The kinetics of the hydrolysis of ethyl acetate in acetone-water and dioxane-water systems are reported. The rate constant passes through a minimum when the concentration of the organic solvent in the medium is in the neighbourhood of 80%. The temperature variation conforms strictly to the Arrhenius equation even for media containing extremely high proportions of organic solvent. Even though the activation energy is affected by changes in solvent composition, the variations are not sufficiently marked for an analysis. The frequency factor has got a tendency to follow the trend of activation energies.

The alkaline hydrolysis of ethyl acetate in dioxane-water and acetonewater mixtures have been studied. The trend of the reaction rate shows a maximum in the region of 10% organic solvent except in the case of acetonewater mixtures at 30°C. A close parallelism is observed in the variations of both E and log₁₀ PZ values in the two series of solvent mixtures. Also, the PZ values have a marked tendency to follow changes in energies of activation.

The influence of solvent on the rates of acid catalysed and alkaline hydrolysis of ethyl acetate has been discussed, the main factor taken into consideration being dielectric constant of the medium. Considerable light has been thrown on the precise role of the water molecule in alkaline hydrolysis. Specific solvent effects are also clearly noticeable since the reaction velocities, for both acid and alkaline hydrolysis, are more sensitive to changes in dielectric constant in acetone-water than in dioxane-water mixtures.

Frequency factors for acid and alkaline hydrolysis of esters have been calculated, taking into account the actual shapes of molecules and their necessary orientation at the instant of collision required for the formation of the activated complex. The agreement between calculated and observed values is found to be very satisfactory.