Preparation of Amines - Practice Questions & MCQ

Curtius Reaction
The 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 by 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 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:

The mechanism of the reaction is given as 

It is only the primary amides undergo Hoffmann Bromamide reaction. Secondary amides do not undergo this reaction. However, secondary diamides (also called as IMIDES) undergo this reaction to form amino acids. Thus, it is considered as a special case of Hoffmann Bromamide reaction. The reaction occurs as follows: