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Skeletal formula
Ball-and-stick model of the indene molecule
Preferred IUPAC name
Systematic IUPAC name
Other names
95-13-6 YesY
ChEBI CHEBI:41921 YesY
ChEMBL ChEMBL192812 YesY
ChemSpider 6949 YesY
DrugBank DB02815 YesY
Jmol 3D model Interactive image
KEGG C11565 YesY
PubChem 7219
Molar mass 116.16
Appearance Colorless liquid[1]
Density 0.997 g/mL
Melting point −1.8 °C (28.8 °F; 271.3 K)
Boiling point 181.6 °C (358.9 °F; 454.8 K)
Acidity (pKa) 20.1 (in DMSO)[2]
Main hazards Flammable
Flash point 78.3 °C (172.9 °F; 351.4 K)
US health exposure limits (NIOSH):
PEL (Permissible)
REL (Recommended)
TWA 10 ppm (45 mg/m3)[1]
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Indene is a flammable polycyclic hydrocarbon with chemical formula C9H8. It is composed of a benzene ring fused with a cyclopentene ring. This aromatic liquid is colorless although samples often are pale yellow. The principal industrial use of indene is in the production of indene/coumarone thermoplastic resins.


Indene occurs naturally in coal-tar fractions boiling around 175–185 °C. It can be obtained by heating this fraction with sodium to precipitate solid "sodio-indene." This step exploits indene's weak acidity evidenced by its deprotonation by sodium to give the indenyl derivative. The sodio-indene is converted back to indene by steam distillation.[3]


Indene readily polymerises. Oxidation of indene with acid dichromate yields homophthalic acid (o-carboxylphenylacetic acid). It condenses with ethyl oxalate in the presence of sodium ethoxide to form indene-oxalic ester, and with aldehydes or ketones in the presence of alkali to form benzofulvenes. The latter are highly coloured. An indene is also a precursor to the indenyl anion, a ligand in organometallic chemistry with some notability due to the indenyl effect.

See also[edit]


  1. ^ a b c d "NIOSH Pocket Guide to Chemical Hazards #0340". National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ Bordwell FG (1988). "Equilibrium acidities in dimethyl sulfoxide solution". Accounts of Chemical Research. 21 (12): 456–463. doi:10.1021/ar00156a004.  Bordwell pKa Table in DMSO
  3. ^ Gerd Collin, Rolf Mildenberg, Mechthild Zander, Hartmut Höke, William McKillip, Werner Freitag, Wolfgang Imöhl “Resins, Synthetic” Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2000.

External links[edit]

  • W. v. Miller, Rohde (1890). "Zur Synthese von Indenderivaten". Berichte der deutschen chemischen Gesellschaft. 23 (2): 1881–1886. doi:10.1002/cber.18900230227. 
  • W. v. Miller, Rohde (1890). "Zur Synthese von Indenderivaten". Berichte der deutschen chemischen Gesellschaft. 23 (2): 1887–1902. doi:10.1002/cber.18900230228. 
  • Finar, I. L. (1985). Organic Chemistry. Longman Scientific & Technical. ISBN 0-582-44257-5.