Efficient one-pot synthesis of alkyl levulinate from xylose with an integrated dehydration/transfer-hydrogenation/alcoholysis process†
An integrated catalytic protocol involving dehydration, transfer-hydrogenation and alcoholysis towards one-pot conversion of xylose to alkyl levulinate was invented using a combination of Zr(20)-MCM-41 and H3O40PW12 catalysts. Secondary alcohols like 2-propanol and 2-butanol as the reaction medium exhibit equally superior hydrogen donating capability, but the dehydration step of xylose in 2-butanol is preferred probably due to its stronger hydrophobicity. A good alkyl levulinate yield of 53% can be achieved under optimized conditions. The spent dual catalysts can be effectively recovered and they exhibit good reusability after thermal regeneration of Zr(20)-MCM-41. Research on the catalytic mechanism shows that well-dispersed ZrO2 supported on MCM-41 is responsible for the catalytic transfer hydrogenation step of furfural to furfuryl alcohol. Proper tuning of the Lewis and Brønsted acidities can efficiently promote the acid-driven reaction steps of xylose conversion and simultaneously inhibit the alkyl levulinate-to-γ-valerolactone side reaction. The sustainability of this conversion is greatly improved by process intensification based on the new catalytic strategy and mild reaction conditions.