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Dissociation constants of Br∅nsted acids in D2O and H2O: studies on polyaza and polyoxa-polyaza macrocycles and a general correlation

1991; Elsevier BV; Volume: 245; Linguagem: Inglês

10.1016/s0003-2670(00)80232-9

1873-4324

Rita Delgado, João J. R. Fraústo da Silva, M. T. Pessoa de Amorim, M. Fátima Cabral, Sı́lvia Chaves, Judite Costa,

Chemistry and Chemical Engineering

Using data on a series of polyaza and polyoxa-polyaza macrocyclic compounds, a satisfactory linear correlation was established between the dissociation constants of their acid forms obtained in deuterium oxide (pKD) and in water (pKH). The isotopic effect, ΔpK=pKD - pKH, increases with increasing pK, being larger for the weaker acids. The pKD vs. pKH correlation may be used to determine pKD or pKH values when one of the constants is known; the statistical errors of the estimates are not significatively higher than those of the experimental determinations. By including data available in the literature for a series of different acids (mineral and carboxylic acids, phenols, protonated amines, amino acids, etc.; a total of 138 pairs of data for 70 different compounds), a good general pKD vs. pKH correlation was also obtained (correlation coefficient 0.998), showing that the dependence of the isotopic effect on the nature of the acid is not as important as previous studies, based on limited and not always satisfactory Δpk vs. pKH correlations, suggested.