Kinetics, substrate selectivity, and mechanisms of alkane and alkylbenzene reactions with peroxynitrous acid in the gas phase and solution

Specific features of the kinetics of alkane and alkylbenzene oxidation with HOONO formed in the H₂O₂-NaNO₂ system (pH 4.27) are quantitatively explained assuming the simultaneous occurrence of reactions in the gas and liquid phases. A model of the kinetic distribution method is developed and verified that accounts for the equilibrium distribution of a substrate and a reagent between phases and their interaction in both phases. Relative rate constants for the oxidation ofn-alkanes (C₃-C₈), isobutane, cyclopentane, cyclohexane, benzene, and alkylbenzenes are measured over a wide range of the volume ratios of the gas and liquid phases (λ = V_g/V₁). Relative rate constants for the oxidation of alkanes in the gas phase and alkylbenzenes in gas and solution were determined. Similarity in substrate selectivities and kinetic isotope effects of the gasphase reactions of alkanes and arenes with peroxynitrous acid and^•OH radicals suggest that hydroxyl radical or the ˙OH...NO₂ radical pair is an active species in the gas phase. In solution, alkylbenzenes react nonselectively with HOONO, as well as with ˙OH radicals. In contrast to the liquid-phase oxidation of arenes, the liquidphase oxidation of all alkanes under study insignificantly contribute (5–15%) to the overall rate of the substrate consumption.     

Kinetics,Substrate Selectivity and Mechanism of the Oxidation of Alkenes by Peroxynitrous Acid

The kinetic features of the oxidation of alkenes by peroxynitrous acid (HOONO) generated in the H₂O₂–HNO₂/acetate buffer (pH 4.27) system, are quantitatively explained assuming simultaneous reactions in the gas and liquid phases. A remarkable similarity is found for the substrate selectivities of the gas-phase reactions of alkenes as well as of alkanes and arenes with HOONO and with ^·OH radicals. The reaction mechanism is discussed.     

Interaction between hydrogen peroxide and cobalt(II) acetylacetonate in the system of reverse micelles of triton X-100 nonionic surfactant in cyclohexane

The yield of free radicals upon the decomposition of hydrogen peroxide catalyzed by cobalt acetylacetonate (Co(acac)₂) in the systems of reverse micelles of TX-100/n-hexanol and AOT in cyclohexane at 37°C was studied with the inhibitor method using a stable nitroxyl radical as a spin trap. It is shown that, in micellar AOT solutions in cyclohexane as well as in n-decane, H₂O₂ and Co(acac)₂ in practice do not react, because H₂O₂ is localized in a micelle water pool and Co(acac)₂, in the organic phase. Therefore, the generation of radicals is not observed in AOT solutions in cyclohexane, whereas, in aqueous solution, Co(acac)₂ catalyzes the radical decomposition of H₂O₂. In the system of mixed reverse micelles of TX-100 and n-hexanol in cyclohexane, at equal overall concentrations of H₂O₂ and Co(acac)₂, the rate of radical formation is much higher than in aqueous solution; i.e., the micellar catalysis of the radical decomposition of H₂O₂ takes place. It follows from measurements of UV and ESR spectra and the kinetics of changes in the content of peroxides in the reaction mixture that TX-100 and n-hexanol react with free radicals formed upon H₂O₂ decomposition and with atmospheric oxygen.     

HNO自由基与O2反应机理的理论研究

采用密度泛函理论(DFT)和从头算方法,在B3LYP/6-311++G(d,p)水平上对反应HNO+O_2做了理论计算研究。优化得到了反应物、中间体、过渡态和产物的几何构型以及相应的能量值、振动频率。通过分析反应路径的能量差异,以及异构化难易程度,发现HNO+O_2反应有2种产物通道:HOONO和HNO_3。其中过氧亚硝酸HOONO是主要产物,有3种稳定的构象。     

Oxidation of Cycloalkanes by Hydrogen Peroxide in a Biomimetic Iron Porphyrin System

The kinetics of cyclohexane and cyclopentane oxidation by hydrogen peroxide catalyzed by iron porphyrins (FeTPP and FeTDCPP) in acetonitrile solutions is studied at room temperature by analyzing product accumulation with the GLC method. The effects of various additives (acetic acid, imidazole, and hydroquinone) on the substrate selectivity of the competitive oxidation of C₆H₁₂ and C₅H₁₀ are studied. In the FeTDCPP/H₂O₂/O₂/AcOH/CH₃CN system, cyclohexane is oxidized to the corresponding alcohol, ketone, and hydroperoxide. The fraction of the product (hydroperoxide) formed by the radical mechanism is 20–30%. The alcohol and ketone are formed by the molecular pathway in a ratio of (6–7) : 1. Kinetic parameters of cycloalkane oxidation are compared in a biomimetic system with hydrogen peroxide (the shunt system) and the system based on dioxygen with electron and proton donors. The latter system modeled cytochrome P-450. It is shown that active species are the same in both systems. The kinetic scheme of the alkane oxidation process is proposed for the shunt system.     

