Stable and Water-Tolerant Deep Eutectic Solvent from Biomass-Derived 5‑Hydroxymethylfurfural (HMF) and Levulinic Acid

The development of greener extraction systems is essential to improving the sustainability of biomass valorization processes. Here we report that 5-hydroxymethylfurfural (HMF) and levulinic acid (LEV)two bioderived platform molecules often coproduced in biomass processingspontaneously form a stable liquid phase over a broad compositional range. Differential scanning calorimetry (DSC) and thermodynamic modeling reveal a eutectic composition near x _HMF = 0.39 with a melting temperature of 258 K and significant negative deviation from ideal behavior. The mixture remains liquid across a wide compositional range even in the presence of low water content (0.3-1.0 wt %), exhibiting deep eutectic solvent (DES)-like behavior. Structural and dynamic analyses using DSC, NMR spectroscopy, molecular dynamics (MD) and density functional theory (DFT) calculations uncover a nonideal mixing regime driven by the network of HMF-LEV hydrogen bonding. Notably, water does not disrupt the HMF-LEV network but enhances its structuration at the eutectic composition by moderating LEV-LEV interactions and enabling more favorable HMF-LEV hydrogen bonding. This work shows that the liquid HMF-LEV phase can be generated in situ within a heterogeneous biomass surrogate, enabling substantially higher HMF extraction efficiencies than conventional solvents and eliminating the need for additional organic extractants. This provides a proof of concept for a solvent-minimized route to HMF recovery, indicating the HMF-LEV system as a promising, bioderived liquid platform with potential for integration into future resource-efficient biorefinery schemes.