ALKANES

• General Method of Preparation of Alkanes (Paraffins)

  1. From unsaturated Hydrocarbons

  2. From haloalkanes

  3. By the Reduction of Aldehydes and Ketones

  4. From Grignard's Reagent

  5. From salts of Carboxylic acid

  6. From Metal Carbides
• Preparation of Alkanes from unsaturated Hydrocarbons

  1. Catalytic hydrogenation in presence of Ni or Pt catalyst at 200°C to 300°C

  2. R-CH=CH2 + H2 → R-CH2-CH3
• Preparation of Alkanes from unsaturated Hydrocarbons

  • CH2=CH2 + H2 → CH3-CH3
• Preparation of Alkanes from haloalkanes (Wurtz Reaction)


  1. Heat alkyl halides with sodium metal in presence of dry ether

  2. R-X + 2Na + X-R → R-R + 2NaX
• Preparation of Alkanes from haloalkanes (Wurtz Reaction)

  • CH3-Br + Na + Br-CH3 → CH3-CH3 + 2NaBr
• Preparation of Alkanes by Reduction of Aldehydes and Ketones


  1. Reduce with amalgated zinc and conc. HCl

  2. R-CHO + 4[H] → R-CH3 + H2O

  3. R-CO-R + 4[H] → R-CH2-R + H2O
• Preparation of Alkanes from Grignard's Reagent

  1. Hydrolyse Grignard's reagent in presence of ether

  2. RMgX + H2O → R-H + Mg(OH)X
• Preparation of Alkanes from salts of Carboxylic acid

  1. Heat Na-salt of carboxylic acid with soda lime (NaOH & CaO)

  2. CH3COONa + NaOH → CH4 + Na2CO3
• Preparation of Alkanes from Metal Carbides


  1. Metal carbide (e.g. Al4C3) reacts with pure water

  2. Al4C3 + 12H2O → 4Al(OH)3 + 3CH4