Cyclohexane dehydrogenation over Pt-Dy/Al2O3 catalysts

The conversion of cyclohexane dehydrogenation over Pt–Dy/Al₂O₃ has been studied with a pulsed microcatalytic reactor. Two interesting experiments utilizing CS₂ and thiophene poisoning Pt/Al₂O₃ and Pt–Dy/Al₂O₃ for cyclohexane dehydrogenation are shown and the reaction mechanism is described. The kinetic parameters of cyclohexane dehydrogenation have been calculated. Correlation of the catalytic behavior with the properties of active sites is also discussed.     

Untersuchungen zur temperaturprogrammierten Reduktion und zur katalytischen Wirksamkeit von Ni/Al2O3

Investigations of Temperature-programmed Reduction and of Catalytic Activity of Ni/Al₂O₃ Different Ni/γ-Al₂O₃ catalysts were prepared by varying the Ni content and the temperature of the thermal pretreatment. These samples were investigated by the TPR technique and by the catalytic conversion of cyclohexane. Two species of oxidized Ni were formed during the calcination, easily reducible “bulk” NiO and heavily reducible “fixed” NiO. The proportion of fixed NiO increases with increasing calcination temperature and with decreasing Ni content. The selectivity of the cyclohexane conversion is shifted from hydrogenolytic methane formation towards dehydrogenating benzene formation by catalysts containing increasing amounts of fixed NiO. This shift is explained by an ensemble effect.     

A kinetic and product study of the gas-phase reaction of ozone with vinylcyclohexane and methylene cyclohexane

The gas-phase reaction of ozone with vinylcyclohexane and methylene cyclohexane has been investigated at ambient T and p=1 atm of air in the presence of sufficient cyclo-hexane or 2-propanol added to scavenge OH. The reaction rate constants, in units of 10⁻¹⁸ cm³ molecule⁻¹ s⁻¹, are 7.52±0.97 for vinylcyclohexane (T=292±2 K) and 10.6±1.9 for methylene cyclohexane (T=293±2 K). Carbonyl reaction products were cyclohexyl meth-anal (0.62±0.03) and formaldehyde (0.47±0.04) from vinylcyclohexane and cyclohexanone (0.55±0.10) and formaldehyde (0.60±0.05) from methylene cyclohexane, where the yields given in parentheses are expressed as carbonyl formed, ppb/reacted ozone, ppb. The sum of the yields of the primary carbonyls is close to the value of 1.0 that is consistent with the simple mechanisms: O₃+cyclo(C₆H₁₁)−CH(DOUBLEBOND)CH₂→α(HCHO+cyclo(C₆H₁₁)CHOO)+(1−α)(HCHOO+cyclo(C₆H₁₁)CHO) for vinylcyclohexane and O₃+(CH₂)₅C(DOUBLEBOND)CH₂→α(HCHO +(CH₂)₅COO)+(1−α)(HCHOO+(CH₂)₅C(DOUBLEBOND)O) for methylene cyclohexane. The coefficients α are 0.43±0.10 for vinylcyclohexane and 0.52±0.05 for methylene cyclohexane, i.e., (formaldehyde+the substituted biradical) and (HCHOO+cyclohexyl methanal or cyclo-hexanone) are formed in ca. equal yields. Reaction rate constants, carbonyl yields, and reaction mechanisms are compared to those for alkene structural homologues. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 855–860, 1997     

Kinetics and mechanism for the oxidation of alkanes by peroxynitrous acid in the gas phase: the slow step involving reaction with oh radicals

The relative rate constants (kRH/kEtH), the temperature dependence of these constants at from 5 to 55 °C, and the activation parameters were found for reactions of propane, butane, pentane, hexane, isobutane, cyclopentane, and cyclohexane with peroxynitrous acid (HOONO) in water. The similarity of these results to the data for the reaction of alkanes with OH radicals confirms that the active species in the reactions of HOONO with hydrocarbons in water are OH radicals formed in the homolysis of the HO—ONO bond.     

