benzenedicarboxylic

Benzenedicarboxylic refers to any compound in which a benzene ring bears two carboxyl groups. In common nomenclature the three structural isomers are the ortho-, meta-, and para- benzenedicarboxylic acids, corresponding to carboxyl groups at positions 1 and 2 (phthalic acid), 1 and 3 (isophthalic acid), and 1 and 4 (terephthalic acid). The acids are often encountered as their anhydrides, phthalic anhydride, isophthalic anhydride, and terephthalic anhydride.

Industrial production typically proceeds by oxidation of the corresponding xylene isomers to the dicarboxylic acids or their anhydrides. Phthalic anhydride is primarily produced by oxidation of o-xylene. Terephthalic acid is produced by oxidation of p-xylene. Isophthalic acid is produced from m-xylene in various routes.

These compounds are colorless crystalline solids with two acidic carboxyl groups; they are dibasic acids and exhibit limited water solubility, with solubility increasing under basic conditions. They form polymerizable derivatives and serve as building blocks in plastic resins.

Terephthalic acid is a major precursor for polyethylene terephthalate (PET) and other polyesters used in textiles, bottles, and films. Phthalic anhydride is a key intermediate in the production of alkyd resins, unsaturated polyesters, and plasticizers derived from phthalate esters. Isophthalic acid is used in specialty polyesters and resins with specific properties.

Handling requires standard chemical safety practices. As with related phthalate esters, certain derivatives pose environmental or health concerns, leading to regulatory considerations. The acids themselves are less volatile but can be irritants.