Fluorene /ˈflʊəriːn/, or 9H-fluorene is an organic compound with the formula (C6H4)2CH2. It forms white crystals that exhibit a characteristic, aromatic odor similar to that of naphthalene. Despite its name, it does not contain the element fluorine, but rather it comes from the violet fluorescence it exhibits. For commercial purposes it is obtained from coal tar,[3] where it was discovered and named by Marcellin Berthelot in 1867.[4]
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| Preferred IUPAC name
9H-Fluorene[2] | |
| Systematic IUPAC name
Tricyclo[7.4.0.02,7]trideca-2,4,6,9,11,13-hexaene | |
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| ECHA InfoCard | 100.001.541 |
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CompTox Dashboard (EPA)
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| Properties | |
| C13H10 | |
| Molar mass | 166.223 g·mol−1 |
| 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) |
| 1.992 mg/L | |
| Solubility | organic solvents |
| log P | 4.18 |
| Acidity (pKa) | 22.6 |
| -110.5·10−6 cm3/mol | |
| Hazards | |
| NFPA 704 (fire diamond) | |
| Flash point | 152 °C (306 °F; 425 K) |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
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16000 mg/kg (oral, rat) |
| Safety data sheet (SDS) | Sigma-Aldrich |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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It is insoluble in water and soluble in many organic solvents. Although sometimes classified as a polycyclic aromatic hydrocarbon, the five-membered ring has no aromatic properties.[citation needed] Fluorene is mildly acidic.
Synthesis, structure, and reactivity
editAlthough fluorene is obtained from coal tar, it can also be prepared by dehydrogenation of diphenylmethane.[3] Alternatively, it can be prepared by the reduction of fluorenone with zinc[5] or hypophosphorous acid–iodine.[6] The fluorene molecule is nearly planar,[7] although each of the two benzene rings is coplanar with the central carbon 9.[8]
Fluorene can be found after the incomplete combustion of plastics such as PS, PE and PVC.[9]
Acidity
editThe C9-H sites of the fluorene ring are weakly acidic (pKa = 22.6 in DMSO.[10]) Deprotonation gives the stable fluorenyl anion, nominally C13H9−, which is aromatic and has an intense orange colour. The anion is a nucleophile. 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.[11]
Ligand properties
editFluorene and its derivatives can be deprotonated to give ligands akin to cyclopentadienide.
Uses
editFluorene is a precursor to other fluorene compounds; the parent species has few applications. Fluorene-9-carboxylic acid is a precursor to pharmaceuticals. 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.[3]
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 as a luminophore in organic light-emitting diodes.
Fluorene dyes
editFluorene dyes are well developed. Most are prepared by condensation of the active methylene group with carbonyls. 2-Aminofluorene, 3,6-bis-(dimethylamino)fluorene, and 2,7-diiodofluorene are precursors to dyes.[13]
See also
editReferences
edit- ^ Merck Index, 11th Edition, 4081
- ^ International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 207. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
- ^ a b c Griesbaum, Karl; Behr, Arno; Biedenkapp, Dieter; Voges, Heinz-Werner; Garbe, Dorothea; Paetz, Christian; Collin, Gerd; Mayer, Dieter; Höke, Hartmut (2000). "Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a13_227. ISBN 3527306730.
- ^ Annales de chimie et de physique (in French). Masson. 1867.
- ^ Fittig, Rud. (1873), "Ueber einen neuen Kohlenwasserstoff aus dem Diphenylenketon" Ber. Dtsch. Chem. Ges. volume 6, p. 187.doi:10.1002/cber.18730060169
- ^ Hicks, Latorya D.; Han, Ja Kyung; Fry, Albert J. (2000). "Hypophosphorous acid–iodine: a novel reducing system". Tetrahedron Letters. 41 (41). Elsevier BV: 7817–7820. doi:10.1016/s0040-4039(00)01359-9. ISSN 0040-4039.
- ^ D. M. Burns, John Iball (1954), Molecular Structure of Fluorene Nature volume 173, p. 635. doi:10.1038/173635a0
- ^ Gerkin, R. E.; Lundstedt, A. P.; Reppart, W. J. (1984). "Structure of fluorene, C13H10, at 159 K". Acta Crystallographica Section C Crystal Structure Communications. 40 (11): 1892–1894. Bibcode:1984AcCrC..40.1892G. doi:10.1107/S0108270184009963.
- ^ Wang, Zhenlei; Richter, Henning; Howard, Jack B.; Jordan, Jude; Carlson, Joel; Levendis, Yiannis A. (2004-06-01). "Laboratory Investigation of the Products of the Incomplete Combustion of Waste Plastics and Techniques for Their Minimization". Industrial & Engineering Chemistry Research. 43 (12): 2873–2886. doi:10.1021/ie030477u. ISSN 0888-5885.
- ^ F. G. Bordwell (1988). "Equilibrium acidities in dimethyl sulfoxide solution". Acc. Chem. Res. 21 (12): 456–463. doi:10.1021/ar00156a004.
- ^ G. W. Scherf; 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. 38: 697. doi:10.1139/v60-100..
- ^ Ewen, J. A.; Jones, R. L.; Razavi, A.; Ferrara, J. D. (1988). "Syndiospecific Propylene Polymerizations with Group IVB Metallocenes". Journal of the American Chemical Society. 110 (18): 6255–6256. doi:10.1021/ja00226a056. PMID 22148816.
- ^ Kurdyukova, I. V.; Ishchenko, A. A. (2012). "Organic dyes based on fluorene and its derivatives". Russian Chemical Reviews. 81 (3): 258–290. Bibcode:2012RuCRv..81..258K. doi:10.1070/RC2012v081n03ABEH004211. S2CID 95312830.
External links
edit- Fluorene in the National Institute of Standards and Technology database.