The determination of crown-cation complexation behavior in dioxane/water mixtures by conductometric studies

Using conductance measurements, an attempt has been made to gain detailed i nformation about the specific molecular interactions of crown compounds wit h metal ions in a 1,4-dioxane/water binary system. Analyses of the transpor t data of dioxane/water mixtures yielded the mobility of the crown compound action complexes and the ion-pair dissociation constant of the crown compo und-electrolyte complex. Binary mixed aqueous solvents are frequently emplo yed in broad areas of chemistry. Their applicability ranges from synthetic and mechanistic studies in organic chemistry to biophysical chemistry, with emphasis on molecular interactions in biologically significant structures. Stability constants of crown compound complexes are determined by various methods, such as potentiometry (with ion selective electrodes), polarograph y, voltammetry, spectrophotometry, nuclear magnetic resonance, calorimetry and solubility. In this study the conductometry measurements have been carr ied out with high precision at optimal concentrations in dioxane/water syst ems. Structures of crown-cation complexes in dioxane/water mixtures are est imated from the conductance parameters (kappa, Lambda and alpha) as well as the complex formation constant, K-e = (Lambda(MAm) - Lambda)/(Lambda - Lam bda(MaLbAm)) [L]. The conductance behavior of Na+, K+ chlorides and Na+ per chlorates with 18-crown-6, 15-crown-5, and 12-crown-4 have been studied in various dioxane/water systems (50%, 80%, and 85%) at 25 degrees C. The all experimental studies have been made by the ratio 1:1 of the metal-ion and t he crown ether, K-e. For the calculations, Excel. 5.0 was used as an applic ation program. (C) 1998 John Wiley & Sons, Ltd.