Temperature dependence measurements and molecular interactions for ammonium ionic liquid with N-methyl-2-pyrrolidone

Abstract

We report the synthesis and characterisation of a series of ammonium ionic liquids (ILs) containing acetate and sulphate anions with alkyl ammonium cation. To understand the thermophysical properties of these synthesised ILs with polar solvent N-methyl-2-pyrrolidone (NMP), precise measurements such as densities (ρ), speed of sound (u), and viscosity (η) over the entire mole fraction range have been measured at 5K intervals within the temperature range of (298.15 to 313.15)K under atmospheric pressure. The excess molar volume (VE), the deviation in isentropic compressibility (Δκs), and deviation in viscosity (Δη) were predicted using these temperature dependence properties as a function of the concentration of ILs. The Redlich–Kister polynomial was used to correlate the results. The ILs investigated in the present work included diethylammonium acetate (DEAA) [(CH3CH2)2NH][CH3COO], triethylammonium acetate (TEAA) [(CH3CH2)3NH][CH3COO], diethylammonium hydrogen sulphate (DEAS) [(CH3CH2)2NH][HSO4], and triethylammonium hydrogen sulphate (TEAS) [(CH3CH2)3NH][HSO4]. The intermolecular interactions and structural effects were analysed on the basis of the measured and the derived properties. The information reported here in terms of ion–dipole interactions, ion-pair interactions and hydrogen bonding between ILs and NMP, elucidates the influences of ions and also the temperature effects on the thermophysical properties.