Showing papers on "Cyclohexanone published in 2005"
TL;DR: In this paper, L-proline amides derived from various chiral beta-amino alcohols that bear substituents with various electron natures at their stereogenic centers are prepared and evaluated for catalyzing the direct Aldol reaction of 4-nitrobenzaldehyde with acetone.
Abstract: L-proline amides derived from various chiral beta-amino alcohols that bear substituents with various electron natures at their stereogenic centers are prepared and evaluated for catalyzing the direct Aldol reaction of 4-nitrobenzaldehyde with acetone. Catalysts with strong electron-withdrawing groups are found to exhibit higher catalytic activity and enantioselectivity than their analogues with electron-donating groups. The presence of 2 mol % catalyst 4g significantly catalyzes the direct Aldol reactions of a wide range of aldehydes with acetone and butanone, to give the beta-hydroxy ketones with very high enantioselectivities ranging from 96% to >99% ee. High diastereoselectivity of 95/5 was observed for the anti Aldol product from the reaction of cyclohexanone, and excellent enantioselectivity of 93% ee was provided for anti Aldol product from the reaction of cyclopentanone.
352 citations
TL;DR: Readily tunable and bifunctional L-prolinamides as novel organocatalysts have been developed and their catalytic activities were evaluated in the direct asymmetric Aldol reactions of various aromatic aldehydes and cyclohexanone.
171 citations
TL;DR: Co3O4 nanocrystals with average particle sizes of 30 and 50 run were synthesized using cobalt nitrate as precursor, and were characterized by X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy as mentioned in this paper.
Abstract: Co3O4 nanocrystals with average particle sizes of 30 and 50 run were synthesized using cobalt nitrate as precursor, and were characterized by X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. Catalytic oxidation of cyclohexane with molecular oxygen was studied over Co3O4 nanocrystals. These catalysts showed obviously higher activities as compared to Co3O4 prepared by the conventional methods, Co3O4/Al2O3, or homogeneous cobalt catalyst under comparable reaction conditions. The 89.1% selectivity to cyclohexanol and cyclohexanone at 7.6% conversion of cyclohexane was realized over 50 nm sized Co3O4 nanocrystals at 393 K for 6 h. (c) 2005 Elsevier B.V. All rights reserved.
155 citations
TL;DR: The resulting materials are new compositions in which hydroxyl groups are located along the main chain of commercial, high molecular weight LDPE, HDPE, and LLDPE materials, which have improved wetting properties and serve as macroinitiators to synthesize graft polycaprolactones that compatibilize polyethylene–polycaprolACTone blends.
Abstract: Polyolefins account for 60% of global plastic consumption, but many potential applications of polyolefins require that their properties, such as compatibility with polar polymers, adhesion, gas permeability, and surface wetting, be improved. A strategy to overcome these deficiencies would involve the introduction of polar functionalities onto the polymer chain. Here, we describe the Ni-catalyzed hydroxylation of polyethylenes (LDPE, HDPE, and LLDPE) in the presence of mCPBA as an oxidant. Studies with cycloalkanes and pure, long-chain alkanes were conducted to assess precisely the selectivity of the reaction and the degree to which potential C–C bond cleavage of a radical intermediate occurs. Among the nickel catalysts we tested, [Ni(Me4Phen)3](BPh4)2 (Me4Phen = 3,4,7,8,-tetramethyl-1,10-phenanthroline) reacted with the highest turnover number (TON) for hydroxylation of cyclohexane and the highest selectivity for the formation of cyclohexanol over cyclohexanone (TON, 5560; cyclohexanol/(cyclohexanone + e-...
140 citations
TL;DR: In this paper, a single-step, solvent-free process of producing e-caprolactam using a family of designed bifunctional, heterogeneous, nanoporous catalysts containing isolated acidic and redox sites is described.
