Polychlorinated dibenzothiophenes (PCDTs) in leachates from landfills

Burszta‐Adamiak, Ewa; Kęszycka, Magdalena; Łomotowski, Janusz

doi:10.1201/b10566-30

Cited by 5 publications

(5 citation statements)

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“…The understanding of the reaction mechanism is crucial for any attempt to prevent PCTA/DTs. The high correlation between the concentrations of PCTA/DTs and PCDD/Fs in the environmental samples indicated the formation of PCTA/DTs involve analogous formation steps to the mechanism of formation of PCDD/Fs [ 25 , 26 , 27 ]. Under the pyrolysis or combustion conditions, CTPs can cause loss of the thiophenoxyl-hydrogen to form chlorothiophenoxy radicals (CTPRs).…”

Section: Introductionmentioning

confidence: 99%

Mechanistic and Kinetic Studies on the Homogeneous Gas-Phase Formation of PCTA/DTs from 2,4-Dichlorothiophenol and 2,4,6-Trichlorothiophenol

Shi

et al. 2015

IJMS

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Polychlorinated thianthrene/dibenzothiophenes (PCTA/DTs) are sulfur analogues compounds to polychlorinated dibenzo-p-dioxin/dibenzofurans (PCDD/Fs). Chlorothiophenols (CTPs) are key precursors to form PCTA/DTs. 2,4-DCTP has the minimum number of Cl atoms to form 2,4,6,8-tetrachlorinated dibenzothiophenes (2,4,6,8-TeCDT), which is the most important and widely detected of the PCDTs. In this paper, quantum chemical calculations were carried out to investigate the homogeneous gas-phase formation of PCTA/DTs from 2,4-DCTP and 2,4,6-TCTP precursors at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. Several energetically feasible pathways were revealed to compare the formation potential of PCTA/DT products. The rate constants of the crucial elementary reactions were evaluated by the canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) correction over a wide temperature range of 600–1200 K. This study shows that pathways that ended with elimination of Cl step were dominant over pathways ended with elimination of the H step. The water molecule has a negative catalytic effect on the H-shift step and hinders the formation of PCDTs from 2,4-DCTP. This study, together with works already published from our group, clearly illustrates an increased propensity for the dioxin formation from CTPs over the analogous CPs.

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Section: Introductionmentioning

confidence: 99%

Mechanistic and Kinetic Studies on the Homogeneous Gas-Phase Formation of PCTA/DTs from 2,4-Dichlorothiophenol and 2,4,6-Trichlorothiophenol

Shi

et al. 2015

IJMS

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“…The major known sources of PCDT/TAs in environment are combustion, emissions from municipal and hazardous waste incinerators as well as industrial incinerators [ 13 , 14 ]. High correlation between concentrations of PCDT/TAs and PCDD/Fs in the environmental samples revealed their similar formation mechanism under the pyrolysis or combustion conditions [ 11 , 15 , 16 ]. The most direct route to the formation of PCDT/TAs is the gas-phase reaction of chemical precursors.…”

Section: Introductionmentioning

confidence: 99%

Formation of Chlorotriophenoxy Radicals from Complete Series Reactions of Chlorotriophenols with H and OH Radicals

Shi

Zhang

et al. 2015

IJMS

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The chlorothiophenoxy radicals (CTPRs) are key intermediate species in the formation of polychlorinated dibenzothiophenes/thianthrenes (PCDT/TAs). In this work, the formation of CTPRs from the complete series reactions of 19 chlorothiophenol (CTP) congeners with H and OH radicals were investigated theoretically by using the density functional theory (DFT) method. The profiles of the potential energy surface were constructed at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants were evaluated by the canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) contribution at 600–1200 K. The present study indicates that the structural parameters, thermal data, and rate constants as well as the formation potential of CTPRs from CTPs are strongly dominated by the chlorine substitution at the ortho-position of CTPs. Comparison with the study of formation of chlorophenoxy radicals (CPRs) from chlorophenols (CPs) clearly shows that the thiophenoxyl-hydrogen abstraction from CTPs by H is more efficient than the phenoxyl-hydrogen abstraction from CPs by H, whereas the thiophenoxyl-hydrogen abstraction from CTPs by OH is less impactful than the phenoxyl-hydrogen abstraction from CPs by OH. Reactions of CTPs with H can occur more readily than that of CTPs with OH, which is opposite to the reactivity comparison of CPs with H and OH.

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“…20 High correlation between concentrations of PCDT/TA and PCDD/F in the environmental samples suggests that, both group form via similar operating mechanisms during homogeneous gas-phase reactions and heterogeneous pathways involving the catalytically assisted coupling of precursors. 21,22 These observations have prompted us to propose similar operating reactions for PCDT/TA formation from CTP and to pursue the elucidation of their formation based on an analogy to the mechanism of formation of PCDD/F. As a first step to confirm this suggestion, we consider gas-phase formation pathways.…”

Section: Introductionmentioning

confidence: 99%

Quantum Chemical Study on Formation of PCDT/TA from 2-Chlorothiophenol Precursor

Dar

Altarawneh

Dlugogorski

2013

Environ. Sci. Technol.

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This contribution investigates the thermochemical and kinetic parameters pertinent to the homogeneous gas-phase formation of two groups of pollutants, polychlorinated dibenzothiophenes (PCDT) and polychlorinated thianthrenes (PCTA) from their 2-chlorothiophenol (2-CTP) precursor. We compare the enthalpic profiles of the formation mechanism of PCDT/TA with the corresponding reactions involved in the gas-phase synthesis of PCDD/F (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, also known as dioxins). Overall, the presence of sulfur atoms greatly reduces the activation enthalpies of the rate determining steps in reference to the oxygenated system of PCDD/F. The rate constants of all elementary reactions are calculated using the transition state theory (TST) over a wide temperature range of 300-1200 K. We performed kinetic calculations for the formation of chlorinated dibenzothiophenes and chlorinated thianthrenes that could be applied to predict yields of these pollutants from 2-CTP up to ∼1200 K, that is, prior to the emergence of dechlorination and oxidation reactions. The results presented herein provide a greatly improved understanding of the gas-phase formation of the sulfur analogs of the notorious dioxins compounds.

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Polychlorinated dibenzothiophenes (PCDTs) in leachates from landfills

Cited by 5 publications

References 1 publication

Mechanistic and Kinetic Studies on the Homogeneous Gas-Phase Formation of PCTA/DTs from 2,4-Dichlorothiophenol and 2,4,6-Trichlorothiophenol

Mechanistic and Kinetic Studies on the Homogeneous Gas-Phase Formation of PCTA/DTs from 2,4-Dichlorothiophenol and 2,4,6-Trichlorothiophenol

Formation of Chlorotriophenoxy Radicals from Complete Series Reactions of Chlorotriophenols with H and OH Radicals

Quantum Chemical Study on Formation of PCDT/TA from 2-Chlorothiophenol Precursor

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