Carbon tetrachloride , also known by many other names (the most famous is tetrachloromethane , also recognized by IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVACR) is an organic compound with the chemical formula CCl 4 . It was previously widely used in fire extinguishers, as a precursor to refrigerant and as a cleaning agent. It is a colorless liquid with a "sweet" smell that can be detected at low levels. There is practically no flammability level at lower temperatures.
Video Carbon tetrachloride
History and synthesis
Carbon tetrachloride was originally synthesized by the French chemist Henri Victor Regnault in 1839 by chloroform reaction with chlorine, but is now mainly produced from methane:
- CH 2 -> CCl 4 4 HCl
Production often uses a by-product of other chlorination reactions, such as from dichloromethane and chloroform synthesis. Higher chlorocarbons also undergo "chlorinolysis":
- C 2 Cl 6 Cl 2 -> 2 CCl 4
Prior to the 1950s, carbon tetrachloride was produced by chlorination of carbon disulfide at 105-130 ° C: 2 2 Cl 2 2 2 /sub>
The production of carbon tetrachloride has declined sharply since the 1980s due to environmental concerns and a decrease in demand for CFCs, derived from carbon tetrachloride. In 1992, production in the US/Europe/Japan was estimated at 720,000 tons.
Maps Carbon tetrachloride
Properties
In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as angles in a tetrahedral configuration joined to a central carbon atom by a single covalent bond. Because of this symmetrical geometry, CCl 4 is non-polar. Methane gas has the same structure, making carbon tetrachloride a halomethane. As a solvent, it is suitable to dissolve compounds, fats, and other non-polar oils. It can also dissolve iodine. Somewhat volatile, removing the vapor with the odor characteristics of other chlorinated solvents, somewhat similar to the smell of tetrachlorethylene reminiscent of a dry cleaning shop.
The solid tetrachloromethane has two polymorphs: crystals II below -47.5 ° C (225.6 K) and crystals I above -47.5 ° C. At -47.3 ° C has a monoclinic crystal structure with the group space C2/c and lattice constants a = 20.3, b = 11.6, c = 19 , 9 (.10 -1 nm) ,? = 111 Â °.
With a specific gravity greater than 1, carbon tetrachloride will be present as a solid, non-aqueous phase liquid if sufficient quantities are shed in the environment.
Usage
In organic chemistry, carbon tetrachloride serves as a source of chlorine in Appel reaction.
Historical usage
Prior to the Montreal Protocol, large amounts of carbon tetrachloride were used to produce R-11 (trichlorofluoromethane) and R-12 (dichlorodifluoromethane) chlorofluorocarbons refrigerants. However, this cooler plays a role in ozone depletion and has been removed. Carbon tetrachloride is still used to produce less destructive refrigerants. Carbon tetrachloride, made of chlorine-37 weight, has been used in neutrino detection.
Lava lamp
Carbon tetrachloride is the main ingredient in the lava lamp, because it adds weight to the floating wax.
Solvent
It was once a popular solvent in organic chemistry, but, due to adverse health effects, it is rarely used today. Sometimes useful as a solvent for infrared spectroscopy, since there is no significant absorption band & gt; 1600 cm -1 . Because carbon tetrachloride does not have a hydrogen atom, it has historically been used in proton NMR spectroscopy. In addition to toxic, low solubility. Its use has largely been replaced by deuterated solvents. The use of carbon tetrachloride in the determination of oil has been replaced by various other solvents, such as tetrachlorethylene. Because it does not have a C-H bond, carbon tetrachloride is not susceptible to free radical reactions. This is a useful solvent for halogenation either by halogen element or by a halogenated reagent such as N -bromosuccinimide (this condition is known as Bromin-Wohl-Ziegler).
Fire suppression
In 1910, the Delaware Pyrene Manufacturing Company filed a patent for using carbon tetrachloride to extinguish the flame. The liquid is evaporated by combustion heat and blazing fire, the initial form of gas fire prevention. At that time it was believed that the gas only replaced the oxygen in the area near the fire, but later the study found that the gas actually inhibited the chemical chain reaction of the combustion process.
In 1911, Pyrene patented a small portable scanner that used chemicals. The extinguisher consists of a brass bottle with an integrated handpump used to remove the liquid jets towards the fire. Since the container is not pressed, it can be recharged easily after use. Carbon tetrachloride suitable for both liquid and electric fires and extinguishers is often performed on aircraft or motor vehicles.
In the first half of the 20th century, other common fire extinguishers were a single and closed glass use world known as "fire grenades," filled with carbon tetrachloride or saltwater. Light bulbs can be thrown to the bottom of the fire to extinguish the fire. This type of carbon tetrachloride can also be installed in a spring wall fixture with a solder-based restrain. When the solder melts due to high heat, the spring will break the globe or launch it out of the bracket, allowing the extinguishing agent to automatically dispersed into the flame. A well-known brand is "Red Comet," which is made with various other fire-fighting equipment in the Denver, Colorado area by Red Comet Manufacturing Company since it was founded in 1919 until manufacturing operations closed in the early 1980s.
Niche
Carbon tetrachloride is widely used as a dry cleaning solvent, as a refrigerant, and in a lava lamp.
One particular use of carbon tetrachloride is in collecting stamps, to reveal watermarks on stamps without damaging them. A small amount of fluid is placed on the back of the stamp, sitting on a black glass or an obsidian tray. The letter or design of the watermark can be seen clearly.
Intoxicant
Like many other volatile substances, carbon tetrachloride is susceptible to abuse if inhaled, because of the possibility of depressant and/or dissociative effects on the central nervous system. The use of carbon tetrachloride in this way poses a serious health risk, and may cause the toxic effects described below.
Security
Carbon tetrachloride is one of the most powerful hepatotoxins (toxic to the liver), so much so that it is widely used in scientific research to evaluate hepatoprotective agents. Exposure to high concentrations of carbon tetrachloride (including steam) can affect the central nervous system, degenerate the liver and kidneys, and prolonged contact may lead to coma or death. Chronic exposure to carbon tetrachloride can cause liver and kidney damage and can cause cancer. See the safety data sheet.
The effects of carbon tetrachloride on human health and the environment have been assessed under REACH in 2012 in the context of substance evaluation by France. After that, further information has been requested from the registrants. Then this decision was canceled.
In 2008, a study of general cleaning products found the presence of carbon tetrachloride in "very high concentrations" (up to 101 mg/m 3 ) as a result of mixing surfactants or soaps with sodium factories. hypochlorite (bleach).
Carbon tetrachloride is also ozone-depleting and greenhouse gas. However, since 1992 atmospheric concentrations have declined for the reasons described above (see also the time series of atmospheric numbers). CCl 4 has an 85-year atmospheric lifetime.
Under high temperatures in the air, it forms toxic phosgene.
References
External links
- International Chemical Safety Card 0024
- "NIOSH Pocket Guide to Chemical Hazards # 0107". National Institute for Occupational Safety and Health (NIOSH).
- "Carbon Tetrachloride (Group 2B)". International Agency for Research on Cancer (IARC) - Summary & amp; Evaluation . 71 : 401. 1999.
- IARC Monography: "Carbon Tetrakloride"
- Toxicological profile for carbon tetrachloride
- Environmental health criteria for carbon tetrachloride
- Carbon tetrachloride MSDS in Hazardous Chemical Database
- Substance profile at ntp.niehs.nih.gov
- ChemSub Online: Carbon tetrachloride
Source of the article : Wikipedia
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