One pot microwave-assisted catalytic upgrading of α-angelicalactone to γ-valerolactone over scandium triflate without H2 supply

Biomass upgrading, which supplies important biomaterials, chemicals and fuels, is considered as an efficient way to realize the goal of carbon neutralization. Recently, γ-valerolactone (GVL) has gained increasing attention due to its wide applications. In this work, a novel protocol of microwave-assisted cascade catalytic upgrading of α-angelicalactone (α-AL) to GVL over metal triflate using alcohol as the hydrogen donor was proposed. The yield of GVL production from α-AL upgrading is strongly influenced by the Lewis acid strength of the metal triflate and the reduction potential of the employed alcohol. Among all tests, Sc (OTf) 3 showed the best catalytic performance in isopropanol media, giving 96.4 % GVL yield and 100 % α-AL conversion at 433 K within 3.0 h. Meanwhile, kinetic study indicated transfer hydrogenation of isopropyl levulinate to isopropyl 4-hydroxyvalerate was the rate-limited step with the apparent activation energy of 94.5 kJ/mol. This Sc (OTf) 3 catalyst was highly stable and could be reused for five cycles by simple vacuum distillation. In a word, this work provides an alternative for GVL production from biomass upgrading.