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

The hydrogenation of levulinic acid (LA) to gamma-valerolactone (GVL) was studied with a homogeneous RuCl2(PPh3)(3) catalyst in supercritical CO2 (scCO(2)). 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 RuHCI(CO)(PPh3)(3) complex and thus enhanced the rate of hydrogenation in the presence of CO2.