Showing papers on "Cyclohexene published in 2008"
TL;DR: In this paper, the performance of cobalt phthalocyanine and iron porphyrin network polymers of intrinsic microporosity (network-PIMs) was compared with that of low molar mass analogues.
Abstract: Cobalt phthalocyanine and iron porphyrin network polymers of intrinsic microporosity (network-PIMs) were prepared and their performance as heterogeneous catalysts compared with that of low molar mass analogues. Spiro-linked Co phthalocyanine network-PIMs prepared from preformed chlorinated phthalocyanines showed lower surface areas and lower catalytic activity than those prepared by a phthalocyanine-forming reaction from a rigid precursor incorporating a spiro-centre. However, all the phthalocyanine network-PIMs were much more effective catalysts than low molar mass Co phthalocyanine for the decomposition of hydrogen peroxide, the oxidation of cyclohexene and the oxidation of hydroquinone. An Fe porphyrin network-PIM showed a higher surface area than any of the phthalocyanine polymers and showed higher activity for the oxidation of hydroquinone, also outperforming a low molar mass FeCl porphyrin.
236 citations
TL;DR: In this article, the first magnetically recoverable Rh(0) nanoparticle-supported catalyst with extraordinary recovery and recycling properties is reported. But it does not require filtration, decantation, centrifugation, or any other separation technique thereby, overcoming traditional time and solvent-consuming procedures.
Abstract: We here report the first magnetically recoverable Rh(0) nanoparticle-supported catalyst with extraordinary recovery and recycling properties. Magnetic separation has been suggested as a very promising technique to improve recovery of metal-based catalysts in liquid-phase batch reactions. The separation method is significantly simple, as it does not require filtration, decantation, centrifugation, or any other separation technique thereby, overcoming traditional time- and solvent-consuming procedures. Our new magnetically separable catalytic system, comprised of Rh nanoparticles immobilized on silica-coated magnetite nanoparticles, is highly active and could be reused for up to 20 times for hydrogenation of cyclohexene (180,000 mol/molRh) and benzene (11,550 mol/molRh) under mild conditions.
191 citations
TL;DR: In this article, the influence of solvent on the activity, epoxide selectivity, and H2O2 efficiency of three types of zeolites (TS-1, Ti-Beta, and Ti-MWW) in the liquid phase epoxidation of 1-hexene and cyclohexene was investigated.
136 citations
TL;DR: In this paper, the reaction of 2-thiomethylbenzimidazole (Htmbmz) with polystyrene yielded a product designated by (PS-ligand), which corresponds mostly to the tmbmZ bound to the poly styrene matrix by the sulfur atom.
Abstract: The reaction of 2-thiomethylbenzimidazole (Htmbmz) with chloromethylated polystyrene yielded a product designated by (PS-ligand), which corresponds mostly to the tmbmz bound to the polystyrene matrix by the sulfur atom. [VO(acac) 2 ], [MoO 2 (acac) 2 ] and Cu(CH 3 COO) 2 react with the PS-ligand to give PS-[VO(ligand) n ] ( 1 ), PS-[MoO 2 (ligand) n ] ( 2 ) and PS-[Cu(ligand) n ] ( 3 ), respectively, with n ≈ 2. Non-polymer-bound complexes [VO(tmbmz) 2 ] ( 4 ), [MoO 2 (tmbmz) 2 ] ( 5 ) and [Cu(tmbmz) 2 ] ( 6 ) have also been prepared similarly. The anchored complexes were characterized by elemental analysis, IR, electronic and EPR spectroscopy, field-emission scanning electron micrograph (FE-SEM), energy dispersive X-ray analysis (EDAX) and thermo gravimetric studies and. EPR was particularly useful to characterize the binding modes in PS-[VO(ligand) n ] ( 1 ) and PS-[Cu(ligand) n ] ( 3 ), confirming that the vanadium and copper centers are well dispersed in the polymer matrix and supporting the presence of N 2 O 2 binding modes in both cases and the preservation of the binding mode at the end of the catalytic reactions carried out. The catalytic potential of these complexes was tested for the oxidation of styrene, cyclohexene