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Give one chemical test to distinguish between the following pairs of compounds : Aniline and N-methylaniline |
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Answer» Solution :Aniline `(C_(6)H_(5)NH_(2))` is a primary amine while N-methylamiline `(C_(6)H_(5)NHCH_(3))` is a secondary amine. These may be distinguished by the following tests. 1. Carbylamine TEST : Aniline on heating with an alcoholic solution of KOH and `CHCl_(3)` gives an offensive smell of phenyl ISOCYANIDE. `underset("Aniline")(C_(6)H_(5)NH_(2))+CHCl_(3)+underset(ALC.)(3KOH) rarr underset(underset(underset("(offensive smell)")("isocyanide"))("Phenyl"))(C(6)H_(5)NC)+_3KCl+3H_(2)O` N-methylamine does not give carbylamine test. 2. Azo dye test : Aniline gives azo dye test on treatment with `HNO_(2)(NaNO_(2)+dil.HCl)` at 273 - 278 K, followed by treatment with ALKALINE solution of b-napthol. An orange dye is obtained. For chemical reaction, see (iii) above. N-Methylaniline gives an oily yellow coloured N-methyl-N-nitroaniline as shown by the following EQUATION : `underset(underset(underset("N-Methylaniline")(CH_(3)))(|))(C_(6)H_(5)-NH+HO)-N=O rarr underset(underset(underset(underset("(Yellow oil)")("N-methyl-N-nitrosoaniline"))(CH_(3)))(|))(C_(6)H_(5)-N-N=O)+H_(2)O` N-methyl-N-nitrosoaniline on warming with a crystal of phenol and conc. `H_(2)SO_(4)` gives a green solution which when made alkaline with aqueous NaOH turns deep blue and then red on dilution. This is known as Liebermann.s nitrosoamine reaction. |
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