1,4-Dichlorobenzene

1,4-Dichlorobenzene (para-dichlorobenzene or p-DCB) is the organic compound with the formula ClC₆H₄Cl. This colourless solid has an odor akin to that of camphor. It consists of two chlorine atoms substituted at opposing sites on a benzene ring. p-DCB is used a pesticide and a deodorant, most famously in mothballs in which it is a replacement for the more traditional naphthalene. p-DCB is also used as a precursor in the production of the polymer poly(p-phenylene sulfide).^[1]

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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.^[1]

Uses

Disinfactant, deodorant, and pesticide

p-DCB is used to control moths, molds, and mildew. It finds use as a disinfectant in waste containers and restrooms and is the characteristic smell associated with urinal cakes. Its usefulness in 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

The chlorides on p-DCB can be substituted with oxygen, amine, and sulfide groups. A rapid growing application is in the synthesis of the high performance polymer poly(p-phenylene sulfide):

ClC₆H₄Cl + Na₂S → 1/n [C₆H₄S]_n + 2 NaCl

Environmental effects

In air, 1,4-dichlorobenzene breaks down to harmless products in about one month. 1,4-Dichlorobenzene does not dissolve easily in water, and is not easily broken down by soil organisms. Like many hydrocarbons p-DCB is lipophilic and would accumulate in the fatty tissues.

Health effects

There is no evidence that moderate exposure to p-DCB harms human health. The US Department of Health and Human Services (DHHS) has determined that p-DCB may reasonably be anticipated to be a carcinogen, although there is no direct evidence. Animals given very high levels in water developed liver and kidney tumors. The United States Environmental Protection Agency (EPA) has set a maximum contaminant level of 75 micrograms of p-DCB per liter of drinking water (75 μg/L). p-DCB is also an EPA-registered pesticide. The US 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.

Little information is available on how children react to p-DCB exposure.

References

1. ^ ^{a b} Manfred Rossberg, Wilhelm Lendle, Gerhard Pfleiderer, Adolf Tögel, Eberhard-Ludwig Dreher, Ernst Langer, Heinz Rassaerts, Peter Kleinschmidt, Heinz Strack, Richard Cook, Uwe Beck, Karl-August Lipper, Theodore R. Torkelson, Eckhard Löser, Klaus K. Beutel, “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry, 2006 John Wiley-VCH: Weinheim.DOI: 10.1002/14356007.a06_233.pub2