Structural Heterogeneities in Solutions of Triethylamine Nitrate Ionic Liquid: 1H NMR and LC Model Study

In order to uncover the micro-structural heterogeneities in solutions of ammonium based ionic liquids, triethylamine nitrate (N222NO3) has been synthesized using acid-base neutralization and the H-1 NMR spectra of two binary mixtures, namely N222NO3/dimethyl sulfoxide (DMSO) and N222NO3/acetone at different concentrations, have been measured at 298.15 K. The internal reference method was adopted to obtain the concentration-dependent chemical shifts of -CH3 in N222NO3, which have been correlated using the H-1 NMR local composition (LC) model to obtain the local mole fractions. It has been revealed that within N222NO3 rich region, self-association of the ionic liquid was predominant instead of N222NO3-solvent interactions. However, in the solvent rich region, N222NO3 mainly interacts with solvent molecules, indicating that the self-association network of N222NO3 has been greatly destroyed by solvents. In addition, the different influences of DMSO and acetone have been detected. DMSO molecules more effectively destroy the original network of the ionic liquid, due to its higher dielectric constant. Also, LC behavior in N222NO3/DMSO systems is more significant than in N222NO3/acetone, indicating that DMSO can induce more obvious heterogeneities in DMSO/N222NO3 mixtures, which is consistent with physicochemical properties and cellulose solubility of solutions.