Homogeneous transition metal catalyzed conversion of levulinic acid to gamma-valerolactone

Abstract

Abstract Levulinic acid (LA) is one of the most studied platform chemicals produced from a wide range of carbohydrates containing biomass including agricultural residues and food wastes. The reduction of the carbonyl group of LA leads to the transient formation of 4-hydroxyvaleric acid (4-HVA), which readily undergoes facile dehydration to give gamma-valerolactone (GVL) in very high yields. The homogeneous catalytic conversion of LA to GVL via 4-HVA can be achieved by transition metal complexes by using molecular hydrogen. Alternatively, the transfer hydrogenation of LA with formic acid or sodium formate or isopropanol can be used for the transformation of LA to GVL. Although no catalytic systems have been reported to yield 4-HVA selectively, the formation of chiral GVL by the asymmetric reduction of LA confirms its transient formation. The application of transition metal complexes as catalysts for the hydrogenation and transfer-hydrogenation of LA are reviewed including the use of chiral ligands for the asymmetric catalytic reductions of LA.