Hydrogenation of levulinic acid by RuCl2(PPh3)3 in supercritical CO2: the significance of structural changes of Ru complexes via interaction with CO2

Abstract

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was studied with a homogeneous RuCl₂(PPh₃)₃ catalyst in supercritical CO₂ (scCO₂). The conversion of LA was observed to increase with CO₂ pressure and the possible reasons for this rate acceleration were discussed, including the molecular interactions of CO₂ with the reacting and catalytic species as well as the acidity and phase behavior of the reaction mixture. The interaction between CO₂ and RuCl₂(PPh₃)₃ was significant, which resulted in the production of an active RuHCl(CO)(PPh₃)₃ complex and thus enhanced the rate of hydrogenation in the presence of CO₂.