What comes to your mind when you hear the term CFC? Many people tend to call these compounds “The stuff that destroys our ozone layer”. While this is entirely true, there is so much more to these fascinating compounds than just its effect on the ozone layer.
CFC stands for chlorofluorocarbon. These are a group of organic compounds that closely resemble alkanes, but some, or all of its hydrogen atoms have been replaced with chlorine, or fluorine, or both. For example, if we consider methane (C1H4), the CFC ‘version’ of it could be dichlorodifluoromethane (C1Cl2F2 ), more commonly known as Freon-12. It has same tetrahedral structure like methane; the only difference in terms of structure of the molecule is that it has different atoms ‘attached’ to the carbon in the middle of the molecule. These molecules are less volatile than their ‘corresponding’ alkanes. This is due to halides (ions of group 7 elements) being really electronegative, meaning they are really good at inducing intermolecular interactions.
CFCs have some interesting properties which can be fully exploited; therefore there are plenty of uses for these molecules. CFCs are not flammable; therefore they were used as propellants that would push other molecules out of the aerosol sprays. For the same reason CFCs were used to form foamed plastics. Also low flammability enabled people to use these molecules to dry clean hot electronic components of devices such as air conditioning. However, the most fascinating property of the CFCs is that they are amongst the least toxic compounds known to a man. In fact, it is so safe that American navy has thought of filling human lungs with these molecules in order to combat high pressure exerted on divers working deep underwater. The experiment was eventually scrapped; however it does show just how safe these compounds are. Therefore CFCs were widely used as refrigerants to keep the insides of fridges cool.
Since these molecules are so safe, how could they possibly cause any problems to our environment? CFCs in fact can harm our environment in two ways:
- CFCs, as mentioned earlier, deplete the ozone layer. After being released, they slowly rise to the ozone layer. Once they get there, the halide atoms are detached from the carbon atoms due to the presence of UV rays. The reaction usually produces chlorine, or fluorine atoms with free radicals. Free radicals are the unpaired electrons e.g. chlorine atom has 7 electrons, therefore one of them will be unpaired. The aforementioned Free radicals cause the halogen atoms to become really reactive. Chlorine and fluorine then, react with the Oxygen in the ozone layer converting the oxygen from O3, which is the main constituent of ozone layer that blocks most of UV rays to O2 which is present in the air we breathe. For that reason the production of CFCs has been phased out by the Montreal Protocol. The fact that these compounds are so safe to humans and animals caused Sherry Rowland and Mario Molina many difficulties in proving the connection between CFCs and depletion of the ozone layer.
- The structure of some CFCs is similar to the hydrocarbons which cause global warming, such as methane. Therefore many CFCs contribute to global warming as well.
In nutshell CFCs are very useful and non toxic chemicals, which unfortunately do deplete the ozone layer and contribute to the global warming. This is a real shame, as these compounds were very handy and readily available.
Image from: sciencephoto.com
Article written by: Hubert Bieluczyk