Lactate-based ionic liquids as chiral solvents for cellulose

We report the first example of a chiral polymer-cellulose-being dissolved in both enantiomers of a chiral solvent. We synthesized six room temperature ionic liquids (ILs) based on imidazolium and 1,2,3-triazolium cations and lactate as chiral anion. Some of them have not been described before. We characterize the dissolution of cellulose in the ILs, which are found to be relatively good cellulose solvents with a solubility of up to 18.5 wt.-%. At the same time, we find solubility differences of up to a factor of 3 between the enantiomers of the solvent, which is a very pronounced chiral recognition effect. Interestingly, the racemate of the solvent dissolves significantly less cellulose than either enantiopure form, which is a significant deviation from ideal mixing behavior. We also report the physicochemical properties of the six ILs (density, viscosity, decomposition temperature, NMR and circular dichroism spectra). Based on molecular dynamics simulations of the solutions and a model which we have published before, we attempt a semi-quantitative prediction of the cellulose solubility, which yields solid results for the enantiopure solvents. From the simulation results, we obtain microscopic insight into the hydrogen bond network of the complex mixtures in which many different hydrogen bond donors and acceptors compete.