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Article

Effect of Water Molecule on the Complete Series Reactions of Chlorothiobenzenes with H/·OH: A Theoretical Study

by
Yanan Han
1,
Siyuan Zheng
2,
Zhuochao Teng
1,
Mohammad Hassan Hadizadeh
1,
Qi Zhang
1,
Fei Xu
1,* and
Yanhui Sun
3
1
Environment Research Institute, Shandong University, Qingdao 266237, China
2
Institute for Energy and Climate, Forschungszentrum Jülich, 52425 Jülich, Germany
3
College of Environment and Safety Engineering, Qingdao University of Science & Technology, Qingdao 266042, China
*
Author to whom correspondence should be addressed.
Atmosphere 2022, 13(5), 849; https://doi.org/10.3390/atmos13050849
Submission received: 27 April 2022 / Revised: 13 May 2022 / Accepted: 18 May 2022 / Published: 23 May 2022
(This article belongs to the Special Issue New Insights into Secondary Organic Aerosol Formation)
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Versions Notes

Abstract

:
The chlorothiobenzenes (CTBs) are the principal precursors for the formation of polychlorinated thianthrene/dibenzothiophenes (PCTA/DTs), which have high toxicity and wide distribution in the environment. Under the pyrolysis or combustion conditions, CTBs can react with H/·OH radicals to form the chlorothiobenzyl radicals (CTBRs) through abstraction of the chlorothiobenzyl-hydrogen. The water molecule can play an important role in this process. The coupling of CTBRs is the essential first step in forming PCTA/DTs. In this paper, quantum chemical calculations were carried out to investigate the formation of CTBRs from the complete series reactions of 19 chlorothiobenzene (CTB) congeners with H/·OH radicals in the presence of the water molecule. Using the MPWB1K/6-311 + G(3df,2p)//MPWB1K/6-31 + G(d,p) energy level, schematic energy profiles were constructed with the water molecule and then compared with the non-hydrated case. The present study shows that structural parameters and thermal data, as well as CTBRs formation potential from CTBs, are strongly dominated by the chlorine substitution at the ortho-position of CTBs. Meanwhile, the water molecule can promote the CTBR formation from CTBs abstracted by H/·OH, which has a stronger catalysis effect on the H abstraction from CTBs by OH than from CTBs by H. This study may provide reference parameters for future experimental research, which would enhance measures to reduce dioxin emission and establish dioxin control strategies.

1. Introduction

Polychlorinated thianthrenes (PCTAs) and polychlorinated dibenzothiophenes (PCDTs) are two groups of chlorinated tricyclic aromatic heterocycles, which can be considered as two-sulfur-substituted of polychlorinated dibenzo-p-dioxins (PCDDs) compounds and one-sulfur-substituted of polychlorinated dibenzofurans (PCDFs) compounds, respectively. Therefore, PCTA/DTs exhibit physicochemical, geochemical, ecotoxicological, toxicological, lipophilic, and persistent properties similar to those displayed by PCDD/DFs, which are considered to be dioxin-like compounds [1,2,3,4,5,6,7].
The main sources of PCTA/DTs include a variety of combustion or thermal processes, such as municipal and hazardous waste incinerators, fly ash, stack gas, industrial incinerators, and the metal reclamation of the global environment via global distillation [8,9,10,11]. PCTA/DTs can transport and transform globally through the grasshopper hopping effect and are released into different media due to their resistance and stability to degradation by metabolic and chemical processes. In addition, they have been detected in a variety of environments, including atmosphere, soil/sediment, pulp mill effluents, petroleum spills, petroleum refineries, pine needles, and some aquatic organisms [1,2,3,7,12,13,14,15], causing further environmental pollution. Taking the dioxin atmospheric transformation as an example, an increase in dioxin concentrations can cause an increase in secondary organic aerosol (SOA) concentrations, worsening climatic conditions, and further affecting human health [16]. A significant positive linear correlation between the concentration of dioxins and SOA has been demonstrated by Bi et al. with a high linear correlation coefficient (r2) of 0.96 [17]. In addition, dioxins are eliminated from the atmosphere by migration, diffusion, and deposition, which are closely related to the distribution and temperature of the gas–solid phase [14]. Dioxin-like compounds in the gas phase can be removed by reaction with ·OH radicals or photodegradation, while those in the particulate phase are mainly transferred to the soil and aquatic environment through dry and wet sedimentation [18,19]. Therefore, since PCTA/DTs are extremely toxic and ubiquitous, gaining detailed insights into their formation will deepen our understanding of the formation mechanisms of dioxin-like compounds, which could provide basic input parameters for dioxin formation prediction models and enhance measures to reduce dioxin emission and establish dioxin control strategies. PCTA/DTs are not intentionally synthesized for commercial purposes, rather they are produced as unwanted byproducts of various combustion and thermal processes [17,18,19,20]. It has been well-established that the formation mechanisms of PCTA/DTs contain homogeneous gas-phase reactions and heterogeneous catalytic mechanisms carried out by coupling of precursors [15,21]. Among them, the most direct route to form PCTA/DTs is through the gas-phase reaction from chemical precursors. Chlorothiobenzenes (CTBs) have been demonstrated to be the most important precursors of PCTA/DTs [22,23,24], which are widely used in large quantities in insecticides, printing inks, polyvinyl chloride, tire industry, pharmaceuticals, and dye manufacturing [25,26]. Under high-temperature conditions, CTBs can readily form chlorothiobenzyl radicals (CTBRs) through losing sulfhydryl-hydrogen via direct H loss or abstraction reactions by H, ·OH, Cl, and O(3P). The homogeneous gas-phase formation of PCTA/DTs contains the radical/radical coupling of CTBRs and radical/molecule recombination of CTBR and CTB [23,24,27,28,29,30]. PCTA/DTs formation is widely considered to be more dependent on the radical/radical condensation mechanism than the radical/molecule mechanism. However, Zuo et al. recently found that radical/molecule coupling of 2-chlorobenzyl radical (2-CBR) with 2-chlorobenzene(2-CB) to form pre-PCDD/DF intermediates has a very high potential barrier, whereas radical/molecule coupling of 2-CTBR with 2-CTB to form pre-PCDT intermediates is almost barrierless [30]. This indicates that PCTA/DT formation is largely governed by the radical/molecule pathway [30]. For both radical/radical and radical/molecule pathways, the formation of CTBRs from CTBs is the initial and most significant step in PCTA/DT formation.
Water is the third most abundant species in the atmosphere after N2 and O2, with a typical gas-phase concentration of 7.64 × 1017 molecules cm−3, corresponding to 50% of relative humidity at 298 K. Water has long been considered a subject of chemical interest due to its abundance and unique properties, especially its ability to form hydrogen bonds. Water introduces many unusual features into kinetics and energetics of chemical and biological reaction systems. Water vapor is an ubiquitous and abundant part of waste incineration and industrial operations. In real-world waste incineration, the original waste contains an amount of water. Additionally, flue gases are quenched with cooling water at the end of furnace operations in some plants. Consequently, the effect of water on dioxin formation should be studied, especially the formation of CTBR from CTBs. Several experimental and theoretical studies have been performed to illustrate the influence of water on PCDD/DF and PCTA/DT formations [26,31,32,33,34,35,36], but no agreement has been reached. Shao et al. found that the introduction of the water can reduce PCDD/DFs formation by 96%, while it can increase the percentage of low-chlorinated PCDD/DFs [31]. Li et al. studied the effect of water on de novo PCDD/DF formation in a fixed-bed apparatus and found that water could promote the formation of PCDD/DFs by activating fly ash. However, in the presence of CuCl2, water tends to inhibit PCDD/DF formation [32]. It was observed by Briois et al. that the introduction of the water significantly reduced yields of all PCDD/DF forms, which could play a more important role in the isomer distribution of PCDF compounds than of PCDD [33]. Stieglitz et al. found that the addition of water may have more effective catalytic activity in the formation of PCDDs than of PCDFs [34]. Jay et al. reported that the presence of water vapor can decrease the detection of PCDD and PCDF, while the amount of chlorobenzenes remained unaffected [35]. Shi et al. found that water molecules can promote the formation of PCDD/DFs via the H abstraction reactions of chlorobenzenes (CBs) by H/·OH and the H-shift step of PCDF formation through proton transfer reactions via a bridged ring [36]. The water molecule can lower the reaction energy barriers of the H abstractions from CBs by atomic H and OH, and thus enhance the formation potential of chlorobenzyl radicals (CBRs). However, Xu et al. indicated that the water molecule might have a negative catalytic effect on the H-shift step and hinder the formation of PCDTs from CTBs [29]. The effect of water molecule on the formation of CTBRs is still unclear. In recent studies, we performed quantum chemistry to investigate the complete series of reactions occurring between CTBs and H and ·OH without the involvement of water [37]. Accordingly, we extended and supplemented our previous studies in this field using the density functional theory (DFT) to further examine the influence of water on the formation of CTBR from CTBs containing H and ·OH [37]. The CTBR formations from CTBs with H and ·OH were compared with those of CBR formations from CBs aided by the water molecule [36]. The current results, as well as those obtained in our previous studies, can be used to establish a theoretical basis to improve dioxin formation mechanisms, reduce dioxin emission risks, and establish dioxin control strategies [29,38,39].

