Preparation of Amines MCQ - Practice Questions with Answers

Curtius Reaction
Acid azides on heating in non-polar solvent give alkyl isocyanate via acylnitrene formation, which on hydrolysis gives 1^o amine. The reaction occurs as follows:

Schmidt Reaction
Carboxylic acid on reaction with hydrazoic acid in the presence of acid(H₂SO₄) gives acid azide which on heating gives alkyl isocyanate followed bu hydrolysis to give 1^o amine. The reaction occurs as follows:

Lossen Reaction
Hydroxamic acid in basic medium rearranges to give alkyl isocyanate via acylnitrene formation, which on hydrolysis gives 1^o amine. The reaction occurs as follows:

Reduction of Nitroalkanes
Nitro compounds are reduced to amines by reduction with metals(Fe, Sn or Zn) in dil. HCl or SnCl₂ in HCl or by passing H₂ gas in the presence of finely divided Ni, Pt, or Pd. Reduction with Fe scrap and HCl is preferred because the FeCl₂ formed gets hydrolysed to give HCl during the reaction, and thus only a small amount of HCl is required for the initiation of the reaction. The reactions occur as follows:

This reaction is used for the preparation of 1^o aliphatic amine and 1^o aromatic amine. Phthalimide on treatment with ethanolic KOH forms potassium salt of phthalimide which on heating with RX followed by either alkaline hydrolysis or hydrazinolysis with hydrazine(H₂N.NH₂) produces the corresponding 1^o amine. 1^o aromatic amine cannot be synthesised by this method because ArX does not undergo SN reaction with anion formed by phthalimide. The reaction occurs as follows:

Amides on reaction with Br₂ or Cl₂ in alkali give 1^o amine with one C atom less than the parent amide. This is known as Hofmann bromamide rearrangement or degradation reaction. The reaction occurs as follows:

Since only primary amides undergo Hoffmann Bromamide reaction but secondary amides do not undergo this reaction. But secondary diamide undergoes this reaction. Thus, it is consider as the special case of Hoffmann Bromamide reaction. The reaction occurs as follows: