An addition-elimination mechanism for CH/CD exchange in thiazole

From a study of the pH-exchange rate profile and other data, it is shown that two mechanisms are important in the substitution of deuterium for hydrogen at C₂ in thiazole in deuterio-hydroxylic solvents. These pathways are a simple base-induced proton abstraction which is important at high pH and a process involving an equilibrium protonation on nitrogen followed by a rate determining CH ionization which is the primary exchange route at intermediate pH. It is suggested that the latter scheme has much greater generality and may even be involved in the biological activity of certain heterocyclic drugs.