Phenol (FEE-nol) is a white, crystalline solid with a characteristic odor and a sharp, burning taste. It tends to turn pink or pale red when exposed to light if not perfectly pure. Phenol has a tendency to absorb moisture from the air, changing into an aqueous solution of the compound. Such solutions have a slightly sweet flavor.
Hydroxybenzene; carbolic acid; phenylic acid; benzophenol; phenic acid
Carbon, hydrogen, oxygen
Aromatic alcohol (organic)
Soluble in water, ethyl alcohol, ether, chloroform, acetone, benzene, and other organic solvents
Phenol was probably first observed by German chemist Johann Rudolf Glauber (1604–1668). Glauber obtained phenol by condensing coal tar vapors and separating them into individual compounds. Coal tar is a thick black liquid left over when coal is heated in the absence of air to make coke. Phenol was largely ignored for almost 200 years until another German chemist, Friedlieb Ferdinand Runge (1795–1867), isolated phenol in 1834, also from coal tar. Runge gave the name carbolic acid to his discovery, a name that is still used occasionally for the compound. In 1843, French chemist Charles Frederic Gerhardt (1816–1856) suggested the modern name of phenol for the compound.
The term phenol is also used to describe a class of aromatic organic compounds. Such compounds have a six-carbon ring structure like that of benzene (C6H6) to which is attached one or more hydroxyl (-OH) groups. Benzene is the simplest member of this group. Other members include the cresols (CH3C6H4OH), xylenols ((CH3)2C6H3OH), and the resorcinols (C6H4(OH)2). The production of phenol amounts to about 6 million metric tons (about 6.5 million short tons) annually in the United States. The largest single use of phenol is in the production of bisphenol A ((CH3)2C(C6H4OH)2) and a variety of plastics, primarily formaldehyde resins.
- The only source of phenol until World War I (1914–1918) was coal tar.
- German chemist Friedrich Raschig (1863–1928) developed the first synthetic method for making phenol in 1915. The process involves the hydrolysis of chlorobenzene (C6H5Cl).
- Demand for phenol increased significantly in 1909 when German chemist Leo Hendrik Baekeland (1863–1944) announced the discovery of a new synthetic material, Bakelite, made from phenol and formaldehyde (CH2O). Bakelite was the first thermosetting plastic ever discovered. A thermosetting plastic is one that, once shaped into some form, cannot be remelted again.
- The use of carbolic acid as an antiseptic was first suggested by Sir Joseph Lister (1827–1912) in 1865. Lister found that sterilizing medical instruments and treating wounds with carbolic acid dramatically reduced the number of deaths resulting from post-operative infections.
- The effectiveness of a substance in preventing bacterial infection is still expressed by a measure known as the phenol coefficient, the effectiveness of the material compared to that of a comparable amount of phenol.
HOW IT IS MADE
In the early twenty-first century, virtually all of the phenol made is produced from cumene (C6H5CH(CH3)2). Cumene is first oxidized to produce cumene hydroperoxide: C6H5CH(CH3)2 + O2 → C6H5(COOH)(CH3)2. The cumene hydroperoxide is then treated with concentrated sulfuric acid (H2SO4) to obtain a mixture of acetone (CH3COCH3) and phenol: C6H5(COOH)(CH3)2 + H2SO4 → CH3COCH3 + C6H5OH.
COMMON USES AND POTENTIAL HAZARDS
The primary use for phenol is as an intermediary chemical, a compound used in the synthesis of other chemicals. About 40 percent of all the phenol produced in the United States is used to make bisphenol A, while a similar amount is used in the production of a variety of polymers, such as phenol-formaldehyde plastics and nylon-6. The third largest application of phenol is in the manufacture of a host of other chemicals, xylene and aniline being the most important.
Phenol is no longer widely used as an antiseptic, partly because more efficient substances have been developed and partly because phenol may cause irritation and burning of the skin after prolonged use. The compound is still used in low concentrations in a number of health and medical applications, however, as in antipruritics (substances that reduce or prevent itching), cauterizing agents (substances for the burning of tissue by heat or chemicals), topical anesthetics (anesthetics used on the skin), chemexfoliants (substances that remove skin), throat sprays and lozenges (such as Chloraseptic®, Ambesol®, and Cepastat®), and in skin ointments (such as PRID salve® and CamphoPhenique® lotion). Phenol is also used in combination with slaked lime (calcium hydroxide; Ca(OH)2) and other materials as a disinfectant for toilets, stables, cesspools, floors, and drains.
Phenol is a highly corrosive material that can cause serious burns to the skin, eyes, and respiratory system. It is toxic if ingested. The compound can enter the body in a variety of ways, such as absorption through the skin, inhalation of vapors, and ingestion of the solid compound or its solutions. Symptoms of phenol poisoning include nausea, vomiting, headache, respiratory failure, muscular weakness, severe depression, collapse, coma, and death. Skin exposure may cause redness, blisters, and/or minor to severe chemical burns. Ingestion of phenol may cause damage to the central nervous system, lungs, kidneys, liver, pancreas, and spleen. The concentration of phenol in most consumer and industrial products is low enough not to cause health problems for users. However, prolonged exposure to such products or their overuse may result in serious health risks. Handling of the pure compound or concentrated solutions of phenol also involves health hazards.
Words to Know
- AQUEOUS SOLUTION
- A solution that consists of some material dissolved in water.
- The process by which a compound reacts with water to form two new compounds.
- A compound consisting of very large molecules made of one or two small repeated units called monomers.
- A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.
FOR FURTHER INFORMATION
"Occupational Safety and Health Guideline for Phenol." Occupational Safety and Health Administration. http://www.osha.gov/SLTC/healthguidelines/phenol/recognition.html (accessed on December 29, 2005).
"Phenol." Greener Industry. http://www.uyseg.org/greener_industry/pages/phenol/1PhenolAnnualProd.htm (accessed on December 29, 2005).
"Phenol." International Programme on Chemical Safety. http://www.inchem.org/documents/pims/chemical/pim412.htm (accessed on December 29, 2005).
"ToxFAQs™ for Phenol." Agency for Toxic Substances and Disease Registry. http://www.atsdr.cdc.gov/tfacts115.html (accessed on December 29, 2005).
Tyman, J. H. P. Synthetic and Natural Phenols. Amsterdam: Elsevier, 1996.
See AlsoCumene; Polyamide 6,6
phe·nol / ˈfēˌnôl; -ˌnäl/ • n. Chem. a mildly acidic toxic white crystalline solid, C6H5OH, obtained from coal tar and used in chemical manufacture, and in dilute form (under the name carbolic) as a disinfectant. ∎ any compound with a hydroxyl group linked directly to a benzene ring. DERIVATIVES: phe·no·lic / fiˈnälik/ adj.