Ball-and-stick model of 1,4-dichlorobenzene
IUPAC name
Other names
Para crystals
ChemSpider  N
Jmol-3D images Image
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; 326.7 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
Harmful Xn
Dangerous for the Environment (Nature) N
Carc. Cat. 3
R-phrases R50/53
S-phrases (S2) S36/37 S46 S60 S61
NFPA 704
Flash point 66 °C (151 °F; 339 K)
Explosive limits 2.5%-?[1]
Lethal dose or concentration (LD, LC):
LD50 (Median dose)
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)
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  (: Y/N?)

1,4-Dichlorobenzene (p-DCB or para-dichlorobenzene, sometimes abbreviated as PDB or para) is an formula C6H4Cl2. This colorless solid has a strong odor. In terms of its structure, the molecule consists of two chlorine atoms substituted for hydrogen at opposing sites on a benzene ring. p-DCB is used as a pesticide and a deodorant, most familiarly in mothballs in which it is a replacement for the more traditional naphthalene due to its flammability. p-DCB is also used as a precursor in the production of the polymer poly(p-phenylene sulfide).[3]


  • Production 1
  • Uses 2
    • Disinfectant, deodorant, and pesticide 2.1
    • Precursor to other chemicals 2.2
  • Environmental and health effects 3
  • See also 4
  • References 5
  • External links 6


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 centres 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

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] p-DCB is also an EPA-registered pesticide.[10] 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.

Under California's Proposition 65, p-DCB is listed as "known to the State to cause cancer".[11] A probable mechanism for the carcinogenic effects of mothballs and some types of air fresheners containing p-DCB has been identified.[12][13]

See also


  1. ^ a b c d e f g "NIOSH Pocket Guide to Chemical Hazards #0190".  
  2. ^ a b -Dichlorobenzene"p". 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.  
  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.  
  7. ^ IARC MonographsPreamble to the 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. ^ "Reregistration Eligibility Decision for Para-dichlorobenzene" (PDF). December 2008. Archived from the original (PDF) on 26 September 2009. Retrieved 10 August 2009. 
  11. ^ Proposition 65, Office of Environmental Health Hazard Assessment
  12. ^ "Scientists May Have Solved Mystery Of Carcinogenic Mothballs", Physorg.com, 20 June 2006.
  13. ^ "Mothballs, air fresheners and cancer". Environmental Health Association of Nova Scotia. Environmental Health Association of Nova Scotia. Retrieved 24 May 2013. 

External links

  • International Chemical Safety Card 0037
  • Mothball sniffing warning issued, BBC News, 27 July 2006
  • NIOSH Pocket Guide to Chemical Hazards, Centers for Disease Control and Prevention