Oxidation Of Methylcyclohexane Research Articles

Insights into the high-temperature oxidation of methylcyclohexane

Reactive molecular dynamics simulations were performed under different conditions in order to investigate in-detail the chemical events associated with high-temperature oxidation of methylcyclohexane (MCH). The corresponding kinetic behaviors of the major intermediates and products were systematically analyzed at the atomistic level. Thus the overall reaction scheme of MCH oxidation was established from the initial step to the final products. It was observed that the oxidation of MCH was mainly initiated by two kinds of reactions, including unimolecular decomposition and H abstraction, with the former being more important. In agreement with the available experimental results, C2H4, CH2O, CO, CO2 and H2O were found to be the major products during the oxidation process. The results revealed that CH3O2, CH3O and C3H5O radicals were the precursors for CH2O production, which was the key intermediate to generate CO. Additionally, C2H3O also had closed relationship with the formation of CO. For a better description of the combustion behavior, small oxides related to intermolecular reactions should be considered in the oxidation of MCH mechanisms. The temperature and density had a positive effect on the oxidation of MCH; it was also found that an increase of the equivalence ratio had a negligible effect on the MCH oxidation.

Mixed-Metal Metal–Organic Frameworks as Catalysts for Liquid-Phase Oxidation of Toluene and Cycloalkanes

A series of isostructural mixed-metal metal–organic frameworks (MM-MOFs) of 1,3,5-benzenetricarboxylate (BTC), M–Zn–BTC, where M = Cu(II), Co(II) and Fe(II) have been synthesized using the post-synthetic exchange method. The catalytic activities of the M–Zn–BTC have been investigated for the oxidation of toluene and cycloalkanes in the presence of hydrogen peroxide as oxidant. The M–Zn–BTC catalysts show improved activity and selectivity for toluene oxidation. The introduction of the second metal to the node of the MOFs improved the toluene conversion from 22 to 70% and the selectivity of benzaldehyde improved from 22 to 57%. The Fe–Zn–BTC showed the best activity in terms of benzaldehyde selectivity for the oxidation of toluene. However, Cu–BTC gave the highest conversion for cyclohexane and methylcyclohexane oxidation.

Mild oxidative C−H functionalization of alkanes and alcohols using a magnetic core-shell Fe3O4@mSiO2@Cu4 nanocatalyst

A new hybrid Fe3O4@mSiO2@Cu4 material was constructed by loading a bio-inspired tetracopper(II) coordination compound [Cu4(μ4-O){N(CH2CH2O)3}4(BOH)4][BF4]2 (Cu4) onto the Fe3O4@mSiO2 core-shell nanoparticles (NPs) composed of a magnetite (Fe3O4) core and mesoporous silica (mSiO2) shell with perpendicularly aligned channels. The obtained Fe3O4@mSiO2@Cu4 magnetic nanoparticles were characterized by transmission electron microscopy (TEM), FT-IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and field-dependent magnetization. This hybrid material acts as a magnetically recoverable C−H functionalization nanocatalyst, namely for the mild oxidation, by t-butyl hydroperoxide at 50–70°C in acetonitrile medium, of cycloalkanes (cyclopentane, cyclohexane, cycloheptane, and cyclooctane) to the corresponding alcohols and ketones (with up to ∼15% yields based on cycloalkane; TON 335). A related oxidation process using cyclohexanol as a more reactive substrate leads to the formation of cyclohexanone in up to ∼25% yield (TON 570). The Fe3O4@mSiO2@Cu4 nanocatalyst can be recycled five times without an appreciable loss of activity. The bond-, regio-, and stereoselectivity parameters were investigated in the oxidation of different alkane substrates (n-hexane, n-heptane, n-octane, methylcyclohexane, adamantane, cis- and trans-1,2-demethylcyclohexane), and the obtained results were compared with the homogeneous systems based on the Cu4 catalyst. In particular, the high bond selectivity parameters detected in the oxidation of methylcyclohexane (1°:2°:3° of 1:8:142) and adamantane (2°:3° of 1:21) catalyzed by Fe3O4@mSiO2@Cu4 suggest that the reactions possibly occur in hydrophobic pockets of the nanocatalyst.

P-Tolylimido rhenium(v) complexes with phenolate-based ligands: synthesis, X-ray studies and catalytic activity in oxidation with tert-butylhydroperoxide.

