Halogenation of Alkanes

Halogenation of Alkanes Introduction:

• Halogenation of alkanes is a chemical reaction where hydrogen atoms in an alkane are replaced by halogen atoms through a free radical mechanism.
• This process is crucial in organic chemistry for the functionalization of alkanes and the synthesis of halogenated compounds.

Mechanism:

• The reaction proceeds in three steps: initiation, propagation, and termination.

  1. Initiation:

     • UV light or heat breaks the diatomic chlorine molecule into two chlorine radicals.
       • Cl2 + UV light/heat → 2Cl•Cl2 ​+ UV light/heat → 2Cl•

  2. Propagation:

     • A chlorine radical abstracts a hydrogen atom from the alkane, creating a carbon-centered radical and hydrochloric acid.
       • R-H + Cl• →R• + HClR-H + Cl• → R• + HCl
     • The carbon-centered radical reacts with another chlorine molecule, forming the chlorinated alkane and another chlorine radical.
       • R• + Cl2 → R-Cl + Cl•R• + Cl2 ​→ R-Cl + Cl•

  3. Termination:

     • The reaction stops when two radicals recombine to form a stable molecule.
     • Possible reactions include:
       • Two chlorine radicals forming a chlorine molecule.
       • A carbon-centered radical and a chlorine radical forming a chlorinated alkane.
       • Two carbon-centered radicals forming a new alkane.

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