What NEET Asks
- Identify reagents and products for Wurtz, Corey-House, and Decarboxylation reactions.
- Understand the limitations of Wurtz reaction for unsymmetrical alkane synthesis.
- Predict major products and differentiate reaction mechanisms.
Key Points
- Wurtz Reaction: Couples two alkyl halides (R-X) using sodium (Na) in dry ether to form symmetrical alkanes (R-R) with an even number of carbon atoms.
- Corey-House Synthesis (Gilman Reagent): Versatile method for preparing symmetrical and unsymmetrical alkanes from alkyl halides, utilizing lithium dialkylcuprate (R₂CuLi).
- Decarboxylation: Sodium salts of carboxylic acids (RCOONa) heated with soda lime (NaOH + CaO) yield alkanes (R-H) with one less carbon atom.
- Wurtz reaction with two different alkyl halides yields a mixture of products (R-R, R-R', R'-R'), making separation difficult.
- Reactivity of alkyl halides in Wurtz: RI > RBr > RCl. Tertiary halides favor elimination.
Must-Know Formula / Reaction
- Wurtz Reaction:
2 R-X + 2 Na --(dry ether)--> R-R + 2 NaX- R-X: Alkyl halide (e.g., CH₃CH₂Br)
- R-R: Symmetrical alkane (e.g., CH₃CH₂CH₂CH₃)
- Corey-House Synthesis:
R-X + 2 Li --> RLi + LiX2 RLi + CuI --> R₂CuLi (Gilman Reagent) + LiIR₂CuLi + R'-X --> R-R' + RCu + LiX
- R-R': Symmetrical or unsymmetrical alkane
- Decarboxylation:
RCOONa + NaOH/CaO --(heat)--> R-H + Na₂CO₃- RCOONa: Sodium salt
- R-H: Alkane with one less carbon
Common Mistakes
- Students often attempt Wurtz reaction for preparing unsymmetrical alkanes, leading to a complex mixture of products.
- Don't forget that decarboxylation always reduces the carbon chain by one carbon atom.
- Confusing reagents: Wurtz uses Na/dry ether; Corey-House uses Li/CuI; Decarboxylation uses NaOH/CaO.
Rapid Revision
Wurtz makes symmetrical alkanes by coupling. Corey-House is best for unsymmetrical alkanes using Gilman reagent. Decarboxylation shortens the carbon chain using soda lime. Focus on product prediction and limitations.