2.4.2.2 Quercetin
Synonyms Quercitroside; Quercimelin; Quercitin – 3-L-rhamnoside; Thujin; Quercitin; Quercetin.
Biological Sources Quercetin occurs in the bark of Quercus tinctoria and some other species of Quercus. It is also obtained from Alsculus hippocastarum L., horse chest nut, belonging to family Hippocastanaceae. Besides, it is also found in Thuja occidentalis L., Morus alba L., Humulus lupulus L., Fraxinus excelsior L., Vitis vinifera and a host of other plants.
Geographical Source A. hippocastanum is found in India and the African continent.
Description The crystals are yellow in colour when obtained from ethanol or methanol. It is practically insoluble in cold water and ether. Flavine yellow shade obtained from the quercitron bark by extraction under high pressure steam which is used exclusively in dyeing fabrics.
Chemical Structure The structure of quercetin is as shown below:
Quercitin on hydrolysis in an acidic medium gives rise to rhamnose and quercetin (i.e., 5, 7, 3’, 4’-tetrahyroxy flavonol).
It has been observed that the fully methylated quercetin upon hydrolysis yields 5, 7, 3’, 4’-tetramethyl flavonol which amply suggests that the residue is duly attached at C-3 of the aglycone moiety and also quercitin is nothing but quercetin-3-rhamnoside.
Chemical Tests
1. It exhibits a brown fluorescence under the UV-light.
2. It gives a distinct yellow precipitate initially with a solution of basic lead acetate, but it gets dissolved on further addition of the reagent in excess.
3. It reduces Tollen’s reagent to give a silver mirror.
4. It gives a negative test with Fehling’s solution i.e., not yielding brick red precipitate.
Uses It has been used as textile dye.
