Assessing the Potential for Oligomer Formation from the Reactions of Lactones in Secondary Organic Aerosols,The Journal of Physical Chemistry A

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Assessing the Potential for Oligomer Formation from the Reactions of Lactones in Secondary Organic Aerosols
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2018-01-02 00:00:00 , DOI: 10.1021/acs.jpca.7b10411
Kallie Jiang ₁ , Daniel R. Hill ₁ , Matthew J. Elrod ₁

Affiliation

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, β-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.

中文翻译：

从内有机有机溶胶中内酯的反应评估低聚物形成的潜力

实验室和现场测量表明，2-甲基甘油酸（2-MG）是在甲基丙烯醛衍生的二级有机气溶胶（SOA）中发现的多种化学物质的基本成分。为了探索最近提出的内酯氧化中间体是2-MG及其衍生物在SOA中的起源的假说，使用核磁共振技术研究了模型内酯β-的水相反应的动力学和反应产物。丙内酯（BPL）。通过一般的酸催化机理，发现BPL的反应寿命为4-10小时（取决于溶液条件），这表明与BPL相似的内酯在与大气有关的时间尺度上具有反应性。还显示出BPL会形成多种亲核加成产物（有机硫酸盐，硝酸盐和低聚物），类似于先前涉及甲基丙烯醛的光氧化和SOA处理的实验中观察到的基于2-MG的物质。虽然许多BPL反应产物可以通过类似环氧化物的亲核加成机理进行合理化，但通过观察无机离子催化的低聚物形成，可以证明存在类似酯的亲核加成的证据。发现低聚物的形成在很大程度上取决于以去质子化形式存在的有机酸亲核试剂的比例。因此，由于一般酸催化的性质以及去质子化酸对于高效BPL低聚的重要性，有人提出，在较高的SOA pH值下，内酯中间体的低聚反应会更有效。该结果可能有助于解释为什么观察到总体上异戊二烯衍生的SOA形成很大程度上与pH无关。总的来说，这些结果强烈支持先前的结论，即内酯中间体是在甲基丙烯醛来源的SOA中发现的2-MG相关物种形成的原因。

更新日期：2018-01-02

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