| Preferred IUPAC name
| Other names
|3D model (Jmol)||Interactive image|
|Molar mass||147.00 g·mol−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)|
|Main hazards||Suspected carcinogen|
EU classification (DSD)
Carc. Cat. 3
|R-phrases||R36 R40 R50/53|
|S-phrases||(S2) S36/37 S46 S60 S61|
|Flash point||66 °C (151 °F; 339 K)|
|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)
LDLo (lowest published)
| 857 mg/kg (human, oral)|
4000 mg/kg (rat, oral)
2800 mg/kg (guinea pig, oral)
|US health exposure limits (NIOSH):|
|TWA 75 ppm (450 mg/m3)|
IDLH (Immediate danger)
|Ca [150 ppm]|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|(what is ?)|
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).
- 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.
Disinfectant, deodorant, and pesticide
p-DCB is used to control moths, moulds, and mildew. It also finds use as a disinfectant 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.
Precursor to other chemicals
Nitration gives 1,4-dichloronitrobenzene, a precursor to commercial dyes and pigments. 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):
Environmental and health effects
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. This has been indicated by animal studies, although a full-scale human study has not been done. 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), but publishes no information on the cancer risk. p-DCB is also an EPA-registered pesticide. 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". A probable mechanism for the carcinogenic effects of mothballs and some types of air fresheners containing p-DCB has been identified.
- "NIOSH Pocket Guide to Chemical Hazards #0190". National Institute for Occupational Safety and Health (NIOSH).
- "p-Dichlorobenzene". National Institute for Occupational Safety and Health (NIOSH). 4 December 2014. Retrieved 6 March 2015.
- 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.
- "National Pesticide Information Center – Mothballs Case Profile" (PDF). Retrieved 10 August 2009.
- K. Hunger. W. Herbst "Pigments, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012. doi:10.1002/14356007.a20_371
- 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.
- Preamble to the IARC Monographs definition of "Group 2B: Possibly carcinogenic to humans", the International Agency for Research on Cancer classification of this chemical
- "ToxFAQs™ for Dichlorobenzenes". Toxic Substances Portal. Agency for Toxic Substances and Disease Registry. Retrieved 24 May 2013.
- "Consumer Factsheet on: PARA-DICHLOROBENZENE (p-DCB)". 28 November 2006. Archived from the original on 6 October 2009. Retrieved 10 August 2009.
- 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.
- "Reregistration Eligibility Decision for Para-dichlorobenzene" (PDF). December 2008. Archived from the original (PDF) on 26 September 2009. Retrieved 10 August 2009.
- "Chemical Sampling - p-Diclorobenzine". United States Department of Labor. Occupational Safety & Health Administration. Retrieved 23 March 2016.
- "Common Name: 1,4-DICHLOROBENZENE" (PDF). New Jersey Department of Health and Senior Services. December 2005. Retrieved 24 March 2016.
- Proposition 65, Office of Environmental Health Hazard Assessment
- "Scientists May Have Solved Mystery Of Carcinogenic Mothballs", Physorg.com, 20 June 2006.
- "Mothballs, air fresheners and cancer". Environmental Health Association of Nova Scotia. Environmental Health Association of Nova Scotia. Retrieved 24 May 2013.
- 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