Thermodynamic properties of selected ionic liquids with carboxylic acids at several temperatures

Abstract

Over the years, ionic liquids (ILs) have become an essential tool in chemistry owing to their various applications such as catalysis, electrochemistry, pharmaceuticals, nanotechnology, biotechnology, separation and extraction processes, amongst many others. With respect to the above applications, ionic liquids have desired properties like low flammability, low vapour pressure, high thermal and chemical stability, good electrical conductivity and low volatility. Ionic liquids possess the ability of being “tailored” to meet specific needs for different applications due to the flexibility in their physicochemical properties. This is done by replacing or substituting the side chain length of cation or anion structure.This project focused on the thermodynamic as well as thermo-physical parameters of two-component combinations of ionic liquids (ILs) and carboxylic acids (ethanoic or propanoic or butanoic or pentanoic or 2-methylpropanoic acids) which were investigated at several temperatures. The ionic liquidsutilized for this research investigation includes: •1-ethyl-3-methylimidazolium ethylsulphate ([EMIM]+[EtSO4]−)•1-butyl-3-methylimidazolium methylsulphate ([BMIM]+[MeSO4]−)•N-2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium salicylate ([EPMpyr]+[SAL]−)•N-2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium acetate ([EPMpyr]+[OAC]−)•N-2′, 3′-dihydroxypropyl-N-methyl-2-oxopyrrolidinium chloride ([PYR-PDO]+[Cl]−)Density and speed of sound measurements were examined obtained for the following two component systems: {([EMIM]+[EtSO4]−) + pentanoic or 2-methylpropanoic acid, ([BMIM]+[MeSO4]−) + ethanoic or propanoic acid, ([EPMpyr]+[SAL]−) + ethanoic or propanoic acid, [EPMpyr]+[OAC]−+ propanoic or butanoic acid, [PYR-PDO]+[Cl]−+ ethanoic or propanoic or butanoic acid) throughout the concentration of the ionic liquid at T= (288.15, 293.15, 298.15, 303.15, 308.15 and 313.15) K). Parameters such as excess molar volumes (VmE), isentropic compressibilities (ks) is entropic compressibilities deviation (Δks) and intermolecular free length (Lf) were computed from the measured values of densities and speeds of sound.The experimental data revealed that densities and speeds of sound value decrease with rise in temperature. Furthermore, excess molar volumes and is entropic compressibility deviation for all systems studied were found to be negative and increased with a rise in temperature. The negative outcomes obtained for excessmolar volumes of all the two-component systems studied suggest chemical interactions occur between unlike molecules in the component mixtures. These interactions are ascribed to formation of weak bonds and electron donor and acceptor complexes. Furthermore, the interaction interstices of IL gave some space for the acids to achieve structural arrangement.The Redlich-Kister equation was used to correlate the derived parameters; VmE, Δks and Lf whereas a least squares method was utilized in determining the fitting parameters and standard errors. These was done to check the precision of the measured data and the standard deviations which show moderately lower values for VmE, Δks and Lf with the examined temperatures for all the binary systems.