Kinetics of the oxidation of aromatic C-nitroso compounds by nitrogen dioxide

The oxidation of nitrosobenzene by nitrogen dioxide in carbon tetrachloride has been re-examined, the rate of reaction exhibiting first-order dependence upon the concentrations of both nitrosobenzene and nitrogen dioxide, with a reactant stoichiometry of 1:1. The rate of reaction is found to be highly sensitive to the presence of trace quantities of water and intensive drying procedures for the solvent have been developed such that the reaction rate could be reduced to a constant level. For nitrosobenzene and a range of substituted nitrosobenzenes the kinetics of the oxidation reaction in carbon tetrachloride have been studied over the temperature range 291-313 K using the stopped flow technique and pseudo-first-order conditions with the nitrogen dioxide in excess. Arrhenius parameters have been obtained for 15 nitrosoarenes and the results obtained are discussed with reference to the Hammett s constants and the electron population at the nitroso nitrogen as determined by CNDO calculations. It is concluded that the reaction occurs by a radical addition mechanism to the nitroso nitrogen atom giving an unstable aminoxyl intermediate which decomposes rapidly giving the corresponding nitrobenzene and nitric oxide.