2. Results and Discussion

2.1. Effect of Water on the Structural Parameters of Chlorothiobenzene Molecules

Due to the number of chlorine substitutions of thiobenzene (TBe), hydrated CTBs have 19 congeners, including three hydrated monochlorothiobenzenes (2-CTB-H2O, 3-CTB-H2O, and 4-CTB-H2O), six hydrated dichlorothiobenzenes (2,3-DCTB-H2O, 2,4-DCTB-H2O, 2,5-DCTB-H2O, 2,6-DCTB-H2O, 3,4-DCTB-H2O, and 3,5-DCTB-H2O), six hydrated trichlorothiobenzenes (2,3,4-TCTB-H2O, 2,3,5-TCTB-H2O, 2,3,6-TCTB-H2O, 2,4,5-TCTB-H2O, 2,4,6-TCTB-H2O, and 3,4,5-TCTB-H2O), three hydrated tetrachlorothiobenzenes (2,3,4,5-TeCTB-H2O, 2,3,4,6-TeCTB-H2O, and 2,3,5,6-TeCTB-H2O), and hydrated pentachlorothiobenzenes (PCTB-H2O).
The structures of CTB-H2O complexes along with the structure of TBe-H2O are presented in Figure 1 and Figure S1. Among the 19 hydrated CTBs, due to the different ortho-substitution patterns of hydrated TBe, hydrated CTBs contain three kinds of congeners: Hydrated CTBs with two ortho-chlorine substituents (2,6-DCTB-H2O, 2,3,6-TCTB-H2O, 2,4,6-TCTB-H2O, 2,3,4,6-TeCTB-H2O, 2,3,5,6-TeCTB-H2O, and PCTB-H2O), hydrated CTBs with two ortho-hydrogen substituents (3-CTB-H2O, 4-CTB-H2O, 3,4-DCTB-H2O, 3,5-DCTB-H2O, and 3,4,5-TCTB-H2O), and hydrated CTBs with one ortho-chlorine substituent and one ortho-hydrogen substituent (2-CTB-H2O, 2,3-DCTB-H2O, 2,4-DCTB-H2O, 2,5-DCTB-H2O, 2,3,4-TCTB-H2O, 2,3,5-TCTB-H2O, 2,4,5-TCTB-H2O, and 2,3,4,5-TeCTB-H2O). In particular, CTB-H2O complexes with one ortho-hydrogen atom have two conformers. A conformer with sulfhydryl-hydrogen pointing toward the closest neighboring Cl is referred to as a syn-conformer; otherwise, it is called an anti-conformer (Figure 2). For a given CTB-H2O complex, the syn-conformer is about 0.7 kcal mol−1 more stable than the corresponding anti-form, suggesting a stabilization effect caused by intramolecular hydrogen bonding. Therefore, throughout this paper, CTB-H2O complexes denote the syn-conformers. The electron density from total SCF density of 2-CTB, 3-CTB, 2,6-DCTB, 2-CTB-H2O, 3-CTB-H2O, and 2,6-DCTB-H2O at MPWB1K/6-311 + G(3df,2p) level are listed in Figure S2 of Supplementary Materials.
To further investigate the effect of water on the strength as well as the reactivity of the S−H bonds in CTBs, we also calculated the S−H bond lengths, L(S−H), and the S−H dissociation energies, D0(S−H), in hydrated CTBs. The values calculated at the MPWB1K/6-311 + G(3df,2p)//MPWB1K/6-31 + G(d,p) level are presented in Table 1 and compared with the values of the non-hydrated cases [11]. In Table 1, the S−H bond lengths are longer by 0.01 Å in hydrated CTBs compared with those values in non-hydrated cases [37]. At the same time, the S−H bond dissociation energies are lower by 0.53−10.25 kcal mol−1 in hydrated CTBs compared with those values in non-hydrated cases, except for 2,6-DCTB, 2,3,6-TCTB, and 2,3,5,6-TeCTB [37]. The hydration of CTBs appears to increase its bond lengths and decrease the strength of the O−H bonds, resulting in the enhancement of S−H reactivity. It is interesting to note that the hydrogen bond between the chlorothiobenzyl-sulfur of CTBs and the water hydrogen atom attracts the electron density from the sulfhydryl group, thus weakening the strength of the S−H bonds in hydrated CTBs. Therefore, the chlorothiobenzyl-hydrogen in hydrated CTBs can be inferred to be more easily abstracted by H/·OH than non-hydrated CTBs, which can be further demonstrated in the energy analysis below.
The structures of CTBR-H2O complexes along with the structure of chlorothiobenzyl-H2O radicals are presented in Figure 1 and Figure S3. For CTBRs with one or two hydrogen atoms at the ortho-positions, CTBR-H2O complexes have a six-member-ring-like structure, in which CTBR and water both act as hydrogen donors and acceptors. There are two hydrogen bonds formed, ·O–H and ·S–H. For CTBRs with two chlorine atoms at the ortho-positions, CTBR-H2O complexes have a five-member-ring-like structure, in which CTBR acts as a hydrogen acceptor and water acts as a hydrogen donor. As a result, the hydrogen atom in the water binds to the chlorothiobenzyl-sulfur and ortho-chlorine atoms of CTBs simultaneously and forms two hydrogen bonds. A comparison of the S−C bond lengths of hydrated CTBRs at the MPWB1K/6-31 + G(d,p) level with the non-hydrated cases [37] is given in Table 1, where the S−C bond lengths are shorter by 0.00−0.05 Å in hydrated CTBRs than those values in non-hydrated cases. Meanwhile, the hydration of CTBRs appears to decrease their S−C bond lengths and increase the stability of CTBRs compared with CTBRs in non-hydration cases.

2.2. H Abstraction from CTB-H2Os by H Atom

The schematic energy profile involved in the aid of water molecule on the chlorothiobenzyl-hydrogen abstraction from hydrated TBe, 2-CTB, 3-CTB, and 2,6-DCTB by H atom is illustrated in Figure 3. The schematic energy profile in the absence of water (non-hydrated case) is presented in Figure 3 as well to better determine its effect. Meanwhile, the schematic energy profiles of other CTBs are displayed in Figure S4. In the case of the water-assisted reaction, it is most probable that one reactant first forms a complex with water, and then reacts with the third reactant in this chain. However, the direct complexation of H with water is difficult. Therefore, as shown in Figure 3, for the water-assisted H abstraction from CTBs by H atom, the water molecule is first added to CTB to form a CTB-H2O complex, which continues to react with H, where the calculated binding energy is −1.66 to −0.49 kcal mol−1 to form CTB-H2O complexes. The H abstraction from CTB-H2O complexes proceeds through a hydrated transition state to form a post-reactive hydrogen-bonded complex CTBR-H2O, prior to the release of the products, CTBR and H2. The hydrated transition states were located at the MPWB1K/6-31 + G(d,p) level. They were confirmed by only one negative eigenvalue of the Hessian matrix, thus by one imaginary frequency.
The structures of the 2-CTB-H2O-H, 3-CTB-H2O-H, and 2,6-CTB-H2O-H transition states were located at the MPWB1K/6-31 + G(d,p) level and are shown in Figure 1, and the remaining structures are shown in Figure S5. Similar to the conformations of CTB-H2Os and CTBR-H2Os, there is a six-member-ring-like structure for the hydrated CTB-H2O-H transition states with one or two hydrogen atoms at the ortho-positions, which is stabilized by two hydrogen O−H and S−H bonds. In contrast, there is a five-member-ring-like structure for the hydrated transition states with two chlorine atoms at the ortho-positions. Therefore, the hydrogen atom in the water binds simultaneously to the chlorothiobenzyl-sulfur atom and ortho-chlorine atom of CTBs and forms two hydrogen bonds. The S−H and S−C bonds in CTB-H2Os complexes with ortho-substitution (1.332−1.334 Å for S−H, and 1.753−1.763 Å for S−C) are systematically shorter than those without ortho-substitution (1.333−1.337 Å for S−H, and 1.762−1.780 Å for S−C). In addition, all of the ortho-substituted transition states have relatively longer S−H bond lengths (1.394−1.402 Å) compared with those without ortho-substitution (1.388−1.401 Å).
As shown in Figure 3, the potential barrier is the relative energy of the transition state with respect to the total energy of the separated reactants (the corresponding CTB, H, OH, and H2O), without considering the very shallow pre-reactive intermediate, where the reaction heat is the relative energy of the total energy of the separated product (the corresponding CTBR, H2, and H2O) with respect to the total energy of the separated reactants, and without considering the post-reactive complex. It can be seen in Figure 3 that the most notable change between the non-hydrated and hydrated cases is the potential barrier. In the introduction of the water molecule, the potential barrier for the chlorothiobenzyl-hydrogen abstraction from 2-CTB by H is decreased from 3.42 to 1.48 kcal mol−1. As shown in Figure 3 and Figure S4 of Supplementary Materials, the potential barriers are also evidently decreased for other CTBs with the addition of a water molecule. The presence of water appears to weaken the reactivity of the S−H bonds in CTBs and stabilize the CTB-H2O-H transition state, resulting from the existence of the hydrogen bonds in the hydrated CTBs and transition states. Therefore, the introduction of the water molecule can promote the formation of CTBRs from the H abstraction reactions of CTBs with the H atom.
Table 2 provides the potential barriers and reaction heats of chlorothiobenzyl-hydrogen abstraction from hydrated CTBs by H obtained at the MPWB1K/6-311 + G(3df,2p)//MPWB1K/6-31 + G(d,p) level. To better determine the effect of water, the values of non-hydrated cases [37] and the difference between the non-hydrated and hydrated cases, ΔE−ΔEH2O at the same level are also presented in Table 2. From Table 2, the potential barriers are significantly correlated with the position of the chlorine substitution at the thiobenzlic ring, but not with the number of chlorine substituents. For example, for dichlorothiobenzenes, the potential barriers of the chlorothiobenzyl-hydrogen abstraction from 2,3-DCTB, 2,4-DCTB, 2,5-DCTB, and 2,6-DCTB are higher than those from 3,4-DCTB and 3,5-DCTB. For trichlorothiobenzenes, the potential barriers of the phenoxyl-hydrogen abstraction from 2,3,4-TCTB, 2,3,5-TCTB, 2,3,6-TCTB, 2,4,5-TCTB, and 2,4,6-TCTB are higher than those from 3,4,5-TCTB. Evidently, for a given number of chlorine substitutions, the potential barriers for the chlorothiobenzyl-hydrogen abstraction from the ortho-substituted CTBs are consistently higher than those for other structural conformers. The chlorine substitution at the ortho-position can lower the barrier heights of chlorothiobenzyl-hydrogen abstraction from CTBs by H. Intramolecular hydrogen bond appears to stabilize the CTBs and reduce the reactivity of S−H bonds in CTBs with the ortho-substitution. A similar result was also observed in our previous study of CBs with H [39].

