From Plastic Waste to Pharmaceutical Precursors: PET Upcycling through Ruthenium Catalysed Semi-Hydrogenation

We report here the upcycling of PET (polyethylene terephthalate) waste via semi-hydrogenation to make ethyl 4-(hydroxymethyl)benzoate. The reaction is catalysed by a ruthenium pincer catalyst at 80 °C in bio-derived solvents – a combination of 2-methyl THF and ethanol. A detailed mechanistic investigation through kinetic studies and chemical exchange saturation transfer (CEST) NMR spectroscopy provides insights into the nature of active species and factors that promote and inhibit the catalytic hydrogenation of PET. Using this mechanistic knowledge, a record high turnover number of > 30,000 was achieved. The semi-hydrogenation product, ethyl 4-(hydroxymethyl)benzoate, was utilised to make precursors of various known pharmaceutical drugs, an agrochemical, as well as a new and recyclable polyester.