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Compounds Containing Nitrogen question

2022 · 25 Jun · Shift 1 · Q14
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Compounds Containing Nitrogen question

2022 · 25 Jun · Shift 1 · Q14

JEE MainChemistryCompounds Containing NitrogenMCQ+4 / −1
The reaction of JEE Main 2022 (Online) 25th June Morning Shift Chemistry - Compounds Containing Nitrogen Question 99 English with bromine and KOHKOHKOH gives RNH2RNH_2RNH2​ as the end product. Which one of the following is the intermediate product formed in this reation?
  1. A
    JEE Main 2022 (Online) 25th June Morning Shift Chemistry - Compounds Containing Nitrogen Question 99 English Option 1
  2. B
    R −-− NH −-− Br
  3. C
    R −-− N = C = O
  4. D
    JEE Main 2022 (Online) 25th June Morning Shift Chemistry - Compounds Containing Nitrogen Question 99 English Option 4
View written solutionFree

Correct answer: C

  1. The reaction of an amide with bromine and KOHKOHKOH giving RNH2RNH_2RNH2​ is the Hofmann bromamide degradation (also called Hofmann rearrangement).

  2. General reaction: RCONH2→Br2/KOHRNH2RCONH_2 \xrightarrow{Br_2/KOH} RNH_2RCONH2​Br2​/KOH​RNH2​ This converts an amide into a primary amine with loss of one carbon atom.

  3. Mechanism outline:

    1. The amide first reacts with bromine in base to form N-bromoamide: RCONH2→RCONHBrRCONH_2 \rightarrow RCONHBrRCONH2​→RCONHBr
    2. On treatment with base, rearrangement occurs to give an isocyanate intermediate: RCONHBr→R−N=C=ORCONHBr \rightarrow R-N=C=ORCONHBr→R−N=C=O
    3. The isocyanate then hydrolyzes to form the amine: R−N=C=O+H2O→RNH2+CO2R-N=C=O + H_2O \rightarrow RNH_2 + CO_2R−N=C=O+H2​O→RNH2​+CO2​
  4. Therefore, the key intermediate product formed in this reaction is: R−N=C=OR-N=C=OR−N=C=O which is an isocyanate.

  5. Checking options:

  • Option B: R−NH−BrR-NH-BrR−NH−Br is not the correct rearranged intermediate; the actual initial brominated species is RCONHBrRCONHBrRCONHBr, not simply R−NH−BrR-NH-BrR−NH−Br.
  • Option C: R−N=C=OR-N=C=OR−N=C=O ✔ correct, the isocyanate intermediate.

Hence, the correct answer is Option C.

  1. Comparison with stored correct answer: Stored correct answer = C Derived answer = C They match.
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