摘要:
氯自由基(·Cl)的高氧化性及其内陆来源的新发现使得·Cl在评估有机污染物的大气归趋方面起着比以往更为重要的作用。含有NHx (x=1, 2)结构的有机化合物不仅是大气中一类潜在的有机污染物,也是大气中致癌性亚硝胺的前驱体——N中心自由基的重要来源。前人研究发现,·Cl与含有NHx (x=1, 2)结构的有机化合物具有独特的相互作用且其反应具有结构依赖性。目前,大多数研究只关注链状含有NHx (x=1, 2)结构有机化合物的反应,而对于环状含有NH结构有机化合物的反应研究却很少。本研究使用量子化学和动力学模拟相结合的方法研究·Cl引发3种环状含有NH结构有机化合物(吗啉(MOR)、哌啶(PIP)和吡咯烷(PYR))的大气转化机制及动力学。结果发现,·Cl夺取3种环状含有NH结构有机化合物中N-H的H原子形成N中心自由基是最可行的反应路径。在298 K和1 atm下,计算的反应速率常数分别为5.0×10-10 (MOR)、5.1×10-10 (PIP)和4.9×10-10 (PYR)cm3·molecule-1·s-1,且具有正的温度依附性。结合可获得的·OH引发反应的反应速率常数,评估·Cl对MOR和PIP转化的贡献分别为·OH的2.6%~26%和6.9%~69%。上述研究结果为将来建立·Cl引发含有NHx (x=1, 2)结构有机化合物反应的结构-活性关系、全面评估含有NHx (x=1, 2)结构有机化合物的大气归趋和环境风险提供数据支持。
Abstract:
The new findings on continental source of ·Cl and its high reactivity toward organic compounds make the importance of ·Cl in determining the atmospheric fate of volatile organic pollutants be higher than previously expected. NHx-containing (x =1, 2) compounds are potential organic pollutants in atmosphere and also the important source of N-center radicals, the precursors of carcinogenic nitrosamines. Early studies indicated that there is special interaction between ·Cl and NHx-containing compounds and their reaction kinetics and mechanism mainly depend on the specific structure of NHx-containing compounds. Up to now, many studies focused on ·Cl initiated reactions of chain organic compounds containing NHx structure. However, little study has been done on the cyclic NHx-containing compounds. In the present work, quantum chemical methods and kinetic modeling were employed to investigate the reaction mechanisms and kinetics of ·Cl initiated reactions of three cyclic NHx-containing compounds i.e. morpholine (MOR), piperidine (PIP) and pyrrolidine (PYR). Results showed that ·Cl initiated three cyclic NHx-containing compounds reactions exclusively lead to N-center radicals via N—H abstraction. At 298 K and 1 atm, the calculated reaction rate constants (kCl) are 5.0×10-10, 5.1×10-10 and 4.9×10-10 cm3·molecule-1·s-1 for MOR, PIP and PYR, respectively. The kCl values of three reactions have positive temperature dependence. Combined with available data of corresponding ·OH initiated reactions of MOR and PIP, the contributions of ·Cl in the transformation of MOR and PIP are estimated to be 2.6%-26% and 6.9%-69% relative to ·OH, respectively. This study provides the indispensable data to establish the structure-activity relationship analysis for ·Cl initiated reactions of NHx-containing compounds and to assess the atmospheric fate and environmental risk of NHx-containing compounds.
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