Transfer Hydrogenation of Methyl and Ethyl Levulinate Promoted by a ZrO2 Catalyst: Comparison of Batch vs Continuous Gas-Flow Conditions

The catalytic conversion of methyl and ethyl levulinates into γ-valerolactone (GVL) by using methanol, ethanol, and 2-propanol as the H-donor/solvent, promoted by the ZrO2 catalyst, is described as carried out under both batch and gas-flow conditions. Under batch conditions, 2-propanol was found to be the best H-donor molecule, with ethyl levulinate giving the highest yield in GVL. The reactions occurring under continuous gas-flow conditions were found to be much more efficient, also showing excellent yields in GVL when EtOH was used as the reducing agent. These experiments clearly show that the ability to release hydrogen from the alcoholic H-donor/solvent is the main factor driving CTH processes, while the tendency to attack the esteric group is the key step in the formation of transesterification products.