A note on certain useful colour reactions of anthoxanthins and related compounds

Abstract

Employing a large number of natural and synthetic flavones, flavonols, flavanones and certain related compounds the scope of the following colour reactions has been examined: (1) reduction with magnesium and alcoholic hydrochloric acid, (2) reduction with sodium amalgam and alcohol and (3) Wilson's boric acid test using boric and citric acid mixture in acetone solution. For the first two reactions the nature of the colour depends in general upon the number of hydroxyl or methoxyl groups in the molecule. In qualitative reactions it is not easily possible to effect minor distinctions between flavones, flavonols and flavanones. The boric acid test is very specific for 5-hydroxy- and 5-methoxyflavones and flavonols and o-hydroxy- and methoxy chalkones. It is not given by flavanones and simple aromatic ketones which do not satisfy the specific conditions. A combination of these three colour reactions gives a great deal of useful information.