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. 2019 Mar 27;20(7):1542.
doi: 10.3390/ijms20071542.

Quantum Chemical and Kinetic Study on Radical/Molecule Formation Mechanism of Pre-Intermediates for PCTA/PT/DT/DFs from 2-Chlorothiophenol and 2-Chlorophenol Precursors

Chenpeng Zuo  1 , Hetong Wang  2 , Wenxiao Pan  3 , Siyuan Zheng  4 , Fei Xu  5   6 , Qingzhu Zhang  7
Affiliations

Quantum Chemical and Kinetic Study on Radical/Molecule Formation Mechanism of Pre-Intermediates for PCTA/PT/DT/DFs from 2-Chlorothiophenol and 2-Chlorophenol Precursors

Chenpeng Zuo et al. Int J Mol Sci. .

Abstract

Polychlorinated phenoxathiins (PCPTs), polychlorinated dibenzothiophenes (PCDTs), and polychlorinated thianthrenes (PCTAs) are sulfur analogues of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/DFs). Chlorothiophenols (CTPs) and chlorophenols (CPs) are key precursors for the formation of PCTA/PT/DTs, which can react with H or OH to form chloro(thio)phenoxy radical, sulfydryl/hydroxyl-substituted phenyl radicals, and (thio)phenoxyl diradicals. However, previous radical/radical PCTA/DT formation mechanisms in the literature failed to explain the higher concentration of PCDTs than that of PCTAs under the pyrolysis or combustion conditions. In this work, a detailed thermodynamics and kinetic calculations were carried out to investigate the pre-intermediate formation for PCTA/PT/DTs from radical/molecule coupling of the 2-C(T)P with their key radical species. Our study showed that the radical/molecule coupling mechanism explains the gas-phase formation of PCTA/PT/DTs in both thermodynamic and kinetic perspectives. The S/C coupling modes to form thioether-(thio)enol intermediates are preferable over the O/C coupling modes to form ether-(thio)enol intermediates. Thus, although the radical/molecule coupling of chlorophenoxy radical with 2-C(T)P has no effect on the PCDD/PT formation, the radical/molecule coupling of chlorothiophenoxy radical with 2-C(T)P plays an important role in the PCTA/PT formation. Most importantly, the pre-PCDT intermediates formation pathways from the couplings of sulfydryl/hydroxyl-substituted phenyl radical with 2-C(T)P and (thio)phenoxyl diradicals with 2-C(T)P are more favorable than pre-PCTA/PT intermediates formation pathways from the coupling of chlorothiophenoxy radical with 2-C(T)P, which provides reasonable explanation for the high PCDT-to-PCTA ratio in the environment.

Keywords: PCTA/PT/DTs; density functional theory; formation mechanism; radical/molecule coupling; rate constant.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Formation of radical species C(T)PR1, C(T)PR2, C(T)PDR, (T)PR2, and (T)PDR embedded with the potential barriers ΔE (in kcal/mol) and reaction heats ΔH (in kcal/mol) from reactions of 2-CTP (a) and 2-CP (b) with H/OH radicals, respectively. ΔH is calculated at 0 K.
Figure 2
Figure 2
Optimized structures of 2-CP and 2-CTP molecules and related radicals in this paper: 2-chlorophenol (2-CP), 2-chlorophenoxy (CPR1), 2-hydroxyl-3-chloro-phenyl (CPR2), chlorinated phenoxyl diradical (CPDR), 2-hydroxylphenyl radical (PR2), phenoxyl diradical (PDR), 2-chlorothiophenol (2-CTP), 2-chlorothiophenoxy (CTPR1), 2-sulfydryl-3-chloro-phenyl (CTPR2), chlorinated thiophenoxyl diradical (CTPDR), 2-sulfydrylphenyl radical (TPR2), thiophenoxyl diradical (TPDR). All the values are in Å.
Figure 3
Figure 3
Pre-PCTA/PT/DT/DF formation routes embedded with the potential barriers ΔE (in kcal/mol) and reaction heats ΔH (in kcal/mol) from the cross-condensation reactions of CPR1 with 2-CTP (a), CTPR1 with 2-CTP (b), and CTPR1 with 2-CP (c). ΔH is calculated at 0 K.
Figure 4
Figure 4
Pre-PCDT/DF formation routes embedded with the potential barriers ΔE (in kcal/mol) and reaction heats ΔH (in kcal/mol) from the coupled reactions of CPR2 with 2-CTP (a), CTPR2 with 2-CTP (b), CTPR2 with 2-CP (c), PR2 with 2-CTP (d), TPR2 with 2-CTP (e), and TPR2 and 2-CP (f). ΔH is calculated at 0 K.
Figure 5
Figure 5
Pre-PCDT/DF formation routes embedded with the potential barriers ΔE (in kcal/mol) and reaction heats ΔH (in kcal/mol) from the coupled reactions of CPDR with 2-CTP (a), CTPDR with 2-CTP (b), CTPDR with 2-CP (c), PDR with 2-CTP (d), TPDR with 2-CTP (e), and TPDR and 2-CP (f). ΔH is calculated at 0 K.
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References

    1. Wang Y., Zeng X.L., Chen H.J., Wang H.J. Thermodynamic properties and relative stability of polychlorinated thianthrenes by density functional theory. J. Chem. Eng. Data. 2007;52:1442–1448. doi: 10.1021/je700127w. - DOI
    1. Chen S.D., Liu H.X., Wang Z.Y. Study of structural and thermodynamic properties for polychlorinated dibenzothiophenes by density functional theory. J. Chem. Eng. Data. 2007;52:1195–1202. doi: 10.1021/je0604885. - DOI
    1. Sinkkonen S. New Types of Persistent Halogenated Compounds. Volume 3. Springer; Berlin, Germany: 2000. pp. 289–314.
    1. Puzyn T., Rostkowski P., Swieczkowski A., Jędrusiak A., Falandysz J. Prediction of environmental partition coefficients and the Henry’s law constants for 135 congeners of chlorodibenzothiophene. Chemosphere. 2006;62:1817–1828. doi: 10.1016/j.chemosphere.2005.07.055. - DOI - PubMed
    1. Kopponen P., Sinkkonen S., Poso A., Gynther J., Karenlampi S. Sulfur analogues of polychlorinated dibenzo-p-dioxins, dibenzofurans and diphenyl ethers as inducers of CYP1A1 in mouse hepatoma cell culture and structure-activity relationships. Environ. Toxicol. Chem. 1994;13:1543–1548. doi: 10.1002/etc.5620130917. - DOI

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