Microenvironment\nEffect Catalysis with Phosphoric\nAcid-Based Covalent Organic Frameworks

Drawing inspiration from enzymatic\ncatalysis, a phosphoric\nacid-based\ncovalent organic framework (<b>PA-COF</b>) was engineered for\nthe efficient synthesis of optically pure lactide. <b>PA-COF</b> catalyst features precisely engineered microenvironments within\nwell-defined porous channels decorated with phosphoric acid as the\ncatalytically active sites. Much like enzymatic catalysis, where product\nselectivity is governed by the protein pocket, <b>PA-COF</b> provides precise microenvironments due to its highly ordered channels\nand adjustable structures. The phosphoric acids in the channels as\ncatalytically active sites play key roles in directly converting lactic\nacid monomers into the cyclic dimer lactide. The process effectively\navoided oligomerization, achieving an excellent yield of approximately\n95%. This approach significantly differs from the traditional two-step\nstrategy. It avoids the use of metal catalysts and high-temperature\n(∼200 °C) reaction conditions, thus avoiding metal residues\nand racemization. This microenvironment effect catalysis strategy\nprovides a new pathway for the synthesis of lactide and may be extended\nto other useful condensation reactions.