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. The ...
with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
C
6H
4Cl
2. This colorless solid has a strong
odor
An odor (American English) or odour (English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is caused by one or more volatilized chemical compounds ...
. 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 (chemistry), 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 betwee ...
atoms (replacing hydrogen atoms) on opposing sites of the ring.
It is used as a
disinfectant
A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...
,
pesticide
Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampri ...
, 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 s ...
, most familiarly in
mothballs in which it is a replacement for the more traditional
naphthalene
Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromati ...
because of naphthalene's greater
flammability (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 unr ...
in the production of the chemically and thermally resistant polymer
poly(''p''-phenylene sulfide).
Production
''p''-DCB is produced by
chlorination 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 colo ...
as a catalyst:
:C
6H
6 + 2 Cl
2 → C
6H
4Cl
2 + 2
HCl HCL may refer to:
Science and medicine
* Hairy cell leukemia, an uncommon and slowly progressing B cell leukemia
* Harvard Cyclotron Laboratory, from 1961 to 2002, a proton accelerator used for research and development
* Hollow-cathode lamp, a spe ...
The chief impurity is the 1,2
isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers.
Iso ...
. The compound can be purified by
fractional crystallization Fractional crystallization may refer to:
* Fractional crystallization (chemistry), a process to separate different solutes from a solution
* Fractional crystallization (geology)
Fractional crystallization, or crystal fractionation, is one of the ...
, 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 depends ...
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 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 ...
s, molds, and mildew. 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 solubil ...
in water and its relatively high volatility: it sublimes
Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point i ...
readily near room temperature.[
]
Precursor to other chemicals
Nitration gives 1,4-dichloronitrobenzene, a precursor to commercial dyes and pigments.[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
A substitution reaction (also known as single displacement reaction or single substitution reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions ar ...
with hydroxylamine and sulfide groups. In a growing application, ''p''-DCB is the precursor to the high performance polymer 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 ex ...
s, ''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 (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 substan ...
. 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 be ...
(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 whe ...
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
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 be ...
-registered pesticide
Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampri ...
. 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
The weekdays and weekend are the complementary parts of the week devoted to labour and rest, respectively. The legal weekdays (British English), or workweek (American English), is the part of the seven-day week devoted to working. In most of th ...
.
Under California's Proposition 65, ''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.
See also
* Air freshener
Air fresheners are consumer products that typically emit fragrance and are used in homes or commercial interiors such as restrooms, foyers, hallways, vestibules and other smaller indoor areas, as well as larger areas such as hotel lobbies, auto d ...
* Camphor
Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel ('' Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the k ...
* Dichlorobenzene
* 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