Diesel exhaust and pyrene nitration

Diesel exhaust extracts contain the arenes pyrene, nitropyrene, and dinitropyrenes in the ratio 1:10/sup -2/:10/sup -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 NO/sub 2//N/sub 2/O/sub 4/(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.