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Bahauddin Zakaria University, Multan*
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ACCOUNTING MISC
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Feb 11, 2024
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- e 7 N - § |- T Account for the following: (i) pK. 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, 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. Answer : (i) pK. of aniline is more than that of methylamine: \H, CH; - NH, Amline 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. v On the other hand. in case of methylamine (due to the +1 effect of methyl group), the electron density on the N-atom is increased. As a result, aniline is less basic than methylamine. Thus, pK, 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. www.ncrtsclutions.in www.ncrtsolutions.in ------ Ne——=H s eeeee QuemH+eoooe N Heoeeee Q=—H CH, H C,H, H Ethylamune But aniline does not undergo H - bonding with water to a very large extent due to the presence of a large hydrophobic - CH. group. Hence, aniline is insoluble in water. NH, Amiline (iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide: CHy —e— NH, H—OH Methylanune Water Due to the +I effect of - CH, group, methylamine is more basic than water. Therefore, in water. methylamine produces OH-ions by accepting H* ions from water. CH, ~NH, + H-OH —> CH, -NH, + OH" Ferric chloride (FeCl,) dissociates in water to form Fe* and Cl-ions. FeCl, Fe™ + 3CI Then, OH-ion reacts with Fe* ion to form a precipitate of hydrated fernc oxide. 2Fe" + 60H° —— Fe,0,-3H,0 Hydrated ferric oxide (iv) Although amino group is op - directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline: Nitration is carried out in an acidic medium. In an acidic medium, aniline is protonated to give anilinium ion (which is meta-directing). (@ 3
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