Environ. Sci. Technol. 1987,21, 1130-1 13 1
Turner, R. R.; Lowry, P.; Levin, M.; Lindberg, S. E.; Tamura, T. Leachability and Aqueous Speciation of Selected Trace Constituents of Coal Fly Ash; Electric Power Research Institute: Palo Alto, CA, 1982; EA-2588. Watanabe, I.; Tanabe, K.; Furuya, K.; Matsushita, H. Bunseki Kagaku 1985, 34, T45-T50 (in Japanese). Sato, K. Leaching Characteristics of Various Elements from Coal Fly Ash; Central Research Institute of Electric Power Industry: Tokyo, Japan, 1986; No. ET86001. Misra, S. G.; Tiwari, R. C. Soil Sci. Plant Nutr. (Tokyo) 1963, 9, 216-219.
Sims, J. R.; Bingham, F. T. Soil Sci. SOC.Am. Proc. 1968, 32, 364-369.
Bingham, F. T.; Page, A. L.; Coleman, N. T.; Flach, K. Soil Sci. SOC.Am. Proc. 1971, 35, 546-550. McPhail, M.; Page, A. L.; Bingham, F. T. Soil Sci. SOC.Am. Proc. 1972, 36, 510-514. Pierce, M. L.; Moore, C. B. Environ. Sci. Technol. 1980,
Method of Grain-Size Analysis of Soils; Japan Standard Association: Tokyo, Japan, 1978; JIS A 1204 (in Japanese). Peech, M.; Cowan, R. L.; Baker, J. H. Soil Sci. SOC.Am. Proc. 1962, 26, 37-40. Kitano, Y.; Sakata, M.; Matsumoto, E. J. Oceanogr. SOC. Jpn. 1981, 37, 259-266. McKeague, J. A.; Day, J. H. Can. J. Soil Sci. 1966,46,13-22. McKeague, J. A.; Brydon, J. E.; Miles, N. M. Soil Sci. SOC. Am. Proc. 1971, 35, 33-38. Holmgren, G. G. S. Soil Sci. SOC.Am. Proc. 1967, 31, 210-2 11.
Sakata, M. Environ. Sci. Technol. 1987, 21, 771-777. Summers, K. V.; Rupp, G. L.; Davis, G. F.; Gherini, S. A. Groundwater Data Analyses at Utility Waste Disposal Sites; Electric Power Research Institute: Palo Alto, CA, 1985; EA-4165.
Sugano, I. Soil Types of Japan; Noson Gyoson Bunkakyokai: Tokyo, Japan, 1964; p 469 (in Japanese).
14, 214-216.
Elkatib, E. A,; Bennett, 0. L.; Wright, R. J. Soil Sci. SOC. Am. J . 1984,48, 1025-1030.
Received for review November 18, 1986. Accepted July 8, 1987.
Diesel Exhaust and Pyrene Nitration David S. Ross," Georglna P. Hum, and Robert J. Schmitt SRI International, Menlo Park, California 94025
Diesel exhaust extracts contain the arenes pyrene, nitropyrene, and dinitropyrenes in the ratio 1:10-2:10-5, formed under conditions where the nitrating agent is limiting. This ratio is inconsistent with the sequence pyrene nitropyrene dinitropyrenes, since the deactivation brought about by the introduction of the first nitro group would virtually stop the nitration of nitropyrene under the given conditions. Thus, the production of the very highly mutagenic dinitropyrenes from pyrene cannot be through the intermediacy of nitropyrene. We explain the presence of the dinitropyrenes through experimental results demonstrating the direct polynitration of pyrene in a scheme involving initial production of the radical cation of pyrene. Our results show that pyrene is nitrated directly by NOz/N204[N(IV)] and not nitric acid [N(V)]. Kinetics studies show that the apparent N(V) nitration of pyrene and presumably other similar arenes is, rather, initial redox chemistry involving the arene and N(V) producing N(IV), which then is responsible for the nitration.
