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Chlorofluorocarbon - Wikipedia. A chlorofluorocarbon (CFC) is an organic compound that contains only carbon, chlorine, and fluorine, produced as volatile derivative of methane, ethane, and propane. They are also commonly known by the Du. Pont brand name Freon.
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The most common representative is dichlorodifluoromethane (R- 1. Freon- 1. 2). Many CFCs have been widely used as refrigerants, propellants (in aerosol applications), and solvents. Because CFCs contribute to ozone depletion in the upper atmosphere, the manufacture of such compounds has been phased out under the Montreal Protocol, and they are being replaced with other products such as hydrofluorocarbons (HFCs). Because the fluorine and chlorine atoms differ greatly in size and effective charge from hydrogen and from each other, the methane- derived CFCs deviate from perfect tetrahedral symmetry. In general they are volatile, but less so than their parent alkanes.
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The decreased volatility is attributed to the molecular polarity induced by the halides, which induces intermolecular interactions. Thus, methane boils at . The CFCs have still higher boiling points because the chloride is even more polarizable than fluoride. Because of their polarity, the CFCs are useful solvents, and their boiling points make them suitable as refrigerants. The CFCs are far less flammable than methane, in part because they contain fewer C- H bonds and in part because, in the case of the chlorides and bromides, the released halides quench the free radicals that sustain flames. The densities of CFCs are higher than their corresponding alkanes. In general the density of these compounds correlates with the number of chlorides.
CFCs and HCFCs are usually produced by halogen exchange starting from chlorinated methanes and ethanes. Illustrative is the synthesis of chlorodifluoromethane from chloroform: HCCl. HF . The production of the anesthetic. Ozone absorbs UV- B radiation, so its depletion allows more of this high energy radiation to reach the Earth's surface. Bromine atoms are even more efficient catalysts; hence brominated CFCs are also regulated. Applications. Every permutation of fluorine, chlorine, and hydrogen based on methane and ethane has been examined and most have been commercialized.
Furthermore, many examples are known for higher numbers of carbon as well as related compounds containing bromine. Uses include refrigerants, blowing agents, propellants in medicinal applications, and degreasing solvents. Billions of kilograms of chlorodifluoromethane are produced annually as precursor to tetrafluoroethylene, the monomer that is converted into Teflon. The rightmost value indicates the number of fluorine atoms, the next value to the left is the number of hydrogen atoms plus 1, and the next value to the left is the number of carbon atoms less one (zeroes are not stated). Remaining atoms are chlorine.
Thus, Freon- 1. 2 indicates a methane derivative (only two numbers) containing two fluorine atoms (the second 2) and no hydrogen (1- 1=0). It is therefore CCl. F2. Another, easier equation that can be applied to get the correct molecular formula of the CFC/R/Freon class compounds is this to take the numbering and add 9. The resulting value will give the number of carbons as the first numeral, the second numeral gives the number of hydrogen atoms, and the third numeral gives the number of fluorine atoms.
The rest of the unaccounted carbon bonds are occupied by chlorine atoms. The value of this equation is always a three figure number.
An easy example is that of CFC- 1. CCl. 2F2. The main advantage of this method of deducing the molecular composition in comparison with the method described in the paragraph above is that it gives the number of carbon atoms of the molecule. Freons containing bromine are signified by four numbers. Isomers, which are common for ethane and propane derivatives, are indicated by letters following the numbers. Principal CFCs. Systematic name. Common/trivialname(s), code. Boiling point (. Experimentation with chloroalkanes for fire suppression on military aircraft began at least as early as the 1.
Freon is a trade name for a group of CFCs which are used primarily as refrigerants, but also have uses in fire- fighting and as propellants in aerosol cans. Bromomethane is widely used as a fumigant. Dichloromethane is a versatile industrial solvent. The Belgian scientist Fr. He developed an effective exchange agent to replace chloride in carbon tetrachloride with fluoride to synthesize CFC- 1. CCl. 3F) and CFC- 1.
CCl. 2F2). In the late 1. Thomas Midgley, Jr. In searching for a new refrigerant, requirements for the compound were: low boiling point, low toxicity, and to be generally non- reactive. In a demonstration for the American Chemical Society, Midgley flamboyantly demonstrated all these properties by inhaling a breath of the gas and using it to blow out a candle. Nevertheless, after the war they slowly became more common in civil aviation as well. In the 1. 96. 0s, fluoroalkanes and bromofluoroalkanes became available and were quickly recognized as being highly effective fire- fighting materials.
