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

Abstract

AbstractLactide 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 LnA oligomers. Therefore, carbonyl‐carbon with the enhanced electrophilicity is easier being attacked by a hydroxyl terminal of LnA oligomers, leading to high yield and high purity for lactide synthesis.