fluorene

Although fluorene is obtained from coal tar, it can also be prepared by dehydrogenation of diphenylmethane.{{Ullmann|doi=10.1002/14356007.a13_227|title=Hydrocarbons|year=2000|last1=Griesbaum|first1=Karl|last2=Behr|first2=Arno|last3=Biedenkapp|first3=Dieter|last4=Voges|first4=Heinz-Werner|last5=Garbe|first5=Dorothea|last6=Paetz|first6=Christian|last7=Collin|first7=Gerd|last8=Mayer|first8=Dieter|last9=Höke|first9=Hartmut|isbn=3527306730}} Alternatively, it can be prepared by the reduction of fluorenone with zincFittig, Rud. (1873), "Ueber einen neuen Kohlenwasserstoff aus dem Diphenylenketon" Ber. Dtsch. Chem. Ges. volume 6, p. 187.{{doi|10.1002/cber.18730060169}} or hypophosphorous acid–iodine.{{cite journal | last1=Hicks | first1=Latorya D. | last2=Han | first2=Ja Kyung | last3=Fry | first3=Albert J. | title=Hypophosphorous acid–iodine: a novel reducing system. | journal=Tetrahedron Letters | publisher=Elsevier BV | volume=41 | issue=41 | year=2000 | issn=0040-4039 | doi=10.1016/s0040-4039(00)01359-9 | pages=7817–7820}} The fluorene molecule is nearly planar,D. M. Burns, John Iball (1954), Molecular Structure of Fluorene Nature volume 173, p. 635. {{doi|10.1038/173635a0}} although each of the two benzene rings is coplanar with the central carbon 9.{{cite journal |doi=10.1107/S0108270184009963|title=Structure of fluorene, C13H10, at 159 K|year=1984|last1=Gerkin|first1=R. E.|last2=Lundstedt|first2=A. P.|last3=Reppart|first3=W. J.|journal=Acta Crystallographica Section C Crystal Structure Communications|volume=40|issue=11|pages=1892–1894|bibcode=1984AcCrC..40.1892G }}

Fluorene can be found after the incomplete combustion of plastics such as PS, PE and PVC.{{Cite journal|last1=Wang|first1=Zhenlei|last2=Richter|first2=Henning|last3=Howard|first3=Jack B.|last4=Jordan|first4=Jude|last5=Carlson|first5=Joel|last6=Levendis|first6=Yiannis A.|date=2004-06-01|title=Laboratory Investigation of the Products of the Incomplete Combustion of Waste Plastics and Techniques for Their Minimization|url=https://doi.org/10.1021/ie030477u|journal=Industrial & Engineering Chemistry Research|volume=43|issue=12|pages=2873–2886|doi=10.1021/ie030477u|issn=0888-5885|url-access=subscription}}

The C9-H sites of the fluorene ring are weakly acidic (pK_a = 22.6 in DMSO.{{cite journal | title = Equilibrium acidities in dimethyl sulfoxide solution | author = F. G. Bordwell | journal = Acc. Chem. Res. | volume = 21 | year = 1988 | pages = 456–463 | doi = 10.1021/ar00156a004 | issue = 12}}) 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.{{cite journal|author1=G. W. Scherf|author2=R. K. Brown|year=1960|title=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|journal=Canadian Journal of Chemistry|volume=38|page=697|doi=10.1139/v60-100}}.

Fluorene and its derivatives can be deprotonated to give ligands akin to cyclopentadienide.

File:Syndiotactic-zirconocene-front-3D-balls.png for producing syndiotactic polypropylene.{{cite journal|author1=Ewen, J. A.|author2=Jones, R. L.|author3=Razavi, A.|author4=Ferrara, J. D.|title=Syndiospecific Propylene Polymerizations with Group IVB Metallocenes|journal=Journal of the American Chemical Society|year=1988|volume=110|issue=18|pages=6255–6256|doi=10.1021/ja00226a056|pmid=22148816|bibcode=1988JAChS.110.6255E }}]]

Fluorene 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.

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 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.{{cite journal|title=Organic dyes based on fluorene and its derivatives|author1=Kurdyukova, I. V. |author2=Ishchenko, A. A. |journal=Russian Chemical Reviews|year=2012|volume=81|issue=3|pages=258–290|doi=10.1070/RC2012v081n03ABEH004211|bibcode=2012RuCRv..81..258K|s2cid=95312830 }}

• CataCXium F sulf
• Fluorenol
• Indecainide
• PD-137889
• Carbazole
• Dibenzothiophene

{{reflist}}

• [http://webbook.nist.gov/cgi/cbook.cgi?ID=86-73-7&Units=SI Fluorene] in the National Institute of Standards and Technology database.

{{PAHs}}

Category:Molecular electronics

Category:Polycyclic aromatic hydrocarbons