2.3. H Abstraction from CTB-H2Os by ·OH Radicals

The schematic energy profile involved in the aid of water molecule of the chlorothiobenzyl-hydrogen from hydrated 2-CTBs, 3-CTBs, and 2,6-CTBs by ·OH is illustrated in Figure 4, as well as the schematic energy profile for the case where no water is present (non-hydrated). The schematic energy profiles of other CTBs are displayed in Figure S6. The reaction pathway begins with the barrierless formation of a pre-reactive hydrogen-bonded intermediate, occurring between the reaction and transition state in a hydrated case. Since both CTB and ·OH can form hydrogen-bonded complexes with water, there are two pre-reactive intermediates that can be formed for the water-assisted H abstraction from CTBs by ·OH radical. In one mechanism of the water-assisted reaction, the water molecule is first added to CTB to form a CTB-H2O complex, which continues to react with ·OH to form a CTB-H2O-OH adduct. In the other mechanism, the water molecule is first added to ·OH to form an ·OH-H2O complex, which then combines with CTB to form the CTB-H2O-OH adduct, as presented in Figure 1 and Figure S7. As shown in Figure 4 and Figure S6, the calculated binding energies for the formation of CTB-H2O and ·OH-H2O complexes are −1.66 to −0.49 and −3.73 kcal mol−1, respectively. In the non-hydrated intermediates, pre-reactive CTBs-OH adducts also exist [37], and the formation of the non-hydrated CTB-OHs adducts releases −1.71 to −0.59 kcal mol−1 with respect to the energy of CTB + OH adducts [37]. The CTB-H2O-OH adduct proceeds through a hydrated CTB-H2O-OH transition state to form a post-reactive hydrogen-bonded CTBR-H2O complex + H2O or H2O-H2O complex + CTBR, prior to the release products (CTBR and other two H2O molecules).
The structures of the hydrated transition states of the H abstraction from CTB-H2Os by ·OH radical at the MPWB1K/6-31 + G(d,p) level were illustrated in Figure 1 and Figure S8. There is a six-member ring structure for all the hydrated transition states, and thus two hydrogen bonds are formed. One hydrogen bond is the O−H(2) formed between the oxygen of the water and the hydrogen of the ·OH radical, and another one is the S−H(1) bond formed between the chlorothiobenzyl-sulfur of CTBs and a hydrogen atom of the water. It should be noted that in the case of non-hydrated intermediates, only one hydrogen bond is formed between the chlorothiobenzyl-hydrogen atom of CTB and the oxygen atom of ·OH radical [37]. In Figure 1 and Figure S8, the ortho-substitution also impacts other essential structural parameters of the hydrated transition states. Generally, for the given number of chlorine substitutions, the breaking S−H(1) bonds in the ortho-substituted transition states are shorter than those without ortho-substitution, while the forming O−H(2) bonds in the transition states with ortho-substitution are longer than those without ortho-substitution. For example, the S−H(1) bond lengths of hydrated transition states for 2,3-CTB-H2O-OH, 2,4-CTB-H2O-OH, 2,5-CTB-H2O-OH, and 2,6-CTB-H2O-OH are 1.756, 1.754, 1.755, and 1.752 Å, which are shorter than those of 1.760 and 1.760 Å for 3,4-CTB-H2O-OH and 3,5-CTB-H2O-OH. Similarly, the O−H(2) bond lengths of hydrated transition states for 2,3-CTB-H2O-OH, 2,4-CTB-H2O-OH, 2,5-CTB-H2O-OH, and 2,6-CTB-H2O-OH are 1.888, 1.889, 1.884, and 1.871 Å, which are longer than those of 1.861 and 1.859 Å for 3,4-CTB-H2O-OH, and 3,5-CTB-H2O-OH.
As shown in Figure 4 and Figure S6, for hydrated 2-CTB, there is a pre-reactive intermediate 2-CTB-H2O-OH prior to the transition state, and the energy of the 2-CTB-H2O-OH adduct is 6.07 kcal mol−1 below the total energy of 2-CTB + ·OH + H2O. In addition, for non-hydrated 2-CTB, there is a pre-reactive intermediate 2-CTB-OH prior to the transition state, and the energy of the 2-CTB-OH adduct is 0.90 kcal mol−1 below the total energy of 2-CTB + ·OH. Therefore, the formation of the 2-CTB-H2O-OH adduct in the hydrated case is more energetically favorable than the 2-CTB-OH adduct in the non-hydrated case. Moreover, the energy of the hydrated transition state lies 4.00 kcal mol−1 below the total energy of 2-CTB + ·OH + H2O (Figure 4), whereas the energy of the non-hydrated transition state lies 8.67 kcal mol−1 above the separated reactants [37]. A hydrated transition state is characterized by a potential barrier of 2.07 kcal mol−1 relative to the pre-reactive intermediate 2-CTB-H2O-OH, while the non-hydrated transition state is characterized by a barrier of 9.57 kcal mol−1 relative to the pre-reactive intermediate 2-CTB-OH. [37]. Therefore, it is evident that the introduction of water promotes the H abstraction from CTBs by ·OH radical by lowering the potential barrier. The presence of water appears to weaken the reactivity of the S−H bonds in CTBs and stabilize the CTB-H2O-OH transition state.
Table 3 illustrates the potential barriers and reaction heats of chlorothiobenzyl-hydrogen abstraction from hydrated and non-hydrated CTBs by ·OH obtained at the MPWB1K/6-311 + G(3df,2p)//MPWB1K/6-31 + G(d,p) level. The potential barrier difference between the non-hydrated and hydrated cases, ΔE−ΔEH2O, is also presented in Table 3 to determine the influence of the water molecule. It can be seen in Table 3, that for each CTBs, the introduction of the water molecule can promote the H abstraction from CTBs by ·OH radical by lowering the potential barrier. Additionally, for a given number of chlorine substitutions, the potential barriers for the chlorothiobenzyl-hydrogen abstraction from the ortho-substituted CTBs by ·OH in the existence of water molecule are consistently higher than those for other structural conformers. For example, in the case of trichlorothiobenzenes in the introduction of the water molecule, the potential barriers of the chlorothiobenzyl-hydrogen abstraction from 2,3,4-TCTB, 2,3,5-TCTB, 2,3,6-TCTB, 2,4,5-TCTB, and 2,4,6-TCTB by ·OH are −4.25, −3.69, −4.06, −4.33, and −4.23 kcal mol−1, which are higher than the value of −6.23 kcal mol−1 from 3,4,5-TCTB by ·OH. This reaffirms the conclusion above that the chlorine substitution at the ortho-position increases the strength of the S−H bonds and decreases their reactivity. Similar to the chlorothiobenzyl-hydrogen abstraction by H, the difference between the non-hydrated and hydrated cases, ΔE−ΔEH2O, from CTBs with two ortho-chlorine substituents by ·OH are higher than in others. For example, in the case of tetrachlorothiobenzenes, the ΔE−ΔEH2O of the chlorothiobenzyl-hydrogen abstraction from 2,3,4,5-TeCTB in the introduction of the water molecule is 13.52 kcal mol−1, which is higher than the value of 14.82 and 14.97 kcal mol−1 from 2,3,4,6-TeCTB and 2,3,5,6-TeCTB by ·OH in the introduction of the water molecule.

2.4. Comparison of H Abstraction from CTB-H2Os by H and ·OH

A comparison of the values presented in Table 2 and Table 3 shows that for a given CTB, the potential barrier for the chlorothiobenzyl-hydrogen abstraction by ·OH in the introduction of the water molecule is approximately 5−8 kcal mol−1 lower than the chlorothiobenzyl-hydrogen abstraction by H in the introduction of the water molecule, which indicates that the water-assistant H abstraction from CTBs by ·OH is more likely to occur than the chlorothiobenzyl-hydrogen abstraction by H. This is entirely contrary to the non-hydrated fact that chlorothiobenzyl-hydrogen abstraction from CTBs by ·OH is less impactful than the chlorothiobenzyl-hydrogen abstraction by H [37]. Additionally, it is also necessary to compare the ΔE−ΔEH2O values between chlorothiobenzyl-hydrogen abstraction from CTBs by H and ·OH. A larger value of ΔE−ΔEH2O indicates a more significant reduction in the potential barrier from the non-hydrated case to the hydrated case, which indicates that the water molecule has a more pronounced catalytic effect. More specifically, in Table 2 and Table 3, the ΔE−ΔEH2O values for chlorothiobenzyl-hydrogen abstraction from CTBs by H are in the range of 0.81 to 2.38 kcal mol−1, which are considerably lower than those of 12.67 to 14.97 kcal mol−1 for chlorothiobenzyl-hydrogen abstraction from CTBs by ·OH. This indicates that the water molecule has a more effective catalysis effect on the H abstraction from CTBs by ·OH than from CTBs by H.

2.5. Comparison of H Abstraction from CB-H2Os and CTB-H2Os by H/·OH

Notably, it is also interesting to compare the phenoxyl-hydrogen abstraction from hydrated CBs by H and ·OH along with chlorothiobenzyl-hydrogen abstraction from hydrated CTBs by H and ·OH. The potential barriers and reaction heats obtained in our previous studies of phenoxyl-hydrogen abstraction from CBs by H/·OH with and without water [36,38,39], are shown in Tables S1 and S2 of Supplementary Materials, respectively. The difference between the non-hydrated and hydrated cases, ΔE−ΔEH2O, is also calculated and shown in Tables S1 and S2. To be displayed and compared more clearly, all the values of CB-H2Os with H/·OH as well as the values of CTB-H2Os with H/·OH are drawn as histograms and shown in Figure 5 and Figure 6.
As presented in Table 2 and Table S1, the potential barriers for the chlorothiobenzyl-hydrogen abstractions from CTBs by H in the introduction of the water molecule are in the range of 0.12 to 3.62 kcal mol−1, which are considerably lower than the values of 7.92 to 12.79 kcal mol−1 from the phenoxyl-hydrogen abstraction by H in the introduction of the water molecule. This indicates that water-assistant H abstractions from CTBs by H are more likely to occur than those from CBs by H. A comparison of the ΔE−ΔEH2O values between H abstractions from CTBs by H and CBs by H shows that for the given CTB and CB, the ΔE−ΔEH2O value for chlorothiobenzyl-hydrogen abstraction from CTB by H is similar to the value for phenoxyl-hydrogen abstraction from CB by H. This indicates that the water molecule has an analogous catalytic effect on the H abstractions from CTBs by H and CBs by H.
From Table 3 and Table S2, in the introduction of the water molecule, the potential barriers for the chlorothiobenzyl-hydrogen abstractions from CTBs by ·OH radical are −6.29 to −3.69 kcal mol−1, which are lower than the values of −4.83 to −0.82 kcal mol−1 from the phenoxyl-hydrogen abstraction by ·OH. This implies that, energetically, ·OH radicals are more likely to extract H from CTBs than from CBs. As can be seen in Table 3 and Table S2, the ΔE−ΔEH2O values for chlorothiobenzyl-hydrogen abstraction from CTBs by ·OH are in the range of 12.67 to 14.97 kcal mol−1, which are considerably higher than those of 3.84 to 6.40 kcal mol−1 for phenoxyl-hydrogen abstraction from CBs by ·OH. A larger value of ΔE–ΔEH2O indicates a more significant decrease in the potential barrier, which indicates that the catalytic effect of water is more pronounced. Therefore, the water molecule can play a considerably more positive catalytic role in the H abstraction from CTBs by ·OH than from CBs by ·OH.
Our previous study has investigated the homogeneous gas-phase formation of PCTA/DTs from 2,4-DCTB precursors. The water molecule has a negative catalytic effect on the H-shift step and hinders the formation of PCDTs from 2,4-DCTB by an increase in the potential barrier of 16 kcal/mol. In this study, in the initial step of PCDF formation (CTBR formation), the water molecule has a positive catalytic effect by the decrease in the potential barrier of 1–2 kcal/mol by H and 12–15 kcal/mol by ·OH. Therefore, considering the two elementary steps, the water molecule has a negative catalytic effect on the formation of PCDTs. This agrees well with Stieglitz and Jay’s experimental studies that the presence of water vapor can decrease the detection of PCDF [34,35]. The cartesian coordinates of hydrated reactants CTB-H2Os, transition states, CTBR-H2Os, and pre-reactive intermediates are listed in Tables S3–S7 of Supplementary Materials.

