Thermodynamics of Protonation of some Dicarboxylic Acids Containing Heteroatoms from Group 6B.

Using potentiometric and calorimetric techniques, we have determined the protonation constants and the relative protonation enthalpies of the diacetate and dipropionate derivatives X(CH2 · COO−)2 and X(CH2 · CH2 · COO−)2 (X = O, S, Se), and of the iminodiacetate and pyridine-2,6-dicarboxylate anions at 25°C and I = 0.1 mole dm−3 (Na[ClO4]). From the data obtained in this work together with those in the literature we have been able to obtain a relationship between log K and the temperature and ionic strength for the above acids. The thermodynamic protonation parameters are discussed in relation to the structures of the acids studied, and compared to those of analogous compounds.