3.3.3 Halogenoalkanes

• Ozone depletion:

  Ozone is formed in the atmosphere by free radical reactions in the presence of UV light

  O3 ->O2 + *O*

  The rate of ozone production= rate if ozone depletion therefore the atmosphere stays constant
• Ozone depletion:

  CFCs can get into the atmosphere as they are so unreactive. There the UV light causes the C-Cl bond in CFCs to break causing chlorine free radicals

  CF2CL2 -> Cl* + *CF2Cl

  The chlorine radical reacts with the ozone

  *Cl + O3 -> ClO* + O2

  ClO* + O3 -> 2O2 + Cl*

  Chlorine free radical is not used up and it acts as an catalyst.

  As a result small amounts of chlorine radicals can decompose large amounts of ozone causing a hole
• Ozone depletion:

  Ozone is beneficial as it absorbs UV radiation
• Ozone depletion:

  After the Montreal Protocol, Chemists found an alternative to CFCs which was HFC which chlorine free. HFCs are less likely to form free radicals under UV light due to the C-F bond being stronger than C-Cl bond so it is less likely to be broken up by UV light
• Nucleophilic substitution - Haloalkanes

  Conditions: Warm aqueous, Hot aqueous ethanolic , Excess

  Reagent: :OH- , :CN- , :NH3

  Forms: Alcohol, nitrile , amine
• Basic Elimination - Haloalkanes

  Conditions: Hot ethanolic

  Reagents: NaOH , KOH

  Forms: Alkene