and ethylbenzene using 30% H 2 O 2 as an oxidant. Various parameters, such as concentration of oxidant, amount of catalyst and temperature of the reaction mixture, have been optimized to obtain the maximum oxidation of substrates. Under the optimized reaction conditions, styrene gave three products with the selectivity order: benzaldehyde > 1-phenylethane-1,2-diol > styrene oxide. Oxidation of cyclohexene gave three products, the order of selectivity being: cyclohexane-1,2-diol > 2-cyclohexene-1-one > cyclohexeneoxide. At least four reaction products with the selectivity order: benzaldehyde > phenylacetic acid > acetophenone > 1-phenylethane-1,2-diol have been obtained on oxidation of ethylbenzene. The recycle ability of polymer-anchored metal complexes was checked; the results confirm that the polymer-bound complexes are not leached during the reaction/recovery procedures. Catalytic activities of the PS-supported complexes are higher than those of the corresponding non-polymer-bound complexes. Possible mechanisms are outlined and discussed. In all cases, peroxo or peroxy–metal complexes form; the formation of other intermediates is also discussed.
115 citations
TL;DR: In this paper, the structural characterization of certain dimeric compounds (esters) formed during the ozonolysis of cyclohexene and α-pinene mixtures is presented.
Abstract: . The build-up of oligomeric compounds during secondary organic aerosol (SOA) formation is subject of atmospheric research since several years. New particle formation and especially the SOA mass yield might be influenced significantly by oligomer formation. However, the chemical nature of observed oligomers and their formation pathways are still unclear. In this paper, the structural characterization of certain dimeric compounds (esters) formed during the ozonolysis of cyclohexene and cyclohexene/α-pinene mixtures are presented. The identification is based on the comparison of the mass spectra and the retention times (LC) of the oligomeric products with synthesized reference compounds. Cyclohexene is used here as a model compound for terpenes as globally most important SOA precursors, since it possesses a simpler structure than the biogenic alkenes and therefore offers the possibility to get access to reference compounds for certain of its oxidation products. In addition to cyclohexene, the formation of esters could also be observed in experiments with α-pinene as reactant.
111 citations
TL;DR: The first generation free-base anionic porphyrin [H2(TSPP)]4−, its iron(III) porphrin [Fe(TSA)3−, and the second generation anionic complexes [Fe[TDFSPP]3− and Fe[TDCSPP]-3− were intercalated into the layered double hydroxide ZnnAl-LDH (n = 2n=2, 4 or 5) by coprecipitation at constant pH.
100 citations
TL;DR: In this article, a metal-organic framework (MOF) containing redox active CoII atoms, [CoII(BPB)]·3DMF (1), has been prepared from the solvothermal reaction of CoII nitrate and 1,4-bis(4′-pyrazolyl)benzene (H2-BPB) in dimethylformamide (DMF).
Abstract: A metal-organic framework (MOF) containing redox active CoII atoms, [CoII(BPB)]·3DMF (1), has been prepared from the solvothermal reaction of CoII nitrate and 1,4-bis(4′-pyrazolyl)benzene (H2-BPB) in dimethylformamide (DMF). Compound 1 constitutes a porous coordination framework that is built up by interconnecting 1D CoII polymer chains with (BPB)2− ligands. The thermal stability of 1 was investigated by thermogravimetric (TG) analysis and variable-temperature X-ray powder diffraction (VTXRPD), which indicate that the framework of 1 is stable upon removal of solvent molecules. The argon adsorption isotherm of 1 at 77 K indicates a porous structure with a BET surface area of 1207 m2/g. As a test reaction for catalytic activity of 1, the oxidation of cyclohexene was examined employing tert-butyl hydroperoxide as oxidant. The maximum substrate conversion achieved after 12 h was 62 % with an estimated turn-over number (TON) of 44 based on the number of converted substrate molecules (cyclohexene) per CoII atom.
