New understanding of the formation of PCDD/Fs from chlorophenol precursors: a mechanistic and kinetic study.
New understanding of the formation of PCDD/Fs from chlorophenol precursors: a mechanistic and kinetic study.
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DOI：
10.1021/jp410077g
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发表时间：
2014-01
期刊：
影响因子：
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通讯作者：
Yanfang Zhang;Dongju Zhang;Jun Gao;J. Zhan;Chengbu Liu
中科院分区：
文献类型：
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作者：
Yanfang Zhang;Dongju Zhang;Jun Gao;J. Zhan;Chengbu Liu
虽然氯酚(CP)被认为是多氯二苯并对二恶英和二苯并呋喃(PCDD/FS)最重要和最直接的前体，但我们对PCDD/FS的形成机理的理解仅限于一个不变的概念，即氯苯氧基(CPRs)只是必要的中间体。本工作提供了一项系统的理论研究，旨在为从CPS中均匀形成PCDD/FS提供新的见解。来自CPRs的两种不同类型的自由基，即取代的苯基自由基和苯氧基双自由基，被认为是导致PCDD/FS形成的潜在来源。采用密度泛函理论计算和直接动力学方法研究了以2-氯苯酚(2-CP)为代表的2-氯苯酚(2-CP)与H原子反应生成PCDD/F的热力学和动力学性质。新提出的自由基，特别是取代苯氧基二自由基(PCDD/Fs的最直接中间体)，可以通过2-CP与H原子反应生成，势垒小，反应能大。他们应该对高温下PCDD/Fs的均匀生成负责。几种典型的PCDD/F产物是通过新提出的自由基的直接自偶联和交叉偶合来预测的。本工作提出的自由基偶联模式拓展了我们对多氯二苯并二恶英形成机理的理解。
Although chlorophenols (CPs) are considered to be the most important and direct precursors of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), our understanding of the formation mechanism of PCDD/Fs is exclusively limited to an invariable idea that chlorophenoxy radicals (CPRs) are only necessary intermediates. The present work presents a systematic theoretical study that aims at providing new insight into the homogeneous formation of PCDD/Fs from CPs. Two different types of radicals from CPRs, i.e., substituted phenyl radicals and phenoxyl diradicals, are proposed to serve as potential sources contributing to the formation of PCDD/Fs. The thermodynamic and kinetic properties of reactions of 2-chlorophenol (2-CP), as a representative of CP congeners, with atomic H to produce various potential radicals forming PCDD/Fs are studied by performing density functional theory calculations and direct kinetics studies. The newly proposed radicals, especially substituted phenoxyl diradicals (the most direct intermediates of PCDD/Fs), can be formed via reactions of 2-CP with atomic H with small barriers and large reaction energies. They should be expected to be responsible for the homogeneous formation of PCDD/Fs under high temperature. Several typical PCDD/F products are predicated through direct self- and cross-couplings of the newly proposed radicals. The radical coupling patterns proposed in the present work expand our understanding of the formation mechanism of PCDD/Fs from CP precursors.