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Chlorofluorocarbons

Chlorofluorocarbons


The chlorofluorocarbons (CFCs) are a family of organic compounds containing carbon , hydrogen (usually), and either chlorine or fluorine, or both. The members of this family can be produced by replacing one or more hydrogen atoms in hydrocarbons with a chlorine or fluorine atom. In the simplest possible case, treating methane (CH4) with chlorine yields chloromethane, CH3Cl. Treating this product with fluorine causes the replacement of a second hydrogen atom with a fluorine atom, producing chlorofluoromethane, CH2ClF.

This process can be continued until all hydrogen atoms have been replaced by chlorine and/or fluorine atoms. By using larger hydrocarbons, an even greater variety of CFCs can be produced. The compound known as CFC-113, for example, is made from ethane (C2H6) and has the formula C2F3Cl3.

Over the last three decades, the CFCs have become widely popular for a number of commercial applications. These applications fall into four general categories: refrigerants, cleaning fluids, propellants , and blowing agents. As refrigerants, CFCs have largely replaced more harmful gases such as ammonia and sulfur dioxide in refrigerators, freezers, and air conditioning systems. Their primary application as cleaning fluids has been in the computer manufacturing business where they are used to clean circuit boards. CFCs are used as propellants in hair sprays, deodorants, spray paints, and other types of sprays. As blowing agents, CFCs are used in the manufacture of fast-food take-out boxes and similar containers. By the early 1990s, CFCs had become so popular that their production was a multi-billion dollar business worldwide.

For many years, little concern was expressed about the environmental hazards of CFCs. The very qualities that made them desirable for commercial applicationstheir stability , for exampleappeared to make them environmentally benign.

However, by the mid-1970s, the error in that view became apparent. Scientists began to find that CFCs in the stratosphere decomposed by sunlight. One product of that decomposition , atomic chlorine, reacts with ozone (O3) to form ordinary oxygen (O2). The apparently harmless CFCs turned out, instead, to be a major factor in the loss of ozone from the stratosphere.

By the time this discovery was made, levels of CFCs in the stratosphere were escalating rapidly. The concentration of these compounds climbed from 0.8 part per billion in 1950 and 1.0 part per billion in 1970 to 3.5 parts per billion in 1987.

A turning point in the CFC story came in the mid-1980s when scientists found that a large hole in the ozone layer was opening up over the Antarctic each year. This discovery spurred world leaders to act on the problem of CFC production. In 1987, about 40 nations met in Montreal to draft a treaty that will reduce the production of CFCs worldwide.

This action is encouraging, but it hardly solves the CFC problem. These compounds remain in the atmosphere for long periods of time (about 77 years for CFC-11 and 139 years for CFC-12), so they will continue to pose a threat to the ozone layer for many decades to come.

[David E. Newton ]


RESOURCES

BOOKS


Selinger, B. Chemistry in the Marketplace. 4th ed. Sydney: Harcourt Brace Jovanovich Publishers, 1989.

PERIODICALS

O'Sullivan, D. A. "International Gathering Plans Way to Safeguard Atmospheric Ozone." Chemical & Engineering News (26 June 1989): 33-36.

Zurer, P. S. "Producers Grapple with Realities of CFC Phaseout." Chemical & Engineering News (24 July 1989): 7-13.

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