Air Pollutants Formed in Thermal Decomposition of Folpet Fungicide

Dec 1, 2010 - It appears that the availability of easily abstractable. H atoms, in the structure of captan but not in that of folpet, defines the prod...
0 downloads 0 Views 929KB Size
Download PDF
Environ. Sci. Technol. 2011, 45, 554–560

Air Pollutants Formed in Thermal Decomposition of Folpet Fungicide under Oxidative Conditions KAI CHEN, JOHN C. MACKIE,† ERIC M. KENNEDY, AND BOGDAN Z. DLUGOGORSKI* Process Safety and Environmental Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, New South Wales 2308, Australia

Received August 4, 2010. Revised manuscript received October 20, 2010. Accepted October 31, 2010.

This contribution studies the decomposition of folpet fungicide under oxidative conditions and compares the product species with those of captan fungicide, which is structurally related to folpet. Toxic products arising from folpet comprised carbon disulfide(highestemissionfactorof4.9mgg-1 folpet),thiophosgene (14.4),phosgene(34.1),hydrogencyanide(2.6),tetrachloroethylene (111), hexachloroethane (167), and benzonitrile (4.5). Owing to their related molecular structures, folpet emitted similar products to captan but at different yields, under the same experimental conditions. It appears that the availability of easily abstractable H atoms, in the structure of captan but not in that of folpet, defines the product distribution. In conjunction with the quantum chemical calculations, these experimental measurements afford an enhanced explanation of the formation pathways of hazardous decomposition products of these two structurally related fungicides.

Introduction Folpet belongs to the sulfenimide group of pesticides also containing captan and captafol (1). First introduced in 1952, folpet has been widely employed on grapevines and other fruit trees (2). In France, it still plays an important role in preventing the fungi-caused diseases in grapes, with the spraying frequency of 10 to 15 times from May to September (3). The agricultural applications of folpet also include wood preservation and curative treatment of several vegetable crops (4). Regarding its industrial applications, folpet serves as feedstock for production of several manufactured goods, especially oil-based paints, coatings, and plastics (5). Accidental fires of folpet that take place periodically in storage facilities and the widespread burning of biomass treated or contaminated with pesticides may impose significant impact to the surrounding environment (6). An assessment of this impact requires improved knowledge of the formation of toxic products during oxidation of folpet. The same knowledge possesses immediate applications to evaluate risks related to burning of agricultural residue or waste, for energy recovery, as pesticides are widely present in today’s agricultural activities (7, 8). Studies of the thermal decomposition of folpet in oxidative atmospheres have been rarely documented. One thermo* Corresponding author phone: +61 2 4985 4433; fax: +61 2 4921 6893; e-mail: [email protected]. † Also at School of Chemistry, The University of Sydney. 554

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 45, NO. 2, 2011

gravimetric analysis (TGA) of solid folpet revealed a multistage decomposition taking place immediately above folpet’s melting point (180 °C), with steep weight losses observed at 250, 290, and 350 °C, respectively (9). Costa et al. have studied pool fires of folpet by a modified Tewarson apparatus, to assess the thermal and toxic effects (10). Online gas analysis quantified several gaseous pollutants including the highly toxic hydrogen cyanide. However, the study included no analyses of initial and condensed products and developed no decomposition pathways. The absence of a comprehensive set of measurements comprising all products formed thermally from folpet prevents one from performing a rigorous risk assessment on this fungicide. In terms of their molecular structure, both folpet and captan incorporate the trichloromethylthio (SCCl3) group. Folpet is the aromatic version of captan, with the SCCl3 group bonded to a phthalimide (PI) moiety rather than to the tetrahydrophthalimide (THPI) group in captan (Figure 1). We have previously determined the toxic air pollutants from the oxidation of captan and discovered that the abstraction of hydrogen atoms from the cyclohexene ring may facilitate the decomposition process (11). With its stronger C-H bonds and hence less abstractable hydrogen on the aromatic ring, folpet would be expected to yield similar products as a result of the reactions involving the SCCl3 group and to exhibit different products arising from reactions of chemically dissimilar THPI and PI moieties. This article constitutes a comprehensive investigation into the thermal decomposition of folpet under oxidative conditions in the gas phase. Experiments were performed under the same conditions as implemented in our previous study of captan, viz., temperatures between 200 to 500 °C, O2 level at 6% (v/v), and residence time of 1 s. Besides the identification of toxic species in the decomposition of folpet, we compare the quantitative results with those of captan. The experimental observations are explained with the assistance of quantum chemical calculations, providing an improved understanding of the formation pathways of toxic pollutants from these two structurally related fungicides.

