Indene

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. Substituted indenes and their closely related indane derivatives are important structural motifs found in many natural products and biologically active molecules, such as sulindac.[3]

Indene
Names
Preferred IUPAC name
1H-Indene
Systematic IUPAC name
Bicyclo[4.3.0]nona-1,3,5,7-tetraene
Other names
Benzocyclopentadiene
Indonaphthene
Identifiers
3D model (JSmol)
635873
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.002.176
27265
KEGG
UNII
Properties
C9H8
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)
Insoluble
Acidity (pKa) 20.1 (in DMSO)[2]
-80.89·10−6 cm3/mol
Hazards
Main hazards Flammable
Flash point 78.3 °C (172.9 °F; 351.4 K)
NIOSH (US health exposure limits):
PEL (Permissible)
 none[1]
REL (Recommended)
 TWA 10 ppm (45 mg/m3)[1]
IDLH (Immediate danger)
 N.D.[1]
Related compounds
Related compounds
 Benzofuran, Benzothiophene, Indole
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

Isolation

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.[4]

Reactivity

Indene readily polymerises. Oxidation of indene with acid dichromate yields homophthalic acid (o-carboxylphenylacetic acid). It condenses with diethyl 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. Treatment of indene with organolithium reagents give lithium indenyl compounds:

C9H8 + RLi → LiC9H7 + RH

Indenyl is a ligand in organometallic chemistry, giving rise to many transition metal indenyl complexes.[5]

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See also

References
  1. 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 Archived 2008-10-09 at the Wayback Machine
  3. Wu, Jie; Qiu, Guanyinsheng (2014). "Generation of Indene Derivatives by Tandem Reactions". Synlett. 25 (19): 2703–2713. doi:10.1055/s-0034-1379318.
  4. 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.
  5. O'Connor, Joseph M.; Casey, Charles P. (1987). "Ring-Slippage Chemistry of Transition Metal Cyclopentadienyl and Indenyl Complexes". Chemical Reviews. 87 (2): 307–318. doi:10.1021/cr00078a002.
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