Converting waste PET into dimethyl terephthalate and diverse boronic esters under metal-free conditions

Abstract

PET chemical upcycling is essential for advancing sustainable development and a circular economy, while also presenting a dependable option to produce value-added chemicals. Herein, we report a boronic acid involved EG valorization strategy for the upgradation of waste PET into DMT and diverse boronic esters under metal-free conditions without protodeboronation of boronic acids. Based on the remarkable catalytic performance of 1-ethyl-3-methylimidazolium acetate ([EMIm][OAc]) both in PET methanolysis and p-tolylboronic acid esterification, this method achieves complete PET degradation, resulting in 99% yield of DMT and 98% yield of 2-(p-tolyl)-1,3,2-dioxaborolane (PTDB). This approach not only preserves the high DMT yield in various waste PET and other polyester treatment processes, but also facilitates the transformation of EG into a variety of aryl, heterocyclic, and alkyl boronic esters. The ¹H NMR and FT-IR results confirmed that the hydrogen-bonding interaction between [EMIm][OAc] and reactants (PET, EG, and MeOH) enhances both PET methanolysis and boronic acid esterification processes. This method underscores its applicability for upcycling a variety of discarded polyesters and polycarbonates. The conversion of PTDB into other valuable chemicals (phenols, amines, and biaryl compounds) further illustrates the practical utility of this approach in PET disposal.