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| Name | salicylic acid | acetylsalicylic acid (aspirin) |
|---|---|---|
| Systematic name | 2-hydroxybenzoic acid | 2-acetoxybenzoic acid |
| Formula | C6H4(OH)CO2H | C6H4(OCOCH3)CO2H |
| Melting point | 159°C (318°F) | |
| Boiling point | 211°C (412°F) | |
| Color | white, crystalline | |
| Structure |
Salicylic acid is a colorless, crystalline organic carboxylic acid. It is usually prepared by Kolbe synthesis (aka Kolbe-Schmitt reaction), which works by heating sodium phenolate (the sodium salt of phenol) with carbon dioxide under pressure (100 atm, 125°C), then treating it with sulfuric acid.
Salicylic acid is also found in plants, especially in fruit, in the form of methyl salicylate. It is toxic if digested in large quantities, but in small quantities is used as a food preservative and antiseptic in toothpaste. The carboxyl group (-COOH) can react with alcohols, forming several useful esters. The hydroxyl group (-OH) can react with acetic acid to acetylsalicylic acid.
Salicylic acid is the active ingredient in many skin-care products for the treatment of acne. It helps acne by causing skin cells to slough off more readily, preventing pores from clogging up.
Acetylsalicylic acid (ASA) can be prepared by the esterification of the phenolic hydroxyl group of salicylic acid. It is used in medicine as an analgesic, as an anti-inflammatory agent, and as an antipyretic compound. Acetylsalicylic acid is usually known by the name Aspirin, although that is a trademark of Bayer AG in North America; see Aspirin for medical information.
The medicinal properties of acetylsalicylate were observed in 1763 by a clergyman called Edmund Stone, who lived in Chipping Norton in England. Stone wrote to the president of the Royal Society describing his discovery that powdered willow bark helped treat the "agues", or fevers affecting people who lived near rivers. Willow trees commonly grew on river banks, and Stone argued that this was evidence of the doctrine of signatures, an unscientific but commonly accepted idea of the time that includes the notion that nature provides information about its remedies by virtue of where they are located. The name Salicylic acid is derived from the latin name for the Willow tree - Salix.
Stone's discovery helped drive the development of one of the most widely used drugs of today: aspirin.
"Vitamin S" is a proposed alternative name for salicylate, which would have the effect of classifying it as a vitamin. There is no generally agreed definition of what constitutes a vitamin, though salicylate meets at least one of the requirements:
This last point is controversial because salicylate deficiency, unlike, say, Vitamin C deficiency, which causes scurvy, does not result in any particular known symptoms. A low salicylate intake seems to be related to longer term problems, resulting in higher risks of age-related chronic diseases.
Whereas most vitamins are an enzyme cofactors, promoting cellular biochemical reactions - Vitamin C boosts production of collagen - salicylate is not, but then nor is Vitamin E, which is an antioxidant, like salicylate.
Lack of salicylate appears to predispose humans to:
It can be argued that salicylate has a better claim to be called a vitamin than vitamins A and D.
Whether or not you choose to call aspirin a vitamin, there is still a case to be made that salicylate is an important micronutrient.
It also functions as a plant hormone. see Salicylic acid (plant hormone)
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