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A chlorofluorocarbon (CFC) is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. A common subclass is the hydrochlorofluorocarbons (HCFCs), which contain hydrogen, as well. They are also commonly known by the DuPont trade name Freon. The most common representative is dichlorodifluoromethane (R-12 or Freon-12). Many CFCs have been widely used as refrigerants, propellants (in aerosol applications), and solvents. The manufacture of such compounds is being phased out by the Montreal Protocol because they contribute to ozone depletion.

Contents

Structure, properties, production

As in simpler alkanes, carbon in the CFCs and the HCFCs is tetrahedral. Since the fluorine and chlorine atoms differ greatly in size from hydrogen and from each other, the methane derived CFCs deviate from perfect tetrahedral symmetry.[1]

The physical properties of the CFCs and HCFCs are tunable by changes in the number and identity of the halogen atoms. In general they are volatile, but less so than parent alkane. The decreased volatility is attributed to the molecular polarity induced by the halides and the polarizability of halides, which induces intermolecular interactions. Thus, methane boils at -161 °C whereas the fluoromethanes boil between -51.7 (CF2H2) and -128 °C (CF4). 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. 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 invariably higher than the 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:

HCCl3 + 2 HF → HCF2Cl + 2 HCl

The brominated derivatives are generated by free-radical reactions of the chlorofluorocarbons, replacing C-H bonds with C-Br bonds. The production of the anesthetic 2-bromo-2-chloro-1,1,1-trifluoroethane ("halothane") is illustrative:

CF3CH2Cl + Br2 → CF3CHBrCl + HBr

Reactions

The most important reaction of the CFCs is the photo-induced scission of a C-Cl bond:

CCl3F → CCl2F. + Cl.

The chlorine atom, written often as Cl., behaves very differently from the chlorine molecule (Cl2). The radical Cl. is long-lived in the upper atmosphere, where it catalyzes the conversion of ozone into O2. Ozone absorbs UV-radiation better than does O2, 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

Applications exploit the low toxicity, low reactivity, and low flammability of the CFCs and HCFCs. Every permutation of fluorine, chlorine, and hydrogen on the methane and ethane have 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 a precursor to tetrafluoroethylene, the monomer that is converted into Teflon.[2]

Classes of compounds, nomenclature

  • Chlorofluorocarbons (CFCs): when derived from methane and ethane these compounds have the formulae CClmF4-m and C2ClmF6-m, where m is nonzero.
  • Hydrochlorofluorocarbons (HCFCs): when derived from methane and ethane these compounds have the formulae CClmFnH4-m-n and C2ClxFyH6-x-y, where m, n, x, and y are nonzero.
  • Bromochlorofluorocarbons and bromofluorocarbons have formulae similar to the CFCs and HCFCs but also bromine.
  • Hydrofluorocarbons (HFC's): when derived from methane, ethane, propane, and butane, these compounds have the respective formulae CFmH4-m, C2FmH6-m, C3FmH8-m, and C4FmH10-m, where m is nonzero.

Commercial names

Freon is DuPont's brand name for CFCs, HCFCs and related compounds. Other commercial names from around the world are Algofrene, Arcton, Asahiflon, Daiflon, Eskimon, FCC, Flon, Flugene, Forane, Fridohna, Frigen, Frigedohn, Genetron, Isceon, Isotron, Kaiser, Kaltron, Khladon, Ledon, Racon, and Ucon.

Numbering system

A numbering system is used for fluorinated alkanes, prefixed with Freon-, R-, CFC-, and HCFC-. 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 (zero's are not stated). Remaining atoms are chlorine. Thus, Freon-12 indicates a methane derivative (only two numbers) containing two fluorine atoms (the second 2) and no hydrogen (1-1). It is therefore CCl2F2.

