Collect. Czech. Chem. Commun. 1987, 52, 1087-1096

Overlapping equilibria: Applications to m-aminobenzoic acid

Begoña García, Pedro L. Domingo and José M. Leal

Universidad de Valladolid, Departamento de Química Física, Colegio Universitario Integrado, Burgos, Spain


m-Aminobenzoic acid displays two protonation equilibria which overlap in the pH region, where pK2 - pK1 < 3. The results show that the equilibria occur between the pH values 6.16–1.77, with the limit of separation of the two equilibria lying between 3.60–3.44. Use has been made of several theoretical methods put forward in the bibliography for calculating pK values of overlapping equilibria and these have been corrected by including the terms of the activity coefficients, by means of the coefficients n1 and n2, which are defined and calculated by the method of separation of equilibria. The values pK1 = 3.237 ± 0.091 and pK2 = 4.767 ± 0.002 are proposed.