Study on zinc oxide-creatinine hybrid catalyst for efficient lactide synthesis with low racemization

Lactide is the crucial intermediate for polylactic acid (PLA) synthesis via ring-open polymerization, but it suffers low yield and low purity induced by racemization reaction. In this work, we have developed a zinc oxide-creatinine (ZnO-CR) hybrid catalyst, which offers high yield (the distilled lactide yield and pure l -lactide yield are 95.73% and 61.64%) and high purity (81.53%) for green l -lactide synthesis at the cyclization temperature of 240°C. Furthermore, NMR and HPLC results show that CR addition significantly restrains the racemization by reducing α-proton abstraction, where guanidine derived from the CR plays a main catalytic role to provide a tight association with the carbonyl oxygen in the carboxyl of L n A oligomers. Therefore, carbonyl-carbon with the enhanced electrophilicity is easier being attacked by a hydroxyl terminal of L n A oligomers, leading to high yield and high purity for lactide synthesis.