Abstract: The ever-increasing industrial demand for nylon-6 (polycaprolactam) necessitates the development of environmentally benign methods of producing its precursor, e-caprolactam, from cyclohexanone. It is currently manufactured in two popular double-step processes, each of which uses highly aggressive reagents, and each generates substantial quantities of largely unwanted ammonium sulfate as by-product. Here we describe a viable laboratory-scale, single-step, solvent-free process of producing e-caprolactam using a family of designed bifunctional, heterogeneous, nanoporous catalysts containing isolated acidic and redox sites, which smoothly convert cyclohexanone to e-caprolactam with selectivities in the range 65–78% in air and ammonia at 80°C. The catalysts are microporous (pore diameter 7.3 A) aluminophosphates in which small fractions of the and tetrahedra constituting the 4-connected open framework are replaced by and tetrahedra, which become the loci of the redox and acidic centers, respectively. The catalysts may be further optimized, and already may be so designed as to generate selectivities of ≈80% for the intermediate oxime, formed from NH2OH, which is produced in situ within the pore system. The advantages of such designed heterogeneous catalysts, and their application to a range of other chemical conversions, are also adumbrated.
110 citations
TL;DR: It is shown how the very reactive CyOOH intermediate is the predominant source of ketone and alcohol, while it also leads to some side products, which is largely applicable to the oxidation of other hydrocarbons, such as toluene, xylene, and ethylbenzene.
Abstract: In spite of its industrial importance, the detailed reaction mechanism of cyclohexane autoxidation by O2 is still insufficiently known. Based on quantum chemical potential energy surfaces, rate coefficients of the primary and secondary chain propagation steps involving the cyclohexylperoxyl (CyOO) radical were evaluated using multiconformer transition-state theory. Including tunneling and hindered-internal-rotation effects, the rate coefficient for hydrogen-atom abstraction from cyclohexane (CyH) by CyOO was calculated to be k(T)= 1.46 x 10(-11) x exp(-17.8 kcal mol(-1)/ RT) cm3s(-1) (300-600K), close to the experimental data. A "Franck-Rabinowitch cage" reaction between the nascent cyclohexylhydroperoxide (CyOOH) and cyclohexyl radical, products from CyOO + CyH, is put forward as an initially important cyclohexanol (CyOH) formation channel. alphaH abstraction by CyOO. from cyclohexanone was calculated to be only about five times faster than that from CyH, too slow to explain all the observed side products. The a-hydrogen (alphaH) abstractions from CyOH and CyOOH by CyOO. are predicted to be about 10 and 40 times faster, respectively, than the CyOO. +CyH reaction. The very fast CyOO.+CyOOH reaction proceeds through the unstable Cy-alphaH .OOH radical that decomposes spontaneously into the ketone (Q=O) plus the OH radical; the "hot" .OH is found to produce the bulk of the alcohol via a second, "activated cage" reaction analogous to that above. It is thus shown how the very reactive CyOOH intermediate is the predominant source of ketone and alcohol, while it also leads to some side products. The alpha-hydroxycyclohexylperoxyl radical formed during the moderately fast oxidation of CyOH is shown to decompose fast into HO2 + cyclohexanone in a rapidly equilibrated reaction, which constitutes a smaller, second ketone source. These two fast cyclohexanone forming routes avoid the need for unfavorable molecular routes hitherto invoked as ketone sources. The theoretical predictions are supported and complemented by experimental findings. The newly proposed scheme is also largely applicable to the oxidation of other hydrocarbons, such as toluene, xylene, and ethylbenzene.
104 citations
TL;DR: The quantum-chemical results and the kinetic study indicate that the reaction follows mechanism 1, and that the catalyst active site consists of two centers: the Lewis acid Sn atom to which cyclohexanone has to coordinate, and the oxygen atom of the Sn-OH group that interacts with H2O2 forming a hydrogen bond.
