Salicylic acid

• 2- Hydroxybenzencarbonsäure (IUPAC)
• 2- hydroxybenzoic acid
• Ortho -hydroxybenzoic acid
• O- hydroxybenzoic acid
• Spirsäure
• Spiroylsäure

• D01AE12
• S01BC08

Colorless and odorless, sweet-and- sour-tasting scratching crystals with an unpleasant aftertaste

Fixed

1.44 g · cm -3

158.3 ° C

211 ° C (27 hPa)

• PKsCOOH = 2.75
• PKsOH = 12.38

• Well in ethanol ( 496 g · l-1 at 15 ° C )
• Poorly in cold water ( 2 g · l-1 at 20 ° C)

Risk

• 400 mg · kg -1 ( LD50, cat, oral)
• 480 mg · kg -1 ( LD50, mouse, oral)
• 1300 mg · kg -1 ( LD50, rabbit, oral)
• 891 mg · kg -1 ( LD50, rat, oral)
• > 2000 mg · kg -1 ( LD50, rat, transdermal)
• 57 mg · kg -1 ( TDLo, man, transdermal)
• 111 mg · kg -1 ( TDLo 10 days, woman, transdermal)

Template: Infobox chemical / molecular formula search available

Salicylic acid (o- hydroxybenzoic acid ) comes in the form of its methyl ester in essential oils and as a plant hormone in the leaves, flowers and roots of various plants and is used for plant defense against pathogens of importance. It got its name because it was once mainly by the oxidative treatment of salicin, which is contained in the bark of various willows ( Salix spec scientifically. ) Won.

It is also known under the name Spirsäure, because it can be made ​​from the sap of the plant Spier, also meadowsweet, won. From the name Spirsäure also the brand name Aspirin is derived from the aspirin: Acetylspirsäure. The salts of salicylic acid are called salicylates.

Chemical classification

Salicylic acid is one of the aromatics due to the presence of benzene ring. As it contains a carboxyl and hydroxyl group, it is one of the hydroxycarboxylic acids. Due to the resistance of the β - carboxy to hydroxy, it can be also referred to as β - hydroxy carboxylic acid. Since the hydroxyl group is bonded directly to the aromatic benzene ring, it is also one of the phenols.

Representation and extraction

Technically it is determined by the Kolbe -Schmitt reaction (or simply as salicylic acid synthesis) from carbon dioxide and sodium prepared. This artificial production, the production from willow bark largely obsolete.

Already in 1874 the synthesis of salicylic acid was transferred from an idea by Hermann Kolbe from the laboratory to the factory-like production, the Schmitt -student Friedrich von Heyden Salicylsäurefabrik Dr. F. von Heyden founded in Dresden, who moved to Radebeul a year later.

Properties and Uses

During the fast, strong heating salicylic acid is decarboxylated to form phenol.

The - in comparison with other hydroxy benzoic acids - high acidity is due to the stabilization of the anion by a hydrogen bond with the adjacent hydroxyl group.

Salicylic acid is used to produce color and fragrances and of acetylsalicylic acid (ASA, better known under the brand name aspirin), which is used as analgesic, anti-inflammatory and blood-thinning drug. In the form of the insoluble salt of bismuth subsalicylate it is used against diarrhea and disorders of the gastrointestinal tract.

Salicylic acid also has an antimicrobial effect, its use as a preservative in food, however, is prohibited. Up to 2 % concentration, it is often a component of cosmetics.

From 5% salicylic acid solution shows sufficient for the treatment of acne kerato - and thus comedolytic effect. In a 10% solution, it is used for the treatment of corns, warts.

The plasma half-life of salicylic acid is approximately 2-3 hours.

Proof

Salicylic acid, formally, the enol (in this case, a phenol ) of a β -ketocarboxylic acid, and therefore is formed with iron ( III) chloride solution, a violet colored complex, tris - salicylate, iron ( III) complex:

This evidence is not specific, since similar compounds such as ethyl acetoacetate have the same reaction.

Adverse effects and toxicity

On the skin, mucous membranes and eyes for salicylic acid in the acute irritant to gewebsschädigend. Furthermore, the acid causes the case of oral ingestion or other attenuation of the respiratory center and a fault of important metabolic processes as well as the central nervous system. In chronic exposure, disturbances of the gastrointestinal tract show.

Salicylic acid is a metabolite of aspirin, which is rapidly hydrolyzed in the organism. Side effects are especially allergic reactions, bleeding, bronchoconstriction ( asthma ), gastric mucosal injury with bleeding, in individual cases, liver damage. Also, uric acid retention, hyperuricemia and renal damage were observed. An important pathway in the liver via the conversion to salicyluric acid.

In animal experiments showed salicylic acid for oral and dermal administration variety of effects on animals (cat, mouse, rabbit and rat) as drowsiness, muscle weakness and organ damage in liver and kidney. The acute oral toxicity LD50 was 400-1300 mg / kg in the rat dermal at 2 g / kg.

In humans, the dermal route TDLo values ​​were determined 57-111 mg / kg.

Esters of salicylic acid

Salicylic acid reacts with an alcohol, the result is the elimination of water a carboxylic acid ester or a salicylate. They may also form esters with organic acids, which then act as the alcohol in the reaction. Salicylic acid is mainly used in the cosmetics and perfume industry as anti-inflammatory drugs in bath salts, ointments or creams, as well as fragrances and as UV filters in sunscreens. Probably the best known is acetylsalicylic acid esters of salicylic acid. Here, the hydroxyl group of salicylic acid was esterified with the carboxyl group of acetic acid. Other relevant salicylic acid are methyl salicylate, ethyl salicylate, benzyl salicylate, Salicylsäureisobutylester, Salicylsäureisopentylester, phenyl salicylate and Salicylsäurehydroxyethylester.

Derivatives

By bromination with elemental bromine in glacial acetic acid produced the 3.5 - dibromosalicylic acid whose copper salt is used as a fungicide and bactericide.

By iodination with iodine chloride to give the 3,5- Diiodsalicylsäure biochemically relevant. At the 4-position of halogenated salicylic acid derivatives, such as 4- Iodsalicylsäure can not be obtained in a direct way.