Halogenoalkanes - 2

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  • Created by: Shannon
  • Created on: 09-05-14 14:25
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  • Halogenoalkanes
    • Hydrocarbon chain attached to a halogen atom
    • Classification
      • Primary
        • Carbon attached to halogen is also attached to one other carbon
      • Secondary
        • Carbon attached to halogen is also attached to 2 other carbons
      • Tertiary
        • Carbon attached to halogen is also attached to 3 other carbons
    • Reactivity
      • Tertiary halogenoalkanes are the most reactive
        • Shorter bonds are stronger, and so do not break as easily
      • Tested using water and silver nitrate solution
        • Formation of a ppt
    • Preparation of halogenoalkane from an alcohol
      • Reacted with a metal halide and conc H2SO4 to produce a hydrogen halide
        • Hydrogen halide reacts with the corresponding alcohol to make a halogenoalkane
      • This method is not used to make a bromoalkane or an iodoalkane
        • The sulfuric acid will oxidise the iodide ions to iodine and reduce to hydrogen sulfide
        • The sulfuric acid will oxidise the bromide ions to bromine and reduce to sulfur dioxide
        • End up with by-products and a reduced yield of halogenoalkane
    • Uses
      • Produce polymers
        • E.g chloroethane, which makes PVC
      • Refrigerants
      • Fire retardants
        • Due to being non-flammable
    • Chlorofluorocarbons have caused ozone depletion
    • Reactions with...
      • Aqueous alkali to form alcohols
        • Warm aqueous NaOH or KOH under refux
        • Nucleophilic substitution reaction
      • Alcoholic KOH
        • Elimination reaction occurs
        • Heated under reflux in ethanol
        • The halogen atom is eliminated along with a hydrogen from a neighbouring carbon atom
          • A double bond is formed between the two carbon atoms
      • Alcoholic ammonia
        • Warmed under reflux with an excess of ethanolic ammonia
        • Occurs in 2 stages
          • Stage 1
            • Salt formed
            • Nucleophilic substitution
          • Stage 2
            • Ammonia molecule removes a H from NH3 group, forming an ammonium ion
              • Ammonium ion reacts with the bromine ion to form ammonium bromide


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