Chapter 13: Organic Compounds contaning Nitrogen

Amines

Amines are derivatives of ammonia in which one or more hydrogen atoms are replaced by alkyl group(s).

Amines are classified as primary, secondary and tertiary depending on the number of alkyl groups attached to nitrogen atom.

General methods of preparation

(1) Ammonolysis of alkyl halides and alcohols :

(a) From Ammonolysis of alkyl halides (Hofmann's ammonolysis) : When an aqueous solution of ammonia is heated with alkyl halide all the three types of amines and quaternary ammonium salt are formed.

                                                                                                                                                                                      (Quaternary ammonium salt)

If ammonia is taken in excess, 1° amine is the main product.

(b) Ammonolysis of alcohols : When ROH and NH3 are passed over At2O3 or ThO2 at 350°  

Call the three types of amines are formed.                   

  • Quaternary ammonium hydroxide is not formed.
  • If excess of ammonia is used, then main product will be primary amine.

(2) By reduction :

(a) With RCONH2RCONH2   RCH2NH2

(b) With RCN : RCN + 4[H]   RCH2NH2

This reaction (b) is called mendius reaction.

The reduction of alkyl isocynides gives secondary amines.

R–NC + 4[H]RNHCH3

(c) With Oximes : R­–CH=N–OH + 4[H]RCH2–NH2 + H2O

(d) With RNO2 : RNO2 + 6[H]  RNH2 + 2H2O

Sn/HCl is used in laboratory preparation

(3)     By hydrolysis of :

(a) R–NC : Alkyl isocyanide undergoes hydrolysis with mineral acid and forms alkyl amine.

R­–NC + 2H2ORNH2 + HCOOH

(b) RNCO : Alkyl isocyarlate undergoes hydrolysis on heating with KOH and form alkyl amine.

(4) By Hofmann's bromamide reaction (Hofmann's Hypobromite reaction) : This is a general method for the conversion of alkanamides into primary amines having one less carbon.

(5)  From Grignard reagent : Alkyl magnesium iodide reacts with chloramine to yield alkyl amine.

(6) Gabriel phthalimide synthesis : Phthalimide is first treated with KOH to obtain potassium phthalimide which is then treated with alkyl iodide. Then alkyl phthalimide  on hydrolysis yields alkylamine. This method is used in the formation of pure aliphatic primary amines.

Phthalic acid

  • Aniline is not formed by this reaction.

(7) Curtius reaction :

(8) Schmidt reaction : In presence of conc. H2SO4 alkanoic acid reacts with hydrazoic acid (N3H) followed by hydrolysis to yield alkylamine.

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