Facile synthesis of DBU-based protic ionic liquid for efficient alcoholysis of waste poly(lactic acid) to lactate esters

摘要

Several DBU-based protic ionic liquids were facilely synthesized, they were successfully used as solvents and catalysts for alcoholysis of poly(lactic acid) (PLA) to yield lactate esters. The structure of ionic liquids and reaction parameters were optimized. Using [HDBU][AA] as the catalytic medium, which was composed by a 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) cation and an acetate anion, the PIA could be completely depolymerized with a 91% methyl lactate yield under the conditions of 100 degrees C, 5 mol% catalyst loading for 5 h. The effect of alcohol structures on the catalytic behaviors was studied, and good to excellent product yields were obtained. Moreover, the developed [HDBU][AA] showed excellent recyclability and structure stability. A possible reaction mechanism concerning the synergistic effect of the anion-cation ions was proposed. The DBU-based protic ionic liquids presented herein are low-cost and one-step synthesized, exhibiting great potential as green and efficient platform for direct and selective alcoholysis of PLA. (C) 2019 Elsevier Ltd. All rights reserved.