Insights into Ionic Liquid/Aromatic Systems from NMR Spectroscopy: How Water Affects Solubility and Intermolecular Interactions
Noemí Delgado-Mellado1,2, Julián García2, Francisco Rodríguez2
1College of Arts and Sciences, The University of Alabama, Tuscaloosa, AL 35487, USA.
Abstract:
Hydrocarbon solubility and chemical interactions in ten imidazolium- and pyridinium-based ionic liquids (ILs) with four different anions (thiocyanate [SCN]- , dicyanamide [DCA]- , tricyanomethanide [TCM]- , and bis(trifuoromethylsulfonyl)imide [NTf2 ]- ) have been studied by 1 H and 13 C NMR spectroscopy. The anion structure has the main influence on the anion-aromatic chemical interaction strength; it is directly correlated to the NMR chemical shift deviations but not to the hydrocarbon solubility. The [TCM]- anion shows the largest chemical shift deviations, but the [NTf2 ]- anion has the highest hydrocarbon solubility due to steric effects. Higher water contents decrease the hydrocarbon solubility in ILs. Ion-water solvation mainly occurs until 1 molwater /molIL with the saturation limit at 10 molwater /molIL . Toluene-ion interactions are stronger than water-ion interactions in [DCA]- and [TCM]- -based ILs, but they have a similar or even lower strength in [SCN]- -based ILs.
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