Selective Conversion of Levulinic and Formic Acids to γ‑Valerolactone with the Shvo Catalyst

The selective transfer hydrogenation of levulinic acid (LA) with formic acid (FA) to 4-hydroxyvaleric acid (4-HVA) and carbon dioxide followed by the intramolecular dehydration of 4-HVA to γ-valerolactone (GVL) are key steps of the conversion of carbohydrate-based biomass to GVL, which can be used for the production of both energy and carbon-based products. LA was converted to GVL in the presence of a small excess of FA and the Shvo catalysts {[2,5-Ph2-3,4-(Ar)2(η5-C4CO)]2H}Ru2(CO)4(μ-H)]} (Ar = p-MeOPh (1a), p-MePh (1b), Ph (1c)). The reactions were performed at 100 °C with yields higher than 99% after a few hours. The formation of 1,4-pentanediol and 2-methyltetrahydrofuran remained below detection limits. The only side products were water and carbon dioxide, as expected, which were easily removed and separated from the product GVL under reduced pressure. The Shvo catalyst 1c was recycled four times without losing catalytic activity, and the product GVL was isolated each time as a colorless liquid of 99.9% purity with only trace amounts of water present.