Salicylic acid
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| Salicylic acid | |
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| IUPAC name | 2-Hydroxybenzoic acid |
| Identifiers | |
| CAS number | |
| EINECS number | |
| SMILES | OC(=O)c1ccccc1O |
| Properties | |
| Molecular formula | C7H6O3 |
| Molar mass | 138.123 g/mol |
| Density | 1.44 g/cm³ (at 20 °C) |
| Melting point |
159 °C |
| Boiling point |
211 °C (2666 Pa) |
| Related Compounds | |
| Related compounds | Methyl salicylate, Benzoic acid, Phenol, Aspirin, 4-Hydroxybenzoic acid, Magnesium salicylate, Bismuth subsalicylate (Pepto Bismol), Sulfosalicylic acid |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references | |
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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 formula C6H4(OH)CO2H, where the OH group is adjacent to the 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 but not identical to the active component of aspirin.
Production
Salicylic acid is biosynthesized from the amino acid phenylalanine.
Sodium salicylate is commercially prepared by treating sodium phenoxide with a high pressure of carbon dioxide at high temperature via the Kolbe-Schmitt reaction. Acidification of the product solution gives salicylic acid:
It can be prepared by the hydrolysis of Aspirin (acetylsalicylic acid)[1] or methyl salicylate (Oil of Wintergreen) with a strong acid or base.
Analysis
Salicylic acid is an enol of an β-ketocarbonic acid and therefore forms purple complexes with iron(III) salts:
This tris(chelate) complex forms more readily in basic solution.
History
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. 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.[1] 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.[1]
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 French pharmacist, and Raffaele Piria, an 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 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.
Medicinal and cosmetic uses
Also known as 2-hydroxybenzoic acid, one of several beta hydroxy acids (compare to AHA), salicylic acid is a key ingredient in many skin-care products for the treatment of acne, psoriasis, calluses, corns, keratosis pilaris, and warts. It works by causing the cells of the epidermis to slough off more readily, preventing pores from clogging up, and allowing room for new cell growth. Because of its effect on skin cells, salicylic acid is used in several shampoos used to treat dandruff. Salicylic acid is also used as an active ingredient in gels which remove verrucas (plantar warts). 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.[1][1]
The medicinal properties of salicylate, mainly for fever relief, have been known since ancient times, and it was used as an anti-inflammatory drug.[1]
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 Pepto-Bismol. When combined, the two key ingredients help control diarrhea, nausea, heartburn, and gas. It is also a very mild antibiotic.
Safety
Salicylic acid has an ototoxic effect, and 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.
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 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. [1]
Footnotes
Acne-treating agents (D10) | |
|---|---|
| Topical agents | Azelaic acid • Benzoyl peroxide • Glycolic acid • Light therapy • Salicylic acid • Tea tree oil |
| Antibiotics | Clindamycin • Erythromycin • Sulfacetamide • Tetracyclines • Trimethoprim |
| Hormonal | Antiandrogens • Contraceptives |
| Retinoids | Adapalene • Isotretinoin • Tazarotene • Tretinoin |
Anesthetic: Ancient anaesthesia | |
|---|---|
| Plants/animals | Aconite • Argyreia speciosa • Castoreum • Cannabis • Coca • Deadly nightshade • Henbane • Lactucarium • Mandrake • Metel nut • Opium • Poison hemlock • Saussurea • Toloatzin • Willow |
| People | Abulcasis • Avicenna • Celsus • Dioscorides • Galen • Hippocrates • Rhazes • Sabuncuoğlu • Susrutha • Theophrastus • Zhang |
| Molecules | Aconitine • Δ9-THC • Atropine • Cocaine • Coniine • Hyoscyamine • Morphine • Salicylate • Scopolamine |
Antifungals (D01 and J02) | |
|---|---|
| Antibiotics | Griseofulvin • polyene antimycotics (Natamycin, Nystatin) |
| Topical azoles | imidazoles (Bifonazole, Clomidazole, Clotrimazole, Econazole, Fenticonazole, Ketoconazole, Isoconazole, Miconazole, Oxiconazole, Sertaconazole, Sulconazole, Tioconazole) • triazoles (Fluconazole) • benzimidazole (Thiabendazole) |
| Other topicals | Ciclopirox • Ethylparaben • Flucytosine • Salicylic acid • Selenium sulfide • Tolnaftate • Undecylenic acid • allylamines (Amorolfine, Butenafine, Naftifine, Terbinafine) |
| For systemic use | Griseofulvin • allylamine (Terbinafine) • polyene antimycotic (Amphotericin B) • triazoles (Itraconazole, Posaconazole, Voriconazole) • echinocandins (Anidulafungin, Caspofungin, Micafungin) |
| Other | Tea tree oil • citronella oil • lemon grass • orange oil • patchouli • lemon myrtle |
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Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
