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STD 12 - 9. Amines — NEET STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceNEETSTD 12 - 9. Amines4 Marks
MCQ
Which of the following statements about primary amines is false ?
  • A
    Alkyl amines are stronger bases than aryl amines.
  • B
    Alkyl amines react with nitrous acid to produce alcohols.
  • ✓
    Aryl amines react with nitrous acid to produce phenols.
  • D
    Alkyl amines are stronger bases than ammonia.
✓

Answer

Correct option: C.
Aryl amines react with nitrous acid to produce phenols.
c
$(i)$ Presence of electron withdrawing substituent decreases the basicity while the presence of electron releasing substituent like, $-C H_{3},-C_{2} H_{5},$ etc, increases the acidity.

$(ii)$ $H NO_{2}$ converts $-N H_{2}$ group of aliphatic amine into$-OH$ while that of aromatic amines into $-N=N C$. Since, phenyl group is a electron withdrawing group, it decreases the basicity. Alkyl group, on the other hand, being electron releasing, increases the basicity. Thus, alkyl amines are more basic as compared to aryl amines as well as ammonia.

$R-N H_{2} \stackrel{H N O_{2}}{\longrightarrow} R-O H$

Thus, $H NO_{2}$ (nitrous acid) converts alkyl amines to alcohols. But aryl amines react with nitrous acid to form diazonium salt.

$\quad C_{6} H_{5} N H_{2} \frac{H N O_{2}}{0.5\,^{o} C(273-278 \,K)} C_{6} H_{5}-N_{2}^{+} C l$ at $0.5\,^{o} \mathrm{C}$

temperature

$\mathrm{NaNO}_{2}+\mathrm{HCl} \longrightarrow \mathrm{HNO}_{2}+\mathrm{NaCl},$

Thus $\mathrm{HNO}_{2}$ does not convert aryl amines into phenol.

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