|Molecular formula||C 6 H 6 O|
colorless needle-shaped crystals with a penetrating odor
|External identifiers / databases|
|Molar mass||94.11 g mol −1|
1.07 g cm −3
41 ° C
182 ° C
0.2 hPa (20 ° C)
|pK s value||
moderate in water (84 g l −1 at 20 ° C)
1.5408 (41 ° C)
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C|
Phenol or hydroxybenzene (outdated also carbolic acid or carbol for short ) is an aromatic , organic compound and consists of a phenyl group (–C 6 H 5 ) to which a hydroxyl group (–OH) is attached. The colorless, crystalline solid is an important industrial chemical and is used as an intermediate product, particularly in the manufacture of various plastics . Phenol is the simplest representative of the phenols . Phenol forms salts with bases , the phenolates .
Phenol was discovered in 1834 by the chemist Friedlieb Ferdinand Runge while distilling coal tar ; he called the substance "carbolic acid". Auguste Laurent rediscovered it in 1841 and determined the molecular formula as C 6 H 6 O. Charles Gerhardt called it phenol . The name refers to the coal gas, which was created in addition to coal tar during the production of coke. At that time, illuminating gas ( town gas ) was used to illuminate cities (gr. Phainomai : to shine).
Joseph Lister used it in 1865 - in a five percent solution - as an antiseptic for wound disinfection; At that time carbolic acid was almost the only available remedy for wound infections. Because of its skin-irritating side effects, it was soon replaced by other antiseptics. Because of its bactericidal effect, it was used as a disinfectant and is now replaced by derivatives of phenol.
Phenol is combined with formaldehyde to prepare the phenolic resin - Resins used: under the trademark Bakelite phenolic resin was at the beginning of the 20th century as the first fully-synthetic, industrially produced plastic produced.
Extraction and presentation
Phenols cannot be represented by electrophilic aromatic substitution , since a corresponding oxygen electrophile is not accessible.
Benzene and propene are first converted into isopropylbenzene ( cumene ) by a Friedel-Crafts alkylation in an acid . Cumene is oxidized by oxygen in the air to form the hydroperoxide , which decomposes by acidic work-up with rearrangement to phenol and acetone . The simultaneous creation of two easily separable, valuable products makes this process particularly economical.
Production from renewable raw materials
Research is currently being carried out into ways of producing phenol from renewable raw materials and especially from lignin . Various pyrolysis variants with subsequent product preparation are suitable for this. However, it is estimated that it will take another 10 to 20 years for such phenol production to become commercialized.
Manufacture in the laboratory
Another possibility for representation consists in melting the sodium salt of benzenesulfonic acid with alkali hydroxide in a nucleophilic aromatic substitution according to the addition-elimination mechanism ( ipso-substitution ):
In the sense of a radical substitution , benzene can be converted to phenol in the Fenton reaction . The Baeyer-Villiger oxidation of acetophenone yields phenyl acetate , which liberates phenol after saponification.
Pure phenol forms colorless crystal needles at room temperature, but the commercially available product is usually pink to reddish-brown in color due to slight but intensely colored impurities. The melting point is 41 ° C and the boiling point is 182 ° C. It has a characteristic, aromatic odor. Because of the hydrophilic OH group, phenol is hygroscopic . A limited amount of water dissolves in phenol. With around 6% water, the mixture is liquid at 20 ° C. Phenol is only moderately soluble in water. Between the solutions with high and low phenol content, there is a miscibility gap . Phenol liquefied with water was called Phenolum liquefactum in the medical field .
The hydroxyl group of phenol is more acidic than alcohol ; therefore phenol is a weak organic acid . The cause is the mesomerism stabilization of the corresponding base of the phenol ionic ion. The negative charge can be delocalized into the ring.
In contrast to alcohols, phenols only enter into nucleophilic substitution reactions at high temperatures and in the presence of special catalysts, with the hydroxyl group being replaced by other nucleophiles . The hydroxy function shows a pronounced + M effect , especially in the deprotonated state . In addition, it shows an −I effect . Since this is significantly smaller than the + M effect, phenol is very easily attacked by electrophiles. The attack takes place preferably in the ortho and para position to the hydroxyl group. Because of the electron-donating nature of the hydroxy group, phenol is about a thousand times more reactive than benzene. The preference for ortho or para attack by electrophiles can be understood on the one hand by looking at the boundary structures of the phenolate anion. The negative charge is delocalized in the aromatic ring to the ortho and para positions. Since electrophiles prefer to attack electron-rich positions, the observed regioselectivity occurs . On the other hand, the σ-complex (carbenium ion) formed as an intermediate stage in the substitution is more mesomeric stabilized in the ortho and para positions than in the meta position, since more low-energy boundary structures are possible and the delocalization of the electrons is therefore more pronounced. The substitution in the para position is also preferred, since there is no steric interaction of the attacking electrophile with the lone electron pairs of the oxygen.
