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Chloroform
Identifiers
CAS number 67-66-3 Yes check.svgY
PubChem 6212
ChemSpider 5977
EC number 200-663-8
KEGG C13827
ChEBI 35255
RTECS number FS9100000
SMILES
InChI
InChI key HEDRZPFGACZZDS-UHFFFAOYAG
Properties
Molecular formula CHCl3
Molar mass 119.38 g/mol
Appearance Colorless liquid
Density 1.483 g/cm3
Melting point

-63.5 °C

Boiling point

61.2 °C

Solubility in water 0.8 g/100 ml (20 °C)
Refractive index (nD) 1.4459
Structure
Molecular shape Tetrahedral
Hazards
MSDS External MSDS
R-phrases R22, R38, R40, R48/20/22
S-phrases (S2), S36/37
NFPA 704
NFPA 704.svg
0
2
0
Flash point Non-flammable
U.S. Permissible
exposure limit (PEL)
50 ppm (240 mg/m3) (OSHA)
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references
Chloroform in its liquid state shown in a test tube

Chloroform is the organic compound with formula CHCl3. This colorless, sweet-smelling, dense liquid is a trihalomethane. It is also considered somewhat hazardous. Several million tons are produced annually as a precursor to Teflon and refrigerants, but its use for refrigerants is being phased out.[1]

Contents

Production

Chloroform was reported in 1831 by the French chemist Eugène Soubeiran, who prepared it from acetone (2-propanone) as well as ethanol through the action of chlorine bleach powder (calcium hypochlorite).[2] The American physician Samuel Guthrie prepared gallons of the material and described its "deliciousness of flavor."[3] Independently, Justus von Liebig also described the same compound.[4] All early preparations used variations of the haloform reaction. Chloroform was named and chemically characterised in 1834 by Jean-Baptiste Dumas.[5]

Industrial routes

In industry, chloroform is produced by heating a mixture of chlorine and either chloromethane or methane.[1] At 400-500 °C, a free radical halogenation occurs, converting these precursors to progressively more chlorinated compounds:

CH4 + Cl2 → CH3Cl + HCl
CH3Cl + Cl2CH2Cl2 + HCl
CH2Cl2 + Cl2 → CHCl3 + HCl

Chloroform undergoes further chlorination to give CCl4:

CHCl3 + Cl2 → CCl4 + HCl

The output of this process is a mixture of the four chloromethanes, chloromethane, dichloromethane, chloroform, and carbon tetrachloride, which are then separated by distillation.[1]

Deuterochloroform

An archaic industrial route to chloroform involved the reaction of acetone (or ethanol) with sodium hypochlorite or calcium hypochlorite, the aforementioned haloform reaction.[1] The chloroform can be removed from the coproducts by distillation. A related reaction is still used in the production of bromoform and iodoform. Although the haloform process is obsolete for the production of ordinary chloroform, it is used to produce CDCl3.[citation needed] Deuterochloroform can also be prepared by the reaction of sodium deuteroxide with chloral hydrate,[citation needed] or from ordinary chloroform.[6]

Inadvertent formation of chloroform

The haloform reaction can also occur inadvertently in domestic settings. Sodium hypochlorite solution (chlorine bleach) mixed with common household liquids such as acetone, butanone, ethanol, or isopropyl alcohol can produce some chloroform, in addition to other compounds such as chloroacetone, or dichloroacetone.

Uses

The major use of chloroform today is in the production of the chlorodifluoromethane (R-22), a major precursor to tetrafluoroethylene:

CHCl3 + 2 HF → CHClF2 + 2 HCl

The reaction is conducted in the presence of a catalytic amount of antimony pentafluoride. Chlorodifluoromethane is then converted into tetrafluoroethylene, the main precursor to Teflon. Before the Montreal Protocol, chlorodifluoromethane (R22) was also popular refrigerant.

As a solvent

Chloroform is a common solvent in the laboratory because it is relatively unreactive, miscible with most organic liquids, and conveniently volatile. Chloroform is used as a solvent in the pharmaceutical industry and for producing dyes and pesticides. Chloroform is an effective solvent for alkaloids in their base form and thus plant material is commonly extracted with chloroform for pharmaceutical processing. For example, it is used in commerce to extract morphine from poppies and scopolamine from Datura plants. Chloroform containing deuterium (heavy hydrogen), CDCl3, is a common solvent used in NMR spectroscopy. It can be used to bond pieces of acrylic glass (also known under the trade names Perspex and Plexiglas). A solvent of phenol:chloroform:isoamyl alcohol 25:24:1 is used to dissolve non-nucleic acid biomolecules in DNA and RNA extractions.