Experimental Section The experimental apparatus consisted of a pesticide vaporizer, an isothermal tubular reactor, and a product sampling train, with details described elsewhere (12) and schematic elucidated in Figure S1 of the Supporting Information. Folpet (>95%, AmFineCom) powder was loaded into a vaporizer unit constructed of polytetrafluoroethylene (PTFE) tubing, which itself was housed vertically inside a GC oven (150 °C) to slowly generate folpet vapor (approximate 0.042 mg min-1). Diluted with nitrogen (99.999% purity), the mixture entrained a controlled amount of oxygen (6.0 ( 0.5% O2 in N2 (v/v)) at a flow rate of 19 cm3 min-1. We monitored the O2 concentration in the carrier gas by a Varian CP 2003 micro gas chromatograph (µGC). A heated transfer line (175 °C) coupled the vaporizer to the reactor which comprised an alumina tube maintained at a preset temperature by a threezone furnace. The same residence time of 1 s was maintained by adjusting the length of the reaction zone for experimental runs performed at different temperatures. Sampling from the reactor continued for 1 h in each run, enabling the sampling train to collect a wide range of products. Connection tubes, made solely of PTFE, were prewashed with a solution of acetone and methanol to minimize contamination and adsorption loss (13). The dehydrated gaseous species flowed into a tedlar sampling 10.1021/es102652w

 2011 American Chemical Society

Published on Web 12/01/2010

FIGURE 1. Molecular structures of folpet and PI; captan and THPI. bag for FTIR spectroscopic analysis, while, in a separate run, VOC were captured in a glass tube loaded with 100 mg of activated charcoal. To conclude the sampling train, a dichloromethane-methanol solvent trap, chilled in a cold glycol bath (0 °C), served to collect the condensed products. Only a brief description of the analytical procedure is presented here. Sections 2 and 3 of the Supporting Information convey further information on the instrumentation parameters and list additional details of the analytical procedure. We recorded infrared spectra on a Varian 660-IR spectrometer, equipped with a 10 m long path gas cell, over the range of 4000-500 cm-1 at 0.5 cm-1 resolution. The identification of gaseous species was assisted by a library of reference spectra included in the QASoft software package. The software also provided a region integration and subtraction routine for quantitative analysis. The in-cell dilution of reaction gas samples with nitrogen (99.999% purity) ensured a valid absorbance range (425 °C). Clearly, less SCCl2 and COCl2 are formed in the oxidation of folpet than in the oxidation of captan. The profile of HCl increases over the whole temperature range, climbing steeply between 350 to 450 °C. In the oxidation of captan, HCl exhibits a similar trend with yields exceeding those of folpet. Additionally, we observed a trace yield of CHCl3 (e0.7%) arising from the decomposition of folpet, less than the 1.6% from captan. Carbon tetrachloride, detected only in the oxidation of folpet, increased in yield with rising temperature to a peak value of 1.5% (425 °C) and then decreased to 0.7% at 500 °C. It is evident that the gaseous products from the oxidation of folpet contain much less chlorine than those of captan. In the end of this section, we demonstrate that this deficit of chlorine in HCl, COCl2, SCCl2, and CHCl3 is balanced by significantly higher formation of C2Cl4 and C2Cl6 in oxidation of folpet than in captan. Regarding sulfur-containing gases, SO2 dominates the sulfur content in both cases. The yield of SO2 from folpet increases rapidly from 300 to 425 °C, with the values exceeding those from captan (>400 °C). However, we observed less COS and CS2 formed in the oxidation of folpet than in oxidation of captan. The yields of COS increase with elevated temperature, gently sloping toward maxima of 10.4% for folpet and 17.3% for captan, both occurring at 500 °C. Carbon disulfide increased its yields to maxima of 1.9 and 5.3%, at 425 °C, for folpet and captan, respectively, and then declined at higher temperatures. The yield-temperature profiles of benzene, HCN, CO, and CO2 all monotonically increase with temperature in the oxidation of folpet, similar to the trends displayed by the decomposition of captan (for CO2 refer to Figure S4). For folpet, the yields of HCN exceed those of benzene, with the VOL. 45, NO. 2, 2011 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

