Preparation of Alkyl Halides

• The preparation of alkyl halides can be accomplished through various methods, each involving different reactants and mechanisms.

1. Halogenation of Alkanes (Free Radical Substitution)

1. Process:

   • This method involves the reaction of alkanes with halogens (Cl₂ or Br₂) in the presence of ultraviolet light or heat.
   • The reaction proceeds through a free radical mechanism, leading to the formation of alkyl halides.

2. Example:

   • Methane reacts with Chlorine under UV light or heat to produce chloromethane and hydrochloric acid.
   • CH4 + Cl2 →(UV/light) CH3Cl + HCl

2. From Alcohols (Nucleophilic Substitution)

1. Process:

   • Alcohols can be converted into alkyl halides by reacting with hydrogen halides (HCl, HBr, or HI) or phosphorus halides (PCl₃, PCl₅, or PBr₃).
   • This transformation occurs via a nucleophilic substitution mechanism.

2. Example with Hydrogen Halides:

   • Ethanol reacts with hydrogen bromide to produce ethyl bromide and water.
   • CH3CH2OH + HBr → CH3CH2Br + H2O

3. Example with Phosphorus Halides:

   • 3CH₃CH₂OH + PCl₃ → 3 CH₃CH₂Cl + H₃PO₃

3. Halogen Exchange (Finkelstein Reaction)

1. Process:

   • This technique involves converting one alkyl halide into another by reacting it with a sodium or potassium halide salt in a polar aprotic solvent.
   • This reaction is driven by the precipitation of the less soluble halide salt.

2. Example:

   • Bromoethane reacts with sodium iodide to produce iodoethane and sodium bromide.
   • CH3CH2Br + NaI → CH3CH2I + NaBr

4. From Alkenes (Addition Reaction)

1. Process:

   • Alkenes can be converted to alkyl halides through the reaction with hydrogen halides (HCl, HBr, or HI).
   • This process involves electrophilic addition, where the double bond of the alkene opens up to attach the halogen atom.

2. Example:

   • Propene reacts with hydrogen chloride to form 2-chloropropane.
   • CH3CH=CH2 + HCl → CH3CHClCH3

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