Science of the Total Environment 505 (2015) 787–794
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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
Mechanism and kinetic properties for the OH-initiated atmospheric oxidation degradation of 9,10-Dichlorophenanthrene Juan Dang, Xiangli Shi, Qingzhu Zhang ⁎, Jingtian Hu, Wenxing Wang Environment Research Institute, Shandong University, Jinan 250100, P. R. China
H I G H L I G H T S • • • •
We studied a comprehensive mechanism of OH-initiated degradation of 9,10-Cl2Phe. The atmospheric lifetime of 9,10-Cl2Phe determined by OH radical is about 5.05 d. The rate constants of the crucial elementary steps were evaluated. Water plays an important role in the formation of nitro-9,10-Cl2Phe.
a r t i c l e
i n f o
Article history: Received 24 July 2014 Received in revised form 22 October 2014 Accepted 22 October 2014 Available online 5 November 2014 Editor: P. Kassomenos Keywords: 9,10-Dichlorophenanthrene OH radicals Oxidation mechanism Degradation products Rate constants
a b s t r a c t Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) have become a serious environmental concern due to their widespread occurrence and dioxin-like toxicities. In this work, the mechanism of the OH-initiated atmospheric oxidation degradation of 9,10-dichlorophenanthrene (9,10-Cl2Phe) was investigated by using high-accuracy quantum chemistry calculations. The rate constants of the crucial elementary reactions were determined by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The theoretical results were compared with the available experimental data. The main oxidation products are a group of ring-retaining and ringopening compounds including chlorophenanthrols, 9,10-dichlorophenanthrene-3,4-dione, dialdehydes, chlorophenanthrenequinones, nitro-9,10-Cl2Phe and epoxides et al. The overall rate constant of the OH addition reaction is 2.35 × 10−12 cm3 molecule−1 s−1 at 298 K and 1 atm. The atmospheric lifetime of 9,10-Cl2Phe determined by OH radicals is about 5.05 days. This study provides a comprehensive investigation of the OHinitiated oxidation degradation of 9,10-Cl2Phe and should contribute to clarifying its atmospheric fate. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) are PAH derivatives, which are ubiquitous contaminants found in urban air, snow, automotive exhaust, tap water, and sediments (Ohura, 2007; Ma et al., 2013). Their main sources include municipal incineration, chlorine disinfection of water, and atmospheric reactions of PAHs et al (Sankoda et al., 2013). Due to the structural similarities with polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs), some of ClPAHs have been shown enhanced toxicities, mutagenicities and aryl hydrocarbon receptor activities compared with corresponding parent PAHs (Kakimoto et al., 2014; Kitazawa et al., 2006; Sankoda et al., 2012). Because of the different chlorine substitution pattern, ClPAHs have many congeners. The toxicity of the individual congeners is largely
⁎ Corresponding author. Fax: +86 531 8836 1990. E-mail address: [email protected] (Q. Zhang).
http://dx.doi.org/10.1016/j.scitotenv.2014.10.081 0048-9697/© 2014 Elsevier B.V. All rights reserved.
depended on the number and position of the chlorine substituents (Sankoda et al., 2013). In general, ClPAHs are primarily present in the gaseous phase in the atmosphere, and only approximately 19% of total ClPAHs are associated with atmospheric particulates (Sun et al., 2013). ClPAHs have been detected in urban air at concentrations ranging from 11 to 143 pg m− 3 in Japan (Horii et al., 2008). On account of their widespread occurrence and dioxin-like toxicities, the atmospheric fate of ClPAHs has become a serious environmental concern as well as a public health priority (Horii et al., 2008; Kakimoto et al., 2014). 9,10-Dichlorophenanthrene (9,10-Cl2Phe) is one of disubstituted phenanthrene derivatives, which has been frequently detected worldwide in the atmosphere. In December 2009, air samples collected from the urban area of Shizuoka in Japan revealed that the maximum concentration of 9,10-Cl2Phe is up to 28.08 pg m− 3 (Ohura et al., 2013). The field measurement in the urban street of Sweden showed that the ambient total air concentration of 9,10-dichlorophenanthrene and 9,10-dichloroanthracene was 5.6 pg m− 3 (Nilsson and Ostman, 1993). Due to its prevalent presence in air, it is critical to clarify the atmospheric degradation of 9,10-Cl2Phe. However, to our best of
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J. Dang et al. / Science of the Total Environment 505 (2015) 787–794
Cl
Cl
OH
E=1.57 H=-19.81
pathway 1 IM1 Cl
Cl
E=2.60 H=-16.73
OH
pathway 2
IM2 Cl 9 8 8a
Cl
Cl 10 10a 1
4b 4a
7 6
5
+OH
E=2.16 H=-17.68
3
pathway 3 OH
IM3
W ðEÞ hρðEÞ
ð1Þ
kðT Þ ¼
Z
1 Q ðT Þ
kðEÞρðEÞ expð−βEÞdE
ð2Þ
where Q(T) is the reactant partition function.
Cl
Cl
kðEÞ ¼
where W(E) is the rovibrational sum of states at the transition state, ρ(E) is density of states of reactants, and h is Planck's constant. Then, the canonical rate constant k(T) is determined from the equation:
Cl
2 4
A more flexible basis set, 6-311 + G(3df,2p), was used to determine the single point energies of various species. The overall energetic profile was constructed to locate the energetically favorable reaction pathways. By means of the MESMER program (Glowacki et al., 2012), the rate constants of the crucial elementary reactions were deduced by using Rice–Ramsperger–Kassel–Marcus (RRKM) theory (Robinson and Holbrook, 1972). The RRKM rate constant is given by:
3. Results and discussion
E=0.83 H=-21.2
pathway 4 Due to the lack of experimental information on the thermochemical parameters for the present reaction system, it is difficult to compare the theoretical results with experimental data directly. For purpose of verifying the reliability of the computational results, we optimized the geometries and calculated the vibrational frequencies of CCl4, benzene,
OH IM4 Cl
Cl
E =3.08 H=-27.23
OH pathway 5
Cl
Cl
IM5 Fig. 1. The OH addition reaction scheme of 9,10-Cl2Phe embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol). ΔH is calculated at 0 K.
knowledge, none have been clearly illustrated in any previous studies for the atmospheric degradation of ClPAHs (9,10-Cl2Phe included). In general, the tropospheric removal of PAHs involves wet and dry deposition, and atmospheric oxidation degradation such as the reactions with OH, NO3 and O3 et al. The wet and dry deposition of gaseous PAHs is relatively insignificant as a removal route. Among the various oxidants, OH radicals play the essential role in determining the oxidation power of the atmosphere (Keyte et al., 2013; Liu and Wang, 2008). So, in consideration of the structural similarity of 9,10-Cl2Phe with phenanthrene, the reaction with OH radicals should be an important removal process for gaseous 9,10-Cl2Phe. A full analysis of the atmospheric processes is limited in the laboratory studies, largely due to the lack of efficient detection schemes for intermediate radical species. With the aid of the density functional theory (DFT) and the Rice–Ramsperger–Kassel–Marcus (RRKM) theory, this paper carried out a rather comprehensive theoretical investigation on the OHinitiated atmospheric oxidation degradation of 9,10-Cl2Phe in the presence of O2/NOx, which is expected to be helpful for elucidating the atmospheric fate of 9,10-Cl2Phe.
+HO 2 P1
OH
+O2 E=14.74 H=-28.60
OH
Cl
Cl
Cl
+O2 E=9.73 H=-27.55
+HO2
OH
OH
IM3 Cl
P3
Cl
Cl
Cl
+O2 E=16.47 H=-18.05
+HO 2
OH
OH
IM4 Cl
+HO2
P2
IM2 Cl
Cl
Cl
Cl
2. Computational method The high-accuracy quantum chemical calculations were performed with the Gaussian 09 software package (Frisch et al., 2009) on a supercomputer. The geometries of the reactants, intermediates, transition states and products were optimized at the BB1K/6-31 + G(d,p) level, which has yielded satisfying results in previous studies (Qu et al., 2006). The vibrational frequencies were calculated to identify the structures obtained as true minima or first-order saddle points. The intrinsic reaction coordinate (IRC) analysis was carried out to confirm that each transition state connects to the right minima along the reaction path.
OH
+O2 E=16.15 H=-20.11
IM1 Cl
Cl
Cl
OH
P4
Cl
Cl
OH
OH Cl H=9.40 IM5
P5
Fig. 2. The O2 abstraction scheme of OH-9,10-Cl2Phe adducts embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol). ΔH is calculated at 0 K.
