Phthalic anhydride is the organic compound with the formula C6H4(CO)2O. It is the anhydride of phthalic acid. Phthalic anhydride is a principal commercial form of phthalic acid. It was the first anhydride of a dicarboxylic acid to be used commercially. This white solid is an important industrial chemical, especially for the large-scale production of plasticizers for plastics.

Applications

Phthalic anhydride is a toxic, white crystalline compound used in the manufacture of phthaleins and other dyes, resins, plasticizers, and insecticides. Phthalic anhydride is the anhydride of phthalic acid. This colorless solid is an important industrial chemical, especially for the large–scale production of plasticizers for plastics. It is presently obtained by catalytic oxidation of ortho–xylene or naphthalene. Phthalic anhydride can also be prepared from phthalic acid.

Phthalic anhydride is a versatile intermediate in organic chemistry, in part because it is bifunctional and readily available. The primary use of phthalic anhydride (PA) is as a chemical intermediate in the production of plasticizers from polyvinyl chloride (PVC).

The primary use of  phthalic anhydride (PA) is as a chemical intermediate in the production of plastics from vinyl chloride. Phthalate esters that function as plasticizers are derived from phthalic anhydride. Phthalic anhydride has another major use in the production of polyester resins and other minor uses in the production of alkyd resins used in paints and lacquers, certain guys, insect repellents, and urethane polyester polyols.

Phthalic anhydride has also been used as a rubber scorch inhibitor and retarder.The second largest outlet for PA is in unsaturated polyester resins (UPR) which are usually blended with glass fibers to produce fiberglass-reinforced plastics. Principal markets are construction, marine and transportation.

The third largest outlet is PA-based alkyd resins that are used in solvent-based coatings for architectural, machinery, furniture and fixture applications.Small volume uses for PA include the manufacture of dyes and pigments, detergents, herbicides and insecticides, fire retardants, saccharin and polyester resin cross-linking agents.