Terephthalic acid
Skeletal formula
Ball-and-stick model of the terephthalic acid molecule
Preferred IUPAC name
Benzene-1,4-dicarboxylic acid
Other names
Terephthalic acid
para-Phthalic acid
3D model (JSmol)
ECHA InfoCard 100.002.573 Edit this at Wikidata
EC Number
  • 202-830-0
RTECS number
  • WZ0875000
  • InChI=1S/C8H6O4/c9-7(10)5-1-2-6(4-3-5)8(11)12/h1-4H,(H,9,10)(H,11,12) checkY
  • InChI=1/C8H6O4/c9-7(10)5-1-2-6(4-3-5)8(11)12/h1-4H,(H,9,10)(H,11,12)
  • O=C(O)c1ccc(C(O)=O)cc1
Molar mass 166.132 g·mol−1
Appearance White crystals or powder
Density 1.519 g/cm3[1]
Melting point 300 °C (572 °F; 573 K) Sublimes[1]
Boiling point Decomposes
0.065 g/L at 25 °C[2]
Solubility polar organic solvents aqueous base
Acidity (pKa) 3.54, 4.34[3]
−83.5×10−6 cm3/mol[4]
2.6D [5]
−816.1 kJ/mol
GHS labelling:
GHS07: Exclamation mark
H315, H319, H335
P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
Flash point 260 °C (500 °F; 533 K)[9]
496 °C (925 °F; 769 K)[9]
10 mg/m3[7] (STEL)
Lethal dose or concentration (LD, LC):
>1 g/kg (oral, mouse)[8]
Safety data sheet (SDS) MSDS sheet
Related compounds
Phthalic acid
Isophthalic acid
Benzoic acid
p-Toluic acid
Related compounds
Polyethylene terephthalate
Dimethyl terephthalate
Supplementary data page
Terephthalic acid (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Terephthalic acid is an 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 tons are produced annually.[8] The common name is derived from the turpentine-producing tree Pistacia terebinthus and phthalic acid.

Terephthalic acid is also used in the production of PBT plastic (polybutylene terephthalate).[10]


Terephthalic acid was first isolated (from turpentine) by the French chemist Amédée Cailliot (1805–1884) in 1846.[11] Terephthalic acid became industrially important after World War II. Terephthalic acid was produced by oxidation of p-xylene with dilute nitric acid. Air oxidation of p-xylene gives p-toluic acid, which resists further air-oxidation. Conversion of p-toluic acid to methyl p-toluate (CH3C6H4CO2CH3) opens the way for further oxidation to monomethyl terephthalate, which is further esterified to dimethyl terephthalate. In 1955, Mid-Century Corporation and ICI announced the bromide-promoted oxidation of p-toluic acid to terephthalic acid. This innovation enabled the conversion of p-xylene to terephthalic acid without the need to isolate intermediates. Amoco (as Standard Oil of Indiana) purchased the Mid-Century/ICI technology.[12]


Amoco process

In the Amoco process, which is widely adopted worldwide, terephthalic acid is produced by catalytic oxidation of p-xylene:[12]

Terephthalic acid

The process uses a cobaltmanganesebromide catalyst. The bromide source can be sodium bromide, hydrogen bromide or tetrabromoethane. Bromine functions as a regenerative source of free radicals. Acetic acid is the solvent and compressed air serves as the oxidant. The combination of bromine and acetic acid is highly corrosive, requiring specialized reactors, such as those lined with titanium. A mixture of p-xylene, acetic acid, the catalyst system, and compressed air is fed to a reactor.


