Structural changes of flavylium salts. I. Polarographic and spectrometric examination of 7,4'-Dihydroxyflavylium perchlorate

Abstract

From polarographic and spectrometric studies a sequence of molecular changes is proposed for 7,4?-dihydroxyflavylium perchlorate in solutions of increasing pH in the absence of oxygen. Below pH 2 the flavylium ion is stable. Between pH 2 and 7.5 the chalcone is formed, the reaction occurring rapidly and completely in less than 1 hr between pH 4 and 6. This transformation involves the anhydrobase, the ionized form of which is stable from pH 7.5 to 10. Further increase in pH causes ring opening to the ionized chalcone, which is almost instantaneously formed at pH 13. Electrode reactions are proposed and diffusion coefficients calculated for the various forms.