Organic Reactions

This reaction involves sodium amide (NaNH₂) in liquid ammonia, which are conditions for nucleophilic aromatic substitution proceeding via an elimination-addition (benzyne) mechanism.
(A) Elimination (Formation of Benzyne): The strong base, amide ion (NH₂^-), removes a proton from a carbon adjacent to the carbon bearing the leaving group (Cl). In m-chloroanisole, protons are available ortho to Cl (at C2 and C4 relative to OCH₃).Both pathways lead to benzyne intermediates where the triple bond involves C3. Example (deprotonation at C4): OCH₃- --> Benzyne
(D) Addition (Attack by Nucleophile): The nucleophile (NH₂^-) attacks one of the carbons of the benzyne triple bond. The direction of addition is influenced by the substituent (-OCH₃).The methoxy group (-OCH₃) has a significant inductive electron-withdrawing effect (-I) which dominates in directing the addition to benzyne. This effect stabilizes the negative charge when it is further away from the electronegative oxygen. Therefore, the nucleophile (NH₂^-) preferentially adds to the carbon atom meta to the OCH₃ group (C3 in both benzyne possibilities), placing the resulting carbanion at C2 or C4.
(G) Protonation: The resulting aryl anion is quickly protonated by the solvent (liquid NH₃) to give the final product. Addition of NH₂^- at the C3 position (meta to OCH₃) leads to the formation of m-anisidine (3-methoxyaniline).