555

FIGURE 2. Yield-temperature profiles of gaseous products formed in the oxidation of folpet (F) and captan (C): Cl containing gases (a) and (b); S containing gases (c); CO, HCN, and benzene (d). The concentration of HCl was divided by 3 to calculate the yield because of the stoichiometry of Cl; similarly we multiplied the concentration of CS2 by 2 and divided the concentration of CO by 9. See Section 2 of the Supporting Information for estimates of experimental errors (as relative standard deviation). highest yields of 2.9% and 0.9% respectively. In comparison, the oxidation of captan resulted in significantly higher yields of these two compounds. The profiles of carbon oxides arising from the oxidation of folpet both increase with temperature up to 500 °C, attaining maxima of 25.2% and 8.0% for CO2 and CO respectively. Similarly, the yields of CO2 are higher than those of CO over the whole temperature range for the oxidation of both fungicides. Overall, carbon oxides arising from the decomposition of captan exhibit larger yields, compared to those of folpet. The analyses of VOC identified two major products in the oxidation of folpet, viz., tetrachloroethylene (TCE) and hexachloroethane (HCE), both classified as suspected carcinogens (17). For folpet, we have only been able to detect a trace level of benzonitrile (BZN) in the CS2 extract from the activated charcoal trap. The yields of each VOC product arising from folpet between 400 to 500 °C are compared with those from captan in Figure 3. The yield of HCE from the folpet experiments increased with temperature to a peak of 20.9% at 425 °C and then declined to 6.7% at 500 °C. TCE exhibits an increase in yield with elevated temperature, with the maximum yield corresponding to 19.8%. The peak yields of HCE and TCE from folpet are higher than those from captan (1.8% and 4.3%, respectively). However, the oxidation of captan leads to more BZN compared to folpet. The yield of BZN in the oxidation of folpet exhibits a maximum of only 1.3% at 500 °C. The GC-MS chromatograms of condensed compounds from folpet identified two compound peaks; viz., undecom556

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 45, NO. 2, 2011

FIGURE 3. Yields of VOC compounds arising from the oxidation of folpet (F) and captan (C). posed folpet and phthalimide. Figure 4 displays the yield/ temperature profiles of each compound, with the results of captan included in the same graph for comparison. The conversion of folpet increases rapidly above 350 °C, reaching 100% at 425 °C. The overall decomposition of folpet occurs at slightly higher temperature, achieving a complete conversion at a temperature 25 °C higher than that for captan. We have been unable to detect THPI in the oxidation of folpet, though THPI is an important product of oxidation of captan. Nor was captan detected as a product of decomposition of folpet in the current experiments despite the observation of

FIGURE 4. Yield profiles of condensed products in the oxidation of folpet (F) and captan (C) as a function of temperature. For folpet (denoted as Folpet (F) in the legend) and captan (denoted as Captan (C) in the legend), the profiles correspond to the conversion. folpet being a product of captan oxidation. Phthalimide, arising from folpet, has its yield increasing to the peak value of 56.6% at 425 °C, whereupon it slightly decreases toward 500 °C. The profile of PI reaches the maximum at the same temperature at which folpet decomposes completely. In comparison, for captan, the combined yields of THPI and PI add to the top value of 54.7%, at 400 °C; i.e., at the temperature characterized by 100% conversion of captan. Generally, the results of folpet indicated satisfactory sulfur mass balances (recovery >80%). However, we only recovered 73.5% of sulfur in gaseous, VOC, and condensed products at 400 °C. The observation of sulfur residue on the reactor tubes (12) is responsible for deficiency in sulfur balance under such experimental conditions. A chlorine sink also exists in the experiments on folpet, owing to losses of gas phase HCl in the sampling and analysis procedures, hence resulting in the underestimation of HCl in FTIR analyses (11). For instance, the typical chlorine balance was 55.6% at 500 °C in the experiment of folpet. The additional ion chromatographic analysis of Cl-, in the trapping solution (NaOH) of reaction gases, led to a reasonable chorine balance of 84.7%. The oxidative thermal decomposition of a compound, under vapor phase condition, generally initiates via unimolecular decomposition, biomolecular reaction with O2, or a combination of both. The intermolecular rearrangement, expulsion of an appropriate leaving group, and bond fission are expected as the preferences to initiate the unimolecular reaction, while bimolecular reaction with O2 would take place through abstraction of a relatively weakly bonded H atom or addition of O2. With the assistance of quantum chemical calculations, we have already postulated that the thermal decomposition of vapor phase captan, in the presence of O2, would initiate with the fission of the weakest bond (C-S bond) (11). The molecule of folpet appears to have no facile leaving groups nor low energy rearrangement pathways. We can also rule out initiation via a bimolecular abstraction reaction between folpet and O2 which would produce HO2 and a folpetderived radical. The rate of a bimolecular initiation is equal to kbi[folpet][O2], while the rate of a unimolecular initiation corresponds to kuni[folpet]. In the structure of folpet, H atoms on the aromatic ring are more strongly bonded than those on the cyclohexene ring of captan. To estimate a rate constant for abstraction of H by O2 from the aromatic ring, we adopt the experimental rate constant for abstraction of H by O2 from benzene to form HO2 of 6 × 1013 exp (-60 kcal mol-1/ RT) cm3 mol-1 s-1 (18). Under the O2 level of this study (6.0

