The surface-mediated hydride-transfer reaction of 1,4-cyclohexadiene with triphenylmethylium induced by two silicas, an alumina, and an aluminosilicate as solid acid catalyst, respectively, has been kinetically studied as a function of the polarity of the surrounding solvent. The specific rate constants V have been determined in 10 different solvents. Generally, k' decreases with increasing polarity of the solvent. Kamlet-Taft's alpha (hydrogen-bond acidity) and pi* (dipolarity/polarizability) parameters of the solid acid/solvent interface have been determined for alumina and aluminosilicate in various solvents. Fe(phen)(2)(CN)(2) [cis-dicyanobis(1,10-phenanthroline)iron(II), (1)] and Michler's ketone [4,4'-bis(NN-dimethylamino)benzophenone, (2)] were used as solvatochromic surface polarity indicators. The UV/vis spectra of the two surface polarity indicators 1 and 2 adsorbed on solid acid catalysts from the solvents were measured by the reflection mode and the UV/vis absorption maxima were used to calculate the alpha and pi* values of the catalysts. alpha of the solid acid catalyst/ solvent interface decreases with increasing term (hydrogen-bond accepting) ability of the solvent, whereas the pi* term of the solvent marginally modifies the interfacial polarity. k' increases for each individual solvent with increasing beta of the catalyst solvent interface in the order series silica < alumina < aluminosilicate. It can be shown that alpha of the solid acid catalyst/solvent interface decreases with increasing beta term (hydrogen-bond accepting) ability of the solvent, whereas the pi* term of the solvent marginally modifies the interfacial polarity.