:1,4-Dichlorobenzene

p-DCB is produced by chlorination of benzene using ferric chloride as a catalyst:

:C₆H₆ + 2 Cl₂ → C₆H₄Cl₂ + 2 HCl

The chief impurity is the 1,2 isomer. The compound can be purified by fractional crystallization, taking advantage of its relatively high melting point of 53.5 °C; the isomeric dichlorobenzenes and chlorobenzene melt well below room temperature.

File:1,4 dichlorobenzene balls.jpg disinfectant]]

p-DCB is used to control moths, molds, and mildew.{{cite web |url= http://npic.orst.edu/capro/Mothballs1.pdf |title= National Pesticide Information Center – Mothballs Case Profile |access-date= 10 August 2009 |archive-url= https://web.archive.org/web/20100622021329/http://npic.orst.edu/capro/Mothballs1.pdf |archive-date= 22 June 2010 |df= dmy-all}} It also finds use as a disinfectant in waste containers and restrooms and is the characteristic smell associated with urinal cakes. Its usefulness for these applications arises from p-DCB's low solubility in water and its relatively high volatility: it sublimes readily near room temperature.

Nitration gives 1,4-dichloronitrobenzene, a precursor to commercial dyes and pigments.K. Hunger. W. Herbst "Pigments, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012. {{doi|10.1002/14356007.a20_371}} The chloride sites on p-DCB can be substituted with hydroxylamine and sulfide groups. In a growing application, p-DCB is the precursor to the high performance polymer poly(p-phenylene sulfide):{{Cite journal | last1 = Fahey | first1 = D. R. | last2 = Ash | first2 = C. E. | doi = 10.1021/ma00015a003 | title = Mechanism of poly(p-phenylene sulfide) growth from p-dichlorobenzene and sodium sulfide | journal = Macromolecules | volume = 24 | issue = 15 | page = 4242 | year = 1991 | bibcode = 1991MaMol..24.4242F }}

:File:Synthesis Poly(p-phenylene sulfide).svg

2% Paradichlorobenzene used as a ceruminolytic agent for the treatment of impacted wax. {{Cite web |url=https://pmc.ncbi.nlm.nih.gov/articles/PMC3449978 |title=Archived copy |access-date=26 March 2025 |archive-date=25 March 2025 |archive-url=https://web.archive.org/web/20250325160305/https://pmc.ncbi.nlm.nih.gov/articles/PMC3449978/ |url-status=live }}

p-DCB is poorly soluble in water and is not easily broken down by soil organisms. Like many hydrocarbons, p-DCB is lipophilic and will accumulate in fatty tissues if consumed by a person or animal.

The United States Department of Health and Human Services (DHHS) and the International Agency for Research on Cancer (IARC) have determined that p-DCB may reasonably be anticipated to be a carcinogen.[http://monographs.iarc.fr/ENG/Preamble/currentb6evalrationale0706.php Preamble to the IARC Monographs] {{Webarchive|url=https://web.archive.org/web/20160809225810/http://monographs.iarc.fr/ENG/Preamble/currentb6evalrationale0706.php |date=9 August 2016 }} definition of "Group 2B: Possibly carcinogenic to humans", the International Agency for Research on Cancer classification of this chemical This has been indicated by animal studies, although a full-scale human study has not been done.{{cite web|title=ToxFAQs for Dichlorobenzenes|url=https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsLanding.aspx?id=703&tid=126|work=Toxic Substances Portal|publisher=Agency for Toxic Substances and Disease Registry|access-date=24 May 2013|archive-date=26 November 2020|archive-url=https://web.archive.org/web/20201126191021/https://www.atsdr.cdc.gov/toxfaqs/tf.asp?id=703&tid=126|url-status=live}}