J. Dang et al. / Science of the Total Environment 505 (2015) 787–794
Cl
Cl
Cl
Cl
O
O
HOO
P6 Cl
OH
HOO IM10
IM11 Cl
Cl
Cl
+OH H2O H=-37.14
OH E=8.66 H=-7.04
O
789
Cl
+O2 E=7.91 H=-8.35
+O2 E=13.51 HO2 H=-13.11
Cl
H OO H OH IM6
H OH IM3
Cl
Cl
H shift E=23.97 H=-14.07
H OH HOO IM8 HO2 E=11.44 H=-5.13 Cl
Cl
P3
Cl
Cl
H OH
IM3 Cl
Cl
+O2 E=10.63 H=-8.52
Cl
H OO H OH IM6
H shift E=22.68 H=21.08
HO2
Cl
H shift E=38.01 H=-14.80
Cl
H HOO IM9
E=1.20 H=-6.42
H HOO
Cl
H O P7
H O
OH
H shift E=28.07 H=22.21 H OO H OH IM7
Cl
H O
IM14 OH E=1.27 H=-28.35 Cl
Cl
OH
Cl
Cl
H HOO H O IM12
Cl
Cl
Cl
H OO H OH IM7 Cl
OH E=12.19 H=-4.22
Cl
E=8.29 H=-3.56 H HOO H O IM13
Cl
H=-30.27 Cl
H HOO
H O
IM15
Fig. 3. The O2 addition reaction scheme of OH-9,10-Cl2Phe adducts (IM3) embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol).
phenol and naphthalene. The results agree well with the available experimental values, and the maximum relative errors are within 3.0% for geometrical parameters and 8.4% for vibrational frequencies (Kuchitsu, 1998; Herzberg, 1966; Shimanouchi, 1972; Hellwege and Hellwege, 1976; Martin et al., 1996). 3.1. Reaction of with OH radicals For convenience of description, the C atoms in 9,10-Cl2Phe are numbered, as presented in Fig. 1. There exist C = C, C-H and C-Cl
bonds in the molecular structure of 9,10-Cl2Phe. So, addition of OH to the C = C bonds, H abstraction from the C-H bonds and Cl abstraction from the C-Cl bonds are possible pathways for the reaction of 9,10Cl2Phe with OH radicals. The reaction schemes embedded with the potential barriers (△ E) and reaction heats (△ H, 0 K) are presented in Fig. 1 and Figure S1 of Supporting Information. It can be seen from Figure S1 that the Cl abstraction cannot occur under the general atmospheric conditions due to the extremely high barrier and strong endothermicity. At the BB1K/6-311 + G(3df,2p) level, the potential barriers of H abstractions are 5.36 ~ 37.04 kcal/mol. Clearly, the H
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J. Dang et al. / Science of the Total Environment 505 (2015) 787–794
Cl
Cl
Cl
Cl
Cl
Cl
OH +NO H OO H=-15.72
OH NO2 H E=24.14 OONO H=-9.88
OH H O
IM16
IM17
Cl
Cl
OO
OH
O
NO2 E=38.04 H=-2.56
IM21
IM20
IM19
Cl
Cl
OH
+NO H=-15.20
IM5
O P8
Cl
Cl
ONOO
OH
+O2 E=17.82 H=-13.81
OH
IM18
Cl
Cl
OH
Cl
Cl
+O2 HO2 E=29.57 H=7.06
E=0.14 H=-9.27 Cl
Cl
+O2 HO2 H=-17.19
Cl
Cl
Cl
+O2 E=11.01 H=-2.81
OH H
O H
H OONO
OH H
OH H
NO2 E=42.48 H=6.77
OH H IM25
IM24 +O2 HO2
Cl
Cl
Cl
O
O P10
+O2 HO2 E=22.90 H=-28.79
Cl
Cl
+NO H=-14.21 IM23
IM4
IM22
Cl
Cl
H OO
OH
O
P9 Cl
Cl
Cl
O
O
Cl
Cl
O
OH IM28
+OH H 2O E=7.90 H=-0.84
Cl
Cl
O H
E=15.24 H=-10.23 Cl
O H H=-2.81
OH IM27
OH IM26
Fig. 4. The reaction scheme of IM16, IM4 and IM5 embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol).
abstraction from the C4-H bond is energetically unfavorable because of the much high barrier of 37.04 kcal/mol. All H abstraction pathways are exothermic, and the reaction heats are from − 5.76 to −3.82 kcal/mol. The barriers of OH additions are 0.83 ~ 3.08 kcal/mol, and the reaction heats are from −27.23 to −16.73 kcal/mol. Obviously, the OH additions have lower barriers and are much more exothermic compared with the H abstractions. Hence, the OH additions are the energetically more favorable reaction pathways for the reaction of 9,10-Cl2Phe with OH radicals. Previous experimental research showed that additions of OH to C = C bonds are the dominant pathways compared with H abstractions for anthracene, naphthalene and monocyclic aromatic compounds under typical atmospheric conditions (Ananthula et al., 2006; Lorenz and Zellner, 1983; Perry et al., 1977). Our calculation result is consistent with the experimental studies. In addition, as shown in Fig. 1, the OH addition to the C4 atom is the thermodynamically most favorable because of the lowest barrier and highest exothermicity. 3.2. Secondary reactions 3.2.1. Reactions with O2 The study above shows that the addition reaction of 9,10-Cl2Phe with OH radicals can occur readily under the general atmospheric conditions. The adducts, OH-9,10-Cl2Phe, are important intermediates produced from the reaction of 9,10-Cl2Phe with OH radicals. In the atmosphere, they will further react with O2/NOx as their removal. Firstly, OH-9,10-Cl2Phe with O2 can react via a simple metathesis
mechanism to yield 9,10-dichlorophenanthrol and HO2 through H abstraction from the C-H bonds. The reaction schemes are depicted in Fig. 2. The potential barriers of these H abstraction processes are 9.73 ~ 16.47 kcal/mol at the BB1K/6-311 + G(3df,2p) level. The transition states lie at 11.89 ~ 17.72 kcal/mol above the sum energy of 9,10-Cl2Phe + OH + O2. The processes are strongly exothermic by 18.05 ~ 28.60 kcal/mol. The overall reactions, 9,10-Cl2Phe + OH + O2 → 9,10-dichlorophenanthrol + HO2, are strongly exothermic by 39.25 ~ 45.33 kcal/mol. It implies that the degradation pathways leading to the formation of 9,10-dichlorophenanthrol can occur easily under the general atmospheric conditions. Comparison of the reaction pathways presented in Fig. 2 shows that the H abstraction by O2 from 3-OH-9,10-Cl2Phe (IM3 in Fig. 2) has the lowest barrier and is energetically most favorable relative to the other H abstraction pathways. In addition, as shown in Fig. 2, the OH-9,10-Cl2Phe adduct IM5 can react via a unimolecular decomposition through cleavage of the C-Cl bond to yield 9-chlorophenanthrol. Secondly, O2 can attack on the C atoms with an unpaired electron in OH-9,10-Cl2Phe via an addition mechanism from two different directions: the cis or trans-position of the -OH group with respect to the aromatic ring. The reaction schemes are displayed in Fig. 3, Figure S2 and Figure S3 of Supporting Information. Therefore, ten O2-OH-9,10-Cl2Phe adduct isomers can be formed from the reaction of OH-9,10-Cl 2Phe with O2. Due to the structural similarity of OH9,10-Cl 2Phe, just the reaction scheme of 3-OH-9,10-Cl2Phe (IM3) with O2 and the subsequent reaction of OH-O2-9,10-Cl2Phe adduct
J. Dang et al. / Science of the Total Environment 505 (2015) 787–794
Cl
Cl
Cl
OH H OO
E=34.23 H=10.82
IM29
Cl
O O
Cl
Cl
O IM31
OO H OH IM6
Cl
H OH IM32
E=32.15 H=-44.75
CHO
Cl
Cl
+O2 HO2 E=19.46 H=-34.66
OH H
P11
O
CHO
Cl
Cl
O O
E=15.63 H=-7.10
OH H
E=25.27 H=-55.84
IM30
Cl
Cl
Cl
OH H
791
O
E=32.69 H=-44.18
O
H H OH P12
Cl
Cl
O O H OH H P13 Cl
Cl
Cl
Cl
H
OH H
E=35.70 OO H=10.96
IM33 Cl
Cl
O O OH H IM36
O O OH H
+O2 IM34 E=20.26 H=-30.31 H
Cl
Cl
H E=37.78 H=-36.02
OH H
H
O
O
+O2 HO2 E=20.45 H=-32.75
OH H
IM35
+NO OO H=-18.14
O O
OONO
OH H IM37
Cl
Cl
Cl
H
Cl
NO2 E=41.58 H=-1.12
O O
Cl
O OH H P15
O
+O2 HO2 E=28.54 H=-27.45
H O
OH H IM38
O
O
P14
Cl
Cl
Cl
Cl
O
E=7.94 H=-32.10
Cl
O
H O
OH H IM39
O
Fig. 5. The reaction scheme of IM29, IM6 and IM33 embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol) in the presence of O2 and NO. ΔH is calculated at 0 K.
