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首页> 外文期刊>Atmospheric chemistry and physics >Oligomer formation during gas-phase ozonolysis of small alkenes and enol ethers: new evidence for the central role of the Criegee Intermediate as oligomer chain unit
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Oligomer formation during gas-phase ozonolysis of small alkenes and enol ethers: new evidence for the central role of the Criegee Intermediate as oligomer chain unit

机译：小烯烃和烯醇醚的气相臭氧分解过程中低聚物的形成：Criegee中间体作为低聚物链单元的核心作用的新证据

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An important fraction of secondary organic aerosol (SOA) formed byatmospheric oxidation of diverse volatile organic compounds (VOC) hasrecently been shown to consist of high-molecular weight oligomeric species.In our previous study (Sadezky et al., 2006), we reported the identificationand characterization of oligomers as main constituents of SOA from gas-phaseozonolysis of small enol ethers. These oligomers contained repeated chainunits of the same chemical composition as the main Criegee Intermediates(CI) formed during the ozonolysis reaction, which were CH2O2 (mass46) for alkyl vinyl ethers (AVE) and C2H4O2 (mass 60) forethyl propenyl ether (EPE). In the present work, we extend our previousstudy to another enol ether (ethyl butenyl ether EBE)and a variety of structurally related small alkenes (trans-3-hexene,trans-4-octene and 2,3-dimethyl-2-butene).Experiments have been carried out in a 570 l spherical glass reactor atatmospheric conditions in the absence of seed aerosol. SOA formation wasmeasured by a scanning mobility particle sizer (SMPS). SOA filter sampleswere collected and chemically characterized off-line by ESI(+)/TOF MS andESI(+)/TOF MS/MS, and elemental compositions were determined byESI(+)/FTICR MS and ESI(+)/FTICR MS/MS. The results for all investigated unsaturated compoundsare in excellent agreement with the observations of our previous study. Analysis of the collected SOA filter samples revealthe presence of oligomeric compounds in the mass range 200 to 800 u as majorconstituents. The repeated chain units of these oligomers are shown tosystematically have the same chemical composition as the respective mainCriegee Intermediate (CI) formed during ozonolysis of the unsaturatedcompounds, which is C3H6O2 (mass 74) for ethyl butenyl ether(EBE), trans-3-hexene, and 2,3-dimethyl-2-butene, and C4H8O2 (mass88) for extit{trans}-4-octene. Analogous fragmentation pathways among the oligomersformed by gas-phase ozonolysis of the different alkenes and enol ethers inour present and previous study, characterized bysuccessive losses of the respective CI-like chain unit as a neutralfragment, indicate a similar principal structure. In this work, we confirm the basic structure of a linearoligoperoxide – [CH(R)-O-O]n – for all detected oligomers, with therepeated chain unit CH(R)OO corresponding to the respective major CI. The elemental compositions of parent ions, fragment ions and fragmented neutrals determined by accurate mass measurements with the FTICR technique allow us to assign a complete structure to the oligomer molecules. We suggest that the formation of the oligoperoxidic chain units occurs through a new gas-phase reaction mechanism observed for the first time in our present work, which involves the addition of stabilized CI to organic peroxy radicals.Furthermore, copolymerization of CI simultaneously formed in the gas phasefrom two different unsaturated compounds is shown to occur during theozonolysis of a mixture of extit{trans}-3-hexene and ethyl vinyl ether (EVE), leading toformation of oligomers with mixed chain units C3H6O2 (mass74) and CH2O2 (mass 46). We therefore suggest oligoperoxideformation by repeated peroxy radical-stabilized CI addition to be a general reaction pathway of smallstabilized CI in the gas phase, which represents an alternative way tohigh-molecular products and thus contributes to SOA formation.
机译：大气中各种挥发性有机化合物（VOC）氧化形成的次要有机气溶胶（SOA）的重要组成部分最近已证明是由高分子低聚物组成的。在我们以前的研究中（Sadezky et al。，2006），我们报道了小烯醇醚的气相臭氧分解法鉴定和表征低聚物是SOA的主要成分。这些低聚物包含与在臭氧分解反应过程中形成的主要Criegee中间体（CI）相同的化学组成的重复链单元，其中烷基乙烯基为CH 2 O 2 （质量46）醚（AVE）和C 2 H 4 O 2 （质量60）用作乙基丙烯基醚（EPE）。在当前的工作中，我们将先前的研究扩展到另一种烯醇醚（乙基丁烯基醚EBE）和各种与结构相关的小烯烃（ trans -3-己烯， trans - （4-辛烯和2，3-二甲基-2-丁烯）。实验是在570 l球形玻璃反应器中，在没有种子气溶胶的大气压条件下进行的。通过扫描迁移率粒度仪（SMPS）测量SOA的形成。收集SOA过滤器样品并通过ESI（+）/ TOF MS和ESI（+）/ TOF MS / MS进行离线化学表征，并通过ESI（+）/ FTICR MS和ESI（+）/ FTICR MS / MS确定元素组成。所有研究的不饱和化合物的结果与我们先前研究的观察结果非常吻合。对收集的SOA过滤器样品的分析表明，存在质量范围为200至800 u的低聚化合物为主要成分。这些低聚物的重复链单元显示出与不饱和化合物臭氧分解过程中形成的相应主中间体中间体（CI）具有相同的化学组成，即C 3 H 6 乙基丁烯基醚（EBE），反式 -3-己烯和2,3-二甲基-2-丁烯的O 2 （质量74）和C textit {trans} -4-辛烯的4 H 8 O 2 （mass88）。目前和以前的研究中，不同烯烃和烯醇醚的气相臭氧分解形成的低聚物之间类似的断裂途径（其特征是各自的CI样链单元连续损失为中性片段）表明相似的主结构。在这项工作中，我们确定了线性低聚过氧化物的基本结构-[CH（R）-OO] n -对于所有检测到的低聚物，其重复的链单元CH（R）OO分别对应于各自的主要CI 。通过使用FTICR技术进行精确质量测量确定的母离子，碎片离子和碎片中性离子的元素组成，使我们能够为低聚物分子分配完整的结构。我们建议通过我们本工作中首次观察到的新的气相反应机理来形成低氧过氧化物链单元，该机理涉及将稳定的CI添加到有机过氧自由基中。结果表明， textit {trans} -3-己烯和乙基乙烯基醚（EVE）的混合物进行臭氧分解时，会出现两种不同的不饱和化合物形成的气相，导致形成具有混合链单元C 3 的低聚物H 6 O 2 （质量74）和CH 2 O 2 （质量46）。因此，我们建议通过重复的过氧自由基稳定的CI加成来形成低过氧化物，这是气相中小的稳定的CI的一般反应途径，这代表了高分子产物的另一种替代方法，因此有助于SOA的形成。

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