Heterogeneous Pt Catalysts for Reductive Amination of Levulinic Acid to Pyrrolidones

Supported platinum catalysts have been studied for the reductive amination of levulinic acid (LA) by H2 to N-alkyl-5-methyl-2-pyrrolidones under solvent-free conditions. The activity depends on the type of metal (Pt, Re, Pd, Rh, Ru, Cu, Ni), support material, and coloaded oxides of transition metals (V, Cr, Mo, W, Re). In 24 kinds of catalyst tested, Pt and MoOX (molybdenum oxide) coloaded TiO2 (Pt-MoOX/TiO2) shows the highest activity. Pt-MoOX/TiO2 is effective for reductive amination of LA with wide varieties of amines under mild conditions (3 bar of H2, 100 °C, solvent-free) to give high isolated yield of pyrrolidinones and shows higher turnover number (TON) than previously reported catalysts for reductive amination of LA with an aliphatic amine. The catalyst can be separated from the reaction mixture by filtration, and the recovered catalyst can be reused. This is the first general and reusable heterogeneous catalytic system for the reductive amination of LA. On the basis of mechanistic studies, high activity of Pt-MoOX/TiO2 can be attributed to acid–base interaction between the acid sites of Pt-MoOX/TiO2 and carboxyl groups in LA and an intermediate.