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Compounds Containing Nitrogen question

2010 · Shift 2 · Q12
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Compounds Containing Nitrogen question

2010 · Shift 2 · Q12

JEE AdvancedChemistryCompounds Containing NitrogenMCQ+3 / −1
In the reaction, IIT-JEE 2010 Paper 2 Offline Chemistry - Compounds Containing Nitrogen Question 4 English The structure of the product T is :
  1. A
    IIT-JEE 2010 Paper 2 Offline Chemistry - Compounds Containing Nitrogen Question 4 English Option 1
  2. B
    IIT-JEE 2010 Paper 2 Offline Chemistry - Compounds Containing Nitrogen Question 4 English Option 2
  3. C
    IIT-JEE 2010 Paper 2 Offline Chemistry - Compounds Containing Nitrogen Question 4 English Option 3
  4. D
    IIT-JEE 2010 Paper 2 Offline Chemistry - Compounds Containing Nitrogen Question 4 English Option 4
View written solutionFree

Correct answer: C

The problem asks for the structure of the final product T in a multi-step organic reaction starting from aniline. Let's analyze each step of the reaction sequence.

Step 1: Aniline → S

  • Reactants: Aniline (C6H5NH2C_6H_5NH_2C6​H5​NH2​) and Acetic anhydride ((CH3CO)2O(CH_3CO)_2O(CH3​CO)2​O) in pyridine.
  • Reaction: This is the acetylation of aniline. The amino group (−NH2-NH_2−NH2​) is highly activating, and direct reaction with electrophiles like Br2Br_2Br2​ often leads to polysubstitution. To control the reaction, the amino group is first 'protected' by converting it into a less activating acetamido group (−NHCOCH3-NHCOCH_3−NHCOCH3​). The lone pair on the nitrogen of the amino group attacks one of the carbonyl carbons of acetic anhydride.
  • Product S: N-phenylacetamide, also known as acetanilide (C6H5NHCOCH3C_6H_5NHCOCH_3C6​H5​NHCOCH3​). C6H5NH2+(CH3CO)2O→PyridineC6H5NHCOCH3+CH3COOHC_6H_5NH_2 + (CH_3CO)_2O \xrightarrow{Pyridine} C_6H_5NHCOCH_3 + CH_3COOHC6​H5​NH2​+(CH3​CO)2​OPyridine​C6​H5​NHCOCH3​+CH3​COOH (Aniline) (S, Acetanilide)

Step 2: S → U

  • Reactants: Acetanilide (S) and Bromine (Br2Br_2Br2​) in acetic acid (CH3COOHCH_3COOHCH3​COOH).
  • Reaction: This is an electrophilic aromatic substitution (bromination). The acetamido group (−NHCOCH3-NHCOCH_3−NHCOCH3​) is an ortho, para-directing group. Because it is bulky, the para-substituted product is formed as the major product due to less steric hindrance compared to the ortho positions.
  • Product U: p-bromoacetanilide. C6H5NHCOCH3→Br2,CH3COOHp−Br−C6H4−NHCOCH3+HBrC_6H_5NHCOCH_3 \xrightarrow{Br_2, CH_3COOH} p-Br-C_6H_4-NHCOCH_3 + HBrC6​H5​NHCOCH3​Br2​,CH3​COOH​p−Br−C6​H4​−NHCOCH3​+HBr (S, Acetanilide) (U, p-bromoacetanilide)

Step 3: U → V

  • Reactants: p-bromoacetanilide (U) and H2O/H+H_2O/H^+H2​O/H+ (acidic hydrolysis).
  • Reaction: The amide group is hydrolyzed back to an amino group and a carboxylic acid. This step is the 'deprotection' of the amino group.
  • Product V: p-bromoaniline. p−Br−C6H4−NHCOCH3+H2O→H+p−Br−C6H4−NH2+CH3COOHp-Br-C_6H_4-NHCOCH_3 + H_2O \xrightarrow{H^+} p-Br-C_6H_4-NH_2 + CH_3COOHp−Br−C6​H4​−NHCOCH3​+H2​OH+​p−Br−C6​H4​−NH2​+CH3​COOH (U, p-bromoacetanilide) (V, p-bromoaniline)

Step 4: V → T

  • Reactants: p-bromoaniline (V), followed by a two-step process: (1) NaNO2+HClNaNO_2 + HClNaNO2​+HCl at 0−5∘C0-5^\circ C0−5∘C, and (2) H3PO2H_3PO_2H3​PO2​.
  • Reaction 1 (Diazotization): p-bromoaniline, a primary aromatic amine, reacts with nitrous acid (formed in situ from NaNO2NaNO_2NaNO2​ and HClHClHCl) at low temperatures to form a diazonium salt. p−Br−C6H4−NH2→NaNO2,HCl,0−5∘Cp−Br−C6H4−N2+Cl−p-Br-C_6H_4-NH_2 \xrightarrow{NaNO_2, HCl, 0-5^\circ C} p-Br-C_6H_4-N_2^+Cl^-p−Br−C6​H4​−NH2​NaNO2​,HCl,0−5∘C​p−Br−C6​H4​−N2+​Cl− (V, p-bromoaniline) (p-bromobenzenediazonium chloride)
  • Reaction 2 (Deamination): The resulting diazonium salt is treated with hypophosphorous acid (H3PO2H_3PO_2H3​PO2​). This is a reduction reaction where the diazonium group (−N2+-N_2^+−N2+​) is replaced by a hydrogen atom. This reaction is known as deamination. p−Br−C6H4−N2+Cl−→H3PO2,H2OC6H5Br+N2+H3PO3+HClp-Br-C_6H_4-N_2^+Cl^- \xrightarrow{H_3PO_2, H_2O} C_6H_5Br + N_2 + H_3PO_3 + HClp−Br−C6​H4​−N2+​Cl−H3​PO2​,H2​O​C6​H5​Br+N2​+H3​PO3​+HCl
  • Product T: The final product is bromobenzene.

Conclusion By following the reaction sequence, the final product T is identified as bromobenzene (C6H5BrC_6H_5BrC6​H5​Br).

Matching with Options:

  • Option A is p-bromoaniline (product V).
  • Option B is p-dibromobenzene.
  • Option C is bromobenzene (product T).
  • Option D is benzene.

Therefore, the correct structure for product T is given in option C.

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