(5f) Two-Dimensional Correlation Spectroscopy (2D-COS) As a Tool for Understanding Solvent Effects in Biomass Upgrading

Addressing solvent selection in reaction engineering necessitates a comprehensive understanding of reaction kinetics and solvent-solute interactions. Uncovering molecular-level insights under real conditions regarding the impact of solvents poses a challenge. Vibrational spectroscopy has played a significant role in elucidating solvent-solute interactions in biomass reactions, but much of the available research is concentrated on room temperature measurements.

The synthesis of 5-Hydroxymethylfurfural (HMF) is hampered by its own reactivity, yielding polymer-like byproducts, namely humins. HMF selectivity has been shown to be higher in polar aprotic solvents such as DMSO over water, effect that has been indirectly linked to possible intermolecular interactions between HMF and DMSO.[1] However, the previous spectroscopic studies were solely performed with D₂O where H/D exchange complicates molecular interpretations. H₂O presents challenges because of the baseline of H₂O in ATR-FTIR, shifting, and broadening of key peaks. Strongly overlapping peaks make it nearly impossible to distinguish interactions between HMF and DMSO monomers and dimers.

In this work, for the first time, we show that we can unveil molecular interactions of HMF in complex solvent media through 2D-COS vibrational spectra where the perturbation can be (a) HMF concentration, (b) solvent ratio and, (c) temperature. By means of synchronous and asynchronous data, we disentangle the sequence of molecular interactions involved either between solvents or between solvents and HMF, such as those between HMF and DMSO in Figure 1. Additionally, 2D-COS analysis allows us to clearly discern the changes occurring in these mixtures as temperature rises. We note a clear trend of increasing interaction between HMF and water, while the interaction between HMF and DMSO appears to vary slightly with increasing temperature. In this work, the 2D-COS approach is extended to address these interactions to a large variety of co-solvents that have shown a promise in the literature.

1. Tsilomelekis,G., et.al. ChemSusChem 7.1, p117–126