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The mutagenic activity of diesel exhaust components is an area of present concern and study. Nitroarenes are detected in exhaust extracts, and l-nitropyrene (1-NP) and 1,6- and l,&dinitropyrenes (1,6-DNP and 1,8-DNP) are three of the several candidates considered as the significant mutagens ( I ) . In fact, 1,8-DNP is the most mutagenic nitroarene known, with the l,6-isomer only slightly less active (2). Pyrene (P) itself is a major extractable component of diesel exhaust particulate and is present in excess over nitropyrenes (3). In cases where the fuel is purposefully enriched in pyrene, P levels are 2-3 orders of magnitude greater than 1-NP. In turn, the DNP levels are usually 2 orders of magnitude below 1-NP (1). Thus, in round numbers DNP:NP:P = 10-5:10-2:l. The fact that P >> NP demonstrates either that nitration is slow compared to the mass transfer components in the exhaust process or more likely that the nitrating agent is present in limiting quantities (P >> NO,) (3, 4). Under such conditions however, the anticipated sequence P N P DNP cannot be responsible for the dinitroarenes, as discussed below. We conclude that there must be an-
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other source for the polynitrato aromatic products. The inconsistency is demonstrated from the kinetics aspects of conventional electrophilic nitration and the action of nitric acid (5). Thus, the addition of a first nitro group to an aromatic system brings about a 6 order of magnitude decrease in the rate of substitution of a second. [This value can be estimated from the data a t 25 "C for the nitric acid nitrations of both toluene (6) and p-nitrotoluene (7) in 80% sulfuric acid.] With this value in calculations based on consecutive second-order reactions (8),it can be estimated that, at conditions where both the nitrating agent is limiting and unnitrated arene remains in the product mixture, the ratio dinitroarene:mononitroarene should be in the range of to or far below what is observed. Even lowering that estimate to account for the use of toluenes rather than polycyclic aromatic hydrocarbons (PAHs) for the rate differences, it is clear that the dinitropyrenes in diesel exhaust are present at far too high levels to be formed in conventional electrophilic nitration. Insight into how the polynitroarenes are formed can be found in results from our recent study of the nitration of pyrene (9). We studied the actions of N(V) [HN03] and of N(1V) [NOz/N2O4]under conditions where generally N204> NOz. The work was conducted both in methylene chloride and in condensed, neat N(1V). The substrates were pyrene and l-nitropyrene, and the reactions were studied in both the presence and absence of oxygen. The work included a study of the kinetics bf nitration and the distribution of products formed under various conditions. This work gave two results important to the present question: (i) under our conditions, N(1V) and not nitric acid nitrates pyrene, and (ii) nitropyrene is not an intermediate in the formation of polynitropyrenes from the pyrene/N(IV) reaction. The former finding runs contrary to several recent reports summarized by Chan and Gibson (IO). However our findings, the results of separate runs with carefully purified Nz04 and anhydrous H N 0 3 in doubly distilled methylene chloride, are unequivocal. Some data are presented in Figure 1,which shows the product profiles for pyrene nitrations at 25 "C. The pyrene concentrations in both cases are comparable, while the nitric
0013-936X/87/0921-1130$01.50/0
0 1987 American Chemical Society
04
0.4
0.3 Pd"d 0.5
0.1
0.c 200
600
400
so0
1000
Tlrn. (uc)
Figwe 1. Nibation 01 pyrsim by born N(IW and nlbic ackl In memylene chloride at 25 "C. Nkric ackllpyrene = 7.5 X I O 4 M14.9 X 10.' M. N(1V)lpyrene = 8.4 X Ml5.7 X M.
-6 Plod.
'0.2%
Nlntlon Products
Flgure 2. at 25 OC.
