Freon

DuPont_freon.jpg

Introduction


Freon is the registered trade name for chlorofluorocarbons (CFCs) belonging to El du Pont de Nemours & Company (DuPont). According to DuPont, up to the 1920s, most commonly used refrigerants were exceedingly hazardous substances until scientists from General Motors’ (GM) Frigidaire subsidiary developed an “inert, nontoxic and odorless replacement chlorofluorocarbon gas (CFC) called Freon” (DuPont). It met the search for a refrigerant with a low boiling point, low toxicity, and was generally non-reacting.Mixed_refrigerant_gas_R401A_Freon_R-401a.jpg

After continuing the development of the product on a large scale, DuPont scientists discovered that Freon also made an effective aerosol propellant. Extensively tested for their possible toxic effects on the air we breathe, CFCs provided energy-efficient substitutes for ammonia in refrigerators (Cooper). Inexpensively produced, related CFCs also proved effective as degreasing agents, the propellants for spray cans, plastics in seat cushions, packing materials, and insulation.


Chemical Principles

A CFC is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. CFC substitutes, hydrochlorofluorocarbons (HCFCs), contain hydrogen and are also commonly called Freon as well. CFCs and HCFCs carry a tetrahedral structure.
Freon_21_or_Dichlorodifluoromethane.png
Compliments of Wikipedia
At room temperature, CFCs are either gases or liquids with low boiling points. They are insoluble in water and inert toward most other substances. Once released into air, Freon exists solely as a gas. In the atmosphere, fully halogenated Freons diffuse to the troposphere, where they are very stable and can be transported great distances.

Freon has many different variations which are represented in a numbering system. The number farthest right is the number of fluorine atoms. The next number to the left is the number of hydrogen atoms plus 1. The next number to the left is the number of carbon atoms less one. Remaining atoms are chlorine. For example, Freon-12 is a methane derivative (only two numbers) with two fluorine atoms (the second 2) and no hydrogen (1-1). It is CCl2F2. Lewis structure examples for Freon 11 and Freon 114 are shown here:
Lewis_diagram_for_Freon_11_and_Freon_114.png
Compliments of cnx.org




Ozone (O3) is a powerful oxidizing agent that is formed when ordinary oxygen molecules are split into oxygen atoms by high-ozone_formation_269181155.jpgenergy UV radiation [O2 + energy(UV radiation) à 2O]. The highly reactive atoms diffuse down to the stratosphere where they react with O2 molecules, forming ozone [O2 + O à O3]. Once absorbing the harmful rays, ozone is reverted back to oxygen molecules and oxygen atoms, creating the reactants of the previous reaction making possible a continuing cycle of reactions.

CFCs are so durable that they do not break down under the forces of solar radiation and precipitation in the lower atmosphere, but continue to float around in their original state for many years, eventually drifting upward into the stratosphere (Cooper). One of the most attractive features of CFCs – their low reactivity—is the key to their most destructive effects. Their lifespan can exceed 100 years, and once diffused into the upper stratosphere, the sun’s ultraviolet radiation is strong enough to cause the cleavage of the C-Cl bond. A series of ozone_and_cfc.gifreactions is formed:

CF2Cl2 + energy (UV light) à CF2Cl + Cl
Cl + O3 à ClO + O2
ClO + O à Cl + O2

With free radicals playing key roles in reacting with ozone molecules to produce molecular oxygen, the last step results in the formation of another chlorine atom that can break down another molecule of ozone. The last two steps are repeated many times, and the breaking down of one CFC molecule can result in the ruin of thousands of molecules of ozone.

SAMII_CFC_Ozone.jpg
Compliments of www.esrl.noaa.gov/.../samii/SAMII_Activity3.html


Societal Impacts


During the 1970s, scientific studies proved that CFCs were depleting the ozone layer that shields the earth from damaging
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Roland (left) and Molina. Compliments of undsci.berkeley.edu
ultraviolet radiation. Mario J. Molina and F.S. Roland, two California chemists, announced in June of 1974 that the CFCs being emitted into the atmosphere might decrease the earth’s surrounding ozone layer by ten percent within the next fifty to eighty years. This was the third study within just two years which confirmed the terrifying news of the ozone layer’s depletion. All of the studies indicated that the use of aerosol spray cans were responsible for the CFC emission. The effects of the added CFCs included widespread climatic changes, - melting of polar ice, a consequent rise in sea levels and a flooding of coastal cities. With this new discovery came much controversy. Despite the dangers of CFCs, the demand for Freon refrigerants and propellants was increasing.

The largest producer of CFCs, the Du Pont Company, was unwilling to terminate their successful business without a fight. Du Pont management argued that the ozone depletion theory could not be proven. One of the authors of the ozone depletion theory, Ralph Cicerone, stated that “decision-makers do not have much room to hedge their bets . . . whatever the effects of fluorocarbons will be, the full impact will not be felt for a decade after release and it will persist for many decades. . . . Complete scientific proof to everyone's satisfaction will take years, so we are faced with a benefit-risk analysis. I have come to the reluctant conclusion that the risks are greater than the benefits and the evidence is already strong.” During the 1980s Du Pont began developing more environmentally friendly hydroflourocarbons. Around this same time, federal regulatory agencies banned the use of CFCs, resulting in the ending of production, aside from the last CFCs produced in the developed countries in 1995. Today, chlorofluorocarbons have been declared illegal in the United States, though they may be obtained from other countries.


References

CQ Researcher Online - "Ozone Depletion" by Mary H. Cooper

DuPont

OEHHA

Office of Pollution Prevention--U.S. Environmental Protection Agency​​=

Wikipedia




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