Densities and Viscosities of Aqueous Amino Acid Ionic Liquids [C_nmim][Ala](n = 3, 4, 5)

Abstract

Amino acid ionic liquids [C n mim]­[Ala] (n = 3, 4, 5) (1-alkyl-3-methylimidazolium alanine salt) were prepared by the neutralization method. The density and viscosity for aqueous solutions of the ionic liquids (ILs) with various molalities were measured at T = (288.15 to 328.15) K with an interval of 5 K. In terms of the Jones–Dole equation, the viscosity B-coefficients with large positive values and dB/dT < 0 were obtained, and these facts implied that the ionic liquids are water-structure-making. According to Feakins, the contribution of the solute per mole to the free energy of activation for viscous flow of the solution, Δμ2 ⧧0, or called as the standard molar activation free energy, was obtained at different temperatures. Under the constant molality of solution, ΔH 2 ⧧0 (the activation enthalpy of the activation for viscous flow of aqueous [C n mim]­[Ala] (n = 3, 4, 5)) is a temperature-independent constant. This implies that the activation process of the solute for viscous flow of aqueous [C n mim]­[Ala] (n = 3, 4, 5) is an isoCoulombic reaction. A semiempirical method to estimate the viscosity of aqueous [C n mim]­[Ala] (n = 3, 4, 5) was put forward based on Eyring’s theory, and the estimated viscosity values of the aqueous ILs are in good agreement with the corresponding experimental ones.

A New Compartmentalized Scale (PN) for Measuring Polarity Applied to Novel Ether-Functionalized Amino Acid Ionic Liquids

“…N -Methylimidazole (AR grade) was purified by distillation, while 2-chloroethyl methyl ether and 2-chloroethyl ethyl ether (both AR grade) were used as purchased. DL-Alanine was recrystallized from water and dried in a vacuum oven [ 62 ].…”