Confinement effect catalysis with covalent organic frameworks for highly efficient synthesis of lactide

The efficient synthesis of lactide with high purity is the key to poly-lactic acid (PLA) production. Here, we demonstrated a 2D COFs-based catalyst, which could convert L-lactic acid into L-lactide directly in an excellent yield (80%) under mild conditions. Similar to enzymatic catalysis in which the product selectivity is controlled by the enzyme pocket, the precision confinement effect of the highly ordered channels and adjustable structures with functional moieties of the COFs play key roles in converting the monomer to the cyclic dimer directly and avoiding oligomerization. This strategy is sharply different from the current two-stage process for synthesizing lactide and renders COFs materials as an ideal heterogeneous catalyst with confinement effect.