(495g) Solvent Effects on the Stability of 5-Hydroxymethylfurfural: Understanding the Undesirable Side Reactions

While the energy needs of the developed world are currently over-dependent on the utilization of finite resources, research efforts are markedly shifting the overall picture towards processes that use alternative or renewable sources for the production of fuels and chemicals. In this direction, there is a growing body of research demonstrating the use of lignocellulosic biomass as feedstock that meets the renewable carbon demands. 5-Hydroxymethylfurfural (HMF) is an important bio-based chemical building block produced from the dehydration of hexoses, and holds a key position in the production of biomass-derived intermediates such as 2,5-furandicarboxylic acid, 2,5-dimethylfuran, adipic and levulinic acids etc. [1]. HMF yields are typically low since acid catalyzed dehydration in an aqueous environment is accompanied by side reactions which convert HMF to insoluble humins and rehydration products (levulinic and formic acid). The highly functionalized nature of HMF has been held responsible for its reactivity to side products. Even though it is well established that the use of organic co-solvents enhances HMF stability towards degradation reactions by suppressing their rates, the reasons behind this enhanced stability, unfortunately, still remains elusive.

In the present work we investigate the effect of a variety co-solvents that encompass polar aprotic as well as protic co-solvents, on the stability of HMF towards degradation reaction. The catalytic results clearly show a strong dependence of HMF stability on the nature of the co-solvent. The effect of aqueous dimethyl sulfoxide (DMSO) reaction media on the kinetics of Brønsted acid catalyzed degradation reactions of HMF spanning a range of solvent compositions, acid concentrations and temperatures will be discussed as a case study. The relative contribution of each of these factors on the individual degradation reactions of HMF (rehydration and humin formation) is determined by means of extensive kinetics and isotopic labeling experiments. Although the use of polar aprotic co-solvents appeared to retard both the HMF rehydration and humin formation side reactions, the selectivity to humins increases with increasing DMSO concentration. Emphasis will be also placed on how vibrational spectroscopy can be utilized for unravelling solvent-solute interactions at the molecular level [2]. To this end, an approach will be presented that allow us to monitor the interactions between specific functional groups and solvent molecules providing insights into solvation effects [3]. Our findings will also be discussed with respect to the possible HMF rehydration and humin formation reaction mechanisms. A methodology for expanding this analysis to different co-solvents will also be discussed.

References

[1] R.J. van Putten, J.C. van der Waal, E. de Jong, C.B. Rasrendra, H.J. Heeres, J.G. de Vries, Chem Rev, 113, 2013, 1499

[2] G. Tsilomelekis, T.R. Josephson, V. Nikolakis, S. Caratzoulas, Chemsuschem, 7, 2014, 117

[3] T.R. Josephson, G. Tsilomelekis, C. Bagia, V. Nikolakis, D.G. Vlachos, S. Caratzoulas, J Phys Chem A, 118, 2014, 12149