Methods of preparation
Haloalkanes are prepared by the following methods
Alcohols can be converted into halo alkenes by reacting it with any one of the following reagent 1. hydrogen halide 2. Phosphorous halides 3. Thionyl chloride
Mixture of con.HCl and anhydrous ZnCl2 is called Lucas reagent.
The order of reactivity of halo acids with alcohol is in the order HI > HBr > HCl. The order of reactivity of alcohols with halo acid is tertiary > secondary > primary.
Alcohols react with PX5 or PX3 to form haloalkane. PBr3 and PI 3 are usually generated in situ (produced in the reaction mixture) by the reaction of red phosphorus with bromine and iodine, respectively.
This reaction is known as Darzen's halogenation
Alkenes react with halogen acids (HCl, HBr, HI) to give haloalkane. The mode of addition follows Markovnikov’s rule.
Alkanes react with halogens (Cl2 or Br2) in the presence of ultra violet light to form haloalkane. This reaction is a free radical substitution reaction and gives a mixture of mono, di or poly substituted haloalkane.
Chlorination of methane gives different products which have differences in the boiling points. Hence, these can be separated by fractional distillation.
Chloro or bromoalkane on heating with a concentrated solution of sodium iodide in dry acetone gives iodo alkanes. This reaction is called Finkelstein reaction, (SN2 reaction).
Chloro or bromo alkanes on heating with metallic fluorides like AgF, SbF3 or Hg2F2 gives fluoro alkanes. This reactions is called Swarts reaction.
Silver salts of fatty acids when refluxed with bromine in CCl4 gives bromo alkane
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