Fluorene

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Not to be confused with fluorine or fluorane.
Fluorene[1]
Fluorene.svg
Fluorene-from-xtal-3D-balls.png
Fluorene-3D-vdW.png
Identifiers
CAS number 86-73-7 YesY
PubChem 6853
ChemSpider 6592 YesY
UNII 3Q2UY0968A YesY
EC number 201-695-5
KEGG C07715 YesY
ChEBI CHEBI:28266 YesY
ChEMBL CHEMBL16236 YesY
RTECS number LL5670000
Jmol-3D images Image 1
Properties
Molecular formula C13H10
Molar mass 166.223 g/mol
Density 1.202 g/mL
Melting point 116 to 117 °C (241 to 243 °F; 389 to 390 K)
Boiling point 295 °C (563 °F; 568 K)
Solubility in water 1.992 mg/L
Solubility soluble in CS2, ether, benzene, hot alcohol, pyrimidine, CCl4, toluene, acetone, DMSO
log P 4.18
Acidity (pKa) 22.6
Hazards
MSDS Sigma-Aldrich
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 152 °C (306 °F; 425 K)
LD50 16000 mg/kg (oral, rat)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Fluorene /flɔrn/, or 9H-fluorene, is a polycyclic aromatic hydrocarbon. It forms white crystals that exhibit a characteristic, aromatic odor similar to that of naphthalene. It is combustible. It has a violet fluorescence, hence its name. For commercial purposes it is obtained from coal tar. It is insoluble in water and soluble in benzene and ether.

Synthesis, structure, and reactivity[edit]

Although fluorene is obtained from coal tar, it can also be prepared by dehydrogenation of diphenylmethane.[2]

Alternatively, it can be prepared by the reduction of diphenylene with zinc.

The fluorene molecule is nearly planar,[3] although each of the two benzene rings is coplanar with the central carbon 9.[4]

Acidity[edit]

The C9-H sites of the fluorene ring are weakly acidic (pKa = 22.6 in DMSO.[5]) Deprotonation gives the stable fluorenyl "anion", nominally C13H9, which is aromatic and has an intense orange colour. The anion is a nucleophile, and most electrophiles react with it by adding to the 9-position. The purification of fluorene exploits its acidity and the low solubility of its sodium derivative in hydrocarbon solvents.

Both protons can be removed from C9. For example, 9,9-fluorenyldipotassium can be obtained by treating fluorene with potassium metal in boiling dioxane.[6]

Uses[edit]

Fluorene is a precursor to other fluorene compounds; the parent species has few applications. Fluorene-9-carboxylic acid is a precursor to pharmaceuticals. 2-Aminofluorene, 3,6-bis-(dimethylamino)fluorene, and 2,7-diiodofluorene are precursors to dyes. Oxidation of fluorene gives fluorenone, which is nitrated to give commercially useful derivatives. 9-Fluorenylmethyl chloroformate (Fmoc chloride) is used to introduce the 9-fluorenylmethyl carbamate (Fmoc) protecting group on amines in peptide synthesis.[2]

Polyfluorene polymers (where carbon 7 of one unit is linked to carbon 2 of the next one, displacing two hydrogens) are electrically conductive and electroluminescent, and have been much investigated for use as a luminophore in organic light-emitting diodes.

See also[edit]

References[edit]

  1. ^ Merck Index, 11th Edition, 4081
  2. ^ a b Karl Griesbaum, Arno Behr, Dieter Biedenkapp, Heinz-Werner Voges, Dorothea Garbe, Christian Paetz, Gerd Collin, Dieter Mayer, Hartmut Höke “Hydrocarbons” in Ullmann's Encyclopedia of Industrial Chemistry 2002 Wiley-VCH, Weinheim. doi:10.1002/14356007.a13_227
  3. ^ D. M. Burns, John Iball (1954), Molecular Structure of Fluorene Nature volume 173, p. 635. doi:10.1038/173635a0
  4. ^ R. E. Gerkin, A. P. Lundstedt and W. J. Reppart (1984) Structure of fluorene, C13H10, at 159 K Acta Crystallographica, volume C40, pp. 1892–1894 doi:10.1107/S0108270184009963
  5. ^ F. G. Bordwell (1988). "Equilibrium acidities in dimethyl sulfoxide solution". Acc. Chem. Res. 21 (12): 456–463. doi:10.1021/ar00156a004. 
  6. ^ G. W. Scherf and R. K. Brown (1960), POTASSIUM DERIVATIVES OF FLUORENE AS INTERMEDIATES IN THE PREPARATION OF C9-SUBSTITUTED FLUORENES. I. THE PREPARATION OF 9-FLUORENYL POTASSIUM AND THE INFRARED SPECTRA OF FLUORENE AND SOME C9-SUBSTITUTED FLUORENES. Canadian Journal of Chemistry, Vol. 38, p. 697.

External links[edit]