KINETICS OF PROTON EXCHANGE IN IONIZATION AND ACID DISSOCIATION OF IMIDAZOLE IN AQUEOUS ACID

Rates of proton exchange of imidazolium ion (ImH+) have been measured in aqueous acid by the nmr method over a wide range of conditions. The rate law is unusually complex. A comparison of rates of proton exchange with rates of relaxation subsequent to temperature jump shows that acid dissociation of the imidazolium ion occurs in two distinct steps, ionization and dissociation. The immediate product of ionization (II, see text) makes a contribution to the rate of proton exchange by the breaking of the Im. HOH hydrogen bond. Dissociation of this ionized intermediate appears to be distinctly slower than 1011 sec-1. Criteria for the general detection of ionized intermediates are discussed. © 1969, American Chemical Society. All rights reserved.