Chlorofluorocarbons (CFCs)

Jai Ganesh · 2025-06-01 00:07:35

Chlorofluorocarbons (CFCs)

Gist

CFCs, or chlorofluorocarbons, are a class of synthetic chemical compounds containing carbon, chlorine, and fluorine. They are known as "miracle chemicals" due to their properties like stability, non-reactivity, non-toxicity, and non-flammability, making them useful in various applications. However, CFCs are also known for causing significant environmental damage, particularly stratospheric ozone depletion and contributing to global warming.

Chlorofluorocarbons (CFCs) are nontoxic, nonflammable chemicals containing atoms of carbon, chlorine, and fluorine. They are used in the manufacture of aerosol sprays, blowing agents for foams and packing materials, as solvents, and as refrigerants.

Summary

Chlorofluorocarbons (CFCs) are nontoxic, nonflammable chemicals containing atoms of carbon, chlorine, and fluorine. They are used in the manufacture of aerosol sprays, blowing agents for foams and packing materials, as solvents, and as refrigerants. CFCs are classified as halocarbons, a class of compounds that contain atoms of carbon and halogen atoms. Individual CFC molecules are labeled with a unique numbering system. For example, the CFC number of 11 indicates the number of atoms of carbon, hydrogen, fluorine, and chlorine (e.g. CCl3F as CFC-11). The best way to remember the system is the "rule of 90" or add 90 to the CFC number where the first digit is the number of carbon atoms (C), the second digit is the number of hydrogen atoms (H), and the third digit is number of the fluorine atoms (F). The total number of chlorine atoms (Cl) are calculated by the expression: Cl = 2(C+1) - H - F. In the example CFC-11 has one carbon, no hydrogen, one fluorine, and therefore 3 chlorine atoms.

Refrigerators in the late 1800s and early 1900s used the toxic gases, ammonia (NH3), methyl chloride (CH3Cl), and sulfur dioxide (SO2), as refrigerants. After a series of fatal accidents in the 1920s when methyl chloride leaked out of refrigerators, a search for a less toxic replacement begun as a collaborative effort of three American corporations- Frigidaire, General Motors, and Du Pont. CFCs were first synthesized in 1928 by Thomas Midgley, Jr. of General Motors, as safer chemicals for refrigerators used in large commercial appilications1. Frigidaire was issued the first patent, number 1,886,339, for the formula for CFCs on December 31, 1928. In 1930, General Motors and Du Pont formed the Kinetic Chemical Company to produce Freon (a Du Pont tradename for CFCs) in large quantities. By 1935 Frigidaire and its competitors had sold 8 million new refrigerators in the United States using Freon-12 (CFC-12) made by the Kinetic Chemical Company and those companies that were licensed to manufacture this compound. In 1932 the Carrier Engineering Corporation used Freon-11 (CFC-11) in the worldís first self-contained home air-conditioning unit, called the "Atmospheric Cabinet".; Because of the CFC safety record for nontoxicity, Freon became the preferred coolant in large air-conditioning systems. Public health codes in many American cities were revised to designate Freon as the only coolant that could be used in public buildings. After World War II, CFCs were used as propellants for bug sprays, paints, hair conditioners, and other health care products. During the late 1950s and early 1960s the CFCs made possible an inexpensive solution to the desire for air conditioning in many automobiles, homes, and office buildings. Later, the growth in CFC use took off worldwide with peak, annual sales of about a billion dollars (U.S.) and more than one million metric tons of CFCs produced.

Whereas CFCs are safe to use in most applications and are inert in the lower atmosphere, they do undergo significant reaction in the upper atmosphere or stratosphere. In 1974, two University of California chemists, Professor F. Sherwood Rowland and Dr. Mario Molina, showed that the CFCs could be a major source of inorganic chlorine in the stratosphere following their photolytic decomposition by UV radiation. In addition, some of the released chlorine would become active in destroying ozone in the stratosphere2. Ozone is a trace gas located primarily in the stratosphere (see ozone). Ozone absorbs harmful ultraviolet radiation in the wavelengths between 280 and 320 nm of the UV-B band which can cause biological damage in plants and animals. A loss of stratospheric ozone results in more harmful UV-B radiation reaching the Earth's surface. Chlorine released from CFCs destroys ozone in catalytic reactions where 100,000 molecules of ozone can be destroyed per chlorine atom.

A large springtime depletion of stratospheric ozone was getting worse each following year. This ozone loss was described in 1985 by British researcher Joe Farman and his colleagues3. It was called ìthe Antarctic ozone holeî by others. The ozone hole was different than ozone loss in the midlatitudes. The loss was greater over Antarctic than the midlatitudes because of many factors: the unusually cold temperatures of the region, the dynamic isolation of this ìholeî, and the synergistic reactions of chlorine and bromine4. Ozone loss also is enhanced in polar regions as a result of reactions involving polar stratospheric clouds (PSCs)5 and in midlatitudes following volcanic eruptions. The need for controlling the CFCs became urgent.

