What are Chlorofluorocarbons?
Do You Know Chlorofluorocarbons Meaning?
CFC stands for chlorofluorocarbon, which is an organic compound made up of carbon, fluorine, and chlorine. Hydrochlorofluorocarbons, or HCFCs, are CFCs that also contain hydrogen in place of one or more chlorines. CFCs are also known as Freons, a brand of Wilmington, Delaware-based E.I. du Pont de Nemours & Company. CFCs were first formulated in the 1930s as a refrigerant.
Chlorofluorocarbons chemical formula is CCl2F2.
What is CFC Gas?
Dichlorodifluoromethane is by far the most common example (R-12 or Freon-12) of CFC gas. Many CFCs have been used as refrigerants, propellants (in aerosols), and solvents. CFCs have been phased out under the Montreal Protocol because they lead to ozone depletion in the upper atmosphere, and they are being replaced by other materials such as hydrofluorocarbons (HFCs).
Chlorofluorocarbon Structure
Carbon in CFCs bonds with tetrahedral symmetry, much as in simpler alkanes. The methane-derived CFCs deviate from perfect tetrahedral symmetry because the fluorine and chlorine atoms vary greatly in size and effective charge from hydrogen and each other.
Properties of Chlorofluorocarbons
Changes in the number and identity of the halogen atoms will alter the physical properties of CFCs and HCFCs. They are unpredictable in general, but not as much as their parent alkanes. The decreased volatility is due to the halides' induction of molecular polarity, which creates intermolecular interactions. Methane boils at 161 degrees Celsius, while fluoromethanes boil between 51.7 (CF2H2) and 128 degrees Celsius (CF4).
Since chloride is more polarizable than fluoride, CFCs have even higher boiling points. CFCs are useful solvents due to their polarity, and their boiling points make them ideal as refrigerants. CFCs are less flammable than methane, in part because they have fewer C-H bonds, and in part, because the released halides, in the case of chlorides and bromides, quench the free radicals that keep flames going.
CFCs have a higher density than their corresponding alkanes. In general, the number of chlorides is proportional to the density of these compounds.
Preparation of Chlorofluorocarbons CFCs
CFCs and HCFCs are usually made from chlorinated methanes and ethanes by halogen exchange. The synthesis of chlorodifluoromethane from chloroform is given below:
HCCl3 + 2 HF → HCF2Cl + 2 HCl
Applications of Chlorofluorocarbons
Due to their low toxicity, reactivity, and flammability, CFCs and HCFCs are used in a variety of applications. Every possible mixture of fluorine, chlorine, and hydrogen-based on methane and ethane has been studied, and the majority of them have been commercialized. As a precursor to tetrafluoroethylene, the monomer that is converted into Teflon, billions of kilograms of chlorodifluoromethane are produced each year. propellants in medical applications and degreasing solvents are only a few of the applications.
Chlorofluorocarbons and Ozone Depletion
Because of their role in ozone depletion, CFCs were phased out under the Montreal Protocol.
CFCs' atmospheric effects, on the other hand, are not limited to their position as ozone-depleting chemicals. Infrared absorption bands prevent heat from leaving the earth's atmosphere at that wavelength. The strongest absorption bands from C-F and C-Cl bonds in CFCs are found in the spectral region 7.8–15.3 m, which is referred to as the "atmospheric window" because of the relative clarity of the atmosphere within this range.
CFCs and other unreactive fluorine-containing gases such as perfluorocarbons, HFCs, HCFCs, bromofluorocarbons, SF6, and NF3 produce a "super" greenhouse effect due to the frequency of CFC absorption bands and the peculiar sensitivity of the atmosphere at wavelengths where CFCs (indeed all covalent fluorine compounds) absorb. The low concentration of each individual CFC amplifies this “atmospheric window” absorption. Since CO2 is close to saturation at high concentrations and has few infrared absorption bands, the greenhouse effect's sensitivity to changes in CO2 concentration is low; the temperature rise is approximately logarithmic.
CFCs, on the other hand, have a low concentration that allows their effects to rise linearly with mass, making them greenhouse gases with a much higher potential to increase the greenhouse effect than CO2.
To reduce the effect of legacy CFCs on the environment, groups are actively disposing of them.
As a result of CFC bans, NASA stated in 2018 that the hole in the ozone layer has started to close.
Did You Know?
From the late 1800s to the end of World War II, carbon tetrachloride (CCl4) was used in fire extinguishers and glass "anti-fire grenades." Chloroalkanes have been used for fire control on military aircraft since the 1920s. Freon is a brand name for a group of CFCs that are mainly used as refrigerants, but also have applications in firefighting and as aerosol propellants. Bromomethane is a commonly used fumigant. Dichloromethane is an industrial solvent with a large range of applications.
