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首页> 外文期刊>The Science of the Total Environment >Analyzing sites of OH radical attack (ring vs. side chain) in oxidation of substituted benzenes via dual stable isotope analysis (δ~(13)C and δ~2H)
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Analyzing sites of OH radical attack (ring vs. side chain) in oxidation of substituted benzenes via dual stable isotope analysis (δ~(13)C and δ~2H)

机译：通过双重稳定同位素分析（δ〜（13）C和δ〜2H）分析取代苯氧化中的OH自由基攻击的位点（环与侧链）

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摘要

OH radicals generated by the photolysis of H_2O_2 can degrade aromatic contaminants by either attacking the aromatic ring to form phenolic products or oxidizing the substituent. We characterized these competing pathways by analyzing the carbon and hydrogen isotope fractionation (ε_C and ε_H) of various substituted benzenes. For benzene and halobenzenes that only undergo ring addition, low values of ε_C (-0.7‰ to - 1.0‰) were observed compared with theoretical values (-7.2‰ to - 8‰), possibly owing to masking effect caused by pre-equilibrium between the substrate and OH radical preceding the rate-limiting step. In contrast, the addition of OH radicals to nitrobenzene ring showed a higher ε_C (-3.9‰), probably due to the lower reactivity. Xylene isomers, anisole, aniline, N,N-dimethylaniline, and benzonitrile yielded normal ε_H values (-2.8‰ to -29‰) indicating the occurrence of side-chain reactions, in contrast to the inverse ε_H (11.7‰ to 30‰) observed for ring addition due to an sp~2 to sp~3 hybridization change at the reacting carbon. Inverse eH values for toluene (14‰) and ethylbenzene (30‰) were observed despite the formation of side-chain oxidation products, suggesting that ring addition has a larger contribution to isotope fractionation. Dual element isotope slopes (Δδ~2H/Δδ~(13)C) therefore allow identification of significant degradation pathways of aromatic compounds by photochemically induced OH radicals. Issues that should be addressed in future studies include quantitative determination of the contribution of each competing pathway to the observed isotope fractionation and characterization of physical processes preceding the reaction that could affect isotope fractionation.
机译：H_2O_2的光解产生的OH自由基可通过攻击芳环形成酚类产物或氧化取代基来降解芳族污染物。我们通过分析各种取代苯的碳和氢同位素分馏（ε_C和ε_H）来表征这些竞争途径。对于仅进行环加成的苯和卤代苯，与理论值（-7.2‰至-8‰）相比，观察到较低的ε_C值（-0.7‰至-1.0‰），这可能是由于两者之间的预平衡引起的掩盖效应限速步骤之前的底物和OH自由基。相反，在硝基苯环上添加OH自由基显示出较高的ε_C（-3.9‰），这可能是由于较低的反应性所致。二甲苯异构体，苯甲醚，苯胺，N，N-二甲基苯胺和苄腈产生正常的ε_H值（-2.8‰至-29‰），表明发生了侧链反应，与相反的ε_H值（11.7‰至30‰）相反由于在反应碳上sp〜2至sp〜3的杂交变化，观察到环加成。尽管形成侧链氧化产物，但仍观察到甲苯（14‰）和乙苯（30‰）的eH值相反，这表明环加成对同位素分馏的贡献更大。因此，双元素同位素斜率（Δδ〜2H /Δδ〜（13）C）可以通过光化学诱导的OH自由基识别芳香族化合物的重要降解途径。在未来的研究中应解决的问题包括定量确定每个竞争途径对观察到的同位素分馏的贡献以及在反应之前可能影响同位素分馏的物理过程的表征。

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  • 来源
    《The Science of the Total Environment》 |2016年第15期|484-494|共11页
  • 作者

    Ning Zhang; Inacrist Geronimo; Piotr Paneth; Janine Schindelka; Thomas Schaefer; Hartmut Hernnann; Carsten Vogt; Hans H. Richnow;

  • 作者单位

    Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstrasse 15,04318 Leipzig, Germany,Department of Pharmacology, Weill Medical College of Cornell University, 1300 York Avenue, New York, New York 10065, USA;

    Institute of Applied Radiation Chemistry, Lodz University of Technology, Zeromskiego 116,90-924 Lodz Poland,Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506, USA;

    Institute of Applied Radiation Chemistry, Lodz University of Technology, Zeromskiego 116,90-924 Lodz Poland;

    Department of Chemistry, Leibniz Institute for Tropospheric Research (TROPOS), Permoserstrasse 15,04318 Leipzig, Germany;

    Department of Chemistry, Leibniz Institute for Tropospheric Research (TROPOS), Permoserstrasse 15,04318 Leipzig, Germany;

    Department of Chemistry, Leibniz Institute for Tropospheric Research (TROPOS), Permoserstrasse 15,04318 Leipzig, Germany;

    Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstrasse 15,04318 Leipzig, Germany;

    Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstrasse 15,04318 Leipzig, Germany;

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  • 正文语种 eng
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  • 关键词

    Isotope fractionation; OH radical reaction; Aromatic compounds; Competing mechanisms;

    机译：同位素分馏;OH自由基反应;芳香化合物;竞争机制;

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