Solubility, activity coefficients and acid-base properties of three naphthol derivatives in NaCl(aq) at different ionic strengths and at TÂ =Â 298.15Â K

Total and intrinsic solubilities of three naphthol derivatives (1-Naphthol, 1,5-Dihydroxynaphthalene and 1-Amino-2-Naphthol-4-Sulfonic acid) were determined in NaCl(aq) at different salt concentrations (0-3 mol L−1) and in pure water at T = 298.15 K. To characterize the acid-base properties of these naphthols, the protonation constants were determined potentiometrically in the same conditions. The solubility of neutral species in pure water is −1.978, −2.886, −2.594 (expressed in logarithmic scale) for 1-Naphthol, 1,5-Dihydroxynaphthalene and 1-Amino-2-Naphthol-4-Sulfonic acid, respectively. The values of Setschenow coefficients (km) for these three ligands, are 0.209, 0.158 and 0.369. The dependence on the ionic strength of protonation constants KiH from potentiometric measurements was studied using three models, namely Debye-Hückel, SIT (Specific ion Ionic Interaction) and Pitzer equations. Therefore infinite dilution KiH and interaction coefficients (SIT and Pitzer) were calculated. The activity coefficients were obtained from solubility and protonation data, in the molal concentration scale. Activity coefficients in NaCl(aq) shown the same behaviour found for other O-donors ligands, previously studied.