p-dichlorobenzene

1,4-Dichlorobenzene (1,4-DCB, ''p''-DCB, or ''para''-dichlorobenzene, sometimes abbreviated as PDCB or para) is an organic compound with the formula C₆H₄Cl₂. This colorless solid has a strong odor. The molecule consists of a benzene ring with two chlorine atoms (replacing hydrogen atoms) on opposing sites of the ring.

It is used as a disinfectant, pesticide, and deodorant, most familiarly in mothballs in which it is a replacement for the more traditional naphthalene because of naphthalene's greater flammability (though both chemicals have the same NFPA 704 rating). It is also used as a precursor in the production of the chemically and thermally resistant polymer poly(''p''-phenylene sulfide).

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.K. Hunger. W. Herbst "Pigments, Organic" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim, 2012. 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):
:

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.

Under California's Proposition 65, ''p''-DCB is listed as "known to the State to cause cancer".Proposition 65
, Office of Environmental Health Hazard Assessment A mechanism for the carcinogenic effects of mothballs and some types of air fresheners containing ''p''-DCB has been identified in roundworms.

Due to the carcinogenic effect the use in European Union is forbidden since 2005 as air freshener and 2008 as mothball.

See also

* Air freshener
* Camphor
* Dichlorobenzene
* Mothball

References

External links

*

Mothball sniffing warning issued
''BBC News'', 27 July 2006


Centers for Disease Control and Prevention

{{DEFAULTSORT:Dichlorobenzene, 1, 4-
Organochloride insecticides
IARC Group 2B carcinogens
Chlorobenzenes