Structural changes of flavylium salts. II. Polargographic and spectrometric investigation of 4'-Hydroxyflavylium perchlorate

Abstract

4?-Hydroxyflavylium perchlorate is examined polarographically and spectrometrically in aqueous methanolic solution over a wide pH range. In solutions below pH 3 the flavonoid moiety exists solely as the flavylium ion, which establishes an equilibrium with the pseudobase, the anhydrobase, and the 2-hydroxychalcone above this pH. The flavylium ion disappears from solution above pH 5, the anhydrobase remains at a constant low concentration, and the ratio of pseudobase to chalcone fluctuates as the pH is increased. Electrode reactions for the various reductions are the same as those previously described for 7,4?- dihydroxyflavylium perchlorate. Without influencing the polarographic reduction, the presence of mercury in the polarographic cell favours chalcone formation in neutral solutions and suppresses resonance in the chalcone ion at high pH, probably through formation of a mercuric chelate.