The surface tension of aqueous glycine ionic liquids: [C<sub>3</sub>mim][Gly] and [C<sub>4</sub>mim][Gly

Abstract

The amino acid ionic liquids (AAILs) [C₃mim][Gly] (1-propyl-3-methylimidazolium glycine) and [C₄mim][Gly] (1-butyl-3-methylimidazolium glycine) were prepared by the neutralization method and characterized by ¹H NMR spectroscopy and differential scanning calorimetry (DSC). The values of their density, surface tension and refractive index were measured at (298.15 ± 0.05) K. Since the AAILs can form strong hydrogen bonds with water, small amounts of water are difficult to remove from the AAILs by common methods. In order to eliminate the effect of the impurity water, the standard addition method (SAM) was applied to these measurements. A new concept which is called the ionic parachor has been put forward. The [C_nmim]⁺ cations were treated as a group of reference ions and the individual values of their ionic parachor were evaluated in terms of an extrathermodynamic assumption. Then, using the values of the ionic parachor of reference ions, the parachor, surface tension γ and refractive index <italic>n</italic>_D of the ionic liquids investigated in this work were estimated. The estimated values correlate quite well with the corresponding experimental values.