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Oxidation of toluene in NO χ free air: Product distribution and mechanism
Author(s) -
Seuwen Ralph,
Warneck Peter
Publication year - 1996
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1996)28:5<315::aid-kin1>3.0.co;2-y
Subject(s) - chemistry , radical , toluene , photochemistry , product distribution , formaldehyde , benzaldehyde , hydrogen atom abstraction , beta scission , benzene , reaction mechanism , medicinal chemistry , organic chemistry , catalysis , radical substitution
Product distributions resulting from the oxidation of toluene in air initiated by chlorine atoms, by toluene photolysis, and by hydroxyl radicals were studied at atmospheric pressure in the absence of nitrogen oxides. In the first case only benzaldehyde and benzylalcohol with a ratio of 7.8 ± 1.7 were observed, from which a branching ratio α = 0.76 ± 0.05 was derived for the radical propagating pathway of the self‐reaction of benzylperoxy radicals. In the second and third case the apparent branching ratio decreased to α = 0.56 ± 0.07 and 0.37 ± 0.08, respectively, indicating the occurrence of additional reactions between benzylperoxy and other peroxy radicals. The major ring retaining products resulting from the reaction of OH with toluene were o ‐cresol, p ‐cresol. and methyl‐ p ‐benzo‐quinone (57.9 ± 12.5% reacted carbon, corrected for secondary losses), in addition to 7.7 ± 1.6% benzaldehyde and benzylalcohol arising from methyl hydrogen abstraction. Formaldehyde, acetaldehyde, glyoxal, methylglyoxal, carbon monoxide, and carbon dioxide were observed as ring cleavage products (25.0 ± 7.2%). Except for CO 2 , which appears to be an important ring cleavage product only under NO χ ‐free conditions, the distribution of ring cleavage products was similar to that found by Gery et al (1985) in the presence of NO χ . Comparison of experimental data and results from computer simulations show that self‐reactions of the hydroxy‐methyl‐cyclo‐hexadienylperoxy radicals are negligible compared to internal rearrangement reactions leading to ring stabilization or ring cleavage. The mechanism of CO 2 production appears to require the formation of a Criegee intermediate. © 1996 John Wiley & Sons, Inc.