Freons containing bromine is 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/Trivial
name(s), code
Boiling point (°C) Chem. formula
Trichlorofluoromethane Freon-11, R-11, CFC-11 23 CCl3F
Dichlorodifluoromethane Freon-12, R-12, CFC-12 −29.8 CCl2F2
Chlorotrifluoromethane CFC -81 CClF3
Chlorodifluoromethane R-22, HCFC-22 -40.8 CHClF2
Dichlorofluoromethane R-21, HCFC-21 8.9 CHCl2F
Chlorofluoromethane Freon 31 CH2ClF
Bromochlorodifluoromethane BCF, Halon 1211 BCF, or Freon 12B1 CBrClF2
1,1,2-Trichloro-1,2,2-Trifluoroethane Trichlorotrifluoroethane, CFC-113 47.7 Cl2FC-CClF2
1,1,1-Trichloro-2,2,2-Trifluoroethane CFC-113a 45.9 Cl3C-CF3
1,2-Dichloro-1,1,2,2-Tetrafluoroethane Dichlorotetrafluoroethane, CFC-114 3.8 ClF2C-CClF2
1-Chloro-1,1,2,2,2-Pentafluoroethane Chloropentafluoroethane, CFC-115 −38 ClF2C-CF3
2-Chloro-1,1,1,2-Tetrafluoroethane HFC-124 −12 CHFClCF3
1,1-Dichloro-1-Fluoroethane HCFC-141b 32 Cl2FC-CH3
1-Chloro-1,1-Difluoroethane HCFC-142b −9.2 ClF2C-CH3
Tetrachloro-1,2-Difluoroethane CFC-112, R-112 91.5 CCl2FCCl2F
Tetrachloro-1,1-Difluoroethane R-112 a, CFC-112 a 91.5 CClF2CCl3
1,1,2-Trichlorotrifluoroethane R-113, CFC-113 48 CCl2FCClF2
1-Bromo-2-Chloro-1,1,2-Trifluoroethane Halon-2311 a 51.7 CHClFCBrF2
2-Bromo-2-Chloro-1,1,1-Trifluoroethane Halon 2311 50.2 CF3CHBrCl
1,1-Dichloro-2,2,3,3,3-Pentafluoropropane R-22 5ca, HCFC-225 ca 51 CF3CF2CHCl2
1,3-Dichloro-1,2,2,3,3-Pentafluoropropane HCFC 225 cb 56 CClF2CF2CHClF

History

Carbon tetrachloride was used in fire extinguishers and glass "anti-fire grenades" from the late nineteenth century until around the end of World War II. Experimentation with chloroalkanes for fire suppression on military aircraft began at least as early as the 1920s. 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 Frédéric Swarts pioneered the synthesis of CFCs in the 1890s. He developed an effective exchange agent to replace chloride in carbon tetrachloride with fluoride to synthesize CFC-11 (CCl3F) and CFC-12 (CCl2F2).

In the late 1920s, Thomas Midgley improved the process of synthesis and led the effort to use CFC as refrigerant to replace ammonia (NH3), chloromethane (CH3Cl), and sulfur dioxide (SO2), which are toxic but were in common use. 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[3] in 1930.[4][5]

Commercial development and use of CFCs and related compounds

CFC-12 suva134a.svg

During World War II, various chloroalkanes were in standard use in military aircraft, although these early halons suffered from excessive toxicity. Nevertheless, after the war they slowly became more common in civil aviation as well. In the 1960s, fluoroalkanes and bromofluoroalkanes became available and were quickly recognized as being highly effective fire-fighting materials. Much early research with Halon 1301 was conducted under the auspices of the US Armed Forces, while Halon 1211 was, initially, mainly developed in the UK. By the late 1960s they were standard in many applications where water and dry-powder extinguishers posed a threat of damage to the protected property, including computer rooms, telecommunications switches, laboratories, museums and art collections. Beginning with warships, in the 1970s, bromofluoroalkanes also progressively came to be associated with rapid knockdown of severe fires in confined spaces with minimal risk to personnel.

By the early 1980s, bromofluoroalkanes were in common use on aircraft, ships, and large vehicles as well as in computer facilities and galleries. However, concern was beginning to be felt about the impact of chloroalkanes and bromoalkanes on the ozone layer. The Vienna Convention on Ozone Layer Protection 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

Since the late 1970s, the use of CFCs has been heavily regulated because of their destructive effects on the ozone layer. 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 concentration of 60 parts per trillion of CFC-11 over Ireland. In a self-funded research expedition ending in 1973, Lovelock went on to measure the concentration of CFC-11 in both the Arctic and Antarctic, finding the presence of the gas in each of 50 air samples collected, but incorrectly concluding that 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 1974. 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 100 years, giving them time to diffuse into the upper stratosphere. Once in the stratosphere, the sun's ultraviolet radiation is strong enough to cause the homolytic cleavage of the C-Cl bond.

