Partial Molar Enthalpy of Solution for Tris(2,4-pentanedionato)cobalt(III) in Mixed Solvents of Water and Dimethyl Sulfoxide

Abstract

Abstract The solubility (Xs) of tris(2,4-pentanedionato)cobalt(III) ([Co(acac)3]) in mixed solvents of water and dimethyl sulfoxide (DMSO) with various compositions was determined over the temperature range 20–60 °C. It was found that the experimental values of Xs could be satisfactorily fitted to lnXs=A(1⁄T)+BlnT+C and the partial molar enthalpy of solution (Δ\barHs) at 25 °C for [Co(acac)3] was estimated from slopes of the solubility curves. When Δ\barHs was plotted against the mole fraction of DMSO (XDMSO), a clear maximum was found at about XDMSO=0.3. This composition profile of Δ\barHs is discussed in connection with the internal pressure of a mixture of water and DMSO. A method to estimate an approximate value of the partial molar enthalpy of hydrophobic hydration (Δ\barHh) in an aqueous DMSO mixture of [Co(acac)3] is also presented by using the solubility data in mixtures with a lower XDMSO than 0.14.