Alkyl halides react with sodium to give alkanes with double number of carbon atoms in

Wurtz reaction

The correct answer is Option (2) → Wurtz reaction

Core Concept

Wurtz reaction couples two alkyl halide molecules using sodium metal to form a higher alkane.

Reaction

$2 R–X + 2 Na → \text{(Dry Ether)} → R–R + 2 NaX$

Explanation of Each Option

1. Sandmeyer reaction involves conversion of diazonium salts into aryl halides using copper salts. It does not involve formation of alkanes by coupling alkyl halides.

2. Wurtz reaction involves the reaction of two alkyl halide molecules with sodium in dry ether, resulting in the formation of a new alkane with double the number of carbon atoms.

3. Wurtz–Fittig reaction involves coupling between an alkyl halide and an aryl halide, producing an alkyl-substituted aromatic compound rather than a simple higher alkane.

4. Williamson synthesis is used for the preparation of ethers by reaction of alkoxide ions with alkyl halides and does not produce alkanes.