Mechanism of reactions of α‐diazosulfones. II: The acid‐catalysed hydrolysis in water and in dioxan‐water mixtures

Abstract

AbstractThe acid‐catalysed hydrolysis of α‐diazosulfones has been studied in water and in dioxan‐water solutions. From the magnitude of the solvent deuterium isotope effect a fast reversible protonation of the substrate is proposed. This result is supported by H‐D exchange experiments. The reaction rates have been measured in moderately concentrated perchloric acid and hydrochloric acid solutions. The logarithm of the pseudo first order rate constant is linear in Hammett's acidity function, H0. The slopes of these linear plots are appreciably larger for hydrochloric acid than for perchloric acid as catalyst. Bunnett's theory has been used to interpret the rate data in water. The influence of added sodium perchlorate and sodium chloride on the reaction rate is compared. A bimolecular rate‐determining step is proposed with a weak participation of the nucleophile in the transition state. The entropies of activation are consistent with this conclusion. The failure of the Zucker‐Hammett hypothesis is discussed.The influence of para substituents in five aryl α‐diazosulfones is correlated with Hammett's σp and Tsuno's σ+ constants. A weak transition state resonance has been proposed for p‐methoxyphenylsulfonyldiazomethane.Preliminary measurements on the hydrolysis of alkyl α‐diazosulfones are pointing to a similar mechanism to that proposed for the aryl α‐diazosulfones.