Abstract
Thermodynamic proton dissociation constants,TpKa of benzoylacetone(HBA) as well as isonitrosobenzoylacetone (HINBA) have been determinedpH-metrically in 10–50% (v/v) dioxane-water mixtures at 25 and 35±0.01°C applying an empiricalpH correction for mixed aqueous media. ThepKa's in aqueous medium (at 0% dioxane) are obtained following the method of extrapolation and least-squares. BothHBA andHINBA are very weak monoprotic acids withTpKa between 7.0 and 10.0.TpKa's do not vary linearly with the reciprocal of the dielectric constant of the medium, but a plot ofTpKa vs. the mole fraction of dioxane is linear at a given temperature. The “true constant”Ka' and solvation number,n, in the expression (H+)(A−)/(HA)=Ka' (S)n=Ka* for these reagents have been evaluated by analysing the experimental data mathematically. Values of ΔG0, ΔH0, and ΔS0 are also computed. Temperature and medium effects are briefly discussed.
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