Complex Formation of Crown Ethers with Cations in the Water–Organic Solvent Mixtures. Part VIII.¹ Thermodynamic of Interactions of Na⁺ Ion with 15-Crown-5 and Benzo-15-Crown-5 Ethers in the Mixtures of Water with Hexamethylphosphortriamide at 298.15 K

Abstract

The equilibrium constants of complex formation of 15-crown-5 and benzo-15-crown-5 ethers with the sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method at 298.15 K. The thermodynamic functions of complex formation of 15-crown-5 and benzo-15-crown-5 ethers with the sodium cation in the mixtures of water with hexamethylphosportriamide at 298.15 K have been calculated. The extent of complex formation in this mixed solvent depends on the enthalpic effect. In water–hexamethylp- hosportriamide mixtures with medium and low water content, the complex of crown ethers with the sodium cation is not formed because of the strong solvation of sodium cation and crown ethers molecules; this implies that the entropy of complex formation is more negative than the enthalpy of complex formation.