Abstract: The molecular mechanism of the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide catalyzed by the Sn-beta zeolite has been investigated by combining molecular mechanics, quantum-chemical calculations, spectroscopic, and kinetic techniques. A theoretical study of the location of Sn in zeolite beta was performed by using atomistic force-field techniques to simulate the local environment of the active site. An interatomic potential for Sn/Si zeolites, which allows the simulation of zeolites containing Sn in a tetrahedral environment, has been developed by fitting it to the experimental properties of quartz and SnO 2 (rutile). The tin active site has been modeled by means of a Sn(OSiH 3 ) 3 OH cluster, which includes a defect in the framework that provides the flexibility necessary for the interaction between the adsorbates and the Lewis acid center. Two possible reaction pathways have been considered in the computational study, one of them involving the activation of the cyclohexanone carbonyl group by Sn (1) and the other one involving hydrogen peroxide being activated through the formation of a tin-hydroperoxo intermediate (2). Both the quantum-chemical results and the kinetic study indicate that the reaction follows mechanism 1, and that the catalyst active site consists of two centers: the Lewis acid Sn atom to which cyclohexanone has to coordinate, and the oxygen atom of the Sn-OH group that interacts with H 2 O 2 forming a hydrogen bond.
93 citations
TL;DR: In this paper, a series of highly efficient hybrid gold nanoparticle/mesoporous-silica catalysts were synthesized and employed for the solvent-free aerobic oxidation of cyclohexane to cyclochexanol and cycloxide under moderate reaction conditions.
Abstract: A series of highly efficient hybrid gold nanoparticle/mesoporous-silica catalysts were synthesized and employed for the solvent-free aerobic oxidation of cyclohexane to cyclohexanol and cyclohexanone under moderate reaction conditions. The catalysts were characterized by XRD, N2 adsorption/desorption, TEM and ICP-AES, which shows the active species are monodispersed gold nanoparticles.
90 citations
TL;DR: Host-guest clathrates of 1 provide an example of spontaneous chirality evolution during crystallization and a two-in-one host-guests crystal (phenol and aniline), and show how weak C-H...F interactions (o- and m-fluorophenol) can change the molecular arrangement in strongly hydrogen-bonded crystal structures.
Abstract: The T-shaped host molecule 4,4-bis(4'-hydroxyphenyl)cyclohexanone (1) has an equatorial phenol group and a cyclohexanone group along the arms and an axial phenol ring as the stem. The equatorial phenyl ring adopts a "shut" or "open" conformation, like a windowpane, depending on the size of the guest (phenol or o/m-cresol), for the rectangular voids of the hydrogen-bonded ladder host framework. The adaptable cavity of host 1 expands to 11x15-18 A through the inclusion of water with the larger cresol and halophenol guests (o-cresol, m-cresol, o-chlorophenol, and m-bromophenol) compared with a size of 10x13 A for phenol and aniline inclusion. The ladder host framework of 1 is chiral (P2(1)) with phenol, whereas the inclusion of isosteric o- and m-fluorophenol results in a novel polar brick-wall assembly (7x11 A voids) as a result of auxiliary C-H...F interactions. The conformational flexibility of strong O-H...O hydrogen-bonding groups (host 1, phenol guest), the role of guest size (phenol versus cresol), and weak but specific intermolecular interactions (herringbone T-motif, C-H...F interactions) drive the crystallization of T-host 1 towards 1D ladder and 2D brick-wall structures, that is, supramolecular isomerism. Host 1 exhibits selectivity for the inclusion of aniline in preference to phenol as confirmed by X-ray diffraction, 1H NMR spectroscopy, and thermogravimetry-infrared (TG-IR) analysis. The T(onset) value (140 degrees C) of aniline in the TGA is higher than those of phenol and the higher-boiling cresol guests (T(onset)=90-110 degrees C) because the former structure has more O-H...N/N-H...O hydrogen bonds than the clathrate of 1 with phenol which has O-H...O hydrogen bonds. Guest-binding selectivity for same-sized phenol/aniline molecules as a result of differences in hydrogen-bonding motifs is a notable property of host 1. Host-guest clathrates of 1 provide an example of spontaneous chirality evolution during crystallization and a two-in-one host-guest crystal (phenol and aniline), and show how weak C-H...F interactions (o- and m-fluorophenol) can change the molecular arrangement in strongly hydrogen-bonded crystal structures.
