Effect of dielectric constant of medium on protonation equilibria of ethylenediamine

The effect of dielectric constant of medium on protonation equilibria has been studied by determining protonation constants of ethylenediamine pH metrically in various concentrations (0-60% v/v) of acetonitrile- and ethylene glycol-water mixtures, at an ionic strength of 0.16 mol L-1 and at 303.0 K. MINIQUAD75 computer program has been used for the calculation of protonation constants. Linear and non-linear variations of step-wise protonation constants with reciprocal of dielectric constant of the solvent mixtures have been attributed to the dominance of the electrostatic and non-electrostatic forces, respectively. The trend is explained on the basis of solute - solute and solute - solvent interactions, solvation, proton transfer processes and dielectric constants of the media.