Terephthalic acid

Terephthalic acid is an aromatic dicarboxylic acid with two carboxyl groups opposite each other on a benzene ring. It is chiefly used to make polyethylene terephthalate and other polyesters.

Polyethylene terephthalate: A thermoplastic polyester used in fibers, films, and beverage containers. Terephthalic acid is one of the two principal monomers used to make PET.
Polycondensation: A step-growth polymerization in which monomers join while releasing small molecules such as water or methanol. Terephthalic acid forms polyester chains through reactions between its carboxyl groups and diols.
Para-xylene: An aromatic hydrocarbon isomer used chiefly as the industrial feedstock for terephthalic acid. Oxidation of para-xylene supplies most commercial terephthalic acid.
Aromatic compound: A molecule containing a conjugated ring system with unusual stability associated with delocalized electrons. Terephthalic acid’s benzene ring gives its polyester chains rigid aromatic segments.
Polybutylene terephthalate: A thermoplastic polyester made from terephthalic acid and 1,4-butanediol. It uses the same acid with a different diol to produce a distinct engineering plastic.
Ethylene glycol: A two-carbon diol used as a feedstock for polyester production and as an antifreeze component. It reacts with terephthalic acid to produce polyethylene terephthalate.
Amoco process: An industrial process that oxidizes para-xylene to terephthalic acid using acetic acid, oxygen, and metal catalysts. It established the dominant route for producing terephthalic acid at scale.
Carboxylic acid: An organic compound containing one or more carboxyl groups, written –COOH. Its two carboxylic acid groups provide the reactive ends used in polyester formation.
Polyethylene naphthalate: A polyester made from ethylene glycol and naphthalenedicarboxylic acid, with properties suited to demanding films and packaging. It is a related polyester whose aromatic monomer is a fused-ring acid rather than terephthalic acid.
Dimethyl terephthalate: The dimethyl ester of terephthalic acid, used as an alternative polyester feedstock. Its ester groups can undergo transesterification with diols instead of direct acid-based polymerization.

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