1Department of Chemistry, Tehran University, Tehran,, I.R. IRAN
2Department of Chemistry, Imam Hossein University, Tehran, I.R. IRAN
3Department of Chemistry, Razi University, Kermanshah, I.R. IRAN
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, Ka, 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 Ka value with varying concentration of cations and found to vary in the order Rb+>Cs+>Tl+>K+>Na+.