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Compounds Containing Nitrogen question

2022 · 28 Jun · Shift 1 · Q11
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  5. /2022 · 28 Jun · Shift 1 · Q11

Compounds Containing Nitrogen question

2022 · 28 Jun · Shift 1 · Q11

JEE MainChemistryCompounds Containing NitrogenMCQ+4 / −1
A primary aliphatic amine on reaction with nitrous acid in cold (273 K) and there after raising temperature of reaction mixture to room temperature (298 K), gives a/an
  1. A
    nitrile
  2. B
    alcohol
  3. C
    diazonium salt
  4. D
    secondary amine
View written solutionFree

Correct answer: B

  1. Identify the reaction type

A primary aliphatic amine reacts with nitrous acid (HNO2)(\mathrm{HNO_2})(HNO2​) at low temperature.

The general reaction is:

RNH2+HNO2→ROH+N2+H2O\mathrm{RNH_2 + HNO_2 \rightarrow ROH + N_2 + H_2O}RNH2​+HNO2​→ROH+N2​+H2​O
  1. What happens first at 273 K273\,\mathrm{K}273K?

Primary aliphatic amines initially form an aliphatic diazonium salt:

RNH2+HNO2+H+→RN2+X−+2H2O\mathrm{RNH_2 + HNO_2 + H^+ \rightarrow RN_2^+X^- + 2H_2O}RNH2​+HNO2​+H+→RN2+​X−+2H2​O

However, unlike aryl diazonium salts, aliphatic diazonium salts are highly unstable.

  1. What happens when temperature is raised to 298 K298\,\mathrm{K}298K?

The unstable aliphatic diazonium salt decomposes immediately:

RN2+X−→R++N2\mathrm{RN_2^+X^- \rightarrow R^+ + N_2}RN2+​X−→R++N2​

Then water attacks the carbocation to give an alcohol:

R++H2O→ROH\mathrm{R^+ + H_2O \rightarrow ROH}R++H2​O→ROH

So the final product is an alcohol.

  1. Check the options
  • A: nitrile — Incorrect
  • B: alcohol — Correct
  • C: diazonium salt — Incorrect as final isolated product; aliphatic diazonium salt is unstable
  • D: secondary amine — Incorrect
  1. Final answer

The reaction gives an alcohol.

B: alcohol\boxed{\text{B: alcohol}}B: alcohol​
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