Efficient selective and atom economic catalytic conversion of glycerol to lactic acid.

The availability of glycerol is rapidly increasing due to the expanding biodiesel industry, which produces this polyol as the main waste material. Several value-added chemicals have been synthesized using glycerol as a feedstock; however, the conversion of glycerol to lactic acid has been investigated to a lesser extent despite the numerous and novel uses of lactic acid. We report a family of iridium complexes as the first homogeneous catalysts for the conversion of glycerol to lactic acid. These have higher activity and selectivity than the previously reported heterogeneous systems. In addition, hydrogen gas is generated as a useful byproduct. Unlike prior systems, the reactions can be performed in air, under mild conditions and without solvent. Our method has even been applied to samples of crude glycerol waste derived from the biodiesel industry without prior purification, albeit with somewhat lower activity while maintaining the same high selectivity.