Dielectric Constant Measurements on the p-Dioxane: Acetonitrile Cosolvent System

Abstract

Static dielectric constant values were re-evaluated for the binary solvents, p-dioxane: acetonitrile and p-dioxane: methanol, over the complete mole fraction range. Earlier investigations on these systems were too incomplete to permit useful comparisons to be made among trends in excess dielectric constant vs. mole fraction functions for the cosolvents. Acetonitrile is one of the common dipolar aprotic solvents used for the study of medium effects upon the electrolytic conductance of ionic solutes, polarographic and cyclic voltammetric behavior of solute species, and nonaqueous acid-base titrations. Similarly, p-dioxane has long been employed as a nonpolar but fundamental solvent for electrochemical investigations; in most instances p-dioxane has been used as a cosolvent paired with a strong hydrogen bond donor, such as water or one of the simpler alkanols. For the latter, mixtures can be selected to represent a very broad dielectric constant range. Ionic association and ion-solvent interactions have been examined by D'Aprano and Triolo (1967) in the specific binary system, p-dioxane: acetonitrile, but their work was limited to only four solvent mixtures for this interesting solvent pair. Because of the very incomplete data base available for the fundamental properties of these solvent mixtures, a new investigation of the dielectric constants for the acetonitrile: p-dioxane system was extended over the total mole fraction range from pure p-dioxane to pure acetonitrile. Comparisons were also made to other binary solvents having one of these components in common.