A direct study of the reaction of benzyl radicals with molecular oxygen: Kinetics and thermochemistry

Hoyermann, K.; Seeba, Johann

doi:10.1016/s0082-0784(06)80719-8

Cited by 7 publications

(10 citation statements)

References 12 publications

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“…In the following we consider the results based on the MRCI + Q MEP to provide our best prediction. Figure 8 presents a comparison of our VRC-TST predictions for the benzyl + O 2 high-pressure recombination rate constant with previous experimental measurements [7,10,34,35] . Fenter [11] .…”

Section: Benzyl + Omentioning

confidence: 90%

“…For benzyl, both Hoyermann et al [10] and Nelson et al [11] observed no temperature dependence over the 243-373 K range (at pressures of 1-3 and 3-15 Torr, respectively), while Fenter et al indicated a significant decline with increasing temperature at analogous temperatures (298-398 K) (and higher pressures of 20-760 Torr) [7] . Only Park et al have measured the rate constant for 2-naphthyl, finding a modest decrease over the 299-444 K temperature range [8] (at 40 Torr).…”

Section: Introductionmentioning

confidence: 96%

“…Phenyl, benzyl, and naphthyl radicals are prototypical aromatic radicals, which have received considerable attention in combustion modeling studies (see, e.g., [2,4,5] ). Such modeling studies have generally estimated the kinetic data for the fuel radical R + O 2 reaction from experience or via extrapolation of relatively low-temperature experimental measurements [6][7][8][9][10][11] .…”

Section: Introductionmentioning

confidence: 99%

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Recombination of aromatic radicals with molecular oxygen

Zhang

Nicolle

Xing

et al. 2017

Proceedings of the Combustion Institute

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The addition of molecular oxygen to hydrocarbon radicals yields peroxy radicals (ROO), which are crucial species in both atmospheric and combustion chemistry. For aromatic radicals there is little known about the recombination kinetics, especially for the high temperatures of relevance to combustion. Here, we have employed direct CASPT2 based variable reaction coordinate transition state theory to predict the high pressure recombination rates for four prototypical aromatic hydrocarbon radicals: phenyl, benzyl, 1-naphthyl, and 2-naphthyl. The variation in the predicted rates is discussed in relation to their molecular structure. The predicted rate coefficients are in reasonably satisfactory agreement with the limited experimental data and are expected to find utility in chemical modeling studies of PAH growth and oxidation.

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Section: Benzyl + Omentioning

confidence: 90%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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Recombination of aromatic radicals with molecular oxygen

Zhang

Nicolle

Xing

et al. 2017

Proceedings of the Combustion Institute

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“…In oxidizing systems, benzyl associates with O 2 in a reaction that is just over 20 kcal mol À1 exothermic. 7 This reaction produces the benzylperoxy radical, but because of the weak C-O 2 bond energy this species rapidly dissociates back to benzyl + O 2 , with only a slow forward reaction to new products. 8 A major process in benzyl oxidation is the reaction with HO 2 , which forms a chemically activated benzylhydroperoxide adduct that dissociates before stabilization, to form the C 7 H 7 O radical benzoxyl (C 6 H 5 CH 2 O) plus OH.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of the benzyl + O(3P) reaction: a quantum chemical/statistical reaction rate theory study

Silva

Bozzelli

2012

Phys. Chem. Chem. Phys.

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The resonance stabilized benzyl radical is an important intermediate in the combustion of aromatic hydrocarbons and in polycyclic aromatic hydrocarbon (PAH) formation in flames. Despite being a free radical, benzyl is relatively stable in thermal, oxidizing environments, and is predominantly removed through bimolecular reactions with open-shell species other than O(2). In this study the reaction of benzyl with ground-state atomic oxygen, O((3)P), is examined using quantum chemistry and statistical reaction rate theory. C(7)H(7)O energy surfaces are generated at the G3SX level, and include several novel pathways. Transition state theory is used to describe elementary reaction kinetics, with canonical variational transition state theory applied for barrierless O atom association with benzyl. Apparent rate constants and branching ratios to different product sets are obtained as a function of temperature and pressure from solving the time-dependent master equation, with RRKM theory for microcanonical k(E). These simulations indicate that the benzyl + O reaction predominantly forms the phenyl radical (C(6)H(5)) plus formaldehyde (HCHO), with lesser quantities of the C(7)H(6)O products benzaldehyde, ortho-quinone methide, and para-quinone methide (+H), along with minor amounts of the formyl radical (HCO) + benzene. Addition of O((3)P) to the methylene site in benzyl produces a highly vibrationally excited C(7)H(7)O* adduct, the benzoxyl radical, which can β-scission to benzaldehyde + H and phenyl + HCHO. In order to account for the experimental observation of benzene as the major reaction product, a roaming radical mechanism is proposed that converts the nascent products phenyl and HCHO to benzene + HCO. Oxygen atom addition at the ortho and para ring sites in benzyl, which has not been previously considered, is shown to lead to the quinone methides + H; these species are less-stable isomers of benzaldehyde that are proposed as important combustion intermediates, but are yet to be identified experimentally. Franck-Condon simulations of the benzaldehyde, o-quinone methide, and p-quinone methide photoelectron spectra suggest that these C(7)H(6)O isomers could be distinguished using tunable VUV photoionization mass spectrometry.

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“…xylyl + O 2 reactions) are important. We have already determined the variable transition state for the dissociation reaction pathway E, o-CH 3 The rate constant for the thermal decomposion of oxylylperoxy radicals 2 to form o-xylyl radicals 1 and oxygen molecules is shown in Figure 12. As shown in Figure 12, the rate constants for reaction channel E at pressures of 10-0.1 atm deviated from the high-pressure limit rate constant above 500 K. This is due to the depletion of the collision-induced energized species because of the fast decomposition and slow collision rates at relatively low pressures, which is called the falloff effect in statistical rate theory.…”

Section: Rate Constant For the Reaction Of O-ch 3 C 6 H 4 Ch 2 + O 2 mentioning

confidence: 99%

Density Functional Study of the High-Temperature Oxidation of o-, m- and p-Xylyl Radicals

et al. 2009

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Theoretical calculations at the CBS-QB3 level of theory have been performed to investigate the potential energy surface for the reaction of o-, m- and p-xylyl with molecular oxygen. The differences of the relative potential energies for the products and the transition states of o-, m- and p-xylyl with molecular oxygen were found to be within 8.5 kJ/mol at the CBS-QB3 level of theory. Although the reaction of m- and p-xylyl radicals with molecular oxygen have the same reaction pathways and also the same reaction thermochemistry as that of benzyl radicals, the o-xylylperoxy radicals formed by the reaction of o-xylyl + O(2) had an additional intramolecular isomerization pathway to form the o-xylyl hydroperoxy radicals. The rate constants and the product branching ratios for the o-xylyl + O(2) and its subsequent reactions were evaluated by the RRKM and master equation analysis. Possible roles for these reaction pathways on the combustion of o-xylenes are discussed.

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A direct study of the reaction of benzyl radicals with molecular oxygen: Kinetics and thermochemistry

Cited by 7 publications

References 12 publications

Recombination of aromatic radicals with molecular oxygen

Recombination of aromatic radicals with molecular oxygen

Kinetics of the benzyl + O(3P) reaction: a quantum chemical/statistical reaction rate theory study

Density Functional Study of the High-Temperature Oxidation of o-, m- and p-Xylyl Radicals

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