88 citations
TL;DR: In this article, three chitosan-Schiff base Co(II) and Pd-II complexes were prepared in a simple way and characterized by FT-IR, XPS and TG.
Abstract: Three chitosan-Schiff base Co(II) and Pd(II) complexes were prepared in a simple way and characterized by FT-IR, XPS and TG. Their abilities to catalyze oxidation of cyclohexane into cyclohexanone and cyclohexanol with oxygen in the absence of any solvents or reducing agents were studied. It has been revealed that the complexes had high catalytic activities for heterogeneous cyclohexane oxidation with oxygen. Especially, the oxidation of cyclohexane catalyzed by chitosan-salicyaldehyde Schiff base Co(II) complex under 1.6 MPa of initial oxygen pressure at 418 K gave excellent results with 9100 turnover numbers (based on the cobalt atom) and 96% selectivity for cyclohexanone and cyclohexanol after reaction of 4.5 h. The influences of oxygen pressure, reaction temperature and reaction time on the oxidation of cyclohexane were also investigated. It has been also revealed that the complexes were efficient for the oxidation of bulky cyclic alkanes and linear alkanes.
84 citations
TL;DR: In this paper, the authors investigated the performance of supported gold catalysts for cyclohexane to cyclochexane and cyclochenanone with mild conditions of temperature and pressure.
Abstract: The oxidation of cyclohexane to cyclohexanol and cyclohexanone are investigated using supported gold catalysts using mild conditions of temperature and pressure. These catalysts are found to show some limited activity at 70 °C. However, the gold catalysts do not exhibit significantly different behaviour from supported Pt or Pd catalysts, and the selectivity observed is solely a function of conversion which in turn is a function of reaction time. It is clear that at very low conversions very high selectivities can be observed, but high selectivity under these mild reaction conditions cannot be maintained at higher conversions.
TL;DR: In this paper, the nano-Au supported mesoporous materials were prepared and characterized by XRD, N 2 adsorption/desorption, UV-vis, XPS, and ICP-AES.
Abstract: The nano-Au supported mesoporous materials were prepared and characterized by XRD, N 2 adsorption/desorption, UV–vis, XPS, and ICP-AES. The liquid-phase selective oxidation cyclohexane to cyclohexanol and cyclohexanone over nano-Au in mesoporous materials catalyst was carried out in a solvent-free system, in which oxygen was the only oxidant and the reaction conditions are very moderate.
TL;DR: In this paper, high-ordered mesoporous Cr-MCM-41 materials with different Si:Cr mole ratios have been synthesized by using the hydrothermal method and avoiding co-precipitation of chromium oxides during synthesis.
Abstract: Highly ordered mesoporous Cr-MCM-41 materials with different Si:Cr mole ratios have been synthesized by using the hydrothermal method and avoiding co-precipitation of chromium oxides during synthesis. Detailed characterizations of these two-dimensional hexagonal mesoporous Cr-MCM-41 materials were carried out using powder XRD, TEM, SEM-EDS, N 2 sorption, FT-IR and UV–vis diffuse reflectance measurements. Cr-MCM-41 materials showed excellent catalytic activity and high selectivity in the direct oxidation of cycloalkanes viz. cyclohexane and cyclooctane to cyclohexanone and cyclooctanone, respectively, using dilute aqueous H 2 O 2 or tert -butyl hydroperoxide (TBHP) as oxidant under mild liquid phase reaction conditions.
TL;DR: A mild and general route for preparing pyrans and dienones from carbonyls and diynes is described and a spiropyran was prepared from the cycloaddition of a diyne and cyclohexanone.
TL;DR: The catalytic activity of the novel binuclear Fe(III) complex suggests that it can be considered as a functional biomimetic analog to methane monooxygenase.
