Dissociation constants of some ethyl [[substituted benzylidene] dithio] diacetates in water organic solvent mixtures

The pKa values of some ethyl[[substituted benzylidene]dithio] diacetates in water-organic solvent mixtures are determined potentiometrically. The results obtained are discussed in terms of medium and structure effects. It has been found that the hydrogen bonding interactions, as well as solvent basicity, play important roles on the pKa values. Also, the calculated standard Gibbs transfer energies provided an evidence that solute-solvent interactions are of considerably greater importance of the solvent effect on the dissociation weak carbon acids. The structure effect is discussed in terms of Hammett correlations and the resulted alpha-values indicate that, for the present system, the negative charge on the benzylidene carbon is extensively delocalized into the two adjacent sulfur atoms