Lithium Amide: A Catalyst for Depolymerization

Abstract

The widespread use of plastic materials leads to significant contamination of ecosystems, posing risks to both wildlife and human health. There is an urgent need for efficient, economical, and environmentally friendly catalysts to depolymerize plastic waste into value-added compounds. In this study, we utilized the easily accessible catalyst [Li{N(SiMe3}2]2.2(THF) and pinacolborane (HBpin) as a hydride donor to convert various types of plastic waste, biodegradable/non-biodegradable polyesters, and polycarbonates into respective borylated value-added alcohols under mild conditions without any pre-treatment, up to 99% yield. The borylated 1,4-benzenediol obtained from polyethylene terephthalate (PET) depolymerization is characterized by single-crystal x-ray diffraction studies, nuclear magnetic resonance (NMR), and routine spectroscopic techniques. Additionally, the catalyst has been employed for the depolymerization of mixed/contaminated waste plastics, achieving selective and excellent yields of the borylated alcohols. This catalyst facilitated the gram-scale depolymerization of PET into eco-friendly alcohols, such as 1,4-benzene-di-methanol and ethylene glycol, via the depolymerization of PET waste bottles. Furthermore, mechanistic studies supported by Density Functional Theory (DFT) calculations provide insights into the catalytic pathway. To the best of our knowledge, this is the first example of alkali metal-catalyzed depolymerization of esters and carbonates containing waste polymers via a homogeneous method.