TL;DR: In this paper, a biphasic system was proposed for the synthesis of cyclohexyl hydroperoxide from cycloheptane in the presence of oxalic acid as a co-catalyst.
TL;DR: In this paper, the kinetics of cyclohexane oxidation with iodosylbenzene, catalyzed by two supramolecular manganese(III) porphyrin isomers, were reported.
TL;DR: In this paper, the effect of acid treatment on the catalytic performance of ultrastable Y catalysts in the Beckmann rearrangement of cyclohexanone oxime has been investigated under liquid phase conditions.
TL;DR: In this article, the separation and purification of stigmasterol and β-sitosterol from phytosterol mixtures by solvent crystallization method was studied based on the difference of the solubility of Stigmasterols and β -sitosterols and with temperature using n-pentanol or cyclohexanone as a solvent.
TL;DR: In this paper, it is shown that ruthenium supported on activated carbon cloths (ACC) obtained by carbonisation of woven rayon fabric are very selective in the hydrogenation of glucose to sorbitol.
TL;DR: In this article, the corresponding E,E′-α,α′-bis(substituted benzylidene) cycloalkanones were prepared in high yields by the cross-aldol reactions of cyclopentanone or cyclohexanone with aromatic aldehydes catalyzed by the lanthanide amides.
TL;DR: Experimental evidence indicates that both spectral and intensity effects emerge as a consequence of the change in the frequency of photon absorption per particle and a mechanism is proposed which accounts for the origin of the selectivity changes.
Abstract: Product selectivity and yields of cyclohexanol and cyclohexanone formation in the photocatalytic air oxidation of cyclohexane on TiO2 particles were determined as a function of the irradiation wavelength (254 ≤ λ/nm ≤ 366) and the photon flux (0.3 ≤ I0/neinstein cm-2 s-1 ≤ 5.0). Photonic efficiencies for total monooxygenated products (cyclohexanol + cyclohexanone) ranged from 10 to 25% depending on photon energy and fluency. The cyclohexanol-to-cyclohexanone ratio linearly increases with the incident photon flux at each wavelength and varies more than a magnitude orderfrom 3 to 32%at the same incident photon fluency5 neinstein cm-2 s-1by changing the irradiation wavelength from 366 to 303 nm. Experimental evidence indicates that both spectral and intensity effects emerge as a consequence of the change in the frequency of photon absorption per particle. A mechanism is proposed which accounts for the origin of the selectivity changes.
TL;DR: In this paper, the synthesis of dimethyl acetals of carbonyl compounds such as cyclohexanone, acetophenone, and benzophenone has successfully been carried out by the reaction between ketones and methanol using different solid acid catalysts.
TL;DR: Cr-Si binary oxide prepared by a sol-gel method, when activated by visible light, catalyses highly selective oxidation of cyclo hexane to cyclohexanone with molecular oxygen.
TL;DR: The bis(maltolato)oxovanadium complexes [VO(ma) 2 ], cis-VO(OCH 3 )(m) 2 ] and VO(py)(m 2 ] have been shown to serve as effective heterogeneous catalysts for cyclohexane oxidation by molecular oxygen without any additive as discussed by the authors.
Abstract: The bis(maltolato)oxovanadium complexes [VO(ma) 2 ], cis -[VO(OCH 3 )(ma) 2 ] and [VO(py)(ma) 2 ] have been covalently bonded to carbamated modified silica gel and these systems are shown to serve as effective heterogeneous catalysts for cyclohexane oxidation by molecular oxygen without any additive. The [VO(ma) 2 ] catalyst gives the best results which are further promoted in the presence of 2-pyrazinecarboxylic acid which acts as a co-catalyst, while picolinic acid proved to be almost inactive. The reaction occurs under mild conditions (175 °C, 10 atm O 2 ) forming two major products, cyclohexanol and cyclohexanone in a smaller amount, with a good selectivity. The TGA analysis of the catalyst shows that it is stable up to 273 °C and inductive couple plasma (ICP) indicates a limited metal loss after 20 h use of the catalyst up to 175 °C. The morphology of the catalyst was analyzed by SEM. Evidence is presented in favour of the involvement of a free-radical mechanism.