92 citations
TL;DR: In this paper, a combination of density functional theory (DFT) and temperature-programmed desorption (TPD) was used to determine trends in the hydrogenation activity of cyclohexene on several bimetallic surfaces prepared by modifying Pt(111) with 3D transition metals (Fe, Co, Ni, and Cu).
83 citations
TL;DR: In this paper, a small amount of Pt addition could increase the chemisorption capacity and make the reduction of Co or Ni much easier, especially for Co-based catalysts.
81 citations
TL;DR: In this paper, four surfactant-type peroxotungstates and peroxomolybdates have been synthesized and characterized for 30-wt.% H2O2 oxidation of cyclohexene, cycloencoder, cycloprocessor and cycloencyclohexanol to adipic acid without organic solvent and phase-transfer catalyst.
77 citations
TL;DR: The role of particle size during the hydrogenation/dehydrogenation of cyclohexene was studied over a series of monodisperse Pt/SBA-15 catalysts in this paper.
Abstract: The role of particle size during the hydrogenation/dehydrogenation of cyclohexene (10 Torr C6H10, 200–600 Torr H2, and 273–650 K) was studied over a series of monodisperse Pt/SBA-15 catalysts. The conversion of cyclohexene in the presence of excess H2 (H2: C6H10 ratio = 20:60) is characterized by three regimes: hydrogenation of cyclohexene to cyclohexane at low temperature ( 573 K). The rate of both reactions demonstrated maxima with temperature, regardless of Pt particle size. For the hydrogenation of cyclohexene, a non-Arrhenius temperature dependence (apparent negative activation energy) was observed. Hydrogenation is structure insensitive at low temperatures, and apparently structure sensitive in the non-Arrhenius regime; the origin of the particle-size dependent reactivity with temperature is attributed to a change in the coverage of reactive hydrogen. Small particles were more active for dehydrogenation and had lower apparent activation energies than large particles. The selectivity can be controlled by changing the particle size, which is attributed to the structure sensitivity of both reactions in the temperature regime where hydrogenation and dehydrogenation are catalyzed simultaneously.
TL;DR: In this paper, the results of synthesis, characterization and application of three metalloporphyrin catalysts (FeTPPCl, MnTPPCl and CoTPP), anchored on MCM-41, in the reaction of cyclohexene oxidation with hydrogen peroxide were presented.
Abstract: Metalloporphyrin catalysts are able to carry out selective oxidation of organic substrates with several oxidizing agents. Recently, mesoporous materials have been studied as supports because they present high specific surface area, better dispersion and regeneration properties. This work presents the results of synthesis, characterization and application of three metalloporphyrin catalysts (FeTPPCl, MnTPPCl and CoTPP, where TPP = tetraphenylporphyrin) anchored on MCM-41, in the reaction of cyclohexene oxidation with hydrogen peroxide. A modified sol–gel preparation was chosen for the synthesis of the MCM-41 mesoporous material, as well as the anchoring was followed by Soxhlet extraction to ensure strong adsorption of the complex. The supported materials were much more stable than pure metalloporphyrins. The synthesized catalysts were characterized by UV–vis, FTIR, XRD, ICP-AES, 29 Si MAS-NMR and thermal analysis, before and after incorporation. Evidence of the metalloporphyrin immobilization was confirmed by elemental analysis and their activity in the oxidation reaction. FeTPPCl/MCM-41 showed higher conversion than CoTPP/MCM-41 and MnTPPCl/MCM-41. However, MnTPPCl/MCM-41 even in low concentration on the support showed a good conversion for the direct oxidation of cyclohexene with the highest turnover number (1.54 × 10 5 ). All catalysts showed similar selectivity that favors allylic oxidation products over epoxidation. No leaching of the metalloporphyrins was observed after the reaction.
