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Encyclopedia > Chlorofluorocarbon
CFC

CFCs (chlorofluorocarbons) are a family of artificial chemical compounds containing chlorine, fluorine and carbon. They were formerly used widely in industry, for example as refrigerants, propellants and cleaning solvents. Their use has been generally prohibited by the Montreal Protocol, because of fears of their possible destructive effects on the ozone layer (see ozone depletion). Hydrochlorofluorocarbons are now used as CFC substitutes.


CFCs were developed by the American engineer Thomas Midgley in 1928 as a replacement for ammonia (then a common refrigerant). The new compound developed had to have a low boiling point, a lack of toxicity and be generally non-reactive. In a demonstration for the American Chemical Association, Midgley flamboyantly demonstrated all these properties by inhaling a breath of the gas and using it to blow out a candle.


Midgley specifically developed CCl2F2 (CFC-12). However one of the attractive features of CFCs is that there exists a whole family of the compounds, each having a unique boiling point which can suit different applications. As well as refrigerants, CFCs have been used as propellants in aerosol cans, cleaning solvents for circuit boards, and as blowing agents for making expanded plastics (such as those once used to store fast-foods.)


There has been a movement since the late 1970s to ban CFCs because of their destructive effect on the ozone layer. This damage was discovered due mainly to the work of scientists Sherry Rowland and Mario Molina, first published in 1974. It turns out that one of CFCs most attractive features - its unreactivity - has been instrumental in making it one of our worst pollutants. CFC's lack of reactivity gives it a lifespan which can exceed 100 years in some cases. This gives it time to diffuse up in to the upper stratosphere. Here the sun's UV radiation is strong enough to break off the chlorine atom, which on its own is a highly reactive free radical. This catalyses the break up of ozone into oxygen:

Cl + O3 → ClO + O2
ClO + O → Cl + O2

CFCs are a problem because the chlorine is regenerated at the end of these reactions, making it able to keep on reacting with millions of other ozone molecules. This disprupts the ionic structure of oxygen atoms, causing their lowest ionisation energy to drop. The ozone hole produced is able to let through UV light, which increases the chances of cancer in humans.


In 1975, Oregon enacted the world's first ban of CFCs (legislation introduced by Walter F. Brown). By 1985, scientists documented a drastic depletion of the ozone layer over Antarctica which led the United Nations to take action in 1987. International attention to CFCs resulted in a meeting of UN diplomats from around the world in Montreal in 1987. They forged a treaty that 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.


One major use of CFCs has been as propellants in aerosol inhalers for drugs used to treat asthma. The conversion of these devices and treatments from CFC to halocarbons that do not have the same effect on the ozone layer is well under way. There are some differences between asthma inhalers using CFCs and the newer propellants, but in general conversion is easy.


CFCs HCFCs and HFCs are named as follows:


CFC-01234a, where:

  • 0 = number of double bonds (omitted if zero)
  • 1 = Carbon atoms - 1 (omitted if zero)
  • 2 = Hydrogen atoms + 1
  • 3 = Fluorine atoms
  • 4 = Chlorine atoms replaced by Bromine ("B" prefix added)
  • a = letter added to identify isomers, the "normal" isomer in any number has the smallest mass difference on each carbon, and a, b, or c are added as the masses diverge from normal.

Examples:

Short name Formula Full name
CFC-12 CCl2F2 dichlorodifluoromethane
HCFC-22 CHClF2 chlorodifluoromethane
HFC-134 CHF2-CHF2 1,1,2,2-tetrafluoroethane
HFC-134a CH2F-CF3 1,2,2,2-tetrafluoroethane

See also

External links

  • CFC Smuggling (http://www.alternet.org/story.html?StoryID=10109)
  • CFC Illegal Trade (http://www.american.edu/projects/mandala/TED/cfctrade.htm)







  Results from FactBites:
 
Haloalkane - Wikipedia, the free encyclopedia (3244 words)
Chlorofluorocarbons (CFC) are haloalkanes with both chlorine and fluorine.
Chlorofluorocarbons (CFC) were developed by the American engineer Thomas Midgley in 1928 as a replacement for ammonia (NH chloromethane (CH Cl), and sulfur dioxide (SO), toxic but in common use at the time as refrigerants.
There is concern that halons are being broken down in the atmosphere to bromine, which reacts with ozone, leading to depletion of the ozone layer (this is similar to the case of chlorofluorocarbons such as freon).
Chlorofluorocarbons, fully halogenated (EHC 113, 1990) (14152 words)
Throughout this monograph, percentages of chlorofluorocarbons in air are expressed as the volume of chlorofluorocarbon divided by the volume of air.
Release of chlorofluorocarbons into the global environment during use, disposal of wastes, transport, and storage are an increasing concern because of the potential impact such uncontrolled releases may have on the future health of mankind, mainly through the depletion of stratospheric ozone.
Chlorofluorocarbons are usually characterized by high vapour pressure (low boiling point) and density and low viscosity, surface tension, refractive index, and solu- bility in water.
  More results at FactBites »

 
 

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