chloroform

Chloroform
IUPAC name	Chloroform
Systematic name	Trichloromethane
Other names	Formyl trichloride, Methane trichloride, Methyl trichloride, Methenyl trichloride, TCM, Freon 20, R-20, UN 1888
Identifiers
CAS number	[67-66-3]
PubChem	6212
EC number	200-663-8
KEGG	C13827
ChEBI	35255
RTECS number	FS9100000
SMILES	C(Cl)(Cl)Cl
InChI	1/CHCl3/c2-1(3)4/h1H
ChemSpider ID	5977
Properties
Molecular formula	CHCl3
Molar mass	119.38 g/mol
Appearance	Colorless liquid
Density	1.48 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	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
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Chloroform is the organic compound with formula CHCl₃. It does not undergo combustion in air, although it will burn when mixed with more flammable substances. It is a member of a group of compounds known as trihalomethanes. Chloroform has myriad uses as a reagent and a solvent. It is also considered an environmental hazard. Several million tons are produced annually.^[1]

Production

Industrially, 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 the methane or chloromethane to progressively more chlorinated compounds.

CH₄ + Cl₂ → CH₃Cl + HCl

CH₃Cl + Cl₂ → CH₂Cl₂ + 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 (trichloromethane), and carbon tetrachloride, which are then separated by distillation.^[1]

Deuterochloroform

The archaic industrial route to chloroform involved the reaction of acetone (or ethanol) with sodium hypochlorite or calcium hypochlorite, known as the haloform reaction.^[1] The chloroform can be removed from the attendant acetate salts (or formate salts if ethanol is the starting material) by distillation. This reaction is still used for the production of bromoform and iodoform. The haloform process is obsolete for the production of ordinary chloroform. It is, however, used to produce deuterated material industrially.^{[citation needed]} Deuterochloroform may be prepared by the reaction of sodium deuteroxide with chloral hydrate,^{[citation needed]} or from ordinary chloroform.^[2]

Inadvertent synthesis 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 may 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 R-22, a major precursor to tetrafluoroethylene, which in turn is converted to Teflon. Before the Montreal Protocol, chlorodifluoromethane (R22) was a 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. Small amounts of chloroform are 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 commercially used 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.^[3] It reacts with aqueous sodium hydroxide (usually in the presence of a phase transfer catalyst) to produce dichlorocarbene, CCl₂.^[4][5] 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.

History

Chloroform was discovered in July, 1831 by the American physician Samuel Guthrie,^[6] and independently a few months later by the French chemist Eugène Soubeiran^[7] and Justus von Liebig^[8] in Germany, all of them using variations of the haloform reaction. Soubeiran produced chloroform through the action of chlorine bleach powder (calcium hypochlorite) on acetone (2-propanone) as well as ethanol. Chloroform was named and chemically characterised in 1834 by Jean-Baptiste Dumas.^[9]

Chloroform was developed on 4 November 1847 by James Young Simpson head of midwifery at Edinburgh Hospital/University and was mainly used as an anesthetic. Inhaling chloroform vapors depresses the central nervous system of a patient, causing dizziness, fatigue and unconsciousness^{[citation needed]}, allowing a doctor to perform simple surgery or various, otherwise painful, operations. 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

As might be expected for an anesthetic, inhaling chloroform vapors depresses the central nervous system. It is immediately dangerous to life and health at approximately 500 ppm according to the United States National Institute for Occupational Safety and Health. Breathing about 900 ppm for a short time can cause dizziness, fatigue, and headache. Chronic chloroform exposure may cause damage to 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 United States since 1976.^[12]

The National Toxicology Program's eleventh report on carcinogens^[13] 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.^[14][15] 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.

During prolonged storage hazardous amounts of phosgene can accumulate in the presence of oxygen and ultraviolet light. To prevent accidents, commercial chloroform is stabilized with ethanol or amylene, but samples that have been recovered or dried no longer contain any stabilizer and caution must be taken. Suspicious bottles should be tested for phosgene. Filter-paper strips, wetted with 5% diphenylamine, 5% dimethylaminobenzaldehyde, and then dried, turn yellow in phosgene vapor.

References

External links

• Chloroform "The Molecular Lifesaver" An article at Oxford University providing facts about chloroform.
• Concise International Chemical Assessment Document 58
• History of chloroform anesthesia
• IARC Summaries & Evaluations: Vol. 1 (1972), Vol. 20 (1979), Suppl. 7 (1987), Vol. 73 (1999)
• International Chemical Safety Card 0027
• NIOSH Pocket Guide to Chemical Hazards 0127
• National Pollutant Inventory - Chloroform and trichloromethane
• NIST Standard Reference Database
• Story on Chloroform from BBC's The Material World (28 July 2005)
• Sudden Sniffer's Death Syndrome article at Carolina Poison Center
• Calculation of vapor pressure, liquid density, dynamic liquid viscosity, surface tension of chloroform