Chloroacetic acid
Template:Use dmy dates Template:Chembox Template:Distinguish Chloroacetic acid, industrially known as monochloroacetic acid (MCA), is a organochlorine compound and carboxylic acid with the formula Template:Chem2; it is the simplest of the chloroacetic acids. This colorless solid is a useful building block in organic synthesis.
Production
Chloroacetic acid was first prepared (in impure form) by the French chemist Félix LeBlanc (1813–1886) in 1843 by chlorinating acetic acid in the presence of sunlight,<ref>LeBlanc, Félix (1844) "Recherches sur les produits dérivés de l'éther acétique par l'action du chlore, et en particulier sur l'éther acétique perchloruré" (in French), Annales de Chimie et de Physique, 3rd series, 10 : 197–221 ; see especially p. 212.</ref> and in 1857 (in pure form) by the German chemist Reinhold Hoffmann (1831–1919) by refluxing glacial acetic acid in the presence of chlorine and sunlight,<ref>Hoffmann, Reinhold (1857) "Ueber Monochloressigsäure" (in German) (On mono-chloroacetic acid), Annalen der Chemie und Pharmacie, 102 (1) : 1–20.</ref> and then by the French chemist Charles Adolphe Wurtz by hydrolysis of chloroacetyl chloride (Template:Chem2), also in 1857.<ref>Wurtz, Adolphe (1857) "Note sur l'aldéhyde et sur le chlorure d'acétyle" (in French) (Note on aldehyde and on acetyl chloride), Annales de chimie et de physique, 3rd series, 49 : 58–62, see p. 61.</ref>
Chloroacetic acid is prepared industrially by two routes. The predominant method involves chlorination of acetic acid, 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. 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 are produced globally per year.<ref name=Ullmann>Template:Ullmann</ref>
Uses and reactions
Most reactions take advantage of the high reactivity of the Template:Chem2 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 herbicides 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 (epinephrine). Displacement of chloride by sulfide gives thioglycolic acid, which is used as a stabilizer in PVC and a component in some cosmetics.<ref name=Ullmann/>
Illustrative of its usefulness in organic chemistry is the O-alkylation of salicylaldehyde with chloroacetic acid, followed by decarboxylation of the resulting ether, producing benzofuran.<ref>Template:OrgSynth.</ref><ref>Template:Cite journal</ref>
Safety
Like other chloroacetic acids and related halocarbons, chloroacetic acid is a hazardous alkylating agent. The Template:LD50 for rats is 76 mg/kg.<ref name=Ullmann/>
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 (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.<ref name="gov-right-know">Template:Citation</ref>