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Salicylic acid

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Salicylic acid
Names
IUPAC name
2-Hydroxybenzoic acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.000.648 Edit this at Wikidata
EC Number
  • 200-712-3
KEGG
UNII
  • InChI=1S/C7H6O3/c8-6-4-2-1-3-5(6)7(9)10/h1-4,8H,(H,9,10) checkY
    Key: YGSDEFSMJLZEOE-UHFFFAOYSA-N checkY
  • InChI=1/C7H6O3/c8-6-4-2-1-3-5(6)7(9)10/h1-4,8H,(H,9,10)
    Key: YGSDEFSMJLZEOE-UHFFFAOYAQ
  • c1ccc(c(c1)C(=O)O)O
Properties
C7H6O3
Molar mass 138.122 g·mol−1
Density 1.443 g/cm3
Melting point 159.0 °C (318.2 °F; 432.1 K)
Boiling point 211 °C (412 °F; 484 K)
0.2 g/100 mL (20 °C)
Acidity (pKa) 2.97[1]
Related compounds
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
1
0
Flash point 157 °C
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Salicylic acid (from Latin salix, willow tree, from the bark of which the substance used to be obtained) is a monohydroxybenzoic acid, a type of phenolic acid and a beta hydroxy acid. 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. In addition to being a compound that is chemically similar to but not identical to the active component of aspirin (acetylsalicylic acid), it is probably best known for its use in anti-acne treatments. The salts and esters of salicylic acid are known as salicylates.

Chemistry

Salicylic acid has the formula C6H4(OH)COOH, where the OH group is ortho to the carboxyl group. It is also known as 2-hydroxybenzenecarboxylic acid. It is poorly soluble in water (0.2 g/100 ml H2O at 20 °C).[2] Aspirin (acetylsalicylic acid or ASA) can be prepared by the esterification of the phenolic hydroxyl group of salicylic acid with the acetyl group from acetic anhydride or acetyl chloride.

Plant hormone

Salicylic acid (SA) is a phenolic phytohormone and is found in plants with roles in plant growth and development, photosynthesis, transpiration, ion uptake and transport. SA also induces specific changes in leaf anatomy and chloroplast structure. SA is involved in endogenous signaling, mediating in plant defense against pathogens.[3] It plays a role in the resistance to pathogens by inducing the production of pathogenesis-related proteins.[4] It is involved in the systemic acquired resistance (SAR) in which a pathogenic attack on one part of the plant induces resistance in other parts. The signal can also move to nearby plants by salicylic acid being converted to the volatile ester, methyl salicylate.[5]

Production

Salicylic acid is biosynthesized from the amino acid phenylalanine. In Arabidopsis thaliana it can also be synthesized via a phenylalanine-independent pathway.

Sodium salicylate is commercially prepared by treating sodium phenolate (the sodium salt of phenol) with carbon dioxide at high pressure (100 atm) and high temperature (390K) -a method known as the Kolbe-Schmitt reaction. Acidification of the product with sulfuric acid gives salicylic acid:

It can also be prepared by the hydrolysis of aspirin (acetylsalicylic acid)[6] or methyl salicylate (oil of wintergreen) with a strong acid or base.

History

Main article: History of aspirin
White willow (Salix alba) is a natural source of salicylic acid

The 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.[citation needed] This remedy was also mentioned in texts from ancient Sumer, Lebanon, and Assyria.[citation needed] The Cherokee and other Native Americans used an infusion of the bark for fever and other medicinal purposes for centuries.[7] 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 Stone, a vicar from Chipping Norton, Oxfordshire, England, noted in 1763 that the bark of the willow was effective in reducing a fever.[8]

The active extract of the bark, called salicin, after the Latin name for the white willow (Salix alba), was isolated and named by the German chemist Johann Andreas Buchner in 1826. A larger amount of the substance was isolated in 1828 by Henri Leroux, a French pharmacist. Raffaele Piria, an Italian chemist was able to convert the substance into a sugar and a second component, which on oxidation becomes salicylic acid.[9]

Salicylic acid was also isolated from the herb meadowsweet (Filipendula ulmaria, formerly classified as 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.