FIGURE 5. Proposed pathways to toxicants in the decomposition of folpet; note, numerical data correspond to the relative energies (in kcal mol-1). mol %), the rate of the bimolecular reaction would be approximately 7 × 107 exp (-60 kcal mol-1/RT) cm3 mol-1 [folpet] s-1. We may compare this rate with the predicted rate of an initiation via bond fission. To calculate bond enthalpies we have used isodesmic work reactions to arrive at values of the S-C and N-S bond enthalpies at 298 K. (See the Supporting Information for detailed procedure.) By far the weakest bond in folpet is the S-C bond whose enthalpy was computed as 55.7 ( 1.5 kcal mol-1. In comparison, the enthalpy of the N-S bond is 80.5 ( 2.0 kcal mol-1. Fission at the S-C linkage will produce CCl3 and a two-ring radical fragment, both heavy groups with large moments of inertia. Huybrechts et al. measured the A-factor for fission of Cl3C-CCl3 as 4 × 1017 s-1 (19). For the reaction, CHCl2CCl3 f CCl3 + CHCl2, Benson and Weissman obtained A ) 4 × 1017 s-1 (20). Thus, we expect the rate constant for unimolecular initiation of folpet decomposition to be about 1017 × exp (-58 ( 2 kcal mol-1/RT) s-1, several orders of magnitude higher than the bimolecular reaction rate with O2. In addition, the quantum chemical calculations have ruled out possibilities for the addition of O2 at the S atom (or at any other atom in folpet). Based on these computations, the oxidations of both folpet and captan start through the unimolecular fission of the S-C bond. In the case of folpet, O2 can react rapidly with radicals produced in the initiation, i.e., CCl3 and radical F1, with the decomposition pathways summarized in Figure 5. In the previous study on the oxidation of captan (11), we proposed the formation pathways of COCl2, to proceed via the reaction between CCl3 radical and oxygen. Briefly, the addition of O2 to CCl3 radical can form trichloromethylperoxy radical (CCl3O2) (21) and the peroxy radical will either react with itself or CCl3 (22, 23), leading to the formation of CCl3O which itself would readily decompose to COCl2 and chlorine atom via the fission of the weak C-Cl bond. Our G3B3 calculations given in the Supporting Information show that the reaction CCl3O f COCl2 + Cl is actually exothermic by 15.9 kcal mol-1 at 298 K. Furthermore, the experimental rate constant for this reaction is a high 8.8 × 106 s-1 at 300 K (24). The oxidation of folpet can also produce COCl2 via the same processes. However, the yield of COCl2 from folpet is less than that from captan, suggesting the existence of some processes either inhibiting the formation of COCl2 in folpet or promoting that in captan. We have been unable to discover any explicit step, in the oxidation of folpet, which might inhibit the reactions between CCl3 radical and O2 to produce COCl2. Thus, it is more likely that some steps facilitate the formation of COCl2 in the case of captan. Once the first H on the cyclohexene ring is abstracted by radicals, quantum chemical calculations indicate that the resulting radical can lose a further H by fission with a low energy barrier. Based VOL. 45, NO. 2, 2011 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