In 1987, 27 nations signed a global environmental treaty, the Montreal Protocol to Reduce Substances that Deplete the Ozone Layer6, that had a provision to reduce 1986 production levels of these compounds by 50% before the year 2000. This international agreement included restrictions on production of CFC-11, -12, -113, -114, -115, and the Halons (chemicals used as a fire extinguishing agents). An amendment approved in London in 1990 was more forceful and called for the elimination of production by the year 2000. The chlorinated solvents, methyl chloroform (CH3CCl3), and carbon tetrachloride (CCl4) were added to the London Amendment.

Large amounts of reactive stratospheric chlorine in the form of chlorine monoxide (ClO) that could only result from the destruction of ozone by the CFCs in the stratosphere were observed by instruments onboard the NASA ER-2 aircraft and UARS (Upper Atmospheric Research Satellite) over some regions in North America during the winter of 19927,8. The environmental concern for CFCs follows from their long atmospheric lifetime (55 years for CFC-11 and 140 years for CFC-12, CCl2F2)9 which limits our ability to reduce their abundance in the atmosphere and associated future ozone loss. This resulted in the Copenhagen Amendment that further limited production and was approved later in 1992. The manufacture of these chemicals ended for the most part on January 1, 1996. The only exceptions approved were for production within developing countries and for some exempted applications in medicine (i.e., asthma inhalators) and research. The Montreal Protocol included enforcement provisions by applying economic and trade penalties should a signatory country trade or produce these banned chemicals. A total of 148 signatory countries have now signed the Montreal Protocol. Atmospheric measurements CFC-11 and CFC-12 reported in 1993 showed that their growth rates were decreasing as result of both voluntary and mandated reductions in emissions9. Many CFCs and selected chlorinated solvents have either leveled off (Figure 1) or decreased in concentration by 19949,10.

The demand for the CFCs was accomodated by recycling, and reuse of existing stocks of CFCs and by the use of substitutes. Some applications, for example degreasing of metals and cleaning solvents for circuit boards, that once used CFCs now use halocarbon-free fluids, water (sometimes as steam), and diluted citric acids. Industry developed two classes of halocarbon substitutes- the hydrochlorofluorocarbons (HCFCs) and the hydrofluorocarbons (HFCs). The HCFCs include hydrogen atoms in addition to chlorine, fluorine, and carbon atoms. The advantage of using HCFCs is that the hydrogen reacts with tropospheric hydroxyl (OH), resulting in a shorter atmospheric lifetime. HCFC-22 (CHClF2) has an atmospheric lifetime of about 13 years11 and has been used in low-demand home air-conditioning and some refrigeration applications since 1975. However, HCFCs still contain chlorine which makes it possible for them to destroy ozone. The Copenhagen amendment calls for their production to be eliminated by the year 2030. The HFCs are considered one of the best substitutes for reducing stratospheric ozone loss because of their short lifetime and lack of chlorine. In the United States, HFC-134a is used in all new domestic automobile air conditioners. For example, HFC-134a is growing rapidly in 1995 at a growth rate of about 100% per year with an atmospheric lifetime of about 12 years12. (The "rule of 90" also applies for the chemical formula of HCFCs and HFCs.)

Use of the CFCs, some chlorinated solvents, and Halons should become obsolete in the next decade if the Montreal Protocol is observed by all parties and substitutes are used. The science that became the basis for the Montreal Protocol resulted in the 1995 Nobel Prize for Chemistry. The prize was awarded jointly to Professors F. S. Rowland at University of California at Irvine, M. Molina at the Massachusetts Institute of Technology, Cambridge, and Paul Crutzen at the Max-Planck-Institute for Chemistry in Mainz, Germany, for their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone (in particular, by the CFCs and oxides of nitrogen).

Details

Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F). They are produced as volatile derivatives of methane, ethane, and propane.

The most common example of a CFC is dichlorodifluoromethane (R-12). R-12, also commonly called Freon, is used as a refrigerant. Many CFCs have been widely used as refrigerants, propellants (in aerosol applications), gaseous fire suppression systems, and solvents. As a result of CFCs contributing to ozone depletion in the upper atmosphere, the manufacture of such compounds has been phased out under the Montreal Protocol, and they are being replaced with other products such as hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs) including R-410A, R-134a and R-1234yf.

Structure, properties and production

As in simpler alkanes, carbons in CFCs bond with tetrahedral symmetry. Because the fluorine and chlorine atoms differ greatly in size and effective charge from hydrogen and from each other, methane-derived CFCs deviate from perfect tetrahedral symmetry.

