Thermochemistry and reaction paths in the oxidation reaction of benzoyl radical: C6H5C·(=O)

Document Type

Article

Publication Date

10-27-2011

Abstract

Alkyl substituted aromatics are present in fuels and in the environment because they are major intermediates in the oxidation or combustion of gasoline, jet, and other engine fuels. The major reaction pathways for oxidation of this class of molecules is through loss of a benzyl hydrogen atom on the alkyl group via abstraction reactions. One of the major intermediates in the combustion and atmospheric oxidation of the benzyl radicals is benzaldehyde, which rapidly loses the weakly bound aldehydic hydrogen to form a resonance stabilized benzoyl radical (C6H5C· - O). A detailed study of the thermochemistry of intermediates and the oxidation reaction paths of the benzoyl radical with dioxygen is presented in this study. Structures and enthalpies of formation for important stable species, intermediate radicals, and transition state structures resulting from the benzoyl radical + O2 association reaction are reported along with reaction paths and barriers. Enthalpies, δfH2980, are calculated using ab initio (G3MP2B3) and density functional (DFT at B3LYP/6-311G(d,p)) calculations, group additivity (GA), and literature data. Bond energies on the benzoyl and benzoyl-peroxy systems are also reported and compared to hydrocarbon systems. The reaction of benzoyl with O2 has a number of low energy reaction channels that are not currently considered in either atmospheric chemistry or combustion models. The reaction paths include exothermic, chain branching reactions to a number of unsaturated oxygenated hydrocarbon intermediates along with formation of CO2. The initial reaction of the C6H5C· - O radical with O 2 forms a chemically activated benzoyl peroxy radical with 37 kcal mol-1 internal energy; this is significantly more energy than the 21 kcal mol-1 involved in the benzyl or allyl + O2 systems. This deeper well results in a number of chemical activation reaction paths, leading to highly exothermic reactions to phenoxy radical + CO2 products. © 2011 American Chemical Society.

Identifier

80054890532 (Scopus)

Publication Title

Journal of Physical Chemistry A

External Full Text Location

https://doi.org/10.1021/jp2078067

e-ISSN

15205215

ISSN

10895639

First Page

11897

Last Page

11914

Issue

42

Volume

115

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