As a reagent in organic synthesis

As a reagent, chloroform serves as a source of the dichlorocarbene CCl2 group.[7] It reacts with aqueous sodium hydroxide usually in the presence of a phase transfer catalyst to produce dichlorocarbene, CCl2.[8][9] This reagent effects ortho-formylation of activated aromatic rings such as phenols, producing aryl aldehydes in a reaction known as the Reimer-Tiemann reaction. Alternatively the carbene can be trapped by an alkene to form a cyclopropane derivative. In the Kharasch addition chloroform forms the CHCl2 free radical in addition to alkenes.

As an anesthetic

Chloroform was once a popular anesthetic; its vapor depresses the central nervous system of a patient, allowing a doctor to perform various otherwise painful procedures. In 1847, the Edinburgh obstetrician James Young Simpson first used chloroform for general anesthesia during childbirth. The use of chloroform during surgery expanded rapidly thereafter in Europe. In the United States, chloroform began to replace ether as an anesthetic at the beginning of the 20th century; however, it was quickly abandoned in favour of ether upon discovery of its toxicity, especially its tendency to cause fatal cardiac arrhythmia analogous to what is now termed "sudden sniffer's death". Ether is still the preferred anesthetic in some developing nations due to its high therapeutic index (~1.5-2.2) [10] and low price. One possible mechanism of action for chloroform is that it increases movement of potassium ions through certain types of potassium channels in nerve cells.[11]

Safety

A fatal oral dose of chloroform is about 10 mL (14.8 g), with death due to respiratory or cardiac arrest.[12]

As might be expected for an anesthetic, chloroform vapors depresses the central nervous system. It is immediately dangerous to life and health at approximately 500 ppm, according to the U. S. National Institute for Occupational Safety and Health. Breathing about 900 ppm for a short time can cause dizziness, fatigue, and headache. Chronic chloroform exposure can damage the liver (where chloroform is metabolized to phosgene) and to the kidneys, and some people develop sores when the skin is immersed in chloroform.

Animal studies have shown that miscarriages occur in rats and mice that have breathed air containing 30 to 300 ppm of chloroform during pregnancy and also in rats that have ingested chloroform during pregnancy. Offspring of rats and mice that breathed chloroform during pregnancy have a higher incidence of birth defects, and abnormal sperm have been found in male mice that have breathed air containing 400 ppm chloroform for a few days. The effect of chloroform on reproduction in humans is unknown.

Chloroform once appeared in toothpastes, cough syrups, ointments, and other pharmaceuticals, but it has been banned as a consumer product in the US since 1976.[13]

The US National Toxicology Program's eleventh report on carcinogens[14] implicates it as reasonably anticipated to be a human carcinogen, a designation equivalent to International Agency for Research on Cancer class 2A. It has been most readily associated with hepatocellular carcinoma.[15][16] Caution is mandated during its handling in order to minimize unnecessary exposure; safer alternatives, such as dichloromethane, have resulted in a substantial reduction of its use as a solvent.

Conversion to phosgene

During prolonged storage in the presence of oxygen and ultraviolet light, chloroform converts slowly to phosgene. To prevent accidents, commercial chloroform is stabilized with ethanol or amylene, but samples that have been recovered or dried no longer contain any stabilizer. Suspicious samples can be tested for phosgene using 5% diphenylamine, 5% dimethylaminobenzaldehyde, and then dried, turn yellow in phosgene vapor.

