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.