question_answer 12)

Account for the following. (i) 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 precipitatehydrated 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 ofaliphatic amines. (vii) Gabriel phthalimide synthesis is preferred for synthesizing primaryamines.   (i) Higher the  value, lesser is the basicity, i.e., tendency to donate electrons. (ii) Hydrogen bonding, which is shown by compounds containing  or  bond. Bulkiness of the group attached to such bonddecreases the extent of H-bonding. (iii) Consider reaction mechanism. (iv) Formation of anilinium ion which is m-directing. (v) Aniline is a Lewis base so form sail with Lewis acid. (vi) Stability due to resonance (vii) No production of secondary and tertiary amines.  

Answer:

(i) In aniline, the electron pair on nitrogen atom is involvedin conjugation with ring and is less available for protonation than in methyl amine. Therefore,  value of aniline is more than thatof methylamine and aniline is less basic. (As higher the  value,less is the basicity). (ii) Ethylamine is soluble in water due to hydrogen bonding. In aniline due to bulky hydrocarbon part, the extent of hydrogenbonding is less and it is not soluble in water.  (iii) Methylamine being more basic than water, accepts a proton from water and  ions are produced.                                                                                                    (iv) In presence of cone. and cone. most of aniline getsprotonated to form anilinium ion. Now aniline and anilimum ionsboth are present in the reaction mixture. In anilinegroup iso- and p-directing but anilinium ion is m-directing. Because ormore amount of anilinium ion, a lot of m-nitroaniline is formed.                                                 (v) Aniline being a Lewis base forms a complex with  a Lewisacid. As a result, nitrogen of aniline becomes positively chargedand acts as a strong deactivating group for electrophilicsubstitution reaction. Consequently, aniline does not undergoFriedel Crafts reaction. (vi) Diazonium salts of aromatic amines are more stable than those ofaliphatic amines because these are resonance stabilized while nosuch resonance stabilization is possible in the corresponding diazonium salts of aliphatic amines. (vii) Gabriel phthalimide synthesis produces primary amines onlywithout the traces of secondary or tertiary amines. So, this methodis preferred for the synthesis of primary amines.