Kinetics and mechanism of N–H and C–H isotopic exchange in pyrrole and indole: acid-catalysed exchange in aqueous acetonitrile solutions

Abstract

The deuteriodeprotonation of the N–H and of the α- and β-C–H positions in pyrrole, and of the N–H and β-C–H positions in indole, has been studied kinetically as a function of the concentration of perchloric acid, medium composition, and temperature in aqueous (2H2O) acetonitrile solutions. The N–H exchange process was followed using the first overtone of the N–H stretching mode. Ancillary i.r. studies define the molecular states of the reactants. The Hammett H0 acidity function is reported for dilute perchloric acid in acetonitrile-water mixtures. Bunnett w values clarify differences between the hydration of the N–H and C–H exchange transition states.