How are alkyl halides reduced?

Alkyl halides can be reduced to alkanes by replacing the halogen atom with a hydrogen atom. This reduction typically involves the use of reducing agents.

Alkyl halides are reduced to alkanes by:

• Nascent hydrogen (Zn/HCl)
• Zn/CH₃COOH
• Zn + NaOH
• LiAlH₄
• Catalytic hydrogenation (H₂/Pd or Ni)
• Zn- Cu Couple +C₂H₅OH
• TPH (Triphenylhydride / Triphenyltin Hydride)
• Via Grignard reagent followed by hydrolysis

Important Note for JEE/NEET

1. Reduction with Nascent Hydrogen Common in laboratory conditions.
2. Reduction with Hydrogen (Catalytic Hydrogenation)
3. Using H₂ with Pd/C, Ni or Pt catalyst , Effective especially for benzyl and allyl halides.
4. LiAlH₄ (Lithium aluminium hydride) Very effective for primary and secondary halides not for 3 degree.With LiAlH₄
5. Hydride (H⁻) acts as a strong nucleophile.$$\text{R–X} + H^- \rightarrow \text{R–H} + X^-$$ Mechanism: Direct S_N2 displacement of X⁻ by H⁻
6. NaBH4 and TPH are used to reduce 3 degree haloalkane to alkane.
7. Zn–Cu couple reduces alkyl halides to alkanes (especially in alcohol medium). Zn–Cu More Reactive than Zn? Copper coating removes oxide layer from zinc, increases surface activity , facilitates electron transfer, acts as better reducing system.
8. Reduction of Alkyl Halides by TPH. Reaction proceeds via free radical mechanism