carbon tetrachloride

Carbon tetrachloride
IUPAC name	Carbon tetrachloride Tetrachloromethane
Other names	Benziform, Carbon chloride, Methane tetrachloride, Perchloromethane, Carbon tet, Benzinoform, Tetraform, Tetrasol, Freon 10, Halon 104, 1,1,1,1-tetrachloromethane
Identifiers
CAS number	56-23-5 Y
PubChem	5943
EC number	200-262-8
UN number	1846
KEGG	C07561
ChEBI	27385
RTECS number	FG4900000
SMILES	ClC(Cl)(Cl)Cl
InChI	1/CCl4/c2-1(3,4)5
InChI key	VZGDMQKNWNREIO-UHFFFAOYAV
ChemSpider ID	5730
Properties
Molecular formula	CCl4
Molar mass	153.82 g/mol
Appearance	colourless liquid ether-like odor
Density	1.5867 g/cm3, liquid 1.831 g.cm-3 at -186 °C (solid) 1.809 g.cm-3 at -80 °C (solid)
Melting point	-22.92 °C (250 K)
Boiling point	76.72 °C (350 K)
Solubility in water	785–800 mg/L at 25 °C
Solubility	soluble in alcohol, ether, chloroform, benzene
log P	2.64
Vapor pressure	11.94 kPa at 20 °C
Refractive index (nD)	1.4601
Structure
Crystal structure	Monoclinic
Molecular shape	Tetrahedral
Hazards
MSDS	External MSDS
EU Index	602-008-00-5
EU classification	Carc. Cat. 3 Toxic (T) Dangerous for the environment (N)
R-phrases	R23/24/25, R40, R48/23, R59, R52/53
S-phrases	(S1/2), S23, S36/37, S45, S59, S61
NFPA 704	0 3 0
Flash point	Not flammable
Autoignition temperature	982 °C
LD50	2350 mg/kg
Related compounds
Related chloromethanes	Chloromethane Dichloromethane Chloroform
Related compounds	Tetrafluoromethane Tetrabromomethane Tetraiodomethane
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Carbon tetrachloride, also known by many other names (see Table) is the organic compound with the formula CCl₄. It is a reagent in synthetic chemistry and was formerly widely used in fire extinguishers, as a precursor to refrigerants, and as a cleaning agent. It is a colourless liquid with a "sweet" smell that can be detected at low levels.

Both carbon tetrachloride and tetrachloromethane are acceptable names under IUPAC nomenclature. Colloquially, it is called "carbon tet".

History and synthesis

The production of carbon tetrachloride has steeply declined since the 1980s due to environmental concerns and the decreased demand for CFCs, which were derived from carbon tetrachloride. In 1992, production in the U.S.-Europe-Japan was estimated at 720,000 tonnes.^[1]

Carbon tetrachloride was originally synthesised in 1839 by reaction of chloroform with chlorine, from the French chemist Henri Victor Regnault,^[2] but now it is mainly synthesized from methane:

CH₄ + 4 Cl₂ → CCl₄ + 4 HCl

The production often utilizes by-products of other chlorination reactions, such as the syntheses of dichloromethane and chloroform. Higher chlorocarbons are also subjected to "chlorinolysis:"

C₂Cl₆ + Cl₂ → 2 CCl₄

Prior to the 1950s, carbon tetrachloride was manufactured by the chlorination of carbon disulfide at 105 to 130 °C:^[1]

CS₂ + 3Cl₂ → CCl₄ + S₂Cl₂

Properties

In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a central carbon atom by single covalent bonds. Because of this symmetrical geometry, the molecule has no net dipole moment; that is, CCl₄ is non-polar. Methane gas has the same structure, making carbon tetrachloride a halomethane. As a solvent, it is well suited to dissolving other non-polar compounds, fats and oils. It can also dissolve iodine. It is somewhat volatile, giving off vapors having a smell characteristic of other chlorinated solvents, somewhat similar to the tetrachloroethylene smell reminiscent of dry cleaners' shops.

Solid tetrachloromethane has 2 polymorphs: crystalline II below -47.5 °C (225.6 K) and crystalline I above -47.5 °C.^[3]

At -47.3 °C it has monoclinic crystal structure with space group C2/c and lattice constants a = 20.3, b = 11.6, c = 19.9 (.10⁻¹ nm), β = 111°.^[4]

Uses

A brass, carbon-tetrachloride, fire extinguisher.

In the early 20th century, carbon tetrachloride was widely used as a dry cleaning solvent, as a refrigerant, and in lava lamps.^[5] Small carbon tetrachloride fire extinguishers were widely used and took the form of a brass bottle with a hand pump to expel the liquid.

