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FLUORESCEIN

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Originally appearing in Volume V10, Page 575 of the 1911 Encyclopedia Britannica.
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FLUORESCEIN , or See also:

RESORCIN-PHTHALEIN, C20H12O5, in See also:chemistry, a See also:compound discovered in 1876 by A. v. See also:Baeyer by the condensation of See also:phthalic anhydride with resorcin at 195—200° C. (See also:Ann., 1876, 183, p. 1). The two reacting substances are either heated alone or with See also:zinc chloride for some See also:hours, and the melt obtained is boiled out with See also:water, washed by dilute See also:alcohol, extracted by means of See also:sodium See also:hydrate, and the See also:solution so obtained is precipitated by an See also:acid. The precipitate is well washed with water and then dried. By repeating this See also:process two or three times, the fluorescein may be obtained in a very pure See also:condition. It forms a yellow amorphous See also:powder, insoluble in water but soluble in alcohol, and crystallizing from the alcoholic solution in small dark red nodules. It is readily soluble in solutions of the See also:caustic alkalis, the solution being of a dark red See also:colour and showing (especially when largely diluted with water) a brilliant See also:green See also:fluorescence. It was so named on See also:account of this last See also:character. By brominating fluorescein in glacial acetic. acid solution, eosin (tetrabromfluorescein) is obtained, the same compound being formed by See also:heating 3.5-dibrom-2.4-dioxybenzoylbenzoic acid above its melting point (R. See also:Meyer, Ber., 1895, z8, p.

1576). It crystallizes from alcohol in yellowish red needles, and dyes See also:

silk, See also:wool, and mordanted See also:cotton a See also:fine See also:pink colour. When heated with caustic alkalis it yields dibromresorcin and dibrommonoresorcin-phthalein. The corresponding iodo compound is known as erythrosin. Fluorescein is readily nitrated, yielding a di- or tetra-nitro compound according to conditions. The entrance of the negative nitro See also:group into the See also:molecule weakens the central pyrone See also:ring in the fluorescein See also:nucleus and the di- and tetra-nitro compounds readily yield hydrates (see J. T. See also:Hewitt and B. W. See also:Perkins, Jour. Chem. See also:Soc., 1900, p.

1326). By the See also:

action of See also:ammonia or See also:amines the di-nitro fluoresceins are converted into yellow dyestuffs (F. Reverdin, Ber., 1897, 30, p. 332). Other dyestuffs obtained from fluorescein are safrosine or eosin See also:scarlet (dibromdinitrofluorescein) and See also:rose See also:Bengal (tetraiodotetrachlorfluorescein). On See also:fusion with caustic See also:alkali, fluorescein yields resorcin, See also:C6H4(OH)2, and monoresorcin phthalein (dioxybenzoylbenzoic acid), (I-IO)2C6H3•CO•C See also:H4.00OH. With zinc dust and caustic soda it yields fluorescin. By warming fluorescein with excess of See also:phosphorus pentachloride it yields fluorescein chloride, C20I-110O3C12 (A. Baeyer), which crystallizes from alcohol in small prisms, melting at 252° C. When heated with See also:aniline and aniline hydrochloride, fluorescein yields a colourless anilide (O. See also:Fischer and E. Hepp, Ber., 1893, 26, p.

2236), which is readily methylated by methyl iodide and potash to a fluoresceinanilidedimethyl See also:

ether, which when heated for six hours to 150° C. with acetic and hydrochloric acids, is hydrolysed and yields a colourless fluoresceindimethyl ether, which melts at 198° C. On the other See also:hand, by heating fluorescein with caustic potash, methyl iodide and methyl alcohol, a coloured (yellow) dimethyl ether, melting at 208° C. is obtained (Fischer and Hepp). By heating the coloured dimethyl ether with caustic soda, the monomethyl ether is obtained (0. Fischer and E. Hepp, Ber., 1895, 28, p. 397); this crystallizes in triclinic tables, and melts at 262° C. It is to be noted that the colourless monomethyl ether fluoresces strongly in alkaline solution, the dimethyl ether of melting point 208° fluoresces only in neutral solution (e.g., in alcoholic solution), and the dimethyl ether of melting point 198° C. only in concentrated hydrochloric or sulphuric acid solution (Fischer and I-lepp). Considerable discussion has taken See also:place as to the position held by the hydroxyl See also:groups in the fluorescein molecule, C. Graebe (See also:Bee., 1895, 28, p. 28) asserting that they were in the ortho position to the linking See also:carbon See also:atom of the phthalic anhydride See also:residue. G. See also:Heller (Ber., 1895, 28, p.

312), however, showed that monoresorcin-phthalein when brominated in glacial acetic acid gives a dibrom derivative which, with fuming sulphuric acid, yields dibromxanthopurpurin (1.3-dioxy-2.4-dibromanthraquinone), a reaction which is only possible if the fluorescein (from which the monoresorcin-phthalein is derived) contains See also:

free hydroxyl groups in the See also:para position to the linking carbon atom of the phthalic anhydride residue.

End of Article: FLUORESCEIN

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