Detailed Understanding of the DBU/CO2 Switchable Solvent System for Cellulose Solubilization and Derivatization

In this article, we present an optimization study of the switchable solvent system DBU/CO2 for cellulose solubilization and derivatization via online Fourier transform infrared spectroscopy (FT-IR). By varying temperature, CO2 pressure, and solubilization time, we succeeded in achieving cellulose solubilization within 10–15 min at 30 °C. Compared to traditionally used ionic liquids, the system presented here is cheaper, is easier to recycle, and enables a very fast cellulose solubilization under mild conditions. The efficiency of our optimized mild conditions were further confirmed by X-ray diffraction (XRD) experiments showing the typical transformation from cellulose I to II upon regeneration. In addition, we prove the existence of the in situ formed carbonate anions by trapping them with benzyl bromide or methyl iodide as electrophiles, leading to the successful synthesis of cellulose benzyl carbonate and cellulose methyl carbonate, respectively, under utilization of CO2 as a renewable building block f...