The keto-enol tautomerism is completely on the enol side because of the formation of the thermodynamically favorable aromatic system.
A technically important nucleophilic substitution reaction is the preparation of aniline from phenol at 250 ° C and the presence of an oxide catalyst ( aluminum , silicon or magnesium oxide , also boric acid ) as a " Halcon process ".
Phenol is mainly used as a raw material for the manufacture of plastics . The production of phenoplasts plays the most important role. Phenol is also converted into caprolactam , a substance used in the manufacture of polyamides . The conversion to bisphenol A provides an important starting material for the production of epoxy resins .
Phenol is highly toxic both locally and systemically; When exposed to the skin, it has irritating to corrosive effects on mucous membranes, skin and eyes. The eyes can suffer damage in the form of clouding of the cornea , swelling and cohesion of the eyelids up to blindness. Skin contact first leads to reddening of the skin, later to a white discoloration; longer exposure time causes a darkening up to the formation of necrosis .
Phenol is mainly absorbed through the skin, but inhalation or oral absorption is also possible. In the human organism, the substance acutely damages the kidneys, blood, central nervous and cardiovascular systems. In the event of chronic exposure, gastrointestinal and nervous disorders, further damage to the liver, kidneys and skin changes are known. Inhalation symptoms of dizziness, headache and ear disorders, vomiting, insomnia and kidney irritation were described as symptoms of intoxication. The ingestion of large amounts led within a few hours to massive kidney dysfunction up to acute kidney failure. Ingestion causes burns in the mouth, throat, esophagus and stomach; swallowing disorders and disorders of the gastrointestinal tract are also known.
The toxicity is attributed to reactive metabolites of phenol, which bind to the DNA and other macromolecules and cause breaks in the chromosomes and mutagenic effects. An oral dose of 1 g or more can occasionally be fatal for a person; individually, however, much higher doses were survived. The oral LD Lo value for humans is between 140 and 1400 mg / kg body weight; in children the minimum oral lethal dose is 10 mg / kg body weight.
In 2015, phenol was included by the EU in the Community's ongoing action plan ( CoRAP ) in accordance with Regulation (EC) No. 1907/2006 (REACH) as part of substance evaluation . The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. Phenol ingestion was caused by concerns about consumer use , worker exposure , high (aggregated) tonnage, high risk characterization ratio (RCR) and other hazard-related concerns, as well as the potential risk of mutagenic properties. The re-evaluation has been running since 2015 and is carried out by Denmark .
“Carbolic acid (coal tar creosote, acidum phenylicum, acidum carbolicum). A substance that has become extremely important for the paint industry and medicine (as a disinfectant ). The trade name is still carbolic acid while the scientific name is now phenol; This substance has the properties of a weak acid and is able to combine with bases, which is why it is also called phenylic acid or phenic acid, but at the same time and to an even greater extent it plays the role of an alcohol, hence the name phenyl alcohol, which is used in Shortened phenol. Carbolic acid is mainly obtained from coal tar and lignite tar ; wood tar only contains extremely small amounts of it, because the creosote of wood tar does not consist of phenol, as was believed for a time, but of the structurally similar cresol and some others other substances. To obtain the carbolic acid, the part of the tar that passes between 150 and 200 ° C is treated with sodium hydroxide solution , which combines with the carbolic acid and the cresol, which is also contained in coal tar, separates this solution from the other tar components and decomposes them with an acid. The oily product which has separated out is then distilled and what passes over 190 ° C. is specially collected; the latter is sold as raw cresol, that which passes below 190 ° C as raw carbolic acid. In this state both substances are still brown, very foul-smelling, oily liquids. This raw carbolic acid (acidum carbolicum crudum) is partly further purified, partly it is used to preserve wood and to disinfect cesspools . "
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