TL;DR: In this article, the synthesis of cyclic carbonate from 4-vinyl-1-cyclohexene-1,2-epoxide (VCHO) and carbon dioxide was investigated without using any solvent in the presence of ionic liquid as a catalyst.
TL;DR: In this paper, a detailed study about the relationship existing between the Ti loading in the catalyst, the acid properties and the catalytic efficacy is presented in this contribution. But the authors did not consider the effect of the presence of tetrahedral Ti species in the framework, the Bronsted acid sites were also generated at high Ti loadings.
TL;DR: Air- and water-tolerant C−H activation is observed in reactions of [(diimine)Pt(μ2-OH)]22+ dimers with allylic and benzylic C −H groups.
Abstract: Air- and water-tolerant C−H activation is observed in reactions of [(diimine)Pt(μ2-OH)]22+ dimers with allylic and benzylic C−H groups. The reactions proceed in good yields under mild conditions. Mechanistic studies indicate that the active species is the monomeric [(diimine)Pt(OH2)]2+ dication. The related palladium species, [(diimine)Pd(μ2-OH)]22+, exhibit similar stoichiometric activations and also effect catalytic oxidation of cyclohexene to benzene with molecular oxygen as the terminal oxidant.
TL;DR: The reaction kinetics of cyclohexeneEpoxidation using aqueous H2O2 oxidant and the highly selective epoxidation catalyst Bu(cap)TaSBA15 were studied and the reaction was determined to be first-order in Ta(V) surface coverage.
Abstract: The reaction kinetics of cyclohexene epoxidation using aqueous H2O2 oxidant and the highly selective epoxidation catalyst BucapTaSBA15 were studied. The reaction was determined to be first-order in Ta(V) surface coverage. The reaction rate exhibited saturation with respect to increasing concentrations of cyclohexene and H2O2. An Eley−Rideal mechanism and rate equation may be used to describe the epoxidation kinetics, which are similar to those for Ti(IV)SiO2-catalyzed epoxidations. The observed kinetics may also be modeled by a double-displacement mechanism typically associated with saturation enzyme catalysts. In addition, 1H NMR spectroscopy was employed to investigate H2O2 decomposition by BucapTaSBA15 and the unmodified TaSBA15 catalysts. Little decomposition occurred over the surface-modified material, but the unmodified material catalyzed a 30% conversion of H2O2 after 6 h. UV−visible absorbance and diffuse reflectance UV−visible (DRUV−vis) spectroscopy were used to investigate the structure of the ...
TL;DR: A series of tethered ammonium ionic liquids have been used to catalyse the Knoevenagel condensation of aldehydes/ketones with malononitrile and ethyl cyanoacetate as discussed by the authors.
Abstract: A series of Hunig's base tethered ammonium ionic liquids have been used to catalyse the Knoevenagel condensation of aldehydes/ketones with malononitrile and ethyl cyanoacetate. The reactions were performed under homogeneous and under biphasic, liquid–liquid and liquid–silica supported ionic liquid, conditions with the biphasic systems employing cyclohexene as the second phase. By increasing the distance between the ammonium head group and Hunig's base the activity of the catalyst was found to increase. Higher activity, in general, was found under homogeneous reaction conditions; however, the recyclability of the catalyst was improved by supporting the BIL under biphasic conditions.
TL;DR: In this paper, hexagonally ordered mesoporous niobiosilicates of SBA-15 type were synthesized by a new synthesis route in which the use of hydrochloric acid was avoided.
TL;DR: In this article, a dilute solution route in sodium hydroxide medium at ambient temperature was used to obtain 80-160 nm in diameter (Ti-MCM-41 NP) nanoparticles.
TL;DR: In this paper, the performance of cyclohexene conversion by functionalized ionic liquid-stabilized palladium nanoparticles has been investigated under very mild hydrogen pressure (1 MPa) and at 35 °C.
