View source for Coal tar

== Composition ==
Coal tar is produced through thermal destruction ([[pyrolysis]]) of [[coal]]. Its composition varies with the process and type of coal used &ndash; [[lignite]], [[bituminous coal|bituminous]] or [[anthracite]].<ref name="Roberts_2014">{{Cite book | vauthors = Roberts L | veditors = Wexler P | chapter = Coal Tar | title = Encyclopedia of Toxicology | location = Oxford | pages = 993–995 | date = 2014 | doi = 10.1016/b978-0-12-386454-3.00012-9 | publisher = Academic Press | isbn = 978-0-12-386455-0 | quote = composition of coal tar will be influenced by the process used for pyrolytic distillation as well as by the original composition of the coal ... He then demonstrated excess cancers occurring in laboratory animals when coal tar is applied to the ears and skin ... [therapeutic effect] is thought to involve decreased epidermal proliferation ... Coal tar is classified as a human carcinogen ... Both inhalation and dermal routes of exposure are considered hazardous. | edition = Third }}</ref>

Coal tar is a mixture of approximately 10,000 chemicals, of which only about 50% have been identified.<ref>{{Cite journal | vauthors = Heinz-Gerhard F | title = The Challenge in Coal Tar Chemicals | journal = Industrial & Engineering Chemistry | volume = 55 | issue = 5 | pages = 38–44 | date = May 1963 | doi = 10.1021/ie50641a006 }}</ref>{{Better source needed|reason=The source cited is over 50 years old and, as such, fails to incorporate research done in the field of chemistry in the last 50 years.|date=May 2015}} Most of the chemical compounds are [[polycyclic aromatic hydrocarbon]]:<ref>{{Cite book | title = Creosote. | location = US | date = 2002 | publisher = Agency for Toxic Substances Disease Registry, Division of Toxicology, Dept. of Health and Human Services, Public Health Service | language = en | oclc = 816079578 }}</ref><ref>{{Cite web | title = Public Health Statement for Creosote | date = September 2002 | url = https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=64&toxid=18 | publisher = Agency for Toxic Substances and Disease Registry }}</ref>

* polycyclic aromatic hydrocarbons (4-rings: [[chrysene]], [[fluoranthene]], [[pyrene]], [[triphenylene]], [[naphthacene]], [[benzanthracene]], 5-rings: [[picene]], [[Benzo(a)pyrene|benzo[a]pyrene]], [[Benzo(e)pyrene|benzo[e]pyrene]], [[benzofluoranthene]]s, [[perylene]], 6-rings: [[dibenzopyrenes]], dibenzofluoranthenes, [[benzoperylene]]s, 7-rings: [[coronene]])
* methylated and polymethylated derivatives, mono- and polyhydroxylated derivatives, and [[heterocyclic compound]]s.<ref name=":0" /><ref>{{Cite book | vauthors = Betts WD | editor-last1 = John Wiley & Sons, Inc | chapter = Tar and pitch | title = Kirk-Othmer Encyclopedia of Chemical Technology | location = New York | year = 1997 | doi = 10.1002/0471238961 | publisher = John Wiley & Sons, Inc. | isbn = 978-0-471-23896-6 | edition = 5th }}</ref>

Others: benzene, [[toluene]], [[xylene]]s, [[cumene]]s, [[Benzofuran|coumarone]], [[indene]], [[benzofuran]], [[naphthalene]] and [[Methylnaphthalene|methyl-naphthalenes]], [[acenaphthene]], [[fluorene]], [[phenol]], [[cresol]]s, [[pyridine]], [[picoline]]s, phenanthracene, [[carbazole]], [[quinoline]]s, [[fluoranthene]].<ref name="Roberts_2014" /> Many of these constituents are known carcinogens.<ref>{{Cite web | title = EUR-Lex - 32013R1272 - EN - EUR-Lex | url = http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32013R1272 | website = eur-lex.europa.eu | language = en | archive-url = https://web.archive.org/web/20151019180649/http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32013R1272 | archive-date = 2015-10-19 | url-status = dead | access-date = 2017-06-10 | quote = ...are classified as carcinogens of category 1B in accordance with Annex VI to Regulation (EC) No 1272/2008 of the European Parliament }}</ref><ref name="cite40d09166">{{Cite web | title = COAL TAR - National Library of Medicine HSDB Database | url = https://www.nlm.nih.gov/toxnet/index.html | website = toxnet.nlm.nih.gov | access-date = 2017-06-10 | url-status = live | archive-url = https://web.archive.org/web/20170528211224/https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb%3A%40term+%40DOCNO+5050 | archive-date = 2017-05-28 }}</ref>

===Derivatives===
Various [[phenols|phenolic]] coal tar derivatives have [[analgesic]] (pain-killer) properties. These included [[acetanilide]], [[phenacetin]], and [[paracetamol]] aka [[acetaminophen]].<ref name="Dronsfield_2005">{{cite magazine | vauthors = Dronsfield A | title = Pain relief: from coal tar to paracetamol | volume = 42 | issue = 4 | pages = 102–105 | date = 1 July 2005 | url = https://eic.rsc.org/feature/pain-relief-from-coal-tar-to-paracetamol/2020140.article | url-status = live | magazine = [[Education in Chemistry]] | publisher = [[Royal Society of Chemistry]] | archive-url = https://web.archive.org/web/20171013013607/https://eic.rsc.org/feature/pain-relief-from-coal-tar-to-paracetamol/2020140.article | archive-date = 13 October 2017 | access-date = 14 June 2018 }}</ref> Paracetamol may be the only coal-tar derived analgesic still in use today.<ref name="Brown_2005">{{cite news | vauthors = Brown T, Dronsfield A, Ellis P | title = Pain relief: from coal tar to paracetamol | date = 1 July 2005 | url = https://edu.rsc.org/feature/pain-relief-from-coal-tar-to-paracetamol/2020140.article | publisher = Royal Society of Chemistry }}</ref> Industrial [[phenol]] is now usually synthesized from crude oil rather than coal tar.<ref name="Jones_2011">{{cite journal | vauthors = Jones AW | title = Early drug discovery and the rise of pharmaceutical chemistry | journal = Drug Testing and Analysis | volume = 3 | issue = 6 | pages = 337–344 | date = June 2011 | pmid = 21698778 | doi = 10.1002/dta.301 }}</ref>

Coal tar derivatives are contra-indicated for people with the inherited red cell blood disorder [[glucose-6-phosphate dehydrogenase deficiency]] (G6PD deficiency), as they can cause [[oxidative stress]] leading to red blood cell breakdown.<ref name="US_EPA_National_Center_for_Environmental_Assessment_2009">{{cite web | vauthors = ((US EPA National Center for Environmental Assessment)) | title = Hematologic Disorders | date = 15 March 2009 | url = https://hero.epa.gov/hero/index.cfm/reference/details/reference_id/1390864 | website = hero.epa.gov | access-date = 21 April 2020 | language = en }}</ref>