Terephthalic acid is one isomer of the three phthalic acids. It finds important use as a commodity chemical, principally as a starting compound for the manufacture of polyester (specifically PET), used in clothing and to make plastic bottles. It is also known as 1,4-benzenedicarboxylic acid, and it has the chemical formula C6H4(COOH)2. It has recently become an important component in the development of hybrid framework materials.
On an industrial scale, terephthalic acid is produced, similar to benzoic acid, by oxidation of p-xylene by oxygen from air. This is done using acetic acid as solvent, in the presence of a catalyst such as cobalt-manganese, using a bromide promoter. The yield is close to 100%. The crude product is purified by hydrogenation while in a water solution to convert trace amounts of impurities to less harmful species. The solution is then cooled in a stepwise manner to crystallize out a highly pure terephthalic acid. Over 90% of the terephalate feedstock for the polyester industry uses this process, and all plants built within the last few decades are of this technology. Alternatively, but not commercially, it can be made, via the Henkel process (company) also known as Raecke process (patent holder), which involves the rearrangement of phthalic acid to terephthalic acid via the corresponding potassium salts. Terephthalic acid and dimethyl terephthalate are essentially all used as a monomer component in the production of polymers, principally polyethylene terephthalate (polyester or PET). World production in 1970 was around 1.75 million tonnes.. By 2006, global PTA demand had substantially exceeded 30 million tonnes.