Chloroacetic acid, industrially known as monochloroacetic acid (MCA), is the
organochlorine compound with the formula . This
carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...
is a useful building block in
organic synthesis
Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...
. It is a colorless solid. Related compounds are
dichloroacetic acid and
trichloroacetic acid.
Production
Chloroacetic acid was first prepared (in impure form) by the French chemist
Félix LeBlanc (1813–1886) in 1843 by
chlorinating acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...
in the presence of sunlight, and in 1857 (in pure form) by the German chemist Reinhold Hoffmann (1831–1919) by refluxing
glacial acetic acid in the presence of
chlorine
Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
and
sunlight
Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...
, and then by the French chemist
Charles Adolphe Wurtz by
hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
of
chloroacetyl chloride (), also in 1857.
Chloroacetic acid is prepared industrially by two routes. The predominant method involves
chlorination of
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...
, with
acetic anhydride as a
catalyst:
:
This route suffers from the production of
dichloroacetic acid and
trichloroacetic acid as impurities, which are difficult to separate by
distillation:
:
:
The second method entails hydrolysis of
trichloroethylene:
:
The hydrolysis is conducted at 130–140 °C in a concentrated (at least 75%) solution of
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
. This method produces a highly pure product, unlike the
halogenation route. However, the significant quantities of
HCl released have led to the increased popularity of the halogenation route. Approximately 420,000
tonnes
The tonne ( or ; symbol: t) is a unit of mass equal to 1,000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the s ...
are produced globally per year.
Uses and reactions
Most reactions take advantage of the high reactivity of the bond.
In its largest-scale application, chloroacetic acid is used to prepare the thickening agent
carboxymethyl cellulose and
carboxymethyl starch.
Chloroacetic acid is also used in the production of
phenoxy herbicide
Phenoxy herbicides (or "phenoxies") are two families of chemicals that have been developed as commercially important herbicides, widely used in agriculture. They share the part structure of phenoxyacetic acid.
Auxins
The first group to be discove ...
s by etherification with chlorophenols. In this way
2-methyl-4-chlorophenoxyacetic acid (MCPA),
2,4-dichlorophenoxyacetic acid, and
2,4,5-trichlorophenoxyacetic acid (2,4,5-T) are produced. It is the precursor to the herbicide
glyphosate and
dimethoate. Chloroacetic acid is converted to
chloroacetyl chloride, a precursor to
adrenaline
Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands a ...
(epinephrine). Displacement of chloride by sulfide gives
thioglycolic acid, which is used as a stabilizer in
PVC and a component in some
cosmetics
Cosmetics are substances that are intended for application to the body for cleansing, beautifying, promoting attractiveness, or altering appearance. They are mixtures of chemical compounds derived from either Natural product, natural source ...
.
[
Illustrative of its usefulness in organic chemistry is the ''O''-alkylation of salicylaldehyde with chloroacetic acid, followed by decarboxylation of the resulting ]ether
In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R� ...
, producing benzofuran
Benzofuran is the heterocyclic compound consisting of fused benzene and furan rings. This colourless liquid is a component of coal tar. Benzofuran is the structural nucleus (parent compound) of many related compounds with more complex stru ...
.
Safety
Like other chloroacetic acids and related halocarbons, chloroacetic acid is a hazardous alkylating agent. The for rats is 76 mg/kg.[
It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. ]Emergency Planning and Community Right-to-Know Act
The Emergency Planning and Community Right-to-Know Act of 1986 is a United States federal law passed by the 99th United States Congress located at Title 42, Chapter 116 of the U.S. Code, concerned with emergency response preparedness.
On Octobe ...
(42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.
See also
* Fluoroacetic acid
References
External links
*
*
Sublimed crystals of the acid in a brown glass bottle
(photo)
{{Authority control
Acetic acids
Alkylating agents
Organochlorides
Organic compounds with 2 carbon atoms