View source for Coal tar

'''Coal tar''' is a brown or black liquid of high [[viscosity]], which smells of [[naphthalene]] and [[aromatic hydrocarbon]]s. Coal tar is among the by-products when [[coal]] is 
[[carbonization|carbonized]] to make [[coke (fuel)|coke]] or [[coal gasification|gasified]] to make [[coal gas]]. Coal tars are complex and variable mixtures of [[phenols]], [[polycyclic aromatic hydrocarbon]]s (PAHs), and [[heterocyclic compound]]s. It is a mixture of about 200 substances. <ref name="c">[http://www.atsdr.cdc.gov/toxprofiles/tp85-c2.pdf Toxicological profile for wood creosote, coal tar creosote, coal tar, coal tar pitch, and coal tar pitch volatiles] U.S. Department of Health and Human Services, page 19, September 2002</ref>

==Applications==
Being flammable, coal tar is sometimes used for heating or to fire [[boiler]]s. Like most heavy oils, it must be heated before it will flow easily.

Like [[pine tar]], it can be used in medicated [[shampoo]], [[Wrights Coal Tar Soap|soap]] and [[ointment]], as a treatment for [[dandruff]] and [[psoriasis]], as well as being used to kill and repel [[head lice]]. When used as a medication in the [[United States|U.S.]], coal tar preparations are considered an OTC ([[over-the-counter drug]]) pharmaceutical and are subject to regulation by the [[United States Food and Drug Administration]]. Name brands include [[Denorex]], Balnetar, Psoriasin, Tegrin, [[T-Gel]], and Neutar. When used in the extemporaneous preparation of topical medications, it is supplied in the form of Coal Tar Topical Solution [[United_States_Pharmacopeia|USP]], which consists of a  [[percentage_solution|20% w/v]] solution of coal tar in [[alcohol]], with an additional 5% w/v of [[polysorbate 80]]; <ref>USP30-NF25 page 1817</ref> this must then be diluted in an ointment base such as [[petrolatum]]. Coal tar is also used to synthesize [[paracetamol]] (acetaminophen). It is also used to manufacture paints,synthetic dyes and photographic materials.

[[Tar]] is used in treatment of the skin disease [[psoriasis]], where coal tar is the most effective. Petroleum tar was also used in [[ancient Egypt]]ian [[Mummy|mummification]] circa [[1st millennium BC|1000 BC]].<ref>http://www.geotimes.org/feb05/NN_mummytar.html</ref>

Tar was a vital component of the first sealed, or "[[tarmac]]", roads. The streets of [[Baghdad]] were the first to be paved with tar from the 8th century AD.<ref name=Ajram>{{cite book|author=Dr. Kasem Ajram|title=The Miracle of Islam Science|edition=2nd Edition|publisher=Knowledge House Publishers|year=1992|isbn=0-911119-43-4}}</ref> Coal tar was formerly used as one of the primary ingredients of [[Tarmac|Tarmacadam]] pavements, when mixed with ironworks [[slag]]. <ref>John Sheail, ‘Hooley, Edgar Purnell (1860–1942)’, Oxford Dictionary of National Biography, online edn, Oxford University Press, Sept 2004 [http://www.oxforddnb.com/view/article/49486, accessed 21 June 2010]</ref> Today, petroleum derived binders and sealers are more commonly used. These sealers are used to extend the life and lower maintenance cost associated with asphalt pavements, primarily in asphalt road paving, car parks and walkways.

==Safety==
According to the [[International Agency for Research on Cancer]], preparations that include more than 5 percent of crude coal tar are [[List of IARC Group 1 carcinogens|Group 1]] [[carcinogen]]. 

According to the [[National Psoriasis Foundation]] and the FDA, coal tar is a valuable, safe and inexpensive treatment option for millions of people with psoriasis and other scalp or skin conditions. <ref>[[National Psoriasis Foundation]], [http://www.psoriasis.org/news/stories/2001/20011202_coalcala.php The battle to save coal tar in California], December 3 2001.</ref> Coal tar concentrations between 0.5% and 5% are safe and effective for psoriasis, and no scientific evidence suggests that the coal tar in the concentrations seen in non-prescription treatments is carcinogenic. The NPF states that coal tar contains approximately 10,000 chemicals, of which only about 50% have been identified <ref>[http://www.psoriasis.org/treatment/psoriasis/topicals/tar.php National Psoriasis Foundation: Tar<!-- Bot generated title -->]</ref>, and the composition of coal tar varies with its origin and type of coal (eg: [[lignite]], [[bituminous coal|bituminous]] or [[anthracite]]) used to make it.

The residue from the [[distillation]] of high-temperature coal tar, primarily a complex mixture of three or more membered condensed ring [[aromatic hydrocarbon]]s, was listed on 28 October 2008 as a [[substance of very high concern]] by the [[European Chemicals Agency]].

==See also==
{{Wiktionary}}
* [[Creosote]]
* [[Cresolene]]
* [[Preservative]]
* [[Red 40]]
* [[Tar]]

==References==
{{reflist|1}}

==External links==
*[http://www.osha.gov/SLTC/coaltarpitchvolatiles/index.html ''Coal Tar Pitch Volatiles'' by OSHA]  
*[http://pubs.acs.org/doi/full/10.1021/es803118b?cookieSet=1 ''Parking lots create sticky pollution problem'' by Erica Engelhaupt  Environmental Science and Technology]

{{Antipsoriatics}}

[[Category:Coal]]
[[Category:Materials]]
[[Category:IARC Group 1 carcinogens]]

[[ar:قطران الفحم]]
[[cs:Uhelný dehet]]
[[de:Steinkohlenteer]]
[[es:Alquitrán de hulla]]
[[fa:کول تار]]
[[fr:Goudron de houille]]
[[hi:अलकतरा]]
[[ja:コールタール]]
[[pl:Smoła pogazowa]]
[[pt:Alcatrão da hulha]]
[[ru:Каменноугольная смола]]
[[sv:Stenkolstjära]]
[[zh:煤焦油]]
[[Category:2Fix]]