(IM6) is depicted in Fig. 3. The subsequent reaction of IM6 has three pathways. The first one involves two elementary steps, H shift from the C-H bond and C-O bond cleavage, leading to the formation of 9,10-dichlorophenanthren-3-ol (P3). The second one includes four elementary reactions, H shift, H abstraction by O2, H abstraction by OH radicals and elimination of OH, leading to the formation of 9,10-dichlorophenanthrene-3,4-dione (P6). The H shift process is the rate-determining step because of the high barrier of 23.97 kcal/mol. The third pathway starts with H shift, followed by C-C bond rupture and elimination of OH and ultimately results in the formation of a dialdehyde (P7). Similarly, other OH-9,10-Cl2Phe adducts (IM1, IM2, and IM4) can also react with O2 to form dialdehydes, chlorophenanthrols and chlorophenanthrenequinones, and the reaction scheme is depicted in Figures S2 and S3 of Supporting Information. As shown in Fig. 4, the OH-O2-9,10-Cl2Phe intermediate IM16 react with NO, followed by the rupture of the O-ONO bond and H abstraction by O2, resulting in the formation of an epoxide compound (P8). The reaction of NO addition is barrierless and exothermic. The last elementary step of H abstraction by O2 has a potential barrier of 29.57 kcal/mol and
is exothermic by 7.06 kcal/mol. IM5 also can react with O2 to form an intermediate IM19. The subsequent reactions of IM19 are similar to those of IM16, with the exception of the extra ring-opening reaction. These processes ultimately lead to the formation of NO2 and dialdehyde. The reaction channel of IM4 contains seven elementary reactions: the addition of O2 to form organic peroxy radicals, the association of resulting radicals with NO, cleavage of the O-ONO bond to form epoxide intermediates, H abstraction by O2 , rupture of the C-O bond, H abstraction by hydroxyl radicals and H abstraction by O2 . 9,10dichlorophenanthrene-1,4-dione (P10) is formed from these reactions. Similar products have been detected in the experiments of phenanthrene and OH radicals (Lee and Lane, 2010). The reaction of the cleavage of O-ONO bond is the rate-determining process due to its high potential barrier. Other O2/NO reaction channels are presented in Figure S4 of support information, which have some similarities to those discussions above. So no more explanation is covered here. As shown in Fig. 5, the intermediate IM29 formed by O2 addition can undergo cyclization to produce bicyclic peroxy radicals (IM30). The subsequent reactions of IM30 lead to the formation of the product
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J. Dang et al. / Science of the Total Environment 505 (2015) 787–794
Cl
Cl
H=-32.81 Cl
Cl
NO2 +H2O
IM40
OH
2H2O E=22.19 H=-15.18 TS3 -3H2O
H=-29.50 NO2 IM41
OH H=-20.90
Cl
Cl
H=-36.66
NO2
IM42
OH Cl
Cl
Cl
Cl
Cl
OH
IM44 OH
IM3
Cl
Cl
H=-35.48
Cl
IM4
Cl
OH
H=-32.07
OH+H2O
+H2O NO2 OH IM46 Cl
NO2
H=-29.84
IM47
NO2
E=21.11 H=-37.06 -2H2O
P16
NO2 P17
OH
Cl
Cl
Cl
E=29.54 H=-22.02 -2H2O
2H2O E=26.32 H=-11.36 -3H2O
Cl
Cl
E=35.58 H=-11.33 -2H2O
Cl
Cl
Cl
E=42.66 H=-22.02 -H2O
Cl
NO2
P19
E=49.75 H=-11.33 -H2O
NO2 IM45
Cl
+H2O
Cl
Cl
E=37.92 H=-37.06 -H2O
NO2
H=-20.15
NO2
P18
E=36.06 H=-9.01 -2H2O
IM43
Cl
Cl
E=51.52 H=-9.01 -H2O
OH +H2O Cl
NO2 P17
E=25.29 H=-37.68 -2H2O
+H2O
NO2
IM2
Cl
E=36.83 H=-37.68 -H2O
Cl
Cl
P16
Cl
OH
IM1
NO2
E=26.46 H=-22.19 TS2 -2H2O
Cl
Cl
Cl
Cl
E=42.57 H=-22.19 TS1 -H2O
OH
P18
NO2
Cl
NO2
P19
Fig. 6. The formation scheme of nitro-9,10-Cl2Phe embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol) in the presence of O2 and NO. ΔH is calculated at 0 K.
P11. Calculations show that the formation of the bicyclic peroxy radical is the rate-determining step due to its high potential barrier. Compared with IM29, IM6 is easier to produce the bicyclic peroxy radical (IM32) because of the lower barrier height. The potential barrier of the formation of IM32 is calculated to be 15.63 kcal/mol, and the process is exothermic by 7.10 kcal/mol. Subsequently, two kinds of ring-opening processes of IM32 are proceeded, which results in the generation of the products P12 and P13. For the bicyclic peroxy radical IM34 formed by IM33, there exist two subsequent reaction pathways. The first one involves two elementary steps: rupture of the O-O bond and H abstraction by O2, which lead to the formation of P14. The second one
includes five elementary reactions: O2 addition, NO addition, cleavage of the O-ONO bond, ring-opening process and H abstraction by O2. The calculated profiles of the potential energy surface show that the step of the O-ONO bond cleavage is difficult to occur because of the high potential barrier of 41.58 kal/mol. 3.2.2. Reactions with NO2 The OH-9,10-Cl2Phe adducts (IM1-IM4) also can react with NO2 to form OH-NO2-9,10-Cl2Phe adducts via barrierless associations. These processes are strongly exothermic by 20.15 ~ 36.66 kcal/mol. The OHNO2-9,10-Cl2Phe adducts may subsequently undergo unimolecular
J. Dang et al. / Science of the Total Environment 505 (2015) 787–794 Table 1 RRKM rate constants (cm3 molecule−1 s−1) of the crucial elementary reactions involved in the OH-initiated oxidation degradation of 9,10-Cl2Phe at 298 K and 1 atm. Reactions 9,10-Cl2Phe + OH 9,10-Cl2Phe + OH 9,10-Cl2Phe + OH 9,10-Cl2Phe + OH 9,10-Cl2Phe + OH 9,10-Cl2Phe + OH IM3 + O2 → IM6 IM6 → IM8 IM8 → P3 IM3 → IM7 IM7 → IM9 IM9 → P3 IM6 → IM12 IM12 → IM14 IM14 → P7 IM7 → IM13 IM13 → IM15 IM15 → P7 IM16 → IM17 IM17 → IM18 IM5 → IM19 IM19 → IM20 IM20 → IM21 IM21 → IM22 IM4 → IM23 IM23 → IM24 IM24 → IM25
Rate constants → → → → → →
OH-9,10-Cl2Phe IM1 IM2 IM3 IM4 IM5
(k) 2.35 × 10−12 (k1) 1.15 × 10−13 (k2) 2.51 × 10−14 (k3) 6.77 × 10−14 (k4) 9.61 × 10−13 (k5) 7.07 × 10−15 2.22 × 10−19 3.69 × 10−7 8.06 × 103 3.63 × 10−19 6.34 × 10−6 3.45 × 103 3.94 × 10−9 1.16 × 108 3.54 × 109 2.42 × 10−8 1.08 × 104 3.24 × 1012 5.48 × 10−13 1.04 × 10−6 4.35 × 10−21 5.51 × 10−13 6.11 × 10−17 1.18 × 108 4.57 × 10−20 5.40 × 10−13 2.01 × 10−20
decomposition to yield nitro-9,10-Cl2Phe through the direct loss of water. As shown in Fig. 6 (black arrows), the barriers of the reactions of the direct loss of water are extremely high (36.83 ~ 51.52 kcal/mol), so the reactions is difficult to occur. Water is one of the most abundant atmospheric constituents and can affect the reactions through forming hydrogen bonded complexes with … … … other molecules, such as O… 3 H2O, SO3 H2O, CH3CHO H2O and H2SO4 H2O in the atmosphere (Frost and Vaida, 1995; Meijer and Sprik, 1998; Iuga et al., 2010; Vaida and Simon, 1995). With the participation of water, the loss of water from the OH-NO2-9,10-Cl2Phe adducts becomes a bimolecular reaction (OH-NO2-9,10-Cl2Phe + H2O). A sixmembered ring transition state (Figure S5 of support information) was identified, in which water molecule acts as a bridge, accepting the hydrogen from the aromatic ring and simultaneously donating another hydrogen atom to the phenolic group. The potential barriers of the loss of water via the bimolecular reaction are 11.54 ~ 16.81 kcal/mol lower than those of the direct loss of water. In particular, when OH adds to the C1 or C4 atoms, the resulting OH-9,10-Cl2Phe adduct is a hybrid of several resonance structures (Figure S6 of support information). The unpaired electron can be distributed to the ortho position and the para position of the -OH group, and NO2 can be added to these positions. With the aid of the water dimer, nitro-9,10-Cl 2Phe can be formed from the degradation pathway through the OH addition to the C1 (or C4) atom, followed by addition of NO2 to the C4 atom (or C 1) and the loss of water. Pfeilsticker detected water dimers in the atmosphere by near infrared spectroscopy and suggested an atmospheric concentration of 6 × 10 14 molecule cm − 3 at 292 K (Tretyakov et al., 2013; Pfeilsticker et al., 2003). With the aid of the water dimer, para-nitro-9,10-Cl2Phe can be formed, as described in Fig. 6 (red arrows).
