Account for the following: (i) pkb 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

(i)In aniline the N atom is attached to the benzene ring and therefore the lone pair on N is declocalised over the entire benzene ring.

due to this it cannot accept a proton. In methylamine the electron density on nitrogen is greater than aniline this is due to the presence of methyl group in methylamine

Thats the reason pKb of aniline is more

(ii) Ethylamine is capable of forming hydrogen bond with water as it is soluble but aniline the bulkycarbon prevents the formation of effective hydrogen bondinf and not soluble

(iii) That is due to the basic strength of CH3NH2. The +I effect of methyl group makes more basicity than water and in water methylamine produce OH- ions

(iv) During Nitration process the mixture used (Con HNO3+Con H2SO4) protonates anilinium ion and nitroaniline is formed. The anilium ion acts as a deactivating group and directs the NO2 nucleophile to meta position and meta isomer of nitroaniline is formed

(v) During Friedal-Crafts reaction,anhydrous AlCl3 is used as a lewis acid for generation of electrophile from electrophilic reagent. If aniline is used as base there wont be any generation of electrophile takes place and hence reaction does not take place

(vi) Diazonium salt of aromatic amine is stable due to the resonance. it carries N atom with a positive charge. such a delocalisation is not possible in aliphatic amines. hence it is less stable

(vii) Gabriel pthalmide reaction gives pure primary amines without any contamination in secondary and tertiary amines. hence they are mpore prefered for synthesis of primary amines