Trichloroacetic acid

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as trichloroethanoic acid) is an analogue of acetic acid in which the three hydrogen atoms of the methyl group have all been replaced by chlorine atoms.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.

Trichloroacetic acid

Names
Preferred IUPAC name Trichloroacetic acid
Identifiers
CAS Number	76-03-9 Y
3D model (JSmol)	Interactive image
Beilstein Reference	970119
ChEBI	CHEBI:30956
ChEMBL	ChEMBL14053
ChemSpider	10772050
ECHA InfoCard	100.000.844
Gmelin Reference	2842
KEGG	C11150 Y
PubChem CID	6421
RTECS number	AJ7875000
UNII	5V2JDO056X Y
CompTox Dashboard (EPA)	DTXSID1021378
InChI InChI=1S/C2HCl3O2/c3-2(4,5)1(6)7/h(H,6,7) Key: YNJBWRMUSHSURL-UHFFFAOYSA-N
SMILES ClC(Cl)(Cl)C(O)=O
Properties
Chemical formula	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]
Solubility in water	1000 g/100 mL[2]
Vapor pressure	1 mmHg (51.1 °C)[1]
Acidity (pKa)	0.66[3]
Magnetic susceptibility (χ)	−73.0·10−6 cm3/mol
Structure
Dipole moment	3.23 D
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314, H410
Precautionary statements	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)	3 1 0
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	Chloroacetic acid Dichloroacetic acid
Related compounds	Acetic acid Trifluoroacetic acid Tribromoacetic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

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

It 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.

See also

• Chloroacetic acids