Ethyl pyruvate hydrogenation under microwave irradiation

Enantioselective and racemic hydrogenation of ethyl pyruvate over Pt/Al2O3 catalyst was investigated under conventional and microwave dielectric heating. Experiments were carried out in a single-mode microwave loop reactor, equipped with a heating band, to directly compare the efficiency of the conventional convective/conductive heating and microwave dielectric heating. A sequence of kinetic experiments was performed, varying the microwave power input and the solvent. A catalyst deactivation study was conducted by recycling the catalyst. The choice of solvent significantly affected reaction rate and enantioselectivity. The highest reaction rate and enantioselectivity (75%) was achieved in toluene. In this solvent, the kinetics and enantioselectivity was unaffected by the mode of heating. In case of ethyl alcohol as solvent, the reaction rate remained the same for conventional and dielectric heating. However, the enantioselectivity dramatically decreased under microwave irradiation. The spent and fresh catalysts were characterized by scanning electron microscopy (SEM), nitrogen physisorption and direct current plasma (DCP) technique. Based on the SEM images and nitrogen physisorption analyses, slight sintering of catalyst surface was observed under microwave irradiation.