793
involved in the OH-initiated oxidation degradation of 9,10-Cl2Phe were evaluated by Rice–Ramsperger–Kassel–Marcus (RRKM) theory (Robinson and Holbrook, 1972) at 298 K and 1 atm. The RRKM method has been successfully used to deal with several similar reactions (Glowacki et al., 2012; Zhou et al., 2011). The calculated rate constants of the crucial elementary reactions are listed in Table 1. The individual rate constants for the OH addition to the C1-H, C2-H, C3-H, C4-H, and C10-H bonds of 9,10-Cl2Phe are noted as k1, k2, k3, k4, k5, respectively. The overall rate constant of the OH addition reaction is denoted as k, k = (k1 + k2 + k3 + k4 + k5) × 2. The overall rate constant k is 2.35 × 10−12 cm3 molecule−1 s−1 at 298 K and 1 atm. Due to the absence of the available experimental values, it is difficult to make a direct comparison of the calculated rate constants with the experimental data for the reaction of 9,10-Cl2Phe with OH radicals. So, this work also calculated the rate constant of the addition reaction of phenanthrene with OH radicals. The RRKM value of 3.98 × 10−11 cm3 molecule− 1 s− 1 at 298 K and 1 atm agree well with the published experimental value of 3.1 × 10−11 cm3 molecule−1 s−1 (Atkinson and Arey, 1994). From the good agreement with the experimental value, it can be inferred that the rate constants of the elementary reactions listed in Table 1 are reasonable. We expect that the rate constant values will contribute to the construction of detailed kinetic models describing the atmospheric fate of 9,10-Cl2Phe. According to the overall rate constant of the reaction of 9,10-Cl2Phe with OH radical and a average OH concentration (COH) of 9.75 × 105 molecule cm−3 (Prinn et al., 1995), from the expression: τOH ¼
1 kðOH þ 9;10‐Cl2 PheÞ cOH
The atmospheric lifetime of 9,10-Cl2Phe determined by OH radicals is calculated about 5.05 days. 4. Conclusions This work carried out a comprehensive theoretical study on the reaction mechanism of the OH radical-initiated atmospheric oxidation degradation of 9,10-Cl2Phe. The rate constants were determined by using the RRKM method. Two conclusions can be drawn from this study: (1) The OH-initiated atmospheric oxidation of 9,10-Cl2Phe generates a class of ring-retaining and ring-opening products containing chlorophenanthrols, 9,10-dichlorophenanthrene-3,4-dione, dialdehydes, chlorophenanthrenequinones, nitro-9,10-Cl2Phe and epoxides et al. (2) The overall rate constant of the OH addition to 9,10-Cl2Phe is 2.35 × 10− 12 cm3 molecule−1 s− 1 at 298 K and 1 atm. The atmospheric lifetime of 9,10-Cl2Phe by OH radicals is about 5.05 days. Acknowledgment The work was financially supported by NSFC (National Natural Science Foundation of China, project Nos. 21337001, 21377073 and 21177076), Taishan Grand (No. ts20120522) and Independent Innovation Foundation of Shandong University (IIFSDU, project No. 2012JC030).
3.3. Rate constant calculations
Appendix A. Supplementary data
In order to clarify the transport and atmospheric fate of ClPAHs, it is critical to determine accurate rate constants of the elementary reactions involved in the atmospheric oxidation degradation of ClPAHs (Keyte et al., 2013). On the basis of the BB1K/6-311 + G(3df,2p)//BB1K/6-31 + G(d,p) energies, the rate constants of the elementary reactions
The H abstraction reaction scheme of 9,10-Cl2Phe. The O2 addition reaction scheme of OH-9,10-Cl2Phe adducts (IM1, IM2, IM4 and IM5). The O 2 addition reaction scheme of OH-9,10-Cl 2 Phe adducts (IM1, IM2, IM4 and IM5). The NO addition reaction scheme of five OH-O2-9,10-Cl2Phe adducts. Configuration of the transition states for
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the loss of water from the OH-NO2-9,10-Cl2Phe adducts. Resonance structures of the OH-9,10-Cl2Phe adducts. The material is available free of charge via the Internet at http://www.elsevier.com/. Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j. scitotenv.2014.10.081. References Ananthula R, Yamada T, Taylor PH. Kinetics of OH radical reaction with anthracene and anthracene-d10. J Phys Chem A 2006;110:3559–66. Atkinson R, Arey J. Atmospheric chemistry of gas-phase polycyclic aromatic hydrocarbons: formation of atmospheric mutagens. Environ Health Perspect 1994;102(Suppl. 4): 117–26. Frisch M, Trucks G, Schlegel HB, Scuseria G, Robb M, Cheeseman J, et al. Gaussian 09, Revision A.1. Wallingford, CT 270: Gaussian Inc.; 2009. p. 271. Frost GJ, Vaida V. Atmospheric implications of the photolysis of the ozone-water weakly bond complex. J Geophys Res 1995;100:18803–9. Glowacki DR, Liang CH, Morley C, Pilling MJ, Robertson SH. MESMER: an open-source master equation solver for multi-energy well reactions. J Phys Chem A 2012;116: 9545–60. Hellwege KH, Hellwege AM. Landolt-Bornstein: group II: atomic and molecular physics volume 7: structure data of free polyatomic molecules. Berlin: Springer-Verlag; 1976. Herzberg G. Electronic spectra and electronic structure of polyatomic molecules. New York: Van Nostrand; 1966. Horii Y, Ok G, Ohura T, Kannan K. Occurrence and profiles of chlorinated and brominated polycyclic aromatic hydrocarbons in waste incinerators. Environ Sci Technol 2008; 42(6):1904–9. Iuga C, Alvarez-Idaboy JR, Reyes L, Vivier- Bunge A. Can a single water molecule really catalyze the acetaldehyde + OH reaction in tropospheric conditions? J Phys Chem Lett 2010;1:3112–5. Kakimoto K, Nagayoshi H, Konishi Y, Kajimura K, Ohura T, Hayakawa K, et al. Atmospheric chlorinated polycyclic aromatic hydrocarbons in East Asia. 2014;111(0):40–6. Keyte IJ, Harrison RM, Lammel G. Chemical reactivity and long-range transport potential of polycyclic aromatic hydrocarbons – a review. Chem Soc Rev 2013;42:9333–91. Kitazawa A, Amagai T, Ohura T. Temporal trends and relationships of particulate chlorinated polycyclic aromatic hydrocarbons and their parent compounds in urban air. Environ Sci Technol 2006;40(15):4592–8. Kuchitsu K. Structure of free polyatomic molecules - basic data. Berlin: Springer; 1998. Lee JY, Lane DA. Formation of oxidized products from the reaction of gaseous phenanthrene with the OH radical in a reaction chamber. Atmos Environ 2010;44:2469–77. Liu B, Wang HX. Determination of atmospheric hydroxyl radical by HPLC coupled with electrochemical detection. J Environ Sci 2008;20:28–32.
