The mechanisms of some reactions of nitrogen dioxide with alkenes and aromatic compounds

The reactions in solution with nitrogen dioxide/ dinitrogen tetraoxide of a range of organic compounds, chosen as model compounds for those present in car engine fuel and oil, have been studied. A main emphasis has been on the reactivity of a number of alkenes. Allylbenzene, which has the possibility of allylic reaction, has been studied in detail. The products of these reactions were dinitro, α, β-nitro-nitrite, α, β-nitro-hydroxy and a,0-nitro-nitrate adducts. Allylic products were absent. Kinetic studies established both NO2 and N2O4 as reactive species with the alkenes, but studies of chemically induced dynamic nuclear polarisation were dominated by the NO2 reaction. The intermediacy of radical pair species on the pathways to the dinitro and nitro-nitrite adducts was confirmed. Naphthalene and 2-methylnaphthalene were much less reactive towards nitrogen dioxide/dinitrogen tetraoxide, although rates relative to benzene were established. No compelling evidence for a greater reactivity of 1-methylbutylbenzene than the hexadecane solvent towards nitrogen dioxide/dinitrogen tetraoxide was obtained even at 150°C. Studies of the commercial antioxidants AN2 (bis (4-hydroxy-3,5-di-t-butylphenyl) methane) and IONOX 400 (2,2-bis (4-hydroxy-3,5-di-t-butylphenyl) propane) revealed a noteworthy difference. The former gave a reaction second-order in NO2 and yielded the corresponding 2,5- dienone, whereas the latter gave two equivalents of 2,6- di-t-butyl-4-nitrophenol in a reaction first-order in NO2