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Purified terephthalic acid PTA

(Click here for a model of a molecule of Purified terephthalic acid)

News about Purified terephthalic acid




Other names
Benzene-1,4-dicarboxylic acid
para-Phthalic acid
TPA
PTA
Identifiers
CAS number 100-21-0 Y
ChemSpider 7208 Y
RTECS number WZ0875000

Properties
Molecular formula C8H6O4
Molar mass 166.13 g/mol
Appearance white crystals or powder
Density 1.522 g/cm³
Melting point 300°C in a sealed tube (sublimes at 402°C (675 K) in air)


Terephthalic acid is the organic compound with formula C6H4(COOH)2. This colourless solid is a commodity chemical, used principally as a precursor to the polyester PET, used to make clothing and plastic bottles. Several billion kilograms are produced annually. It is one of three isomeric phthalic acids.


Properties
Terephthalic acid is poorly soluble in water and alcohols, consequently up until around 1970 most crude terephthalic acid was converted to the dimethyl ester for purification. It sublimes when heated.

Production
Terephthalic acid is produced by oxidation of p-xylene by oxygen in air:


The oxidation is conducted using acetic acid as solvent and a catalyst composed of cobalt and manganese salts, using a bromide promoter. The yield is nearly quantitative. The most problematic impurity is 4-formylbenzoic acid, which is removed by hydrogenation of a hot aqueous solution. The solution is then cooled in a stepwise manner to crystallize highly pure terephthalic acid.

Alternatively, but not commercially significant, is the so-called "Henkel process" or "Raecke process," named after the company and patent holder, respectively. This process involves the rearrangement of phthalic acid to terephthalic acid via the corresponding potassium salts.[2][3] Terephthalic acid can be prepared in the laboratory by oxidizing various para-disubstituted derivatives of benzene including Caraway Oil or a mixture of cymene and cuminol with chromic acid.

Applications
Virtually the entire world's supply of terephthalic acid and dimethyl terephthalate are consumed as precursors to polyethylene terephthalate (PET). World production in 1970 was around 1.75 million tonnes. By 2006, global purified terephthalic acid (PTA) demand had exceeded 30 million tonnes.

In the research laboratory, terephthalic acid has been popularized as a component for the synthesis of metal-organic frameworks.