Indene

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 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, which are highly coloured. Treatment of indene with organolithium reagents gives lithium indenyl compounds:

C₉H₈ + RLi → LiC₉H₇ + RH

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

At temperatures ranging from 30-75 Kelvin (the temperature range of most dark molecular clouds and photodissociation regions), Indene undergoes a process called superhydrogenation. It begins with saturation of carbon atoms in the pentagonal ring which is then followed by the hydrogenation of the benzene unit. Quantum tunneling also plays a role is this.

• Indene can also be used directly to synthesize 2-Aminoindan & NM-2-AI.

• Indene is used as a starting material to make 2-indanone [615-13-4]. 2-indanone in-turn is used to synthesize the following drugs: Aprindine, Delapril, Indanorex, Indantadol, Pip-AI [23928-93-0], Pyr-AI, S-15535 & BChE-IN-7 [2416910-85-3], 2-aminoindane analog of fentanyl: O=C(CC)N(C1=CC=CC=C1)C2CCN(C3CC(C=CC=C4)=C4C3)CC2.

Additionally, there is a fragrance called Magnolan [27606-09-3], made from indene.