Dietary sources

Fruits and vegetables are natural sources of salicylic acid, particularly blackberries, blueberries, cantaloupes, dates, raisins, guavas, apricots, green pepper, olives, tomatoes, radish, mushrooms and chicory. Some herbs and spices contain quite high amounts, although meat, poultry, fish, eggs and dairy products all have little to no salicylates. Of the legumes, seeds, nuts, and cereals, only almonds, water chestnuts and peanuts have significant amounts.[10]

Medicinal and cosmetic uses

Salicylic acid is known for its ability to ease aches and pains and reduce fevers. These medicinal properties, particularly fever relief, have been known since ancient times, and it is used as an anti-inflammatory drug.[11] Some researchers[who?] believe that salicylate is an essential micronutrient in the human diet, potentially qualifying as a vitamin, namely Vitamin S.[12]

In modern medicine, salicylic acid and its derivatives are used as constituents of some rubefacient products. For example, methyl salicylate is used as a liniment to soothe joint and muscle pain, and choline salicylate is used topically to relieve the pain of aphthous ulcers.

Cotton pads soaked in salicylic acid can be used to chemically exfoliate skin

As with other beta hydroxy acids, salicylic acid is a key ingredient in many skin-care products for the treatment of Seborrhoeic dermatitis, acne, psoriasis, calluses, corns, keratosis pilaris, and warts.[13] The standard treatment for calluses is a 6% aspirin suspension in vaseline, applied on the callus for one hour and then removed with washing. It works as a keratolytic, bacteriocide and comedolytic agent by causing the cells of the epidermis to shed more readily, opening clogged pores and neutralizing bacteria within, preventing pores from clogging up again by constricting pore diameter, and allowing room for new cell growth.[14] Because of its effect on skin cells, salicylic acid is used in several shampoos used to treat dandruff. Use of concentrated solutions of salicylic acid may cause hyperpigmentation on unpretreated skin for those with darker skin types (Fitzpatrick phototypes IV, V, VI), as well as with the lack of use of a broad spectrum sunblock.[15][16]

Bismuth subsalicylate, a salt of bismuth and salicylic acid, is the active ingredient in stomach relief aids such as Pepto-Bismol.[citation needed]

Mechanism of action

One effect of salicylic acid is to activate AMP-activated protein kinase, and this has been suggested as a possible explanation for some of the effects of both salicylic acid and aspirin.[17][18]

Other uses

Although toxic in large quantities, salicylic acid is used as a food preservative and as bactericidal and an antiseptic.[19] For some people with salicylate sensitivity even these small doses can be harmful. [citation needed]

Sodium salicylate is a useful phosphor in the vacuum ultraviolet with nearly flat quantum efficiency for wavelengths between 10 to 100 nm.[20] 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.

Safety

Topically, as a beta-hydroxy acid (and unlike alpha-hydroxy acids) salicylic acid is capable of penetrating and breaking-down fats and lipids, making it capable of causing moderate chemical burns of the skin if at very high concentrations (such as near or actually the majority ingredient) within a solvent. It is capable of damaging the lining of pores in such cases if the solvent is alcohol, acetone, or an oil. Over-the-counter limits are set at 2% for topical left on the face and 3% for those expected to be washed off, such as acne cleansers or shampoo. Caution should be exercised when handling large volumes of salicylic acid, and protective gloves are recommended for any repeat, prolonged exposure. 17% salicylic acid, which is often sold for wart removal, should not be applied to the face and should not be used for acne treatment. Even for wart removal, such a solution should only be applied twice a day - more frequent use may lead to an increase in side effects without an increase in efficacy.[21]

When ingested, salicylic acid has a possible ototoxic effect by inhibiting prestin.[22] It can induce transient hearing loss in zinc-deficient individuals. This finding is based on clinical studies with rats. 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.

There are no studies specifically looking at topical salicylic acid in pregnancy. Oral salicylic acid has not been associated with an increase in malformations if used during the first trimester, but use in late pregnancy has been associated with bleeding, especially intracranial bleeding.[23] The risks of aspirin late in pregnancy are probably not relevant for a topical exposure to salicylic acid, even late in the pregnancy, because of its low systemic levels. Topical salicylic acid is common in many over-the-counter dermatological agents, and the lack of adverse reports suggests a low teratogenic potential.[24]

Salicylic acid overdose can lead to salicylate intoxication, which often presents clinically in a state of metabolic acidosis with compensatory respiratory alkalosis. In patients presenting with an acute overdose, a 16% morbidity rate and a 1% mortality rate are observed.[25]

Some people are 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.[26]

There is data that supports an association between exposure to salicylic acid and Reye's Syndrome. The National Reye's Syndrome Foundation cautions against the usage of these substances, and other substances similar to aspirin, on children and adolescents.

Epidemiological research has shown an association between the development of Reye's Syndrome and the use of aspirin (a salicylate compound) for treating the symptoms of influenza-like illnesses, chicken pox, colds, etc.

