A theoretical and experimental study of adsorption from dilute cyclohexane solutions of non-electrolytes: 4-X-chalcones on silica gel

Abstract

Adsorption experiments of 4-X-chalcones (X=H, Cl, F, OCH 3, N(CH 3) 2, CH 3) from dilute cyclohexane were carried out using silica gel as adsorbent. The data fitted Langmuir's isotherms allowing to determine the strength of adsorption for each substrate. The results are explained on the basis of the reactivity indices, and the thermodynamic and geometric magnitudes of the 4-X-chalcones and silica gel calculated by the AM1 method using optimized molecular geometries. The adsorption of 4-substituted chalcones with electron-withdrawing groups is generally weaker than that of chalcones with electron-donating p-substituents in ring B. The polarity of the molecules is not a determining factor in the degree of adsorption of compounds. Instead, the α,β-unsaturated carbonyl system seems to be responsible for these adsorptive properties. Also, the hydrogen atom bound to carbon at the o-position in ring B plays an important role in these adsorptions. On the other hand, the adsorption is mostly due to hydrogen bonds and electrostatic interactions of considerable energy.