1,4-Dichlorobenzene

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 ;
3D model (JSmol)	Interactive image;
Beilstein Reference	1680023
ChEBI	CHEBI:28618 ;
ChEMBL	ChEMBL190982 ;
ChemSpider	13866817 ;
ECHA InfoCard	100.003.092
EC Number	203-400-5;
Gmelin Reference	49722
KEGG	C07092 ;
PubChem CID	4685;
RTECS number	CZ4550000;
UNII	D149TYB5MK ;
UN number	3077
CompTox Dashboard (EPA)	DTXSID1020431 ;
	InChI InChI=1S/C6H4Cl2/c7-5-1-2-6(8)4-3-5/h1-4H Key: OCJBOOLMMGQPQU-UHFFFAOYSA-N ;
	SMILES ClC1=CC=C(Cl)C=C1;
Properties
Chemical formula	C6H4Cl2
Molar mass	147.00 g·mol−1
Appearance	Colorless/white crystals
Odor	mothball-like
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)
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%-?
	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)
LDLo (lowest published)	857 mg/kg (human, oral); 4000 mg/kg (rat, oral); 2800 mg/kg (guinea pig, oral)
	NIOSH (US health exposure limits):
PEL (Permissible)	TWA 75 ppm (450 mg/m3)
REL (Recommended)	Ca
IDLH (Immediate danger)	Ca [150 ppm]
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). verify (what is ?) Infobox references

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.

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

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]

References

^ ^a ^b ^c ^d ^e ^f ^g NIOSH Pocket Guide to Chemical Hazards. "#0190". National Institute for Occupational Safety and Health (NIOSH).
^ ^a ^b "p-Dichlorobenzene". National Institute for Occupational Safety and Health (NIOSH). 4 December 2014. Retrieved 6 March 2015.
^ ^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. Weinheim: Wiley-VCH. doi:10.1002/14356007.a06_233.pub2. ISBN 978-3527306732.
^ "National Pesticide Information Center – Mothballs Case Profile" (PDF). Archived from the original (PDF) on 22 June 2010. 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. Bibcode:1991MaMol..24.4242F. doi:10.1021/ma00015a003.
^ 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
^ "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.
^ "1,4-Dichlorobenzene (para-Dichlorobenzene)". US Environmental Protection Agency. Archived from the original on 4 April 2016. Retrieved 24 March 2016.
^ "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. Archived from the original on 31 July 2017. Retrieved 23 March 2016.
^ "Common Name: 1,4-DICHLOROBENZENE" (PDF). New Jersey Department of Health and Senior Services. December 2005. Retrieved 24 March 2016.
^ 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.
^ 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.