Indene

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
CAS Number	95-13-6 Y
3D model (Jmol)	Interactive image
Beilstein Reference	635873
ChEBI	CHEBI:41921 Y
ChemSpider	6949 Y
DrugBank	DB02815 Y
ECHA InfoCard	100.002.176
Gmelin Reference	27265
KEGG	C11565 Y
PubChem CID	7219
InChI InChI=1S/C9H8/c1-2-5-9-7-3-6-8(9)4-1/h1-6H,7H2 Y Key: YBYIRNPNPLQARY-UHFFFAOYSA-N Y InChI=1/C9H8/c1-2-5-9-7-3-6-8(9)4-1/h1-6H,7H2 Key: YBYIRNPNPLQARY-UHFFFAOYAJ
SMILES c1ccc2c(c1)CC=C2
Properties
Chemical formula	C9H8
Molar mass	116.16
Appearance	Colorless liquid
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)
Solubility in water	Insoluble
Acidity (pKa)	20.1 (in DMSO)
Magnetic susceptibility (χ)	-80.89·10−6 cm3/mol
Hazards
Main hazards	Flammable
Flash point	78.3 °C (172.9 °F; 351.4 K)
US health exposure limits (NIOSH):
PEL (Permissible)	none
REL (Recommended)	TWA 10 ppm (45 mg/m3)
IDLH (Immediate danger)	N.D.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
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.

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.