A New Approach to the Determination of pK <sub>a</sub> and pK <sub>b</sub> of Brønsted-Lowry Weak Acid and Weak Base in Aprotic Solvent

Abstract

It is difficult to accurately determine the pKa and pKb of Bronsted-Lowry weak acids and weak bases in aprotic solvents. We found that in aprotic solvent, the conjugated base of weak acid can cause a new unambiguous anodic peak of hydroquinone, and the conjugated acid of weak base can cause a new cathodic peak of p-benzoquinone. The new peaks are due to the drastic change of pH near the electrode surface, and their potentials are dependent on the strength of conjugated acids and bases, but independent of the concentration of hydroquinone and quinone. Therefore, the conjugated acid-base dissociation constant can be measured by the new peak potential. Then the weak acid-base dissociation constant can be obtained by the difference between the autoprotolysis constant of the aprotic solvent and the conjugated acid-base dissociation constant. The experimental results are consistent with those in the literatures.