3. Materials and Methods

3.1. Density Functional Theory

A high-accuracy quantum chemical calculation was performed using the Gaussian 09 software suite [40], along with the hybrid DFT functional MPWB1K [41], to calculate chemical structures, energies, and frequencies of reactants, transition states, and products. This computational approach was selected due to its excellent performance in thermochemistry, thermochemical kinetics, hydrogen bonding, and weak interactions. The geometrical parameters calculations were performed at the MPWB1K level with a standard 6-31 + G(d,p) basis set. At the same level, a vibrational frequency analysis was performed to verify the nature of the stationary point, the zero-point energy (ZPE) [41], and the thermal contribution to the free energy of activation. There was no imaginary frequency in the minima, while the transition states had a single imaginary frequency. Additionally, the complete reactions discussed in this paper were verified using intrinsic reaction coordinate (IRC) calculations and the minimum energy path (MEP) analysis for each transition state [42]. In both directions, the final structures of the IRC have been further optimized to find out which transition states are related to which desired minima [42]. To obtain more reliable potential barriers and reaction heats, single-point energy calculations were performed at the MPWB1K/6-311 + G(3df,2p) level based on the optimized geometries. The schematic energy profiles were constructed at the same level, and ZPE corrections were applied to all of the relative energies cited and discussed in this paper.

3.2. Accuracy Verification

Our previous research on the reaction of chloro(thio)benzenes with H/·OH has demonstrated the validity and accuracy of this method for the calculation of geometry, vibrational frequency, and energy at the MPWB1K/6-311 + G(3df,2p)//MPWB1K/6-31 + G(d,p) level [37,38,39]. The optimized geometries of thiobenzene and the calculated vibrational frequencies of thiobenzene and 4-chlorothiobenzene at the MPWB1K/6-31 + G(d,p) level are consistent with the available experimental values, and the relative deviation remains within 1.0% for the geometry parameters and 9.0% for the vibrational frequencies [37]. In addition, we calculated the S–H bond dissociation energy for the reaction of thiobenzene → chlorothiobenzyl + H at the MPWB1K/6-311 + G(3df,2p)//MPWB1K/6-31 + G(d,p) level [37]. The calculated value of 86.51 kcal/mol at 298.15 K and 1.0 atm was in excellent agreement with the corresponding experimental value of 86.5 kcal/mol [42]. To better determine the influence of water molecules in these essential reactions, we selected the same level for the subsequent calculations.

4. Conclusions

In this study, the effect of the water molecule in the homogeneous formation of CTBRs from CTBs with H/·OH was investigated by the DFT theory. All of the calculations were at the MPWB1K/6-311 + G(3df,2p)//MPWB1K/6-31 + G(d,p) level, including the geometry, vibrational frequency, and energy calculations. The structure parameters and energy changes of all reactants, products, pre-reaction complexes, and transition states during the formation of CTBRs from hydrated CTRs are discussed. The following conclusions can be drawn by comparing this study with our previous studies on the formation of CBRs and CTBRs from CBs and CTBs with H/·OH in the presence or absence of water:
  • The presence of water appears to weaken the reactivity of the S–H bonds in CTBs and stabilize the CTB-H2O-H and CTB-H2O-OH transition states, resulting from the existence of the hydrogen bonds in the hydrated CTBs and transition states. Therefore, the introduction of the water molecule can promote the formation of CTBRs from the chlorothiobenzyl-hydrogen abstraction reactions of CTBs with H/·OH.
  • The structural parameters and thermal data as well as the formation potential of CTBRs from CTBs by H and ·OH are strongly dominated by the chlorine substitution at the ortho-position of CTBs, but not by the number of the chlorine substituents.
  • The water-assistant H abstraction from CTBs by ·OH occurs more easily than the chlorothiobenzyl-hydrogen abstraction by H; the water molecule has a more effective catalytic effect on the H abstraction from CTBs by ·OH than from CTBs by H.
  • The water-assistant H abstractions from CTBs by H/·OH are more likely to occur than those from CBs by H/·OH; the water molecule can play a considerably more positive catalytic role in the H abstraction from CTBs by H/·OH than from CBs by H/·OH.

Supplementary Materials

The following Supplementary Materials can be downloaded at: https://www.mdpi.com/article/10.3390/atmos13050849/s1, Figure S1: Structures of the hydrated reactants CTB-H2Os. Distances are in angstrom, Figure S2: Electron density from total SCF density of 2-CTB, 3-CTB, 2,6-DCTB, 2-CTB-H2O, 3-CTB-H2O and 2,6-DCTB-H2O at MPWB1K/6-311+G(3df,2p) level, Figure S3: Structures of the hydrated products CTBR-H2Os, Figure S4: The schematic energy profiles of the H abstraction from CTBs by H atom with and without the aid of water, Figure S5: Structures of the CTB-H2O-H transition states for H abstraction from CTBs by H atom, Figure S6: The schematic energy profiles of the H abstraction from CTBs by OH radicals in hydrated and non-hydrated cases, Figure S7: Structures of the CTB-H2O-OH pre-reactive intermediates of the H abstraction from CTBs by ·OH radical. Figure S8. Structures of the CTB-H2O-OH transition states of the H abstraction from CTBs by ·OH radical, Table S1: Potential barriers ΔE and reaction heats ΔH of the H abstraction from CBs by H atom in hydrated and non-hydrated cases, Table S2: Potential barriers ΔE and reaction heats ΔH of the H abstraction from CBs by OH radical in hydrated and non-hydrated cases, Table S3: Cartesian coordinates of the hydrated reactants CTB-H2Os, Table S4: Cartesian coordinates of the hydrated CTB-H2O-H transition states for H abstraction from CTBs by H atom, Table S5: Cartesian coordinates of the hydrated products CTBR-H2Os, Table S6: Cartesian coordinates of the hydrated CTB-H2O-OH pre-reactive intermediates for H abstraction from CTBs by ·OH radical, Table S7: Cartesian coordinates of the hydrated CTB-H2O-OH transition states for H abstraction from CTBs by ·OH radical.

Author Contributions

Y.H. designed and performed the mechanism calculations; S.Z., Z.T. and Q.Z. prepared the Tables and Figures; M.H.H., F.X. and Y.S. analyzed the data in the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (project Nos. 21876102 and 21976107), the Fundamental Research Funds of Shandong University (No. 2016WLJH51), and the China Postdoctoral Science Foundation funded project (Nos. 2017M612277 and 2017T100493).

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflict of interest.