By 1987, 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 March 2, 1989, 12 European Community nations agreed to ban the production of all CFCs by the end of the century. In 1990, diplomats met in London and voted to significantly strengthen the Montreal Protocol by calling for a complete elimination of CFCs by the year 2000. By the year 2010 CFCs should be completely eliminated from developing countries as well.

Ozone-depleting gas trends

Because the only CFCs available to countries adhering to the treaty is from recycling, their prices have increased considerably. A worldwide end to production should also terminate the smuggling of this material, such as from Mexico to the United States.

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

While the production and consumption of CFCs are regulated under the Montreal Protocol, emissions from pre-existing banks of CFCs are not regulated under the agreement. As of 2002, there were 5,791 kilotons of CFCs in existing products such as refrigerators, air conditioners, aerosol cans and others.[6] Approximately one-third of these CFCs are projected to be emitted over the next decade if action is not taken, posing a threat to both the ozone layer and the climate.[7] A proportion of these CFCs can be safely captured and destroyed.

Regulation and duPont

In 1978 the United States banned the use of CFCs such as Freon in aerosol cans, the beginning of a long series of regulatory actions against their use. The critical DuPont manufacturing patent for Freon ("Process for Fluorinating Halohydrocarbons", U.S. Patent #3258500) was set to expire in 1979. In conjunction with other industrial peers DuPont sponsored efforts such as the "Alliance for Responsible CFC Policy" to question anti-CFC science, but in a turnabout in 1986 DuPont, with new patents in hand, publicly condemned CFCs.[8] DuPont representatives appeared before the Montreal Protocol urging that CFCs be banned worldwide and stated that their new HCFCs would meet the worldwide demand for refrigerants.[8].

Phase out of CFCs

Use of certain chloroalkanes as solvents for large scale application, such as dry cleaning, have been phased out, for example, by the IPPC directive on greenhouse gases in 1994 and by the Volatile Organic Compounds (VOC) directive of the EU in 1997. Permitted chlorofluoroalkane uses are medicinal only.

Bromofluoroalkanes have been largely phased out and the possession of such equipment is prohibited in some countries like the Netherlands and Belgium, from 1 January 2004, based on the Montreal Protocol and guidelines of the European Union.

Production of new stocks ceased in most (probably all) countries as of 1994. However many countries still require aircraft to be fitted with halon fire suppression systems because no safe and completely satisfactory alternative has been discovered for this application. There are also a few other, highly specialized uses. These programs recycle halon through "halon banks" coordinated by the Halon Recycling Corporation[9] to ensure that discharge to the atmosphere occurs only in a genuine emergency and to conserve remaining stocks.

The interim replacements for CFCs are hydrochlorofluorocarbons (HCFCs), which deplete stratospheric ozone, but to a much lesser extent than CFCs.[10] Ultimately, hydrofluorocarbons (HFCs) will replace HCFCs with essentially no ozone destruction (although all three groups of halocarbons are powerful greenhouse gases). DuPont began producing hydrofluorocarbons as alternatives to Freon in the 1980s. These included Suva refrigerants and Dymel propellants.[11] Natural refrigerants are climate friendly solutions that are enjoying increasing support from large companies [12] and governments interested in reducing global warming emissions from refrigeration and air conditioning. 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 due to the recognition of halocarbon contributions to climate change [13].

