One-pot reductive etherification of biomass-derived 5-hydroxymethylfurfural to 2,5-bis(isopropoxymethyl)furan over a sulfonic acid-functionalized zirconium-based coordination catalyst

Abstract

2,5-Bis(isopropoxymethyl)furan (BIPMF) is a typical biomass-derived furanic diether, which has been widely considered to be a high-quality biodiesel or diesel additive. At present, converting 5-hydroxymethylfurfural to BIPMF via a one-pot process is still challenging because it involves the Meerwein–Ponndorf–Verley (MPV) reduction and etherification reactions in isopropanol (iPrOH) at the same time. Hence, developing a bifunctional catalyst is highly necessary. In this work, sulfonic acid-functionalized zirconium-based coordination catalysts (Zr-BDC-S_x) were synthesized by a convenient solvothermal self-assembly approach, in which 1,4-benzenedicarboxylic acid (BDC) and 2-sulfo-1,4-benzenedicarboxylic acid monosodium (BDC-SO₃Na) were used as dual ligands to regulate the acid–base properties of catalysts. Due to the superior cooperative actions of Lewis acid–base sites (Zr⁴⁺–O²⁻) and Brønsted acid sites (–SO₃H), Zr-BDC-S₆₀ displayed the highest catalytic activity, affording 100.0% HMF conversion and 96.9% BIPMF yield in 3 h at 120 °C. Furthermore, analysis of the reaction process proved that the MPV reduction of HMF to 2,5-bis(hydroxymethyl)furan (BHMF) followed by its etherification reaction was the preferential and principal reaction pathway for the formation of BIPMF in iPrOH over Zr-BDC-S₆₀. Additionally, Zr-BDC-S₆₀ was a robust catalyst and could be reused in at least three runs without an obvious loss in catalytic activity. To sum up, this work offered an easy-to-prepare and high-efficiency bifunctional catalyst for the one-pot reductive etherification of HMF to BIPMF, which provided excellent theoretical and technical references for the direct synthesis of BIPMF from biomass-derived carbohydrates.