One-Pot Synthesis of Cyclic Biofuel Intermediates from Biomass in Choline Chloride/Formic Acid-Based Deep Eutectic Solvents

The incompatibility of the aldol condensation reaction of furfural (FF) and upstream FF conversion limits the direct production of cyclic biofuel intermediates (C10, C15) from lignocellulosic biomass. Herein, an efficient catalytic system comprised of choline chloride–formic acid–SnCl4·5H2O (ChCl-Fa-SnCl4) has been developed, which gives high intermediate yields of 92.03, 88.24, and 56.78%, respectively, from the one-pot conversion of FF xylose and corncob with cyclopentanone (CPO). These data are higher than the reported intermediate recovery of 61.55% observed using FF/CPO and a solid acid catalyst (Nafion resin) under solvent-free conditions and 44% using xylose/acetone and CrCl3/VCl3/[BMIM]Cl. Moreover, Sn(IV) and H+ ions in ChCl-Fa-SnCl4 contribute toward catalyzing the aldol condensation reaction, and far-infrared spectroscopy indicated that deep eutectic solvents may strengthen the coordination of Sn(IV) to the carbonyl group.