Zr Oxo Cluster for Cascade Conversion of Furfural to Alkyl Levulinates

A novel dodecanuclear Zr oxo cluster [Zr₆O₄(OH)₄ (HSCH₂CH₂COO)₁₂]₂ (ZrO-SH-10) has been constructed under the room temperature, followed by oxidation of the sulfhydryl group with H₂O₂ to achieve a bifunctional catalyst with Lewis acid and Brönsted acid sites. The characterization of catalysts indicated that {Zr₆O₄} cluster core can be stabilized with a shell of carboxylate ligands, and the resulting ZrO-SO₃H was formed as a discrete molecular catalyst, exhibiting superior activity and recyclability for the cascade conversion of furfural to alkyl levulinate by the integration of transfer hydrogenation and alcoholysis in n-butanol. The yield of n-butyl levulinate can achieve as high as 91 % under the optimum conditions. Meanwhile, no leaching of the active species was found, which confirmed the structure of the Zr oxo cluster was air and moisture-stable. On the basis of the studies on the reaction kinetics and isotope tracking, the reaction mechanism was proposed accordingly.