Reactions of Halogenoalkanes Edexcel AS Unit 2

Reactions and Preparation of Halogenoalkanes, including mechanisms

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Halogenoalkanes are compounds with one or more Hydrogen atom is an alkane has been replaced by halogen atoms and has only single bonds in the molecule.

They can be Primary, Secondary, or Tertiary. Tertiary halogenoalkanes are the most reactive of the three.

Halogenoalkanes have London forces which are stronger than the corresponding alkanes, and they have permanent dipole-dipole forces.

They are insoluble in water.

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Preparation Of Halogenoalkanes.


- Add Phosporus Pentachloride to the alcohol.

- Add concentrated  Sulphuric Acid to a mixture of propan-2-ol and potassium chloride. The sulphuric acid protonates the alcohol and releases hydrogen chloride.


- Add 50% Sulphuric Acid, slowly, with cooling to the alcohol. Add to Solid Potassium Bromide and heat. Then distill off the bromoalkane.


- Warm alcohol with a mixture of damp red phosphorus and iodine. the iodine reacts with the phosphorus to produce phosphorus triiodide, which reacts with the alcohol to form the iodoalkane.

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Reaction with Aqueous Alkali.

Reagent: Sodium (or Potassium) Hydroxide.

Conditions: Heat under reflux in aqeous solution.

Product: Alcohol.

Mechanism:  Nucleophilic Substitution.

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Reaction with Alcohol Alkali.

Reagent:concentrated Potassium Hydroxide.

Conditions: Heat under reflux in ethanol solution.

Product: Alkene.

Mechanism: Elimination.

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Reaction with Alcoholic Ammonia

Reagent: Excess Ammonia.

Conditions: Concentrated solution of ammonia at room temperature, or heated in a sealed tube.

Procuct: Amine.

Mechanism: Nucleophilic Susbtitution.

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Reaction with Water containing Silver Nitrate.

Reagents: Water containing dissolved Silver Nitrate.

Condtitions: Water, ethanol and silver nitrate.

Products: Alcohol and AgX precipitate.

Mechanism: Nucleophilic Substitution.

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