The U.S. Surgeon General, the Food and Drug Administration, the Centers for Disease Control and Prevention, and the American Academy of Pediatrics recommend that aspirin and combination products containing aspirin not be given to children under 19 years of age during episodes of fever-causing illnesses, because of a concern about Reye's Syndrome.[27]

See also

Footnotes

  1. ^ pKa from drugbank
  2. ^ "Salicilyc acid". Retrieved 2008-10-13.
  3. ^ S. Hayat, A. Ahmad (2007). Salicylic acid - A Plant Hormone. Springer. ISBN 1-4020-5183-2.
  4. ^ HOOFT VAN HUIJSDUIJNEN. "Induction by Salicylic Acid of Pathogenesis-related Proteins and Resistance to Alfalfa Mosaic Virus Infection in Various Plant Species" (PDF). Retrieved 2009-05-28. {{cite journal}}: Cite journal requires |journal= (help)
  5. ^ Plant Physiology Third Edition, Taiz and Zeiger, 2002, page 306
  6. ^ "Hydrolysis of ASA to SA". Retrieved July 31, 2007.
  7. ^ 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.[1] A search of this database for "salix AND medicine" finds 63 entries.
  8. ^ Stone, E (1763). "An Account of the Success of the Bark of the Willow in the Cure of Agues". Philosophical Transactions. 53: 195–200. doi:10.1098/rstl.1763.0033.
  9. ^ Diarmuid Jeffreys. (2005). Aspirin : the remarkable story of a wonder drug. New York, NY: Bloomsbury. pp. 38–40. ISBN 978-1-58234-600-7.
  10. ^ http://www.food-info.net/uk/qa/qa-fi27.htm
  11. ^ Philip A. Mackowiak (2000). "Brief History of Antipyretic Therapy". Clinical Infectious Diseases,. 31: 154–156. doi:10.1086/317510. PMID 11113017.{{cite journal}}: CS1 maint: extra punctuation (link)
  12. ^ Kamran Abbasi (2003). "Rapid Responses to: Aspirin protects women at risk of pre-eclampsia without causing bleeding". British Medical Journal. 327 (7424): 7424. doi:10.1136/bmj.327.7424.0-h.[dead link]
  13. ^ http://www3.interscience.wiley.com/journal/119449119/abstract?CRETRY=1&SRETRY=0
  14. ^ Salicylic Acid Essential Actives, KAVI.
  15. ^ Grimes P.E. (1999). "The Safety and Efficacy of Salicylic Acid Chemical Peels in Darker Racial-ethnic Groups". Dermatologic Surgery. 25 (1): 18–22. doi:10.1046/j.1524-4725.1999.08145.x. PMID 9935087.
  16. ^ Roberts W. E. (2004). "Chemical peeling in ethnic/dark skin". Dermatologic Therapy. 17 (2): 196. doi:10.1111/j.1396-0296.2004.04020.x. PMID 15113287. {{cite journal}}: More than one of |pages= and |page= specified (help)
  17. ^ "The Ancient Drug Salicylate Directly Activates AMP-Activated Protein Kinase" by Simon Hawley et al., Science, Published online April 19, 2012.
  18. ^ "Clues to aspirin's anti-cancer effects revealed" by Lisa Raffensperger, New Scientist online, 19 April 2012.
  19. ^ "Definition of Salicylic acid". MedicineNet.com.
  20. ^ JAR Samson Techniques of Vacuum Ultraviolet Spectroscopy
  21. ^ " salicylic acid 17 % Topical Liquid." Kaiser Permanente Drug Encyclopedia. Accessed 28 Sept 2011. https://members.kaiserpermanente.org/kpweb/drugency/drugdetails.do?drugID=213643&name=salicylic+acid+17+%25+Topical+Liquid&index=true
  22. ^ Wecker, H.; Laubert, A. (2004). "Reversible hearing loss in acute salicylate intoxication". HNO (in German). 52 (4): 347–51. doi:10.1007/s00106-004-1065-5. PMID 15143764.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. ^ Rumack, Cm; Guggenheim, Ma; Rumack, Bh; Peterson, Rg; Johnson, Ml; Braithwaite, Wr (1981). "Neonatal intracranial hemorrhage and maternal use of aspirin". Obstetrics and gynecology. 58 (5 Suppl): 52S–6S. ISSN 0029-7844. PMID 7312229. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  24. ^ Acne and Pregnancy
  25. ^ http://emedicine.medscape.com/article/818242-overview
  26. ^ "Beta Hydroxy Acids in Cosmetics". Archived from the original on 2007-12-21. Retrieved 2007-11-23.
  27. ^ "Aspirin / Salicylates and Reye's Syndrome". Retrieved 2009-05-22.
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