LACTIM-LACTAM TAUTOMERIC INTERCONVERSION MECHANISM IN WATER POLAR APROTIC-SOLVENT WATER-SYSTEMS .2. HYDRATION OF 2-HYDROXYPYRIDINES - EVIDENCE FOR A BIFUNCTIONAL WATER-CATALYZED PROTON-TRANSFER

In previous work, lactim/lactam tautomeric intcrconvcrsion of 2-hydroxypyridines has been shown to partly involve in aqueous solution a nondissociative proton-transfer mechanism, whereas, in aprotic solvents, the interconversion occurs totally within a cyclic dimer. Therefore, in order to determine whether water could also catalyze the tautomeric interconversion within a water/substrate association, temperature-jump experiments were performed in the water/propylene carbonate solvent system. Indeed, evidence is presented which suggests that the tautomeric interconversion partly involves a bifunctional water-catalyzed proton transfer. A combination of kinetic and UV spectral data indicates the formation of stoichiometric hydrates which inhibit the substrate dimerization. A deuterium kinetic isotope effect confirms the dimerization step to be rate-encounter controlled. © 1979, American Chemical Society. All rights reserved.