Trichloroacetic acid
Chemical compound
From Wikipedia, the free encyclopedia
Trichloroacetic acid (TCA; TCAA; also known as trichloroethanoic acid) is an analogue of acetic acid in which the three hydrogen atoms of the methyl group have all been replaced by chlorine atoms. Salts and esters of trichloroacetic acid are called trichloroacetates.
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| Names | |||
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| Preferred IUPAC name
Trichloroacetic acid | |||
| Identifiers | |||
3D model (JSmol) |
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| 970119 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| ECHA InfoCard | 100.000.844 | ||
| 2842 | |||
| KEGG | |||
PubChem CID |
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| RTECS number |
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| UNII | |||
CompTox Dashboard (EPA) |
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| Properties | |||
| C2HCl3O2 | |||
| Molar mass | 163.38 g·mol−1 | ||
| Appearance | Colorless to white, crystalline solid | ||
| Odor | Sharp, pungent [1] | ||
| Density | 1.63 g/cm3 | ||
| Melting point | 57 to 58 °C (135 to 136 °F; 330 to 331 K)[2] | ||
| Boiling point | 196 to 197 °C (385 to 387 °F; 469 to 470 K)[2] | ||
| 1000 g/100 mL[2] | |||
| Vapor pressure | 1 mmHg (51.1 °C)[1] | ||
| Acidity (pKa) | 0.66[3] | ||
| −73.0·10−6 cm3/mol | |||
| Structure | |||
| 3.23 D | |||
| Hazards | |||
| GHS labelling: | |||
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| Danger | |||
| H314, H410 | |||
| P260, P264, P273, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P391, P405, P501 | |||
| NFPA 704 (fire diamond) | |||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) |
5000 mg/kg orally in rats[2] | ||
| NIOSH (US health exposure limits): | |||
PEL (Permissible) |
None[1] | ||
REL (Recommended) |
TWA 1 ppm (7 mg/m3)[1] | ||
IDLH (Immediate danger) |
N.D.[1] | ||
| Related compounds | |||
Related chloroacetic acids |
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Related compounds |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Synthesis
Trichloroacetic acid was discovered by Jean-Baptiste Dumas in 1830.[4]
It is prepared by the reaction of chlorine with acetic acid in the presence of a suitable catalyst such as red phosphorus. This reaction is Hell–Volhard–Zelinsky halogenation.
- CH
3COOH + 3 Cl
2 → CCl
3COOH + 3 HCl
Another route to trichloroacetic acid is the oxidation of trichloroacetaldehyde.
Use
Trichloroacetic acid is widely used in biochemistry for the precipitation of macromolecules, such as proteins, DNA, and RNA. TCA is used during oligonucleotide synthesis during the "deblocking" step to remove the dimethoxytrityl protecting group from the growing DNA/RNA strand for the next nucleotide incorporation. TCA and DCA are both used in cosmetic treatments (such as chemical peels and tattoo removal) and as topical medication for chemoablation of warts, including genital warts. It can kill normal cells as well. It is considered safe for use for this purpose during pregnancy.[5][6]
The sodium salt (sodium trichloroacetate) was used as an herbicide starting in the 1950s but regulators removed it from the market in the late 1980s and early 1990s.[7][8][9][10]
Environmental and health concerns
According to the European Chemicals Agency, "This substance causes severe skin burns and eye damage, is very toxic to aquatic life and has long lasting toxic effects."[11]
History
The discovery of trichloroacetic acid by Jean-Baptiste Dumas in 1839 delivered a striking example to the slowly evolving theory of organic radicals and valences.[12] The theory was contrary to the beliefs of Jöns Jakob Berzelius, starting a long dispute between Dumas and Berzelius.[13]
Popular culture
In the 1958 film The Blob, a bottle of trichloroacetic acid is tossed at the Blob in a futile attempt to fend it off.