Thermodynamic stabilities of copper(II)-ethyl α-(phenyl)phenylpropioloyl-acetato complexes in dioxane-water media

Abstract

The acid dissociation constant, K a , of ethyl α-(phenyl)phenylpropioloylacetate is determined potentiometrically in 75 vol % dioxane-water solution at 30°C as a function of ionic strength (μ) in the range 0·02–0·10 in a sodium perchlorate medium. A value of p K a ( μ → 0) of 11·66 is calculated with the aid of an extended form of the Debye-Hückel equation while a recalculation using reported values of γ± gives a value of 11·85. This is in agreement with the value calculated from results obtained in very dilute solution. The stoichiometric stability constants of the complexes formed with copper(II) are determined as a function of μ in the same range. Calculation of “thermodynamic” stability constants from these values using the Debye-Hückel equation or using reported values of γ ± does not give consistent results. It is concluded that it is incorrect to perform such calculations on results obtained in such a medium having an ionic strength μ ⩾ 0·02. The “thermodynamic” stability constants calculated from titration results in very dilute solution are log K 1 = 11·69 and log K 2 = 8·95.