Which one of the following is not correct with respect to properties of amines?
- $pK_b$ of aniline is more than that of methylamine.
- Ethylamine is soluble in water whereas aniline is not
Aniline does not undergo Friedel-Crafts reaction.
- Ethylamine reacts with nitrous acid to give ethanol.
Ethanamide on reaction with $Br_2$ and NaOH gives ethylamine.
The Correct Option is
Solution and Explanation
Let’s analyze each statement about amines:
\( pK_b \) of aniline is more than that of methylamine: True. Aniline is a weaker base than methylamine due to resonance delocalization of the lone pair on nitrogen into the benzene ring. Hence, it has a higher \( pK_b \).
Ethylamine is soluble in water whereas aniline is not: True. Ethylamine, being a small and polar molecule, forms hydrogen bonds with water and is soluble. Aniline is less polar and has limited solubility because of the bulky aromatic ring.
Ethanamide on reaction with \( Br_2 \) and NaOH gives ethylamine: False. This is incorrect. The reaction of ethanamide with bromine and sodium hydroxide (Hofmann bromamide reaction) gives methylamine, not ethylamine.
Ethylamine reacts with nitrous acid to give ethanol: True. Primary aliphatic amines like ethylamine react with nitrous acid to form ethanol through diazonium salt decomposition.
Aniline does not undergo Friedel–Crafts reaction: True. The lone pair on nitrogen in aniline interacts with the Lewis acid catalyst (such as AlCl₃), which deactivates the aromatic ring and prevents the Friedel–Crafts reaction.
Correct Answer: (C)
Top Questions on Amines
- Identify correct statements: (A) Primary amines do not give diazonium salts when treated with \({NaNO}_2\) in acidic condition.
(B) Aliphatic and aromatic primary amines on heating with \({CHCl}_3\) and ethanolic \({KOH}\) form carbylamines.
(C) Secondary and tertiary amines also give carbylamine test.
(D) Benzenesulfonyl chloride is known as Hinsberg’s reagent.
(E) Tertiary amines react with benzenesulfonyl chloride very easily.
Choose the correct answer from the options given below: Amines have a lone pair of electrons on the nitrogen atom, due to which they behave as Lewis bases. Greater the value of \( K_b \) or smaller the value of \( pK_b \), stronger is the base. Amines are more basic than alcohols, ethers, esters, etc. The basic character of aliphatic amines should increase with the increase of alkyl substitution. However, it does not occur in a regular manner, as a secondary aliphatic amine is unexpectedly more basic than a tertiary amine in aqueous solutions. Aromatic amines are weaker bases than ammonia and aliphatic amines. Electron-releasing groups such as \( -CH_3 \), \( -NH_2 \), etc., increase the basicity, while electron-withdrawing substituents such as \( -NO_2 \), \( -CN \), halogens, etc., decrease the basicity of amines. The effect of these substituents is more pronounced at the para-position than at the meta-position.
(a) Arrange the following in increasing order of their basic character. Give reason:
\[ \includegraphics[width=0.5\linewidth]{ch29i.png} \]- Amines have a lone pair of electrons on nitrogen atom due to which they behave as Lewis base. Greater the value of \( K_b \) or smaller the value of \( pK_b \), stronger is the base. Amines are more basic than alcohols, ethers, esters, etc. The basic character of aliphatic amines should increase with the increase of alkyl substitution. But it does not occur in a regular manner as a secondary aliphatic amine is unexpectedly more basic than a tertiary amine in aqueous solutions. Aromatic amines are weaker bases than ammonia and aliphatic amines. Electron releasing groups such as \(–CH_3\), \(–NH_2\), etc., increase the basicity while electron-withdrawing substituents such as \(–NO_2\), –CN, halogens, etc., decrease the basicity of amines. The effect of these substituents is more at the p₊ than at m₋ position.
- Assertion (A): Aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis. Reason (R): Aryl halides do not undergo nucleophilic substitution reaction with the anion formed by phthalimide.
- Give plausible explanation for each of the following:
Amides are less basic than amines.
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