MECHANISMS FOR THE SOLVOLYTIC DECOMPOSITIONS OF NUCLEOSIDE ANALOGUES-I. ACIDIC HYDROLYSIS OF 2-SUBSTITUTED 1-(1-ETHOXYETHYL)BENZIMIDAZOLES

Article abstract of DOI:10.1016/0040-4020(80)80042-1

A few 2-substituted 1-(1-ethoxyethyl)benzimidazoles have been prepared and the rate constants for their hydrolysis measured at various temperatures and oxonium ion concentrations.The formal kinetics followed and the effect of varying the 2-substitution on the hydrolysis rate suggest that the acid-catalyzed cleavage of these compounds involves a rapid initial protonation of the benzimidazole ring and a subsequent rate-limiting heterolysis of the protonated substrate to form a free nitrogen base and an oxocarbenium ion derived from the ethoxyethyl group.The values obtained for the entropy of activation are consistent with the assumed u nimolecular nature of the rate-limiting step.The effects of 2-substituents on the acidities of the protonated substrates and their heterolysis rates have been compared.The latter partial reaction has been suggested to be the subject of steric acceleration.