Studies in isodielectric media. Part IV. Thermodynamics of protonation of p-nitroaniline in ethylene glycol-Diethylene glycol mixtures at 25°C

The thermodynamic ionisation constant of p-nitroanilinium ion was determined spectrophotometrically at 25°C in the near isodielectric mixtures of ethylene glycol (EG) and diethylene glycol (DEG) over the complete range of solvent compositions. the pK of the ion decreases continuously with the addition of diethylene glycol, passes through a minimum around 80 wt% of the same solvent and then increases. The variation of ΔpK (pKmixed solvent-pKEG) with solvent composition was analyzed in terms of the changes in Gibbs energies of transfer of the different species involved in the ionisation process in these mixtures. © 1981 Springer-Verlag.