Dissociation constants of p-nitroaniline in mixed solvents and a critical assessment of the solvent-sorting equilibrium method for the determination of the single ion Gibbs energy of transfer of H+ ion from aqueous to aquo rich organic solvents

The dissociation constants of p-nitroaniline (B) (BH+ reversible arrow B H+) in methanol + water and propan-1-ol + water mixtures have been determin ed. Due to the presence of -NH2 and -NO2 groups in complimentary para posit ions, the dissociation constants for p-nitroaniline decrease with increase in percentage of organic co-solvents contrary to those observed in case of aniline, metanitroaniline etc. A critical assessment of the solvent-sorting equilibrium method using p-nit roaniline as indicator has been made. The method is not suitable to determi ne the Gibbs energy of transfer of H+ from aqueous to aquo-rich organic sol vents.