Preparation of Alkanes

Preparation of Alkanes:

1. Hydrogenation

Hydrogenation involves the addition of hydrogen to unsaturated hydrocarbons (alkenes or alkynes) in the presence of a metal catalyst such as Ni, Pd, or Pt, under elevated temperature (250°C).

2. Reduction of Alkyl Halides

Alkyl halides can be reduced using zinc (Zn) in hydrochloric acid (HCl) to form alkanes.

3. Hydrolysis of Grignard Reagents

Grignard reagents ($)$are highly reactive organometallic compounds that react with water to produce alkanes. The reaction involves the cleavage of the carbon-metal bond, and it must occur in the presence of dry ether as a solvent to prevent premature hydrolysis of the Grignard reagent.

4. Corey-House Synthesis

This is a coupling reaction of alkyl halides with organo-metallic compounds, specifically lithium dialkyl copper, to produce higher alkanes.

5. Reduction of Carbonyl Compounds

The reduction of carbonyl compounds (aldehydes and ketones) to alkanes can be achieved using two main methods: Clemmensen Reduction and Wolff-Kishner Reduction. These reactions differ in terms of the reagents, reaction conditions, and applicability.

1. Clemmensen Reduction

Clemmensen reduction involves the reduction of aldehydes or ketones to alkanes using zinc amalgam (Zn-Hg) in the presence of concentrated hydrochloric acid (HCl). This method is suitable for compounds stable in acidic conditions.

2. Wolff-Kishner Reduction

Wolff-Kishner reduction converts aldehydes or ketones to alkanes by reacting them with hydrazine in the presence of a strong base (typically KOH/NaOH ) under high temperature. 

Key Differences: