Ferrate(VI) oxidation of aniline

A detailed kinetic and thermodynamic study of ferrate(VI) oxidation of aniline (aminobenzene) has been carried out in isotopic solvents, H2O and D2O, as a function of reductant concentration, solution pH, temperature and pressure by means of conventional stopped-flow and high-pressure stopped-flow spectrophotometric methods. Under pseudo first-order conditions with reductant in at least 10-fold excess over ferrate, these redox processes give rise to a simple exponential change of optical density. The temperature profile reveals relatively low activation enthalpies, and the activation entropies found for these processes are very negative. In addition, the significant negative activation volumes estimated from the pressure dependence of the rate constants indicate a substantial decrease in partial molar volume during the formation of the transition state, suggesting that highly structured transition states are formed in these reactions. An EPR result indicates a free radical reaction mechanism. The kinetic isotopic results for aniline systems measured in H2O and in D2O solvent indicate that the amino hydrogen/deuterium plays a role in the formation of the transition states.