(544g) A Spectroscopic Study on the Glucose and Fructose Mutarotation Reactions in the Presence of Lewis and Brønsted Homogeneous Acids

Research on biomass conversion to produce fuels and chemicals is unambiguously nowadays a topic of interest in both academic and industrial level. Among the many catalytic routes reported in the literature, cellulose deconstruction to valuable platform chemicals like 5-hydroxymethylfurfural (5-HMF) has been studied in recent years the most. In this reaction scheme, after cellulose hydrolysis, the isomerization of glucose to fructose usually takes place in the presence of Lewis acid catalysts followed by dehydration reaction to produce 5-HMF.[1] Since this reaction network involves aldoses and ketoses, it is expected that the relative distribution of their anomers (α, β or open chain) might affect product distribution and finally selectivity of the desired 5-HMF.[2]

In this work, we combine Attenuated Total Reflectance Infrared Spectroscopy (ATR-IR), Raman Spectroscopy (RS) and Nuclear Magnetic Resonance (NMR) to study the glucose and fructose anomerization in the presence of either Lewis acids such as AlCl₃, CrCl₃, and SnCl₄, or Bronsted acids such as HCl and H₂SO₄ or both. Results shown that there is a strong dependence of anomerization kinetics on the nature of Lewis acids as well as Broensted acids with the SnCl₄ to deliver the fastest rates. However, although this strong dependence of the rates, Raman and ATR-IR data revealed very minimal Glucose-Lewis acid interactions. This result might be indicative that the presence of Lewis acids in water changes the physicochemical properties of the solvent, i.e. water, which in turn might govern the reaction rates. In this work we will further investigate the alterations that can be observed in the molecular structure of humins that are derived from glucose, fructose or 5-HMF in the presence of Lewis acid catalysts as opposed to those derived in Bronsted acids that are well reported in the open literature.

References

1. Hu, S. Q., Zhang, Z. F., Song, J. L., Zhou, Y. X., & Han, B. X. (2009). Efficient conversion of glucose into 5-hydroxymethylfurfural catalyzed by a common Lewis acid SnCl4 in an ionic liquid. Green Chemistry, 11(11), 1746-1749.
2. Van Putten, R. J., Soetedjo, J. N., Pidko, E. A., van der Waal, J. C., Hensen, E. J., de Jong, E., & Heeres, H. J. (2013). Dehydration of different ketoses and aldoses to 5-hydroxymethylfurfural. ChemSusChem, 6(9), 1681-1687.