Chlorofluorocarbon (CFC): what it is, uses, effects

Chlorofluorocarbons (CFC) are volatile compounds that derive from hydrocarbons (usually methane and ethane), in which one or more hydrogen atoms are replaced by fluorine or chlorine atoms. Also called chlorofluorocarbons, such compounds are commonly referred to by the acronym CFC. CFCs are known for their low reactivity, the fact that they are non-flammable, have a low boiling point, and are odorless, tasteless, colorless, and have low toxicity.

Chlorofluorocarbons are mainly used as coolants, production having begun in the 1930s and peaked in the 1970s, when it was realized that such compounds were responsible for the depletion of the ozone layer in stratosphere. Since then, the Montreal Protocol has established strict rules for its consumption, import and export, making CFC consumption much lower than it was decades ago.

Read too: Carbon Monoxide—The Dangers of This Colorless, Odorless, and Highly Toxic Gas

Topics of this article

• 1 - Summary on chlorofluorocarbon (CFC)
• 2 - What is CFC?
• 3 - CFC formula
• 4 - Characteristics of chlorofluorocarbons (CFC)
• 5 - Where to find CFC?
• 6 - Consequences of CFC use for the environment
• 7 - Control of CFCs in the atmosphere
• 8 - How did chlorofluorocarbons (CFCs) appear?

Summary on Chlorofluorocarbon (CFC)

• Chlorofluorocarbons or chlorofluorocarbons are volatile derivatives of hydrocarbons that have chlorine or fluorine atoms in place of hydrogen atoms.
• They are commonly referred to by the acronym CFC.
• CFCs are chemically stable, non-flammable, odorless, tasteless, colorless, with low toxicity and have a low boiling point.
• They are mainly used as coolants and were sold under the trade name Freon.
• They began to be produced in the 1930s, reaching a great peak in the 1970s, however, it was realized that such compounds were responsible for reducing the ozone layer in the stratosphere.
• At the end of the 1970s, the Montreal Protocol was established, which brought strict control to consumption, production, import and export of CFCs, considerably reducing the use and commercialization of such compounds.

What is CFC?

CFC is the acronym for a class of compounds known as chlorofluorocarbons (also called chlorofluorocarbons or chlorofluorocarbons), consisting of volatile derivatives of hydrocarbons (in general, methane and ethane), in which one or more hydrogen atoms are replaced by fluorine or chlorine atoms.

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CFC formula

CFCs commonly have general formula CCl_nF_4–n, when derived from methane, and C₂Cl_nF_6–n, when derived from ethane. In this case, the value of “n” cannot be zero. CFCs are also well known for their commercial nomenclature, which uses numbers to indicate which CFC we are referring to. The general formula for this nomenclature isCFC-XY, where X is the number of hydrogens plus one unit (H + 1), while Y is the number of fluorine atoms.

Chlorine atoms do not appear in this nomenclature, but they are easily identified if we remember that carbon atoms make only four chemical bonds. Therefore, CFC-11 has 1 carbon atom, no hydrogen atom (X = 1, therefore, H + 1 = 1, therefore, H = 0) and 1 fluorine atom (Y = 1). As carbon makes 4 bonds, and so far only 1 fluorine atom has been identified, then there are 3 chlorine atoms, that is, CFC-11 is CCl₃F.

Similarly, CFC-22 has 1 carbon atom, 1 hydrogen atom, 2 fluorine atoms and, because carbon makes 4 chemical bonds, only 1 chlorine atom; therefore, CFC-22 is CHClF₂.

For CFCs with two or more carbon atoms, the general formula CFC-XYZ is adopted, on what:

• X is the number of carbons subtracted from one unit (C – 1).
• Y is the number of hydrogens plus one unit (H + 1).
• Z is the number of fluorine atoms present.

Similarly, chlorine atoms are taken by the difference based on the four bonds of the carbon atom. However, remember that there will be a carbon-carbon bond, so the total number of linkers equals six (just like in ethane).

