Question

Account for the following:

(i) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.

(ii) Although amino group is o- and p- directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.

Answer 1

(i) Methylamine + H₂O ⇌ Methyl ammonium hydroxide

OH- can precipitate out Fe, AI, Cr etc…
3 [CH₃NH₃]⁺ OH + FeCl₃ → Fe (OH)₃↓+ 3CH₃NH₃Cl
Fe (OH)₃ is unstable, so can be hydrated ferric oxide

(ii) In aniline NH₂ increases e density at o- and p- positions due to +R effect. But when it is nitrated by nitrating mixture, substantial amount of m-nitro aniline is formed.
But in acidic medium (Nitrating mixture – HNO₃ (c) + H₂SO₄ (c)).
NH₂ + H⁺ ⇌ NH₃⁺, NH₃⁺ is e^– withdrawing group and so is m – directing. So gives larger amount of m- nitroaniline.