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. [Google Scholar] [CrossRef]
  2. 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. [Google Scholar] [CrossRef]
  3. Sinkkonen, S. New Types of Persistent Halogenated Compounds; Springer: Berlin/Heildeberg, Germany, 2000; Volume 3, pp. 289–314. [Google Scholar]
  4. Puzyn, T.; Rostkowski, P.; Świeczkowski, 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. [Google Scholar] [CrossRef]
  5. 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. Int. J. 1994, 13, 1543–1548. [Google Scholar] [CrossRef]
  6. Weber, R.; Hagenmaier, H.; Schrenk, D. Elimination kinetics and toxicity of 2,3,7,8-tetrachlorothiantheren, a thio analogue of 2,3,7,8-TCDD. Chemosphere 1998, 36, 2635–2641. [Google Scholar] [CrossRef]
  7. Nakai, S.; Kishita, S.; Nomura, Y.; Hosomi, M. Polychlorinated dibenzothiophenes in Japanese environmental samples and their photodegradability and dioxin-like endocrine-disruption potential. Chemosphere 2007, 67, 1852–1857. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  8. Nakai, S.; Espino, M.P.; Nomura, Y.; Hosomi, M. Detection of polychlorinated dibenzothiophenes (PCDTs) in the environmental samples and investigation of their photodegradability and dioxin-like endocrine disruption potentcy. J. Environ. Chem. Eng. 2004, 14, 835–844. [Google Scholar] [CrossRef] [Green Version]
  9. Sinkkonen, S.; Paasivirta, J.; Lahtiperä, M. Chlorinated and methylated dibenzothiophenes in sediment samples from a river contaminated by organochlorine wastes. J. Soil. Sediment. 2001, 1, 9–14. [Google Scholar] [CrossRef]
  10. Sinkkonen, S. Sources and environmental fate of PCDTs. Toxicol. Environ. Chem. 1998, 66, 105–112. [Google Scholar] [CrossRef]
  11. Sinkkonen, S. PCDTs in the environment. Chemosphere 1997, 34, 2585–2594. [Google Scholar] [CrossRef]
  12. Menon, S.; Hansen, J.; Nazarenko, L.; Luo, Y. Climate effects of black carbon aerosols in China and India. Science 2002, 297, 2250–2253. [Google Scholar] [CrossRef] [Green Version]
  13. Bi, C.; Chen, Y.; Zhao, Z.; Li, Q.; Zhou, Q.; Ye, Z.; Ge, X. Characteristics, sources and health risks of toxic species (PCDD/Fs, PAHs and heavy metals) in PM2.5 during fall and winter in an industrial area. Chemosphere 2020, 238, 124620. [Google Scholar] [CrossRef]
  14. Yu, F.; Cui, K.; Sheu, H.-L.; Hsieh, Y.-K.; Tian, X. Atmospheric concentration, particle-bound content, and dry deposition of PCDD/FS. Aerosol. Air Qual. Res. 2021, 21, 210059. [Google Scholar] [CrossRef]
  15. Koester, C.J.; Hites, R.A. Photodegradation of polychlorinated dioxins and dibenzofurans adsorbed to fly ash. Environ. Sci. Technol. 1992, 26, 502–507. [Google Scholar] [CrossRef]
  16. Lohmann, R.; Gioia, R.; Eisenreich, S.J.; Jones, K.C. Assessing the importance of ab-and adsorption to the gas-particle partitioning of PCDD/Fs. Atmos. Environ. 2007, 41, 7767–7777. [Google Scholar] [CrossRef]
  17. Buser, H.R. Identification and sources of dioxin-like compounds: I. Polychlorodibenzothiophenes and polychlorothianthrenes, the sulfur-analogues of the polychlorodibenzofurans and polychlorodibenzodioxins. Chemosphere 1992, 25, 45–48. [Google Scholar] [CrossRef]
  18. Sinkkonen, S.; Paasivirta, J.; Koistinen, J.; Tarhanen, J. Tetra-and pentachlorodibenzothiophenes are formed in waste combustion. Chemosphere 1991, 23, 583–587. [Google Scholar] [CrossRef]
  19. Sinkkonen, S.; Kolehmainen, E.; Koistinen, J.; Lahtiperä, M. High-resolution gas chromatographic-mass spectrometric determination of neutral chlorinated aromatic sulphur compounds in stack gas samples. J. Chromatogr. A 1993, 641, 309–317. [Google Scholar] [CrossRef]
  20. Sinkkonen, S.; Vattulainen, A.; Aittola, J.P.; Paasivirta, J.; Tarhanen, J.; Lahtiperä, M. Metal reclamation produces sulphur analogues of toxic dioxins and furans. Chemosphere 1994, 28, 1279–1288. [Google Scholar] [CrossRef]
  21. Czerwiński, J. Pathways of polychlorinated dibenzothiophenes (PCDTs) in the environment. Archi. Environ. Prot. 2008, 34, 169–181. [Google Scholar]
  22. Parette, R.; Pearson, W.N. 2,4,6,8-Tetrachlorodibenzothiophene in the Newark Bay Estuary: The likely source and reaction pathways. Chemosphere 2014, 111, 157–163. [Google Scholar] [CrossRef]
  23. Dar, T.; Altarawneh, M.; Dlugogorski, B.Z. Theoretical study in the dimerisation of 2-chlrothiophenol/2-chlorothiobenzyl: Precursors to PCDT/TA. Organohalog. Compd. 2012, 74, 657–660. [Google Scholar]
  24. Dar, T.; Altarawneh, M.; Dlugogorski, B.Z. Quantum chemical study on formation of PCDT/TA from 2-chlorothiophenol precursor. Environ. Sci. Technol. 2013, 47, 11040–11047. [Google Scholar] [CrossRef]
  25. Navarro, R.; Bierbrauer, K.; Mijangos, C.; Goiti, E.; Reinecke, H. Modification of poly(vinyl chloride) with new aromatic thiol compounds. Synthesis and characterization. Polym. Degrad. Stab. 2008, 93, 585–591. [Google Scholar] [CrossRef]
  26. Benz, T.; Hagenmaier, H.; Lindig, C.; She, J. Occurrence of the sulphur analogue of octachlorodibenzo-p-dioxin in the environment and investigations on its potential source. Fresen. J. Anal. Chem. 1992, 344, 286–291. [Google Scholar] [CrossRef]
  27. Yu, X.Q.; Chang, J.M.; Liu, X.; Pan, W.X.; Zhang, A.Q. Theoretical study on the formation mechanism of polychlorinated dibenzothiophenes/thianthrenes from 2-chlorothiophenol molecules. J. Environ. Sci. 2018, 66, 318–327. [Google Scholar] [CrossRef]
  28. Wang, H.; Zuo, C.; Zheng, S.; Sun, Y.; Xu, F.; Zhang, Q. Mechanistic and Kinetic Study on Self-/Cross-Condensation of PCTA/DT Formation Mechanisms from Three Types of Radicals of 2,4-Dichlorothiophenol. Int. J. Mol. Sci. 2019, 20, 2623. [Google Scholar] [CrossRef] [Green Version]
  29. Xu, F.; Shi, X.; Li, Y.; Zhang, Q. Mechanistic and kinetic studies on the homogeneous gas-phase formation of PCTA/DTs from 2,4-dichlorothiophenol and 2,4,6-trichlorothiophenol. Int. J. Mol. Sci. 2015, 16, 20449–20467. [Google Scholar] [CrossRef] [Green Version]
  30. Zuo, C.; Wang, H.; Pan, W.; Zheng, S.; Xu, F.; Zhang, Q. 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. Int. J. Mol. Sci. 2019, 20, 1542. [Google Scholar] [CrossRef] [Green Version]