The physical properties of CFCs and HCFCs can be affected by changes in the number and identity of the halogen atoms. They are generally volatile, but less so than their parent alkanes. The decreased volatility is attributed to the molecular polarity induced by the halides, which induces intermolecular interactions. Thus, methane boils at −161 °C whereas the fluoromethanes boil between −51.7 (CF2H2) and −128 °C (CF4). CFCs still have higher boiling points because the chloride is even more polarizable than fluoride. Because of their polarity, CFCs are useful solvents, and their boiling points make them suitable as refrigerants. 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 higher than their corresponding alkanes. In general, the density of these compounds correlates with the number of chlorides.

Applications

CFCs and HCFCs are used in various applications because of their low toxicity, reactivity and flammability. Every permutation of fluorine, chlorine and hydrogen based on methane and ethane has 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, aerosol 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.

Impact as greenhouse gases

CFCs were phased out via the Montreal Protocol due to their part in ozone depletion.

The atmospheric impacts of CFCs are not limited to their role as ozone-depleting chemicals. Infrared absorption bands prevent heat at that wavelength from escaping Earth's atmosphere. CFCs have their strongest absorption bands from C-F and C-Cl bonds in the spectral region of 7.8–15.3 μm—referred to as the "atmospheric window" due to the relative transparency of the atmosphere within this region.

The strength of CFC absorption bands and the unique susceptibility of the atmosphere at wavelengths where CFCs (indeed all covalent fluorine compounds) absorb radiation creates a "super" greenhouse effect from CFCs and other unreactive fluorine-containing gases such as perfluorocarbons, HFCs, HCFCs, bromofluorocarbons, SF6, and NF3. This "atmospheric window" absorption is intensified by the low concentration of each individual CFC. Because CO2 is close to saturation with high concentrations and few infrared absorption bands, the radiation budget and hence the greenhouse effect has low sensitivity to changes in CO2 concentration; the increase in temperature is roughly logarithmic. Conversely, the low concentration of CFCs allow their effects to increase linearly with mass, so that chlorofluorocarbons are greenhouse gases with a much higher potential to enhance the greenhouse effect than CO2.

Groups are actively disposing of legacy CFCs to reduce their impact on the atmosphere.

According to NASA in 2018, the hole in the ozone layer has begun to recover as a result of CFC bans. However, research released in 2019 reported an alarming increase in CFCs, pointing to unregulated use in China.

Additional Information

Chlorofluorocarbon (CFC) is any of several organic compounds composed of carbon, fluorine, and chlorine. When CFCs also contain hydrogen in place of one or more chlorines, they are called hydrochlorofluorocarbons, or HCFCs. CFCs are also called Freons, a trademark of the E.I. du Pont de Nemours & Company in Wilmington, Del. CFCs were originally developed as refrigerants during the 1930s. Some of these compounds, especially trichlorofluoromethane (CFC-11) and dichlorodifluoromethane (CFC-12), found use as aerosol-spray propellants, solvents, and foam-blowing agents. They are well suited for these and other applications because they are nontoxic and nonflammable and can be readily converted from a liquid to a gas and vice versa.

Their commercial and industrial value notwithstanding, CFCs were eventually discovered to pose a serious environmental threat. Studies, especially those of American chemists F. Sherwood Rowland and Mario Molina and Dutch chemist Paul Crutzen, indicated that CFCs, once released into the atmosphere, accumulate in the stratosphere, where they contribute to the depletion of the ozone layer. Stratospheric ozone shields life on Earth from the harmful effects of the Sun’s ultraviolet radiation; even a relatively small decrease in the stratospheric ozone concentration can result in an increased incidence of skin cancer in humans and genetic damage in many organisms. Ultraviolet radiation in the stratosphere causes the CFC molecules to dissociate, producing chlorine atoms and radicals (i.e., chlorodifluoromethyl radical; free radicals are species that contain one or more unpaired electrons).

Because of a growing concern over stratospheric ozone depletion and its attendant dangers, a ban was imposed on the use of CFCs in aerosol-spray dispensers in the late 1970s by the United States, Canada, and the Scandinavian countries. In 1990, 93 nations agreed, as part of the Montreal Protocol (established 1987), to end production of ozone-depleting chemicals by the end of the 20th century. By 1992 the list of participating countries had grown to 140, and the timetable for ending production of CFCs advanced to 1996. This goal has largely been met. HCFCs pose less of a risk than CFCs because they decompose more readily in the lower atmosphere; nevertheless, they too degrade the ozone layer and are scheduled to be phased out by 2030.

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Chlorofluorocarbons (CFCs)

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