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| Names | |
|---|---|
| Preferred IUPAC name Benzene-1,4-dicarboxylic acid | |
| Other names Terephthalic acid para-Phthalic acid TPA PTA BDC | |
| Identifiers | |
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3D model (JSmol) | |
| 1909333 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider |
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| ECHA InfoCard | 100.002.573 |
| EC Number |
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| 50561 | |
| KEGG | |
| RTECS number |
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| UNII | |
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| Properties | |
| C8H6O4 | |
| Molar mass | 166.132 g·mol−1 |
| Appearance | White crystals or powder |
| Density | 1.519 g/cm3[1]: 3.492 |
| Melting point | 300 °C (572 °F; 573 K) Sublimes[1]: 3.492 |
| Boiling point | Decomposes |
| 0.017 g/L at 25 °C[1]: 5.163 | |
| Solubility | polar organic solvents aqueous base |
| Solubility inAcetic acid | Per 100 grams 0.035 g at 25 °C (77 °F) 0.3 g at 120 °C (248 °F) 0.75 g at 160 °C (320 °F) 1.8 g at 200 °C (392 °F) 4.5 g at 240 °C (464 °F)[citation needed] |
| Solubility inDimethyl formamide | 6.7 g per 100 g at 25 °C (77 °F)[citation needed] |
| Solubility inDimethyl sulfoxide | 20 g per 100 g at 25 °C (77 °F)[citation needed] |
| Solubility inFormic acid | 0.5 g per 100 g 25 °C (77 °F)[citation needed] |
| Solubility inMethanol | Per 100 grams 0.1 g at 25 °C (77 °F) 2.9 g at 160 °C (320 °F) 15 g at 200 °C (392 °F) [citation needed] |
| Vapor pressure | 1.3 kPa (303 °C (577 °F)) 13.3 kPa (353 °C (667 °F)) 26.7 kPa (370 °C (698 °F)) 53.3 kPa (387 °C (729 °F)) 101.3 kPa (404 °C (759 °F)) [citation needed] |
| Acidity (pKa) | 3.54, 4.34[1]: 5.96 |
| −83.5×10−6 cm3/mol[1]: 3.579 | |
| Structure | |
| 2.6D[2] | |
| Thermochemistry[1]: 5.37 | |
Std enthalpy of formation(ΔfH⦵298) | −816.1 kJ/mol |
| Hazards | |
| GHS labelling: | |
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| Warning | |
| 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)[1]: 16.29 |
| 496 °C (925 °F; 769 K)[1]: 16.29 | |
Threshold limit value (TLV) | 10 mg/m3[1]: 16.42 (STEL) |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | >1 g/kg (oral, mouse)[3] |
| Safety data sheet (SDS) | MSDS sheet |
| Related compounds | |
Relatedcarboxylic acids | Phthalic acid Isophthalic acid Benzoic acid p-Toluic acid |
Related compounds | p-Xylene Polyethylene terephthalate Dimethyl terephthalate |
| Supplementary data page | |
| Terephthalic acid (data page) | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Terephthalic acid is anorganic compound withformula C6H4(CO2H)2. This white solid is acommoditychemical, used principally as a precursor to thepolyesterPET, used to make clothing andplastic bottles. Several million tons are produced annually.[3] The common name is derived from theturpentine-producing treePistacia terebinthus andphthalic acid.
Terephthalic acid is also used in the production ofPBT plastic (polybutylene terephthalate).[4]
Terephthalic acid was first isolated (from turpentine) by the French chemist Amédée Cailliot (1805–1884) in 1846.[5] Terephthalic acid became industrially important afterWorld War II. Terephthalic acid was produced by oxidation ofp-xylene with 30-40%nitric acid. Air oxidation ofp-xylene givesp-toluic acid, which resists further air-oxidation. Esterification ofp-toluic acid tomethylp-toluate (CH3C6H4CO2CH3) opens the way for further oxidation to monomethyl terephthalate. In the Dynamit−Nobel process these two oxidations and the esterification were performed in a single reactor. The reaction conditions also lead to a second esterification, producingdimethyl terephthalate, which could be hydrolysed to terephthalic acid. In 1955, Mid-Century Corporation and ICI announced the bromide-catalysed oxidation ofp-toluic acid directly to terephthalic acid, without the need to isolate intermediates and still using air as the oxidant. Amoco (as Standard Oil of Indiana) purchased the Mid-Century/ICI technology, and the process is now known by their name.[6]
In the Amoco process, which is widely adopted worldwide, terephthalic acid is produced by catalyticoxidation ofp-xylene:[6]
The process uses acobalt–manganese–bromidecatalyst. The bromide source can besodium bromide,hydrogen bromide ortetrabromoethane. Bromine functions as a regenerative source offree radicals.Acetic acid is the solvent andcompressed air serves as the oxidant. The combination of bromine and acetic acid is highlycorrosive, requiring specialized reactors, such as those lined withtitanium. A mixture ofp-xylene,acetic acid, thecatalyst system, and compressed air is fed to a reactor.
The oxidation ofp-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 top-toluic acid, which is less reactive than the p-xylene owing to the influence of theelectron-withdrawingcarboxylic acid group. Incomplete oxidation produces4-carboxybenzaldehyde (4-CBA), which is often a problematic impurity.[6][7][8]
Approximately 5% of the acetic acid solvent is lost by decomposition or "burning". Product loss bydecarboxylation tobenzoic 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 oftoxins andozone depleters such asmethylbromide before being released. Additionally, the corrosive nature of bromides at high temperatures requires the reaction be run in expensive titanium reactors.[9][10]
The use ofcarbon dioxide overcomes many of the problems with the original industrial process. Because CO2 is a better flame inhibitor thanN2, 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, lowercarbon monoxide production, less decarboxylation and higher purity than the commercial process.[9][10]
Insupercritical 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 more demanding conditions than the industrial process (300–400 °C, >200 bar).[11]
As with any large-scale process, many additives have been investigated for potential beneficial effects. Promising results have been reported with the following.[6]
Terephthalic acid can also be made fromtoluene by theGattermann-Koch reaction, which gives4-methylbenzaldehyde. Oxidation of the latter gives terephthalic acid.[12]
Terephthalic acid can be prepared in the laboratory by oxidizing manypara-disubstituted derivatives ofbenzene, includingcaraway oil or a mixture ofcymene andcuminol withchromic 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 route involves the transfer of carboxylate groups. Eitherpotassium benzoate disproportionates to potassium terephthalate andbenzene orpotassium phthalate rearranges to the terephthalate.[13][14]Phthalic anhydride can be used as a raw material and then potassium can be recycled.[15]
Virtually the entire world's supply of terephthalic acid anddimethyl terephthalate are consumed as precursors topolyethylene terephthalate (PET).[3] A smaller, but nevertheless significant, demand for terephthalic acid exists in the production ofpolybutylene terephthalate and several other engineeringpolymers.[16]Kevlar is apolyamide derived from terephthalic acid. Poly(ester amide)s are another class of polymers that have novel properties.[17]
InComamonas thiooxydans strain E6,[19] terephthalic acid is biodegraded toprotocatechuic acid, a common natural product, via a reaction pathway initiated byterephthalate 1,2-dioxygenase. Combined with the previously knownPETase andMHETase, a full pathway forPET plastic degradation can be engineered.[20]
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