Abstract: Palladium nanoparticles in the size range of 5–6 nm were prepared conveniently by reducing palladium(II) with atmospheric pressure hydrogen and stabilized by 2,2′-dipyridylamine-functionalized imidazolium cations according to our approach The efficient catalytic conversion of cyclohexene into cyclohexane by the functionalized ionic liquid-stabilized palladium nanoparticles has been performed under very mild hydrogen pressure (01 MPa) and at 35 °C It was found that the concentration of palladium and the reaction temperature considerably affected the size and degree of aggregation of Pd nanoparticles in ionic liquid, which further changed the performance of the catalyst activity The synthesized nanocatalysts can be recycled at least five times without any loss of the activity Finally, the scope of substrates was also investigated The excellent catalytic activity of the present system can be attributed to good stabilization and high dispersion of palladium nanoparticles
TL;DR: The heat of adsorption and sticking probability of cyclohexene on Pt(111) were measured as a function of coverage using single-crystal adsorptive calorimetry in the temperature range from 100 to 300 K.
Abstract: The heat of adsorption and sticking probability of cyclohexene on Pt(111) were measured as a function of coverage using single-crystal adsorption calorimetry in the temperature range from 100 to 300 K. At 100 K, cyclohexene adsorbs as intact di-sigma bonded cyclohexene on Pt(111), and the heat of adsorption is well described by a second-order polynomial (130 - 47 theta - 1250 theta(2)) kJ/mol, yielding a standard enthalpy of formation of di-sigma bonded cyclohexene on Pt(111) at low coverages of -135 kJ/mol and a C-Pt sigma bond strength of 205 kJ/mol. At 281 K, cyclohexene dehydrogenates upon adsorption, forming adsorbed 2-cyclohexenyl (c-C6H(9,a)) and adsorbed hydrogen, and the heat of adsorption is well described by another second-order polynomial (174 - 700 theta + 761 theta(2)) kJ/mol. This yields a standard enthalpy of formation of adsorbed 2-cyclohexenyl on Pt(111) at a low coverage of -143 kJ/mol. At coverages below 0.10 ML, the sticking probability of cyclohexene on Pt(111) is close to unity (>0.95), independent of temperature.
TL;DR: In this paper, the effect of impregnation sequence on the formation of Pt/Ni bimetallic nanoparticles supported on γ-Al2O3 was investigated for catalysts with 3/1 and 1/1.
Abstract: The effect of impregnation sequence on the formation of Pt/Ni bimetallic nanoparticles supported on γ-Al2O3 was investigated for catalysts with Pt/Ni atomic ratios of 3/1 and 1/1. These bimetallic catalysts were prepared with a fixed Pt loading (5 wt.%) by incipient impregnation of one metal precursor and calcination, followed by the impregnation of the second metal precursor and a second calcinations step. The disproportionation activity of cyclohexene and the hydrogenation selectivity of acetylene in ethylene were used as probe reactions to compare the effect of the impregnation sequence. The bimetallic Pt/Ni catalysts showed significantly higher activity toward the disproportionation of cyclohexene than either Pt/γ-Al2O3 or Ni/γ-Al2O3. For catalysts with the Pt/Ni ratio of 3/1, the Pt-first catalyst, 1/3Ni-1Pt/γ-Al2O3, showed higher activity than the Ni-first catalyst, 1Pt-1/3Ni/γ-Al2O3. The effect of impregnation sequence was not as significant for catalysts with the Pt/Ni ratio of 1/1. In addition, kinetic analysis of the selective hydrogenation of acetylene in ethylene revealed an increase in the acetylene hydrogenation selectivity for 1/3Ni-1Pt/γ-Al2O3 as compared to both 1Pt-1/3Ni/γ-Al2O3 and monometallic 1Pt/γ-Al2O3. Extended X-ray absorption fine structure (EXAFS) measurements of the Pt LIII edge indicated that Pt Ni bimetallic bonds were formed in 1/3Ni-1Pt/γ-Al2O3 but not in 1Pt-1/3Ni/γ-Al2O3. The Pt Ni bonds were formed for the 1/1 ratio catalysts with both impregnation sequences. Overall, our results indicate that, at low Ni loadings, the impregnation sequence has a significant effect on the formation of Pt Ni bimetallic bonds, which in turn lead to different catalytic behavior for both the disproportionation of cyclohexene and the selective hydrogenation of acetylene in ethylene.