Woducts of nltratlon of pyrene and 1-nltropyrene In N,O,
acid concentration is about an order of magnitude greater than that of the N ( N . It is clear from the f w e , however, that there is no nitric acid nitration at periods where the N(IV) process is complete. Slow nitric acid nitration was observed after an induction period in runs where the pyrene concenrations were substantially increased from 10" M to 10.' M levels. In these cases, the arene likely acts 89 an initiator, with small quantities being oxidized by the nitric acid to yield some N2O4,which then carries out the nitration on the remaining pyrene. As regards the intermediacy of nitropyrene, we found that in neat NUV) pyrene rapidly forms di- and trinitropyrenes. Under the same conditions on the other hand, 1-nitropyrene equally rapidly forms almost solely dinitropyrenes, with only a trace of the trinitro derivative. The results are shown in Figure 2. Moreover, as shown in the figure, the dinitropyrene distributions from the two nitrations are very different, with l,&DNP formed as a major product only in 1-NP nitration. Thus in pyrene nitration, nitropyrene is not necessarily an intermediate in the production of the more highly nitrated pyrenes. Pyrene, and presumably other PAH substrates, can proceed directly and rapidly to polynitrated arenes. We have explained these fmdings with a reaction scheme involving initial one-electron oxidation of the arene by molecular N20,. In parallel, competitive reactions, the Py-H
+
N204
-
tPy-H
.+
***N02*-.N02-1
/
nltrODYreW
o.;.\ DOlYnllrOPY'BneS
radical cation-like arene intermediate then proceeds to mononitroarene through collapse of the caged chargeseparated complex or to polynitro arenes by reaction ex-
ternally with one or more additional tetroxides (9). Because its N204nitration is so rapid, we presume that lnitropyrene goes through a similar sequence. We conclude therefore that the DNPs in diesel exhaust arise from this kind of chemistry. Jensen e t al. in their exhaust study account mention 1,6- and 1,8-DNP but not the 1,3-isomer (I), a result cleanly in line with ours, pointing specifically to direct pyrene dinitration. In a diesel engine exhaust train, however, the N(IV) must be virtually fully dissociated (NOz >> N204),and accordingly, there must be other sources of the charge-separated arene. We can surmise that the surfaces of the exhaust soot particles or perhaps other surfaces in the system could generate such species; it is known, for example, that some acidic surfaces can generate arene radical cations ( I l ) . However, the issue at present remains unresolved. Finally, it is of interest to consider the recent results of Grosjean and co-workers (I2). They found under conditions of limited nitrating agent that the nitration of PAHs by N 0 2 / N 2 0 4was suppressed when the arenes were deposited on diesel soot and that nitric acid was necessary for the nitration. Since we find that nitric acid does not directly nitrate PAHs, the observations of Grosjean e t al. require another explanation. We assert that the suppression they observed was rather the result of the consumption of the limited NOz/N204by rapid reaction with the soot support. In other words the soot is more reactive toward nitration than is the PAH, a result consistent with the observations of Smith e t al. (13). We propose that the apparent enhancement of nitration by the addition of nitric acid is thus due to its decomposition on the soot surface, both deactivating the surface toward nitration and yielding N W ) . which then brings about the arene nitration. Literature Cited (1) Jensen, T. E.; Schuetzle, D.; Prater, T. J.; Ball, J. C.; Salmeen, I. In Polynuclear Aromatic Hydrocarbons: Mechanisms, Methods and Metabolism, 8th International Symposium; Cooke, M., Dennis, A. J., Eds.; Battelle Press:
Columbus, OH, 1985; pp 643-661. (2) Rosenkranz, H. S.; Mermelstein, R. In Nitrated Polycyclic Aromatic Hydrocarbons; White, C. M., Ed.; Verlag: New York, 1985; Chapter 6. (3) Henderson, T. R.; Sun, J. D.; Li, A. P.; Hanson, R. L.; Bechtold, W. E.; Harvey, T. M.; Shahanowitz, J.;Hunt, D. F. Enuiron. Sci. Technol. 1984. 18. 428-434. (4) Williams, P. T.; Bartle, K. D.; Andrews, G. E. Fuel 1986, 65,1150-1157. (5) Schofield,K. Aromatic Nitration: Cambridge University
Press: Camhridee. U.K. 1980. (6) Coomhes, R. G.; M h i e , R. B.; Schofield, K.J. Chem. Soc.
B 1968,800-804. (7) Vinnik. M. I.: Grabovskava. Zh. E.: Arzamaskova. L. N. Russ. J. Phys. Chem. (Engi. Transl.) 1967, 4 1 , 580. (8) Frost, A,; Pearson, R. G. Kinetics and Meehanims, 2nd ed.;
Wiley: New York, 1965; Chapter 8. (9) Ross, D. S.; Hum, G. P.; Schmitt, R.
J. Presented at the 192nd National Meeting of the American Chemical Society, Anaheim, CA, Sept 1986; Polynuclear Aromatic Compounds; Liebert, Ed.; Advances in Chemistry 217: American Chemical Society: Washington, DC, 1987 (in press). (10) Chan, T. L.; Gibson, T. L. In Nitrated Polycyclic Aromatic Hydrocarbons; White,C. M., Ed.; Verlag: Hiedelberg, 1985; pp 237-266 and citations therein. (11) Kuria, Y.; Sonda, Y.; Sato, M. J. Catalysis 1970,19,82-85. (12) Grosjean, D.; Fung, K.; Harrison, J. Enuiron. Sci. Technol. 1983,17,673-679. (13) Smith, D. M.; Akhter, M. S.;Chughtai, A. R. J.Phys. Chem. 1984,88,5334-5342. Received for review February 24, 1987. Accepted July 24, 1987.
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