Acid-base interaction of probes at silica surface. Microcalorimetry and adsorption.

The interaction of four benzyl derivatives with silica surface sites in anhydrous cyclohexane is investigated. The strength and extent of adsorption is determined from the Langmuir adsorption isotherm. The enthalpy of immersion is determined microcalorimetrically, which is recalculated to the enthalpy of adsorption. The aim is to distinguish between the Lewis-type (electron exchange) and Brønsted-type (proton exchange) of interaction by selecting methanol-acetone and acetic acid-methylamine, respectively as acid-base substituent in benzene. Moreover, the experiments were performed in anhydrous cyclohexane in order to screen out hydrocarbon interactions from the energy balance. The monomolecular adsorption is also distinguished from the bulk wetting of solids. The results are evaluated in terms of possible proton exchange in anhydrous media.