Chemistry:1,4-Dichlorobenzene

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1,4-Dichlorobenzene
1,4-Dichlorobenzene
Ball-and-stick model of 1,4-dichlorobenzene
1,4 dichlorobenzene crystallised.jpg
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
3D model (JSmol)
1680023
ChEBI
ChEMBL
ChemSpider
EC Number
  • 203-400-5
49722
KEGG
RTECS number
  • CZ4550000
UNII
UN number 3077
Properties
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)
10.5 mg/100 mL (20 °C)
Vapor pressure 1.3 mmHg (20 °C)[1]
-82.93·10−6 cm3/mol
Hazards
Main hazards Suspected carcinogen
GHS pictograms GHS07: HarmfulGHS08: Health hazardGHS09: Environmental hazard
GHS Signal word Warning
H302, H315, H317, H319, H332, H335, H351, H410
P201, P202, P261, P264, P270, P271, P272, P273, P280, P281, P301+312, P302+352, P304+312, P304+340, P305+351+338, P308+313, P312, P321, P330, P332+313, P333+313, P337+313, P362, P363, P391
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
2
2
0
Flash point 66 °C (151 °F; 339 K)
Explosive limits 2.5%-?[1]
Lethal dose or concentration (LD, LC):
500 mg/kg (rat, oral)
2950 mg/kg (mouse, oral)
2512 mg/kg (rat, oral)
2830 mg/kg (rabbit, oral)[2]
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).
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Infobox references
Tracking categories (test):

1,4-Dichlorobenzene (1,4-DCB, p-DCB, or para-dichlorobenzene, sometimes abbreviated as PDCB or para) is an 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

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]

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 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

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 NIOSH Pocket Guide to Chemical Hazards. "#0190". National Institute for Occupational Safety and Health (NIOSH). https://www.cdc.gov/niosh/npg/npgd0190.html. 
  2. ↑ 2.0 2.1 "p-Dichlorobenzene". National Institute for Occupational Safety and Health (NIOSH). 4 December 2014. https://www.cdc.gov/niosh/idlh/106467.html. 
  3. ↑ 3.0 3.1 3.2 3.3 Rossberg, M.; Lendle, W.; Pfleiderer, G.; Tögel, A.; Dreher, E. L.; Langer, E.; Rassaerts, H.; Kleinschmidt, P. et al. (2006). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a06_233.pub2. 
  4. ↑ "National Pesticide Information Center – Mothballs Case Profile". http://npic.orst.edu/capro/Mothballs1.pdf. 
  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. doi:10.1021/ma00015a003. Bibcode: 1991MaMol..24.4242F. 
  7. ↑ Preamble to the IARC Monographs 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. https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsLanding.aspx?id=703&tid=126. 
  9. ↑ "Consumer Factsheet on: PARA-DICHLOROBENZENE (p-DCB)". 28 November 2006. http://www.epa.gov/ogwdw000/contaminants/dw_contamfs/p-dichlo.html. 
  10. ↑ "1,4-Dichlorobenzene (para-Dichlorobenzene)" (in en). https://www3.epa.gov/airtoxics/hlthef/dich-ben.html. 
  11. ↑ "Reregistration Eligibility Decision for Para-dichlorobenzene". December 2008. http://www.epa.gov/oppsrrd1/REDs/para-dichlorobenzene-red-revised.pdf. 
  12. ↑ "Chemical Sampling – p-Diclorobenzine". Occupational Safety & Health Administration. https://www.osha.gov/dts/chemicalsampling/data/CH_232900.html. 
  13. ↑ "Common Name: 1,4-DICHLOROBENZENE". New Jersey Department of Health and Senior Services. December 2005. http://nj.gov/health/eoh/rtkweb/documents/fs/0643.pdf. 
  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. 
  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



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