Glycolic acid
Glycolic acid (or hydroxyacetic acid; chemical formula Template:Chem2) is a colorless, odorless and hygroscopic crystalline solid, highly soluble in water. It is used in various skin-care products. Glycolic acid is widespread in nature. A glycolate (sometimes spelled "glycollate") is a salt or ester of glycolic acid.
History
The name "glycolic acid" was coined in 1848 by French chemist Auguste Laurent (1807–1853). He proposed that the amino acid glycine—which was then called glycocolle—might be the amine of a hypothetical acid, which he called "glycolic acid" (acide glycolique).[1]
Glycolic acid was first prepared in 1851 by German chemist Adolph Strecker (1822–1871) and Russian chemist Nikolai Nikolaevich Sokolov (1826–1877). They produced it by treating hippuric acid with nitric acid and nitrogen dioxideTemplate:Contradictory inline to form an ester of benzoic acid and glycolic acid (Template:Chem2), which they called "benzoglycolic acid" (Benzoglykolsäure; also benzoyl glycolic acid). They boiled the ester for days with dilute sulfuric acid, thereby obtaining benzoic acid and glycolic acid (Glykolsäure).[2][3]
Preparation
Glycolic acid can be synthesized in various ways. The predominant approaches use a catalyzed reaction of formaldehyde with synthesis gas (carbonylation of formaldehyde), for its low cost.[4]
It is also prepared by the reaction of chloroacetic acid with sodium hydroxide followed by re-acidification.
Other methods, not noticeably in use, include hydrogenation of oxalic acid, and hydrolysis of the cyanohydrin derived from formaldehyde.[5] Some of today's glycolic acids are formic acid-free. Glycolic acid can be isolated from natural sources, such as sugarcane, sugar beets, pineapple, cantaloupe and unripe grapes.[6]
Glycolic acid can also be prepared using an enzymatic biochemical process that may require less energy.[7]
Properties
Glycolic acid is slightly stronger than acetic acid due to the electron-withdrawing power of the terminal hydroxyl group. The carboxylate group can coordinate to metal ions, forming coordination complexes. Of particular note are the complexes with Pb2+ and Cu2+ which are significantly stronger than complexes with other carboxylic acids. This indicates that the hydroxyl group is involved in complex formation, possibly with the loss of its proton.[8]
Applications
Glycolic acid is used in the textile industry as a dyeing and tanning agent.[9]
Organic synthesis
Glycolic acid is a useful intermediate for organic synthesis, in a range of reactions including: oxidation-reduction, esterification and long chain polymerization. It is used as a monomer in the preparation of polyglycolic acid and other biocompatible copolymers (e.g. PLGA). Commercially, important derivatives include the methyl (CAS# 96-35-5) and ethyl (CAS# 623-50-7) esters which are readily distillable (boiling points 147–149 °C and 158–159 °C, respectively), unlike the parent acid. The butyl ester (b.p. 178–186 °C) is a component of some varnishes, being desirable because it is nonvolatile and has good dissolving properties.[5]
Glycolide is the cyclic dimer, a bislactone, which is used in some of the polymerization processes.
Occurrence
Plants produce glycolic acid during photorespiration. It is recycled by conversion to glycine within the peroxisomes and to tartronic acid semialdehyde within the chloroplasts.[10]
Because photorespiration is a wasteful side reaction in regard to photosynthesis, much effort has been devoted to suppressing its formation. One process converts glycolate into glycerate without using the conventional BASS6 and PLGG1 route; see glycerate pathway.[11][12]
Safety
Glycolic acid is an irritant to the skin.[13] It occurs in all green plants.[5]
References
External links
- ↑ Laurent, Auguste (1848). "Sur les acides amidés et le sucre de gélatine" Template:Webarchive ("On aminated acids and the sugar of gelatine [i.e., glycine]"), Annales de Chimie et de Physique, 3rd series, 23: 110–123. From p. 112: "Appelons ce dernier acide glycolique ... " ("Let us call the latter 'glycolic acid' ...")
- ↑ Socoloff, Nicolaus and Strecker, Adolph (1851) "Untersuchung einiger aus der Hippursäure entstehenden Producte" Template:Webarchive ("Investigation of some products that arise from hippuric acid"), Annalen der Chemie und Pharmacie, 80: 17–43. For their production of glycolic acid, see pp. 34–37. Note: Strecker and Sokolov's empirical formula for glycolic acid (viz, Template:Chem2) was incorrect, because like many chemists at that time, they used the wrong atomic masses for carbon (6 instead of 12) and for oxygen (8 instead of 16).
- ↑ (Socoloff and Strecker, 1851), p. 37. In recognition of Laurent's correct surmise, Strecker and Sokolov named glycolic acid: "Die in dem Barytsalz enthaltene Säure Template:Chem2 oder als Säurehydrat gedacht Template:Chem2 kommt mit der Säure überein, als deren Amidverbindung man das Glycocoll betrachten kann, und welche daher von Laurent den Namen Glycolsäure erhalten hat." (The acid Template:Chem2 contained in the barium salt — or considered as the acid hydrate Template:Chem2 — is consistent with the acid whose amide can be regarded as glycocoll and which therefore obtained from Laurent the name "glycolic acid".)
- ↑ D.J. Loder, U.S. patent 2152852 (1939).
- ↑ a b c Template:Ullmann
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