Lorenz K, Zellner R. Kinetics of the reactions of hydroxyl radicals with benzene, benzene-d6 and naphthalene. Ber Bunsenges 1983;87:629–36. Ma J, Chen ZY, Wu MH, Feng JL, Horii Y, Ohura T, et al. Airborne PM2.5/PM10-associated chlorinated polycyclic aromatic hydrocarbons and their parent compounds in a suburban area in Shanghai, China. Environ Sci Technol 2013;47(14):7615–23. Martin JML, El-Yazal J, Francois J-P. Structure and vibrational spectrum of some polycyclic aromatic compounds studied by density functional theory. 1. naphthalene, azulene phenanthrene, and anthracene. J Phys Chem 1996;100:15358–67. Meijer EJ, Sprik MA. Density functional study of the addition of water to SO3 in the gas phase and in aqueous solution. J Phys Chem A 1998;102:2893–8. Nilsson UL, Ostman CE. Chlorinated polycyclic aromatic hydr ocarbons: method of analysis and their occurrence in urban air. Environ Sci Technol 1993;27:1826–31. Ohura T. Environmental behavior, sources, and effects of chlorinated polycyclic aromatic hydrocarbons. Sci World J 2007;7:372–80. Ohura T, Horii Y, Kojima M, Kamiya Y. Diurnal variability of chlorinated polycyclic aromatic hydrocarbons in urban air, Japan. Atmos Environ 2013;81:84–91. Perry RA, Atkinson R, Pitts JN. Kinetics and mechanism of the gas phase reaction of hydroxyl radicals with aromatic hydrocarbons over the temperature range 296473 K. J Phys Chem 1977;81:296–304. Pfeilsticker K, Lotter A, Peters C, Bösch H. Atmospheric detection of water dimers via nearinfrared absorption. Science 2003;300:2078–80. Prinn RG, Weiss RF, Miller BR, Huang J, Alyea FN, Cunnold DM, et al. Atmospheric trends and lifetime of CH3CCI3 and global OH concentrations. Science 1995;269:187–92. Qu XH, Zhang QZ, Wang WX. Mechanism for OH-initiated photooxidation of naphthalene in the presence of O2 and NOx: a DFT study. Chem Phys Lett 2006;429:77–85. Robinson PJ, Holbrook KA. Unimolecular reactions. John Wiley & Sons; 1972. Sankoda K, Nomiyama K, Yonehara T, Kuribayashi T, Shinohara R. Evidence for in situ production of chlorinated polycyclic aromatic hydrocarbons on tidal flats: environmental monitoring and laboratory scale experiment. Chemosphere 2012;88(5):542–7. Sankoda K, Kuribayashi T, Nomiyama K, Shinohara R. Occurrence and source of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) in tidal flats of the Ariake Bay, Japan. Environ Sci Technol 2013;47(13):7037–44. Shimanouchi T. Tables of molecular vibrational frequencies, consolidated volume 1, NSRDS NBS-39; 1972. Sun JL, Zeng H, Ni HG. Halogenated polycyclic aromatic hydrocarbons in the environment. Chemosphere 2013;90(6):1751–9. Tretyakov MY, Serov EA, Koshelev MA, Parshin VV, Krupnov AF. Water dimer rotationally resolved millimeter-wave spectrum observation at room temperature. Phys Rev Lett 2013;110:093001. Vaida V, Simon JD. The photoreactivity of chlorine dioxide. Science 1995;268:1443–8. Zhou J, Chen JW, Liang C-H, Xie Q, Wang Y-N, Zhang SY, et al. Quantum chemical investigation on the mechanism and kinetics of PBDE photooxidation by OH: a case study for BDE-15. Environ Sci Technol 2011;45:4839–45.
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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
Mechanism and kinetic properties for the OH-initiated atmospheric oxidation degradation of 9,10-Dichlorophenanthrene Juan Dang, Xiangli Shi, Qingzhu Zhang ⁎, Jingtian Hu, Wenxing Wang Environment Research Institute, Shandong University, Jinan 250100, P. R. China
H I G H L I G H T S • • • •
We studied a comprehensive mechanism of OH-initiated degradation of 9,10-Cl2Phe. The atmospheric lifetime of 9,10-Cl2Phe determined by OH radical is about 5.05 d. The rate constants of the crucial elementary steps were evaluated. Water plays an important role in the formation of nitro-9,10-Cl2Phe.
a r t i c l e
i n f o
Article history: Received 24 July 2014 Received in revised form 22 October 2014 Accepted 22 October 2014 Available online 5 November 2014 Editor: P. Kassomenos Keywords: 9,10-Dichlorophenanthrene OH radicals Oxidation mechanism Degradation products Rate constants
a b s t r a c t Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) have become a serious environmental concern due to their widespread occurrence and dioxin-like toxicities. In this work, the mechanism of the OH-initiated atmospheric oxidation degradation of 9,10-dichlorophenanthrene (9,10-Cl2Phe) was investigated by using high-accuracy quantum chemistry calculations. The rate constants of the crucial elementary reactions were determined by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The theoretical results were compared with the available experimental data. The main oxidation products are a group of ring-retaining and ringopening compounds including chlorophenanthrols, 9,10-dichlorophenanthrene-3,4-dione, dialdehydes, chlorophenanthrenequinones, nitro-9,10-Cl2Phe and epoxides et al. The overall rate constant of the OH addition reaction is 2.35 × 10−12 cm3 molecule−1 s−1 at 298 K and 1 atm. The atmospheric lifetime of 9,10-Cl2Phe determined by OH radicals is about 5.05 days. This study provides a comprehensive investigation of the OHinitiated oxidation degradation of 9,10-Cl2Phe and should contribute to clarifying its atmospheric fate. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) are PAH derivatives, which are ubiquitous contaminants found in urban air, snow, automotive exhaust, tap water, and sediments (Ohura, 2007; Ma et al., 2013). Their main sources include municipal incineration, chlorine disinfection of water, and atmospheric reactions of PAHs et al (Sankoda et al., 2013). Due to the structural similarities with polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs), some of ClPAHs have been shown enhanced toxicities, mutagenicities and aryl hydrocarbon receptor activities compared with corresponding parent PAHs (Kakimoto et al., 2014; Kitazawa et al., 2006; Sankoda et al., 2012). Because of the different chlorine substitution pattern, ClPAHs have many congeners. The toxicity of the individual congeners is largely
⁎ Corresponding author. Fax: +86 531 8836 1990. E-mail address: [email protected] (Q. Zhang).
http://dx.doi.org/10.1016/j.scitotenv.2014.10.081 0048-9697/© 2014 Elsevier B.V. All rights reserved.
depended on the number and position of the chlorine substituents (Sankoda et al., 2013). In general, ClPAHs are primarily present in the gaseous phase in the atmosphere, and only approximately 19% of total ClPAHs are associated with atmospheric particulates (Sun et al., 2013). ClPAHs have been detected in urban air at concentrations ranging from 11 to 143 pg m− 3 in Japan (Horii et al., 2008). On account of their widespread occurrence and dioxin-like toxicities, the atmospheric fate of ClPAHs has become a serious environmental concern as well as a public health priority (Horii et al., 2008; Kakimoto et al., 2014). 9,10-Dichlorophenanthrene (9,10-Cl2Phe) is one of disubstituted phenanthrene derivatives, which has been frequently detected worldwide in the atmosphere. In December 2009, air samples collected from the urban area of Shizuoka in Japan revealed that the maximum concentration of 9,10-Cl2Phe is up to 28.08 pg m− 3 (Ohura et al., 2013). The field measurement in the urban street of Sweden showed that the ambient total air concentration of 9,10-dichlorophenanthrene and 9,10-dichloroanthracene was 5.6 pg m− 3 (Nilsson and Ostman, 1993). Due to its prevalent presence in air, it is critical to clarify the atmospheric degradation of 9,10-Cl2Phe. However, to our best of
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Cl
Cl
OH
E=1.57 H=-19.81
pathway 1 IM1 Cl
Cl
E=2.60 H=-16.73
OH
pathway 2
IM2 Cl 9 8 8a
Cl
Cl 10 10a 1
4b 4a
7 6
5
+OH
E=2.16 H=-17.68
3
pathway 3 OH
IM3
W ðEÞ hρðEÞ
ð1Þ
kðT Þ ¼
Z
1 Q ðT Þ
kðEÞρðEÞ expð−βEÞdE
ð2Þ
where Q(T) is the reactant partition function.
