Salicylic acid
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2008-07-01T14:56:17Z
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/* Other uses */ wikify
{{Chembox new
| Name = Salicylic acid
| ImageFileL1 = Salicylic-acid-skeletal.svg
| ImageSizeL1 = 120px
| ImageFileR1 = Salicylic-acid-3D-balls.png
| ImageSizeR1 = 120px
| IUPACName = 2-Hydroxybenzoic acid
| Section1 = {{Chembox Identifiers
| CASNo = 69-72-7
| EINECS = 200-712-3
| SMILES = OC(=O)c1ccccc1O
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>7</sub>H<sub>6</sub>O<sub>3</sub>
| MolarMass = 138.123 g/mol
| MeltingPt = 159 °C
| BoilingPt = 211 °C (2666 Pa)
| Density = 1.44 g/cm³ (at 20 °C)
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Methyl salicylate]],<br/>[[Benzoic acid]],<br/>[[Phenol]], [[Aspirin]],<br/>[[4-Hydroxybenzoic acid]],<br/> [[Magnesium salicylate]],<br/>[[Bismuth subsalicylate|Bismuth subsalicylate (Pepto Bismol)]],<br/>[[Sulfosalicylic acid]]
}}
}}
'''Salicylic acid''' (from the Latin word for the willow tree, ''[[Salix]]'', from whose bark it can be obtained) is a [[beta hydroxy acid]] (BHA) with the [[chemical formula|formula]] C<sub>6</sub>H<sub>4</sub>(OH)CO<sub>2</sub>H, where the OH group is adjacent to the [[carboxylic acid|carboxyl group]]. This colorless crystalline organic [[acid]] is widely used in [[organic synthesis]] and functions as a [[plant hormone]]. It is derived from the metabolism of [[salicin]]. It is probably best known as a compound that is chemically similar to but not identical to the active component of [[aspirin]] (''acetylsalicylic acid''). In fact, salicylic acid is a metabolite of [[aspirin]], the product of esterase hydrolysis in the liver.
==Plant Hormone==
Salicylic acid (SA) is a [[phytohormone]]; and a [[phenol]], ubiquitous in plants generating a significant impact on plant growth and development, [[photosynthesis]], [[transpiration]], [[ion]] uptake and transport and also induces specific changes in leaf anatomy and [[chloroplast]] structure. SA is recognized as an [[endogenous]] signal, mediating in plant defense, against [[pathogens]]<ref>{{cite book | title = Salicylic acid - A Plant Hormone | author = S. Hayat, A. Ahmad | isbn = 1402051832| year = 2007 | publisher = [[Springer Science+Business Media|Springer]]}}</ref> It plays a role in the resistance of pathogens by inducing the production of 'pathogenesis-related proteins'. It is involved in the [[systemic acquired resistance]] [SAR] in which a pathogenic attack on older leaves causes the development of resistance in younger leaves, though whether SA is the transmitted signal is debatable. SA is the [[calorigenic]] substance that causes [[thermogenesis]] in ''[[Arum]]'' flowers.<ref>{{cite book | last = Davies | first = Peter J. | title = Plant Hormones: Biosynthesis, Signal Transduction, Action! | publisher = [[Springer Science+Business Media|Springer]] | date = 2004 | pages = 13 | isbn = 1402026846}}</ref>
==Production==
Salicylic acid is an organic acid [[biosynthesis|biosynthesize]]d from the amino acid [[phenylalanine]].
[[Sodium salicylate]] is commercially prepared by treating sodium [[phenol|phenoxide]] with a high pressure of [[carbon dioxide]] at high temperature via the [[Kolbe-Schmitt reaction]]. Acidification of the product solution gives salicylic acid:
:[[Image:Kolbe-Schmitt.png|left|400px]]<br clear=left/>
It can be prepared by the [[hydrolysis]] of [[Aspirin]] (acetylsalicylic acid)<ref>{{cite web | title=Hydrolysis of ASA to SA | url=http://www.crscientific.com/article-aspirin.html | accessmonthday=July 31 | accessyear=2007 }}</ref> or [[methyl salicylate]] (Oil of Wintergreen) with a strong acid or base.
==Analysis==
Salicylic acid is an [[enol]] of a β-[[keto carbonic acid]] and therefore forms purple complexes with iron(III) salts:
[[Image:Betaketocarbonicacid iron complex.png|450px]]
This tris(chelate) complex forms more readily in basic solution.