For example, CFC-113 has X = 1, so it has 2 carbon atoms (C – 1 = 1, C = 2); has Y = 1, so has no hydrogen atoms (H + 1 = 1, H = 0); has Z = 3, so it has 3 fluorine atoms. Thus, we can state that CFC-113 is the C₂Cl₃F₃.

See too: How is the nomenclature of hydrocarbons defined

Characteristics of chlorofluorocarbons (CFCs)

CFCs have physical and chemical characteristics that justify their main industrial and commercial uses, they are/have:

• flammable;
• insipid (tasteless);
• odorless (no smell);
• low toxicity;
• good chemical stability;
• low corrosivity during use;
• low cost;
• volatiles (boiling point close to 0 °C);
• reasonable cost.

Where are chlorofluorocarbons (CFCs) used?

CFCs are used as refrigerants.

Due to their safety, volatility, cost and chemical stability, CFCs have proven to be good compounds to be used as:

• solvents;
• fire extinguishers;
• propellants in aerosol cans (such as spray deodorant);
• as refrigerant gases (in refrigerators, freezers and refrigerating appliances);
• as blowing agents in the production of foams, such as polyurethane.

CFCs were sold on the market by the DuPont chemical industry under the registered name Freon.

Where to find CFC?

Most of the CFCs that exist on the planet today are of anthropogenic (human) origin. Studies prove that the amount of CFC derived from natural activity is tiny compared to that produced by humans. Readings of layers not much lower than the ice indicate that, in the 19th century, the concentration of CFCs in the atmosphere was practically zero.

In fact, CFC production began in the 1930s, with peaks in the 1970s and 1980s, and data demonstrate that production of CFC-11 and CFC-12 increased from 100 tons in 1931 to 583 thousand tons in 1980. Its production only stopped at the end of the 1980s, with the institution of the Montreal Protocol. Most of the CFCs produced migrate to upper layers of the atmosphere, such as the stratosphere, which has severe consequences for our life on Earth.

Consequences of CFC use for the environment

The massive use of CFCs has affected the ozone layer abruptly.

CFCs are closely linked to a problem known as thehole in the ozone layer, a layer rich in ozone (O₃), responsible for absorbing part of the solar radiation, and which is located in the stratosphere (15-30 km in relation to the terrestrial soil).

Despite being denser than air, CFCs are chemically stable and end up being carried from the lower layers from the atmosphere (the troposphere) to the stratosphere as a result of differences in pressure and temperature. Such interlayer mixing mechanisms end up being faster than the time required for chemical processes to remove CFCs from the air. They end up being carried in packages of air and contaminants, much like people being carried in a hot air balloon.

To be eliminated in the troposphere and not reach the stratosphere, There are only two ways to dispose of CFCs:deposition (by rain) or reaction. It so happens that such compounds are poorly soluble in water and, therefore, rain is not a good mechanism for eliminating CFC gases. As far as the reactions are concerned, oxidizing agents are required, such as hydroxyl radicals, nitrate or ozone.

However, given the stability and low reactivity with such oxidizing radicals, CFCs end up staying in the air for a long time and quietly reach the stratosphere. Just for the sake of comparison, the hydroxyl radical needs 80 years to react with CFCs, something it takes about 17 days to do with methanol.

Once in the stratosphere, CFCs may undergo a photolysis reaction (breaks down by the action of light) and release chlorine radicals. As an example, we will use CFC-11 (CFCl₃) and CFC-12 (CF₂Cl₂):

• Photolysis of CFC: CFCl₃ (or CF₂Cl₂) + light → CFCl₂ (or CF₂Cl) + Cl
• O loss₃ in middle and upper stratosphere:

Cl + O₃ → ClO + O₂

ClO + O → Cl + O₂

Global: The₃ +O → 2O₂

• O loss₃ in lower stratosphere:

Cl + O₃ → ClO + O₂

ClO + HO₂ → HOCl + O₂

HOCl + light → Cl + OH

OH + O₃ → HO₂ + O₂

Overall: 2O₃ → 30₂

It is now scientific consensus that you CFCs are key agents in the hole detected in the ozone layer, in the late 1970s, in the Antarctic region.

