Carbon tetrachloride

Carbon tetrachloride

Names
IUPAC name Carbon tetrachloride, Tetrachloromethane
Other names Benziform, Benzinoform, Carbon chloride, Carbon tet, Freon-10, Refrigerant-10, Halon-104, Methane tetrachloride, Perchloromethane, Tetraform, Tetrasol
Identifiers
CAS Number	56-23-5 Y
ChEBI	CHEBI:27385 Y
ChEMBL	ChEMBL44814 Y
ChemSpider	5730 Y
EC Number	200-262-8
Jmol 3D model	Interactive image
KEGG	C07561 Y
PubChem	5943
RTECS number	FG4900000
UNII	CL2T97X0V0 Y
UN number	1846
InChI InChI=1S/CCl4/c2-1(3,4)5 Y Key: VZGDMQKNWNREIO-UHFFFAOYSA-N Y InChI=1/CCl4/c2-1(3,4)5 Key: VZGDMQKNWNREIO-UHFFFAOYAV
SMILES ClC(Cl)(Cl)Cl
Properties
Chemical formula	CCl4
Molar mass	153.81 g·mol−1
Appearance	colourless liquid
Odor	ether-like odor
Density	1.5867 g cm−3 (liquid) 1.831 g cm−3 at −186 °C (solid) 1.809 g cm−3 at −80 °C (solid)
Melting point	−22.92 °C (−9.26 °F; 250.23 K)
Boiling point	76.72 °C (170.10 °F; 349.87 K)
Solubility in water	0.097 g/100 mL (0 °C) 0.081 g/100 mL (25 °C)
Solubility	soluble in alcohol, ether, chloroform, benzene, naphtha, CS2, formic acid
log P	2.64
Vapor pressure	11.94 kPa at 20 °C
Henry's law constant (kH)	2.76x10−2 atm-cu m/mol
Refractive index (nD)	1.4607
Dipole moment	0 D
Structure
Crystal structure	Monoclinic
Molecular shape	Tetrahedral
Thermochemistry
Specific heat capacity (C)	132.6 J/mol K
Std molar entropy (So298)	214.42 J/mol K
Std enthalpy of formation (ΔfHo298)	-139.3 kJ/mol
Gibbs free energy (ΔfG˚)	-686 kJ/mol
Vapor pressure	{{{value}}}
Related compounds
Other cations	Silicon tetrachloride Germanium tetrachloride Tin tetrachloride Lead tetrachloride
Related chloromethanes	Chloromethane Dichloromethane Chloroform
Related compounds	Tetrafluoromethane Tetrabromomethane Tetraiodomethane
Supplementary data page
Structure and properties	Refractive index (n), Dielectric constant (εr), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	UV, IR, NMR, MS
Y verify (what is YN ?)
Infobox references

Carbon tetrachloride, also known by many other names (the most notable being tetrachloromethane (also recognized by the IUPAC), carbon tet in the cleaning industry, Halon-104 in firefighting and Refrigerant-10 in HVACR), is an organic compound with the chemical 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.

History and synthesis

Carbon tetrachloride was originally synthesized 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

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.

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 with 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°. With a specific gravity greater than 1, carbon tetrachloride will be present as a dense nonaqueous phase liquid if sufficient quantities are spilled in the environment.

Uses

Historically, carbon tetrachloride was used for a variety of purposes. However, once it became apparent that carbon tetrachloride exposure had severe adverse health effects, such as causing acute liver failure, 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.

Prior to the Montreal Protocol, large quantities of carbon tetrachloride were used to produce the chlorofluorocarbon refrigerants R-11 (trichlorofluoromethane) and R-12 (dichlorodifluoromethane). However, these refrigerants 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.

Current uses

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

Carbon tetrachloride has practically no flammability at lower temperatures. Under high temperatures in air, it forms poisonous phosgene. In organic chemistry, carbon tetrachloride serves as a source of chlorine in the Appel reaction.

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 (these conditions are known as Wohl-Ziegler Bromination).

It is used as a solvent in synthetic chemistry research, but, because of its adverse health effects, it is no longer commonly used, and in general chemists 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, such as tetrachloroethylene.

Historical uses

A brass, Pyrene carbon-tetrachloride, fire extinguisher.

In 1910, The Pyrene Manufacturing Company of Delaware filed a patent to use 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.) In 1911, they patented a small, portable extinguisher that used the chemical. This consisted of a brass bottle with an integrated handpump that was used to expel a jet of liquid toward the fire. As the container was unpressurized, it could be easily refilled after use. Carbon tetrachloride was suitable for liquid and electrical fires and the extinguishers were often carried on aircraft or motor vehicles.

A formerly common form of fire extinguishers consisted of a glass globe, known as a "fire grenades", and were filled with either carbon tetrachloride or salt-water. It was intended that the bulb simply be thrown at the base of the flames.

A glass globe "fire grenade"

Carbon tetrachloride was widely used as a dry cleaning solvent, as a refrigerant, and in lava lamps.

One specialty use of carbon tetrachloride was in stamp collecting, to reveal watermarks on postage stamps without damaging them. 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 seen.

Safety

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. See safety data sheets.

The effects of carbon tetrachloride on human health and the environment have been assessed under REACH in 2012 in the context of the substance evaluation by France. Thereafter, further information has been requested from the registrants. Later this decision was reversed.

In 2008, a study of common cleaning products found the presence of carbon tetrachloride in "very high concentrations" (up to 101 mg/m³) as a result of manufacturers' mixing of surfactants or soap with sodium hypochlorite (bleach).

Like many other volatile substances, carbon tetrachloride is prone to misuse by inhalation, due to its possible depressant and/or dissociative effect upon the central nervous system. Use of carbon tetrachloride in this manner presents serious health risks, and may result in toxic effects described above.

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). CCl₄ has an atmospheric lifetime of 85 years.

External links

• International Chemical Safety Card 0024
• 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
• |
• Substance profile at ntp.niehs.nih.gov
• ChemSub Online: Carbon tetrachloride.