The United States Environmental Protection Agency (EPA) has set a target maximum contaminant level of 75 micrograms of p-DCB per liter of drinking water (75 μg/L),{{cite web |url= http://www.epa.gov/ogwdw000/contaminants/dw_contamfs/p-dichlo.html |title= Consumer Factsheet on: PARA-DICHLOROBENZENE (p-DCB) |date= 28 November 2006 |access-date=10 August 2009 | archive-url= https://web.archive.org/web/20091006081817/http://www.epa.gov/ogwdw000/contaminants/dw_contamfs/p-dichlo.html| archive-date= 6 October 2009 }} but publishes no information on the cancer risk.{{Cite web|url=https://www3.epa.gov/airtoxics/hlthef/dich-ben.html|title=1,4-Dichlorobenzene (para-Dichlorobenzene) |website=US Environmental Protection Agency |language=en|access-date=24 March 2016|archive-date=4 April 2016|archive-url=https://web.archive.org/web/20160404214242/https://www3.epa.gov/airtoxics/hlthef/dich-ben.html}} p-DCB is also an EPA-registered pesticide.{{cite web |url= http://www.epa.gov/oppsrrd1/REDs/para-dichlorobenzene-red-revised.pdf |title= Reregistration Eligibility Decision for Para-dichlorobenzene |date= December 2008 |access-date=10 August 2009 | archive-url= https://web.archive.org/web/20090926200251/http://www.epa.gov/oppsrrd1/REDs/para-dichlorobenzene-red-revised.pdf| archive-date= 26 September 2009 }} The United States Occupational Safety and Health Administration (OSHA) has set a maximum level of 75 parts of p-DCB per million parts air in the workplace (75 ppm) for an 8-hour day, 40-hour workweek.{{Cite web|url=https://www.osha.gov/dts/chemicalsampling/data/CH_232900.html|title=Chemical Sampling – p-Diclorobenzine|website=United States Department of Labor|publisher=Occupational Safety & Health Administration|access-date=23 March 2016|archive-date=31 July 2017|archive-url=https://web.archive.org/web/20170731224645/https://www.osha.gov/dts/chemicalsampling/data/CH_232900.html}}{{Cite web|url=http://nj.gov/health/eoh/rtkweb/documents/fs/0643.pdf|title=Common Name: 1,4-DICHLOROBENZENE|date=December 2005|publisher=New Jersey Department of Health and Senior Services|access-date=24 March 2016|archive-date=4 April 2016|archive-url=https://web.archive.org/web/20160404084953/http://nj.gov/health/eoh/rtkweb/documents/fs/0643.pdf|url-status=live}}

A mechanism for the carcinogenic effects of mothballs and some types of air fresheners containing p-DCB has been identified in roundworms.{{cite journal|title=The nongenotoxic carcinogens naphthalene and para-dichlorobenzene suppress apoptosis in Caenorhabditis elegans|last=Kokel|first=David|date=14 May 2006|volume=2|issue=6|doi=10.1038/nchembio791|pmid=16699520|pages=338–345|journal=Nature Chemical Biology|s2cid=18402091 }}

Due to its carcinogenic nature, use of paradichlorobenzene in the European Union is forbidden as an air freshener (since 2005) and in mothballs (since 2008).

Rhodococcus phenolicus is a bacterium species able to degrade dichlorobenzene as its sole carbon source.{{Cite journal | last1 = Rehfuss | first1 = M. | last2 = Urban | first2 = J. | doi = 10.1016/j.syapm.2005.05.011 | title = Rhodococcus phenolicus sp. nov., a novel bioprocessor isolated actinomycete with the ability to degrade chlorobenzene, dichlorobenzene and phenol as sole carbon sources | journal = Systematic and Applied Microbiology | volume = 28 | issue = 8 | pages = 695–701 | year = 2005 | pmid = 16261859}}

• Air freshener
• Camphor
• Mothball

{{reflist}}

• {{ICSC|0037|00}}
• [http://news.bbc.co.uk/2/hi/health/5219646.stm Mothball sniffing warning issued], BBC News, 27 July 2006
• [https://www.cdc.gov/niosh/npg/npgd0190.html NIOSH Pocket Guide to Chemical Hazards], Centers for Disease Control and Prevention

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Category:Organochloride insecticides

Category:IARC Group 2B carcinogens

Category:Chlorobenzenes