Hemiketal formation between alcohol solvents and cr-keto esters is shown to be catalyzed not only by the basic cinchonidine modifier but also by the acidic Pt/Al2O3 catalyst. Theoretical considerations and experimental results demonstrate that reaction calorimetry is a valid and accurate measure of the hydrogenation reaction, provided that the substrate and its hemiketal remain in equilibrium over the course of the reaction. The rate of hemiketal formation and, thus, the probability that the preequilibrium step will remain unperturbed during the hydrogenation reaction, is sensitive to the acidic properties of the support.