Highly effective synthesis of biomass-derived furanic diethers over a sulfonated zirconium–carbon coordination catalyst in alcohol systems

Abstract

Directly converting biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-bis(alkoxymethyl)furans (BAMFs) via a one-pot process in alcohol systems is a very important approach for the synthesis of high-quality biofuels; however, this approach is highly challenging because it simultaneously involves the cascading Meerwein–Ponndorf–Verley (MPV) reduction and etherification reactions. Thus, designing an acid–base bifunctional catalyst is extremely desirable. Herein, we employed a glucose-based carbonaceous solid acid as a cheap organic ligand to prepare a series of new-type sulfonated zirconium–carbon coordination catalysts (Zr-GC-SO₃H-X) via a simple solvothermal self-assembly method. By regulating the usage proportion of zirconium ions and organic ligand, Zr-GC-SO₃H-1.0, possessing a proper Lewis/Brønsted acid ratio as well as strong Lewis acid–base (Zr⁴⁺–O²⁻) and Brønsted acid (–SO₃H) sites, showed the optimum acid–base synergistic effects, so it displayed the highest catalytic performance. When the one-pot reductive etherification (OPRE) of HMF was performed in isopropanol, 2,5-bis(isopropoxymethyl)furan (BIPMF) yield could reach 95.8% in 6 h at 180 °C. Additionally, the analysis results of reaction processes demonstrated that the MPV reduction reaction of HMF was much easier than its etherification reaction in the presence of Zr-GC-SO₃H-1.0, so initially forming 2,5-bis(hydroxymethyl)furan (BHMF) and then forming 2-hydroxymethyl-5-(isopropoxymethyl)furan (HIPMF) were the predominant reaction pathway for the OPRE of HMF to BIPMF. More significantly, Zr-GC-SO₃H-1.0 also exhibited excellent universality and catalyzed the high-yield synthesis of various BAMFs in ethanol, n-propanol, n-butanol and sec-butanol. Conclusively, this work provided momentous references to construct high-efficiency catalysts for the OPRE of HMF.