Preparation of Nitroarenes

Two routes give nitroarenes. (1) DIRECT NITRATION: benzene heated at 330 K with a nitrating mixture (concentrated HNO3 + concentrated H2SO4) undergoes electrophilic substitution to give nitrobenzene ('oil of mirbane') + water; nitrating nitrobenzene further gives m-dinitrobenzene, since -NO2 is a meta director. (2) INDIRECT METHOD for p-dinitrobenzene: since direct nitration of nitrobenzene can only give the META isomer, the PARA isomer is instead built via p-nitroaniline -- diazotised with NaNO2/HBF4 to give p-nitrodiazonium fluoroborate, which is then treated with NaNO2 in the presence of copper to replace the diazonium group with a second -NO2, giving p-dinitrobenzene + N2 + NaF + BF3. An amino group can also be converted directly into a nitro group using a strong oxidising agent such as Caro's acid (H2 …