Enantioselective synthesis of D-lactic acid via chemocatalysis using MgO: Experimental and molecular-based rationalization of the triose's reactivity and preliminary insights with raw biomass

The widespread applications of D-lactic acid (D-LaA) significantly prompted the research of its synthesis from renewable biomass via chemo-catalysis. Herein, we developed a robust but simple MgO-D-LaA system without using extra chiral ligand, achieving the highest LaA yield similar to 90 % with similar to 75 % enantiomeric excess (ee) value to D-LaA from dihydroxyacetone, glyceraldehyde, and pyruvaldehyde. The experimental and quantum chemistry computational results revealed that MgO and D-LaA presented a pronounced synergetic effect, where pre-added D-LaA provided suitable pH to promote [Mg(OH)(H2O)(3)](+) formation, acting as the active species to facilitate the production of pyruvaldehyde, from dihydroxyacetone and glyceraldehyde. D-LaA interacted with Mg-II species forming a chiral pocket-like complex, Mg-II-2(D-Lactate), which combined to pyruvaldehyde giving the transition state with lower strain energy due to the smaller steric repulsion, thus enabling 1, 2-H shift of hydrated-pyruvaldehyde preferentially via si-face attack, leading to D-LaA. The catalytic system could also be applied for the conversion of raw corn stover.

Automated summary

The development of a robust MgO-D-LaA system without using extra chiral ligand achieved high LaA yield and enantiomeric excess. Experimental and computational results revealed a synergistic effect between MgO and D-LaA, facilitating the production of pyruvaldehyde from dihydroxyacetone and glyceraldehyde.