Structural isomerism of hydrophobic ionic liquids: Thermophysical properties and solution behaviour

C. Neves1, M. Freire1, L. Santos2 and J. Coutinho1

1Departamento de Química, CICECO, Universidade de Aveiro, Aveiro, Portugal
2CIQ, Departamento de Química, Faculdade de Ciências da Universidade do Porto, Porto, Portugal

Keywords: ionic liquids
property: density, viscosity, phase equilibria
material: water

Low melting temperature organic salts or ionic liquids (ILs) are novel solvents with a rather specific blend of physical and solution properties that make of them interesting for the most diverse applications. Particularly, their use in separation science is an emerging and promising field. Therefore, a detailed picture of the ILs physicochemical properties and solvent behavior will allow their tailoring aiming at defining their extraction capabilities. Thus, in this work, physical properties, such as densities and viscosities, as well as the mutual solubilities between ILs and water, and their depence with the temperature were determined. The selected ILs comprise imidazolium-based cations combined with the anion bis(trifluoromethylsulfonyl)imide. The effect of the ILs structural combinations in their physical properties and mutual solubilities with water - with particular emphasis in the cation structural isomerism - was analyzed and discussed. The molar thermodynamic functions of solution such as Gibbs energy, enthalpy and entropy of the ILs in water were estimated and rationalized. It is shown that despite the cation and anion nature contributions, the structural isomerism in ILs is crucial and an additional feature that manages the ILs physical properties and solution behaviour.

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