Polycarboxylic acids in sea water: acid–base properties, solubilities, activity coefficients, and complex formation constants at different salinities

This paper reports the results of the investigations carried out in synthetic sea water at different salinities for different classes of polycarboxylic acids. The investigations can be summarized as follows: (a) Determination of the protonation constants in such multicomponent solution in a salinity range 15 ≤ S ≤ 45, at t = 25 °C, for the linear dicarboxylic acids HOOC-(CH2)n–COOH (0 ≤ n ≤ 8), and aromatic polycarboxylic acids (o-phthalic and 1,2,4-benzenetricarboxylic acids). For malonic, succinic, 1,2,3-benzenetricarboxylic, and 1,2,3,4-benzenetetracarboxylic acids, investigations were also carried out at t = 10 and 37 °C; (b) Determination of the total and intrinsic solubility (ST and S0, respectively) of the linear dicarboxylic acids HOOC-(CH2)n-COOH (0 ≤ n ≤ 8), o-phthalic, 1,2,4-benzenetricarboxylic acids at t = 25 °C and 15 ≤ S ≤ 45, and calculation of the corresponding Setschenow parameters and activity coefficients; (c) Modeling the dependence of the experimental and literature protonation constants of the polycarboxylic acids on salinity, acid concentration, temperature, and number of the methylene groups in the molecules by means of new empirical equations; (d) Determination of the specific interaction parameters in synthetic sea water of the ionic species of the acids by means of the specific ion interaction theory and Pitzer models; (e) Determination of the protonation constant of the anion A1.117− of the single salt BA at different salinities and temperatures; (f) Determination and modeling in dependence of the salinity of the ΔH/kJ mol−1 of protonation of the linear dicarboxylic acids and of the A1.117− anion, by means of a Debye-Hückel type equation; (g) Determination of the complex formation constants (log βBpLHi) between the cation B1.117+ and the different deprotonated species of the carboxylic acids at different salinities and temperatures. Independent of the thermodynamic aqueous properties determined, a significant dependence of these parameters (log βiH, log βBpLHi, ΔH/kJ mol−1 of protonation, ST and S0) on the ionic medium, salinity, and temperature was observed. Moreover, the huge number of data collected allowed us to propose some empirical equations to model/predict the behavior of these classes of O-donor ligands in a multicomponent solution such as synthetic sea water. Graphical abstract: [Figure not available: see fulltext.]