The kinetics of hydrogen-isotope exchange at the nitrogen atom of substituted anilinium ions. Part 2. The nitrosonium-ion-catalysed reaction

Abstract

Nitrosonium ions catalyse hydrogen-isotope exchange between the N–H protons of NN-dimethylanilinium ions and aqueous sulphuric acid (83–93%). At the acidities used, the subsequent chemical reactions between the amines and nitrosonium ions occur much more slowly. The rate of the catalysed exchange is proportional to the concentration of nitrosonium ions and inversely proportional to the appropriate acidity function (h₀‴). A mechanism is put forward for the catalysed exchange based on the formation of a loose complex between the nitrosonium ion and the anilinium ion followed by proton loss from the nitrogen pole. This process is shown to be related to the direct diazotisation of some anilinium ions and to the nitrous-acid-catalysed nitration and oxidation of the NN-dimethylanilinium ion. Substituent effects on the nitrosonium-ion-catalysed exchange are much less than those on the acid-catalysed exchange and resemble those on the acid-catalysed mechanism of diazotisation.