Carbon tetrachloride

Carbon tetrachloride
File:Carbon Tetrachloride.svg	File:Carbon-tetrachloride-3D-vdW.png
IUPAC name Tetrachloromethane
Other names 1,1,1,1-Tetrachloromethane, Benziform, Benzinoform, Carbon chloride, Carbon tet, Freon 10, Halon 104, Methane tetrachloride, Perchloromethane, Tetraform, Tetrasol
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number	56-23-5 Y
PubChem	5943
ChemSpider	5730
EC number	200-262-8
UN number	1846
KEGG	C07561
ChEBI	27385
RTECS number	FG4900000
SMILES
InChI
InChI key	VZGDMQKNWNREIO-UHFFFAOYAV
style="background: #F8EABA; text-align: center;" colspan="2" | 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
style="background: #F8EABA; text-align: center;" colspan="2" | Structure
Crystal structure	Monoclinic
Molecular shape	Tetrahedral
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
MSDS	ICSC 0024
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	75px 0 3 0
Flash point	Not flammable
Autoignition temperature	982 °C
LD50	2350 mg/kg
style="background: #F8EABA; text-align: center;" colspan="2" | Related compounds
Other cations	Silicon tetrachloride Germanium tetrachloride Tin tetrachloride Lead tetrachloride
Related chloromethanes	Chloromethane Dichloromethane Chloroform
Related compounds	Tetrafluoromethane Tetrabromomethane Tetraiodomethane
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 (notably, carbon tet in the cleaning industry, and as a Halon or Freon in HVAC, see Table for others) is the organic compound with the formula CCl₄. It 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 may be 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.

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

CH₄ + 4 Cl₂ → CCl₄ + 4 HCl

The production often utilizes by-products of other chlorination reactions, such as from 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:

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, 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.

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°.

Uses

File:070707-092045.jpg

A brass, Pyrene carbon-tetrachloride, fire extinguisher.

In the 20th century, carbon tetrachloride was widely used as a dry cleaning solvent, as a refrigerant, and in lava lamps.

In 1910, The Pyrene Manufacturing Company of Delaware filed a patent for a using carbon tetrachloride to extinguish fires. The liquid vaporized and extinguished the flames by inhibiting the chemical chain reaction of the combustion process. It was an early 20th century presupposition that the fire suppression ability of carbon tetrachloride relied on oxygen removal. A carbon tetrachloride fire extinguisher was patented in 1911, taking the form of a brass bottle with a hand pump to expel a jet of liquid. Such extinguishers were commonly used until the mid-20th century.

One specialty use of carbon tetrachloride was by stamp collectors to reveal watermarks on the backs of postage stamps without damaging the stamp. 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.

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. The fact that high temperatures cause it to react to produce phosgene made it especially hazardous when used against fires. This reaction also caused a rapid depletion of oxygen. 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.

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.

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. 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. Its use has been largely superseded by deuterated solvents. Use of carbon tetrachloride in determination of oil has been replaced by various other solvents.

Safety

File:AYool CCl4 history.png

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

Exposure to high concentrations of carbon tetrachloride (including vapor) can affect the central nervous system, degenerate the liver and kidneys and may result (after prolonged exposure) in coma and even death. Chronic exposure to carbon tetrachloride can cause liver and kidney damage and could result in cancer. 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).

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

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. 
• 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
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• Substance profile at ntp.niehs.nih.gov

cs:Tetrachlormethan zh:四氯化碳