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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Assessing the Potential for Oligomer Formation from the Reactions of Lactones in Secondary Organic Aerosols
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Assessing the Potential for Oligomer Formation from the Reactions of Lactones in Secondary Organic Aerosols

机译：评估二次有机气溶胶中内酯反应的低聚物形成的潜力

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Laboratory and field measurements have demonstrated that 2-methyl glyceric acid (2-MG) is the base component of a wide range of chemical species found in methacrolein-derived secondary organic aerosol (SOA). In order to explore the recently proposed hypothesis that a lactone oxidation intermediate is the origin of 2-MG and its derivatives in SOA, nuclear magnetic resonance techniques were used to study kinetics and reaction products of the aqueous phase reactions of a model lactone, beta-propiolactone (BPL). BPL was found to react with a lifetime of 4-10 h (depending on solution conditions) via a general acid catalyzed mechanism, which suggests that lactones similar to BPL are reactive on an atmospherically relevant time scale. BPL was also shown to form a variety of nucleophilic addition products (organosulfates and nitrates and oligomers) similar to the 2-MG-based species observed in previous experiments involving the photooxidation and SOA processing of methacrolein. While many of the BPL reaction products could be rationalized via an epoxide-like nucleophilic addition mechanism, evidence for ester-like nucleophilic addition was suggested through the observation of inorganic ion-catalyzed oligomer formation. The formation of oligomers was found to depend strongly on the proportion of organic acid nucleophile present in its deprotonated form. Therefore, due to the nature of the general acid catalysis and importance of deprotonated acids for efficient BPL oligomerization, it is suggested that oligomerization from lactone intermediates will be more efficient at higher SOA pH values. This result may help explain why overall isoprene-derived SOA formation has been observed to be largely pH-independent. Overall, the results strongly support the previous conclusion that a lactone intermediate is responsible for the formation of 2-MG-related species found in methacrolein-derived SOA.
机译：实验室和田间测量表明，2-甲基甘油酸（2-Mg）是在甲基丙烯醛衍生的二次有机气溶胶（SOA）中发现的各种化学物质的基础组分。为了探讨最近提出的假设，即内酯氧化中间体是2mg的起源及其在SOA中的衍生物，核磁共振技术用于研究模型内酯的水相反应的动力学和反应产物，β-丙唑酮（BPL）。发现BPL通过一般酸催化机制与4-10小时（取决于溶液条件）的寿命反应，这表明类似于BPL的内酯在大气相关的时间尺度上是反应性的。还显示BPL类似于在先前实验中观察到的基于2mg的物种的各种亲核加成产物（有机硫酸盐和硝酸盐和低聚物），所述实验涉及甲基丙醇的光氧化和SOA加工。虽然许多BPL反应产物可以通过环氧化物的亲核加成机制合理化，但是通过观察无机离子催化的低聚物形成，提出了酯样亲核添加的证据。发现寡聚体的形成依赖于在其去质子化形式中存在的有机酸亲核试核官的比例。因此，由于普通酸催化的性质和前质子酸酸的重要性，提出了从内酯中间体的低聚在更高的SOA pH值下更有效。该结果可以有助于解释为什么已经观察到总体异戊二烯衍生的SOA形成在很大程度上是彼此独立的。总体而言，结果强烈支持前一个结论，即内酯中间体负责形成2mg相关的甲基丙烯醛衍生的SOA中的物种。

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