Question

Which of the following aryl chlorides on warming with water forms the corresponding phenol?

• A. 4-Methylchlorobenzene
• B. 4-Nitrochlorobenzene
• C. 2, 4, 6-Trinitrochlorobenzene
• D. 2-Nitrochlorobenzene
• E. 2, 4-Dinitrochlorobenzene

Answer 1

The Correct Option is C

When 2, 4, 6-Trinitrochlorobenzene is warmed with water, the chlorine atom is replaced by the hydroxyl group, forming the corresponding phenol. This is because the nitro groups present at the ortho and para positions to the chlorine atom increase the electrophilicity of the carbon attached to the chlorine, making it easier for the nucleophilic substitution to occur with water, leading to phenol formation.

The correct option is (C) : 2, 4, 6-Trinitrochlorobenzene

Answer 2

Aryl halides are generally unreactive towards nucleophilic substitution reactions like hydrolysis (reaction with water) under normal conditions. However, the presence of electron-withdrawing groups (like nitro groups, \(-NO_2\)) at ortho- and para- positions to the halogen significantly increases the reactivity of the aryl halide.

The more nitro groups present at ortho- and para- positions, the more stabilized the intermediate carbanion is, making the nucleophilic aromatic substitution (SNAr) reaction easier. This is because the nitro groups are electron-withdrawing and help to delocalize the negative charge.

Among the given options:

• 4-Methylchlorobenzene: Methyl group is electron-donating, decreasing reactivity.
• 4-Nitrochlorobenzene: One nitro group, increases reactivity, but not as much.
• 2,4,6-Trinitrochlorobenzene: Three nitro groups, significantly increases reactivity.
• 2-Nitrochlorobenzene: One nitro group, increases reactivity, but not as much.
• 2,4-Dinitrochlorobenzene: Two nitro groups, increases reactivity.

2,4,6-Trinitrochlorobenzene will form the corresponding phenol most readily on warming with water due to the presence of three strongly electron-withdrawing nitro groups, which significantly enhance the reactivity towards nucleophilic aromatic substitution.

Therefore, the answer is 2,4,6-Trinitrochlorobenzene.