Structural Characteristics of Homogeneous Hydrophobic Ionic Liquid-HNO3-H2O Ternary System: Experimental Studies and Molecular Dynamics Simulations.

The solubility of water in the hydrophobic ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]) increases significantly in the presence of HNO3. [C2mim][NTf2] is completely miscible with HNO3 but immiscible with water. The triangular phase diagram of the ternary system [C2mim][NTf2]-HNO3-H2O was determined at 300.1 K. The homogeneous [C2mim][NTf2]-HNO3-H2O phase is thermodynamically stable, while it can be separated into two phases with an increase of water content. Experiments (electrospray ionization mass spectrometry, Fourier transform infrared spectrometry, and (1)H-nuclear magnetic resonance spectrometry) and molecular dynamics simulations were carried out to investigate the interaction between [C2mim][NTf2], HNO3, and water in the homogeneous phase. It was found that NO3(-) ions interact with both C2mim(+) and water via H-bonding and act as a "bridge" to induce a large amount of water to be dissolved in the hydrophobic IL phase. This confirms that the complexes [C2mim-NTf2-C2mim](+) and [NTf2-C2mim-NTf2](-) exist in the homogeneous [C2mim][NTf2]-HNO3-H2O system at the concentration of HNO3 up to 27.01 wt % and of water as high as 20.74 wt %.