Cfc reduction

Courtesy : en.wikipedia.org

Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methaneethane, and propane. They are also commonly known by the DuPont brand name Freon.

The most common representative is dichlorodifluoromethane (R-12 or Freon-12). Many CFCs have been widely used as refrigerantspropellants (in aerosol applications), and solvents. Because CFCs contribute 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)[1] including R-410A and R-134a.[2][3]

Structure, properties and production

Main article: Organofluorine chemistry

As in simpler alkanes, carbon in the CFCs bond with tetrahedral symmetry. Because the fluorine and chlorine atoms differ greatly in size and effective charge from hydrogen and from each other, the methane-derived CFCs deviate from perfect tetrahedral symmetry.[4]

The physical properties of 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 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). 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, and their boiling points make them suitable as refrigerants. 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 higher than their 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

Brominated derivatives are generated by free-radical reactions of hydrochlorofluorocarbons, 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

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 refrigerantsblowing agentsaerosol 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.[5]

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.
  • Hydro-chlorofluorocarbons (HCFCs): when derived from methane and ethane these compounds have the formula CClmFnH4−m−n and C2ClxFyH6−x−y, where m, n, x, and y are nonzero.
  • and bromofluorocarbons have formulae similar to the CFCs and HCFCs but also include bromine.
  • Hydrofluorocarbons (HFCs): when derived from methaneethanepropane, and butane, these compounds have the respective formulae CFmH4−m, C2FmH6−m, C3FmH8−m, and C4FmH10−m, where m is nonzero.

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CFC reduction

What is CFC reduction CFC reduction refers to the collective efforts and actions taken to decrease the production, consumption, and release of chlorofluorocarbons (CFCs) into the atmosphere. CFCs are synthetic

Cfc reduction

Cfc reduction Courtesy : news.mit.edu/ The chemical in question is CFC-11, a chlorofluorocarbon that was once commonly used for refrigeration, insulation, and other purposes. When emitted to the atmosphere, CFC-11

Cfc reduction

CFc reduction Courtesy : news.mit.edu/ The chemical in question is CFC-11, a chlorofluorocarbon that was once commonly used for refrigeration, insulation, and other purposes. When emitted to the atmosphere, CFC-11