Cl
Cl
kðEÞ ¼
where W(E) is the rovibrational sum of states at the transition state, ρ(E) is density of states of reactants, and h is Planck's constant. Then, the canonical rate constant k(T) is determined from the equation:
Cl
2 4
A more flexible basis set, 6-311 + G(3df,2p), was used to determine the single point energies of various species. The overall energetic profile was constructed to locate the energetically favorable reaction pathways. By means of the MESMER program (Glowacki et al., 2012), the rate constants of the crucial elementary reactions were deduced by using Rice–Ramsperger–Kassel–Marcus (RRKM) theory (Robinson and Holbrook, 1972). The RRKM rate constant is given by:
3. Results and discussion
E=0.83 H=-21.2
pathway 4 Due to the lack of experimental information on the thermochemical parameters for the present reaction system, it is difficult to compare the theoretical results with experimental data directly. For purpose of verifying the reliability of the computational results, we optimized the geometries and calculated the vibrational frequencies of CCl4, benzene,
OH IM4 Cl
Cl
E =3.08 H=-27.23
OH pathway 5
Cl
Cl
IM5 Fig. 1. The OH addition reaction scheme of 9,10-Cl2Phe embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol). ΔH is calculated at 0 K.
knowledge, none have been clearly illustrated in any previous studies for the atmospheric degradation of ClPAHs (9,10-Cl2Phe included). In general, the tropospheric removal of PAHs involves wet and dry deposition, and atmospheric oxidation degradation such as the reactions with OH, NO3 and O3 et al. The wet and dry deposition of gaseous PAHs is relatively insignificant as a removal route. Among the various oxidants, OH radicals play the essential role in determining the oxidation power of the atmosphere (Keyte et al., 2013; Liu and Wang, 2008). So, in consideration of the structural similarity of 9,10-Cl2Phe with phenanthrene, the reaction with OH radicals should be an important removal process for gaseous 9,10-Cl2Phe. A full analysis of the atmospheric processes is limited in the laboratory studies, largely due to the lack of efficient detection schemes for intermediate radical species. With the aid of the density functional theory (DFT) and the Rice–Ramsperger–Kassel–Marcus (RRKM) theory, this paper carried out a rather comprehensive theoretical investigation on the OHinitiated atmospheric oxidation degradation of 9,10-Cl2Phe in the presence of O2/NOx, which is expected to be helpful for elucidating the atmospheric fate of 9,10-Cl2Phe.
+HO 2 P1
OH
+O2 E=14.74 H=-28.60
OH
Cl
Cl
Cl
+O2 E=9.73 H=-27.55
+HO2
OH
OH
IM3 Cl
P3
Cl
Cl
Cl
+O2 E=16.47 H=-18.05
+HO 2
OH
OH
IM4 Cl
+HO2
P2
IM2 Cl
Cl
Cl
Cl
2. Computational method The high-accuracy quantum chemical calculations were performed with the Gaussian 09 software package (Frisch et al., 2009) on a supercomputer. The geometries of the reactants, intermediates, transition states and products were optimized at the BB1K/6-31 + G(d,p) level, which has yielded satisfying results in previous studies (Qu et al., 2006). The vibrational frequencies were calculated to identify the structures obtained as true minima or first-order saddle points. The intrinsic reaction coordinate (IRC) analysis was carried out to confirm that each transition state connects to the right minima along the reaction path.
OH
+O2 E=16.15 H=-20.11
IM1 Cl
Cl
Cl
OH
P4
Cl
Cl
OH
OH Cl H=9.40 IM5
P5
Fig. 2. The O2 abstraction scheme of OH-9,10-Cl2Phe adducts embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol). ΔH is calculated at 0 K.
J. Dang et al. / Science of the Total Environment 505 (2015) 787–794
Cl
Cl
Cl
Cl
O
O
HOO
P6 Cl
OH
HOO IM10
IM11 Cl
Cl
Cl
+OH H2O H=-37.14
OH E=8.66 H=-7.04
O
789
Cl
+O2 E=7.91 H=-8.35
+O2 E=13.51 HO2 H=-13.11
Cl
H OO H OH IM6
H OH IM3
Cl
Cl
H shift E=23.97 H=-14.07
H OH HOO IM8 HO2 E=11.44 H=-5.13 Cl
Cl
P3
Cl
Cl
H OH
IM3 Cl
Cl
+O2 E=10.63 H=-8.52
Cl
H OO H OH IM6
H shift E=22.68 H=21.08
HO2
Cl
H shift E=38.01 H=-14.80
Cl
H HOO IM9
E=1.20 H=-6.42
H HOO
Cl
H O P7
H O
OH
H shift E=28.07 H=22.21 H OO H OH IM7
Cl
H O
IM14 OH E=1.27 H=-28.35 Cl
Cl
OH
Cl
Cl
H HOO H O IM12
Cl
Cl
Cl
H OO H OH IM7 Cl
OH E=12.19 H=-4.22
Cl
E=8.29 H=-3.56 H HOO H O IM13
Cl
H=-30.27 Cl
H HOO
H O
IM15
Fig. 3. The O2 addition reaction scheme of OH-9,10-Cl2Phe adducts (IM3) embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol).
phenol and naphthalene. The results agree well with the available experimental values, and the maximum relative errors are within 3.0% for geometrical parameters and 8.4% for vibrational frequencies (Kuchitsu, 1998; Herzberg, 1966; Shimanouchi, 1972; Hellwege and Hellwege, 1976; Martin et al., 1996). 3.1. Reaction of with OH radicals For convenience of description, the C atoms in 9,10-Cl2Phe are numbered, as presented in Fig. 1. There exist C = C, C-H and C-Cl
bonds in the molecular structure of 9,10-Cl2Phe. So, addition of OH to the C = C bonds, H abstraction from the C-H bonds and Cl abstraction from the C-Cl bonds are possible pathways for the reaction of 9,10Cl2Phe with OH radicals. The reaction schemes embedded with the potential barriers (△ E) and reaction heats (△ H, 0 K) are presented in Fig. 1 and Figure S1 of Supporting Information. It can be seen from Figure S1 that the Cl abstraction cannot occur under the general atmospheric conditions due to the extremely high barrier and strong endothermicity. At the BB1K/6-311 + G(3df,2p) level, the potential barriers of H abstractions are 5.36 ~ 37.04 kcal/mol. Clearly, the H
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Cl
Cl
Cl
Cl
Cl
Cl
OH +NO H OO H=-15.72
OH NO2 H E=24.14 OONO H=-9.88
OH H O
IM16
IM17
Cl
Cl
OO
OH
O
NO2 E=38.04 H=-2.56
IM21
IM20
IM19
Cl
Cl
OH
+NO H=-15.20
IM5
O P8
Cl
Cl
ONOO
OH
+O2 E=17.82 H=-13.81
OH
IM18
Cl
Cl
OH
Cl
Cl
+O2 HO2 E=29.57 H=7.06
E=0.14 H=-9.27 Cl
Cl
+O2 HO2 H=-17.19
Cl
Cl
Cl
+O2 E=11.01 H=-2.81
OH H
O H
H OONO
OH H
OH H
NO2 E=42.48 H=6.77
OH H IM25
IM24 +O2 HO2
Cl
Cl
Cl
O
O P10
+O2 HO2 E=22.90 H=-28.79
Cl
Cl
+NO H=-14.21 IM23
IM4
IM22
Cl
Cl
H OO
OH
O
P9 Cl
Cl
Cl
O
O
Cl
Cl
O
OH IM28
+OH H 2O E=7.90 H=-0.84
Cl
Cl
O H
E=15.24 H=-10.23 Cl
O H H=-2.81
OH IM27
OH IM26
Fig. 4. The reaction scheme of IM16, IM4 and IM5 embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol).