Photoactivation mechanism of orthovanadate-like (V=O)O3 species

The photoluminescence spectrum and action spectrum for the photooxidation of orthovanadate-like (V=O)O₃ species exhibiting photoluminescence at 520 nm indicate that the triplet excited state T₁ of the orthovanadate-like species, which is formed from the singlet excited states S₁ and S₂ by intersystem crossing, is directly involved in the photooxidation of cyclohexane into cyclohexanone in the presence of molecular oxygen.     

Molybdovanadophosphoric Acid Catalyzed Oxidation of Hydrocarbons by H2O2 to Oxygenates

Heteropoly acids of the general formula H_3+x[PMo_12-xV_xO₄₀] (where x = 1,2,3) catalyzed the oxidation of aromatic hydrocarbons at 65°C with H₂O₂ to give oxygenated products. Among the catalysts, H₄[PMo₁₁VO₄₀] was found to be a more active catalyst and its activities have been reported in the oxidation of cyclohexane, methyl cyclohexane, naphthalene, 1-methyl naphthalene and biphenyl.     

Isomerization of <Emphasis Type="Italic">n</Emphasis>-Heptane on Platinum-Zeolite Catalysts in the Presence of Cyclohexane and Benzene

Effect of cyclohexane and benzene on the isomerization of n-heptane on Pt/BEA-Al₂O₃ and Pt/MORAl₂O₃ catalysts was studied. In the presence of catalysts with platinum deposited from a [Pt(NH₃)₄]Cl₂ solution, cyclohexane and benzene inhibit the conversion of n-heptane. At the same time, the presence of cycloalkanes and aromatic hydrocarbons leads to an increase in the isomerization selectivity due to the suppression of side reactions of hydrocracking. Samples based on the BEA zeolite were found to be more active as compared with similar samples based on mordenite.     

X‐ray investigations of bicyclic α‐methylene‐δ‐valerolactones. V. (4aS,7R,8aR)‐7‐Isopropenyl‐4a‐methyl‐3‐methyleneperhydrochromen‐2‐one

The title compound, C₁₄H₂₀O₂, adopts a conformation in which the δ‐valerolactone and cyclohexane rings are almost coplanar with one another. The γ‐methyl substituent occupies an axial position with respect to the cyclohexane ring. The δ‐valerolactone moiety adopts an envelope arrangement, while the cyclohexane ring exists in a chair conformation.     

Oxidations by a H2O2-VO3 −-pyrazine-2-carboxylic acid reagent

Alkanes (cyclohexane, hexane, heptane isomers) are effectively oxidized in CH₃CN at 20–70°C by hydrogen peroxide when catalyzed by a Bu₄NVO₃-pyrazine-2-carboxylic acid system. Alkyl hydroperoxide is the main product; an alcohol and a ketone or an aldehyde are also formed. Under these conditions benzene is oxidized to give phenol, while alkyl benzenes yield oxygenation products both of the ring and the side chain. It has been assumed that the interaction of H₂O₂ with VO₃ ^– gives rise to generation of HO radicals and other radical-like vanadium containing species that abstract a hydrogen atom from an alkane, RH. The radical R^. formed reacts with O₂ to produce ROO^. which is then transformed to alkyl hydroperoxide.Presented at the VIII International Symposium on Homogeneous Catalysis (Amsterdam, 1992).Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 64–68, January, 1993.     

Composition of peroxide products in reaction of ozone with cyclohexane

Conclusions A modified iodometric method was developed for determining H₂O₂, hydroperoxides, and peroxides in reaction mixtures. Employing this method, the nature of the peroxide compounds formed in the reaction of ozone and cyclohexane was established, and also the rate of their accumulation. The principal peroxide product in the reaction is cyclohexyl peroxide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2104–2106, September, 1976.     

Formation of O(3P) atoms and epoxides from the gas- phase reaction of O3 with isoprene

The formation yields of 1,2-epoxy-2-methyl-3-butene and 1,2-epoxy-3-methyl-3-butene have been measured from the reaction of O₃ with isoprene at room temperature and one atmosphere total pressure of N₂ and air diluents, with and without cyclohexane to scavenge the OH radicals formed in this reaction system. In addition, a relative rate method was used to determine a rate constant for the gas-phase reaction of O₃ with 1,2-epoxy-2-methyl-3-butene of (2.5 ± 0.7) x 10^-18 cm³ molecules^-1 s^-1 at 296 ± 2 K. Our data show that the epoxide yields in N₂ and air diluents are the same, with formation yields of 1,2-epoxy-2-methyl-3-butene of 0.028 ± 0.007 and of 1,2-epoxy-3-methyl-3-butene of 0.011 ± 0.004. These data further show that the epoxides arise from the primary O₃ reaction with isoprene, and not via the formation of O(³P) atoms from the O₃ - isoprene reaction followed by reaction of these O(³P) atoms with isoprene.     