On September 21, 2007, approximately 200 countries agreed to accelerate the elimination of hydrochlorofluorocarbons entirely by 2020 in a United Nations-sponsored Montreal summit. Developing nations were given until 2030. Many nations, such as the United States and China, who had previously resisted such efforts, agreed with the accelerated phase out schedule.[14]

Development of alternatives for CFCs

Work on alternatives for chlorofluorocarbons in refrigerants began in the late 1970s after the first warnings of damage to stratospheric ozone were published. The hydrochlorofluorocarbons (HCFCs) are less stable in the lower atmosphere, enabling them to break down before reaching the ozone layer. 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-134a, is now used in place of CFC-12 in automobile air conditioners. Hydrocarbon refrigerants (a propane/isobutane blend) are also used extensively in mobile air conditioning systems in Australia, the USA and many other countries, as they have excellent thermodynamic properties and perform particularly well in high ambient temperatures. One of the natural refrigerants (along with Ammonia and Carbon Dioxide), hydrocarbons have negligible environmental impacts and are also used worldwide in domestic and commercial refrigeration applications, and are becoming available in new split system air conditioners.[15] Various other solvents and methods have replaced the use of CFCs in laboratory analytics.[16]

Applications and replacements for CFCs
Application Previously used CFC Replacement
Refrigeration & air-conditioning CFC-12 (CCl2F2); CFC-11(CCl3F); CFC-13(CClF3); HCFC-22 (CHClF2); CFC-113 (Cl2FCCClF2); CFC-114 (CClF2CClF2); CFC-115 (CF3CClF2); HFC-23 (CHF3); HFC-134a (CF3CFH2); HFC-507 (a 1:1 azeotropic mixture of HFC 125 (CF3 CHF2) and HFC-143a (CF3CH3)); HFC 410 (a 1:1 azeotropic mixture of HFC-32 (CF2H2) and HFC-125 (CF3CF2H))
Propellants in medicinal aerosols CFC-114 (CClF2CClF2) HFC-134a (CF3CFH2); HFC-227ea (CF3CHFCF3)
Blowing agents for foams CFC-11 (CCl3F); CFC 113 (Cl2FCCClF2); HCFC-141b (CCl2FCH3) HFC-245fa (CF3CH2CHF2); HFC-365 mfc (CF3CH2CF2CH3)
Solvents, degreasing agents, cleaning agents CFC-11 (CCl3F); CFC-113 (CCl2FCClF2) None

Safety

According to their Material Safety Data Sheets, CFCs and HCFCs are colourless, volatile, relatively non-toxic liquids and gases with a faintly sweet ethereal odour. Overexposure may cause dizziness, loss of concentration, Central Nervous System depression and/or cardiac arrhythmia. Although non-flammable, their combustion products include hydrofluoric acid, phosgene, and related species.[17]

References

  1. ^ Günter Siegemund, Werner Schwertfeger, Andrew Feiring, Bruce Smart, Fred Behr, Herward Vogel, Blaine McKusick “Fluorine Compounds, Organic” Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a11_349
  2. ^ M. Rossberg et al. “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2
  3. ^ Inventors accessed December 21, 2007
  4. ^ Carlisle, Rodney (2004). Scientific American Inventions and Discoveries, p.351. John Wiley & Songs, Inc., New Jersey. ISBN 0-471-24410-4.
  5. ^ McNeill, J.R. Something New Under the Sun: An Environmental History of the Twentieth-Century World (2001) New York: Norton, xxvi, 421 pp. (as reviewed in the Journal of Political Ecology)
  6. ^ IPCC/TEAP Special Report on Ozone and Climate
  7. ^ Chlorofluorocarbons: An Overlooked Climate Threat, EESI Congressional Briefing
  8. ^ a b "Ethics of Du Pont's CFC Strategy 1975–1995", Smith B. Journal of Business Ethics, Volume 17, Number 5, April 1998, pp. 557-568(12)
  9. ^ Welcome to the Halon Corporation
  10. ^ "Ozone Layer Depletion", U.S. Environmental Protection Agency accessed June 25, 2008
  11. ^ "1930: Freon", DuPont Heritage accessed June 25, 2008
  12. ^ [1] "Refrigerants Naturally"
  13. ^ Velders et.al., PNAS March 20, 2007 vol. 104 no. 12 4814-4819 [2] "The importance of the Montreal Protocol in protecting climate"
  14. ^ HCFC Phaseout Schedule
  15. ^ "Greenpeace, Cool Technologies" [3]
  16. ^ Use of Ozone Depleting Substances in Laboratories. TemaNord 516/2003
  17. ^ "MSDS R12" [4]

