Preferred IUPAC name
Other names
Para crystals
106-46-7 YesY
3D model (Jmol) Interactive image
ChemSpider 13866817 N
ECHA InfoCard 100.003.092
KEGG C07092 YesY
RTECS number CZ4550000
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]
Main hazards Suspected carcinogen
Carc. Cat. 3
R-phrases R36 R40 R50/53
S-phrases (S2) S36/37 S46 S60 S61
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 fuel Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special 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 (oral, rat)
2950 mg/kg (oral, mouse)
2512 mg/kg (oral, rat)
2830 mg/kg (oral, rabbit)[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).
N verify (what is YesYN ?)
Infobox references

1,4-Dichlorobenzene (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 pesticide and a deodorant, most familiarly in mothballs in which it is a replacement for the more traditional naphthalene because of its flammability (though both chemicals have the same NFPA 704 rating). It is also used as a precursor in the production of the 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 crystallisation, 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

p-DCB is used to control moths, moulds, 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

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]

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 the fatty tissues.

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] Animals given very high levels in water developed liver and kidney tumors.

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 probable mechanism for the carcinogenic effects of mothballs and some types of air fresheners containing p-DCB has been identified.[15][16]

See also


  1. 1 2 3 4 5 6 7 "NIOSH Pocket Guide to Chemical Hazards #0190". National Institute for Occupational Safety and Health (NIOSH).
  2. 1 2 "p-Dichlorobenzene". National Institute for Occupational Safety and Health (NIOSH). 4 December 2014. Retrieved 6 March 2015.
  3. 1 2 3 4 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). 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 2016-03-24.
  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. "Scientists May Have Solved Mystery Of Carcinogenic Mothballs", Physorg.com, 20 June 2006.
  16. "Mothballs, air fresheners and cancer". Environmental Health Association of Nova Scotia. Environmental Health Association of Nova Scotia. Retrieved 24 May 2013.

External links

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