A DICHOTOMY IN THE NITRATION OF FLUORANTHENE WITH NO2/N2O4 - MECHANISTIC AND TOXICOLOGICAL IMPLICATIONS

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 CH2C12 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 CC14 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 Brønsted acid catalysis, particularly in CH2C12, and is inhibited by nonnucleophilic bases like 2,6-di-tert-butylpyridine. At temperatures lower than 25 °C, the ionic reaction pathway predominates, even in CC14. 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 NO2 may occur under atmospheric conditions. © 1990, American Chemical Society. All rights reserved.