Theoretical study on the formation mechanism of polychlorinated dibenzothiophenes/thianthrenes from 2-chlorothiophenol molecules  

作　　者：Xiaoqing Yu Jiamin Chang Xian Liu Wenxiao Pan Aiqian Zhang 

机构地区：[1]State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences [2]College of Resources and Environment, University of Chinese Academy of Sciences

出　　处：《Journal of Environmental Sciences》2018年第4期318-327,共10页环境科学学报（英文版）

基　　金：supported by the National Natural Science Foundation (Nos. 21407167, 21621064, and 21607168);the Chinese Academy of Sciences (No. XDB14030500)

摘　　要：Homogeneous formation of polychlorinated dibenzothiophenes/thianthrenes（PCDT/TAs）,sulfurated compounds analogous to polychlorinated dibenzo-p-dioxin/dibenzofurans（PCDD/Fs）, has been well-documented to occur via radical–radical coupling reactions from chlorinated thiophenol precursors. However, the current understanding of the formation mechanism of PCDT/TAs is exclusively limited to the inherent point of view that chlorothiophenoxy radicals act as the only required intermediates for PCDT/TAs. This study investigates reaction pathways for the formation of PCDT/TAs involving two new types of radical species, i.e., substituted phenyl radicals and substituted thiophenoxyl diradicals. Taking 2-chlorothiophenol（2-CTP） as a model compound for chlorothiophenols,we found that apart from the mostly discussed chlorothiophenoxy radicals, substituted phenyl radicals and substituted thiophenoxyl diradicals could also be readily formed via the reaction of 2-CTP with H radicals. Furthermore, direct self-and cross-coupling of these radicals can result in the formation of PCDT/TAs, including 1-monochlorothianthrene（1-MCTA）, 1,6-dichlorothianthrene（1,6-DCTA）, 4,6-dichlorodibenzothiophene（4,6-DCDT）and 1,6-dichlorodibenzothiophene（1,6-DCDT）. The pathways proposed in this work are proven to be both thermodynamically and kinetically favorable. Particularly, comparisons were made between the formation mechanisms of sulfurated and oxygenated dioxin systems from an energetic point view, showing that replacing oxygen with sulfur atoms greatly reduces the activation barriers of the rate-controlling steps involved in the PCDT/TA formation processes compared with those involved for PCDD/Fs. The calculated results in this work may improve our understanding of the formation mechanism of PCDT/TAs from chlorothiophenol precursors and should be informative to environmental scientists.Homogeneous formation of polychlorinated dibenzothiophenes/thianthrenes（PCDT/TAs）,sulfurated compounds analogous to polychlorinated dibenzo-p-dioxin/dibenzofurans（PCDD/Fs）, has been well-documented to occur via radical–radical coupling reactions from chlorinated thiophenol precursors. However, the current understanding of the formation mechanism of PCDT/TAs is exclusively limited to the inherent point of view that chlorothiophenoxy radicals act as the only required intermediates for PCDT/TAs. This study investigates reaction pathways for the formation of PCDT/TAs involving two new types of radical species, i.e., substituted phenyl radicals and substituted thiophenoxyl diradicals. Taking 2-chlorothiophenol（2-CTP） as a model compound for chlorothiophenols,we found that apart from the mostly discussed chlorothiophenoxy radicals, substituted phenyl radicals and substituted thiophenoxyl diradicals could also be readily formed via the reaction of 2-CTP with H radicals. Furthermore, direct self-and cross-coupling of these radicals can result in the formation of PCDT/TAs, including 1-monochlorothianthrene（1-MCTA）, 1,6-dichlorothianthrene（1,6-DCTA）, 4,6-dichlorodibenzothiophene（4,6-DCDT）and 1,6-dichlorodibenzothiophene（1,6-DCDT）. The pathways proposed in this work are proven to be both thermodynamically and kinetically favorable. Particularly, comparisons were made between the formation mechanisms of sulfurated and oxygenated dioxin systems from an energetic point view, showing that replacing oxygen with sulfur atoms greatly reduces the activation barriers of the rate-controlling steps involved in the PCDT/TA formation processes compared with those involved for PCDD/Fs. The calculated results in this work may improve our understanding of the formation mechanism of PCDT/TAs from chlorothiophenol precursors and should be informative to environmental scientists.

关 键 词：Polychlorinated dibenzothiophenes/thianthrenes Formation mechanism Phenyl radicals Thiophenoxyl diradicals Density functional theory study 

分 类 号：O626[理学—有机化学] X13[理学—化学]