(51e) Unraveling Solvation Effects on 5-Hydroxylmethylfurfural Degradation: Insights from Catalytic and Spectroscopic Studies

The prospective use of lignocellulosic biomass as a feedstock of value-added chemicals and fuels requires the effective and synergistic utilization of catalysts and solvents. The necessity to develop efficient and economic processes for the production of biomass derived platform chemicals, such as 5- hydroxymethylfurfural (HMF) has motivated research for the development of carbohydrate dehydration processes using heterogeneous[1, 2] and/or homogeneous[3, 4] catalysts. The use of organic co-solvents is one of the methods used to enhance HMF yields by reducing the rates of its rehydration and humin-formation reactions. Although many solvent mixtures have been tested in this respect, the reasons of enhanced HMF stability in aqueous aprotic co-solvent mixtures are still not clearly understood.

In the present work, vibrational spectroscopy is coupled with catalytic experiments in an effort to elucidate the origins of HMF stability and to provide “solvent-solute interactions” – activity relationships. Attenuated total reflection FTIR spectra of HMF in a wide composition range of aqueous aprotic (i.e. DMSO, g-valerolactone, THF etc.) and protic (i.e. methanol, ethanol etc.) solvent mixtures were measured in order to unravel the effect of the co-solvent on the structural and vibrational properties of dissolved HMF.  Deconvolution of pertinent wavenumber regions was carried out in an attempt to discriminate HMF-solvent interactions at different mixed solvent compositions. Different intermolecular interaction have been ascribed that are responsible for the non-conventional change of the HMF C=O and O-H vibrational modes under different solvent composition[5]. Our spectroscopic analysis has revealed the first experimental evidence of preferential interaction of HMF by aprotic solvents that that also depends on the co-solvent nature and amount.

HMF rehydration experiments were carried out in several mixed-solvent mixtures under different conditions (i.e. temperature, and acid concentration), and the effect of co-solvent type and concentration on the HMF stability is quantified. In addition to the possible effects of co-solvent on the intrinsic reaction rate constant, the rehydration and humin formation reaction rates can also be affected by the water activity, and proton concentration. The realative contribution of each of these factors on HMF stability/ reactivity is determined and will be analyzed in an effort to provide solvation/activity relationships based on our spectroscopic analysis. Our findings will also be discussed with respect to the possible HMF rehydration and humin formation reaction mechanisms.

References

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