  31. Shao, K.; Yan, J.; Li, X.; Lu, S.; Wei, Y.; Fu, M. Experimental study on the effects of H2O on PCDD/Fs formation by de novo synthesis in carbon/CuCl2 model system. Chemosphere 2010, 78, 672–679. [Google Scholar] [CrossRef]
  32. Li, X.-D.; Zhang, J.; Yan, J.-H.; Chen, T.; Lu, S.-Y.; Cen, K.-F. Effect of water on catalyzed de novo formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans. J. Hazard. Mater. 2006, 137, 57–61. [Google Scholar] [CrossRef] [PubMed]
  33. Briois, C.; Ryan, S.; Tabor, D.; Touati, A.; Gullett, B.K. Formation of polychlorinated dibenzo-p-dioxins and dibenzofurans from a mixture of chlorophenols over fly ash: Influence of water vapor. Environ. Sci. Technol. 2007, 41, 850–856. [Google Scholar] [CrossRef] [PubMed]
  34. Stieglitz, L.; Zwick, G.; Beck, J.; Bautz, H.; Roth, W.J.C. The role of particulate carbon in the de-novo synthesis of polychlorinated dibenzodioxins and-furans in fly-ash. Chemosphere 1990, 20, 1953–1958. [Google Scholar] [CrossRef]
  35. Jay, K.; Stieglitz, L. On the mechanism of formation of polychlorinated aromatic-compounds with copper(II) chloride. Chemosphere 1991, 22, 987–996. [Google Scholar] [CrossRef]
  36. Shi, X.L.; Zhang, R.M.; Zhang, H.J.; Xu, F.; Zhang, Q.Z.; Wang, W.X. Influence of water on the homogeneous gas-phase formation mechanism of polyhalogenated dioxins/furans from chlorinated/brominated phenols as precursors. Chemosphere 2015, 137, 142–148. [Google Scholar] [CrossRef]
  37. Xu, F.; Shi, X.L.; Zhang, Q.Z.; Wang, W.X. Formation of Chlorotriophenoxy Radicals from Complete Series Reactions of Chlorotriophenols with H and OH Radicals. Int. J. Mol. Sci. 2015, 16, 18714–18731. [Google Scholar] [CrossRef] [Green Version]
  38. Zhang, Q.Z.; Qu, X.H.; Wang, H.T.; Xu, F.; Shi, X.L.; Wang, W.X. Mechanism and Thermal Rate Constants for the Complete Series Reactions of Chlorophenols with H. Environ. Sci. Technol. 2009, 43, 4105–4112. [Google Scholar] [CrossRef]
  39. Xu, F.; Wang, H.T.; Zhang, Q.; Zhang, R.M.; Qu, X.H.; Wang, W.X. Kinetic properties for the complete series reactions of chlorophenols with OH radicals-relevance for dioxin formation. Environ. Sci. Technol. 2010, 44, 1399–1404. [Google Scholar] [CrossRef]
  40. Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G.A. Gaussian 09, Revision A.1; Gaussian Inc.: Wallingford, CT, USA, 2009. [Google Scholar]
  41. Zhao, Y.; Truhlar, D.G. Hybrid Meta Density Functional Theory Methods for Thermochemistry, Thermochemical Kinetics, and Noncovalent Interactions: The MPW1B95 and MPWB1K Models and Comparative Assessments for Hydrogen Bonding and van der Waals Interactions. J. Phys. Chem. A 2004, 108, 6908–6918. [Google Scholar] [CrossRef]
  42. Fukui, K. The path of chemical reactions—The IRC approach. Acc. Chem. Res. 1981, 14, 363–368. [Google Scholar] [CrossRef]
Atmosphere 13 00849 g001 550
Figure 1. Configuration of reactants, transition states, pre-reactive intermediates, and products for H abstraction from 2-CTB, 3-CTB, and 2,6-DCTB by H and ·OH in hydrated cases (denoted by (a–r), respectively). Distances are in angstroms. Gray sphere, C; White sphere, H; Red sphere, O; Yellow sphere, S; Green sphere, Cl.
Figure 1. Configuration of reactants, transition states, pre-reactive intermediates, and products for H abstraction from 2-CTB, 3-CTB, and 2,6-DCTB by H and ·OH in hydrated cases (denoted by (a–r), respectively). Distances are in angstroms. Gray sphere, C; White sphere, H; Red sphere, O; Yellow sphere, S; Green sphere, Cl.
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Atmosphere 13 00849 g002 550
Figure 2. Syn- and anti-conformers of CTB (a,b) and CTB-H2O (c,d).
Figure 2. Syn- and anti-conformers of CTB (a,b) and CTB-H2O (c,d).
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Atmosphere 13 00849 g003 550
Figure 3. The reaction mechanism (a) and schematic energy profile (b) of the H abstraction from TBe, 2-CTB, 3-CTB, and 2,6-DCTB by H atom in hydrated and non-hydrated cases. ΔE and ΔH are calculated at 0 K.
Figure 3. The reaction mechanism (a) and schematic energy profile (b) of the H abstraction from TBe, 2-CTB, 3-CTB, and 2,6-DCTB by H atom in hydrated and non-hydrated cases. ΔE and ΔH are calculated at 0 K.
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Figure 4. The reaction mechanism (a) and schematic energy profile (b) of the H abstraction from TBe, 2-CTB, 3-CTB, and 2,6-DCTB by ·OH radical in hydrated and non-hydrated cases. ΔE and ΔH are calculated at 0 K.
Figure 4. The reaction mechanism (a) and schematic energy profile (b) of the H abstraction from TBe, 2-CTB, 3-CTB, and 2,6-DCTB by ·OH radical in hydrated and non-hydrated cases. ΔE and ΔH are calculated at 0 K.
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Figure 5. Histograms of potential barriers ΔE (in kcal mol−1, including ZPE correction) of the H abstraction from CTBs and CBs by H atom in hydrated and non-hydrated cases. For comparison, ΔE of the H abstraction from CBs in hydrated and non-hydrated cases are provided by References [36,38], respectively.
Figure 5. Histograms of potential barriers ΔE (in kcal mol−1, including ZPE correction) of the H abstraction from CTBs and CBs by H atom in hydrated and non-hydrated cases. For comparison, ΔE of the H abstraction from CBs in hydrated and non-hydrated cases are provided by References [36,38], respectively.
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Figure 6. Histograms of potential barriers ΔE (in kcal mol−1, including ZPE correction) of the H abstraction from CTBs and CBs by ·OH radical in hydrated and non-hydrated cases. For comparison, ΔE of the H abstraction from CBs in hydrated and non-hydrated cases are provided by References [36,39], respectively.
Figure 6. Histograms of potential barriers ΔE (in kcal mol−1, including ZPE correction) of the H abstraction from CTBs and CBs by ·OH radical in hydrated and non-hydrated cases. For comparison, ΔE of the H abstraction from CBs in hydrated and non-hydrated cases are provided by References [36,39], respectively.
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Table
