Atmospheric oxidation mechanism of toluene.
Atmospheric oxidation mechanism of toluene.
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DOI：
10.1021/jp500077f
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发表时间：
2014-06
期刊：
影响因子：
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通讯作者：
Runrun Wu;S. Pan;Yun Li;Liming Wang
中科院分区：
文献类型：
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作者：
Runrun Wu;S. Pan;Yun Li;Liming Wang
在M06-2X、G3MP2-RAD和ROCBS-QB3水平上通过量子化学计算和动力学计算，采用过渡态理论和单分子反应理论耦合主方程(RRKM-ME)研究了羟基自由基加成引发甲苯大气氧化的机理。预测的分支比分别为0.15、0.59、0.05和0.14，其中羟基加成到异丙基、邻位、间位和对位(形成R1-R4加合物)。详细研究了R2、R4和R1的命运。在大气中，R2与O2通过不可逆氢抽提生成邻甲酚(36%)，或通过可逆重组生成R2-100-SYN和R2-300-SYN，后者随后环化成双环自由基R2-1300-SYN(%)。类似地，R4与O2反应，对甲酚的支化率为61%，R4-35OO-syn的支化率为39%，而R1和O2的反应生成了R1-260O-syn。RRKM-ME计算表明，R2/R4与O2的反应在760Torr时已达到其高压极限，R2-16O-3O-S的生成仅在低压下才重要，即100Torr时为5.4%。双环自由基(R2-1300-syn、R4-3500-syn和r1-2600-syn)与NO反应后与O2重新结合生成双环烷氧基。双环烷氧基将开环生成甲基乙二醛/乙二醛(MGLY/GLY)及其对应的副产物丁烯二醛/甲基取代丁烯二醛。然而，对于双环烷氧基，发现了一条新的反应途径，导致产物MGly/Gly和2，3-epoxybutandial/2-methyl-2，3-epoxybutandial.根据现有的理论和前人的理论和实验结果，提出了甲苯大气氧化的新机理。新的机理预测，与其他大气模型和最近的实验测量相比，GLY的产率要低得多，丁二醛的产率要高得多。新的机制要求检测拟议的产品2，3-环氧丁二醛和2-甲基-2，3-环氧丁二醛。
The atmospheric oxidation mechanism of toluene initiated by OH radical addition is investigated by quantum chemistry calculations at M06-2X, G3MP2-RAD, and ROCBS-QB3 levels and by kinetics calculation by using transition state theory and unimolecular reaction theory coupled with master equation (RRKM-ME). The predicted branching ratios are 0.15, 0.59, 0.05, and 0.14 for OH additions to ipso, ortho, meta, and para positions (forming R1-R4 adducts), respectively. The fate of R2, R4, and R1 is investigated in detail. In the atmosphere, R2 reacts with O2 either by irreversible H-abstraction to form o-cresol (36%), or by reversible recombination to R2-1OO-syn and R2-3OO-syn, which subsequently cyclize to bicyclic radical R2-13OO-syn (64%). Similarly, R4 reacts with O2 with branching ratios of 61% for p-cresol and 39% for R4-35OO-syn, while reaction of R1 and O2 leads to R1-26OO-syn. RRKM-ME calculations show that the reactions of R2/R4 with O2 have reached their high-pressure limits at 760 Torr and the formation of R2-16O-3O-s is only important at low pressure, i.e., 5.4% at 100 Torr. The bicyclic radicals (R2-13OO-syn, R4-35OO-syn, and R1-26OO-syn) will recombine with O2 to produce bicyclic alkoxy radicals after reacting with NO. The bicyclic alkoxy radicals would break the ring to form products methylglyoxal/glyoxal (MGLY/GLY) and their corresponding coproducts butenedial/methyl-substituted butenedial as proposed in earlier studies. However, a new reaction pathway is found for the bicyclic alkoxy radicals, leading to products MGLY/GLY and 2,3-epoxybutandial/2-methyl-2,3-epoxybutandial. A new mechanism is proposed for the atmospheric oxidation mechanism of toluene based on current theoretical and previous theoretical and experimental results. The new mechanism predicts much lower yield of GLY and much higher yield of butenedial than other atmospheric models and recent experimental measurements. The new mechanism calls for detection of proposed products 2,3-epoxybutandial and 2-methyl-2,3-epoxybutandial.