pK_a Determination of Strongly Acidic C-H Acids Bearing a (Perfluoroalkyl)sulfonyl Group in Acetonitrile by Means of Voltammetric Reduction of Quinone

Abstract

A voltammetric method has been developed for the determination of the acid dissociation constant (pK_a) of (RfSO₂)₂CHR (Rf = perfluoroalkyl), which is a strongly acidic molecule that serves as an acid catalyst. In acetonitrile solution containing small quantity of the acid, the reduction peak potential of quinone caused by the acid shifted to a more positive side accompanied by an increase in the acidity of the acid. This relationship was in good agreement with an equation derived from the Nernst equation. The present finding has been successfully applied to the determination of the pK_a of the acids in acetonitrile with values ranging from 7 to 17.