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

Abstract

Abstract The dissociation constants of p-nitroaniline (B) (BH+ ⇔ B + H+ ) in methanol + water and propan-1-ol + water mixtures have been determined. Due to the presence of -NH2 and -NO2 groups in complimentary para positions, 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-nitroaniline as indicator has been made. The method is not suitable to determine the Gibbs energy of transfer of H+ from aqueous to aquo-rich organic solvents.