Terephthalic acid

Terephthalic acid
Other names	Benzene-1,4-dicarboxylic acid para-Phthalic acid TPA PTA
Identifiers
CAS number	100-21-0 Y
RTECS number	WZ0875000
SMILES	C1=CC(=CC=C1C (=O)O)C(=O)O
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)
Boiling point	sublimes
Solubility in water	0.0017 g/100 mL at 25°C
Solubility	polar organic solvents aqueous base
Acidity (pKa)	pKa1=3.54 at 25°C pKa2=4.46 at 25°C[1]
Structure
Dipole moment	zero
Hazards
MSDS	External MSDS
EU classification	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	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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 rather than melting 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.^[4] 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 metal-organic frameworks.

References

1. ^ CHEMINFO: Terephthalic acid
2. ^ Yoshiro Ogata, Masaru Tsuchida, Akihiko Muramoto (1957). "The Preparation of Terephthalic Acid from Phthalic or Benzoic Acid". Journal of the American Chemical Society 79 (22): 6005–6008. doi:10.1021/ja01579a043. 
3. ^ Yoshiro Ogata, Masaru Hojo, Masanobu Morikawa (1960). "Further Studies on the Preparation of Terephthalic Acid from Phthalic or Benzoic Acid". Journal of Organic Chemistry 25 (12): 2082–2087. doi:10.1021/jo01082a003. 
4. ^ Richard J. Sheehan, "Terephthalic Acid, Dimethyl Terephthalate, and Isophthalic Acid" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a26_193 Article Online Posting Date: June 15, 2000.

• 1911 Encyclopedia

External links and further reading

• Basic Organic Chemistry: Part 5, Industrial Products, J.M. Tedder, A. Nechvatal, A.H. Tubb (editors), John Wiley & Sons, Chichester, UK (1975).
• International Chemical Safety Card 0330