Adsorption of Phenols from Non-polar Solvents on to Silica Gel

Abstract

A series of p-substituted phenols have been adsorbed from benzene solution on to silica gel. With the exception ofp-t-butylphenol, limiting adsorptions of the solutes are almost equal in magni tude and suggest a solute-solvent molecular ratio on the silica surface of 1 : 1. An index of adsorption Ki, is defined in terms of an ideal model of adsorption at the solid-solution interface and log is found to decrease linearly with increase in a, the Hammett p-substituent constant. Composite adsorption isotherms have been constructed for the adsorption of phenol from a series of non-polar solvents whose reactivities arc characterised by their Ey values. The isotherms deter mine, qualitatively, the order of solvent/surface reactivity as n-hexane < cyclohexane < carbon tetrachloride < toluene < benzene. Quantitatively log A?! is found to decrease linearly with increase in solvent ET value.