TL;DR: The mechanism of the Kharasch-Sosnovsky reaction has been investigated using B3 LYP/6-31G* calculations on a chiral reaction model and the proposed reaction mechanism is consistent with all known experimental results (including enantioselectivity data).
Abstract: The mechanism of the Kharasch-Sosnovsky reaction has been investigated using B3 LYP/6-31G* calculations on a chiral reaction model [cyclohexene+tert-butyl perbenzoate-->cyclohex-2-enyl benzoate+tert-butyl alcohol, catalyzed by a chiral bisoxazoline-copper(I) complex]. Although two previous reaction mechanisms have been considered, the results are consistent with a new mechanistic pathway. This path involves ligand exchange between the catalyst-cyclohexene complex with tert-butyl perbenzoate to give a catalyst-perester complex, which undergoes an (either one- or two-step) oxidative addition reaction to yield a copper(III) complex. The limiting step of the Kharasch-Sosnovsky reaction consists of an intramolecular step involving the abstraction of an allylic hydrogen from cyclohexene [which is pi-bound to the copper(III) complex]. The resulting allyl-copper(III) complex (subsequent to the loss of tert-butanol) can undergo a haptotropic rearrangement by means of an eta1-allyl/eta3-allyl equilibrium, leading to scrambling between vinylic and allylic positions when an isotopically labeled substrate is used. The allyl-copper(III) ion undergoes a stereospecific reductive elimination involving the pi-bond migration to yield a reaction product-catalyst complex, which can regenerate the alkene-copper(I) complex by ligand exchange. The proposed reaction mechanism is consistent with all known experimental results (including enantioselectivity data).
TL;DR: Kinetic measurements suggest that the rate limiting step in the heterogeneous C=C double bond oxidation reactions is likely to be the formation of the primary ozonide, and reaction pathways involving vibrationally hot Criegee intermediates that compete with pathways that involve thermalized surface species are suggested.
Abstract: We report vibrational sum frequency generation (SFG) spectra of glass surfaces functionalized with 1-pentene, 2-hexene, cyclopentene, cyclohexene, and a menthenol derivative. The heterogeneous reactions of ozone with hydrocarbons covalently linked to oxide surfaces serve as models for studying heterogeneous oxidation of biogenic terpenes adsorbed to mineral aerosol surfaces commonly found in the troposphere. Vibrational SFG is also used to track the C=C double bond oxidation reactions initiated by ozone in real time and to characterize the surface-bound product species. Combined with contact angle measurements carried out before and after ozonolysis, the kinetic and spectroscopic studies presented here suggest reaction pathways involving vibrationally hot Criegee intermediates that compete with pathways that involve thermalized surface species. Kinetic measurements suggest that the rate limiting step in the heterogeneous C=C double bond oxidation reactions is likely to be the formation of the primary ozonide. From the determination of the reactive uptake coefficients, we find that ozone molecules undergo between 100 and 10000 unsuccessful collisions with C=C double bonds before the reaction occurs. The magnitude of the reactive uptake coefficients for the cyclic and linear olefins studied here does not follow the corresponding gas-phase reactivities but rather correlates with the accessibility of the C=C double bonds at the surface.
