Influence of anion structure on volumetric properties of dilute binary systems containing carboxylate functioned trihexylammonium ionic liquids in toluene / dodecane

Abstract

We are actively involved in synthesis of hydrophobic ionic liquids, their volumetric behaviour in various solvents of different polarity and their application in metal ions extraction from water. In continuation of previous work, we are presenting new protic ionic liquids (PILs) containing Trihexylammonium cation and carboxylate anions namely Trihexylammonium propionate [THA][Pro] and Trihexylammonium pentanoate [THA] [Pent]. The simultaneous measurements of densities, ρ along with speeds of sound, u for binary systems of [THA][Pro] and [THA][Pent] in toluene and in dodecane were collected. The measurements were carried out in dilute concentrations range of PILs, at 0.1 MPa and different temperatures from 293.15 K to 328.15 K. The experimental values of densities, ρ and speeds of sound, u, were utilized to obtain calculated values of apparent molar properties: Vϕ (apparent molar volume) and Ks,ϕ (apparent molar isentropic compressibility). It is observed that the apparent molar properties of investigated systems are quite sensitive to variation in temperature, solvent and anion’s structure of PILs. The values of Vϕ and Ks,ϕ increases with each increment in studied temperature and when toluene was replaced by dodecane as a solvent in the system. The each addition of –CH2 group in anion chain of PILs leading to increase Vϕ whereas decrease with concentration of PILs in the binary system. The limiting values of apparent molar volume, Vϕ∞ and apparent molar isentropic compressibility, Kϕ∞ were also reported. The strength of interactions between PIL-PIL and PIL-solvent in studied binary systems was explained by Sk and Sv parameters. The PILs + dodecane systems exhibit greater interaction between PILs and solvent than binary systems of PIL + toluene.