557

FIGURE 6. Proposed formation of benzonitrile from cyclohexadienyl-derived radical. See Figure S7a of the Supporting Information for the potential energy surface of the rearrangement. on the NIST Chemical Kinetics Database, H atom can react readily with O2 to form HO2 or undergo chain branching to form OH + O, depending on the temperature (25). The reaction of HO2 + CCl3O2 has been investigated experimentally, with COCl2 as the only observed product (23). A computational study using coupled cluster and DFT/B3LYP methods has revealed that the reaction between HO2 and CCl3O2 to form CCl3OOH (step A) is essentially barrierless (26), taking place via an initial barrierless addition followed by a rearrangement and fissioning off of O2 involving a subsequent barrier of only 2 kcal mol-1. These computations were carried out at the CCSD(T)/cc-pVDZ level of theory (26). Subsequently, CCl3OOH will decompose unimolecularly to CCl3O (step B) which itself can lead to COCl2 CCl3O2 + HO2 f CCl3OOH + O2 ∆rE0 ) -44.2 kcal mol-1 (A) CCl3OOH f CCl3O + OH ∆rE0 ) 38.0 kcal mol-1 (B) We believe that these steps as well as possible reactions with OH and O promote the consumption of CCl3 radicals, accelerating the overall decomposition of captan compared to that of folpet. With less abstractable H on the aromatic ring, the formation of HO2, OH, and O and the subsequent conversion of CCl3 to COCl2 are limited in the oxidation of folpet. Thus, more CCl3 radicals are expected to undergo self-combination to form HCE and TCE, leading to the observed higher yields of HCE and TCE in the measurements of folpet compared to those of captan. TCE can be formed by Cl attack on C2Cl6 with subsequent Cl fission from C2Cl5. Additionally, the formation of TCE from two CCl3 should be a feasible process as shown in the Supporting Information. The initial HCE product is formed in a well 70 kcal mol-1 below the reactants. A barrier of 54 kcal mol-1 must then be surmounted to form TCE + Cl2. This is a multiwell problem, and the rate of formation of TCE by chemical activation from two CCl3 will depend on pressure and collisional deactivation rates; TCE formation should be significant as it only needs overcome a barrier located 16 kcal mol-1 below the reactants’ energy. In the products of folpet, the presence of HCl and CHCl3, albeit at lower concentrations than for captan, indicates that H can still be abstracted from the aromatic ring of folpet. Since the abstraction of H from the aromatic ring is more difficult than from the cyclohexene ring, we would expect to detect less CHCl3 in the oxidation of folpet. Typically aromatic C-H bond enthalpies are approximately 110 kcal mol-1, whereas aliphatic C-H bond enthalpies are around 99 kcal mol-1. Abstraction of H by Cl from the aromatic ring has been reported (25), but there have been no reports of abstraction of aromatic H by CCl3 radical. The observed CHCl3 may arise from reaction between HCl and CCl3 radicals, a reaction whose rate constant has been measured previously as 4.5 × 1011 exp(-11.3 kcal mol-1/RT) cm3 mol-1 s-1 between 303 and 426 K (27). Consequently, more CCl3 radicals can react with the free chlorine radical, resulting in the formation of CCl4, as evidenced by the experimental observations of decomposition of folpet. 558