The reactions of mer-[Re(p-NTol)X3(PPh3)2] (X = Cl, Br) with chelating phenolate-based ligands (2-(2-hydroxy-5-methylphenyl)benzotriazole (HL(1)), 2-(2-hydroxyphenyl)benzothiazole (HL(2)) or 2-(2-hydroxyphenyl)benzoxazole (HL(3))) afforded a series of p-tolylimido rhenium(v) complexes cis- or trans-(X,X)-[Re(p-NTol)X2(L)(PPh3)]·yMeCN (where X = Cl, Br; L = L(1), L(2), L(3) and y = 0-2) and [Re(p-NTol)X(L)(PPh3)2]Z·pPPh3 (where X = Cl, Br; Z = ReO4, PF6; L = L(1), L(2), L(3) and p = 0 or 1). The reported compounds were characterized by elemental analysis, FT-IR, NMR ((1)H, (13)C and (31)P) and X-ray crystallography. Interestingly, the halide ions of [Re(p-NTol)Cl2(L(1))(PPh3)]·MeCN (1) and [Re(p-NTol)Cl2(L(2))(PPh3)]·2MeCN (3) are in cis relative dispositions, whereas the complexes [Re(p-NTol)Br2(L)(PPh3)] (L(1) for 2, L(2) for 4 and L(3) for 6) and [Re(p-NTol)Cl2(L(3))(PPh3)] (5) were found to be trans-(X,X) isomers. The compounds [Re(p-NTol)X(L)(PPh3)2](PF6) (X = Cl, Br; L = L(1) and L(2)) and [Re(p-NTol)X(L(3))(PPh3)2](PF6)·PPh3 (X = Cl, Br) have been tested in oxidative catalysis. A few compounds exhibited very good catalytic properties in oxidation of alcohols with tert-BuOOH (TBHP) in acetonitrile solution at moderate temperatures. Complex [Re(p-NTol)Cl(L(2))(PPh3)2]PF6 (13) is the catalyst of choice for oxidation of 1-phenylethanol to acetophenone (in 80% yield; turnover number attained 290 after 30 h) and cyclooctanol to cyclooctanone (in 88% yield). Notably lower activity has been found in the oxidation of alkanes with TBHP. Product distribution in the oxidation of methylcyclohexane indicates some steric hindrance around the reaction center.

Comparative Study on Autoignition Characteristics of Methylcyclohexane and Cyclohexane

Ignition delay times were measured behind reflected shock waves for cyclohexane and methylcyclohexane at pressures of 1.1, 5.0, and 16.0 atm, temperatures from 1075 to 1750 K, and equivalence ratios of 0.5, 1.0, and 2.0. Correlations of the ignition delay times were performed at the three equivalence ratios in Arrhenius form. Measured ignition delay times showed fairly good agreements with previous data. Several accepted mechanisms (JetSurF 2.0, Wang et al., Sirjean et al., Orme et al., and Silke et al.) were used to simulate the experimental measurements and conduct flux analyses and sensitivity analyses. Comparisons of the simulations and analyses between the mechanisms give insights into the oxidation of methylcyclohexane and cyclohexane. Methylcyclohexane has an evidently longer ignition delay time than cyclohexane at ϕ = 0.5, while its ignition delay time becomes comparative to those of cyclohexane at ϕ = 1.0. Chemical kinetic interpretation is given for this observation.

Understanding promotion of photocatalytic activity of TiO2 by Au nanoparticles

Au nanoparticles prepared by deposition–precipitation were evaluated in promoting photocatalytic activity of TiO2 (P25) in the oxidation of methylcyclohexane. At 375nm and in particular at 425nm, Au was found to significantly enhance the rate induced by P25. Illumination of Au-promoted P25 at 525nm did not result in any measureable activity. To validate whether the enhancement at 425nm is purely catalytic, or if plasmonic effects are relevant, we compared the rates of Au/TiO2 with Pt-promoted TiO2 at 375 and 425nm. At 375nm, Pt nanoparticles induced larger catalytic effects than Au nanoparticles, whereas the rate enhancement induced by Pt was much lower than of Au at 425nm. We assign the thus demonstrated Au based plasmonic phenomena at 425nm to the so-called plasmon resonance energy transfer, rather than to hot electron transfer, given the absence of activity at 525nm.

Characterization of nickel(ii)-acylperoxo species relevant to catalytic alkanehydroxylation by nickel complex with mCPBA

Nickel complexes with hydrotris(pyrazolyl)borate ( = Tp(R)) ligands catalyze alkane oxidation with organic peroxide meta-Cl-C(6)H(4)C([double bond, length as m-dash]O)OOH ( = mCPBA). The electronic and steric hindrance properties of Tp(R) affect the catalyses. The complex with an electron-withdrawing group containing a less-hindered ligand, that is, Tp(Me2,Br), exhibits higher alcohol selectivity. Higher selectivity for secondary over tertiary alcohols upon oxidation of methylcyclohexane indicates that the oxygen atom transfer reaction proceeds within the coordination sphere of the nickel centers. A reaction of the catalyst precursor, dinuclear nickel(ii)-bis(μ-hydroxo) complexes, with mCPBA yields the corresponding nickel(ii)-acylperoxo species, as have been characterized by spectroscopy. Thermal decomposition of the nickel(ii)-acylperoxo species in CH(2)Cl(2) yields the corresponding nickel(ii)-chlorido complexes through Cl atom abstraction. Employment of the brominated ligand increases the thermal stability of the acylperoxo species. Kinetic isotope effects observed on decay of the nickel(ii)-acylperoxo species indicate concerted O-O breaking of the nickel-bound acylperoxide and H-abstraction from the solvent molecule.