Much early research with Halon 1. US Armed Forces, while Halon 1. UK. By the late 1.
Beginning with warships, in the 1. By the early 1. 98.
However, concern was beginning to be expressed about the impact of chloroalkanes and bromoalkanes on the ozone layer. The Vienna Convention for the Protection of the Ozone Layer did not cover bromofluoroalkanes as it was thought, at the time, that emergency discharge of extinguishing systems was too small in volume to produce a significant impact, and too important to human safety for restriction.
Regulation. After the development of his electron capture detector, James Lovelock was the first to detect the widespread presence of CFCs in the air, finding a mole fraction of 6. CFC- 1. 1 over Ireland. In a self- funded research expedition ending in 1. Lovelock went on to measure CFC- 1.
Arctic and Antarctic, finding the presence of the gas in each of 5. CFCs are not hazardous to the environment. The experiment did however provide the first useful data on the presence of CFCs in the atmosphere.
The damage caused by CFCs was discovered by Sherry Rowland and Mario Molina who, after hearing a lecture on the subject of Lovelock's work, embarked on research resulting in the first publication suggesting the connection in 1. It turns out that one of CFCs' most attractive features—their low reactivity— is key to their most destructive effects. CFCs' lack of reactivity gives them a lifespan that can exceed 1. Once in the stratosphere, the sun's ultraviolet radiation is strong enough to cause the homolytic cleavage of the C- Cl bond. By 1. 98. 7, in response to a dramatic seasonal depletion of the ozone layer over Antarctica, diplomats in Montreal forged a treaty, the Montreal Protocol, which called for drastic reductions in the production of CFCs. On 2 March 1. 98. European Community nations agreed to ban the production of all CFCs by the end of the century.
In 1. 99. 0, diplomats met in London and voted to significantly strengthen the Montreal Protocol by calling for a complete elimination of CFCs by the year 2. By the year 2. 01. CFCs should have been completely eliminated from developing countries as well. A worldwide end to production should also terminate the smuggling of this material. However, there are current CFC smuggling issues, as recognized by the United Nations Environmental Programme (UNEP) in a 2. UNEP estimates that between 1.
CFCs passed through the black market in the mid- 1. The report estimated between 7,0. CFCs are smuggled annually into developing countries.
Asian countries are those with the most smuggling; as of 2. China, India and South Korea were found to account for around 7.
CFC production. The cost of replacing the equipment of these items is sometimes cheaper than outfitting them with a more ozone- friendly appliance. Additionally, CFC smuggling is not considered a significant issue, so the perceived penalties for smuggling are low. While the eventual phaseout of CFCs is likely, efforts are being taken to stem these current non- compliance problems. By the time of the Montreal Protocol it was realised that deliberate and accidental discharges during system tests and maintenance accounted for substantially larger volumes than emergency discharges, and consequently halons were brought into the treaty, albeit with many exceptions.
Regulatory gap. In 2. CFCs in existing products such as refrigerators, air conditioners, aerosol cans and others.
The critical Du. Pont manufacturing patent for Freon (. Patent #3. 25. 85. In conjunction with other industrial peers Du. Pont sponsored efforts such as the . Permitted chlorofluoroalkane uses are medicinal only. Bromofluoroalkanes have been largely phased out and the possession of equipment for their use is prohibited in some countries like the Netherlands and Belgium, from 1 January 2.
Montreal Protocol and guidelines of the European Union. Production of new stocks ceased in most (probably all) countries in 1. There are also a few other, highly specialized uses. These programs recycle halon through .
Unlike CFCs and HCFCs, HFCs have an ozone depletion potential (ODP) of 0. Du. Pont began producing hydrofluorocarbons as alternatives to Freon in the 1. These included Suva refrigerants and Dymel propellants. Hydrofluorocarbons are included in the Kyoto Protocol because of their very high Global Warming Potential and are facing calls to be regulated under the Montreal Protocol.
Developing nations were given until 2. Many nations, such as the United States and China, who had previously resisted such efforts, agreed with the accelerated phase out schedule. Nevertheless, a significant fraction of the HCFCs do break down in the stratosphere and they have contributed to more chlorine buildup there than originally predicted. Later alternatives lacking the chlorine, the hydrofluorocarbons (HFCs) have an even shorter lifetimes in the lower atmosphere. One of these compounds, HFC- 1.