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 45, NO. 2, 2011

As the yield of COCl2 decreases above 400 °C, the further oxidation of COCl2 produces carbon oxides and Cl atoms (28, 29). The latter can either abstract H to form HCl or recombine to produce traces of Cl2. Owing to the lower formation of COCl2 and higher yields of HCE and TCE, we observed a lower yield of HCl from folpet than from captan. The presence of SCCl2 in the oxidation of folpet indicates that the N-S bond can also break. We have already calculated that the energy of N-S bond and initiation by direct bond fission is likely to be uncompetitive with S-C fission. Using the model compound H2N-S-CCl3 to investigate the feasibility of N-S breakage via the addition of H to the nitrogen of captan, forming THPI and SCCl3 we have located a transition state for concerted addition of H to the N atom and fission of the SCCl3 group (see ref 11 and the Supporting Information). The barrier for this addition/fission was found to be only 7.2 kcal mol-1 at the B3LYP/6-31G(d) level of theory. Although the computed barrier height at this level of theory would only be approximate, it nonetheless gives strong support for the feasibility of N-S fission in captan via H atom addition. H atoms are readily available because the abstraction of H on the cyclohexene ring (in captan) by radicals (i.e., CCl3 and Cl) would concomitantly lead to the loss of a further H from the resulting cyclohexenyl or cyclohexadienyl radicals (11). In the case of folpet, once the H on the aromatic ring is abstracted, oxidation of the remainder may release H or HO2. Similarly, cleavage of the N-S bond in folpet can also take place by the addition of H to N, producing SCCl3 and PI, with SCCl3 readily decomposing to SCCl2. Our G3B3 calculations (see the Supporting Information) yield the low value of 16.5 kcal mol-1 for the C-Cl bond enthalpy in SCCl3. The lower yields of SCCl2 from folpet can be attributed to the lower availability of H from its aromatic ring than from the cyclohexene ring of captan. Although PI was detected as an important product from both pesticides, the experiments on folpet resulted in higher yields of PI than those from captan. The reason is somewhat uncertain, but we observed more benzonitrile arising from the decomposition of captan at elevated O2 concentration (11). As the O2 promotes radical formation, radical attack may facilitate the cleavage of the C-C bond between carbonyl group and the ring. Thus, there exists another possibility during the aromatization of THPI (Figure 6), competitive to the formation of PI. Consecutive abstractions of ring hydrogens from THPI can produce 3a,7a-dihydrophthalimide. Further abstraction of a bridge hydrogen from the 3a- or 7aposition will produce a radical which can undergo ringopening of the five-membered ring. The potential energy surface arising from ring-opening has been computed at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d,p) level of theory. As shown in the Supporting Information, alternative pathways to BZN have been discovered. The open-chain PhCONHCO radical can either undergo H fission to benzoyl isocyanate (BIC) or HNCO fission to PhCO radical. Barriers for these two eliminations are moderate and similar. A further barrier of 52.9 kcal mol-1 must be surmounted to eliminate CO2 from BIC to form BZN. A lower energy pathway shown in the Supporting Information involves the elimination of CO from PhCO and the subsequent addition of HCN (an observed product) and elimination of H to form BZN. Although HNCO was not observed in the present studies, we have detected

this species as a product in the oxidation of THPI and PI themselves (30). The formation of benzonitrile has also been documented from further decomposition of PI (31). The lower yields of benzonitrile from folpet would be expected owing to the less availability of abstractable H in folpet and PI. As more THPI converted into benzonitrile, we observed less PI from captan compared to folpet. Benzene and HCN, two products of benzonitrile decomposition (32), were formed in smaller amounts in the experiments on folpet than those on captan as a consequence of lower yields of benzonitrile from folpet. The further oxidation of sulfur in SCCl2 produces SO2 (33, 34), with the remaining part eventually expected to form CO2 and HCl. Alternatively, we have also revealed that the abstraction of Cl by H or other radicals may convert SCCl2 to CS (11), which itself is crucial in the formation of CS2 (18). In the case of folpet, the latter fate of SCCl2 is limited by the lower availability of H, as evidenced by the lower yields of CS2 in comparison with those from captan. Once the C-S bond in the structure of folpet breaks, the sulfur site will be available for further reactions. In addition to the oxidation to SO2, there is a possibility that F1 radical can react with CO to form COS. We have speculated a similar reaction in the study of captan, based on the analogy of CH3S radical reacting with CO to form COS (35). The >N-S · group in F1 would also be expected to behave analogously to CH3S. The low yields of both COS and CO in the oxidation of folpet compared with captan support this proposition.

Acknowledgments This study has been funded by the Australian Research Council. We acknowledge with gratitude discussions with Professors Mohammednoor Altarawneh of Al-Hussein University, Jordan and Adam Grochowalski of the Cracow Technical University, Poland as well as the technical supports from Ms Annabel Mitchell of Varian Australia.

Supporting Information Available (1) Schematic of the experimental apparatus; (2) operational parameters of instruments and analytical procedures; (3) identification of gas-phase components and their quantification features; (4) quantum chemical calculations; (5) comparison of yields of carbon dioxide between folpet and captan. This material is available free of charge via the Internet at http://pubs.acs.org.

