Introduction to Haloalkanes

  • Haloalkanes are organic compounds in which one or more hydrogen atoms in an alkane have been replaced by halogen atoms (fluorine, chlorine, bromine or iodine).
  • They have the general formula R-X, where R is an alkyl group and X is a halogen atom.

Properties of Haloalkanes

  • Haloalkanes are typically more dense than their corresponding alkanes due to the higher atomic weight of halogens.
  • As the size of the halogen increases, the boiling point of the haloalkane also generally increases due to greater London dispersion forces.
  • They are generally poor conductors of electricity and have low reactivity under normal conditions.

Reactions of Haloalkanes

  • Haloalkanes undergo a variety of chemical reactions, including substitution, elimination and addition reactions.
  • In the presence of sunlight or UV radiation, haloalkanes can go through a homolytic fission producing free radicals, which can initiate chain reactions.
  • These free radicals can damage the ozone layer, leading to ozone depletion. This has led to strict regulation and reduced usage of certain haloalkanes called chlorofluorocarbons (CFCs).

Haloalkanes and the Ozone Layer

  • Certain haloalkanes are responsible for the breakdown of the ozone layer.
  • Compounds such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) were used widely as refrigerants, aerosols, and in air conditioners.
  • These CFCs and HCFCs can diffuse into the stratosphere where they are broken down by solar radiation to release chlorine radicals.
  • These chlorine radicals are capable of catalysing the breakdown of ozone into oxygen, leading to the thinning of the ozone layer.

Impact on the Environment

  • The depletion of the ozone layer by these compounds has serious environmental impacts, including increased levels of harmful UV radiation reaching the Earth’s surface.
  • Measures have been taken to reduce the production and usage of ozone-depleting haloalkanes, including the Montreal Protocol on Substances that Deplete the Ozone Layer.