Question

The nucleophilic substitution of primary alkyl chlorides with sodium acetate is catalysed by sodium iodide. Explain why.

Answer 1

Primary alkyl chlorides (R − CH₂ − I) are less reactive to nucleophilic substitution than primary alkyl iodides (R − CH₂ − I) because the C−I bond is more easily cleaved than the C−Cl bond due to lower bond dissociation enthalpy.

As a result, the catalyst sodium iodide transforms alkyl chloride to alkyl iodide via the finkelstin reaction. The latter reacts with sodium acetate to generate an ester.

\[\ce{\underset{Ethyl chloride}{CH3 - CH2 - Cl} + NaI -> \underset{Ethyl Iodide}{CH3 - CH2 - I} + NaCl}\]

\[\ce{\underset{Ethyl Iodide}{CH3 - CH2I} + CH3COONa -> \underset{Ethyl acetate}{CH3 COOC2H5 + NaI}}\]

Alkyl chlorides react with Nal to generate more reactive alkyl iodides, which catalyze nucleophilic substitution processes.