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Compounds Containing Nitrogen question

2015 · Shift 2 · Q14
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Compounds Containing Nitrogen question

2015 · Shift 2 · Q14

JEE AdvancedChemistryCompounds Containing NitrogenMultiple correct+4 / −2
In the following reactions, the major product W is JEE Advanced 2015 Paper 2 Offline Chemistry - Compounds Containing Nitrogen Question 19 English
  1. A
    JEE Advanced 2015 Paper 2 Offline Chemistry - Compounds Containing Nitrogen Question 19 English Option 1
  2. B
    JEE Advanced 2015 Paper 2 Offline Chemistry - Compounds Containing Nitrogen Question 19 English Option 2
  3. C
    JEE Advanced 2015 Paper 2 Offline Chemistry - Compounds Containing Nitrogen Question 19 English Option 3
  4. D
    JEE Advanced 2015 Paper 2 Offline Chemistry - Compounds Containing Nitrogen Question 19 English Option 4
View written solutionFree

Correct answer: A, C

The user wants me to identify the major product W from a given reaction sequence. The provided reaction schematic consists of two separate pathways starting from Aniline. However, the problem description implies a single pathway. Based on standard JEE question formats and the provided reagents, the reaction sequence leading to W starts with Aniline. Let's analyze this pathway step-by-step.

Reaction Pathway to W: Aniline → (HNO₃, H₂SO₄, 288K) → S → (H₂, Pd, EtOH) → T → (Ac₂O) → U → (Br₂, CH₃COOH) → V → (H₃O⁺) → W

Step 1: Aniline → S

  • Reaction: Nitration of aniline.
  • Mechanism: Direct nitration of aniline with a mixture of concentrated nitric acid and sulfuric acid is complex. The strongly acidic medium protonates most of the aniline to form the anilinium ion (-NH₃⁺). The anilinium ion is a meta-directing and deactivating group. However, a small equilibrium concentration of unprotonated aniline (-NH₂) remains, which is a strongly activating and ortho, para-directing group. This leads to a mixture of products. Under the given conditions (288K), the approximate yield is:
    • p-nitroaniline: ~51%
    • m-nitroaniline: ~47%
    • o-nitroaniline: ~2%
  • Since the yields of para and meta isomers are very close and both are substantial, they must both be considered as major products. The question is of a multiple-correct type, which supports considering both pathways.

Pathway A: Starting from p-nitroaniline (S_p)

  1. S_p → T_p: p-nitroaniline is reduced by catalytic hydrogenation (H₂/Pd). The nitro group is reduced to an amino group.

    • T_p is p-phenylenediamine (benzene-1,4-diamine).
  2. T_p → U_p: p-phenylenediamine is treated with acetic anhydride (Ac₂O). Both amino groups are acetylated.

    • U_p is N,N'-(1,4-phenylene)diacetamide.
  3. U_p → V_p: The ring in U_p is activated by two ortho, para-directing -NHCOCH₃ groups. Bromination with Br₂/CH₃COOH occurs at the activated positions (2, 3, 5, 6). Due to high activation, polysubstitution is expected. The first bromine adds to an available position (e.g., 2). The second bromine adds to the next most favorable position, which is 5 (ortho to the second -NHCOCH₃ group and para to the first bromine).

    • V_p is N,N'-(2,5-dibromo-1,4-phenylene)diacetamide.
  4. V_p → W_A: Acidic hydrolysis (H₃O⁺) of the diacetamide V_p removes the acetyl groups.

    • W_A is 2,5-dibromobenzene-1,4-diamine.
    • This structure matches Option A.

Pathway B: Starting from m-nitroaniline (S_m)

  1. S_m → T_m: m-nitroaniline is reduced by H₂/Pd.

    • T_m is m-phenylenediamine (benzene-1,3-diamine).
  2. T_m → U_m: m-phenylenediamine is acetylated with Ac₂O.

    • U_m is N,N'-(1,3-phenylene)diacetamide.
  3. U_m → V_m: The ring in U_m has three highly activated positions: 2, 4, and 6. Position 2 is ortho to both -NHCOCH₃ groups. Position 4 is ortho to one and para to the other. Position 6 is ortho to one and meta to the other. The ring is extremely activated, and bromination is expected to occur at all three positions.

    • V_m is N,N'-(2,4,6-tribromo-1,3-phenylene)diacetamide.
  4. V_m → W_C: Acidic hydrolysis (H₃O⁺) of the triacetamide V_m removes the acetyl groups.

    • W_C is 2,4,6-tribromobenzene-1,3-diamine.
    • This structure matches Option C.

Conclusion: Since the initial nitration step produces both p-nitroaniline and m-nitroaniline as major products in comparable amounts, the final products derived from both these intermediates are considered the major products of the overall reaction sequence. Therefore, both Option A and Option C are correct.

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