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

Abstract

Using conductance measurements, an attempt has been made to gain detailed information about the specific molecular interactions of crown compounds with metal ions in a 1,4-dioxane/water binary system. Analyses of the transport data of dioxane/water mixtures yielded the mobility of the crown compound action complexes and the ion-pair dissociation constant of the crown compound-electrolyte complex. Binary mixed aqueous solvents are frequently employed 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), polarography, voltammetry, spectrophotometry, nuclear magnetic resonance, calorimetry and solubility. In this study the conductometry measurements have been carried out with high precision at optimal concentrations in dioxane/water systems. Structures of crown-cation complexes in dioxane/water mixtures are estimated from the conductance parameters (kappa, Lambda and alpha) as well as the complex formation constant, K-e = (Lambda(MAm) - Lambda)/(Lambda - Lambda(MaLbAm)) [L]. The conductance behavior of Na+, K+ chlorides and Na+ perchlorates 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 the crown ether, K-e. For the calculations, Excel. 5.0 was used as an application program.