Acid degradation of flavonoids as an aid in their identification

Abstract

In the course of previous studies of constituents from Larix needles, small quantities of flavonol glycosides were hydrolysed according to standard procedures in ethanolic or aqueous HCl. In many cases, especially when very low concentrations were used, partial or complete degradation of the aglycone occurred, even when the time of hydrolysis was restricted to 5 min. Autoxidation of flavonols under acid conditions, leading to a benzoic acid, phloroglucinol (phloroglucinol carboxylic acid) and carbon monoxide, has been described. The rate of autoxidation in 1 N HCl at 1OO ° given, however, is much lower than that found in our experiments, This is probably due to the concentration used; higher concentrations of the flavonol glycosides produced under similar conditions a reasonable yield of the aglycone.