Renewable Route To p-Xylene

A large portion of the petrochemicals that go into making ubiquitous polyethylene terephthalate (PET) containers—which hold everything from soda to soap—could be replaced by compounds from renewable resources, thanks to an inexpensive new process for preparing p-xylene (ACS Catal., DOI: 10.1021/cs300011a). PET is made by polymerizing ethylene glycol and terephthalic acid. Ethylene glycol can be derived from sugar, but terephthalic acid generally comes from a petrochemical source. Now, a team led by Paul J. Dauenhauer of the University of Massachusetts, Amherst, reports a biobased route to p-xylene, which can be converted into terephthalic acid. While other renewable routes to p-xylene have been reported, they are either expensive or suffer from low yields, Dauenhauer says. His team uses Y zeolite catalysts in an aliphatic solvent at 300 °C to combine ethylene and glucose-derived 2,5-dimethyl­furan via a Diels-Alder reaction. Subsequent dehydration produces p-xylene in 75% overall yield. The researchers believe that confinement of the reactants within the zeolite’s micro­porous structure is what prompts the reluctant dienophile ethylene to react with 2,5-dimethylfuran. The catalyst’s Brønsted acid sites spur dehydration of the Diels-Alder cycloadduct.