Thermophysical Properties of 1‑Hexyl-3-methylimidazolium Salicylate as an Active Pharmaceutical Ingredient Ionic Liquid (API-IL) in Aqueous Solutions of Glycine and l‑Alanine

The effect of 1-hexyl-3-methylimidazolium salicylate, [HMIm]­[Sal] as an ionic liquid form of active pharmaceutical ingredient (API-IL) on the thermodynamic behavior of two simple amino acids, glycine and l-alanine have been investigated. The densities, speeds of sound, viscosities, and refractive indices of the amino acids in the mixtures of ([HMIm]­[Sal] + water) have been determined at T = 298.15 K. Moreover, the electrical conductivities of the studied API-IL in water and aqueous mixtures of the amino acids have been calculated using the measured specific conductivities. The measured data were utilized to compute the partial molar volume of transfer (ΔtraVϕ0), partial molar isentropic compressibility of transfer (Δtraκϕ0), viscosity B-coefficient of transfer (ΔtraB), ion association constant (KA), and molar refraction (RD) quantities. The increase in the positive values of ΔtraVϕ0, Δtraκϕ0 and ΔtraB with an increase in the API-IL concentration indicates that the ion–polar and polar–polar interactions between the API-IL and amino acid are dominant. Besides, the decrease in the KA values of [HMIm]­[Sal] with the addition of amino acid concentration suggests that the formation of ion pair does not proceed spontaneously due to the ions solvated by the zwitterions of amino acid