Know more: What are the greenhouse gases?

Control of CFCs in the atmosphere

As a way of containing CFCs in the atmosphere and demonstrating their concern with the reduction of the ozone layer, in 1985, several countries met in Austria, more precisely in Vienna, Vienna Convention for the Protection of the Ozone Layer. This event was extremely important for, in 1987, the creation of the Montreal Protocol on Substances that Deplete the Ozone Layer, an international treaty that took effect on day one from 1989.

The Montreal Protocol was signed by several countries, including Brazil, which gave legal effect to its actions through Decree No. The main objective would be the progressive reducing the production and consumption of so-called substances that deplete the ozone layer (SDO) until its total elimination.

The Montreal Protocol is the only multilateral environmental agreement whose adoption is universal, that is, the 197 States are committed to protecting the ozone layer. In Brazil, CFCs are forbidden to be imported, just as there is no national production of ODS. The control is in charge of Ibama, and only some SDO are allowed to be imported, but with restrictions and broad control.

How did chlorofluorocarbons (CFCs) come about?

In the 1920s, refrigerators and air conditioning systems used composts such as ammonia, chloromethane, propane and sulfur dioxide as coolants. Despite being effective, such compounds were toxic and flammable. Furthermore, an exposure to them could not only cause severe damage but also lead to death.

It was there that a team, led by Thomas Midgley Jr., worked to develop an alternative that had no such issues to serve as coolant. The team focused on halogenated compounds, known for their volatility and chemical inertness, properties of interest for the substances.

The first compound to be developed was CF₂Cl₂, at that time known as Freon (or CFC-12). For her scholarship, Midgley has received numerous honors, including the Chemical Industry Society's Perkin Medal in 1937, and the Priestley Medal, the highest award of the American Chemical Society (the American Chemical Society).

In the 1970s, CFCs were widespread, with annual production reaching close to 1 million tons, representing a share of almost 500 million dollars of the chemical industry.

Sources:

ANDINO, J. M. Chlorofluorocarbons (CFCs) are heavier than air, so how do scientists suppose that these chemicals reach the altitude of the ozone layer to adversely affect it? Scientific American. 21 Oct. 1999. Available at: < https://www.scientificamerican.com/article/chlorofluorocarbons-cfcs/>. Accessed on 25 Jun. 2023.

AMERICAN CHEMICAL SOCIETY – ACS. Chlorofluorocarbons and Ozone Depletion. ACS National Historic Chemical Landmark. 18 Apr. 2017. Available in: https://www.acs.org/education/whatischemistry/landmarks/cfcs-ozone.html. Accessed on 25 Jun. 2023.

BUTLER, J. H. et al. A record of atmospheric halocarbons during the twentieth century from polar firn air. nature. 399, p. 749-755. 1999.

FINLAYSON-PITTS, B. J.; PITTS, J. No. Homogeneous and Heterogeneous Chemistry in the Stratosphere. in: Chemistry of Upper and Lower Atmosphere. Chap. 12. P. 657-726. San Diego, California: Academic Press, 2000.

BRAZILIAN INSTITUTE OF THE ENVIRONMENT AND RENEWABLE NATURAL RESOURCES – IBAMA. Montreal Protocol. 29 Nov. 2022. Available in: https://www.gov.br/ibama/pt-br/assuntos/emissoes-e-residuos/emissoes/protocolo-de-montreal. Accessed on 25 Jun. 2023.

KIM, K.; SHON, Z.; NGUYEN, H. T.; JEON, E. A review of major chlorofluorocarbons and their halocarbon alternatives in the air. Atmospheric Environment. n. 45. P. 1369-1382. 2011.

MINISTRY OF THE ENVIRONMENT AND CLIMATE CHANGE. Vienna Convention and Montreal Protocol. 29 Apr. 2022. Available in: https://www.gov.br/mma/pt-br/assuntos/climaozoniodesertificacao/camada-de-ozonio/convencao-de-viena-e-protocolo-de-montreal. Accessed on 25 Jun. 2023.

By Stefano Araujo Novais
Chemistry teacher

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