The Mechanistic Study of Palladium-Catalyzed Conversion of Glycerol to Dihydroxyacetone.

Glycerol can be efficiently converted to dihydroxyacetone using organometallic Pd catalysts. However, the entire catalytic cycle and reaction mechanism have not been comprehensively studied. In this work, we performed detailed theoretical calculations of the mechanism of glycerol conversion to dihydroxyacetone catalyzed by the Pd/2,9-dimethyl-1,10-phenanthroline complex. The results demonstrate that when benzoquinone serves as the oxidant, C-H bond activation constitutes the rate-determining step of the overall reaction. The activation barrier for the midposition C-H in glycerol is lower than that of the terminal C-H bond, which explains the observed high selectivity toward dihydroxyacetone formation. Mechanistic analysis reveals that protons generated during glycerol oxidation are efficiently transferred to benzoquinone via water-mediated proton transport. In contrast, when molecular oxygen is employed as the oxidant, the rate-limiting step shifts to the hydrogen atom abstraction step that involves an oxygen molecule directly abstracting a hydrogen atom coordinated on a Pd catalyst through an intermolecular hydrogen transfer mechanism. The acetic acid molecules can promote the catalytic cycle of the reaction.