2616 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA J. zyxwvutsr Org. Chem. 1990,55, zyxwvu 2616-2621 "C); zyxwvutsrq 4,4'-dinitrodiphenylmethane, mp 181 "C (lit.w mp 181-182 "C); 4-nitrodiphenylmethane, mp 32 "C mp 29-32 "C). Solvents were purified and solutions made up as described pre- viou~ly.~ Buffers were purified commercial products. (50) Bowden, K.; Stewart, R. Tetrahedron 1965, 21,261. (51) Russell, G. A.; Moye, A. J.; Janzen, E. G.; Mak, S.; Talaty, E. R. (52) Robinson, G. E.; Thomas, C. B.; Vernon, J. M. J. Chem. SOC. B zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA J. Org. Chem. 1967, 32,137. 1971,1273. Measurements. Kinetic studies were made using a Durrum stopped-flow spectrophotometer, with a thermostatted cell com- partment (25 i 0.2 "C). Some slow kinetic measurements were made using a Shimadzu UV-160 spectrophotometer. pH deter- minations in water-DMSO mixtures containing 0.5 M NMe,Cl were carried out at 25 "C using the same procedure as that previously de~cribed.~ A Tacussel Isis 2oooO electronic pH meter was used for this purpose. Registry No. la, 32255-27-9; lb, 32255-280; C-la, 126083-71-4; C-lb, 126083-72-5. A Dichotomy in the Nitration of Fluoranthene with N02/N204: Mechanistic and Toxicological Implications Giuseppe L. Squadrito, Frank R. Fronczek,' Daniel F. Church, and William A. Pryor* Biodynamics Institute, Louisiana State University, Baton Rouge, Louisiana 70803 Received May 16, 1989 The nitration of fluoranthene with nitrogen dioxide can occur by two distinctive reaction pathways. These paths can be distinguished by product analysis, since fluoranthene is a nonalternant hydrocarbon. Free-radical nitration and electrophilic nitration give different products. In solvents with dielectric constants lower than that of CHZClz and in the absence of acid catalysis, the exclusive reaction pathway is homolytic in nature. The products of the homolytic reaction pathway can be interpreted as arising via a multiple-step addition-elimination mechanism and are notable for the formation of 2-nitrofluoranthene (the major product in CCll but absent under electrophilic nitration conditions) and the unusually large amounts of the expected 1,2-dinitrofluoranthene and 1,3-dinitrofluoranthene. The ionic reaction pathway is subject to both Lewis and Br0nsted acid catalysis, particularly in CH2ClZ, and is inhibited by nonnucleophilic bases like 2,s-di-tert-butylpyridine. At temperatures lower than 25 "C, the ionic reaction pathway predominates, even in CCl,. 2-Nitrofluoranthene is a marker for the free-radical nitration of fluoranthene, and its presence in polluted tropospheric air suggests that free-radical nitration by NOz may occur under atmospheric conditions. The reactions of polycyclic aromatic hydrocarbons (PAH) with nitrating agents have received much attention recently due to the potential for the formation of nitro- PAH in urban atmosphere^^-^ and the mutagenic and/or carcinogenic properties of many of these compounds.6*7 Nitro-PAH are thought to arise from a variety of human activities including fossil fuel combustion and biomass burning. However, certain nitro-PAH that cannot be ex- plained in terms of the conventional nitration mechanism have been identified in airborne particulate matter.4p8-g For example, 2-nitrofluoranthene (2NF), despite being the most abundant and ubiquitous nitro-PAH p o l l ~ t a n t , ~ ~ ~ ~ ~ has not been observed in combustion emission^.^ It also did not appear to be produced under various nitration (1) Department of Chemistry, Louisiana State University. (2) Pitts, J. N., Jr.; Sweetman, J. A.; Zielinska, B.; Atkinson, Roger; Winer, A. M.; Harger, W. P. Environ. Sci. Technol. 1985,19, 1115-1121. (3) Paputta-Peck, M. C.; Marano, R. S.; Schuetzle, D.; Riley, T. L.; Hampton, C. V.; Prater, T. J.; Skewes, L. M.; Jensen, T. E.; Ruehle, P. H.; Bosch, L. C.; Duncan, W. P. Anal. Chem. 1983,55, 1946-1954. (4) Ramdahl, T.; Zielinska, B.; Arey, J.; Atkinson, R.; Winer, A. M.; Pitts, J. N., Jr. Nature (London) 1986,321,425-427. (5) MacCrehan, W. A,; May, W. E.; Yang, S. D.; Benner, B. A,, Jr. Anal. Chem. 1988,60, 194-199. (6) Tokiwa, H.; Nakagawa, R.; Ohnishi, Y. Mutat. Res. 1981, 91, (7) Rosenkranz, H. S.; Mermelstein, R. Mutat., Res. 1983, 114, (8) Pitts, J. N., Jr.; Sweetman, J. A.; Zielinska, B.; Winer, A. M.; (9) Arey, J.; Zielinska, B.; Atkinson, R.; Winer, A. M. Atm., Enoiron. 321-325. 217-267. Atkinson, R. Atm., Enuiron. 1985, 19, 1601-1608. 1987, 21,1437-1444. conditions;lOJ1 however, recently 2NF has been identified as a product under homolytic nitration condition^,'^-'^ and it was proposed that 2NF arises from radical reactions in Despite the numerous works devoted to nitration of PAH, reports on the reaction of PAH with N02/N204 are often controversial, and mechanisms involving electron- transfer, radical, or electrophilic substitution have been proposed.16 We have recently reported on the radical nitration of fluoranthene, 1, with N02/N204 in CClk14 We proposed the use of 1 as a mechanistic probe for distin- guishing between radical and electrophilic nitration be- cause, being a nonalternant hydrocarbon, it gives a markedly different product distribution according to the type of reaction mechanism. Thus, the positional reactivity found with nitronium ion mediated nitration follows the order 3 zyxwvu > 8 > 7 > 1 > 2, in agreement with the theoretical calculations involving an intermediate a-complex that polluted tropospheric ambient air. 4 zyxw 1 zyxwvut 8 1 9 7 13.14 (10) Radner, F. Acta Chem. Scand. E 1983,37,65-67. (11) Streitweiser, A., Jr.; Fahey, R. C. J. Org. Chem. 1962, 27, (12) Zielinska, B.; Arey, J.; Atkinson, R.; Ramdahl, T.; Winer, A. M.; Pitts, J. N., Jr. J. Am. Chem. SOC. 1986,108,4126-4132. (13) Sweetman, J. A.; Zielinska, B.; Atkinson, R.; Ramdahl, T. Winer, A. M.; Pitts, J. N. Jr. Atm. Enoiron. 1986, 20,235-238. (14) Squadrito, G. L.; Church, D. F.; Pryor, W. A. J. Am. Chem. SOC. 1987,109,6535-6537. (15) Shane, B. S.; Squadrito, G. L.; Church, D. F.; Pryor, W. A. Presented at the 19th Annual Meeting of the Environmental Mutagen Society, Charleston, SC, March 1988. 2352-2355. (16) Reference 14 and references cited therein. 0022-3263/90/1955-2616$02.50/0 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 0 1990 American Chemical Society