Account for the following:
(i) `pK_(b)` of 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– and 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.

Explanation

(i) `pK_(b)` of aniline is more than that of methylamine:

Aniline undergoes resonance and as a result, the electrons on the N-atom are delocalized over the benzene ring. Therefore, the electrons on the N-atom are less available to donate.
On the other hand, in case of methylamine (due to the +I effect of methyl group), the electron density on the N-atom is increased. As a result, aniline is less basic than methylamine. Thus, `pK_(b)` of aniline is more than that of methylamine.
(ii) Ethylamine is soluble in water whereas aniline is not :
Ethylamine when added to water forms intermolecular H−bonds with water. Hence, it is soluble in water.
`------underset("Ethylamine")underset(C_(2)H_(5))underset(|)overset(H)overset(|)N-H-----underset(H)underset(|)O-H-----underset(C_(2)H_(5))underset(|)overset(H)overset(|)N-H-----underset(H)underset(|)O-H-----`
But aniline does not undero H-bonding with water to a very large extent due to the presence of a large hydrophoboc `-C_(6)H_(5)` group. Hence, aniline is insoluble in water.

(iii) Methylamine in water reacts which ferric chloride to precipitate hydrated ferric oxifr :
`CH_(3)underset("Methylamine")-NH_(2)" "Hunderset("Water")-OH`
Due to the + I effect of `-CH_(3)` groupk methylamines more basic than water. Therefore in waterm methylamine produces `OH^(-)` ions by accepting `H^(+)` ions from water.
`CH_(3) - NH_(2) + H - OH to CH_(3)-overset(+)(N)H_(3) + OH^(-)`
Ferric chloride `(FeCl_(3))` dissociates in water to form `Fe^(3+)` and `Cl^(-)` ions .
`FeCl_(3) to Fe^(3+)+2Cl^(-)`
Then, OH− ion reacts with `Fe^(3+)` ion to form a precipitate of hydrated ferric oxide.

(iv) Although amino group is o,p directing in aromatic electrophilic susubstitution reactionsk, aniiline on nitrotiog gives a substantial amount of m-nitroaniline:
Nitration is carried out in an acidic medium, aniline is protonated to give anilinium uon(which is meta-directing). For this reasoon,aniline onn nitration give a subsrantial amount of m-nitroaniline.
(v) Aniline does not undergo Friedel-Crafts reaction:
A Friedel-Cragts reaction is carried out ijn the presence of `AlCl_(3).` But `AlCl_(3)` is acidic in nature, while aniline is a strong base. Thus, aniline reacts with `AlCl_(3)` to form a salt (as shown in the following equation).

Due to the positive charge on the N-atom, electrophilic substitution in the benzene ring is deactivated. Hence, aniline does not undergo the Friedel-Crafts reaction.
(iv) Diazonium salts of aromatic amines are more stable than those of aliphatic amines:
The diazonium ion undergoes resonance as shown below:

This resonance accounts for the stability of the diazonium ion. Hence, diazonium salts of aromatic amines are more stable than those of aliphatic amines.
(vii) Gabriel phthalimide synthesis is preferred for synthesising primaryamines:
Gabriel phthalimide synthesis results in the formation of `1^(@)` amine only. `2^(@)` or `3^(@)` amines are not formed in this synthesis. Thus, a pure `1^(@)` amine can be obtained. Therefore, Gabriel phthalimide synthesis is preferred for synthesizing primary amines.