A strategy of H-bond confinement catalysis for efficient degradation of polyethylene glycol into glycol diester over an OH-functionalized ionic liquid

Abstract

Upgrading plastic waste into high-value chemicals and achieving recycling is of great significance for sustainable development. Herein, we report a green, mild, solvent- and metal-free catalytic approach that uses hydroxyl-functionalized ionic liquids to induce the cleavage of C–O and O–H bonds in polyethylene glycol (PEG), successfully converting PEG into ethylene glycol diester. Through experiments, NMR analysis and DFT calculations, we find that the anions and cations of [HO-EtMIm][OTf] can respectively act as hydrogen bond acceptors and donors to activate the O–H and C–O bonds in PEG, as well as the C=O double bonds in benzoic anhydride. Subsequently, the activated hydroxyl O atom in PEG can attack the carbonyl C atom in benzoic anhydride through nucleophilic action, and the activated O atom in benzoic anhydride can also attack the C atom in PEG through nucleophilic action, thereby undergoing depolymerization and forming new C–O bonds, ultimately generating the target product. This mechanism clearly demonstrates the importance of the unique confinement effect of ionic liquids, which is achieved through spatial confinement, electrostatic stabilization, directional activation, and hydrogen bonding synergy, providing corresponding innovative support for future research.