Examination of the thermodynamic behavior of binary mixtures of 2-hydroxyethylammonium acetate (2-HEAA) with 1-propanol, 3-amino-1-propanol, 1-amino-2-propanol, and ethanolamine

The thermodynamics of mixtures was investigated, focusing on the protic ionic liquid 2-hydroxyethylammonium acetate ([2-HEAA]) in combination with 1-propanol ([1-Pr]), 3-amino-1-propanol ([AP]), 1-amino-2-propanol ([MIPA]), and ethanolamine ([EA]). Density ( ρ ), speed of sound ( u ), and refractive index \\(\\:{(n}_{\\text{D}}\\) ) were measured for both the pure components and their mixtures at temperatures of 298.15, 308.15, and 318.15 K. The study determined the excess molar volume ( \\(\\:{V}_{\\text{m}}^{\\text{E}}\\) ), excess partial molar volume ( \\(\\:{V}_{\\text{m},\\text{i}}^{\\text{E}}\\) ), excess thermal expansion coefficient ( \\(\\:{\\alpha\\:}^{\\text{E}}\\) ), the isothermal coefficient of excess molar enthalpy \\(\\:{\\left(\\partial\\:{H}_{\\text{m}}^{\\text{E}}/\\partial\\:p\\right)}_{T,x}\\) , as well as deviations in isentropic compressibility (Δ \\(\\:{\\kappa\\:}_{\\text{s}}\\) ) and refractive index \\(\\:{({\\Delta\\:}n}_{\\text{D}}).\\) The resulting data were correlated using the Redlich-Kister polynomial relation. The Prigogine-Flory-Patterson (PFP) and Extended Real Associated Solution (ERAS) models were employed to correlate excess molar volume data and to distinguish between physical, chemical, and structural contributions to the mixing behavior. The results contribute to a deeper thermodynamic understanding of protic ionic liquid-alcohol systems and their underlying interaction mechanisms. Spectroscopic techniques, including FT-IR and H-NMR, were used to confirm the structures of the ionic liquids.