Absence of expected side-reactions in the dehydration reaction of fructose to HMF in water over niobic acid catalyst

The catalytic dehydration of fructose (FRU) to 5-hydroxymethylfurfural (HMF) usually runs with the formation of several side products. Among these, levulinic acid (LA) is often reported as the product of a consecutive reaction of HMF re-hydration. In this work, side reactions of the dehydration of FRU performed in very green conditions (water as solvent and niobic acid as solid catalyst) are taken into account. Experimental evidences are given that, in the used conditions: i) HMF is a final stable product, ii) no formation of LA, either deriving from a consecutive reaction of HMF or directly from FRU transformation, was observed, and iii) LA does not react to give condensation products with any other chemical species present in the reaction mixture.