, poor regeneration and more hydrogen conversion has put a major hurdle to optimize the catalyst performance in the commercial level. Addition of contaminant level trimethylamine (TMA) could improve the catalyst performance in terms of deactivation, regeneration and hydrogen conversion. In this study we have characterized silylated Au/Ti–SiO2 catalyst by in situ UV–vis–NIR, BET S.A, XPS and XAFS technique. The catalytic activity was checked for direct propylene epoxidation reaction in presence of trimethylamine (TMA). An explanation behind the reason of better performance of the catalyst after silylation was found in this study. [Copyright &y& Elsevier]

Abstract: This report presents a study of the epoxidation of limonene employing methyltrioxorhenium (MTO) as catalyst. The influence of base ligands, namely t-butylpyridine, 4,4′-dimethyl-2,2′-bipyridine and pyrazole on the catalytic activity was investigated. The choice of the oxidant (H2O2 in water or H2O2 stabilized by urea) was also examined. The effect of the solvent has been studied in order to determine optimal conditions for the epoxidation of (+)-limonene. The best result was obtained when a molar ratio (+)-limonene:MTO:H2O2:t-butylpyridine of 100:0.5:10:150 was used at 25°C in dichloromethane. 1,2-Limonene oxide was formed with 77% yield and 96% selectivity after 1h with a TOF of ca. 900h−1. [Copyright &y& Elsevier]

Abstract: The catalytic activity of monoatomically dispersed Pd supported on TiO2 toward propylene epoxidation in the presence of H2 and O2 was studied at ambient temperature, and both propylene oxide (PO) and propane were obtained. Short-chain alkanes also reacted but epoxide formation was not observed in those reactions except in the case of isobutane, which formed isobutylene oxide at a low rate. The optimum surface concentration of Pd on TiO2 was 0.005–0.01atom/nm2; because the supported amount of Pd is extremely small relative to the surface area of the support, the supported Pd is thought to be monoatomically dispersed. Pd/TiO2 catalysts prepared from a tetraphenylporphyrin–Pd chloride complex showed almost the same product distribution for propylene epoxidation as did catalysts prepared from Pd(NO3)2. Isotope exchange between H2 and D2 proceeded over Pd/TiO2 with a low surface concentration (0.0001atom-Pd/nm2), and chemical potential calculations suggested that H2 molecules could dissociatively adsorb onto the monoatomically dispersed Pd/TiO2. A PO formation mechanism over the catalyst is proposed on the basis of these results. The results presented here may provide the first clear evidence of catalysis by monoatomically dispersed noble metals. [Copyright &y& Elsevier]

Abstract: In this study, Ag-based catalysts with different loadings on various oxide supports, including low-surface-area α-Al2O3, Al2O3 C, Al2O3,Acid, SiO2 90, TiO2 and SrTiO3 synthesized by a sol–gel process, were investigated for ethylene epoxidation over a range of reaction temperatures. The specific surface area, crystallinity, surface morphology, oxidation state, metal crystallite size, and oxygen and ethylene adsorption characteristics of all prepared catalysts were characterized and correlated to the ethylene epoxidation activity. Compared with conventional Ag catalysts supported on low-surface-area α-Al2O3, the 17.16wt% Ag/SrTiO3 catalyst exhibited much better catalytic activity for the ethylene epoxidation reaction, providing both the highest EO yield of 4.5% and EO selectivity up to 99%. The results indicate that high oxygen and ethylene uptakes, together with the large size of Ag particles, play an important role in achieving the best catalytic activity of the Ag/SrTiO3 catalyst towards ethylene epoxidation reaction. [Copyright &y& Elsevier]

Abstract: A novel aqueous catalytic method for selective epoxidation of olefins and oxidation of saturated hydrocarbons to ketones using aqueous solution of tetra-n-butylammonium peroxomonosulfate (TBAOX) containing water-insoluble copper (II) phthalocyanine nanoparticles has been developed. No surfactants, additives, toxic reagents or solvents were involved. The impressive turnover numbers obtained for CuPc in this oxidation system displayed the high catalytic activity and relative stability of catalyst. The effective dispersity of CuPc in aqueous solution of TBAOX which yielded particles with average size of 30nm, was the most important factor to affect the reaction rate. The catalyst could easily be recovered and reused without loss of activity and the reduced form of starting oxidant (n-Bu4NHSO4) could also be recycled. [Copyright &y& Elsevier]