Adsorption of phenols from non-polar solvents on to activated alumina

Abstract

A series of p-substituted phenols have been adsorbed from benzene solution on to activated alumina. The limiting adsorption values are found to be similar in magnitude when the p-substituent is small in size, and it is concluded that an almost complete monolayer of the phenol is formed, benzene being mostly excluded from the adsorbed phase at saturation. An affinity of adsorption, K, is defined in terms of an ideal model of adsorption at the solid/solution interface and it is found that in general K increases 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 E_T value is a molar transition energy calculated from the position of the absorption maximum in the visible spectrum of 4-(1-pyridinio)phenolate. The isotherms determine, qualitatively, the order of solvent/surface reactivity as cyclohexane < carbon tetrachloride < benzene < tetrahydrofuran < dioxan. The trend of K with E_T is not so clearly established as in the case of the adsorption on silica gel, the affinity of phenol for alumina being strong in all solvents.