Abstract
The nitration of deactivated aromatic compounds usually requires heating with fum-HNO3/conc-HM2SO4 at elevated temperature. However, a combination of NO2 and O3 was found to exhibit a powerful nitrating ability toward deactivated aromatic systems, giving the corresponding nitro derivatives in good yield. With moderately deactivated aromatic systems such as tolunitriles, xylonitriles and naphthonitriles, nitration can also be smoothly effected using a NO2-O2 system at room temperature in the presence of an appropriate zeolite. A remarkable feature of the latter type of non-acid nitration is a high and unique regioselectivity. Thus, the nitration of 1-naphthonitrile with the NO2-O2 system in acetonitrile gave 5-nitro derivative as the predominant product. The similar nitration of 2-naphthonitrile gave a product mixture in which the 5-nitro/8-nitro isomer ratio was reversed against the classical nitration based on the use of HNO3-H2SO4 (1.33 versus 0.72). Polycyclic azaaromatic compounds such as 6-chloropurine and 6-methoxypurine also underwent smooth nitration under similar conditions to give a moderate yield of 2-nitro derivatives, which are otherwise difficult to obtain by other methods.
