Selective gas-phase conversion of D-fructose to 5-hydroxymethylfuraldehyde through a base-assisted dehydration process

5-hydroxymethylfuraldehyde (5-HMF) is the main product of the thermal acid-catalysed dehydration of monosaccharides and together with other furan compounds is considered a platform molecule for the production of chemicals and fuels. Identifying alternative catalytic strategies to synthesize 5-HMF represents a key-step to increase reaction selectivity and reduce degradation-by-product yields. In this regard, mass spectrometry has proved to be an useful tool for studying reaction mechanisms in absence of solvent molecules. This approach has already been employed to investigate the acid-catalysed D-glucose and D-fructose dehydration mechanism, highlighting the formation in the gas-phase of a 5-HMF protomers and isomers mixed population (1,2). In this work the effect produced by nitrogen-containing bases on the D-fructose dehydration reaction has been evaluated using tandem mass spectrometry. Ionic complexes formed by the protonated sugar and a nitrogen base were allowed to undergo collision-induced dissociation (CID) in an ion trap mass spectrometer. The dehydration process was followed step-by-step by isolating in turn the resulting ionic intermediates that still retain the attached bases depending on their proton affinity values. The sequential fragmentation leads to the formation of [C6H6O3]H+ ions corresponding to a pure protonated 5-HMF population when the base loss occurs as the last reaction event (Figure 1). This evidence demonstrates the existence of a selective and effective base-assisted mechanism. Theoretical calculations are in progress in order to: i) elucidate the structures of the starting reactant ion and of the intermediates ii) validate a feasible reaction mechanism.