(600bd) Catalytic Cycloaddition of Ethylene to Dimethylfuran for the Production of p-Xylene

To reduce independence on non-renewable resources, we investigate the catalytic conversion of sugars to building block chemicals for biorenewable plastics. Glucose, the monomer of cellulose, can be converted to 2,5-dimethylfuran through fructose [1] after isomerization by catalysts such as Sn-BEA zeolite [2]. 2,5-Dimethylfuran can then be upgraded to p-xylene, a precursor of terephthalic acid, which is used in the production of plastic bottles (PET). In this work a renewable route to p-xylene from dimethylfuran and ethylene is investigated with zeolite catalysts.  Cycloaddition of ethylene and 2,5-dimethylfuran and subsequent dehydration to p-xylene has been achieved with 75% selectivity using H-Y zeolite and an aliphatic solvent at 300 °C.  Competitive side reactions include hydrolysis of dimethylfuran to 2,5-hexanedione, alkylation of p-xylene, and polymerization of 2,5-hexanedione. The observed reaction rates and computed energy barriers are consistent with a two-step reaction which proceeds through an oxabicyclic-adduct prior to dehydration to p-xylene.  Cycloaddition of ethylene and dimethylfuran occurs without a catalytic active site, but the reaction is promoted by confinement within microporous materials.  The presence of Brønsted acid sites catalyzes dehydration of the Diels-Alder cycloadduct (to produce p-xylene and water) and this ultimately causes the rate determining step to be the initial cycloaddition.  

[1] Román-Leshkov, Y.; Barrett, C. J.; Liu, Z. Y.; Dumesic, J. A. Nature 2007, 447, 982-5

[2] Moliner, M.; Román-Leshkov, Y.; Davis, M. E. Proceedings of the National Academy of Sciences of the United States of America 2010, 107, 6164-8