TL;DR: A series of Mn(II), Co(II, Ni(II) and Cu(II)-complexes with 12-membered macrocyclic tetradentate ligand have been synthesized and characterized as homogeneous and encapsulated into the nanopores of zeolite.
Abstract: A series of Mn(II), Co(II), Ni(II) and Cu(II) complexes with 12-membered macrocyclic tetradentate ligand; H6C6N6S2 = 1,2,5,6,8,11-hexaazacyclododeca-7,12-dithione-2,4,8,10-tetraene; have been synthesized and characterized as homogeneous and encapsulated into the nanopores of zeolite–Y These catalytic systems show a good activity in the oxidation of cyclohexene to 2-cyclohexene-1-one, 2-cyclohexene-2-ol and 1-(tert-butylperoxy)-2-cyclohexene The chelation of zeolite-exchanged metal(II) by N-containing ligand gives rise to a whole class of Host–Guest Nanocomposite Materials (HGNM) as heterogeneous liquid-phase oxidation, which exhibits similar catalytic performances than the homogeneous ones The encapsulated complexes abbreviated here as [M(H4C6N6S2)]–NaY, catalyze the oxidation of cyclohexene using TBHP as oxidant in good yield Cyclohexene catalyzed by [M(H4C6N6S2)]–NaY under optimized reaction conditions gave three reaction products namely, 2-cyclohexene-1-one, 2-cyclohexene-2-ol and 1-(tert-butylperoxy)-2-cyclohexene In the presence of tert-butylhydroperoxide all catalysts gave 2-cyclohexene-1-one in major yield, though overall conversion has been found low (40–90%)
TL;DR: In this article, a microwave approach to the selective oxidation of cyclohexene is reported whereby, depending on the reaction conditions, the epoxide (65% conversion, 75% selectivity), the enol (70% conversion), or the enone (>99% conversion and 89% selectivities) can be obtained in a short period of time ranging from 1 to 20min.
Abstract: A smart and greener microwave approach to the selective oxidation of cyclohexene is reported whereby, depending on the reaction conditions, the epoxide (65% conversion, 75% selectivity), the enol (70% conversion, 80% selectivity) or the enone (>99% conversion, 89% selectivity) can be obtained in a short period of time ranging from 1 to 20 min. A cobalt-salen-SBA-15 material was employed as catalyst. The reported solventless microwave protocol was simple, greener and more efficient compared to any other reported cyclohexene oxidations.
TL;DR: In this article, Dodecatungstophosphoric acid (HPW) and its metal salts (MPW) were tested for Friedel-Crafts alkylation of aromatics with alcohols and cyclohexene.
Abstract: Dodecatungstophosphoric acid (HPW) and its metal salts (MPW) were tested for Friedel-Crafts alkylation of aromatics with alcohols and cyclohexene. The activity increased with the electronegativity of the cation. Sn4+ and Hf4+ salts (SnPW and HfPW) were among the most effective catalysts for alkylation of toluene with iso-propanol and cyclohexene. SnPW showed higher activity than the starting materials (HPW, SnCl4·6H2O) and Sc(OTf)3, and can be recycled without a marked loss in the activity. Temperature programmed desorption of acetonitrile showed the presence of Lewis acid due to Sn4+ cation in SnPW. The rate for the toluene alkylation with cyclohexene and the number of Lewis acid sites decreased when the number of water adsorbed on SnPW decreased with an increase in the dehydration temperature. The rate correlates well with the number of Lewis acid, indicating that Lewis acid site originated from the Sn4+ cation is responsible for the alkylation reaction.
TL;DR: In this paper, the epoxidation of cyclohexene by hydrogene peroxide and benzonitrile, in methanol as solvent on solid base catalysts, hydrotalcites (HT) and corresponding mixed oxides (C-HT), was investigated.