The oxidation of p-xylene proceeds by a free radical process. Bromine radicals decompose cobalt and manganese hydroperoxides. The resulting oxygen-based radicals abstract hydrogen from a methyl group, which have weaker C–H bonds than does the aromatic ring. Many intermediates have been isolated. p-xylene is converted to p-toluic acid, which is less reactive than the p-xylene owing to the influence of the electron-withdrawing carboxylic acid group. Incomplete oxidation produces 4-carboxybenzaldehyde (4-CBA), which is often a problematic impurity.[12][13] [14]

Oxidation of p-xylene to TPA


Approximately 5% of the acetic acid solvent is lost by decomposition or "burning". Product loss by decarboxylation to benzoic acid is common. The high temperature diminishes oxygen solubility in an already oxygen-starved system. Pure oxygen cannot be used in the traditional system due to hazards of flammable organic–O2 mixtures. Atmospheric air can be used in its place, but once reacted needs to be purified of toxins and ozone depleters such as methylbromide before being released. Additionally, the corrosive nature of bromides at high temperatures requires the reaction be run in expensive titanium reactors.[15][16]

Alternative reaction media

The use of carbon dioxide overcomes many of the problems with the original industrial process. Because CO2 is a better flame inhibitor than N2, a CO2 environment allows for the use of pure oxygen directly, instead of air, with reduced flammability hazards. The solubility of molecular oxygen in solution is also enhanced in the CO2 environment. Because more oxygen is available to the system, supercritical carbon dioxide (Tc = 31 °C) has more complete oxidation with fewer byproducts, lower carbon monoxide production, less decarboxylation and higher purity than the commercial process.[15][16]

In supercritical water medium, the oxidation can be effectively catalyzed by MnBr2 with pure O2 in a medium-high temperature. Use of supercritical water instead of acetic acid as a solvent diminishes environmental impact and offers a cost advantage. However, the scope of such reaction systems is limited by the even harsher conditions than the industrial process (300–400 °C, >200 bar).[17]

Promotors and additives

As with any large-scale process, many additives have been investigated for potential beneficial effects. Promising results have been reported with the following.[12]

Alternative routes

Terephthalic acid can be prepared in the laboratory by oxidizing many para-disubstituted derivatives of benzene, including caraway oil or a mixture of cymene and cuminol with chromic acid.

Although not commercially significant, there is also the so-called "Henkel process" or "Raecke process", named after the company and patent holder, respectively. This process involves the transfer of carboxylate groups. For example potassium benzoate disproportionates to potassium terephthalate, and potassium phthalate rearranges to potassium terephthalate.[18][19]

Lummus (now a subsidiary of McDermott International) has reported a route from the dinitrile, which can be obtained by ammoxidation of p-xylene.


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.[8] By 2006, global purified terephthalic acid (PTA) demand had exceeded 30 million tonnes. A smaller, but nevertheless significant, demand for terephthalic acid exists in the production of polybutylene terephthalate and several other engineering polymers.[20]

Other uses


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.

Solubility (g/100 g solvent)
Solvent 25 °C 120 °C 160 °C 200 °C 240 °C
Methanol 0.1 2.9 15
Water 0.0019 0.08 0.38 1.7 9.0
Acetic acid 0.035 0.3 0.75 1.8 4.5
Formic acid 0.5
Sulfuric acid 2
Dimethyl formamide 6.7
Dimethyl sulfoxide 20
Vapor pressure
303 1.3
353 13.3
370 26.7
387 53.3
404 101.3


Terephthalic acid and its dimethyl ester have very low toxicity, with LD50 >1 g/kg (oral, mouse).[8]


In Comamonas thiooxydans strain E6,[21] terephthalic acid is biodegraded to protocatechuic acid, a common natural product, via a reaction pathway initiated by terephthalate 1,2-dioxygenase. Combined with the previously known PETase and MHETase, a full pathway for PET plastic degradation can be engineered.[22]

