Conductometric Study on Dissociation of Tetrabutylammonium Salts and Behavior of Cations in Pyridine

Abstract

The electrolytic conductivities of several tetrabutylammonium nitrophenolates in pyridine were measured at 25°C, and the dissociation of tetrabutylammonium salts and the behavior of tetrabutylammonium ion (Bu₄N⁺) were examined. The conductance behavior (Fig.1)of all the salts examined was Interpreted as the dissociation of simple ion pairs, similar to that of the strong electrolytes. The conductometric data were analyzed by the FuossKraus method, and the dissociation constants of the tetrabutylammonium salts were calculated. The limiting molar conductivity of Bu₄N⁺ was determined to be 21.87 S.cm².mol^-1 on the basis of the limiting molar conductivity of tetrabutylammonium tetraphenylborate (Table 1). By taking account of the electrophoretic and relaxation effects of the oppositely charged ions, a new method for calculating the electrolytic conductivity of ions was proposed. Through this method, a new relationship was found between the electrolytic conductivity of Bu₄N⁺ and the ionic concentration. The ionic electrolytic conductivity of Bu₄N⁺ was dependent only upon the ionic concentration of Bu₄N⁺ regardless of the kind of counter ions (Fig.3). It was o bserved that the radius of the solvated Bu₄N⁺ in pyridine obtained by using eq. (8)became larger with the increase in the ionic concentration (Fig.5). The Stokes radius of Bu₄N⁺ in pyridine was almost the same as that in water. The difference between the degree of dissociation of the tetrabutylammonium salts in water and that in pyridine is attributable to the difference in the size of the region in which ion pairs are formed, rather than the size of solvated ions.