o-Xylene oxidation displays an autoignition behavior similar to alkanes at low temperatures. This paper presents a detailed investigation of the chemical kinetics of oxygen additions with the o-xylyl radical that control the ignition reactivity of o-xylene at low temperatures. High-level electronic structure calculations, transition state theory, and master equation simulations are combined to predict the rate coefficients of main elementary reactions. For the initially formed o-methylbenzylperoxy (ROO) in the first oxygen addition o-xylyl + O₂, its isomerization to o-hydroperoxymethyl-benzyl (QOOH) proceeds with a much smaller branching ratio compared to the counterpart ROO → QOOH in alkanes. Despite the slow formation of QOOH, the absence of fast dissociation pathways enable QOOH concentration to build up. QOOH that has the unpaired electron located on a side-chain carbon can readily react with a second molecular oxygen. The QOOH + O₂ reaction then efficiently leads to the growth of the radical pool through a highly chain-branching reaction sequence QOOH + O2 → 2-hydroperoxymethyl-benzaldehyde + OH → 1,2-diformylbenzene + 2OH + H. The predicted oxygen addition kinetics offers a good explanation for the alkane-like autoignition behavior of o-xylene. Meanwhile, as the key intermediate to chain branching, the lower yield of QOOH results in its lower ignition reactivity. The present study shows that classical low temperature scheme is also valid for benzylic-type hydrogens and radicals of o-xylene where the transferred hydrogen from the ortho-methyl chain facilitates the isomerization ROO ↔ QOOH. It is also easy to deduce that for m- and p-xylenes, where no such isomerization step is available, little reactivity should be expected at the low temperature.

邻二甲苯氧化在低温下显示出类似于烷烃的自燃行为。本文呈现的氧气补充与化学动力学的详细调查的Ø -二甲苯团，其控制的点火反应Ø在低温下二甲苯。结合了高级电子结构计算，过渡态理论和主方程模拟，以预测主要基本反应的速率系数。对于在第一次氧加成中的最初形成的邻甲基苄基过氧（ROO）邻二甲苯基+ O ₂，其异构化为邻与烷烃中相应的ROO→QOOH相比，-氢过氧甲基-苄基（QOOH）的支化比小得多。尽管QOOH的形成缓慢，但缺乏快速的解离途径使QOOH的浓度得以建立。在侧链碳上具有未配对电子的QOOH可以很容易地与第二分子氧反应。然后，QOOH + O ₂反应通过高度链支化的反应序列QOOH + O2→2-氢过氧甲基苯甲醛+ OH→1,2-二甲酰苯+ 2OH + H有效地导致自由基库的生长。预测的氧添加动力学很好地解释了o的类似烷烃的自燃行为-二甲苯。同时，作为链支化的关键中间体，较低的QOOH收率导致较低的着火反应性。本研究表明，经典的低温方案对苄基型氢和邻二甲苯基也是有效的，其中从邻甲基链转移的氢促进了异构化。这也很容易推断出为米-和p -xylenes，其中没有这样的异构化步骤是可用的，小的反应性应在低温下的预期。