Inside the mechanism of the acid-catalyzed D-Fructose dehydration: a mass spectrometric study.

5-hydroxymethylfuraldehyde (5-HMF) and simpler compounds, such as levulinic acid (LA) and glyceraldehyde, are platform molecules produced by the thermal acid-catalyzed dehydration of carbohydrates coming from biomass. Understanding sugar degradation pathways on a molecular level is necessary to increase selectivity, reduce degradation by-products yields and optimize catalytic strategies, fundamental knowledge’s for the development of a sustainable renewable industry. Experimental gas phase studies can play a key role enlightening the more likely route occurring in the absence of solvent molecules. In this work gaseous protonated D-fructose ions, generated in the ESI source of a triple quadrupole mass spectrometer, were allowed to undergo Collisionally Activated Decomposition (CAD) into the quadrupole collision cell. The ionic intermediates and products derived from protonated D-fructose dehydration were structurally characterized by their fragmentation patterns and the relative water loss dehydration energies measured by energy resolved CAD mass spectra. The data were compared with those obtained from protonated D-glucose decomposition in the same experimental conditions [1]. In the gas phase, D-fructose dehydration leads to the formation of a mixed population of isomeric [C6H6O3]H+ ions, whose structure do not correspond exclusively to 5-hydroxymethyl-2-furaldehyde protonated at the more basic aldehydic group. The whole experimental data collected compared with the computational results reported in the literature allow the mechanism of D-fructose dehydration in the gas-phase to be hypothesized.