Draw the structure of the major product in the following reaction:
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The more \( -NO_{2} \) groups at ortho/para positions, the milder the conditions required.
Picryl chloride (2,4,6-trinitrochlorobenzene) reacts with just warm water!
• Haloarenes are generally less reactive towards nucleophilic substitution reactions due to resonance and partial double bond character of the \( C-X \) bond.
• However, the presence of electron-withdrawing groups (EWG) like \( -NO_{2} \) at ortho and para positions significantly increases the reactivity of haloarenes towards nucleophilic aromatic substitution (\( S_{N}Ar \)).
• These groups stabilize the intermediate carbanion (Meisenheimer complex) by delocalizing the negative charge through resonance. Step 1: Analyze the substrate and reagents
The substrate is 1-chloro-2,4-dinitrobenzene. It has two strong electron-withdrawing nitro groups at the ortho and para positions relative to the chlorine atom.
The reagent is sodium hydroxide (\( NaOH \)), which provides the nucleophile \( OH^{-} \). The temperature of \( 368 \, K \) is sufficient to drive the substitution.
Step 2: Describe the reaction mechanism
The \( OH^{-} \) nucleophile attacks the carbon atom bearing the chlorine. This forms a resonance-stabilized carbanion intermediate where the negative charge is delocalized onto the oxygens of the nitro groups.
Subsequently, the chloride ion (\( Cl^{-} \)) is eliminated to restore aromaticity, resulting in 2,4-dinitrophenoxide.
Step 3: Final acidification
The second step involves treatment with \( H^{+} \). This protonates the phenoxide ion to yield the final neutral product: 2,4-dinitrophenol.
Step 4: Draw the structure
The final answer is 2,4-dinitrophenol.
