1,4-Dichlorobenzene

Production

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.

Uses

Disinfectant, deodorant, and pesticide

p-DCB is used to control moths, molds, and mildew. 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.

Precursor to other chemicals

Nitration gives 1,4-dichloronitrobenzene, a precursor to commercial dyes and pigments. 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): :[[File:Synthesis Poly(p-phenylene sulfide).svg|upright=1.5|Synthesis of polyphenylensulfide]]

As ceruminolytic agent

2% Paradichlorobenzene used as a ceruminolytic agent for the treatment of impacted earwax.

Environmental and health effects

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. This has been indicated by animal studies, although a full-scale human study has not been done.

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), but publishes no information on the cancer risk. p-DCB is also an EPA-registered pesticide. 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.

A mechanism for the carcinogenic effects of mothballs and some types of air fresheners containing p-DCB has been identified in roundworms.

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).

Biodegradation

Rhodococcus phenolicus is a bacterium species able to degrade dichlorobenzene as its sole carbon source.

References

References

1. {{PGCH. 0190
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8. [http://monographs.iarc.fr/ENG/Preamble/currentb6evalrationale0706.php Preamble to the ''IARC Monographs''] {{Webarchive. link. (9 August 2016 definition of "Group 2B: Possibly carcinogenic to humans", the [[International Agency for Research on Cancer]] classification of this chemical)
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14. (December 2005). "Common Name: 1,4-DICHLOROBENZENE". New Jersey Department of Health and Senior Services.
15. Kokel, David. (14 May 2006). "The nongenotoxic carcinogens naphthalene and para-dichlorobenzene suppress apoptosis in Caenorhabditis elegans". Nature Chemical Biology.
16. (2005). "''Rhodococcus phenolicus'' sp. nov., a novel bioprocessor isolated actinomycete with the ability to degrade chlorobenzene, dichlorobenzene and phenol as sole carbon sources". Systematic and Applied Microbiology.