Stability study of a superbase-derived ionic liquid [mTBNH][OAc] with enhanced cellulose dissolution ability: thermal and natural degradation

Abstract

Ionic liquids (ILs) have the potential to revolutionize the production of cellulose fibers by offering more sustainable and eco-friendly processes compared to conventional spinning techniques, which might involve the use of hazardous chemicals and demand significant energy inputs. At the same time, it is crucial to acknowledge that the lack of a comprehensive understanding of the ILs' stability and the nature of possible byproducts remains the central concern associated with their application. In this study, an investigation into the stability of the novel superbase-derived IL, [mTBNH][OAc], under different conditions was carried out. Specifically, the IL was subjected to thermal ageing at 95 °C to investigate intrinsic thermal instabilities in the presence of water and wood polysaccharides. Moreover, natural ageing at room temperature in the absence of light was also examined. Changes in the composition of the IL during ageing processes were monitored and byproducts were identified by means of Nuclear Magnetic Resonance (NMR) spectroscopy and Supercritical Fluid Chromatography coupled with high-resolution Quadrupole Time-of-Flight Mass Spectrometry (SFC-QToF-MS). Under thermal ageing, hydrolysis products, with the six-membered ring being opened and a urea structure being formed, dominated. Upon long-term ageing, either of the two heterocyclic rings was oxygenated, under the introduction of hydroxyl and keto groups, with subsequent ring-opening and elimination reactions.