Re-examination of the Pka1 and Pka2 values of adipic acid in water 25oC.

Abstract

Adipic acid and its derivatives have long been used In the manufacture of nylon 6.6, explosives and as a food additive. In spite of its age-long use it was surprising to note that a variety of different values have been reported in the chemical literature for the two dissociation constants of the acid. It was therefore found both desirable and interesting to investigate the reason(s) for this discrepancy and to determine the precise pKal and pKa2 values in aqueous solutions at 250C. Accordingly pH titration method was used and solutions of adipic acid in the concentration range O.0025M to O.0200M were titrated against KOH solutions. It was found as expected. that pKal and pKa2 values varied with tne concentration. The values so obtained were extrapolated to zero concentration which yielded the two dissociation constants as 4.43258 and 5.63552. All calculations for these pKa values were carried out on a DV-ERGO personal computer and the analysis of the data led to the realization that the literature values corresponded to specific concentrations and are not at infinite dilution.