However, once it became apparent that carbon tetrachloride exposure had severe adverse health effects, safer alternatives such as tetrachloroethylene were found for these applications, and its use in these roles declined from about 1940 onward. Carbon tetrachloride persisted as a pesticide to kill insects in stored grain, but in 1970, it was banned in consumer products in the United States.

One specialty use of "carbon tet" was by stamp collectors to reveal watermarks on the backs of postage stamps. A small amount of the liquid was placed on the back of a stamp sitting in a black glass or obsidian tray. The letters or design of the watermark could then be clearly detected.

Prior to the Montreal Protocol, large quantities of carbon tetrachloride were used to produce the freon refrigerants R-11 (trichlorofluoromethane) and R-12 (dichlorodifluoromethane). However, these refrigerants are now believed to play a role in ozone depletion and have been phased out. Carbon tetrachloride is still used to manufacture less destructive refrigerants.

Carbon tetrachloride has also been used in the detection of neutrinos.

Carbon tetrachloride is one of the most potent hepatotoxins (toxic to the liver), and is widely used in scientific research to evaluate hepatoprotective agents.^[6][7]

Reactivity

Carbon tetrachloride has practically no flammability at lower temperatures. Under high temperatures in air, it forms poisonous phosgene.

Because it has no C-H bonds, carbon tetrachloride does not easily undergo free-radical reactions. Hence it is a useful solvent for halogenations either by the elemental halogen, or by a halogenation reagent such as N-bromosuccinimide.

In organic chemistry, carbon tetrachloride serves as a source of chlorine in the Appel reaction.

Solvent

It is used as a solvent in synthetic chemistry research, but because of its adverse health effects, it is no longer commonly used, and chemists generally try to replace it with other solvents.^{[citation needed]} It is sometimes useful as a solvent for infrared spectroscopy because there are no significant absorption bands > 1600 cm⁻¹. Because carbon tetrachloride does not have any hydrogen atoms, it was historically used in proton NMR spectroscopy. However, carbon tetrachloride is toxic, and its dissolving power is low.^[8] Its use has been largely superseded by deuterated solvents, which offer superior solvating properties and allow for deuterium lock by the spectrometer^{[clarification needed]}. Use of carbon tetrachloride in determination of oil has been replaced by various other solvents^[6].

Safety

Exposure to high concentrations of carbon tetrachloride (including vapor) can affect the central nervous system, degenerate the liver^[7] and kidneys^[9] and may result (after prolonged exposure) in coma and even death.^[10] Chronic exposure to carbon tetrachloride can cause liver^[11][12] and kidney damage and could result in cancer.^[13] More information can be found in Material safety data sheets.

In 2008, a study of common cleaning products found the presence of carbon tetrachloride in "very high concentrations" (up to 101 mg m⁻³) as a result of manufacturers' mixing of surfactants or soap with sodium hypochlorite (bleach).^[14]

Time-series of atmospheric concentrations of CCl₄ (Walker et al., 2000).

Carbon tetrachloride is also both ozone-depleting^[15] and a greenhouse gas.^[16] However, since 1992^[17] its atmospheric concentrations have been in decline for the reasons described above (see also the atmospheric time-series figure).

References

External links

• International Chemical Safety Card 0024
• NIOSH Pocket Guide to Chemical Hazards 0107
• "Carbon Tetrachloride (Group 2B)". International Agency for Research on Cancer (IARC) – Summaries & Evaluations 71: 401. 1999. http://www.inchem.org/documents/iarc/vol71/011-carbontetrac.html. 
• IARC Monograph: "Carbon Tetrachloride"
• Toxicological profile for carbon tetrachloride
• Environmental health criteria for carbon tetrachloride
• Carbon tetrachloride MSDS at Hazardous Chemical Database
• MSDS at Oxford University
• Egli C, Tschan T, Scholtz R, Cook AM, Leisinger T (November 1988). "Transformation of tetrachloromethane to dichloromethane and carbon dioxide by Acetobacterium woodii". Appl. Environ. Microbiol. 54 (11): 2819–24. PMID 3145712. PMC 204379. http://aem.asm.org/cgi/pmidlookup?view=long&pmid=3145712. |
• Picardal FW, Arnold RG, Couch H, Little AM, Smith ME (November 1993). "Involvement of cytochromes in the anaerobic biotransformation of tetrachloromethane by Shewanella putrefaciens 200". Appl. Environ. Microbiol. 59 (11): 3763–70. PMID 8285682. PMC 182529. http://aem.asm.org/cgi/pmidlookup?view=long&pmid=8285682. 
• Substance profile at ntp.niehs.nih.gov