CARBENIUM ION-PAIRS ON SILICA - UV-SPECTROSCOPIC AND ELECTROKINETIC MEASUREMENTS OF TRIARYLMETHYLIUM HALIDE-AEROSIL IN 1,2-DICHLOROETHANE/

The interaction of carbenium ion pairs with silica is studied by means of UV-spectroscopy, electrokinetic and adsorption measurements using triphenylmethyl derivatives, (RC(6)H(4))(3)CX, (X = F, Cl, Br, SCN, OH ; R = Cl, I, H, CH3, C(CH3)(3), OCH3, N(CH3)(2)) in interaction with s ilica particles suspended in 1,2-dichloroethane. The adsorption of tri arylmethyl-halides onto silica is accompanied by the heterolytic disso ciation of the tertiary carbon-halogen bond. The degree of ionization depends on the basicity of the counter anion and acidity of the cation , respectively. The influences of both concentration and structure of triarylmethyl halides on the zeta-potential are discussed with regard to steric and electronic factor. The zeta-potential values of the adso rbates decrease significantly, as compared with the free silica surfac e, from a certain triarylmethyl halide concentration where ionization takes place, to a constant level which is characteristic of the carben ium ion pair. These constant zeta-potential values of the adsorbates d epend on the basicity of the counter ion and the sigma(p) Hammett cons tants of the ring substitutents, with exclusion of sterically hindered substituents and salt derivatives, e.g., crystal violet and malachite green.