Abstract: The epoxidation of cyclohexene by hydrogene peroxide and benzonitrile, in methanol as solvent on solid base catalysts, hydrotalcites (HT) and corresponding mixed oxides (C-HT) was investigated. The employed catalysts were as-synthesized Mg/Al; Mg,Zn/Al; Mg/Ga,Al hydrotalcites, their derived mixed oxides and the corresponding reconstructed hydrotalcite forms (R-HT) obtained via the “memory effect” upon a rehydration treatment of C-HT. The catalysts were characterized by XRD, CO 2 -TPD and N 2 adsorption–desorption measurements. The reconstructed HT samples exhibit higher activity in comparison to the as-synthesized carbonated HT samples. A tentative correlation of the catalytic properties with the base strength of the active sites, the structural and textural characteristics of the catalysts, has been explored.
TL;DR: In this article, it was shown that Pd nanoparticles in polyethylene glycols (PEGs) were very active, stable, and selective for hydrogenation of a range of olefins at mild conditions.
TL;DR: Recycling studies indicate that these catalysts can be reused at least three times without any significant loss in their catalytic potential, and while the polymer supported V(iv)O-complexes do not change after being used, the EPR spectra of the Cu-complexe show significant changes.
Abstract: 3-Formylsalicylic acid (Hfsal), covalently bound to chloromethylated polystyrene (PS) and cross-linked with 5% divinylbenzene reacts with D,L-alanine and L-isoleucine to give the Schiff-base tridentate ligands PS–H2fsal–D,L-Ala and PS–H2fsal–L-Ile, respectively. These anchored ligands upon reaction with VOSO4 and Cu(CH3COO)2·H2O form the complexes PS–[VO(fsal–D,L-Ala)(H2O)], PS–[Cu(fsal–D,L-Ala)(H2O)], PS–[VO(fsal–L-Ile)(H2O)] and PS–[Cu(fsal–L-Ile)(H2O)]. The structures of these immobilized complexes have been established on the basis of scanning electron micrographs, spectroscopic (infrared, electronic and EPR), thermogravimetric and elemental analysis studies. The oxidation of p-chlorotoluene and cyclohexene has been investigated using these complexes as the catalysts in the presence of H2O2 as the oxidant. Reaction conditions have been optimised by considering the concentration of the oxidant, the amount of catalyst used and the temperature of the reaction mixture. Under the optimised conditions, p-chlorotoluene gave a maximum of 14% conversion using PS–[VO(fsal–D,L-Ala)(H2O)] as the catalyst, with the main products having a selectivity order of: p-chlorobenzaldehyde >> p-chlorobenzylalcohol > p-chlorobenzoic acid > 2-methyl-5-chlorophenol > 3-methyl-6-chlorophenol. The oxidation of cyclohexene with PS–[VO(fsal–D,L-Ala)(H2O)] proceeds with 79% conversion, which is followed by PS–[VO(fsal–L-Ile)(H2O)] with 77% conversion, and the oxidation of cyclohexene by Cu-based catalysts occurs with considerably lower conversions (29–32%). The selectivity of the products follows the order: 2-cyclohexene-1-ol > cyclohexene oxide > cyclohexane-1,2-diol > 2-cyclohexene-1-one. Recycling studies indicate that these catalysts can be reused at least three times without any significant loss in their catalytic potential. However, EPR studies indicate that while the polymer supported V(IV)O-complexes do not change after being used, the EPR spectra of the Cu-complexes show significant changes. The corresponding non-polymer bound complexes [VO(fsal–D,L-Ala)(H2O)], [Cu(fsal–D,L-Ala)(H2O)], [VO(fsal–L-Ile)(H2O)] and [Cu(fsal–L-Ile)(H2O)] have also been prepared in order to compare their spectral properties and catalytic activities. The non-polymer bound complexes exhibit lower conversion, along with lower turn-over frequency as compared to their polymer-bound analogues. Several EPR, 51V NMR and UV-vis studies have been undertaken to detect the intermediate species, and outlines for the mechanisms of the catalytic reactions are proposed.