Table 1. Bond length (L) of S−H in reactants CTBs and S−C in products CTBRs in hydrated and non-hydrated cases (in Å), S−H bond dissociation energies, D0(S−H), (in kcal mol−1) in hydrated and non-hydrated CTBs.
Table 1. Bond length (L) of S−H in reactants CTBs and S−C in products CTBRs in hydrated and non-hydrated cases (in Å), S−H bond dissociation energies, D0(S−H), (in kcal mol−1) in hydrated and non-hydrated CTBs.
CTBsL(S−H)CTBRsL(S−C)D0(S−H) aD0(S−H) b
Non-Hydrated aHydrated bNon-Hydrated aHydrated b
TBe1.331.34TbeR1.761.7186.5176.26
2-CTB1.331.332-CTBR1.741.7086.2477.87
3-CTB1.331.343-CTBR1.751.7186.7376.77
4-CTB1.331.344-CTBR1.711.7077.1675.59
2,3-DCTB1.331.332,3-DCTBR1.741.7085.5978.45
2,4-DCTB1.331.332,4-DCTBR1.701.7079.1577.32
2,5-DCTB1.331.332,5-DCTBR1.741.7087.7678.91
2,6-DCTB1.331.332,6-DCTBR1.741.6984.9988.83
3,4-DCTB1.331.343,4-DCTBR1.711.7177.9876.26
3,5-DCTB1.331.333,5-DCTBR1.741.7186.9277.56
2,3,4-TCTB1.331.332,3,4-TCTBR1.701.7079.5777.75
2,3,5-TCTB1.331.332,3,5-TCTBR1.741.7086.0179.23
2,3,6-TCTB1.331.332,3,6-TCTBR1.741.7087.6488.62
2,4,5-TCTB1.331.332,4,5-TCTBR1.701.7079.7277.91
2,4,6-TCTB1.331.332,4,6-TCTBR1.691.6980.5580.02
3,4,5-TCTB1.331.333,4,5-TCTBR1.711.7178.5576.97
2,3,4,5-TeCTB1.331.332,3,4,5-TeCTBR1.701.7080.1078.62
2,3,4,6-TeCTB1.331.332,3,4,6-TeCTBR1.691.6981.0279.75
2,3,5,6-TeCTB1.331.332,3,5,6-TeCTBR1.741.7084.1888.11
PCTB1.331.33PCTBR1.701.6981.6980.82
a The bond length of S−H in reactants and S−C in products, and the S−H bond dissociation energies of CTBs in non-hydrated CTBs. The values are from Reference [37]. b The bond length of S−H in reactants and S−C in products, and the S−H bond dissociation energies of CTBs in hydrated CTBs. The values are from this work.
Table
Table 2. Imaginary frequencies (in cm−1) in transition states, potential barriers ΔE (in kcal mol−1), and reaction heats ΔH (in kcal mol−1, 0 K) of the H abstraction of CTBs by H atom in hydrated and non-hydrated cases, respectively. ΔE and ΔH are calculated at 0 K.
Table 2. Imaginary frequencies (in cm−1) in transition states, potential barriers ΔE (in kcal mol−1), and reaction heats ΔH (in kcal mol−1, 0 K) of the H abstraction of CTBs by H atom in hydrated and non-hydrated cases, respectively. ΔE and ΔH are calculated at 0 K.
CTBsNon-Hydrated aHydrated bΔE−ΔEH2OImaginary Frequencies
ΔEΔHΔEH2OΔHH2O
TBe2.50−14.160.12−14.162.38−794i
2-CTB3.42−14.431.48−14.431.94−868i
3-CTB2.76−13.940.77−13.941.99−904i
4-CTB2.31−23.500.22−23.502.09−873i
2,3-DCTB3.56−14.711.63−14.711.93−883i
2,4-DCTB3.44−21.521.37−21.522.07−855i
2,5-DCTB3.64−12.901.76−12.901.88−882i
2,6-DCTB4.38−15.682.83−15.681.55−922i
3,4-DCTB2.65−22.680.92−22.681.73−804i
3,5-DCTB3.00−13.741.09−13.741.91−948i
2,3,4-TCTB3.21−21.101.06−21.102.15−891i
2,3,5-TCTB3.70−14.652.06−14.651.64−903i
2,3,6-TCTB4.43−13.033.62−13.030.81−919i
2,4,5-TCTB3.48−20.941.55−20.941.93−880i
2,4,6-TCTB4.27−20.123.11−20.121.16−896i
3,4,5-TCTB2.67−22.121.11−22.121.56−915i
2,3,4,5-TeCTB3.17−20.571.32−20.571.85−890i
2,3,4,6-TeCTB4.37−19.653.25−19.651.12−904i
2,3,5,6-TeCTB4.52−16.483.31−16.481.21−930i
PCTB4.62−18.983.29−18.981.33−915i
a Potential barriers and reaction heats of H abstraction from CTBs by H atom in non-hydrated cases. The values are from Reference [37]. b Potential barriers and reaction heats of H abstraction from CTBs by H atom in hydrated cases. The values are from this work.
Table
Table 3. Imaginary frequencies (in cm−1) in transition states, potential barriers ΔE (in kcal mol−1), and reaction heats ΔH (in kcal mol−1) of the H abstraction of CTBs by ·OH radical in hydrated and non-hydrated cases, respectively. ΔE and ΔH are calculated at 0 K.
Table 3. Imaginary frequencies (in cm−1) in transition states, potential barriers ΔE (in kcal mol−1), and reaction heats ΔH (in kcal mol−1) of the H abstraction of CTBs by ·OH radical in hydrated and non-hydrated cases, respectively. ΔE and ΔH are calculated at 0 K.
CTBsNon-Hydrated aHydrated bΔE−ΔEH2OImaginary Frequencies
ΔEΔHΔEH2OΔHH2O
TBe7.03−27.69−6.17−27.6913.20−702i
2-CTB8.67−27.96−4.00−27.9612.67−643i
3-CTB7.64−27.47−5.94−27.4713.58−721i
4-CTB6.99−37.03−6.29−37.0313.28−703i
2,3-DCTB9.29−28.24−4.00−28.2413.29−714i
2,4-DCTB8.80−35.05−4.19−35.0512.99−722i
2,5-DCTB9.20−27.97−3.97−27.9713.17−684i
2,6-DCTB10.27−29.21−3.88−29.2114.15−783i
3,4-DCTB7.39−36.21−6.08−36.2113.47−739i
3,5-DCTB8.13−27.27−5.78−27.2713.91−716i
2,3,4-TCTB9.10−34.63−4.25−34.6313.35−674i
2,3,5-TCTB9.48−28.18−3.69−28.1813.17−689i
2,3,6-TCTB10.48−26.56−4.06−26.5614.54−776i
2,4,5-TCTB8.98−34.47−4.33−34.4713.31−680i
2,4,6-TCTB9.95−33.65−4.23−33.6514.18−742i
3,4,5-TCTB7.66−35.65−6.23−35.6513.89−719i
2,3,4,5-TeCTB9.29−34.10−4.23−34.1013.52−654i
2,3,4,6-TeCTB10.18−33.18−4.64−33.1814.82−746i
2,3,5,6-TeCTB10.85−30.01−4.12−30.0114.97−802i
PCTB10.55−32.51−3.73−32.5114.28−828i
a Potential barriers and reaction heats of H abstraction from CTBs by ·OH radical in non-hydrated cases. The values are from Reference [37]. b Potential barriers and reaction heats of H abstraction from CTBs by ·OH radical in non-hydrated cases. The values are from this work.
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Han, Y.; Zheng, S.; Teng, Z.; Hadizadeh, M.H.; Zhang, Q.; Xu, F.; Sun, Y. Effect of Water Molecule on the Complete Series Reactions of Chlorothiobenzenes with H/·OH: A Theoretical Study. Atmosphere 2022, 13, 849. https://doi.org/10.3390/atmos13050849

AMA Style

Han Y, Zheng S, Teng Z, Hadizadeh MH, Zhang Q, Xu F, Sun Y. Effect of Water Molecule on the Complete Series Reactions of Chlorothiobenzenes with H/·OH: A Theoretical Study. Atmosphere. 2022; 13(5):849. https://doi.org/10.3390/atmos13050849

Chicago/Turabian Style

Han, Yanan, Siyuan Zheng, Zhuochao Teng, Mohammad Hassan Hadizadeh, Qi Zhang, Fei Xu, and Yanhui Sun. 2022. "Effect of Water Molecule on the Complete Series Reactions of Chlorothiobenzenes with H/·OH: A Theoretical Study" Atmosphere 13, no. 5: 849. https://doi.org/10.3390/atmos13050849

APA Style

Han, Y., Zheng, S., Teng, Z., Hadizadeh, M. H., Zhang, Q., Xu, F., & Sun, Y. (2022). Effect of Water Molecule on the Complete Series Reactions of Chlorothiobenzenes with H/·OH: A Theoretical Study. Atmosphere, 13(5), 849. https://doi.org/10.3390/atmos13050849

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