Phthalic anhydride (PA) is an important organic compound with the chemical formula C₆H₄(CO)₂O. It is a colorless or white crystalline solid that is highly reactive and used primarily as an intermediate in the chemical industry. Phthalic anhydride is the anhydride of phthalic acid, formed by the removal of water from two molecules of phthalic acid.
Phthalic anhydride is primarily used in the production of plasticizers, resins, dyes, and pharmaceuticals. It also plays a key role in the manufacturing of unsaturated polyester resins and alkyd resins, which are used in coatings, paints, and automotive products.
Properties of Phthalic Anhydride:
- Molecular Formula: C₆H₄(CO)₂O
- Molar Mass: 148.12 g/mol
- CAS Number: 85-44-9
- Functional Groups: Contains two carbonyl groups (C=O) attached to a benzene ring, making it an anhydride of phthalic acid.
- Reactivity:
- Phthalic anhydride is highly reactive and readily reacts with alcohols, amines, and water to form esters, amines, or phthalic acid.
- It can also react with unsaturated compounds to produce polyester resins.
- Hydrolysis of phthalic anhydride in water leads to the formation of phthalic acid.
- Appearance: Colorless or white crystalline solid with a sharp, acrid odor.
- Odor: Sharp and acrid, similar to acetic acid.
- Density: 1.53 g/cm³ at 20°C.
- Melting Point: 131–133°C (268–271°F).
- Boiling Point: Sublimes at 284°C (543°F) under normal atmospheric pressure.
- Solubility:
- Insoluble in water, but readily reacts with water to form phthalic acid.
- Soluble in organic solvents like benzene, toluene, ether, and acetone.
- Vapor Pressure: 0.001 mmHg at 100°C.
- Refractive Index: 1.630 at 20°C.
Uses of Phthalic Anhydride:
- Plasticizers: Used to make phthalate esters, which are plasticizers in PVC.
- Dyes and Pigments: Used as a precursor in the production of dyes and pigments.
- Polyester Resins: Used in the production of unsaturated polyester resins.
- Pharmaceuticals: Used in the synthesis of various active pharmaceutical ingredients (APIs).