HCFCs

__**Reasons HCFCs are replacing CFCs:**__
 * HCFCs (Hydrochlorofluorocarbons)** are what has replaced CFCs. HCFCs are now used as refrigerants and fire suppressants and solvents for electronics. Although HCFCs still are a risk to depleting ozone because they contain chlorine, they are still an improvement from using CFCs.
 * One reason is because they are more reactive, which means instead of surviving in the atmosphere for a long period of time, they react in the troposphere, causing them to decompose, which prevents them from continuing on into the stratosphere, where the chlorine could potentially breakdown the ozone.
 * Another reason that they are being used over CFCs is due to the fact that it is also energy - efficient, and cost effective.
 * They are energy-efficient, low-in-toxicity, cost effective and can be used safely.
 * HCFCs are up to 98% less ozone depleting and have 80% shorter atmospheric lifetimes, than the corresponding CFCs they replaced.





Structure, properties, production
As in simpler alkanes , carbon in the CFCs and the HCFCs is  tetrahedral. Since the fluorine and chlorine atoms differ greatly in size from hydrogen and from each other, the methane derived CFCs deviate from perfect tetrahedral symmetry. The physical properties of the CFCs and HCFCs are tunable by changes in the number and identity of the halogen atoms. In general they are volatile, but less so than parent alkane. The decreased volatility is attributed to the molecular polarity induced by the halides and the polarizability of halides, which induces intermolecular interactions. Thus, methane boils at −161 °C whereas the fluoromethanes boil between −51.7 (CF2H2) and −128 °C (CF4). The CFCs have still higher boiling points because the chloride is even more polarizable than fluoride. Because of their polarity, the CFCs are useful solvents. The 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 invariably higher than the corresponding alkanes. In general the density of these compounds correlates with the number of chlorides. CFCs and HCFCs are usually produced by halogen exchange starting from chlorinated methanes and ethanes. Illustrative is the synthesis of chlorodifluoromethane from chloroform  : HCCl3 + 2 HF → HCF2Cl + 2 HCl The brominated derivatives are generated by free-radical reactions of the chlorofluorocarbons, replacing C-H bonds with C-Br bonds. The production of the anesthetic   2-bromo-2-chloro-1,1,1-trifluoroethane  ("halothane") is illustrative: CF3CH2Cl + Br2 → CF3CHBrCl + HBr

Reactions
The most important reaction of the CFCs is the photo-induced scission  of a C-Cl bond: CCl3F → CCl2F**.** + Cl**.** The chlorine atom, written often as Cl**.**, behaves very differently from the chlorine molecule (Cl2). The radical Cl**.** is long-lived in the upper atmosphere, where it catalyzes the conversion of ozone into O2. Ozone absorbs UV-radiation better than O2 does, so its depletion allows more of this high energy radiation to reach the Earth's surface. Bromine atoms are even more efficient catalysts, hence brominated CFCs are also regulated.

Applications
Applications exploit the low toxicity, low reactivity, and low flammability of the CFCs and HCFCs. 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  , 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.

Classes of compounds, nomenclature

 * Chlorofluorocarbons (CFCs): when derived from methane and ethane these compounds have the formulae CClmF4-m and C2ClmF6-m, where m is nonzero.
 * Hydrochlorofluorocarbons (HCFCs): when derived from methane and ethane these compounds have the formulae CClmFnH4-m-n and C2ClxFyH6-x-y, where m, n, x, and y are nonzero.
 * Bromochlorofluorocarbons and bromofluorocarbons have formulae similar to the CFCs and HCFCs but also bromine.
 * Hydrofluorocarbons (HFCs): when derived from methane, ethane, propane , and  butane  , these compounds have the respective formulae CFmH4-m, C2FmH6-m, C3FmH8-m, and C4FmH10-m, where m is nonzero.

Commercial names
Freon is DuPont's brand name for CFCs, HCFCs and related compounds. Other commercial names from around the world are Algofrene, Arcton, Asahiflon, Daiflon, Eskimo, FCC, Flon, Flugene, Forane, Fridohna, Frigen, Frigedohn, Genetron, Isceon, Isotron, Kaiser, Kaltron, Khladon, Ledon, Racon, and Ucon.

Numbering system
A numbering system is used for fluorinated alkanes, prefixed with Freon-, R-, CFC-, and HCFC-. The rightmost value indicates the number of fluorine atoms, the next value to the left is the number of hydrogen atoms //plus// 1, and the next value to the left is the number of carbon atoms //less// one (zeroes are not stated). Remaining atoms are chlorine. Thus, Freon-12 indicates a methane derivative (only two numbers) containing two fluorine atoms (the second 2) and no hydrogen (1-1=0). It is therefore CCl2F2. Another, easier equation that can be applied to get the correct molecular formula of the CFC/R/Freon class compounds is this to take the numbering and add 90 to it. The resulting value will give the number of carbons as the first numeral, the second numeral gives the number of hydrogen atoms, and the third numeral gives the number of fluorine atoms. The rest of the unaccounted carbon bonds are occupied by chlorine atoms. The value of this equation is always a three figure number. An easy example is that of CFC-12, which gives: 90+12=102 -> 1 carbon, 0 hydrogens, 2 fluorine atoms, and hence 2 chlorine atoms resulting in CCl2F2. The main advantage of this method of deducing the molecular composition in comparison with the method described in the paragraph above, is that it gives the number of carbon atoms of the molecule.