Thermochemistry and reaction paths in the oxidation reaction of benzoyl radical: C6H5C•(═O).
Thermochemistry and reaction paths in the oxidation reaction of benzoyl radical: C6H5C•(═O).
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DOI：
10.1021/jp2078067
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发表时间：
2011-09
期刊：
影响因子：
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通讯作者：
N. Sebbar;J. Bozzelli;H. Bockhorn
中科院分区：
文献类型：
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作者：
N. Sebbar;J. Bozzelli;H. Bockhorn
烷基取代芳烃存在于燃料和环境中，因为它们是汽油、喷气机和其他发动机燃料氧化或燃烧的主要中间体。此类分子氧化的主要反应途径是通过夺取反应失去烷基上的苄基氢原子。苯甲醛是苯甲基自由基燃烧和大气氧化过程中的主要中间体之一，它会迅速失去弱结合的醛氢，形成共振稳定的苯甲酰自由基(C6H5C(•)=O)。本研究详细研究了中间体的热化学以及苯甲酰自由基与分子氧的氧化反应路径。报告了苯甲酰自由基 +O2 缔合反应产生的重要稳定物质、中间自由基和过渡态结构的结构和形成焓，以及反应路径和势垒。使用从头计算 (G3MP2B3) 和密度泛函（B3LYP/6-311G(d,p) 处的 DFT）计算、基团可加性 (GA) 和文献数据计算焓 ΔfH298(0)。还报告了苯甲酰基和苯甲酰基过氧体系的键能，并与烃体系进行了比较。苯甲酰与 O2 的反应有许多低能反应通道，目前在大气化学或燃烧模型中均未考虑这些通道。反应路径包括多种不饱和含氧烃中间体的放热链支化反应以及二氧化碳的形成。 C6H5C(•)=O自由基与O2初始反应形成化学活化的苯甲酰基过氧自由基，内能37 kcal mol(-1)；这比苯甲基或烯丙基 + O2 系统中涉及的 21 kcal mol(-1) 能量要多得多。这个更深的井导致了许多化学活化反应路径，导致苯氧基自由基+CO2产物的高度放热反应。
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, ΔfH298(0), 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 O2 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.