Ionic parachor and its application to pyridinium-based ionic liquids of {[Cnpy][DCA] (n = 2, 3, 4, 5, 6)}

Abstract

Three novel dicyanamide ionic liquids (ILs) [Cnpy][DCA] (n=3,5,6) and two [Cnpy][DCA] (n=2,4) (N-alkyl-pyridinium dicyanamide) were prepared and characterized by 1H NMR spectroscopy, 13C NMR spectroscopy, differential scanning calorimetry (DSC), High Performance Liquid Chromatography (HPLC) and FT-IR spectroscopy. The density, surface tension and refractive index were determined by the standard addition method (SAM) at T=298.15K. The experiment values of parachor for [Cnpy][DCA] (n=2,3,4,5,6) were calculated and the ionic parachor of anion, [DCA]− as a reference ion was obtained in terms of the extrathermodynamic assumption, and then the ionic parachor, P+, of all corresponding pyridinium cations, [Cnpy]+, were obtained. Using the values of P+ of [Cnpy]+ and [Cnmim]+ in our previous papers, the values of ionic parachor for 10 kinds of anions were obtained. By using the ionic parachor, the values of parachor for 47 ionic liquids were obtained, which are more closed to their experiment values than the values of parachor obtained by Rowley et al. The values of surface tension for 52 ionic liquids and the values of refractive index for 22 ionic liquids were predicted using the estimated values of parachor with their experimental expanded uncertainty at 0.95 confidence level of ±0.3mJ·m−2 and ±0.0003, respectively.