α-Hydroxy acids arestronger acids compared to their non-alpha hydroxy counterparts, a property enhanced by internalhydrogen bonding.[2][3][4] AHAs serve a dual purpose: industrially, they are utilized as additives in animal feed and as precursors for polymer synthesis.[5][6][7][8] In cosmetics, they are commonly used for their ability to chemically exfoliate the skin.[9]
Aldonic acids, a type ofsugar acid, are a class of naturally occurring hydroxycarboxylic acids. They have the general chemical formula, HO2C(CHOH)nCH2OH.Gluconic acid, a particularly common aldonic acid, the oxidized derivative ofglucose.
One common synthesis route involves thehydrolysis of α-halocarboxylic acids, readily available precursors, to produce 2-hydroxycarboxylic acids. For instance, the production of glycolic acid typically follows this method, utilizing a base-induced reaction, followed by acid workup. Similarly, unsaturated acids andfumarate andmaleate esters undergo hydration to yieldmalic acid derivatives from esters, and3-hydroxypropionic acid fromacrylic acid.[11]
The synthesis and utilization ofpolymers based onlactic acid, includingpolylactic acid (PLA) and its cyclic esterlactide, are used in the creation of biodegradable materials such asmedical implants,drug delivery systems, andsutures.[6] Similarly,glycolic acid serves as a foundation for the development of poly(glycolic acid), spelledpolyglycolide (PGA), a polymer distinguished by its high crystallinity, thermal stability, and mechanical strength, despite its synthetic origins.[5] Both PLA and PGA are fully biodegradable.[7]
α-Hydroxy acids, such as glycolic acid, lactic acid, citric acid, and mandelic acid, serve as precursors inorganic synthesis, playing a role in the industrial-scale preparation of various compounds.[11][17] These acids are used when synthesizingaldehydes throughoxidative cleavage.[18][19] α-Hydroxy acids are particularly prone to acid-catalyzeddecarbonylation, yieldingcarbon monoxide, aketone or aldehyde, and water as by-products.[20]
Alpha hydroxy acids are generally safe when used on the skin as a cosmetic agent using the recommended dosage. The most common side-effects are mild skin irritations, redness and flaking.[9] The United StatesFood and Drug Administration (FDA) andCosmetic Ingredient Review expert panels both suggest that alpha hydroxy acids are safe to use as long as they are sold at low concentrations,pH levels greater than 3.5, and include thorough safety instructions.[9]
The FDA has warned consumers that care should be taken when using alpha hydroxy acids after an industry-sponsored study found that they can increase thelikelihood of sunburns.[9] This effect is reversible after stopping the use of alpha hydroxy acids. Other sources suggest thatglycolic acid, in particular, may protect from sun damage.[9]
"Alpha Hydroxy Acids for Skin Care".Cosmetic Dermatology, Supplement:1–6. October 1994.
Kalla G, Garg A, Kachhawa D (2001). "Chemical peeling--glycolic acid versus trichloroacetic acid in melasma".Indian Journal of Dermatology, Venereology and Leprology.67 (2):82–4.PMID17664715.
Kempers S, Katz HI, Wildnauer R, Green B (June 1998). "An evaluation of the effect of an alpha hydroxy acid-blend skin cream in the cosmetic improvement of symptoms of moderate to severe xerosis, epidermolytic hyperkeratosis, and ichthyosis".Cutis.61 (6):347–50.PMID9640557.
^Dawson RM, et al. (1959).Data for Biochemical Research. Oxford: Clarendon Press.
^Handbook of Chemistry and Physics, CRC Press, 58th edition, page D147 (1977)
^The strength of the hydrogen bonding is refelected also in theProton nuclear magnetic resonance-spectrum of these compounds: instead of giving rise to a contribution to the broad signal of rapidly exchanged protons (between COOH, OH, NH, etc) in 2-phenyl-2-hydroxyacetic acid (mandelic acid) the proton on the alpha carbon and the proton trapped in the internal hydrogen bridge show a nice pair of doublets instead a singlet (H on alpha-C) and the formentioned broad signal of exchangable protons. So on the NMR-time scale the exchange equilibrium for the alpha-hydroxy group is frozen.
^Vollhardt KP, Schore NE (2018-01-29).Organic chemistry: structure and function (8th ed.). New York: W. H. Freeman, Macmillan Learning.ISBN9781319079451.OCLC1007924903.
^Nwaukwa S, Keehn P (1982). "Oxidative cleavage of α-diols, α-diones, α-hydroxy-ketones and α-hydroxy- and α-keto acids with calcium hypochlorite [Ca(OCl)2]".Tetrahedron Letters.23 (31):3135–3138.doi:10.1016/S0040-4039(00)88578-0.
^Chandler NR (1993).Principles of organic synthesis. Coxon, J. M. (James Morriss), 1941- (3rd. ed.). London: Blackie Academic & Professional.ISBN978-0751401264.OCLC27813843.
