Phenylation of Nitrobenzene by γ-Radiation

Phenylation takes place during γ-radiolysis of pure nitrobenzene to produce the three isomeric nitrobiphenyls with ortho-para substitution favored over meta. This is in agreement with free radical phenylation. The effects of the DPPH, galvinoxyl, and sulfur hexafluoride on the yields of the isomeric nitrobiphenyls were determined. The results with DPPH indicate that approximately 40% of the overall phenylation process is related to free radicals and excited molecules and, with SF₆, that approximately 33% is related to the anion,${\rm C}_{6}{\rm H}_{5}{\rm NO}_{2}{}^{-}$. The results with galvinoxyl are complicated by the fact that G for 2-nitrobiphenyl increases from 0.076 for pure nitrobenzene to 0.10 with galvinoxyl. This suggests that the galvinoxyl anion reacts with the solvent molecules to produce a phenylating species which exhibits greater ortho selectivity than the radiolytic phenylating species.