Thermalized Epoxide Formation in the Atmosphere
Thermalized Epoxide Formation in the Atmosphere
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DOI：
10.1021/acs.jpca.9b09364
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发表时间：
2019-12-12
影响因子：
2.9
通讯作者：
Kjaergaard, Henrik G.
中科院分区：
文献类型：
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作者：
Moller, Kristian H.;Kurten, Theo;Kjaergaard, Henrik G.
环氧化物的形成是十年前建立的，作为大气中β-氢过氧烷基自由基的可能反应途径。这种环氧化物形成途径需要过量的能量来与O-2加成竞争，因为热反应速率系数太慢了许多数量级。然而，最近，在ISOPOOH + OH氧化途径中发现了热环氧化物形成反应。在这里，我们计算研究了一系列取代的β-氢过氧烷基自由基的环氧化物形成速率系数的取代基的效果。我们发现，热反应可能是竞争性的O-2加成时，烷基基团的碳具有OH基团，这是能够形成一个氢键的取代基上的其他碳原子的环氧环正在形成。满足这些要求的反应物可以在OH引发的许多生物源烃的氧化中形成。此外，我们发现β-OOR烷基自由基与β-OOH烷基自由基的反应类似，使得环氧化物形成为ROOR过氧化物氧化中的可能分解途径。GEOS-Chem建模显示异戊二烯二羟基氢过氧环氧化物的总年产量为23 Tg，使其成为迄今为止来自异戊二烯氧化的最丰富的C-5-四官能物质。
Epoxide formation was established a decade ago as a possible reaction pathway for beta-hydroperoxy alkyl radicals in the atmosphere. This epoxide-forming pathway required excess energy to compete with O-2 addition, as the thermal reaction rate coefficient is many orders of magnitude too slow. However, recently, a thermal epoxide forming reaction was discovered in the ISOPOOH + OH oxidation pathway. Here, we computationally investigate the effect of substituents on the epoxide formation rate coefficient of a series of substituted beta-hydroperoxy alkyl radicals. We find that the thermal reaction is likely to be competitive with O-2 addition when the alkyl radical carbon has a OH group, which is able to form a hydrogen bond to a substituent on the other carbon atom in the epoxide ring being formed. Reactants fulfilling these requirements can be formed in the OH-initiated oxidation of many biogenic hydrocarbons. Further, we find that beta-OOR alkyl radicals react similarly to beta-OOH alkyl radicals, making epoxide formation a possible decomposition pathway in the oxidation of ROOR peroxides. GEOS-Chem modeling shows that the total annual production of isoprene dihydroxy hydroperoxy epoxide is 23 Tg, making it by far the most abundant C-5-tetrafunctional species from isoprene oxidation.