ION-PAIR OF TETRAALKYLAMMONIUM PICRATES

The ion-pair formation equilibria of tetraalkylammonium ion with picrate ion (C6H2(NO2O-) in 1,2-dichloroethane were studied at 25.0 degrees C by means of conductivity measurement. The cation studied were the symmetric (TAAn(+); (CnH2n+1N+, n = 1-8) and asymmetric (TOMA(+); (C8H17)(3)(CH3N+, CTMA; (C16H33)(CH3N+,) tetraalkylammonium ions, Q(+). Limiting molar conductivities of salts, Lambda(0), and ion-pair formation constants, K-ip were obtained by the analysis of the conductometric data with Fuoss-Justice Equation. Stokes radius, r(S), of the tetraalkylammonium ions was estimated from the limiting molar conductivity. The closest approach, a, between the cation and anion of the ion pair was estimated from the ion-pair formation constant. The value of r(S) estimated for asymmetric Q(+) is comparable to that of symmetric Q(+) having a corresponding number of carbon atoms, whereas the closest approach of the asymmetric Q(+) is much smaller than that predicted from the number of carbon atoms. The structures of ions and ion pairs were discussed.