Aust. J. Chem., 1993, 46, 1545-1555 A Non-Linear Correlation Model for the Relative Permittivity of Ternary Amphiprotic (Solvent) Mixtures Fulvio Corradini, Luigi Marcheselli, Andrea Marchetti, Mara Tagliazucchi, Lorenzo Tassi and Giuseppe Tosi Department of Chemistry, University of Modena, 41100 Modena, Italy. Abstract Relative permittivities (E) were determined for ternary ethane-1,2-diol (component 1)/2- methoxyethanol (component 2)/water (component 3) mixtures at five temperatures ranging from 5 to 25OC and over the mole fraction composition range 0 5 X, 5 1. The data have been fitted to a model equation that could be useful for predictive E calculations. From the measured E values, the excess relative permittivity eE has been evaluated in order to test for three-component adducts. The values of eE have been found to be negative for all the ternary mixtures under all the experimental conditions, which suggests a strong interaction network through hydrogen bonding, although evidence for a discrete three-component adduct was not forthcoming. Introduction This paper describes part of our long-term research concerning dielectric behaviour of non-electrolytic systems and acid-base equilibria in pure or mixed non-aqueous or aqueous We first selected ethane-1,2-diol and 2-methoxyethanol as polar amphiprotic solvents that were employed pure and mixed, and picric acid as the solute. The ionization and dissociation reactions4 of picric acid were studied as a function of the temperature (T) and binary solvent composition expressed as the mole fraction (X) of one component. The very different trends of the experimentally determined dissociation constant (K) of picric acid in these mixed solvents have been attributed to changes in the reactant-solvating ability of the medium. In the course of these investigations we decided to extend our studies to ternary solvent systems, where the mixing of the two above-mentioned organic cosolvents with water, in various proportions, would enable us to change the physical properties of the reaction bath. One of the big problems generally encountered in such studies is to correlate the experimental data for the investigated reactions with the physical properties of the corresponding media. Preti, C., Tassi, L., and Tosi, G., Anal. Chem., 1982, 54, 796. Franchini, G.C., Marchetti, A., Tassi, L., and Tosi, G., J. Chem. Soc., Faraday Dans. 1, 1988, 84, 4427. Marchetti, A., Piechioni, E., Tassi, L., and Tosi, G., Anal. Chem., 1989, 61, 1971. Franchini, G.C., Marchetti, A., Tassi, L., and Tosi, G., Anal. Chem., 1990, 62, 1004. Manuscript received 18 February 1993 0004-9425/93/101545$05.00