Sc(OTf)3: An efficient homogeneous catalyst for microwave-assisted transfer hydrogenation of ethyl levulinate to γ-valerolactone under mild conditions

Abstract

γ-Valerolactone (GVL) is considered as a versatile platform chemical obtained from biomass refinery. In this study, eco-friendly group III metal (Sc, Y, La) triflates were examined as homogeneous catalysts for microwave-assisted transfer hydrogenation of ethyl levulinate (EL) to GVL under mild conditions. Experimental results revealed that the selectivity of GVL has a positive relationship with the Lewis acidity of metal ion, which is related to effective charge density of the metal center (3.23, 2.81, 2.60 for Sc3+, Y3+, La3+, respectively). The stronger Lewis acidity of metal ion, the higher catalytic activity of MPV reduction. Among these catalysts, Sc(OTf)3 exhibited the best catalytic activity, achieving 98.4% EL conversion and 92.4% GVL yield at 140 °C in 3.0 h. Furthermore, Sc(OTf)3 showed high stability and recyclability for at least ten reaction cycles. In addition, a plausible reaction pathway and mechanism were proposed.