Reactivities of ions and ion-pairs in the base-catalyzed reaction of phenyl glycidyl ether and benzoic acid in various solvents

Abstract

The conductance of pyridinium benzoate has been measured in various solvents such as nitrobenzene, benzonitrile, o-dichlorobenzene, monochlorobenzene, and toluene, and its dissociation constant, K, was determined, using the Kraus and Bray's equation with the Λ0 value estimated from Walden and Ulich's rule and Stokes's law. The logarithm of K was found to be linear with the reciprocal of the dielectric constant, ε, or with the Kirkwood–Laidler–Eyring function, (ε − 1)/(2ε + 1). Kinetic studies for pyridine-catalyzed reaction between phenyl glycidyl ether and benzoic acid were also made in these solvents. Both the free ions and ion-pairs including the molecular addition complex participate in the reaction. The apparent rate constants, k″, of the reaction were shown to be linear with 1(K/c)1/2, c being the concentration of pyridinium benzoate. The intercepts of such lines give the rate constant for formation of ion-pairs, ki and the slopes yield the rate constant for formation of free ion, kf. The free ion rate constant increases fairly rapidly as the dielectric constant decreases, while the ion-pair reaction constant drifts downward comparatively slowly. A plot of the logarithm of kf or kf(K/c)1/2 against 1/ε or (ε − 1)/(2ε + 1) is found to be linear, but the plots of log ki against the same function are curved. The tangent of the curve is steeper for polar solvents than for non-polar solvents. The results have been compared with those predicted from classical dielectric theory.