Literature Cited (1) Schwack, W. N-(dichloromethylthio)-phthalimide, a photometabolite of folpet. Chemosphere 1987, 16 (1), 127–132. (2) Teisseire, H.; Vernet, G. Effects of the fungicide folpet on the activities of antioxidative enzymes in duckweed (Lemna minor). Pestic. Biochem. Physiol. 2001, 69 (2), 112–117. (3) Canal-Raffin, M.; Receveur, M.; Martinez, B.; Titier, K.; Ohayon, C.; Baldi, I.; Molimard, M.; Moore, N.; Brochard, P. Quantification methods of folpet degradation products in plasma with HPLCUV/DAD: Application to an in vivo toxicokinetic study in rats. J. Chromatogr., B: Anal. Technol. Biomed. Life Sci. 2008, 865 (1-2), 106–113. (4) U.S. Environmental Protection Agency. Folpet reregistration eligibility decision (RED); EPA: Washington, DC, 1999. www. epa.gov/oppsrrd1/REDs/0630red.pdf (accessed Jul 19, 2010). (5) U.S. Environmental Protection Agency. Revocation of Folpet Tolerances; EPA: Washington, DC, 1994 http://www.epa.gov/ EPA-PEST/1994/December/Day-02/pr-68.html (accessed Jul 19, 2010). (6) Nelson, G. L. Fire and pesticides, a review and analysis of recent work. Fire Technol. 2000, 36 (3), 163–183. (7) Lu, H.; Zhu, L.; Zhu, N. Polycyclic aromatic hydrocarbon emission from straw burning and the influence of combustion parameters. Atmos. Environ. 2009, 43 (4), 978–983. (8) Senneca, O.; Scherillo, F.; Nunziata, A. Thermal degradation of pesticides under oxidative conditions. J. Anal. Appl. Pyrolysis 2007, 80 (1), 61–76.

(9) Flora, T.; Pfeifer, G. Thermal decomposition of fungcides of the phthalimide type, Proceeding of Analytic Chemistry Conference, 3rd, Akad. Kiado: Budapest, Hungery, 1970; pp 371-377. (10) Costa, C.; Treand, G.; Moineault, F.; Gustin, J. L. Assessment of the thermal and toxic effects of chemical and pesticide pool fires based on experimental data obtained using the Tewarson apparatus. Process Saf. Environ. Prot. 1999, 77 (3), 154–164. (11) Chen, K.; Mackie, J. C.; Kennedy, E. M.; Dlugogorski, B. Z. Thermal decomposition of captan and formation pathways of toxic air pollutants. Environ. Sci. Technol. 2010, 44 (11), 4149– 4154. (12) Chen, K.; Wojtalewicz, D.; Mackie, J. C.; Kennedy, E. M.; Dlugogorski, B. Z. Emission of toxic species in fires of folpet, Proceeding of 6th International Seminar on Fire and Explosion Hazards, Apr 11-16; University of Leeds: Leeds, UK, 2010; in press. (13) Inomata, Y.; Iwasaka, Y.; Osada, K.; Hayashi, M.; Mori, I.; Kido, M.; Hara, K.; Sakai, T. Vertical distributions of particles and sulfur gases (volatile sulfur compounds and SO2) over East Asia: Comparison with two aircraft-borne measurements under the Asian continental outflow in spring and winter. Atmos. Environ. 2006, 40 (3), 430–444. (14) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.; Stratmann, R. E. ; Burant, J. C.; et al. Gaussian 03, Revision C.02; Gaussian, Inc: Pittsburgh, PA, 2004. (15) Becke, A. D. Density-functional thermochemistry. 4. A new dynamical correlation functional and implications for exactexchange mixing. J. Chem. Phys. 1996, 104 (3), 1040–1046. (16) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37 (2), 785. (17) IARC. Overall evaluation of carcinogenicity: an updating of IARC monographs Vol.s 1 to 42. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Suppl. 7; IARC: Lyon, 1987. (18) Chu, L. K.; Han, H. L.; Lee, Y. P. Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy. J. Chem. Phys. 2007, 126 (17), 7. (19) Huybrechts, G.; Theys, J.; VanMele, B. Pyrolysis of hexachloroethane in the gas phase: Computer aided kinetic study. Int. J. Chem. Kinet. 1996, 28 (10), 755–761. (20) Benson, S. W.; Weissman, M. Mechanism of the pyrolysis of C2HCl5, molecular and radical steps. Int. J. Chem. Kinet. 1982, 14 (12), 1287–1304. (21) Atkinson, R.; Baulch, D. L.; Cox, R. A.; Crowley, J. N.; Hampson, R. F.; Hynes, R. G.; Jenkin, M. E.; Rossi, M. J.; Troe, J.; Wallington, T. J. Evaluated kinetic and photochemical data for atmospheric chemistry: Vol. IV-gas phase reactions of organic halogen species. Atmos. Chem. Phys. 2008, 8 (15), 4141–4496. (22) Russell, J. J.; Seetula, J. A.; Gutman, D.; Danis, F.; Caralp, F.; Lightfoot, P. D.; Lesclaux, R.; Melius, C. F.; Senkan, S. M. Kinetics and thermochemistry of the equilibrium CCl3 + O2 T CCl3O2. J. Phys. Chem. A 1990, 3277–3283. (23) Catoire, V.; Lesclaux, R.; Schneider, W. F.; Wallington, T. J. Kinetics and mechanisms of the self-reactions of CCl3O2 and CHCl2O2 radicals and their reactions with HO2. J. Phys. Chem. 1996, 100 (34), 14356–14371. (24) Atkinson, R.; Baulch, D. L.; Cox, R. A.; Hampson, R. F.; Kerr, J. A.; Rossi, M. J.; Troe, J. Evaluated kinetic, photochemical and heterogeneous data for atmospheric chemistry. 5. IUPAC subcommittee on gas kinetic data evaluation for atmospheric chemistry. J. Phys. Chem. Ref. Data 1997, 26 (3), 521–1011. (25) Manion, J. A.; Huie, R. E.; Levin, R. D.; D. R. B., Jr.; Orkin, V. L.; Tsang, W.; McGivern, W. S.; Hudgens, J. W.; Knyazev, V. D.; Atkinson, D. B.; et al. NIST Chemical Kinetics Database; National Institute of Standards and Technology: Gaithersburg, MD, 2008. (26) Hou, H.; Deng, L.; Li, J.; Wang, B. A systematic computational study of the reactions of HO2 with RO2: The HO2 + CH2ClO2, CHCl2O2, and CCl3O2 reactions. J. Phys. Chem. A 2005, 109 (41), 9299–9309. (27) Demare, G. R.; Huybrech, G. Rate constants for recombination of CCl3 radicals and for their reactions with Cl Cl2 and HCl in gas phase. Trans. Faraday Soc. 1968, 64 (545P), 1311–&. (28) Baillet, C.; Fadli, A.; Sawerysyn, J. P. Experimental study on the thermal oxidation of 1,3-hexachlorobutadiene at 500-1100 °C. Chemosphere 1996, 32 (7), 1261–1273. (29) Atkinson, R.; Baulch, D. L.; Cox, R. A.; Crowley, J. N.; Hampson, R. F.; Hynes, R. G.; Jenkin, M. E.; Rossi, M. J.; Troe, J. Evaluated kinetic and photochemical data for atmospheric chemistry: Volume III - gas phase reactions of inorganic halogens. Atmos. Chem. Phys. 2007, 7, 981–1191. VOL. 45, NO. 2, 2011 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