==History==
{{main|History of aspirin}}
[[Image:Thomé Salix alba clean.jpg|thumb|250px|White willow (''Salix alba'') is a natural source of salicylic acid]]
The [[Hellenic civilization|Greek]] physician [[Hippocrates]] wrote in the 5th century BC about a bitter powder extracted from [[willow]] bark that could ease aches and pains and reduce fevers. This remedy was also mentioned in texts from ancient [[Sumer]], [[Lebanon]], and [[Assyria]]. The [[Cherokee]] and other Native Americans used an infusion of the bark for fever and other medicinal purposes for centuries.<ref>Paul B. Hemel and Mary U. Chiltoskey, ''Cherokee Plants and Their Uses -- A 400 Year History,'' Sylva, NC: Herald Publishing Co. (1975); cited in Dan Moerman, A Database of Foods, Drugs, Dyes and Fibers of Native American Peoples, Derived from Plants.[http://herb.umd.umich.edu/] A search of this database for "salix AND medicine" finds 63 entries.</ref> The medicinal part of the plant is the inner bark and was used as a pain reliever for a variety of ailments. The [[Reverend Edward (Edmund) Stone]], a vicar from [[Chipping Norton, Oxfordshire]], [[England]], noted in 1763 that the bark of the willow was effective in reducing a fever.<ref name="RoyalSoc1763EdmundStone">{{cite journal | author=Stone, E | title=An Account of the Success of the Bark of the Willow in the Cure of Agues | journal=Philosophical Transactions | year=1763 | pages=195–200 | volume=53 | url=http://www.journals.royalsoc.ac.uk/openurl.asp?genre=article&issn=0260-7085&volume=53&spage=195}}</ref>
The active extract of the bark, called ''[[salicin]]'', after the [[Latin]] name for the white willow (''[[Salix alba]]''), was isolated in crystalline form in 1828 by [[Henri Leroux]], a [[France|French]] pharmacist, and [[Raffaele Piria]], an [[Italy|Italian]] chemist. Piria was able to convert the substance into a sugar and a second component, which on oxidation becomes [[salicylic acid]].
Salicylic acid was also isolated from the herb [[meadowsweet]] (''[[Filipendula|Filipendula ulmaria]]'', formerly classified as ''[[Spiraea|Spiraea ulmaria]]'') by German researchers in 1839. While their extract was somewhat effective, it also caused digestive problems such as [[gastric]] irritation, bleeding, [[diarrhea]], and even death when consumed in high doses.
==Medicinal and cosmetic uses==
Also known as 2-hydroxybenzoic acid, one of several beta hydroxy acids (compare to [[Alpha hydroxy acid|AHA]]), salicylic acid is a key ingredient in many skin-care products for the treatment of [[Acne vulgaris|acne]], [[psoriasis]], [[callus]]es, [[callus|corns]], [[keratosis pilaris]], and [[wart]]s. It works by causing the cells of the [[Epidermis (skin)|epidermis]] to slough off more readily, preventing [[sebaceous gland|pores]] from clogging up, and allowing room for new cell growth. Because of its effect on skin cells, salicylic acid is used in several [[shampoo]]s used to treat [[dandruff]]. Salicylic acid is also used as an active ingredient in gels which remove [[wart]]s. Use of concentrated solutions of salicylic acid may cause [[hyperpigmentation]] on unpretreated skin for those with darker skin types ([[Fitzpatrick scale|Fitzpatrick]] phototypes IV, V, VI), as well as with the lack of use of a broad spectrum sunblock.<ref>{{cite journal|title=The Safety and Efficacy of Salicylic Acid Chemical Peels in Darker Racial-ethnic Groups| author= Grimes P.E.|journal= Dermatologic Surgery| volume= 25|year= 1999| pages =18–22 | doi = 10.1046/j.1524-4725.1999.08145.x <!--Retrieved from CrossRef by DOI bot-->}}</ref><ref>{{cite journal|title= Chemical peeling in ethnic/dark skin| author= Roberts W. E. |journal=Dermatologic Therapy |volume= 17|issue= 2| pages= 196|year= 2004|doi= 10.1111/j.1396-0296.2004.04020.x}}</ref>
The medicinal properties of salicylate, mainly for [[fever]] relief, have been known since [[1763|ancient times]], and it was used as an anti-inflammatory drug.<ref>{{cite journal|title=Brief History of Antipyretic Therapy|author=Philip A. Mackowiak|journal=Clinical Infectious Diseases,| volume= 31|year=2000 |pages= 154–156|doi= 10.1086/317510}}</ref>
[[Image:Salicylic acid pads.jpg|thumb|right|[[Cotton]] pads soaked in salicylic acid can be used to chemically [[Exfoliation (cosmetology)|exfoliate]] skin]]
[[Aspirin]] (acetylsalicylic acid or ASA) can be prepared by the [[esterification]] of the phenolic hydroxyl group of salicylic acid.
