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Ball-and-stick model of 1,4-dichlorobenzene
Preferred IUPAC name
Other names
Para crystals
3D model (JSmol)
ECHA InfoCard 100.003.092
EC Number 203-400-5
RTECS number CZ4550000
UN number 3077
Molar mass 147.00 g·mol−1
Appearance Colorless/white crystals[1]
Odor mothball-like[1]
Density 1.25 g/cm3, solid
Melting point 53.5 °C (128.3 °F; 326.6 K)
Boiling point 174 °C (345 °F; 447 K)
10.5 mg/100 mL (20 °C)
Vapor pressure 1.3 mmHg (20°C)[1]
-82.93·10−6 cm3/mol
Main hazards Suspected carcinogen
GHS pictograms The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The environment pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Warning
H302, H315, H317, H319, H332, H335, H351, H400, H410
P201, P202, P261, P264, P270, P271, P272, P273, P280, P281, P301+312, P302+352, P304+312, P304+340, P305+351+338, P308+313, P312, P321, P330, P332+313, P333+313, P337+313, P362, P363, P391
NFPA 704
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuelHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
Flash point 66 °C (151 °F; 339 K)
Explosive limits 2.5%-?[1]
Lethal dose or concentration (LD, LC):
500 mg/kg (rat, oral)
2950 mg/kg (mouse, oral)
2512 mg/kg (rat, oral)
2830 mg/kg (rabbit, oral)[2]
857 mg/kg (human, oral)
4000 mg/kg (rat, oral)
2800 mg/kg (guinea pig, oral)[2]
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 75 ppm (450 mg/m3)[1]
REL (Recommended)
IDLH (Immediate danger)
Ca [150 ppm][1]
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

1,4-Dichlorobenzene (1,4-DCB, p-DCB, or para-dichlorobenzene, sometimes abbreviated as PDB or para) 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 (replacing hydrogen 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 (though both chemicals have the same NFPA 704 rating). It is also used as a precursor in the production of the chemically and thermally resistant polymer poly(p-phenylene sulfide).[3]


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 53.5 °C; the isomeric dichlorobenzenes and chlorobenzene melt well below room temperature.[3]


Disinfectant, deodorant, and pesticide[edit]

p-DCB is used to control moths, molds, and mildew.[4] It also finds use as a disinfectant[3] 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.[3]

Precursor to other chemicals[edit]

Nitration gives 1,4-dichloronitrobenzene, a precursor to commercial dyes and pigments.[5] 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):[6]

Synthesis of Polyphenylensulfide

Environmental and health effects[edit]

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 (DHHS) and the International Agency for Research on Cancer (IARC) have determined that p-DCB may reasonably be anticipated to be a carcinogen.[7] This has been indicated by animal studies, although a full-scale human study has not been done.[8]

The United States Environmental Protection Agency (EPA) has set a target maximum contaminant level of 75 micrograms of p-DCB per liter of drinking water (75 μg/L),[9] but publishes no information on the cancer risk.[10] p-DCB is also an EPA-registered pesticide.[11] The United States 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.[12][13]

Under California's Proposition 65, p-DCB is listed as "known to the State to cause cancer".[14] A mechanism for the carcinogenic effects of mothballs and some types of air fresheners containing p-DCB has been identified in roundworms.[15]

See also[edit]


  1. ^ a b c d e f g NIOSH Pocket Guide to Chemical Hazards. "#0190". National Institute for Occupational Safety and Health (NIOSH).
  2. ^ a b "p-Dichlorobenzene". National Institute for Occupational Safety and Health (NIOSH). 4 December 2014. Retrieved 6 March 2015.
  3. ^ a b c d Rossberg, M.; Lendle, W.; Pfleiderer, G.; Tögel, A.; Dreher, E. L.; Langer, E.; Rassaerts, H.; Kleinschmidt, P.; Strack, H.; Cook, R.; Beck, U.; Lipper, K.-A.; Torkelson, T.R.; Löser, E.; Beutel, K.K.; Mann, T. (2006). "Chlorinated Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a06_233.pub2. ISBN 3527306730.
  4. ^ "National Pesticide Information Center – Mothballs Case Profile" (PDF). Archived from the original (PDF) on 22 June 2010. Retrieved 10 August 2009.
  5. ^ K. Hunger. W. Herbst "Pigments, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012. doi:10.1002/14356007.a20_371
  6. ^ Fahey, D. R.; Ash, C. E. (1991). "Mechanism of poly(p-phenylene sulfide) growth from p-dichlorobenzene and sodium sulfide". Macromolecules. 24 (15): 4242. doi:10.1021/ma00015a003.
  7. ^ Preamble to the IARC Monographs definition of "Group 2B: Possibly carcinogenic to humans", the International Agency for Research on Cancer classification of this chemical
  8. ^ "ToxFAQs™ for Dichlorobenzenes". Toxic Substances Portal. Agency for Toxic Substances and Disease Registry. Retrieved 24 May 2013.
  9. ^ "Consumer Factsheet on: PARA-DICHLOROBENZENE (p-DCB)". 28 November 2006. Archived from the original on 6 October 2009. Retrieved 10 August 2009.
  10. ^ Standards, US EPA, OAR, Office of Air Quality Planning and. "1,4-Dichlorobenzene (para-Dichlorobenzene) - Technology Transfer Network Air Toxics Web site | US EPA". www3.epa.gov. Retrieved 24 March 2016.
  11. ^ "Reregistration Eligibility Decision for Para-dichlorobenzene" (PDF). December 2008. Archived from the original (PDF) on 26 September 2009. Retrieved 10 August 2009.
  12. ^ "Chemical Sampling - p-Diclorobenzine". United States Department of Labor. Occupational Safety & Health Administration. Retrieved 23 March 2016.
  13. ^ "Common Name: 1,4-DICHLOROBENZENE" (PDF). New Jersey Department of Health and Senior Services. December 2005. Retrieved 24 March 2016.
  14. ^ Proposition 65, Office of Environmental Health Hazard Assessment
  15. ^ Kokel, David (14 May 2006). "The nongenotoxic carcinogens naphthalene and para-dichlorobenzene suppress apoptosis in Caenorhabditis elegans". Nature Chemical Biology. 2: 338–345. doi:10.1038/nchembio791. Archived from the original on 19 February 2008. Retrieved 24 May 2013.

External links[edit]