1,4-Dichlorobenzene (1,4-DCB, ''p''-DCB, or ''para''-dichlorobenzene, sometimes abbreviated as PDCB or para) is an

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...

with the formula C₆H₄Cl₂. This colorless solid has a strong odor. The molecule consists of a

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...

ring with two

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

atoms (replacing hydrogen atoms) on opposing sites of the ring. It is used as a disinfectant, pesticide, and

deodorant A deodorant is a substance applied to the body to prevent or mask body odor due to bacterial breakdown of perspiration or vaginal secretions, for example in the armpits, groin, or feet. A subclass of deodorants, called antiperspirants, prevents ...

, most familiarly in

mothball Mothballs are small balls of chemical pesticide and deodorant, sometimes used when storing clothing and other materials susceptible to damage from mold or moth larvae (especially clothes moths like '' Tineola bisselliella''). Composition Older ...

s in which it is a replacement for the more traditional naphthalene because of naphthalene's greater

flammability A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...

(though both chemicals have the same NFPA 704 rating). It is also used as a

precursor Precursor or Precursors may refer to: * Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of u ...

in the production of the chemically and thermally resistant polymer poly(''p''-phenylene sulfide).

Production

''p''-DCB is produced by

chlorination Chlorination may refer to: * Chlorination reaction In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transform ...

of benzene using

ferric chloride Iron(III) chloride is the inorganic compound with the formula . Also called ferric chloride, it is a common compound of iron in the +3 oxidation state. The anhydrous compound is a crystalline solid with a melting point of 307.6 °C. The col ...

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 The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...

of 53.5 °C; the isomeric

dichlorobenzene There are three distinct chemical compounds which are dichlorobenzenes: * 1,2-Dichlorobenzene or ''ortho''-dichlorobenzene; *1,3-Dichlorobenzene or ''meta''-dichlorobenzene; *1,4-Dichlorobenzene or ''para''-dichlorobenzene. All three isomers are co ...

s and

chlorobenzene Chlorobenzene is an aromatic organic compound with the chemical formula C6H5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals. Uses Historical The major use of chlorob ...

melt well below room temperature.

Uses

Disinfectant, deodorant, and pesticide

''p''-DCB is used to control

moth Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of w ...

mold A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not ...

s, and

mildew Mildew is a form of fungus. It is distinguished from its closely related counterpart, mould, largely by its colour: moulds appear in shades of black, blue, red, and green, whereas mildew is white. It appears as a thin, superficial growth consi ...

. It also finds use as a disinfectant in waste containers and restrooms and is the characteristic smell associated with

urinal cake Urinal deodorizer blocks (commonly known as urinal cakes, urinal cookies, urinal biscuits (piscuits), urinal donuts, toilet lollies, trough lollies, urinal mints, urinal pucks, hockey pucks, toilet pucks, or urinal peons (pee-ons) are small disinf ...

s. Its usefulness for these applications arises from ''p''-DCB's low

solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

in water and its relatively high volatility: it sublimes readily near room temperature.

Precursor to other chemicals

Nitration In organic chemistry, nitration is a general class of chemical processes for the introduction of a nitro group into an organic compound. The term also is applied incorrectly to the different process of forming nitrate esters between alcohols an ...

gives 1,4-dichloronitrobenzene, a precursor to commercial

dyes and pigments A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

.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): : Synthesis Poly(p-phenylene sulfide)

Environmental and health effects

''p''-DCB is poorly soluble in water and is not easily broken down by

soil organisms Soil biology is the study of microbial and faunal activity and ecology in soil. Soil life, soil biota, soil fauna, or edaphon is a collective term that encompasses all organisms that spend a significant portion of their life cycle within a soil ...

. Like many

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

s, ''p''-DCB is

lipophilic Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipo ...

and will accumulate in fatty tissues if consumed by a person or animal. The United States

Department of Health and Human Services The United States Department of Health and Human Services (HHS) is a cabinet-level executive branch department of the U.S. federal government created to protect the health of all Americans and providing essential human services. Its motto is ...

(DHHS) and the

International Agency for Research on Cancer The International Agency for Research on Cancer (IARC; french: Centre International de Recherche sur le Cancer, CIRC) is an intergovernmental agency forming part of the World Health Organization of the United Nations. Its role is to conduct and ...

(IARC) have determined that ''p''-DCB may reasonably be anticipated to be a

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...

. This has been indicated by animal studies, although a full-scale human study has not been done. The

United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...

(EPA) has set a target maximum contaminant level of 75

micrograms In the metric system, a microgram or microgramme is a unit of mass equal to one millionth () of a gram. The unit symbol is μg according to the International System of Units (SI); the recommended symbol in the United States and United Kingdom wh ...

of ''p''-DCB per liter of

drinking water Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, a ...

(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 The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agenc ...

(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 Proposition 65 (formally titled The Safe Drinking Water and Toxic Enforcement Act of 1986, and also referred to as Prop 65) is a California law passed by direct voter initiative in 1986 by a 63%–37% vote. Its goals are to protect drinking water s ...

, ''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.

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