ON THE DETERMINATION OF POLARITY PARAMETERS OF SILICA BY MEANS OF SOLVATOCHROMIC PROBE DYES

Empirical ''solvent'' parameters of silica surfaces are determined by means of solvatochromic dyes, e.g., Cu(tmen) (acac)(+) ClO4-/B(C6H5)(4 )(-), Fe(phen)(2)(CN)(2), and Michlers Ketone dissolved in 1,2-dichlor oethane or cyclohexane. The values obtained by UV/VIS-measurements are compared with both the polarity scales of Kamlet and Taft and with Gu tmann's donor and acceptor numbers. Kamlet and Taft's alpha-parameter (the hydrogen-bond donation capacity of a solvent) is determined indep endently by means of salicylideneaniline. The pi-parameter of silica is determined using 5-N,N-dimethylamino-5'-nitro-2,2'-bithiophene and the complex of tetracyanoethylene with Michlers Ketone, respectively. Further on the reliabilities of the obtained Kamlet-Taft parameters al pha, beta, and pi are checked by comparism with experimental and calc ulated values of the E(t)(30)-parameter of silica by means of multi-pa rameter regression analysis. The surface properties of silica are infl uenced mainly by HBD-properties alpha (75%) and dipolarity/polarizabil ity pi (20%), but hardly by the HBA-properties beta(< 5%). UV/VIS-mea surements were carried out in a special equipment with glass fiber opt ics. A drawing of the apparatus is given.