J2SE 1.4


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1,4-Dichlorobenzene (para-dichlorobenzene, p-DCB, PDB) is an organic compound with the formula C6H4Cl2. 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).


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 54.5 °C; the isomeric dichlorobenzenes and chlorobenzene melt well below room temperature.


Disinfectant, deodorant, and pesticide

p-DCB is used to control moths, moulds, 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 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. In a growing application, p-DCB is the precursor to the high performance polymer poly(p-phenylene sulfide):
C6H4Cl2 + Na2S → 1/n [C6H4S]n + 2 NaCl

Environmental 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 would accumulate in the fatty tissues.

Health effects

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.


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