Highly Efficient Recycling of Polyethylene Glycol With Benzaldehyde Over OH‐Functionalized Ionic Liquid

The chemical recycling and utilization of plastic waste and its transformation into value‐added chemicals are of great significance for sustainable development and have broad research prospects. Herein, we report a green, simple, mild, metal‐free and efficient strategy to obtain oxygen‐containing heterocyclic compounds by inducing the cleavage of the C–O and O–H bonds of polyethylene glycol (PEG) through the hydrogen bonds (HBs) of hydroxyl‐functionalized ionic liquids (ILs). Through experiments and theoretical calculations, it is found that the anion and cation of IL could respectively activate the O–H bond of polyethylene glycol and the C=O double bond of PhCHO through hydrogen bonds, forming the transition state (TS) M1. Then, the activated hydroxyl O atom of PEG may attack the carbonyl C atom of benzaldehyde through a nucleophilic reaction, thereby forming intermediate I through an addition reaction. Subsequently, in intermediate I, the O atom activated by the ionic liquid anion ([OTf] − ) conducts a nucleophilic attack on the C atom activated by the ionic liquid cation ([HO‐EtMIm] + ), causing the C–O bond to break. Thus, a depolymerization cyclization reaction occurs, forming a new C–O bond and the final target product.