One-step
lactide (LD) synthesis from lactic acid (LA) is a promising
method for an economically viable polylactic acid (PLA) industry.
However, this synthesis is based on a highly water-sensitive esterification
reaction, and few studies focus on developing an efficient method
to improve its activity by water removal from the reaction environment.
Herein, we report a new strategy coupling salt-promoted toluene–water
phase separation with heteroazeotropic distillation to enhance water
removal to realize highly efficient LD synthesis. Different kinds
of chloride salts (LiCl, NaCl, CsCl, MgCl2, and CaCl2) were selected to study their influence on the reaction.
The highest yield of LD (84.7%) was obtained when CaCl2 was added, much higher than that of the salt-free reaction (72.3%).
Hydrated Ca2+ cations with relatively large charge number
and small radius can efficiently reduce the solubility of water in
toluene due to their strong electrostatic force to attract more water
molecules. Mechanism studies demonstrate that the increased yield
of LD after adding CaCl2 was attributed to its significant
inhibition of LD hydrolysis resulting from the deep water removal
from the toluene solvent.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.