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

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 5 K 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.

► We report densities, sound velocities and viscosities for NMP with ionic liquids. ► We have predicted VE, ΔKs, and Δη from measured ρ, u, and η, respectively. ► Redlich Kister polynomial was used to correlate the results. ► We have synthesised the new ammonium based ILs. ► The intermolecular interactions were analyzed on the basis of derived properties.