SILICA-GEL-IMMOBILIZED ACETYLACETONE - SOME THERMODYNAMIC DATA IN NONAQUEOUS SOLVENTS

Acetylacetone was covalently immobilized on silica gel to produce a ne w surface (Sil-ac), having 0.62 mmol of ligand attached per gram of si lica, which was characterized by means of elemental analysis and physi cal measurements, before being submitted to calorimetric measurements, Thus, a suspension of this anchored surface in ethanol or acetone was calorimetrically titrated with divalent cations (Co, Ni, Cu, Zn, Cd, Hg). The resulting isotherms conformed to a modified Langmuir equation . After linearization of these isotherms, the enthalpies of cation/ su rface adsorption and the interfacial equilibrium constant, as well as the variation of free energies and entropies, were calculated. In acet one, adsorption of copper gives rise to an exothermic Delta H of -93.3 8 +/- 0.94 kJ mol(-1), while cobalt, 41.80 +/- 0.42 kJ mol(-1), and zi nc, 2.38 +/- 0.02 kJ mol(-1) give an endothermic adsorption. In ethano l, the endothermic Delta H of 52.64 +/- 0.53 kJ mol(-1) for zinc contr asts with the exothermic enthalpies of adsorption observed for other c ations, especially for mercury, -102.20 +/- 1.02 kJ mol(-1) and nickel , -137.70 +/- 1.38 kJ mol(-1).