Math Is Fun Forum

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 52,128

Phenol

Phenol

Gist

Phenol (C6H5OH) is a white crystalline organic compound with a hydroxyl group attached directly to a benzene ring, also known as carbolic acid. It is a key chemical precursor for producing phenolic resins, nylon, and other industrial chemicals, and is used as a disinfectant, antiseptic, and in certain medical treatments like chemical peels. While a useful chemical, phenol is also mildly acidic, corrosive, and toxic, requiring careful handling.

Phenol is a versatile chemical used as a disinfectant, antiseptic, and anesthetic, particularly in mouthwashes and throat sprays, though its use in healthcare is now uncommon due to toxicity. It is a vital precursor for producing plastics, resins, and pharmaceuticals like aspirin and acetaminophen. Phenol also serves as a laboratory reagent for extracting DNA and RNA and is used in dermatology for chemical peels and in podiatry for nail procedures. 

Summary

Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula C6H5OH. It is a white crystalline solid that is volatile and can catch fire.

The molecule consists of a phenyl group (−C6H5) bonded to a hydroxy group (−OH). Mildly acidic, it requires careful handling because it can cause chemical burns. It is acutely toxic and is considered a health hazard.

Phenol was first extracted from coal tar, but today is produced on a large scale (about 7 million tonnes a year) from petroleum-derived feedstocks. It is an important industrial commodity as a precursor to many materials and useful compounds, and is a liquid when manufactured. It is primarily used to synthesize plastics and related materials. Phenol and its chemical derivatives are essential for production of polycarbonates, epoxies, explosives such as picric acid, Bakelite, nylon, detergents, herbicides such as phenoxy herbicides, and numerous pharmaceutical drugs.

Details

Phenol is any of a family of organic compounds characterized by a hydroxyl (―OH) group attached to a carbon atom that is part of an aromatic ring. Besides serving as the generic name for the entire family, the term phenol is also the specific name for its simplest member, monohydroxybenzene (C6H5OH), also known as benzenol, or carbolic acid.

Phenols are similar to alcohols but form stronger hydrogen bonds. Thus, they are more soluble in water than are alcohols and have higher boiling points. Phenols occur either as colourless liquids or white solids at room temperature and may be highly toxic and caustic.

Phenols are widely used in household products and as intermediates for industrial synthesis. For example, phenol itself is used (in low concentrations) as a disinfectant in household cleaners and in mouthwash. Phenol may have been the first surgical antiseptic. In 1865 the British surgeon Joseph Lister used phenol as an antiseptic to sterilize his operating field. With phenol used in this manner, the mortality rate from surgical amputations fell from 45 to 15 percent in Lister’s ward. Phenol is quite toxic, however, and concentrated solutions cause severe but painless burns of the skin and mucous membranes. Less-toxic phenols, such as n-hexylresorcinol, have supplanted phenol itself in cough drops and other antiseptic applications. Butylated hydroxytoluene (BHT) has a much lower toxicity and is a common antioxidant in foods.

In industry, phenol is used as a starting material to make plastics, explosives such as picric acid, and drugs such as aspirin. The common phenol hydroquinone is the component of photographic developer that reduces exposed silver bromide crystals to black metallic silver. Other substituted phenols are used in the dye industry to make intensely coloured azo dyes. Mixtures of phenols (especially the cresols) are used as components in wood preservatives such as creosote.

Natural sources of phenols

Phenols are common in nature; examples include tyrosine, one of the standard amino acids found in most proteins; epinephrine (adrenaline), a stimulant hormone produced by the adrenal medulla; serotonin, a neurotransmitter in the brain; and urushiol, an irritant secreted by poison ivy to prevent animals from eating its leaves. Many of the more complex phenols used as flavourings and aromas are obtained from essential oils of plants. For example, vanillin, the principal flavouring in vanilla, is isolated from vanilla beans, and methyl salicylate, which has a characteristic minty taste and odour, is isolated from wintergreen. Other phenols obtained from plants include thymol, isolated from thyme, and eugenol, isolated from cloves.

Phenol, the cresols (methylphenols), and other simple alkylated phenols can be obtained from the distillation of coal tar or crude petroleum.

Nomenclature of phenols

Many phenolic compounds were discovered and used long before chemists were able to determine their structures. Therefore, trivial names (i.e., vanillin, salicylic acid, pyrocatechol, resorcinol, cresol, hydroquinone, and eugenol) are often used for the most common phenolic compounds.

Systematic names are more useful, however, because a systematic name specifies the actual structure of the compound. If the hydroxyl group is the principal functional group of a phenol, the compound can be named as a substituted phenol, with carbon atom 1 bearing the hydroxyl group. For example, the systematic name for thymol is 5-methyl-2-isopropylphenol. Phenols with only one other substituent can be named using either the appropriate numbers or the ortho (1,2), meta (1,3), and para (1,4) system. Compounds with other principal functional groups can be named with the hydroxyl group as a hydroxy substituent. For example, the systematic name for vanillin is 4-hydroxy-3-methoxybenzaldehyde.

Physical properties of phenols

Similar to alcohols, phenols have hydroxyl groups that can participate in intermolecular hydrogen bonding; in fact, phenols tend to form stronger hydrogen bonds than alcohols. (See chemical bonding: Intermolecular forces for more information about hydrogen bonding.) Hydrogen bonding results in higher melting points and much higher boiling points for phenols than for hydrocarbons with similar molecular weights. For example, phenol (molecular weight [MW] 94, boiling point [bp] 182 °C [359.6 °F]) has a boiling point more than 70 degrees higher than that of toluene (C6H5CH3; MW 92, bp 111 °C [231.8 °F]).

The ability of phenols to form strong hydrogen bonds also enhances their solubility in water. Phenol dissolves to give a 9.3 percent solution in water, compared with a 3.6 percent solution for cyclohexanol in water. The association between water and phenol is unusually strong; when crystalline phenol is left out in a humid environment, it picks up enough water from the air to form liquid droplets.

Additional Information

Phenol is the organic compound with formula C6H5OH. It is a white solid. It has an OH group (hydroxyl group) bonded to a benzene ring. It is an alcohol. Because the aromatic group attracts electrons, it is quite acidic.

Phenol is produced from petroleum. It is an important molecule because it can be used to make many other products. It is also used in detergents and herbicides.

Properties:

Acidity

Phenol has a pKa of about 10. For normal alcohols this number is usually around 15, making phenol about 100,000 times more acidic. However, phenol is less acidic than compounds like carboxylic acids.

The reason for this high acidity is the resonance stabilization of the molecule when it becomes an anion.

Reactions

Phenol can do electrophilic aromatic substitution reactions very well. This is because the lone pair on the oxygen atom can give electrons through the benzene ring to an electrophile. Because the lone pair is so high in energy however, sometimes phenol reacts too many times.

History:

Phenol was first discovered in 1834. It was found as a product of burning coal. One of its first uses was to kill germs in surgery. It is still used today in some analgesics. During the Second World War, phenol was also used by the Nazis. They used it in concentration camps to quickly kill small groups of people.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.