Kinetic and equilibrium studies of anilinoalkanesulfonate formation

(1)H NMR studies of the reactions of some hydroxyalkanesulfonates, 1, with aniline derivatives, 2, show the formation at equilibrium of anilinoalkanesulfonates, 3. Kinetic studies in water are consistent with a mechanism involving dissociation of 1 to give the parent aldehyde, which reacts with 2 to give a carbinolamine. Acid-catalysed dehydration of the carbinolamine yields an iminium ion which reacts rapidly with sulfite to give the product 3. Study of the variation with pH of the rate constants of the reaction indicates a change in the nature of the rate-determining step from carbinolamine formation to carbinolamine dehydration as the pH is increased. Variations in values of rate and equilibrium constants with the nature of 1 and 2 are discussed in terms of electronic and steric effects.