A Conductance Study of the Complexation Reaction of Dibenzo-24-crown-8 with Alkali Metal Ions in Propylene Carbonate and Methanol

Abstract

Abstract The formation constants (KML+) for 1: 1 complexes of dibenzo-24-crown-8 (DB24C8) with alkali metal ions (Na+, K+, Rb+, and Cs+) in propylene carbonate (PC) and methanol have been determined conductometrically at different temperatures in order to obtain the values of the enthalpy (ΔH) and entropy changes (ΔS). The complexation reactions between DB24C8 and the alkali metal ions in PC and methanol are all exothermic, and the ΔS values of these systems are all negative. In the case of the PC system, there is no considerable difference in ΔS among the alkali metal ions (Na+, K+, Rb+, and Cs+); thus, the KML+ sequences depend entirely on the −ΔH sequences. Since, in methanol, the −ΔH and −ΔS values for K+ are nearly equal to those for Cs+, and since the largest −ΔH value for Rb+ is balanced by the largest −ΔS value, DB24C8 shows no selectivity for the alkali metal ions (K+, Rb+, and Cs+) in methanol.