Account for the following:

(i) Primary amines $(R - N H_{2})$ have higher boiling point than tertiary amines $(R_{3} N)$ .

(ii) Aniline does not undergo Friedel - Crafts reaction.

(iii) $(C H_{3})_{2} N H$ is more basic than $(C H_{3})_{3} N$ in an aqueous solution.

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Solution

(i) It is due to greater extent of association in $1^{\circ}$ amines because the extent of H-bonding in $1^{\circ}$ amines is more than in case $3^{\circ}$ amines. As in $1^{\circ}$ amines N-atom is attached to two H-atoms while in $3^{\circ}$ amines there is no H-atom linked to N-atom.

(ii) Aniline is a Lewis base while $A l C l_{3}$ is a Lewis acid. They combine with each other to form salt.

Due to presence of a positive charge on N-atom in the salt, the group $- + N H_{2} A l C l_{3}^{-}$ acts as a strong electron withdrawing group. As a result it reduces electron density in the benzene ring and hence aniline does not undergo Friedel Craft's reaction.

(iii) $(C H_{3})_{2} N H$ is more basic than $(C H_{3})_{3} N$ due to greater stability of conjugate acid $(C H 3)_{2} + N H_{2}$ over $(C H_{3})_{3} + N H$ due to greater extent of H-bonding.

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Similar questions

Q. Give reasons for the following:
(i) Aniline does not undergo Friedal- Crafts reaction.
(ii)

(C H_{3})_{2} N H

is more basic than

(C H_{3})_{3} N

in an aqueous solution.
(iii) Primary amines have higher boiling point than tertiary amines.

Q. Amines are classified as primary, secondary and tertiary amine.
(a) Represent the structure of secondary and tertiary amine.
(b) How will you convert nitrobenzene to aniline?
(c) Aniline does not undergo Friedel-Crafts reaction. Why?

Account for the following:

(i) pK_bof aniline is more than that of methylamine.

(ii) Ethylamine is soluble in water whereas aniline is not.

(iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.

(iv) Although amino group is o, p− directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.

(v) Aniline does not undergo Friedel-Crafts reaction.

(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines.

(vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines.

Account for the following

(i) $p K_{b}$ of aniline is more than that of methyl amine.

(ii) Ethylamine is soluble in water whereas aniline is not

(iii) Methyl amine in water reacts with ferric chloride to precipitate hydrated ferric oxide

(iv) Although amino group is o- and p- directing in aromatic electrophilic substitution, aniline on nitration gives a substantial amount of m-nitroaniline

(v) Aniline does not undergo Friedel Crafts reaction

(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines

(vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines

Q. Primary amines have higher boiling points than tertiary amines
If this is true enter 1, if false enter 0.

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Account for the following: (i) Primary amines (R−NH2) have higher boiling point than tertiary amines (R3N). (ii) Aniline does not undergo Friedel - Crafts reaction. (iii) (CH3)2NH is more basic than (CH3)3N in an aqueous solution.

Account for the following:

(i) Primary amines $(R - N H_{2})$ have higher boiling point than tertiary amines $(R_{3} N)$ .

(ii) Aniline does not undergo Friedel - Crafts reaction.

(iii) $(C H_{3})_{2} N H$ is more basic than $(C H_{3})_{3} N$ in an aqueous solution.