Experimental study of cyclohexane and methylcyclohexane oxidation at low to intermediate temperature in a motored engine

This work concerns the oxidation of cyclohexane and methylcyclohexane in a motored engine at low to intermediate temperatures, which is largely unknown in the literature. The experiment is conducted with variable compression ratio from 4 to 15 at equivalence ratio 0.25 and intake temperatures of 120°C and 200°C. Results show that overall reaction activity, indicated by fuel conversion and carbon monoxide formation, is largely enhanced by the existence of the methyl group. Cyclohexane shows a stronger negative temperature coefficient (NTC) behavior than methylcyclohexane. Detailed product analyses reveal that conjugated olefins are the major product for cyclohexane and methylcyclohexane in both low temperature oxidation and NTC regime. Four C6 oxygenates, 5-hexen-1-al, 1,2-epoxycyclohexane, 1,4-epoxycyclohexane, and cyclohexanone are detected in cyclohexane oxidation. The relative yields indicate that intramolecular hydrogen abstraction of cyclohexylperoxy radical is more likely to occur on γ-carbons than on α-, β-, or δ-carbons. Four conjugated olefins, 1-, 3-, 4-methylcyclohexenes and methylenecyclohexane, are detected in methylcyclohexane oxidation, with relative yield about 1, 1.2, 1.4 and 0.25, respectively.

Experimental and Modeling Study of Methyl Cyclohexane Pyrolysis and Oxidation

Although the combustion chemistry of aliphatic hydrocarbons has been extensively documented, the oxidation of cyclic hydrocarbons has been studied to a much lesser extent. To provide a deeper understanding of the combustion chemistry of naphthenes, the oxidation of methylcyclohexane was studied in a series of high-temperature shock tube experiments. Ignition delay times for a series of mixtures, of varying methylcyclohexane/oxygen equivalence ratios (phi=0.5, 1.0, 2.0), were measured over reflected shock temperatures of 1200-2100 K and reflected shock pressures of 1.0, 2.0, and 4.0 atm. A detailed chemical kinetic mechanism has been assembled to simulate the shock tube results and flow reactor experiments, with good agreement observed.

A wide range kinetic modeling study of the pyrolysis and combustion of naphthenes

The aim of this paper is to analyze and discuss the kinetics of the pyrolysis and combustion of naphthenes. The primary propagation reactions of cyclohexane and methylcyclohexane are presented to extend the validity of a semi-detailed kinetic model for the pyrolysis and oxidation of hydrocarbons. Naphthenes are relevant species as reference components in liquid fuels and surrogate blends. A lumped approach is used to reduce the complexity of the overall scheme in terms of species and reactions. Particular attention is devoted to the role of the isomerization or internal abstraction of H atoms in competition with β−decomposition ones. Primary oxidation and decomposition reactions of the cyclohexyl radical are discussed to explain and justify this lumping procedure. The modeling predictions are compared with different sets of measurements. The validation of the low temperature oxidation mechanism of cyclohexane is based on the ignition delay times obtained both in the rapid compression machine at Lille and in closed vessels. Jet-stirred reactors at different pressures and stoichiometric ratios also confirm the reliability of the overall mechanism of oxidation. The comparisons between the model’s predictions and the measurements relating to the pyrolysis and oxidation of methylcyclohexane in the Princeton turbulent flow reactor further support this extension of the kinetic scheme to naphthenes. Finally, the agreement with the oxidation experiments using mixtures of toluene + methylcyclohexane is a primary and simple example of the model’s ability to deal with the combustion of real fuels or surrogate blends.

Mechanism of Methylcyclohexane Ozonolysis

A mathematical model of selective oxidation of methylcyclohexane with ozone-oxygen mixtures was substantiated.

Pyrolysis studies of methylcyclohexane and oxidation studies of methylcyclohexane and methylcyclohexane/toluene blends

High-temperature (1050–1200 K) pyrolysis studies of pure methylcyclohexane (MCH) and oxidation studies of pure MCH and MCH/toluene blends were performed in the Princeton Turbulent Flow Reactor. Since MCH is a proposed endothermic jet fuel, as well as a possibly significant constituent of current commercial automotive and aviation fuel blends, high-temperature studies of MCH provide an understanding of its decay characteristics in both aircraft and automobile engine environments. Ethene, 1,3-butadiene, methane, and propene were found to be the major intermediates produced by MCH pyrolysis. Oxidation of MCH also produced the same intermediates. As expected, the observed oxidation reaction rates were faster than the pyrolysis reaction rates. The MCH/toluene-blend oxidation experiments (1160 K and φ = ∼ 1.3) revealed that, while the two fuels appear to oxidize by independent mechanisms, the rates of oxidation of both fuels are strongly related to the initial concentration of MCH.

メチルシクロヘキサンおよびその誘導体の過酢酸酸化

メチルシクロヘキサンおよびその誘導体の過酢酸酸化