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.