The alkaline hydrolysis of some ortho-substituted ethyl benzoates

Rate constants for the saponification of four oiftho substituted benzoic esters have been measm-ed over a range of temperatures in bOfo (w/vj dioxan-water, using a spectrophotometric teclinique for following the rate of reaction. The results for one compound, ethyl o-toluate, have been checiced by a titration technique. Thermodynamic activation parameters have been calculated for the esters studied, and their values have been discussed in terms of substituent and solvent effects. The ultraviolet spectra of five other esters have been measured in the solvent indicated. The spectrophotometric technique has been found to be unsuitable for the study of rates of saponification of these esters, and the applicability and facility of this technique have been discussed. Difficulties have been encountered due to the reaction of hydroxyl ion with a solvent impurity, 2-methyl-1, 3-dioxolane, but aqueous dioxan has been found to be a suitable solvent for the study of ester hydrolysis reactions if it has been carefully purified.