One of a group of flavonoid plant pigments existing as colorless needles, that are insoluble in water and melting at 100C. It fluoresces violet in concentrated sulfuric acid. It can be synthesized. Treatment with alcoholic alkali yields flavanone. The fla
Dissolve it in dilute aqueous NaOH, filter and precipitate it by adding dilute (1:1) HCl. The process is repeated twice more, and the fluorescein is dried at 100o. Alternatively, it has been crystallised from acetone by allowing the solution to evaporate at 37o in an open beaker. It has also been recrystallised from EtOH and dried in a vacuum oven. [Beilstein 19 I 721, 19 II 248, 19 III/IV 2904, 19/8 V 456.]
