Green Synthesis Of Enantiomerically Pure Lactide Using Biogenic Creatinine Catalyst

Poly(lactic acid) (PLA),a biodegradable and environmrnt-friendly polymer which shows great potential to be an alternative to the disposable petroleum-based plastics, been used in a wide area, can be degraded to CO2 and H2O safely and completely without any environmental pollution. The strategy used for the synthesis of the isotactic PLAs, up to date, is predominately the ring-opening polymerization that uses L-lactide (LLA)/D-lactide(DLA). The synthesis of C LLA and DLA is thus of practical importance for the development of high performance materials based on PLA. The lactides are usually synthesized through depolymerization of a preformed oligo-PLA (O-PLLA or O-PDLA) in the presence of a catalyst. Among the catalysts developed, tin(II)-based compounds are considered to be the most efficient for the lactide synthesis. Because the synthesis of LLA/DLA with tin(?)-based catalysts inevitably undergoes racemization, the residues cannot be used for enantiomerically pure LLA/DLA resynthesis. Treatment of the large amounts of the waste products of residues containing the toxic catalysts is a problem in industrial production of lactide.In this thesis, LLA and DLA with enantiomeric purity (ee) of 100% were synthesized via depolymerization of the preformed O-PLLA/O-PDLA using non-toxic biogenic catalyst creatinine(CR) in high yield (LLA of 69.5%, DLA of 68.5%) by screening the optimal reaction conditions?resynthesising the lactide by used the residues of depolymerizations?purificating LLA/DLA safely.The fine molecular 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%. Compared with tin(II)-based catalysts,the calalyst we used in this research was CR 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.