|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|| Xn
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)|
LD50 (Lethal dose)
|500 mg/kg (oral, rat)
2950 mg/kg (oral, mouse)
2512 mg/kg (oral, rat)
2830 mg/kg (oral, rabbit)
|US health exposure limits (NIOSH):|
|TWA 75 ppm (450 mg/m3)|
IDLH (Immediate danger)
|Ca [150 ppm]|
Except where noted otherwise, data is 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. 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. p-DCB 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
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. 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). 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.
- 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.
- "Reregistration Eligibility Decision for Para-dichlorobenzene" (PDF). December 2008. Archived from the original (PDF) on 26 September 2009. Retrieved 10 August 2009.
- 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.