Distinctive features of supported catalysts prepared from platinum carbonyl clusters

The formation of Pt/γ-Al₂O₃ and Pt/C catalysts from platinum carbonyl clusters H₂[Pt₃(CO)₆]_n (n = 2, 5) is studied. The strength of interaction between clusters (strong Lewis bases) and the support and the state of platinum in catalysts are governed by the acceptor strength of the support. The formation of a stable platinum compound with a surface of γ-Al₂O₃ (strong Lewis acid) is shown for a Pt/γ-Al₂O₃ catalyst by the method of radial distribution functions. In a Pt/C catalyst containing the same amount of Pt supported on a carbon material known to be a weaker acceptor, metallic platinum is formed along with surface-bonded platinum. Proceeding from the existence of the active phase of catalysts in the form of a surface platinum complex and platinum crystallites, the properties of catalysts are discussed in the complete oxidation of methane and the dehydrogenation of cyclohexane, as well as the high dispersity of platinum and its thermal stability     

Activated carbon supported Co1.5PW12O40 as efficient catalyst for the production of 1, 2 cyclohexane diol by oxidation of cyclohexene with H2O2 in the presence of CO2

ABSTRACT

Vicinal diols are important building blocks for chemicals and pharmaceuticals. Currently, they are produced from olefins using solvents and harmful oxidants unfavorable from an environmental and economic point of view. This work lies on the synthesis of 1,2 cyclohexane diol from cyclohexene by a green route. To achieve it, a series of Cobalt Keggin heteropolyanion salt (Co_1.5PW₁₂O₄₀) loaded on activated carbon with different contents was prepared, characterized and tested for the synthesis of diol. The effect of various parameters such as reaction temperature, reaction time and CO₂ pressure on the reaction was studied. The effect of reaction temperature in the range 60-80 °C showed that high temperatures favor diol formation while low temperatures favor cyclohexanone and a segmented concave Arrhenius graph was observed. The results of this work showed that oxidation by H₂O₂ in the presence of CO₂ is an efficient oxidant system for the production of 1.2 cyclohexane diol over carbon activated carbon supported Co_1.5PW₁₂O₄₀. Thanks to CO₂ as a soft oxidizing agent, a conversion of 96.9% and a selectivity in 1, 2 cyclohexane diol of 64.2% was obtained. This simple, safe and environmentally method could be an alternative green route for vicinal diols production from alkenes.     

Oxidations catalyzed by osmium compounds. Part 1: Efficient alkane oxidation with peroxides catalyzed by an olefin carbonyl osmium(0) complex

A carbonyl osmium(0) complex with π-coordinated olefin, (2,3-η-1,4-diphenylbut-2-en-1,4-dione)undecacarbonyl triangulotriosmium (1), efficiently catalyzes oxygenation of alkanes (cyclohexane, cyclooctane, n-heptane, isooctane, etc.) with hydrogen peroxide, as well as with tert-butyl hydroperoxide and meta-chloroperoxybenzoic acid in acetonitrile solution. Alkanes are oxidized to corresponding alcohols, ketones (aldehydes) and alkyl hydroperoxides. Thus, heating cyclooctane with the 1-H₂O₂ combination at 70 °C gave products with turnover number as high as 2400 after 6 h. The maximum obtained yield of all products was equal to 20% based on cyclohexane and 30% based on H₂O₂. The oxidation of linear and branched alkanes exhibits very low regio- and bond-selectivity parameters and this testifies that the reaction proceeds via attack of hydroxyl radicals on C-H bonds of the alkane. The oxygenation products were not formed when the reaction was carried out under argon atmosphere and it can be thus concluded that the oxygenation occurs via the reaction between alkyl radicals and atmospheric oxygen. In summary, the Os(0) complex is much more powerful generator of hydroxyl radicals than any soluble derivative of iron (which is an analogue of osmium in the Periodic System).     

Paths and Mechanism for the Oxidation of Alkanes,Alkenes, and Arenes by Peroxynitrous Acid

The bell-shaped relations between the rate constants for the oxidation of hydrocarbons by peroxynitrous acid (HOONO) and the ratio of the volumes of the aqueous and gas phases in the reactor are explained quantitatively on the assumption that the HOONO and the substrate are distributed between the gas and the solution and that OH radicals are formed in the two phases and interact with the hydrocarbon. The distribution coefficient of the HOONO between the gas and aqueous phases is determined [ = (0.4-2)·10^–6].