1,4-Dichlorobenzene


1,4-Dichlorobenzene 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 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. It is also used as a precursor in the production of the chemically and thermally resistant polymer poly.

Production

p-DCB is produced by chlorination of benzene using ferric chloride as a catalyst:
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

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:

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 and the International Agency for Research on Cancer 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 has set a target maximum contaminant level of 75 micrograms of p-DCB per liter of drinking water, but publishes no information on the cancer risk. p-DCB is also an EPA-registered pesticide. The United States Occupational Safety and Health Administration has set a maximum level of 75 parts of p-DCB per million parts air in the workplace 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". A mechanism for the carcinogenic effects of mothballs and some types of air fresheners containing p-DCB has been identified in roundworms.