Protonation of maleic and fumaric acid in aqueous sulfuric acid solutions

The protonations of maleic and fumaric acid in an acidic medium (aqueous solutions of sulfuric acid) were followed spectrophotometrically at room temperature. The acid-base equilibria were characterised qualitatively and quantitatively. The pKBH+ values were determined using the Hammett equation, employing several acid functions in order to determine which of them describes best the protonation process of the studied organic acids. The thermodynamic pKBH+ values as well as those of the solvation parameters m, m* and ? and of the thermodynamic protonation constants (or, rather, the pKa,p values) were also defermined. The method of characteristic vector analysis (CVA) was used to reconstruct the experimental spectra.