abstraction from the C4-H bond is energetically unfavorable because of the much high barrier of 37.04 kcal/mol. All H abstraction pathways are exothermic, and the reaction heats are from − 5.76 to −3.82 kcal/mol. The barriers of OH additions are 0.83 ~ 3.08 kcal/mol, and the reaction heats are from −27.23 to −16.73 kcal/mol. Obviously, the OH additions have lower barriers and are much more exothermic compared with the H abstractions. Hence, the OH additions are the energetically more favorable reaction pathways for the reaction of 9,10-Cl2Phe with OH radicals. Previous experimental research showed that additions of OH to C = C bonds are the dominant pathways compared with H abstractions for anthracene, naphthalene and monocyclic aromatic compounds under typical atmospheric conditions (Ananthula et al., 2006; Lorenz and Zellner, 1983; Perry et al., 1977). Our calculation result is consistent with the experimental studies. In addition, as shown in Fig. 1, the OH addition to the C4 atom is the thermodynamically most favorable because of the lowest barrier and highest exothermicity. 3.2. Secondary reactions 3.2.1. Reactions with O2 The study above shows that the addition reaction of 9,10-Cl2Phe with OH radicals can occur readily under the general atmospheric conditions. The adducts, OH-9,10-Cl2Phe, are important intermediates produced from the reaction of 9,10-Cl2Phe with OH radicals. In the atmosphere, they will further react with O2/NOx as their removal. Firstly, OH-9,10-Cl2Phe with O2 can react via a simple metathesis
mechanism to yield 9,10-dichlorophenanthrol and HO2 through H abstraction from the C-H bonds. The reaction schemes are depicted in Fig. 2. The potential barriers of these H abstraction processes are 9.73 ~ 16.47 kcal/mol at the BB1K/6-311 + G(3df,2p) level. The transition states lie at 11.89 ~ 17.72 kcal/mol above the sum energy of 9,10-Cl2Phe + OH + O2. The processes are strongly exothermic by 18.05 ~ 28.60 kcal/mol. The overall reactions, 9,10-Cl2Phe + OH + O2 → 9,10-dichlorophenanthrol + HO2, are strongly exothermic by 39.25 ~ 45.33 kcal/mol. It implies that the degradation pathways leading to the formation of 9,10-dichlorophenanthrol can occur easily under the general atmospheric conditions. Comparison of the reaction pathways presented in Fig. 2 shows that the H abstraction by O2 from 3-OH-9,10-Cl2Phe (IM3 in Fig. 2) has the lowest barrier and is energetically most favorable relative to the other H abstraction pathways. In addition, as shown in Fig. 2, the OH-9,10-Cl2Phe adduct IM5 can react via a unimolecular decomposition through cleavage of the C-Cl bond to yield 9-chlorophenanthrol. Secondly, O2 can attack on the C atoms with an unpaired electron in OH-9,10-Cl2Phe via an addition mechanism from two different directions: the cis or trans-position of the -OH group with respect to the aromatic ring. The reaction schemes are displayed in Fig. 3, Figure S2 and Figure S3 of Supporting Information. Therefore, ten O2-OH-9,10-Cl2Phe adduct isomers can be formed from the reaction of OH-9,10-Cl 2Phe with O2. Due to the structural similarity of OH9,10-Cl 2Phe, just the reaction scheme of 3-OH-9,10-Cl2Phe (IM3) with O2 and the subsequent reaction of OH-O2-9,10-Cl2Phe adduct
J. Dang et al. / Science of the Total Environment 505 (2015) 787–794
Cl
Cl
Cl
OH H OO
E=34.23 H=10.82
IM29
Cl
O O
Cl
Cl
O IM31
OO H OH IM6
Cl
H OH IM32
E=32.15 H=-44.75
CHO
Cl
Cl
+O2 HO2 E=19.46 H=-34.66
OH H
P11
O
CHO
Cl
Cl
O O
E=15.63 H=-7.10
OH H
E=25.27 H=-55.84
IM30
Cl
Cl
Cl
OH H
791
O
E=32.69 H=-44.18
O
H H OH P12
Cl
Cl
O O H OH H P13 Cl
Cl
Cl
Cl
H
OH H
E=35.70 OO H=10.96
IM33 Cl
Cl
O O OH H IM36
O O OH H
+O2 IM34 E=20.26 H=-30.31 H
Cl
Cl
H E=37.78 H=-36.02
OH H
H
O
O
+O2 HO2 E=20.45 H=-32.75
OH H
IM35
+NO OO H=-18.14
O O
OONO
OH H IM37
Cl
Cl
Cl
H
Cl
NO2 E=41.58 H=-1.12
O O
Cl
O OH H P15
O
+O2 HO2 E=28.54 H=-27.45
H O
OH H IM38
O
O
P14
Cl
Cl
Cl
Cl
O
E=7.94 H=-32.10
Cl
O
H O
OH H IM39
O
Fig. 5. The reaction scheme of IM29, IM6 and IM33 embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol) in the presence of O2 and NO. ΔH is calculated at 0 K.
(IM6) is depicted in Fig. 3. The subsequent reaction of IM6 has three pathways. The first one involves two elementary steps, H shift from the C-H bond and C-O bond cleavage, leading to the formation of 9,10-dichlorophenanthren-3-ol (P3). The second one includes four elementary reactions, H shift, H abstraction by O2, H abstraction by OH radicals and elimination of OH, leading to the formation of 9,10-dichlorophenanthrene-3,4-dione (P6). The H shift process is the rate-determining step because of the high barrier of 23.97 kcal/mol. The third pathway starts with H shift, followed by C-C bond rupture and elimination of OH and ultimately results in the formation of a dialdehyde (P7). Similarly, other OH-9,10-Cl2Phe adducts (IM1, IM2, and IM4) can also react with O2 to form dialdehydes, chlorophenanthrols and chlorophenanthrenequinones, and the reaction scheme is depicted in Figures S2 and S3 of Supporting Information. As shown in Fig. 4, the OH-O2-9,10-Cl2Phe intermediate IM16 react with NO, followed by the rupture of the O-ONO bond and H abstraction by O2, resulting in the formation of an epoxide compound (P8). The reaction of NO addition is barrierless and exothermic. The last elementary step of H abstraction by O2 has a potential barrier of 29.57 kcal/mol and
is exothermic by 7.06 kcal/mol. IM5 also can react with O2 to form an intermediate IM19. The subsequent reactions of IM19 are similar to those of IM16, with the exception of the extra ring-opening reaction. These processes ultimately lead to the formation of NO2 and dialdehyde. The reaction channel of IM4 contains seven elementary reactions: the addition of O2 to form organic peroxy radicals, the association of resulting radicals with NO, cleavage of the O-ONO bond to form epoxide intermediates, H abstraction by O2 , rupture of the C-O bond, H abstraction by hydroxyl radicals and H abstraction by O2 . 9,10dichlorophenanthrene-1,4-dione (P10) is formed from these reactions. Similar products have been detected in the experiments of phenanthrene and OH radicals (Lee and Lane, 2010). The reaction of the cleavage of O-ONO bond is the rate-determining process due to its high potential barrier. Other O2/NO reaction channels are presented in Figure S4 of support information, which have some similarities to those discussions above. So no more explanation is covered here. As shown in Fig. 5, the intermediate IM29 formed by O2 addition can undergo cyclization to produce bicyclic peroxy radicals (IM30). The subsequent reactions of IM30 lead to the formation of the product
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Cl
Cl
H=-32.81 Cl
Cl
NO2 +H2O
IM40
OH
2H2O E=22.19 H=-15.18 TS3 -3H2O
H=-29.50 NO2 IM41
OH H=-20.90
Cl
Cl
H=-36.66
NO2
IM42
OH Cl
Cl
Cl
Cl
Cl
OH
IM44 OH
IM3
Cl
Cl
H=-35.48
Cl
IM4
Cl
OH
H=-32.07
OH+H2O
+H2O NO2 OH IM46 Cl
NO2
H=-29.84
IM47
NO2
E=21.11 H=-37.06 -2H2O
P16
NO2 P17
OH
Cl
Cl
Cl
E=29.54 H=-22.02 -2H2O
2H2O E=26.32 H=-11.36 -3H2O
Cl
Cl
E=35.58 H=-11.33 -2H2O
Cl
Cl
Cl
E=42.66 H=-22.02 -H2O
Cl
NO2
P19
E=49.75 H=-11.33 -H2O
NO2 IM45
Cl
+H2O
Cl
Cl
E=37.92 H=-37.06 -H2O
NO2
H=-20.15
NO2
P18
E=36.06 H=-9.01 -2H2O
IM43
Cl
Cl
E=51.52 H=-9.01 -H2O
OH +H2O Cl
NO2 P17
E=25.29 H=-37.68 -2H2O
+H2O
NO2
IM2
Cl
E=36.83 H=-37.68 -H2O
Cl
Cl
P16
Cl
OH
IM1
NO2
E=26.46 H=-22.19 TS2 -2H2O
Cl
Cl
Cl
Cl
E=42.57 H=-22.19 TS1 -H2O
OH
P18
NO2
Cl
NO2
P19
Fig. 6. The formation scheme of nitro-9,10-Cl2Phe embedded with the potential barrier ΔE (in kcal/mol) and reaction heat ΔH (in kcal/mol) in the presence of O2 and NO. ΔH is calculated at 0 K.
