Wurtz reaction

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The Wurtz reaction, named after Charles-Adolphe Wurtz, is a coupling reaction in organic chemistry, organometallic chemistry and recently inorganic main group polymers where by two alkyl halides are reacted with sodium to form a new carbon-carbon bond:

2R-X + Na → R-R + 2Na⁺X⁻

This reaction involves the radical species R•.

Mechanism:

One electron from sodium is transferred to the halogen to produce a sodium halide and an alkyl radical.

R-X + Na → R• + Na⁺X⁻

The alkyl radical then accepts an electron from another sodium atom to form an alkyl anion and the sodium becomes cationic.

R• + Na → R⁻Na⁺

The alkyl anion then displaces the halide in an S_N2 reaction, forming a new carbon-carbon covalent bond.

R⁻Na⁺ + R-X → R-R + Na⁺X⁻

Example:

Here methyl iodide and ethyl chloride are reacted with powdered sodium metal in anhydrous ether. Alkanes containing double the number of carbon atoms are formed, i.e. methyl iodide gives ethane, and ethyl chloride gives n-butane.

The solvent, ether in this case, must be anhydrous (free of moisture) because the alkyl anions are so basic (the pKa of the alkyl proton is 48–50) that they readily deprotonate water to hydroxide ion, forming alkanes, and reducing the yield of the desired product.