In the late 1920s, Thomas Midgley, Jr. improved the synthesis process and led the drive to use CFC as a refrigerant to replace harmful refrigerants including ammonia (NH3), chloromethane (CH3Cl), and sulfur dioxide (SO2). The following qualities were sought in a new refrigerant: low boiling point, low toxicity, and general non-reactivity. Midgley flamboyantly demonstrated all of these properties in a demonstration for the American Chemical Society in 1930, by inhaling a breath of the gas and using it to blow out a candle.
FAQs on Chlorofluorocarbons (CFCs)
1. What are Chlorofluorocarbons (CFCs) and what is their general chemical structure?
Chlorofluorocarbons, commonly known as CFCs, are a class of synthetic organic compounds. Their structure consists of carbon atoms bonded to both chlorine and fluorine atoms. They are typically derived from methane (CH₄) and ethane (C₂H₆) by replacing the hydrogen atoms with these halogens. A well-known example is Dichlorodifluoromethane (CCl₂F₂), also known as Freon-12.
2. What were the primary uses of CFCs before they were banned?
Before being phased out, CFCs were widely used due to their non-toxic, non-flammable, and highly stable properties. Their primary applications included:
- Refrigerants in air conditioners and refrigerators.
- Propellants in aerosol spray cans for products like deodorants and insecticides.
- Blowing agents for producing insulating foams, such as styrofoam.
- Solvents for cleaning electronic components and degreasing metals.
3. Why are CFCs, which are non-toxic and stable on Earth, considered major environmental hazards?
The very chemical stability that made CFCs useful on the ground is what makes them hazardous in the atmosphere. Because they are inert, they do not break down in the lower atmosphere (troposphere). This allows them to persist for decades, eventually drifting up to the stratosphere. In the stratosphere, they are exposed to intense ultraviolet (UV) radiation, which breaks them apart and releases highly reactive chlorine atoms that initiate the destruction of the protective ozone layer.
4. How does a single chlorine atom from a CFC molecule catalytically destroy the ozone layer?
A single chlorine atom acts as a catalyst, meaning it can destroy many ozone molecules without being consumed itself. The process occurs in a two-step cycle:
- First, a free chlorine atom (Cl) reacts with an ozone molecule (O₃), breaking it apart to form chlorine monoxide (ClO) and an oxygen molecule (O₂).
- Next, the chlorine monoxide (ClO) molecule reacts with a free oxygen atom (O). This reaction breaks the ClO bond, releasing the original chlorine atom (Cl) and forming another oxygen molecule (O₂).
5. What are some common examples of CFCs?
Several types of CFCs were produced commercially, often sold under the trade name Freon. Some of the most common examples as per the NCERT syllabus include:
- CFC-11 (Trichlorofluoromethane - CCl₃F): Used as a refrigerant and a blowing agent for foams.
- CFC-12 (Dichlorodifluoromethane - CCl₂F₂): Widely used in car air conditioning systems and aerosol sprays.
- CFC-113 (Trichlorotrifluoroethane - C₂Cl₃F₃): Used as a solvent for cleaning electronics and in dry cleaning.
6. What is the Montreal Protocol and why was it crucial for controlling CFCs?
The Montreal Protocol on Substances that Deplete the Ozone Layer is a landmark international environmental treaty signed in 1987. It is considered crucial because it established a global schedule to phase out the production and consumption of nearly 100 man-made ozone-depleting substances (ODS), with CFCs being the most prominent. Its success lies in the legally binding commitment from all signatory nations, which led to a dramatic reduction in atmospheric CFC concentrations and has allowed the ozone layer to begin a slow recovery.
7. Are CFCs still being used, and what has replaced them in applications like refrigeration and aerosols?
The production of new CFCs is banned globally under the Montreal Protocol. They have been replaced by several alternatives. Initially, hydrochlorofluorocarbons (HCFCs) were used as a transitional substitute as they have a lower ozone-depleting potential. Now, the primary replacements are hydrofluorocarbons (HFCs), which contain no chlorine and do not harm the ozone layer. However, since HFCs are potent greenhouse gases, the world is now transitioning to newer alternatives like hydrofluoroolefins (HFOs).
8. Besides ozone depletion, do CFCs contribute to any other environmental problems?
Yes, in addition to being potent ozone-depleting substances, CFCs are also highly effective greenhouse gases. A molecule of CFC-12, for example, has a global warming potential (GWP) that is thousands of times greater than that of carbon dioxide (CO₂) over a 100-year period. Although their atmospheric concentration is much lower than CO₂, their contribution to the enhanced greenhouse effect is significant, making their phase-out beneficial for both the ozone layer and for mitigating climate change.
