The nitrous acid-catalysed nitration of p-nitrophenol in aqueous nitric acid. Kinetic evidence for reaction through the p-nitrophenoxyl radical

Previous observations that the nitrous acid-catalysed nitration of p-nitrophenol in aqueous nitric acid becomes zeroth-order with respect to nitrous acid as the concentration of nitrous acid is increased have been confirmed. However, under these conditions, the reaction is shown to remain first-order with respect to p-nitrophenol. This observation, and studies of the u.v. spectra of related solutions, rule out the previously suggested interpretation involving the formation of a high concentration of p-nitrophenyl nitrite in solution. Observations on the kinetic form of the reaction and on the variation of the reaction rate with the concentration of nitric acid in media of constant Ho̧ are shown to be consistent with a reaction in which the p-nitrophenoxide ion is oxidised to the p-nitrophenoxyl radical which then reacts with nitrogen dioxide