Studies of osmotic and activity coefficient properties of aqueous solutions of triethylammonium formate and triethylammonium glycolate protic ionic liquids at 298.15 K

摘要

The triethylammonium-based carboxylate protic ionic liquids (PILs) are called as truly bio-ionic liquids. They can be used as green solvent, additives (biphasic catalysis) and for other considerable effects involving nano-material specially related to biomolecules. In this work, osmotic coefficient (phi) measurements using vapor pressure osmometry technique for aqueous solutions of two PILs, namely, triethylammonium formate [TEAF] (0.01290-0.55988 mol.kg(-1)) and triethylammonium glycolate [TEAG] (0.00989-0.53176 mol.kg(-1)) have been reported at 298.15 K. The water activity (a(w)) and solvent activity coefficient (gamma(1)), mean molal activity coefficient (gamma(+/-)) of PILs and osmotic pressure (pi) of solutions properties in a binary mixture, were determined using experimentally measured phi data. The analysis of osmotic pressure data revealed that the studied PILs are electrolytes in the limit of infinite dilution and yield correct molecular weights as well as show negative values for virial coefficients. The variations of osmotic coefficient and mean molal activity coefficient of studied PILs with concentration indicate positive deviations from Debye-Huckel limiting law similar to that of ammonium ions. Further, Gibbs free energy changes due to mixing (Delta G(m)) and excess Gibbs free energy changes (Delta G(E)) for the studied binary systems are estimated. The solute-solute virial coefficient (NB22*(0)) for the studied PILs in aqueous solutions were estimated by an application of the McMillan-Mayer theory of solutions. The results indicate that the hydration effect is dominant in PILs through the cooperative H-bonding with water-structure making effect suggesting the significance of hydrophobic hydration as observed in tetraalkylammonium salts and aprotic ionic liquids. A need to study the water molecule splitting at nitrogen charge centre and possible attenuation of water structural effects due to hydrophobic moieties present in the molecule is emphasized. (C) 2020 Elsevier B.V. All rights reserved.