# Proton sponge: an aromatic glycolysis catalyst

## TL;DR

This paper introduces a new catalyst, proton sponge, that significantly improves the efficiency of recycling PET plastic through glycolysis.

## Contribution

The use of 1,8-bis(dimethylamino)naphthalene (proton sponge) as a novel organocatalyst for PET glycolysis is presented.

## Key findings

- Proton sponge achieves an 89% BHET yield in 45 minutes at 180 °C with 10 equiv. EG and 20 mol% catalyst.
- The aromaticity of proton sponge improves PET swelling and reduces induction time compared to non-aromatic catalysts.
- PS glycolysis follows pseudo first-order kinetics with an activation energy of 126.3 kJ mol−1.

## Abstract

Chemical depolymerisation of poly(ethylene terephthalate)(PET) is a widely explored method to recycle plastic waste, with particular benefits on waste streams unsuitable for mechanical recycling. Glycolysis, the employment of ethylene glycol (EG) and a catalyst to effect depolymerisation, is a promising technology. Herein, we report the use of 1,8-bis(dimethylamino)naphthalene, commonly known as a proton sponge (PS), as an effective, novel organocatalyst for PET glycolysis. Use of PS enables an 89% bis(2-hydroxyethyl)terephthalate (BHET) yield after only 45 min at 180 °C using 10 equiv. EG and 20 mol% catalyst. The aromaticity of PS allows for a shortened induction time by improving PET swelling compared to comparably basic non-aromatic catalysts such as tributylamine and pempidine. PS glycolysis obeyed pseudo first-order kinetics (R2 > 0.98) with an apparent activation energy of 126.3 kJ mol−1. Depolymerisation catalysed by PS is shown to be tolerant of air and a reduced catalyst loading of 5 mol%, and was demonstrated at 10 g scale, giving a 64% BHET isolated yield (>99% purity). A range of aromatic amines, structurally related to PS, were synthesised and investigated to provide a deeper understanding and mechanistic insights into the reactivity of this class of amine catalyst.

Glycolysis of poly(ethylene terephthalate) by aromatic catalysts has the potential to expedite reactions times by enhancing catalyst–substrate interactions.