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Revision:Haloalkanes

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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > Haloalkanes

Haloalkanes are alkanes with one or more halogen atom. Haloalkanes have the prefix chloro-, bromo-, or iodo-. They can be classed in a similar way to alcohols. Today, these are used for purposes such as fire retardants and modern refrigerants.

Reactions

  • Substitution by hydroxide:

The haloalkane undergoes simple substitution to change into an alcohol. This reaction occurs with alkalis in aqueous solution: \mathrm{CH_3X + OH^- \longrightarrow CH_3OH + X^-}

  • Elimination by hydroxide:

A water molecule is eliminated when alkalis in ethanolic solution are added to haloalkanes: \mathrm{CH_3CH_2X + OH^- \longrightarrow H_2C=CH_2 + X^- + H_2O}. An alkene is formed.

  • Silver nitrate:

An alkali is first added, to convert the haloalkane into an alcohol and the ion in solution. Then silver nitrate is added (this could also be done without the alkali, as water also contains OH- ions), and the silver ions form precipitates with the halide ion: \mathrm{Ag^+ + X^- \longrightarrow AgX}. The colour of the precipitate depends on the halide ion originally present:

  • Chloride - White
  • Bromide - Cream
  • Iodide - Yellow
  • Ammonia in ethanol:

Amines are formed: \mathrm{CH_3X + NH_3 \longrightarrow CH_3NH_2 + HX}

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