P11. Calculations show that the formation of the bicyclic peroxy radical is the rate-determining step due to its high potential barrier. Compared with IM29, IM6 is easier to produce the bicyclic peroxy radical (IM32) because of the lower barrier height. The potential barrier of the formation of IM32 is calculated to be 15.63 kcal/mol, and the process is exothermic by 7.10 kcal/mol. Subsequently, two kinds of ring-opening processes of IM32 are proceeded, which results in the generation of the products P12 and P13. For the bicyclic peroxy radical IM34 formed by IM33, there exist two subsequent reaction pathways. The first one involves two elementary steps: rupture of the O-O bond and H abstraction by O2, which lead to the formation of P14. The second one
includes five elementary reactions: O2 addition, NO addition, cleavage of the O-ONO bond, ring-opening process and H abstraction by O2. The calculated profiles of the potential energy surface show that the step of the O-ONO bond cleavage is difficult to occur because of the high potential barrier of 41.58 kal/mol. 3.2.2. Reactions with NO2 The OH-9,10-Cl2Phe adducts (IM1-IM4) also can react with NO2 to form OH-NO2-9,10-Cl2Phe adducts via barrierless associations. These processes are strongly exothermic by 20.15 ~ 36.66 kcal/mol. The OHNO2-9,10-Cl2Phe adducts may subsequently undergo unimolecular
J. Dang et al. / Science of the Total Environment 505 (2015) 787–794 Table 1 RRKM rate constants (cm3 molecule−1 s−1) of the crucial elementary reactions involved in the OH-initiated oxidation degradation of 9,10-Cl2Phe at 298 K and 1 atm. Reactions 9,10-Cl2Phe + OH 9,10-Cl2Phe + OH 9,10-Cl2Phe + OH 9,10-Cl2Phe + OH 9,10-Cl2Phe + OH 9,10-Cl2Phe + OH IM3 + O2 → IM6 IM6 → IM8 IM8 → P3 IM3 → IM7 IM7 → IM9 IM9 → P3 IM6 → IM12 IM12 → IM14 IM14 → P7 IM7 → IM13 IM13 → IM15 IM15 → P7 IM16 → IM17 IM17 → IM18 IM5 → IM19 IM19 → IM20 IM20 → IM21 IM21 → IM22 IM4 → IM23 IM23 → IM24 IM24 → IM25
Rate constants → → → → → →
OH-9,10-Cl2Phe IM1 IM2 IM3 IM4 IM5
(k) 2.35 × 10−12 (k1) 1.15 × 10−13 (k2) 2.51 × 10−14 (k3) 6.77 × 10−14 (k4) 9.61 × 10−13 (k5) 7.07 × 10−15 2.22 × 10−19 3.69 × 10−7 8.06 × 103 3.63 × 10−19 6.34 × 10−6 3.45 × 103 3.94 × 10−9 1.16 × 108 3.54 × 109 2.42 × 10−8 1.08 × 104 3.24 × 1012 5.48 × 10−13 1.04 × 10−6 4.35 × 10−21 5.51 × 10−13 6.11 × 10−17 1.18 × 108 4.57 × 10−20 5.40 × 10−13 2.01 × 10−20
decomposition to yield nitro-9,10-Cl2Phe through the direct loss of water. As shown in Fig. 6 (black arrows), the barriers of the reactions of the direct loss of water are extremely high (36.83 ~ 51.52 kcal/mol), so the reactions is difficult to occur. Water is one of the most abundant atmospheric constituents and can affect the reactions through forming hydrogen bonded complexes with … … … other molecules, such as O… 3 H2O, SO3 H2O, CH3CHO H2O and H2SO4 H2O in the atmosphere (Frost and Vaida, 1995; Meijer and Sprik, 1998; Iuga et al., 2010; Vaida and Simon, 1995). With the participation of water, the loss of water from the OH-NO2-9,10-Cl2Phe adducts becomes a bimolecular reaction (OH-NO2-9,10-Cl2Phe + H2O). A sixmembered ring transition state (Figure S5 of support information) was identified, in which water molecule acts as a bridge, accepting the hydrogen from the aromatic ring and simultaneously donating another hydrogen atom to the phenolic group. The potential barriers of the loss of water via the bimolecular reaction are 11.54 ~ 16.81 kcal/mol lower than those of the direct loss of water. In particular, when OH adds to the C1 or C4 atoms, the resulting OH-9,10-Cl2Phe adduct is a hybrid of several resonance structures (Figure S6 of support information). The unpaired electron can be distributed to the ortho position and the para position of the -OH group, and NO2 can be added to these positions. With the aid of the water dimer, nitro-9,10-Cl 2Phe can be formed from the degradation pathway through the OH addition to the C1 (or C4) atom, followed by addition of NO2 to the C4 atom (or C 1) and the loss of water. Pfeilsticker detected water dimers in the atmosphere by near infrared spectroscopy and suggested an atmospheric concentration of 6 × 10 14 molecule cm − 3 at 292 K (Tretyakov et al., 2013; Pfeilsticker et al., 2003). With the aid of the water dimer, para-nitro-9,10-Cl2Phe can be formed, as described in Fig. 6 (red arrows).
793
involved in the OH-initiated oxidation degradation of 9,10-Cl2Phe were evaluated by Rice–Ramsperger–Kassel–Marcus (RRKM) theory (Robinson and Holbrook, 1972) at 298 K and 1 atm. The RRKM method has been successfully used to deal with several similar reactions (Glowacki et al., 2012; Zhou et al., 2011). The calculated rate constants of the crucial elementary reactions are listed in Table 1. The individual rate constants for the OH addition to the C1-H, C2-H, C3-H, C4-H, and C10-H bonds of 9,10-Cl2Phe are noted as k1, k2, k3, k4, k5, respectively. The overall rate constant of the OH addition reaction is denoted as k, k = (k1 + k2 + k3 + k4 + k5) × 2. The overall rate constant k is 2.35 × 10−12 cm3 molecule−1 s−1 at 298 K and 1 atm. Due to the absence of the available experimental values, it is difficult to make a direct comparison of the calculated rate constants with the experimental data for the reaction of 9,10-Cl2Phe with OH radicals. So, this work also calculated the rate constant of the addition reaction of phenanthrene with OH radicals. The RRKM value of 3.98 × 10−11 cm3 molecule− 1 s− 1 at 298 K and 1 atm agree well with the published experimental value of 3.1 × 10−11 cm3 molecule−1 s−1 (Atkinson and Arey, 1994). From the good agreement with the experimental value, it can be inferred that the rate constants of the elementary reactions listed in Table 1 are reasonable. We expect that the rate constant values will contribute to the construction of detailed kinetic models describing the atmospheric fate of 9,10-Cl2Phe. According to the overall rate constant of the reaction of 9,10-Cl2Phe with OH radical and a average OH concentration (COH) of 9.75 × 105 molecule cm−3 (Prinn et al., 1995), from the expression: τOH ¼
1 kðOH þ 9;10‐Cl2 PheÞ cOH
The atmospheric lifetime of 9,10-Cl2Phe determined by OH radicals is calculated about 5.05 days. 4. Conclusions This work carried out a comprehensive theoretical study on the reaction mechanism of the OH radical-initiated atmospheric oxidation degradation of 9,10-Cl2Phe. The rate constants were determined by using the RRKM method. Two conclusions can be drawn from this study: (1) The OH-initiated atmospheric oxidation of 9,10-Cl2Phe generates a class of ring-retaining and ring-opening products containing chlorophenanthrols, 9,10-dichlorophenanthrene-3,4-dione, dialdehydes, chlorophenanthrenequinones, nitro-9,10-Cl2Phe and epoxides et al. (2) The overall rate constant of the OH addition to 9,10-Cl2Phe is 2.35 × 10− 12 cm3 molecule−1 s− 1 at 298 K and 1 atm. The atmospheric lifetime of 9,10-Cl2Phe by OH radicals is about 5.05 days. Acknowledgment The work was financially supported by NSFC (National Natural Science Foundation of China, project Nos. 21337001, 21377073 and 21177076), Taishan Grand (No. ts20120522) and Independent Innovation Foundation of Shandong University (IIFSDU, project No. 2012JC030).
3.3. Rate constant calculations
Appendix A. Supplementary data
In order to clarify the transport and atmospheric fate of ClPAHs, it is critical to determine accurate rate constants of the elementary reactions involved in the atmospheric oxidation degradation of ClPAHs (Keyte et al., 2013). On the basis of the BB1K/6-311 + G(3df,2p)//BB1K/6-31 + G(d,p) energies, the rate constants of the elementary reactions
The H abstraction reaction scheme of 9,10-Cl2Phe. The O2 addition reaction scheme of OH-9,10-Cl2Phe adducts (IM1, IM2, IM4 and IM5). The O 2 addition reaction scheme of OH-9,10-Cl 2 Phe adducts (IM1, IM2, IM4 and IM5). The NO addition reaction scheme of five OH-O2-9,10-Cl2Phe adducts. Configuration of the transition states for
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