See also


  1. ^ a b Haynes, p. 3.492
  2. ^ Haynes, p. 5.163
  3. ^ Haynes, p. 5.96
  4. ^ Haynes, p. 3.579
  5. ^ Karthikeyan, N.; Joseph Prince, J.; Ramalingam, S.; Periandy, S. (2015). "Electronic [UV–Visible] and vibrational [FT-IR, FT-Raman] investigation and NMR–mass spectroscopic analysis of terephthalic acid using quantum Gaussian calculations". Spectrochimica Acta Part A. 139: 229–242. Bibcode:2015AcSpA.139..229K. doi:10.1016/j.saa.2014.11.112. PMID 25561302.
  6. ^ Haynes, p. 5.37
  7. ^ Haynes, p. 16.42
  8. ^ a b c d Sheehan, Richard J. "Terephthalic Acid, Dimethyl Terephthalate, and Isophthalic Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a26_193. ISBN 978-3527306732.
  9. ^ a b Haynes, p. 16.29
  10. ^ "Polybutylene Terephthalate (PBT) Material Guide & Properties Info". omnexus.specialchem.com. Archived from the original on 2023-11-24. Retrieved 2023-11-24.
  11. ^ Cailliot, Amédée (1847). "Études sur l'essence de térébenthine" [Studies of the essence of turpentine]. Annales de Chimie et de Physique. Série 3. 21: 27–40. Terephthalic acid is named on p. 29: "Je désignerai le premier de ces acides, celui qui est insoluble, sous le nom d'acide téréphtalique." (I will designate the first of these acids, which is insoluble, by the name of terephthalic acid.)
  12. ^ a b c d e Tomás, Rogério A. F.; Bordado, João C. M.; Gomes, João F. P. (2013). "p-Xylene Oxidation to Terephthalic Acid: A Literature Review Oriented toward Process Optimization and Development". Chemical Reviews. 113 (10): 7421–69. doi:10.1021/cr300298j. PMID 23767849.
  13. ^ Wang, Qinbo; Cheng, Youwei; Wang, Lijun; Li, Xi (2007). "Semicontinuous Studies on the Reaction Mechanism and Kinetics for the Liquid-Phase Oxidation of p-Xylene to Terephthalic Acid". Industrial & Engineering Chemistry Research. 46 (26): 8980–8992. doi:10.1021/ie0615584.
  14. ^ Xiao, Y.; Luo, W.-P.; Zhang, X.-Y.; et al. (2010). "Aerobic Oxidation of p-Toluic Acid to Terephthalic Acid over T(p-Cl)PPMnCl/Co(OAc)2 Under Moderate Conditions". Catalysis Letters. 134 (1–2): 155–161. doi:10.1007/s10562-009-0227-1. S2CID 95855968.
  15. ^ a b Zuo, Xiaobin; Subramaniam, Bala; Busch, Daryle H. (2008). "Liquid-Phase Oxidation of Toluene and p-Toluic Acid under Mild Conditions: Synergistic Effects of Cobalt, Zirconium, Ketones, and Carbon Dioxide". Industrial & Engineering Chemistry Research. 47 (3): 546–552. doi:10.1021/ie070896h.
  16. ^ a b Zuo, Xiaobin; Niu, Fenghui; Snavely, Kirk; et al. (2010). "Liquid Phase Oxidation of p-Xylene to Terephthalic Acid at Medium-high Temperatures: Multiple Benefits of CO2-expanded Liquids". Industrial & Engineering Chemistry Research. 12 (2): 260–267. doi:10.1039/B920262E. hdl:1808/18532.
  17. ^ Pérez, Eduardo; Fraga Dubreuil, Joan; García Verdugo, Eduardo; et al. (2011). "Selective Aerobic Oxidation of para-Xylene in Sub- and Supercritical Water. Part 1. Comparison with Ortho-xylene and the Role of the Catalyst". Green Chemistry. 13 (12): 2389–2396. doi:10.1039/C1GC15137A.
  18. ^ Ogata, Yoshiro; Tsuchida, Masaru; Muramoto, Akihiko (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.
  19. ^ Ogata, Yoshiro; Hojo, Masaru; Morikawa, Masanobu (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.
  20. ^ Ashford's Dictionary of Industrial Chemicals (3rd ed.). Saltash, UK: Wavelength. 2011. p. 8805. ISBN 978-0952267430.
  21. ^ "GTDB – Genome GCF_001010305.1". gtdb.ecogenomic.org.
  22. ^ Kincannon, William M.; Zahn, Michael; Clare, Rita; et al. (29 March 2022). "Biochemical and structural characterization of an aromatic ring–hydroxylating dioxygenase for terephthalic acid catabolism". Proceedings of the National Academy of Sciences. 119 (13): e2121426119. Bibcode:2022PNAS..11921426K. doi:10.1073/pnas.2121426119. PMC 9060491. PMID 35312352.

Cited sources

External links and further reading