References

  1. ^ a b c d M. Rossberg et al. “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2
  2. ^ Eugène Soubeiran (1831). ".". Ann. Chim. 48: 131. 
  3. ^ Samuel Guthrie (1832). "New mode of preparing a spirituous solution of Chloric Ether". Am. J. Sci. and Arts 21: 64. 
  4. ^ Justus Liebig (1832). "Ueber die Verbindungen, welche durch die Einwirkung des Chlors auf Alkohol, Aether, ölbildendes Gas und Essiggeist entstehen". Annalen der Pharmacie 1 (2): 182–230. doi:10.1002/jlac.18320010203. 
  5. ^ Jean-Baptiste Dumas (1834). "Untersuchung über die Wirkung des Chlors auf den Alkohol". Annalen der Pharmacie 107 (41): 650–656. doi:10.1002/andp.18341074103. 
  6. ^ Canadian Patent 1085423
  7. ^ Srebnik, M.; Laloë, E. "Chloroform" Encyclopedia of Reagents for Organic Synthesis" 2001 John Wiley.doi:10.1002/047084289X.rc105
  8. ^ "1,6-Methano[10]annulene", Org. Synth., 1988, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv6p0731 ; Coll. Vol. 6: 731 
  9. ^ Gokel, G. W.; Widera, R. P.; Weber, W. P. (1988), "Phase-Transfer Hofmann Carbylamine Reaction: tert-Butyl Isocyanide", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv6p0232 ; Coll. Vol. 6: 232 
  10. ^ Calderone, F.A. J. Pharmacology Experimental Therapeutics, 1935, 55(1), 24-39, http://jpet.aspetjournals.org/cgi/reprint/55/1/24.pdf
  11. ^ Patel, Amanda J.; Honoré, Eric; Lesage, Florian; Fink, Michel; Romey, Georges; Lazdunski, Michel (May 1999). written at Valbonne, France. "Inhalational anesthetics activate two-pore-domain background K+ channels". Nature Neuroscience 2 (5): 422–426. doi:10.1038/8084. ISSN 1097-6256. PMID 10321245. http://www.nature.com/neuro/journal/v2/n5/abs/nn0599_422.html. 
  12. ^ http://www.epa.gov/ttn/atw/hlthef/chlorofo.html
  13. ^ "The National Toxicology Program: Substance Profiles: Chloroform CAS No. 67-66-3" (pdf). http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s038chlo.pdf. Retrieved 2007-11-02. 
  14. ^ "11th Report on Carcinogens". http://ntp.niehs.nih.gov/ntp/roc/toc11.html. Retrieved 2007-11-02. 
  15. ^ "Centers for Disease Control and Prevention: CURRENT INTELLIGENCE BULLETIN 9". http://www.cdc.gov/Niosh/78127_9.html. 
  16. ^ "National Toxicology Program: Report on the carcinogenesis bioassay of chloroform". http://ntp.niehs.nih.gov/ntp/htdocs/LT_rpts/trChloroform.pdf. 

External links


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Simple English

File:Effects of chloroform (historical)
An illustration showing the effects of Chloroform,from the 1840s

Chloroform (also called trichloromethane) is a chemical substance. It is an organic compound. Chloroform is one of the intermediate substances that occur in the production of Polytetrafluoroethylene, better known as Teflon.

Contents

History

The first who reported to have produced Chloroform was the French chemist Eugène Soubeiran, in 1831. Soubeiran took acetone and ethanol, and used bleach powder for the reaction.[1] The American physician Samuel Guthrie prepared gallons of the material and described its "deliciousness of flavor."[2] Independently, Justus von Liebig also described it.[3] Chloroform was named and chemically characterised in 1834 by Jean-Baptiste Dumas.[4]

Uses

The main uses of Chloroform are:

  • As a solvent
  • As an anaesthetic (though no longer used, as there are side-effects)
  • To help other reactions

Problems

Chloroform was used as an anaesthetic during childbirth and surgery, from about 1847. It replaced ether in this function. Chloroform is very poisonous, and can cause breathing problems, and problems with the heart. Death from chloroform can come from cardiac arrest. When Chloroform is stored for a longer time period, it can decay into Phosgene. Phosgene was a chemical weapon (poison gas) used during the First World War. Chloroform can cause birth defects and lead to miscarriages. It may cause cancer.

References

  1. Eugène Soubeiran (1831). [Expression error: Unexpected < operator "."]. Ann. Chim. 48: 131. 
  2. Samuel Guthrie (1832). [Expression error: Unexpected < operator "New mode of preparing a spirituous solution of Chloric Ether"]. Am. J. Sci. and Arts 21: 64. 
  3. Justus Liebig (1832). [Expression error: Unexpected < operator "Ueber die Verbindungen, welche durch die Einwirkung des Chlors auf Alkohol, Aether, ölbildendes Gas und Essiggeist entstehen"]. Annalen der Pharmacie 1 (2): 182–230. doi:10.1002/jlac.18320010203. 
  4. Jean-Baptiste Dumas (1834). [Expression error: Unexpected < operator "Untersuchung über die Wirkung des Chlors auf den Alkohol"]. Annalen der Pharmacie 107 (41): 650–656. doi:10.1002/andp.18341074103. 







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