Selective Conversion of Glycerol to Lactic Acid in Water via Acceptorless Dehydrogenation Catalyzed by a Water-Soluble Metal-Ligand Bifunctional Iridium Catalyst.

An efficient method for the selective conversion of glycerol, the major byproduct of the biodiesel manufacturing process, to lactic acid in water via acceptorless dehydrogenation has been developed. In the presence of a water-soluble [Cp*Ir(6,6'-(OH)-2,2'-bpy)(HO)][OTf] (0.1 mol %) and KOH (1.1 equiv), the reaction proceeded at 120 °C for 24 h to afford the desired product in >99% yield with >99% selectivity. It was confirmed that OH functional groups in the ligand were crucial for the activity of the iridium complex. Furthermore, density functional theory calculations and mechanistic experiments were also undertaken.