Limiting partial molar volumes and expansions for triethylamine in water and in aqueous tetraethylammonium chloride solutions from 15 to 35 °C

Abstract

The densities of ternary systems of triethylamine in aqueous tetraethylammonium chloride solutions have been measured, at 5 °C intervals from 15 to 35 °C, with a vibrating tube densimeter. The molalities in tetraethylammonium chloride studied were 0, 0.05, 0.4 and 0.9 mol kg⁻¹. The concentration of triethylamine was varied from 0 to ca. 0.35 mol kg⁻¹ in each solvent. Negative excess molar volumes, V_m^E, were obtained for all the systems and their variations with the amine mole fraction were fitted to the Redlich–Kister equation. Limiting partial molar volumes and expansions of triethylamine, V_Et3N^∞ and E_P,Et3N^∞, were evaluated using the derivatives dV_m^E/dx_Et3N and dV_Et3N^∞/dT, respectively. Values of V_Et3N^∞ increase with temperature for all the solvents. Limiting excess partial molar volumes of triethylamine, V_Et3N^E,∞, are considerably negative and decrease with the salt concentration. This means a shift from ideality in the direction of a better packing efficiency of Et₃N in the cage structure of the water and this effect increases as the concentration of the salt is increased. Values of E_P,Et3N^∞ are all positive and increase with the salt concentration. This may signify that the accommodation of Et₃N in the water structure decreases with temperature. Molar expansions were also derived and plotted vs. the amine concentration.