Temperature dependent apparent molar properties of trihexylammonium carboxylate based protic ionic liquids in toluene and dodecane

Abstract

The hydrophobic ionic liquid containing non-fluorinated anion and suitable diluents are two main requirements for the eco-friendly extraction of metal ions from aqueous phase. The information about volumetric properties of their binary solution shed light on the molecular interactions that govern extraction mechanism. In this manuscript, we report the experimental densities, ρ and speeds of sound, u for six binary mixtures of protic ionic liquids (PILs) in toluene and dodecane at various concentrations of PILs, in the temperature range from 293.15 to 328.15 K and at 0.1 MPa. The PILs included in present investigation are Trihexylammonium butanoate [THA][But], Trihexyl ammonium hexanoate [THA][Hex] and Trihexylammonium octanoate [THA][Oct]. The measured values of densities, ρ and speeds of sound, u were used to derive apparent molar volume Vϕ, apparent molar isentropic compressibility Ks,ϕ and limiting apparent molar expansivity Eϕ∞. The apparent molar properties were explained in terms of anion structure, nature of solvent and temperature. The value of Vϕ and Ks,ϕ were found to increase with increase in temperature and by changing solvent whereas decrease with increasing PIL concentration in binary solution. The apparent molar volume, Vϕ∞ and apparent molar isentropic compressibility, Kϕ∞ at infinite dilution were calculated at studied temperature ranges and correlated by Redlich-Mayer type equation. The significance of ion-ion or ion-solvent interactions in binary solution was explained on the magnitude of two parameters Sv and Sk. The ion-solvent interactions were observed to be stronger in binary solution of PIL + dodecane than PIL + toluene.