Fluorescein

fluorescein [‚flu̇′re·sē·ən]

(organic chemistry)

C₂₀H₁₂O₅A yellowish to red powder, melts and decomposes at 290°C, insoluble in water, benzene, and chloroform, soluble in glacial acetic acid, boiling alcohol, ether, dilute acids, and dilute alkali; used in medicine, in oceanography as a marker in sea water, and in textiles to dye silk and wool.

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Fluorescein 

a dye; yellow crystals. Fluorescein is poorly soluble in water; it dissolves better in alcohols and dilute alkalies. Decomposition occurs at the melting point, 314°–316°C. In aqueous solutions, fluorescein exists as a 1:1 mixture of the benzoid (I) and quinoid forms and has a strong yellow-green fluorescence (hence the name). Its structural form is

Fluorescein belongs to a group of triarylmethane (xanthene) dyes. It colors silk and wool yellow but is not used in the textile industry because of poor colorfastness. It is used to trace the course of underground waters. Its disodium salt (uranine) is a component of fluorescing mixtures, and its isothiocyanate derivatives are used as biological stains for identifying antigens and antibodies. Some halogen-substituted fluoresceins, such as eosins, also have practical value.

Fluorescein is produced by the condensation of phthalic anhydride with resorcinol.