Enhancing 5‐Hydroxymethylfurfural Production from Fructose Using Triethylbenzylammonium Chloride‐Based Acidic Deep Eutectic Solvents: Optimization and Acidity Impact.

5‐Hydroxymethylfurfural (5‐HMF) is an important biomass‐based platform compound that links biomass feedstocks with petrochemical refinery products. In this work, we developed a novel approach using triethylbenzylammonium chloride (TEBAC)‐based acidic deep eutectic solvents (ADESs) to synthesize 5‐HMF through the dehydration of fructose. Our approach demonstrates significant improvements in both 5‐HMF yield and process efficiency compared to conventional solvent systems. Under optimal experimental conditions (90 °C, 4.5 h), a maximum 5‐HMF yield of 97.77±3.20 % was achieved at a TEBAC:acetic acid ratio of 2 : 3 with 1 wt % fructose loading, which represents a notable advancement over other methods. Notably, our system inhibits the formation of by‐products such as levulinic acid (LA) and formic acid (FA), which are commonly detected in other dehydration processes. Additionally, higher 5‐HMF yields of 76.67±0.33 % and 73.51±1.14 % were achieved with 10 wt % and 20 wt % fructose loadings, respectively, further highlighting the scalability of the process. The acidity of ADESs was found to significantly affect the dehydration rate and yield, as demonstrated through Hammett's acidity function analysis. The key innovation of our study lies in the strategic selection of hydrogen bond donors and acceptors in the DES, enabling both high efficiency and selectivity in 5‐HMF production. These findings provide a promising pathway for large‐scale biomass conversion with reduced by‐product formation. [ABSTRACT FROM AUTHOR]