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 of p-t-butylphenol, limiting adsorptions of the solutes are almost equal in magnitude and suggest a solute-solvent molecular ratio on the silica surface of 1:1. An index of adsorption K₁, is defined in terms of an ideal model of adsorption at the solid-solution interface and log K₁ is found to decrease linearly with increase in σ, 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 are characterised by their E_T values. The isotherms determine, qualitatively, the order of solvent/surface reactivity as n-hexane < cyclohexane < carbon tetrachloride < toluene < benzene. Quantitatively log K₁ is found to decrease linearly with increase in solvent E_T value.