Green synthesis of enantiomerically pure l-lactide and d-lactide using biogenic creatinine catalyst

Abstract

Enantiomerically pure lactides of l-lactide (LLA) and d-lactide (DLA) were synthesized with high yield (68.5–69.5%) via depolymerization of oligo-poly-l-lactic acid (O-PLLA) and oligo-poly-d-lactic acid (O-PDLA) catalyzed by biogenic creatinine (CR). The structures of synthesized LLA and DLA were characterized with XRD analysis of the prepared single crystals. Gas chromatograph (with a chiral stationary phase capillary column) analysis demonstrated that the synthesized LLA and DLA possessed enantiomeric excess of 100%. The catalytic efficiency of the catalyst creatinine reached to a high level as observed by the turnover frequency in the range of 338.0–347.7 h−1. The residues of the depolymerization were utilized for resynthesizing of the enantiomerically pure lactides for 3 circles without the decrease in the yields of enantiomerically pure LLA/DLA. The catalyst we used in this research was biogenic and the process for lactide synthesis featured a closed-cycle without any waste release. A possible mechanism of CR-catalyzed LLA/DLA synthesis was proposed and discussed.