(i) A Friedel Crafts reactions is carried out in the presence of AlCl3. But AICl3 is used as catalyst and is acidic in nature whereas aniline is a strong base. Thus, aniline reacts with AICl3 to form a salt. Due to the positive charge on the N-atom, electrophilic substitution in the benzene ring is deactivated. Hence, aniline does not undergo Firedel-Crafts reaction.
(ii) (CH3)2‌NH is more basic than (CH3)3N in an aqueous solution. + I effect will increase in alkyl group that results in increasing the case of donation of lone pair electron. Amine accepts a proton and from cation which will be stabilised in water by solvation. Higher the solvation by hydrogen bonding, higher will be the basic strength.Therefore, with increase in methyl group, hydrogen bonding and stabilisation by solvation decreases. This net effect results in decreases of basic strength from secondary to tertiary amine.
(iii) In tertiary amines, there are no H-atoms whereas in primary amines, two H-atoms are present. Due to the presence of H-atoms, primary amines undergo extensive intermolecular H-bonding.As a result, extra energy is required to separate the molecules of primary amine. Therefore, primary amines have higher boiling point than tertiary amines.