External links


Freon is DuPont's trade name for its odorless, colorless, nonflammable, and noncorrosive chlorofluorocarbon and hydrochlorofluorocarbon refrigerants, which are used in air conditioning, refrigeration, and some automatic fire-fighting systems. It is one of a class of chemicals called Haloalkanes; Freon and similar refrigerants have been controversial due to environmental and safety concerns. Inhalation of relatively low concentrations of Freon is unlikely to cause major health problems, but higher concentrations can displace enough oxygen to cause asphyxiation.[1][2]

Contents

History

Freon was initially developed in the early 20th century as an alternative to the toxic gases that were previously used as refrigerants, such as ammonia, chloromethane, and sulfur dioxide. Freon, in this case dichlorodifluoromethane, was invented by Thomas Midgley, Jr. with co-inventor Charles Kettering[3] in 1930.[4] Each Freon product is designated by a number; for instance, Freon-11 is trichlorofluoromethane, while Freon-12 is dichlorodifluoromethane, most commonly used is Freon-113 (1,1,2-Trichloro-1,2,2-trifluoroethane) as a cleaning agent. Freon is no longer produced on any significant level (U.S.) therefore any freon is from stockpiles and will remain so providing that another agent can be discovered to replace its cleaning properties. Freon danger such as oxygen displacement is easily observed with a O2 detector and is safe up to 1000 ppm. The most dangerous issue regarding freon actually comes from fire and extreme heat, Freon at anything higher that 400 degrees Fahrenheit will chemically convert Freon to phosgene gas, commonly known as suffocating gas the agent that gained notoriety in World War 1 for the sweet smell of cut grass it produced before killing its victims.

DuPont began to phase out its production of Freon CFCs in the 1980s after federal regulatory agencies banned their use because they harm the Earth's ozone layer.[5] It is worth to note that DuPont held the Freon patent that was terminated in 1992.

In the 1990s, most uses of Freon chlorofluorocarbons (CFCs) were phased out.

The Montreal Protocol on Substances that Deplete the Ozone Layer classifies Freon-11 and Freon-12 as Annex A substances and bans their production and consumption as of 1996.

The interim replacements for CFCs are hydrochlorofluorocarbons (HCFCs), which contain chlorine that depletes stratospheric ozone, but to a much lesser extent than CFCs.[6] Ultimately, hydrofluorocarbons (HFCs) will replace HCFCs with essentially no ozone destruction (although all three groups of halocarbons are powerful greenhouse gases). DuPont began producing hydrofluorocarbons as alternatives to Freon in the 1980s. These included Suva refrigerants and Dymel propellants.[5] Any of these gases that are used as refrigerants are designated by an "R-" number and colloquially known as "Freon", whether they are made by DuPont or another supplier.

On November 8, 2008, 20 people died and 21 were injured when suffocated by Freon Gas (used in fire suppressant system) on board the Russian submarine K-152 Nerpa when the vessel's extinguishing systems unexpectedly activated during trials.[citation needed]

References

  1. Environment, Health and Safety Online
  2. Safety Data Sheet
  3. Inventors accessed December 21, 2007
  4. Carlisle, Rodney (2004). Scientific American Inventions and Discoveries, p.351. John Wiley & Songs, Inc., New Jersey. ISBN 0471244104.
  5. 5.0 5.1 "1930: Freon", DuPont Heritage accessed June 25, 2008
  6. "Ozone Layer Depletion", U.S. Environmental Protection Agency accessed June 25, 2008

External links

See also


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

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Contents

English

Proper noun

Singular
Freon™

Plural
-

Freon™

  1. (organic chemistry) Any of several non-flammable refrigerants based on halogenated hydrocarbon including R-12 and R-134a.

Translations

See also


Simple English

Freons, also known as CFCs, are a brand name for a group of refrigerants. They generally contained carbon and chlorine, and sometimes bromine. Freon 10 was carbon tetrachloride. Most of them are not toxic. They also are cheap and work good. But they can deplete ozone from the atmosphere, allowing more ultraviolet rays to come through. This makes people get skin cancer.

See also








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