Catalyst-Free Acetalization of Biobased Furfural into Cyclic Acetal Fuel Additives with Biogenic Ethylene Glycol

Acetalization is a promising method for upgrading biomass-derived molecules into valuable chemicals, and acetal products are considered excellent oxygenated fuel additives. Herein, a catalyst-free, facile, and effective protocol for the acetalization of furfural and ethylene glycol is established, affording a 78.6% yield of 2-(furan-2-yl)-1,3-dioxolane with a furfural/ethylene glycol molar ratio of 1:15 in cyclohexane at 160 °C after 2 h. Moreover, the lower activation energy (15.8 kJ/mol) corroborates that the established system is efficient, and the thermodynamic studies demonstrate that catalyst-free acetalization is an endothermic, nonspontaneous, and endergonic reaction. A plausible mechanism including two pathways for catalyst-free acetalization of furfural and ethylene glycol is proposed, wherein the formed water from the acetalization process can render the ethylene glycol to be hydrolyzed, which plays a positive role in facilitating the acetalization of furfural and ethylene glycol. In addition, the excess ethylene glycol in the reaction mixture can be easily recovered and almost shows the same activity as fresh ethylene glycol in catalyst-free acetalization. Furthermore, the established catalyst-free protocol is viable for various biobased furanic compounds and alcohols, enabling broad access to various acetals. Finally, catalyst-free acetalization of furfural and ethylene glycol can be magnified to 10 times, showing the promising potential of large-scale production.