Hydrogen Bond Acceptors Dramatically Promote Fructose Dehydration and Stability of Furanics Like 5-Hydroxymethylfurfural

In this work, it has been demonstrated that the use of hydrogen bond acceptors (HBAs) within the context of deep eutectic solvents (DESs) can be beneficial for fructose dehydration in ethanol to obtain high yields of 5-hydroxymethylfurfural (HMF) and 5-ethoxymethylfurfural (EMF). In this research, several commercial catalysts were screened in the dehydration of fructose under reflux in ethanol. Sulphonated polymers exhibited excellent performance, while zeolites only achieved low yields of HMF due to low acidic strength, rendering them unable to perform the dehydration and etherification of fructose and its subsequent products in the assayed conditions. The addition of an HBA in the form of tetraethyl ammonium bromide (TEAB) was essential to facilitate the dehydration of fructose with zeolites (up to 19% HMF yield with TEAB). In addition, the use of TEAB improved the observed yield of HMF twofold during the reaction when the sulphonated polymer Purolite PD206 was employed (34% with TEAB and 15% HMF yield without TEAB). The investigation of different HBAs showed that tetraethylammonium bromide (TMAC) produced the most promising results, achieving a furanic compound yield of up to 75% after 3 h of reaction at 120 °C, enhancing fructose dehydration kinetics and favoring the stability of furanic rings in the reaction medium.