Subsalicylate in combination with [[bismuth]] form the popular stomach relief aid known commonly as [[Bismuth subsalicylate|Pepto-Bismol]]. When combined, the two key ingredients help control [[diarrhea]], nausea, heartburn, and gas. It is also a very mild [[antibiotic]].
[[Choline]] salicylate is used topically to relieve the pain of [[aphthous ulcer]]s.
==Other uses==
*Although toxic in large quantities, salicylic acid is used as a [[food preservative]] and [[antiseptic]] in [[toothpaste]]. For some people with [[salicylate sensitivity]] even these small doses can be harmful.
*Sodium salicylate is a useful [[phosphor]] in the [[vacuum ultraviolet]] with nearly flat quantum efficiency for wavelengths between 10 to 100 nm.<ref>JAR Samson ''Techniques of Vacuum Ultraviolet Spectroscopy''</ref> It fluoresces in the blue at 420 nm. It is easily prepared on a clean surface by spraying a saturated solution of the salt in [[methanol]] followed by evaporation.
* [[Methyl salicylate]] is used an a [[liniment]], to soothe joint and muscle pain.
==Safety==
Salicylic acid has an [[ototoxic]] effect by inhibiting [[prestin]].<ref>{{cite journal |
journal = [[HNO]] | year = 2004 | volume = 52 | issue = 4 | pages = 347–51 | title = Reversible hearing loss in acute salicylate intoxication | author = Wecker, H.; Laubert, A. | language = German | pmid = 15143764}}</ref> It can induce transient hearing loss in [[zinc]]-deficient individuals.
This finding is based on clinical studies with [[rat]]s. An injection of salicylic acid induced hearing loss in zinc-deficient rats, while a simultaneous injection of zinc reversed the hearing loss. An injection of [[magnesium]] in the zinc-deficient rats did not reverse the salicylic acid-induced hearing loss.
Salicylic acid is toxic in large amounts. Pregnant women are advised not to use products containing salicylic acid due to the danger of [[Reye's syndrome]].
Some people are [[Salicylate sensitivity|hypersensitive to salicylic acid and related compounds]].
The United States [[Food and Drug Administration]] recommends the use of sun protection when using skincare products containing salicylic acid (or any other BHA) on sun-exposed skin areas.<ref>{{cite web |url=http://www.cfsan.fda.gov/~dms/cos-bha.html|title=Beta Hydroxy Acids in Cosmetics |accessdate=2007-11-23 |format= |work=}}</ref>
==Footnotes==
{{reflist}}
{{Acne Agents}}
{{Ancient anaesthesia-footer}}
{{Antifungals}}
{{NSAIDs}}
{{Analgesics}}
{{Plant hormones}}
[[Category:Non-steroidal anti-inflammatory drugs]]
[[Category:Analgesics]]
[[Category:Antiseptics]]
[[Category:Benzoic acids]]
[[Category:Dermatological preparations]]
[[Category:Hydroxy acids]]
[[Category:Keratolytics]]
[[Category:Phenols]]
[[Category:Plant hormones]]
[[bg:Салицилова киселина]]
[[da:Salicylsyre]]
[[de:Salicylsäure]]
[[es:Ácido salicílico]]
[[fr:Acide salicylique]]
[[ko:살리실산]]
[[it:Acido salicilico]]
[[he:חומצה סליצילית]]
[[lv:Salicilskābe]]
[[hu:Szalicilsav]]
[[ml:സാലിസിലിക് അമ്ലം]]
[[nl:Salicylzuur]]
[[ja:サリチル酸]]
[[pl:Kwas salicylowy]]
[[pt:Ácido salicílico]]
[[ru:Салициловая кислота]]
[[simple:Salicylic acid]]
[[sv:Salicylsyra]]
[[tr:Salisilik asit]]
[[zh:水楊酸]]