The Full Wiki

Phenol: Wikis

  
  
  

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

Did you know ...


More interesting facts on Phenol

Include this on your site/blog:

Encyclopedia

From Wikipedia, the free encyclopedia

Phenol
Identifiers
CAS number 108-95-2 Yes check.svgY
ChemSpider 971
RTECS number SJ3325000
SMILES
InChI
Properties
Molecular formula C6H6O
Molar mass 94.11 g mol−1
Appearance White Crystalline Solid
Density 1.07 g/cm³
Melting point

40.5 °C, 314 K, 105 °F

Boiling point

181.7 °C, 455 K, 359 °F

Solubility in water 8.3 g/100 ml (20 °C)
Acidity (pKa) 9.95
Dipole moment 1.7 D
Hazards
EU classification Toxic (T)
Muta. Cat. 3
Corrosive (C)
NFPA 704
NFPA 704.svg
2
3
0
COR
Flash point 79 °C
Related compounds
Related compounds Benzenethiol
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Phenol, also known as carbolic acid, is an organic compound with the chemical formula C6H5OH. It is a white, crystalline solid. It consists of benzene modified by one hydroxyl (-OH) group. It is produced on a large scale (about 7 billion kg/year) as a precursor to many materials and useful compounds.[1] It is a relatively caustic compound that requires careful handling.

Contents

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.

Properties

Phenol has a limited solubility in water (8.3 g/100 mL). It is a reactive molecule.

Acidicity

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 phenolate anion C6H5O, called phenoxide anion.[2][3] Compared to aliphatic alcohols, phenol shows much higher acidity (about 1 million times more acidic). It reacts completely with aqueous NaOH to lose H+, whereas most alcohols do react only partially. Phenols are less acidic however than carboxylic acids.

One explanation for the increased acidity over alcohols 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.[4] In another explanation, increased acidity is the result of orbital overlap between the oxygen's lone pairs and the aromatic system.[5] In a third, the dominant effect is the induction from the sp2 hybridised carbons; the comparatively more powerful inductive withdrawal of electron density that is provided by the sp2 system compared to an sp3 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.[6] 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.[7]

Reactions

Phenol is highly reactive toward electrophilic aromatic substitution. By this general approach, many groups can be appended to the ring, via halogenation, acylation, sulfonation, and other processes.

Production

Phenol can be made from the partial oxidation of benzene, by the cumene process, or by the Raschig-Hooker process. It can also be found as a product of coal oxidation. The dominant method starts from cumene (isopropylbenzene):[1]

C6H5CH(CH3)2 + O2 → C6H5OH + (CH3)2CO

Uses

The major uses of phenol involve its converstions to plastics or related materials. Condensation with acetone gives bisphenol-A, a key building block for polycarbonates. Condensation with formaldehyde gives phenolic resins, the most famous of which is Bakelite. Hydrogenation of phenol gives cyclohexanone, an intermediate en route to nylon. Nonionic detergents are produced by alkylation to give the alkylphenols.[1]

Phenol is also a versatile precursor to a large collection of drugs, most notably aspirin, but also many herbicides and pharmaceuticals.

Niche uses

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. However, formaldehyde is usually preferred over phenol for embalming with intent of public viewing because of phenol's tendency to turn tissues an unpleasant bleach-white color.

Phenol is also used in the preparation of cosmetics including sunscreens,[8] hair dyes, and skin lightening preparations.[9] 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.

In cosmetic surgery, phenol serves 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 nail bed to prevent regrowth of nails. 5% Phenol is sometimes injected near a sensory nerve in order to temporarily (up to a year) stop it from transmitting impulses in some intractable cases of chronic neuropathic pain.

History

Phenol was discovered in 1834, when it was extracted from coal tar, which remained the primary source until the development of the petrochemical industry.

Phenol's antiseptic properties were used by Sir Joseph Lister (1827–1912) in his pioneering technique of antiseptic surgery, although 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[10] covered in carbolic acid. It is also the active ingredient in some oral analgesics such as Chloraseptic spray as well as Carmex. 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.

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, invented by Gerhard Lenz 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 death. 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.[11] One of the best known inmates to be executed with a phenol injection in Auschwitz was St. Maximilian Kolbe, a Catholic priest who volunteered to undergo three weeks of starvation and dehydration in the place of another inmate.[11]

Occurrence

Phenol is a measurable component (up to 30 ppm) in the aroma of Islay scotch whisky.[12]

Toxicity

Phenol and its vapor are corrosive to the eyes, the skin, and the respiratory tract.[13] Repeated or prolonged skin contact with phenol may cause dermatitis, or even second and third-degree burns due to phenol's caustic and defatting properties.[14] Inhalation of phenol vapor may cause lung edema.[13] The substance may cause harmful effects on the central nervous system and heart, resulting in dysrhythmia, seizures, and coma.[15] The kidneys may be affected as well. 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."[16] The substance is a suspected carcinogen. Besides its hydrophobic effects, another mechanism for the toxicity of phenol may be the formation of phenoxyl radicals.[17]

Chemical burns from skin exposures can be decontaminated by washing with polyethylene glycol,[18] isopropyl alcohol,[19] or perhaps even copious amounts of water.[20] Removal of contaminated clothing is required, as well as 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).

