Terephthalic acid

Terephthalic acid
Names


Preferred IUPAC name Benzene-1,4-dicarboxylic acid
Other names Terephthalic acid para-Phthalic acid TPA PTA BDC
Identifiers
CAS Number	100-21-0^Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:15702^Y
ChemSpider	7208^Y
ECHA InfoCard	100.002.573
RTECS number	WZ0875000
UNII	6S7NKZ40BQ^N
InChI InChI=1S/C8H6O4/c9-7(10)5-1-2-6(4-3-5)8(11)12/h1-4H,(H,9,10)(H,11,12)^Y Key: KKEYFWRCBNTPAC-UHFFFAOYSA-N^Y InChI=1/C8H6O4/c9-7(10)5-1-2-6(4-3-5)8(11)12/h1-4H,(H,9,10)(H,11,12) Key: KKEYFWRCBNTPAC-UHFFFAOYAF
SMILES c1cc(ccc1C(=O)O)C(=O)O
Properties
Chemical formula	C₈H₆O₄
Molar mass	166.13 g/mol
Appearance	white crystals or powder
Density	1.522 g/cm³
Melting point	300 °C (572 °F; 573 K) in a sealed tube; sublimes at 402 °C (756 °F; 675 K)
Boiling point	Decompose
Solubility in water	0.0015 g/100 mL at 20°C
Solubility	polar organic solvents aqueous base
Acidity (pK_a)	3.51, 4.82
Magnetic susceptibility (χ)	-83.51·10⁻⁶ cm³/mol
Structure
Dipole moment	zero
Hazards
Safety data sheet	See: data page MSDS sheet
EU classification (DSD)	not listed
Related compounds
Related carboxylic acids	Phthalic acid Isophthalic acid Benzoic acid p-Toluic acid
Related compounds	p-Xylene Polyethylene terephthalate Dimethyl terephthalate
Supplementary data page
Structure and properties	Refractive index (n), Dielectric constant (ε_r), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N (what is ^YN ?)
Infobox references

Terephthalic acid (a portmanteau of the turpentine-producing tree terebinthus, and phthalic acid) is the organic compound with formula C₆H₄(CO₂H)₂. This white solid is a commodity chemical, used principally as a precursor to the polyester PET, used to make clothing and plastic bottles. Several million tonnes are produced annually.

Terephthalic acid was first isolated (from turpentine) by the French chemist Amédée Cailliot (1805-1884) in 1846. The importance of the terephthalic acid was realized after World War II. The first companies to commercialize the use of the fibers made from polyethylene terephthalate were Imperial Chemical Industries in the UK in 1949 and DuPont in the US in 1953. The fibers were made from dimethyl terephthalate by transesterification with ethylene glycol. Terephthalic acid was produced by oxidation of p-xylene with dilute nitric acid. This type of oxidation involved the use of air in the initial oxidation step to minimize the consumption of nitric acid and difficulty in purification. Growth in the textile industry led to increase in demand of TPA. In the 1960s, all the terephthalic acid produced was converted to its dimethyl ester, since TPA was infusible and difficult to purify. Presently TPA is manufactured by oxidation of p-xylene.

Terephthalic acid is poorly soluble in water and alcohols; consequently, until about 1970 terephthalic acid was purified as its dimethyl ester. It sublimes when heated.

In the Amoco process, terephthalic acid is produced by oxidation of p-xylene by oxygen in air:

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