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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).
-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
-DCB is used to control moths
, 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
-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.
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.