References

  1. ^ a b c Manfred Weber, Markus Weber, Michael Kleine-Boymann "Phenol" in Ullmann's Encyclopedia of Industrial Chemistry 2004, Wiley-VCH. doi:10.1002/14356007.a19_299.pub2.
  2. ^ The Free Dictionary/Medical dictionary
  3. ^ About.com:Chemistry
  4. ^ Organic Chemistry 2nd Ed. John McMurry ISBN 0534079687
  5. ^ "The Acidity of Phenol". ChemGuide. Jim Clark. http://www.chemguide.co.uk/organicprops/phenol/acidity.html. Retrieved 2007-08-05. 
  6. ^ For further reading on the fine points of this topic, see David A. Evans's explanation.
  7. ^ Pedro J. Silva (2009). "Inductive and Resonance Effects on the Acidities of Phenol, Enols, and Carbonyl α-Hydrogens.". J. Org. Chem. 74: 914–916. doi:10.1021/jo8018736. (Solvation effects on the relative acidities of acetaldehyde enol and phenol described in the Supporting Information)
  8. ^ A. Svobodová*, J. Psotová, and D. Walterová (2003). "Natural Phenolics in the Prevention of UV-Induced Skin Damage. A Review". Biomed. Papers 147 (2): 137–145. 
  9. ^ DeSelms, R. H.; UV-Active Phenol Ester Compounds; Enigen Science Publishing: Washington, DC, 2008.
  10. ^ Lister, Joseph (1867). "Antiseptic Principle Of The Practice Of Surgery". http://www.fordham.edu/halsall/mod/1867lister.html. 
  11. ^ a b "Killing through phenol injection". Auschwitz - FINAL STATION EXTERMINATION. Johannes Kepler University, Linz, Austria. http://www.wsg-hist.uni-linz.ac.at/AUSCHWITZ/HTML/Phenol.html. Retrieved 2006-09-29. 
  12. ^ "Peat, Phenol and PPM, by Dr P. Brossard" (PDF). http://www.whisky-news.com/En/reports/Peat_phenol_ppm.pdf. Retrieved 2008-05-27. 
  13. ^ a b Budavari, S, ed (1996). The Merck Index: An Encyclopedia of Chemical, Drugs, and Biologicals. Whitehouse Station, NJ: Merck. 
  14. ^ Lin TM, Lee SS, Lai CS, Lin SD (June 2006). "Phenol burn". Burns: Journal of the International Society for Burn Injuries 32 (4): 517–21. doi:10.1016/j.burns.2005.12.016. PMID 16621299. 
  15. ^ Warner, MA; Harper, JV (1985). "Cardiac dysrhythmias associated with chemical peeling with phenol". Anesthesiology 62 (3): 366–7. PMID 2579602. 
  16. ^ World Health Organization/International Labour Organization: International Chemical Safety Cards, http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc00/icsc0070.htm
  17. ^ Hanscha, Corwin; McKarnsb, Susan C; Smith, Carr J; Doolittle, David J (June 15, 2000). "Comparative QSAR evidence for a free-radical mechanism of phenol-induced toxicity". Chemico-Biological Interactions 127 (1): 61–72. doi:10.1016/S0009-2797(00)00171-X. PMID 10903419. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T56-40S0C7X-5&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=e39425b7cfcb3432a346b9604aea350e. 
  18. ^ Brown, VKH; Box, VL; Simpson, BJ (1975). "Decontamination procedures for skin exposed to phenolic substances". Archives of Environmental Health 30 (1): 1–6. PMID 1109265. 
  19. ^ Hunter, DM; Timerding, BL; Leonard, RB; McCalmont, TH; Schwartz, E (1992). "Effects of isopropyl alcohol, ethanol, and polyethylene glycol/industrial methylated spirits in the treatment of acute phenol burns". Annals of Emergency Medicine 21: 1303–7. doi:10.1016/S0196-0644(05)81891-8. 
  20. ^ Pullin, TG; Pinkerton, MN; Johnson, RV; Kilian, DJ (1978). "Decontamination of the skin of swine following phenol exposure: a comparison of the relative efficacy of water versus polyethylene glycol/industrial methylated spirits". Toxicol Appl Pharmacol 43 (1): 199–206. doi:10.1016/S0041-008X(78)80044-1. PMID 625760. 

See also

External links








Got something to say? Make a comment.
Your name
Your email address
Message