What Is Indene?
Indene is a component of coal tar, found in the distillation distillate of coal tar neutral oil and refined by removing tar acids. Pure indene is colorless, turning pale yellow due to polymerization or oxidation during storage. It is unstable and prone to polymerization reactions, absorbing oxygen to form oxides. When heated, it decomposes, emitting irritating smoke and gases.
Uses of Indene
Indene is used in organic synthesis for optical functional materials, functional resins, and pharmaceutical intermediates. It serves as a resin modifier in the polymerization of coumarone and styrene, enhancing the properties of various resins. Coumarone-indene resin, different from petroleum resins, offers adhesiveness, mechanical, and electrical properties, and is used in rubber, paints, and epoxy resins.
Properties of Indene
Indene, a bicyclic hydrocarbon with a molecular formula of C9H8, is a colorless oily liquid at room temperature, insoluble in water but soluble in organic solvents like ethanol and acetone. It has a melting point of -1.8°C and a boiling point of 181.6°C, and is highly irritating to eyes and skin, with potential damage to kidneys, liver, and spleen upon inhalation.
Other Information on Indene
1. Purification of Indene
Indene is obtained from coal tar fractions, extracted by steam distillation after reacting with metallic sodium to form a salt.
2. Indene Reactions
Indene undergoes various reactions, including oxidation to form homophthalic acid, and condensation with ethyl oxalate and ketones or aldehydes to yield indene-oxalate and benzofulvene, respectively.
3. Indene as a Ligand
Indene forms the indenyl anion upon proton withdrawal, acting as an η3- ligand and exhibiting the indenyl effect.
4. Indene in Resin Synthesis
Indene, when polymerized with coumarin, forms a thermoplastic resin with a low degree of polymerization. The resulting coumarone-indene resin, obtained from the 160-180°C fraction of coal tar, is brown or black, soluble in aromatic hydrocarbons, and resistant to acids and alkalis.