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Phenol
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Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell". Its chemical formula is C6H5OH and its structure is that of a hydroxyl group (-OH) bonded to a phenyl ring; it is thus an aromatic compound.
word phenol is also used to refer to any compound that contains a six-membered aromatic ring, bonded directly to a hydroxyl group (-OH).
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Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell". Its chemical formula is C6H5OH and its structure is that of a hydroxyl group (-OH) bonded to a phenyl ring; it is thus an aromatic compound.
Phenols
The word phenol is also used to refer to any compound that contains a six-membered aromatic ring, bonded directly to a hydroxyl group (-OH). In effect, phenols are a class of organic compounds of which the phenol discussed in this article is the simplest member.its chemical name is hydroxybenzene
Properties
Phenol has a limited solubility in water (8.3 g/100 ml). It is slightly acidic: The phenol molecule has weak tendencies to lose the H+ ion from the hydroxyl group, resulting in the highly water-soluble phenoxide anion C6H5O−. Compared to aliphatic alcohols, phenol shows much higher acidity; it even reacts with aqueous NaOH to lose H+, whereas aliphatic alcohols do not. One explanation for the increased acidity is resonance stabilization of the phenoxide anion by the aromatic ring. In this way, the negative charge on oxygen is shared by the ortho and para carbon atoms. In another explanation, increased acidity is the result of orbital overlap between the oxygen's lone pairs and the aromatic system. In a third, the dominant effect is the induction from the sp˛ hybridised carbons; the comparatively more powerful inductive withdrawal of electron density that is provided by the sp˛ system compared to an spł system allows for great stabilization of the oxyanion. In making this conclusion, one can examine the pKa of the enol of acetone, which is 10.9 in comparison to phenol with a pKa of 10.0. However, this similarity of acidities of phenol and acetone enol is not observed in the gas phase, and is due to the fact that the difference of solvation energies of the deprotonated acetone enol and phenoxide almost exactly offsets the experimentally observed gas phase acidity difference. It has been recently shown that only about 1/3 of the increased acidity of phenol is due to inductive effects, with resonance accounting for the rest.
It is a measurable component (up to 30 ppm) in the aroma
of Islay scotch whisky.
Natural occurrence
Phenols are found in the natural world, especially in the plant kingdom. In some cases phenols are present in plant foliage to discourage herbivory, such as in the case of Western poison oak.
Industrial production
Phenol can be made from the partial oxidation of benzene, the reduction of benzoic acid, by the cumene process, or by the Raschig-Hooker process. It can also be found as a product of coal oxidation.
Uses
Phenol has antiseptic properties, and was used by Sir Joseph Lister (1827-1912) in his pioneering technique of antiseptic surgery, though the skin irritation caused by continual exposure to phenol eventually led to the substitution of aseptic (germ-free) techniques in surgery. Lister decided that the wounds themselves had to be thoroughly cleaned. He then covered the wounds with a piece of "rag" or "lint" covered in carbolic acid. It is also the active ingredient in some oral analgesics such as Chloraseptic spray. Phenol was also the main ingredient of the Carbolic Smoke Ball, a device marketed in London in the 19th century as protecting the user against influenza and other ailments.
It is also used in the production of drugs (it is the starting material in the industrial production of aspirin), herbicides, and synthetic resins (Bakelite, one of the first synthetic resins to be manufactured, is a polymer of phenol with formaldehyde).
Phenol is the preferred chemical in use of embalming bodies for anatomical use and study because of its ability to preserve tissues for extended periods of time. Formaldehyde is however usually preferred over phenol for embalming with intent of public viewal because of phenol's tendency to turn tissues an unpleasant bleach-white color.
Repeated or prolonged skin contact with phenol may cause dermatitis, and the substance is a suspected carcinogen. The substance and the vapour is corrosive to the eyes, the skin and the respiratory tract. Inhalation of phenol vapour may cause lung oedema. The substance may cause harmful effects on the central nervous system, heart and kidneys, resulting in convulsions, coma, cardiac disorders or respiratory failure. Exposure may result in death and the effects may be delayed. Long-term or repeated exposure of the substance may have harmful effects on the liver and kidneys."
Exposure of the skin to concentrated phenol solutions causes chemical burns which may be severe; in laboratories where it is used, it is usually recommended that polyethylene glycol solution is kept available for washing off splashes. Washing with large amounts of plain water (most labs have a safety shower or eye-wash) and removal of contaminated clothing are required, and immediate hospital treatment for large splashes. This is particularly important if the phenol is mixed with chloroform (a commonly-used mixture in molecular biology for DNA & RNA purification from proteins).
Phenol is also used in the preparation of cosmetics including sunscreens, hair dyes, and skin lightening preparations. Compounds containing phenol moieties can be used to prevent ultraviolet light-induced damage to hair and skin due to the UV-absorbing properties of the aromatic ring of the phenol.
It is also used in cosmetic surgery as an exfoliant, to remove layers of dead skin. It is also used in phenolization, a surgical procedure used to treat an ingrown nail, in which it is applied to the toe to prevent regrowth of nails. 5% Phenol is sometimes injected near a sensory nerve in order to temporarily (up to a year) stop it transmitting impulses in some intractable cases of chronic neuropathic pain.
Second World War
Injections of phenol have occasionally been used as a means of rapid execution. In particular, phenol was used as a means of extermination by the Nazis before and during the Second World War. Originally used by the Nazis in the 1930s as part of its euthanasia program, phenol, cheap and easy to make and quickly effective, became the injectable toxin of choice through the last days of the War. Although Zyklon-B pellets were used in the gas chambers to exterminate large groups of people, the Nazis learned that extermination of smaller groups was more economical via injection of each victim one at a time with phenol instead. Phenol injections were given to thousands of people in concentration camps, especially at Auschwitz-Birkenau. Approximately one gram is enough to cause fatal outcome. Injections were administered by medical doctors, their assistants, or sometimes prisoner doctors; such injections were originally given intravenously, more commonly in the arm, but injection directly into the heart, so as to induce nearly instant death, was later preferred.
One of the most famous inmates at Auschwitz to be executed by carbolic acid injection was St. Maximilian Kolbe, a Catholic priest who volunteered to undergo three weeks of starvation and dehydration in the place of another inmate and who was finally injected with carbolic acid so that the Nazis could make more room in their holding cells.
Hydrothermal chemistry
Under laboratory conditions mimicking hydrothermal circulation (water, 200 °C, 1.9 GPa), phenol is found to form from sodium hydrogen carbonate and iron powder (1.8% chemical yield). This discovery made in 2007 may be relevant to the origin of life question as phenol is a fragment of the biomolecule tyrosine, though tyrosine is known to result directly from hydroxylation of phenylalanine in modern biological systems.
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