Kinetics and mechanism of the photo-oxidation of formaldehyde. 1. Flash photolysis study

Veyret, B.; Lesclaux, R.; Rayez, Marie-Thérèse; Rayez, Jean-Claude; Cox, R. A.; Moortgat, G. K.

doi:10.1021/j100343a033

Cited by 118 publications

(106 citation statements)

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“…To our knowledge, this reaction has never been reported as a critical step in liquid-phase alcohol oxidation, although similar fast reactions for small homologues are well-established in atmospheric chemistry, for example H 2 C(OH)OOC!H 2 C=O + COOH [45] and CH 3 CH(OH)OOC!CH 3 CH=O + COOH. [46] These reactions proceed via a cyclic, hydrogen-bonded complex that can either revert to the reactant or decompose to the end products.…”

Section: The Oxidation Of Alcohol To Ketone Initiated By the Moderatementioning

confidence: 61%

Autoxidation of Cyclohexane: Conventional Views Challenged by Theory and Experiment

et al. 2005

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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.

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Section: The Oxidation Of Alcohol To Ketone Initiated By the Moderatementioning

confidence: 61%

Autoxidation of Cyclohexane: Conventional Views Challenged by Theory and Experiment

et al. 2005

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“…1) gives a dipole-dipole interaction of about 3 kcal/mol. Because the observed activation energy for the addition is slightly negative [8] 0.60 Ϯ 0.60 kcal/mol we can infer that the concerted addition is the favored path. Its dipole attraction makes it more stable than the alkoxy adduct formed by HO 2…”

Section: ϫ3mentioning

confidence: 94%

Some observations on the kinetics and thermochemistry of the reactions of HO₂ radicals with aldehydes and ketones

Benson

2001

Int J of Chemical Kinetics

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The rapid, gas phase equilibrium addition of HO 2 radicals to CH 2 O to form the peroxy radical HOCH 2 OO• is in agreement with the known thermochemistry of these species. The recent study of the similar addition of HO 2• to ketones shows no significant reaction, which is again in agreement with known thermochemistry. All these reactions are notable for significant dipole attraction between the reactants ranging from 3 to 7 kcal/mol. The thermochemistry shows that the hydroperoxyl alkoxy species, the primary possible adduct, is not favored by the free energy change for direct addition. This and the observed kinetics favor a concerted addition, H-atom transfer, as the transition state for the reactions. Kinetic estimates for forward and reverse reactions are in good agreement with observations. A thermochemical examination of the step-wise addition of HO 2• to the carbonyl shows that the reaction proceeds through a concerted, cyclic transition state involving simultaneous H-transfer, 3 ϩ 2 cycloaddition of HO 2• to the carbonyl group. Encouraged in part by earlier studies of the gas phase reaction and equilibrium between CH 2 O and HO 2 [1] , Gierczak and Ravishankara have made a study of the similar gas phase reaction between a series of ketones and HO 2 [2]. They found that there was no measurable reaction, and from the sensitivity of their analytical system (laser magnetic resonance) and the ketone concentrations, they could put upper limits on the rate constants for reaction of their ketones with HO 2 radicals. These were all in the range of 1 ϫ 10 Ϫ15 cm 3 /molecule-s. The ketones they examined were acetone, butanone-2, pentanone-2, pentanone-3, and hexanone-2. This present note is submitted to point out that these results are consistent with the known and estimated thermochemistry for these reactions.Let us first consider the earlier study of HO 2 with CH 2 O:

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“…[1,2] It is also used to support heterogeneous gold catalysts for catalytic oxidation reactions of HCHO [3,4] and CO. [5][6][7] In these catalytic oxidation reactions with molecular O 2 as the oxidant, O 2 activation is the key step. Therefore, to understand the catalytic origin of these oxidation reactions and to design efficient catalysts, it is essential to know the activation route of molecular O 2 on the catalyst surfaces.…”

Section: Introductionmentioning

confidence: 99%

Correlation of the Catalytic Activity for Oxidation Taking Place on Various TiO₂ Surfaces with Surface OH Groups and Surface Oxygen Vacancies

Zheng

Teo

Chen

et al. 2010

Chemistry A European J

106

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Three catalytic oxidation reactions have been studied: The ultraviolet (UV) light induced photocatalytic decomposition of the synthetic dye sulforhodamine B (SRB) in the presence of TiO(2) nanostructures in water, together with two reactions employing Au/TiO(2) nanostructure catalysts, namely, CO oxidation in air and the decomposition of formaldehyde under visible light irradiation. Four kinds of TiO(2) nanotubes and nanorods with different phases and compositions were prepared for this study, and gold nanoparticle (Au-NP) catalysts were supported on some of these TiO(2) nanostructures (to form Au/TiO(2) catalysts). FTIR emission spectroscopy (IES) measurements provided evidence that the order of the surface OH regeneration ability of the four types of TiO(2) nanostructures studied gave the same trend as the catalytic activities of the TiO(2) nanostructures or their respective Au/TiO(2) catalysts for the three oxidation reactions. Both IES and X-ray photoelectron spectroscopy (XPS) proved that anatase TiO(2) had the strongest OH regeneration ability among the four types of TiO(2) phases or compositions. Based on these results, a model for the surface OH group generation, absorption, and activation of molecular oxygen has been proposed: The oxygen vacancies at the bridging O(2-) sites on TiO(2) surfaces dissociatively absorb water molecules to form OH groups that facilitate adsorption and activation of O(2) molecules in nearby oxygen vacancies by lowering the absorption energy of molecular O(2). A new mechanism for the photocatalytic formaldehyde decomposition with the Au/TiO(2) catalysts is also proposed, based on the photocatalytic activity of the Au-NPs under visible light. The Au-NPs absorb the light owing to the surface plasmon resonance effect and mediate the electron transfers that the reaction needs.

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Kinetics and mechanism of the photo-oxidation of formaldehyde. 1. Flash photolysis study

Abstract: This study was performed as part of the Sonderforschungsbereich 233, "Dynamics and Chemistry of Hydrometeores". It was also supported by the CNRS program "Phase Atmosphérique des Cycles Biogéochimiques".

Cited by 118 publications

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Autoxidation of Cyclohexane: Conventional Views Challenged by Theory and Experiment

Autoxidation of Cyclohexane: Conventional Views Challenged by Theory and Experiment

Some observations on the kinetics and thermochemistry of the reactions of HO₂ radicals with aldehydes and ketones

Correlation of the Catalytic Activity for Oxidation Taking Place on Various TiO₂ Surfaces with Surface OH Groups and Surface Oxygen Vacancies

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Kinetics and mechanism of the photo-oxidation of formaldehyde. 1. Flash photolysis study

Abstract: This study was performed as part of the Sonderforschungsbereich 233, "Dynamics and Chemistry of Hydrometeores". It was also supported by the CNRS program "Phase Atmosphérique des Cycles Biogéochimiques".

Cited by 118 publications

References 0 publications

Autoxidation of Cyclohexane: Conventional Views Challenged by Theory and Experiment

Autoxidation of Cyclohexane: Conventional Views Challenged by Theory and Experiment

Some observations on the kinetics and thermochemistry of the reactions of HO2 radicals with aldehydes and ketones

Correlation of the Catalytic Activity for Oxidation Taking Place on Various TiO2 Surfaces with Surface OH Groups and Surface Oxygen Vacancies

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Some observations on the kinetics and thermochemistry of the reactions of HO₂ radicals with aldehydes and ketones

Correlation of the Catalytic Activity for Oxidation Taking Place on Various TiO₂ Surfaces with Surface OH Groups and Surface Oxygen Vacancies