Sulfonated cyclodextrin polymer as a bio-based catalyst for the synthesis of 5-HMF from fructose

This study describes the synthesis of a biodegradable and efficient sulfonated cyclodextrin nanosponge catalyst (CDNS-SO3H) for the selective dehydration of fructose to 5-hydroxymethylfurfural (5-HMF). Optimization by response surface methodology revealed that the optimum reaction conditions were 9.2 wt% catalyst loading, 90 °C, and 61 min, achieving an outstanding yield (91%) of 5-HMF from 2 mmol fructose in DMSO medium. The activation energy obtained from the kinetic study was 66.5 kJ.mol− 1, indicating an energetically feasible pathway at mild conditions. The thermodynamic parameters (ΔH = 65.73 kJ.mol− 1, ΔS = − 52.54 J.mol− 1 K− 1 and ΔG = 84.8 kJ.mol− 1) reveal the nature of the process as endothermic and entropy driven. The enhanced activity relative to CDNS stems from the uniform distribution of Brønsted acid sites (SO₃H) within the porous nanosponge matrix, which promotes efficient substrate diffusion and enhanced acid-substrate interactions. Furthermore, the CDNS-SO₃H catalyst exhibited excellent stability and could be readily recovered via simple centrifugation, retaining its activity after 8 cycles without significant efficiency loss. Collectively, this work demonstrates a biopolymer-based solid acid catalyst that integrates high performance, reusability, and environmental compatibility, thereby offering a promising pathway toward sustainable 5-HMF production and broader biomass valorization efforts.