Mechanism of Acid-Catalyzed Hydrolysis of Phenylketene O,O and O,S Acetals

Article abstract of DOI:10.1021/jo00335a010

The hydrolysis of a phenylketene O,O acetal (1,1-dimethoxy-2-phenylethene, 1) and an O,S acetal <(Z)-1-methoxy-1-(methylthio)-2-phenylethene, 2> have been studied kinetically at 30 deg C.The observed catalysis by general acids, the deuterium solvent isotope effects (k_H2O/k_D2O = 5.5 with 1), and the lack of nucleophilic acceleration by added 2-mercaptoethanol are in accord with a mechanism involving rate-determining protonation of the double bond.The nonlinear dependence of rate on formate buffer concentration was observed in the hydrolysis of 2, but it does not seem to be ascribable to a possible change in the rate-determining step in contrast to the previous suggestion.