Kinetics and mechanism of the acid‐catalyzed hydration of dihydro‐1,4‐dioxin

The cyclic vinyl ether dihydro‐1,4‐dioxin is converted to its cyclic hemiacetal hydration product, 2‐hydroxy‐1,4‐dioxane, in aqueous solution by an acid‐catalyzed reaction for which k = 1·80 × 10−5 M−1 S−1 at 25°C. This reactivity and the solvent isotope effect k /k = 2·2 show that the reaction occurs by rate‐determining proton transfer from catalyst to substrate and not by a pre‐equilibrium mechanism as recently proposed.2