The formation of PBDFs from the ortho-disubstituted phenol precursors: A comprehensive theoretical study on the PBDD/Fs formation from 2,4,6-tribromophenol
The formation of PBDFs from the ortho-disubstituted phenol precursors: A comprehensive theoretical study on the PBDD/Fs formation from 2,4,6-tribromophenol
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邻位二取代苯酚前体形成 PBDF：关于 2,4,6-三溴苯酚形成 PBDD/F 的综合理论研究
DOI：
10.1016/j.scitotenv.2020.136657
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发表时间：
2020-04-15
影响因子：
9.8
通讯作者：
Zhang, Aiqian
中科院分区：
文献类型：
--
作者：
Chang, Jiamin;Pan, Wenxiao;Zhang, Aiqian
溴代酚是众所周知的多溴代二苯并二恶英/二苯并呋喃（PBDD/Fs）的直接前体。长期以来，人们一直认为，邻位二取代苯酚只能形成毒性更大的二恶英类产物，这与实验观察结果完全相反，即PBDD和PBDF 5都会生成。为了解决这一问题，本研究以2，4，6-三溴苯酚（TBP）为原料，研究了PBDD/Fs的气相生成机理。首先，TBP与活性H自由基反应生成三个关键自由基物种：溴代苯氧基自由基、取代苯基自由基和苯氧基双自由基。这些自由基物种与TBP的自结合和交叉结合不仅产生二恶英类产物1，3，6，8-TeBDD和1，3，7，9-TeBDD，而且产生溴代二苯并呋喃1，3，6，8-TeBDF和2，4，6，8-TeBDF。值得注意的是，涉及取代的苯基和苯氧基双自由基中的苯基C位点的反应被证明是在动力学上和动力学上都比涉及溴苯氧基自由基和TBP分子更有利。最重要的是，本工作的发现是非常重要的，因为它提供了可行的途径，以形成毒性较低的二苯并呋喃型产品从邻二取代苯酚。这些结果将有助于加深对苯酚前体生成PBDD/Fs机理的理解。(C)2020 Elsevier B. V.保留所有权利。
Bromophenols are known as direct precursors of the notorious polybrominated dibenzo-p-dioxin/dibenzofurans (PBDD/Fs). There is a long-held viewpoint that only the more toxic dioxin-type products could be formed from the ortho-disubstituted phenols, totally contrary to the experimental observations that both PBDDs and PBDF5 are generated. To tackle the issue, the gaseous formation mechanism of PBDD/Fs from 2,4,6-tribromophenol (TBP), a typical ortho-disubstituted phenol, was investigated in this study. Firstly, the reactions between TBP and the active H radical produce three key radical species including the bromophenoxyl radical, the substituted phenyl radical and phenoxyl diradical. The self- and cross-combinations of these radical species and TBP yield not only the dioxin-type products 1,3,6,8-TeBDD and 1,3,7,9-TeBDD, but also the brominated dibenzofurans 1,3,6,8-TeBDF and 2,4,6,8-TeBDF. Notably, the reactions involving the phenyl C sites in the substituted phenyl and phenoxyl diradicals are demonstrated to be both thermodynamically and kinetically more favorable than those involving the bromophenoxyl radical and the TBP molecule. Most importantly, the findings of the present work are of great importance as it provides feasible pathways to form less toxic dibenzofuran-type products from the oriho-disubstituted phenols. These results will improve the understanding of the PBDD/Fs formation mechanism from phenol precursors. (C) 2020 Elsevier B.V. All rights reserved.