Characterisation of the approach to equilibrium of the osazone of dihydroxytartaric acid in aqueous solutions by differential pulse polarography

Differential pulse polarography is used to determine the changes in the enthalpy, entropy and Gibbs function for the forward and reverse conversions of the osazone of dihydroxytartaric acid from one tautomeric form to another at pH 11.4 in aqueous solution. This is done by determining the individual rate constants associated with these conversions at different temperatures through combining kinetic measurements with measurements on the system at equilibrium. The equilibrium constant was found to vary widely with pH and to increase with increase in temperature. The driving force for the endothermic conversion of the osazone from the hydrazone form to the azohydrazine form is shown to be the much greater freedom of movement (greater entropy) available to the latter form.