TL;DR: In this paper, a titanium dioxide suspension containing hydrogen peroxide was used to oxidize cyclohexane and nonyl aldehyde to nonylic acid, and the reaction rate for the oxidation on rutile particles was faster than that on anatase particles.
Abstract: Cyclohexane was oxidized under visible light in a titanium dioxide suspension containing hydrogen peroxide. Cyclohexanol and cyclohexanone were detected as products. Under similar experimental conditions, nonyl aldehyde was oxidized to nonylic acid. The reaction rate for the oxidation on rutile particles was faster than that on anatase particles. When hydrogen peroxide was added to suspensions of these particles, both rutile and anatase particles became yellow-colored due to the formation of peroxide complexes on their surfaces. The difference between the reaction rates for rutile and anatase particles suggests that the properties of the peroxide complexes formed on these particles are different. The properties of these complexes were studied by UV–vis spectroscopy.
TL;DR: Several bis-quaternary phosphonium salts of peroxotungstate and peroxomolybdate have been synthesized and characterized by elemental analysis, IR and Raman spectroscopy as mentioned in this paper.
Abstract: Several novel kinds of bis-quaternary phosphonium salts of peroxotungstate and peroxomolybdate, such as Ph3P(CH2)2PPh3[W(O2)4]·2H2O, Ph3P(CH2)2PPh3[WO(O2)2(C2O4)]·2H2O, Ph3P(CH2)3PPh3[W(O2)4]·2H2O, and Ph3P(CH2)2PPh3[MoO(O2)2(C2O4)]·2H2O, have been synthesized and characterized by elemental analysis, IR and Raman spectroscopy Their catalytic properties in oxidation of cyclohexanol and benzyl alcohol to cyclohexanone, benzaldehyde or benzoic acid were investigated with aqueous 30% hydrogen peroxide under halide- and organic solvent-free conditions The results show that the bis-quaternary phosphonium peroxotungstates have excellent catalytic ability to the oxidation reaction of benzyl alcohol and cyclohexanol by hydrogen peroxide The Mo(IV) analog peroxo complexes were less active than peroxotungstates The maximum yields of benzaldehyde, benzoic acid and cyclohexanone can be reached 9389%, 8887%, and 9270%, respectively
TL;DR: In this article, a combined silica sol-gel entrapped catalyst composed of metallic palladium and chloro(1,5-cyclooctadiene) rhodium dimer was used for polychlorinated phenols.
Abstract: Mono and polychlorinated phenols that undergo only partial detoxification by conventional hydrogenation methods undergo exhaustive hydrogenation in the presence of a combined silica sol–gel entrapped catalyst composed of metallic palladium and chloro(1,5-cyclooctadiene)rhodium dimer. While the mono-, di-, tri- and tetrachlorophenols are converted into cyclohexane in a variety of solvents at 120 °C under 27.6 bar H 2 , the pentachlorophenol requires the presence of toluene. Experiments conducted under milder conditions revealed that the hydrodechlorination of the chlorophenols proceeds via gradual evolvement of the chlorine atoms forming HCl and phenol. The C C bonds of the latter compound are saturated stepwise. The 1-cyclohexenol accumulates as cyclohexanone and is further hydrogenated to cyclohexanol. HCl-catalyzed dehydration yields cyclohexene which is readily transformed to cyclohexane. The initial hydrodechlorination of 2-chlorophenol follows a first order rate law with rate constant k = 5.0 × 10 −4 s −1 at 100 °C. The ceramic combined catalyst is leach-proof and recyclable and can be used in at lest six runs without loss in catalyst activity.
TL;DR: The Pt(II)-catalyzed Baeyer-Villiger oxidation of cyclohexanone with H2O2 in a two-phase system is a viable procedure, characterized by synthetically interesting yields as mentioned in this paper.