Influence of Metal Ion Complexation on the Acid Dissociation of 4'-Carboxybenzo-24-Crown-8 in an Ethanol-Water Mixture

Abstract

<em>A spectrophotometric method was used to determine the acidity constant of 4'-carboxybenzo-24-crown-8 in 52% (w/w) ethanol-water mixture. The acid dissociation constant, K_a, was found to increase in the presence of Na⁺, K⁺, Rb⁺, Cs⁺ and Tl⁺ ions. The formation constants of the resulting 1:1 complexes between the carboxycrown and the metal ions used were evaluated from the observed changes of K_a value with varying concentration of cations and found to vary in the order Rb⁺>Cs⁺>Tl⁺>K⁺>Na⁺. </em>