One-Step Conversion of Glutamic Acid into 2-Pyrrolidone on a Supported Ru Catalyst in a Hydrogen Atmosphere: Remarkable Effect of CO Activation

Glutamic acid, an abundant nonessential amino acid, was converted into 2-pyrrolidone in the presence of a supported Ru catalyst under a pressurized hydrogen atmosphere. This reaction pathway proceeded through the dehydration of glutamic acid into pyroglutamic acid, subsequent hydrogenation, and the dehydrogenation-decarbonylation of pyroglutaminol into 2-pyrrolidone. In the conversion of pyroglutaminol, Ru/Al2O3 exhibited notably higher activity than supported Pt, Pd, and Rh catalysts. IR analysis revealed that Ru can hydrogenate the formed CO through dehydrogenation-decarbonylation of hydroxymethyl groups in pyroglutaminol and can also easily desorb CH4 from the active sites on Ru. Furthermore, Ru/Al2O3 showed the highest catalytic activity among the tested catalysts in the conversion of pyroglutamic acid. Consequently, the conversion of glutamic acid produced a high yield of 2-pyrrolidone by using the supported Ru catalyst. This is the first report of this one-pot reaction under mild reaction conditions (433K, 2MPa H-2) which avoids the degradation of unstable amino acids above 473K.