Freon

Freon (frē`ŏn) [trade name], any one of a special class of chemical compounds that are used as refrigerants, aerosol propellants, and solvents. These compounds are haloalkanes, i.e., halogen derivatives of saturated hydrocarbons (see alkane). Every Freon contains at least some fluorine in its molecule, and most contain chlorine or bromine as well. Freons are generally colorless, odorless, nontoxic, noncorrosive, nonflammable, and chemically unreactive. The most commonly used is Freon-12, or dichlorodifluoromethane (CCl₂F₂), which boils at −29.8°C; and is thus a gas at ordinary temperatures and pressures. It is prepared by the reaction of carbon tetrachloride with hydrogen fluoride in the presence of a catalyst. There are a number of other Freons. Some of those containing bromine in their molecules are used in fire extinguishers. See also chlorofluorocarbons.

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Freon

Trademark for any of several organic compounds containing fluorine (fluorocarbons) and sometimes chlorine (chlorofluorocarbons, or CFCs). Nonflammable, nontoxic, and noncorrosive, they have low boiling points, which makes them useful as refrigerants. By the mid-1970s they were in wide use in refrigeration and air conditioning systems, as blowing agents for plastic foams, as fire-extinguishing agents, and in aerosol sprays. Evidence has accumulated that decomposition of CFCs in the stratosphere destroys ozone there (see ozone layer), so most of their uses have been banned. International agreements signed by most of the industrialized countries have called for the phasing out of CFC use.

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Freon

™ any of a group of chemically unreactive chlorofluorocarbons used as aerosol propellants, refrigerants, and solvents

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Freon 

a name used for any one of a series of fluorine-containing saturated hydrocarbons, primarily methane and ethane derivatives, that are used as refrigerants. In addition to fluorine atoms, Freon molecules usually contain chlorine atoms; more rarely, they contain bromine atoms. Of the more than 40 different known Freons, most are manufactured commercially.

Freons are colorless, odorless gases or liquids, which are readily soluble in organic solvents but poorly soluble in water. The most widely used are dichlorodifluoromethane, CC1₂F₂, trichloromonofluoromethane, CC1₃F, and chlorodifluoromethane, CHC1F₂, whose boiling points are – 29.8°, – 23.8°, and – 40.8°C, respectively. Freons do not burn and do not explode, even upon contact with an open flame. They are chemically stable to the action of acids and oxidizing agents and do not decompose in devices made from ordinary structural materials. Upon heating, chlorine- and bromine-containing Freons interact with magnesium, magnesium alloys, and brass, while hydrogen-containing Freons interact with alkalies.

In technology, Freons are designated by the letter F and a three-digit number, the last digit of which indicates the number of F atoms, the middle digit, the number of H atoms plus 1, and the first digit, the number of C atoms minus 1; for example, CCI₂F₂ is designated as F-012, or F-12 (the zero is usually omitted), and CCI₂FCCIF₂ is known as F-113.

Freons are generally obtained by the action of fluorinating agents on the corresponding polychlorinated hydrocarbons, such as carbon tetrachloride, CCI₄, and chloroform, CHC1₃, as well as by the joint action of hydrogen fluoride and chlorine on paraffins and olefins.

In addition to their use in various refrigeration systems, Freons are widely used as propellants in aerosol products (annual world production exceeds 10 million pieces) of the cosmetics, food, and pharmaceuticals industries and in aerosol insecticide and paint products. They are also used as gaseous dielectrics, as inhalation anesthetics, as fire-extinguishing mixtures (monobromotrifluoro-methane, CBrF₃, and dibromotetrafluoroethane, C₂Br₂F₄, known commercially as F-13B1 and F-114B2, respectively), as solvents for cleaning clothes and metallic surfaces, as foaming agents in the manufacture of foamed plastics, and as a raw material in the production of certain fluorocarbons, such as tetrafluoroethylene.

Most Freons have low toxicity and low biological activity. In the body, Freons do not undergo metabolic transformations and are released unchanged through the respiratory organs. The toxicity of Freons from the methane and ethane groups decreases as the number of fluorine atoms in the molecule increases; the introduction of bromine atoms increases toxicity. Freons from the propane group, such as chlorotrifluoropropane, are more toxic. When heated above 200°C, many Freons decompose, forming highly toxic products, such as perfluoroisobutylene, C₄F₈, and fluorophosgene, CF₂O. For Freons from the methane and ethane groups, maximum permissible concentration in air is 1,000–3,000 mg/m³; for Freons from the propane group, it is 1 mg/m³.

REFERENCES

Tomanovskaia, V. F., and B. E. Kolotova. Freony. Leningrad, 1970.
Toksikologiia ftororganicheskikh soedinenii i gigiena truda v ikh proizvodstve. Moscow, 1975.

S. V. SOKOLOV and A. I. KORBAKOVA