The Depolymerization of Poly(ethylene terephthalate) (PET) Using N-Heterocyclic Carbenes from Ionic Liquids

The depolymerization of the plastic polyethylene terephthalate (PET or PETE) is described in this laboratory procedure. The transesterification reaction used to depolymerize PET employs a highly efficient N-heterocyclic carbene catalyst derived from a commercially available imidazolium ionic liquid. N-heterocyclic carbenes are potent nucleophilic organic catalysts that provide an alternative to traditional metal alkoxide depolymerization catalysts. Deprotonation of the imidazolium generates an N-heterocyclic carbene, which catalyzed the glycolysis of PET in 1 h at atmospheric pressure in refluxing anhydrous tetrahydrofuran to afford bis(2-hydroxyethyl) terephthalate (BHET). BHET is characterized by NMR and IR spectroscopy and melting point determination. This laboratory is designed for individual student work where each student depolymerizes PET prepared from a common water bottle or other source. This experiment is well suited for an introductory organic chemistry laboratory course or a polymer chemistry laboratory course.