(101d) Examining Acid Formation during the Selective Dehydration of Fructose to 5-Hydroxymethylfurfural in DMSO and Water

Biomass is a renewable carbon feedstock that can be converted to 5-hydroxymethylfurfural (HMF), a useful platform chemical that can be modified to produce valuable chemicals and fuels. Previous research has shown that high HMF selectivity can be achieved in dimethylsulfoxide (DMSO) due to its capability to stabilize HMF.¹ Interestingly, high fructose conversion is observed in DMSO in absence of an acid catalyst – a phenomenon not completely understood. Homogeneous reactions starting with fructose or HMF are done in absence of catalyst at different DMSO concentrations to better understand the origin of this observed high activity and to inform design of a heterogeneous acid catalyst that incorporates DMSO-like interactions – a potential engineering solution to overcome the limitations accompanied with DMSO. Titration experiments of fructose dehydration reactions show that increased solution acidity with increasing DMSO composition is because of increased humins production. Therefore, DMSO does not degrade to strong acids that would be active species for the dehydration reaction. This experimental evidence supports the hypothesis that high activity observed for non-catalytic reactions in DMSO is due to DMSO stabilization of furanic intermediates² and indicates that stable sulfoxide groups can be incorporated on a catalyst surface. In addition, reaction studies monitoring conversion starting from HMF at different DMSO concentrations show that maximum HMF stabilization can be achieved at a DMSO solution composition of 0.11 D/S (moles of DMSO per total moles of solvent). This value can inform the target loading of sulfoxide groups needed to be incorporated on a catalyst surface providing optimum HMF stabilization in pure water.

References

1. Tsilomelekis, G., Josephson, T. R., Nikolakis, V. & Caratzoulas, S. Origin of 5-hydroxymethylfurfural stability in water/dimethyl sulfoxide mixtures. ChemSusChem 7, 117–126 (2014).
2. Kimura, H., Nakahara, M. & Matubayasi, N. Solvent Effect on Pathways and Mechanisms for D‑Fructose Conversion to 5‑Hydroxymethyl-2-furaldehyde : In Situ ¹³C-NMR Study. J. Phys. Chem. A 117, 2102–2113 (2013).