SUBSTITUENT EFFECTS IN ION-PAIR DISSOCIATION OF ANILINIUM ACETATE AND ANILINIUM P-TOLUENESULFONATE IN ACETIC ACID

Ion-pair dissociation constants for a series of substituted anilinium acetates, KdBH+Ac-, and anilinium p-toluenesulfonates, KdBH+Ts-, have been measured in acetic acid at 26.7° by spectrophotometric and potentiometric methods. Results are listed as follows: substituent, 107KdBH+Ac-, 107KdBH+Ts-; H, 3.07, 0.82; p-OCH3, 3.36, 0.62; p-CH3, 2.98, 0.74; p-F, 1.73, 0.335; p-Cl, 1.78, 0.395; p-Br, 1.30, 0.27; p-I, 1.48, 0.30; m-OCH3, 2.97, 0.61; m-CH3, 2.07, 0.42; m-Cl, 2.46, 0.61; m-CF3, 1.17, 0.345; 3,5-(OCH3)2, 2.97, 0.565; 3,5-(CH3)2, 2.52, 0.475; o-OCH3, 1.20, 0.195; o-CH3, 3.02, 0.58; o-F, 1.28, 0.63; o-Cl, 0.72, 1.37; o-Br, 0.45, 1.03; o-I, 0.36, 0.60; o-CF3, 0.044, 0.25; butter yellow, 27, 2.7. The precision of these results is better than 5% and the accuracy is better than 20% in most cases. Results obtained by spectrophotometry and by potentiometry are in good agreement. For meta and para substituents, there is good linear correlation between log KdBH+Ts- and log KdBH+Ac-, but little or no correlation between substituent effects on log Kd and the Hammett substituent constant σ. For ortho substituents, the substituent effects on Kd are highly specific. Ionization constants, KiB, have been measured for ortho-substituted anilines in acetic acid at 26.7°: substituent, KiB; o-OCH3, 1.9; o-CH3, 4.6; o-F, 0.21; o-Cl, 0.20; o-Br, 0.19; o-I, 0.14; o-CF3, 0.06; butter yellow, 0.110. The base dissociation constant of p-toluenesulfonate ion in acetic acid was found by two methods to be 0.9 × 10-6 M at 26.7°.