Studies with dithizone: Part XXI. The Relationship between pH12 and Molar Solubility

The effect of changes of ionic strength on the partition of an analytically important weak acid between a variety of aqueous and immiscible organic phases has been studied with respect to new measurements on dithizone (3-mercapto-1,5-diphenylformazan) and di(p-tolyl)thiocarbazone. A linear relationship has been deduced between the pH at which 50% extraction takes place and S_r,o (the solubility of the reactant in the organic phase), and confirmed by measurements of pH_{$\text{1}\text{2}$}, and S_r,o for a large number of organic solvents. The solubilities of the reagents in water, S_r, are also reported. The form of the relationship between pH and log D, and between pH_{$\text{1}\text{2}$} and log S_r,o is the same whether a solution of dithizone consists of a single species or a mixture of thiol and thione forms in tautomeric equilibrium.