A dichotomy in the nitration of fluoranthene with NO2/N2O4: Mechanistic and toxicological implications

Article abstract of DOI:10.1021/jo00296a015

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 CH₂Cl₂ 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 CCl₄ 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 Bronsted acid catalysis, particularly in CH₂Cl₂, 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 CCl₄. 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.