1,4-Dichlorobenzene

1,4-Dichlorobenzene (1,4-DCB, p-DCB, or para-dichlorobenzene, sometimes abbreviated as PDCB or para) is an aryl chloride and isomer of dichlorobenzene 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.

1,4-Dichlorobenzene

1,4-Dichlorobenzene Ball-and-stick model of 1,4-dichlorobenzene
1,4-dichlorobenzene crystallised on paper from DCM solution
Names
Preferred IUPAC name 1,4-Dichlorobenzene
Other names 1,4-DCB para-Dichlorobenzene p-Dichlorobenzene p-DCB PDCB Paramoth Para crystals Paracide Dichlorocide
Identifiers
CAS Number	106-46-7 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1680023
ChEBI	CHEBI:28618 Y
ChEMBL	ChEMBL190982 Y
ChemSpider	13866817 N
ECHA InfoCard	100.003.092
EC Number	203-400-5
Gmelin Reference	49722
KEGG	C07092 Y
PubChem CID	4685
RTECS number	CZ4550000
UNII	D149TYB5MK Y
UN number	3077
CompTox Dashboard (EPA)	DTXSID1020431
InChI InChI=1S/C6H4Cl2/c7-5-1-2-6(8)4-3-5/h1-4H N Key: OCJBOOLMMGQPQU-UHFFFAOYSA-N N
SMILES ClC1=CC=C(Cl)C=C1
Properties
Chemical formula	C6H4Cl2
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)
Solubility in water	10.5 mg/100 mL (20 °C)
Vapor pressure	1.3 mmHg (20 °C)[1]
Magnetic susceptibility (χ)	-82.93·10−6 cm3/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Suspected carcinogen
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H315, H317, H319, H332, H335, H351, H410
Precautionary statements	P201, P202, P261, P264, P270, P271, P272, P273, P280, P281, P301+P312, P302+P352, P304+P312, P304+P340, P305+P351+P338, P308+P313, P312, P321, P330, P332+P313, P333+P313, P337+P313, P362, P363, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	2 2 0
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 (rat, oral) 2950 mg/kg (mouse, oral) 2512 mg/kg (rat, oral) 2830 mg/kg (rabbit, oral)[2]
LDLo (lowest published)	857 mg/kg (human, oral) 4000 mg/kg (rat, oral) 2800 mg/kg (guinea pig, oral)[2]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 75 ppm (450 mg/m3)[1]
REL (Recommended)	Ca[1]
IDLH (Immediate danger)	Ca [150 ppm][1]
Related compounds
Related compounds	1,2-Dichlorobenzene 1,3-Dichlorobenzene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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]

Production

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]

Uses

Disinfectant, deodorant, and pesticide

1,4-dichlorobenzene balls sold as urinal disinfectant

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

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 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]

A mechanism for the carcinogenic effects of mothballs and some types of air fresheners containing p-DCB has been identified in roundworms.^[14]

Due to its carcinogenic nature, use of paradichlorobenzene in the European Union is forbidden as an air freshener (since 2005) and in mothballs (since 2008).

Biodegradation

Rhodococcus phenolicus is a bacterium species able to degrade dichlorobenzene as its sole carbon source.^[15]

See also

• Air freshener
• Camphor
• Mothball

References

1. NIOSH Pocket Guide to Chemical Hazards. "#0190". National Institute for Occupational Safety and Health (NIOSH).
2. "p-Dichlorobenzene". National Institute for Occupational Safety and Health (NIOSH). 4 December 2014. Retrieved 6 March 2015.
3. 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. Weinheim: Wiley-VCH. doi:10.1002/14356007.a06_233.pub2. ISBN 978-3527306732.
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. Bibcode:1991MaMol..24.4242F. doi:10.1021/ma00015a003.
7. Preamble to the IARC Monographs Archived 9 August 2016 at the Wayback Machine 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. "1,4-Dichlorobenzene (para-Dichlorobenzene)". US Environmental Protection Agency. Archived from the original on 4 April 2016. 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. Archived from the original on 31 July 2017. 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. Kokel, David (14 May 2006). "The nongenotoxic carcinogens naphthalene and para-dichlorobenzene suppress apoptosis in Caenorhabditis elegans". Nature Chemical Biology. 2 (6): 338–345. doi:10.1038/nchembio791. PMID 16699520. S2CID 18402091.
15. Rehfuss, M.; Urban, J. (2005). "Rhodococcus phenolicus sp. nov., a novel bioprocessor isolated actinomycete with the ability to degrade chlorobenzene, dichlorobenzene and phenol as sole carbon sources". Systematic and Applied Microbiology. 28 (8): 695–701. doi:10.1016/j.syapm.2005.05.011. PMID 16261859.

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