THERMODYNAMICS OF COBALT(II) EXTRACTION BYTHENOYLTRIFLOUROACETONE AND DIBENZO-18-CROWN-6 IN NITROBENZENE-TOLUENE MIXTURES

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Abstract
Cobalt (II) was extracted by thenoyltrifluoroacetone (HTTA) and its mixture with dibenzo-18-crown-6(Dbl8C6) at different temperatures in nitrobenzene (Nb); toluene (Tol) or their mixtures, from perchlorate aqueous media of constant ionic strength (o.l;H+,NaClO4) buffered with acetic acid-sodium acetate solutions. Slop analysis of the experimental results indicated that the stoichiometry of the chelate and the adduct extracted are Co(TTA)2and Co(TTA)2•Dbl8C6, under all the experimental conditions investigated. The extraction constants of the chelate (k2o)’ tne mixed species (k2land the formation constant of the adduct ( B2lwere evaluated for the different diluents used at the different temperatures. It was found that log k2oand log2lincrease by increasing the dielectric constant (€ ) of the diluent whereby log B2ldecreases by increasing €. These results were expressed in terms of linear free energy relationships. From the effect of the temperature on the different constants evaluated; the thermodynamic constants of the systems were calculated and discussed in terms of the nonspecific effect of the diluents used and the dehydration of the extracted chelate to form the adduct.