559

(30) Chen, K.; Wojtalewicz, D.; Mackie, J. C.; Kennedy, E. M.; Dlugogorski, B. Z. Hazardous air pollutants formed in fires of phthalimide compounds, Proceedings of 8th Asia-Oceania Symposium on Fire Science and Technology, Victoria University, Australia, 2010, accepted. ˙ urakowska-Orsza`gh, J.; Chreptowicz, T. Thermal degradation (31) Z of polyimides-II: Mechanism of carbon dioxide formation during thermal degradation. Eur. Polym. J. 1981, 17 (8), 877–880. (32) Etemad-Rad, S.-T.; Metcalfe, E. The pyrolysis of benzonitrile. Fire Mater. 1993, 17 (1), 33–37. (33) Ravichandran, K.; Ayala, I.; Ishikawa, Y.; Weiner, B. R. Bimolecular reaction dynamics of thiophosgene with O(3P) atoms. J. Phys. Chem. A 1997, 101 (46), 8587–8592.

560

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 45, NO. 2, 2011

(34) Lu, C. W.; Wu, Y. J.; Lee, Y. P.; Zhu, R. S.; Lin, M. C. Experiments and calculations on rate coefficients for pyrolysis of SO2 and the reaction O plus so at high temperatures. J. Phys. Chem. A 2003, 107 (50), 11020–11029. (35) Koch, L. C.; Marshall, P.; Ravishankara, A. R. An investigation of the reaction of CH3S with CO. J. Phys. Chem. A 2004, 108 (24), 5205–5212.

ES102652W