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nomenclature and isomerism

physical properties

preparation of amines

examination questions

Amines:

chemical properties.

1. Reaction with water

  • Like ammonia, ethylamine dissolves readily in water.
  • Favourable hydrogen bonds form between the molecules.

  • Some of the dissolved molecules go on to react with water molecules to form the following equilibrium:
    CH3CH2NH2 (aq)    +      H2O (l)      ⇌        CH3CH2NH3+OH ‾(aq)
    Bronsted-Lowry base     +       Bronsted-Lowry acid            ethylammonium hydroxide
  • A 1.0 moldm-3 solution of ethylamine in water has a pH of 12.4
    [The Kb value for ethylamine at 25°C is approximately 5.6 x 10 -4 moldm-3.] 
  • A 1.0 moldm-3 solution of ammonia in water has a pH of 11.6
    [The Kb value for ethylamine at 25°C is approximately 1.8 x 10 -5 moldm-3.] 

2.Reaction with acids.

  • Again, like ammonia, ethylamine reacts even more readily with acids, forming a salt.
  • The acid donates a proton (H + ) to ethylamine to form an ethylammonium ion.
    CH3CH2NH2  +  H +  →  CH3CH2NH3 
  • The reactions are similar to the neutralisation reactions of ammonia with acids.
    For example: 2NH3  +  H2SO4  →  (NH4)2SO4

(a) Ethylamine and hydrochloric acid – to form ethylammonium chloride.
     CH3CH2NH2  +  HCl →  CH3CH2NH3Cl

(a) Propylamine and sulfuric acid – to form propyllammonium sulfate.
     2CH3CH2CH2NH2  +  H2SO4  →   (CH3CH2CH2NH3)2SO4

(c) Phenylamine and nitric acid – to form phenylammonium nitrate.
     C6H5NH2  +  HNO3 →  C6H5NH3NO3

⇓  REVIEW: Phenylamine’s preparation by the reduction nitrobenzene using tin and hydrochloric acid.  ⇓

                                                  C6H5NO2    +    6[H]        →        C6H5NH2    +    2H2O
                                                                              nitrobenzene         [ Sn/ HCl]                           phenylamine (aniline)

C6H5NH2  +  HCl  →  C6H5NH3Cl
                                                            phenylammonium chloride

C6H5NH3Cl  +  NaOH  →  C6H5NH2  +  NaCl  +  H2O
                       phenylamine

The reduction process produces the salt of phenylamine (due the reaction of the phenylamine with hydrochloric).
This is easily remedied, because sodium hydroxide liberates the free amine from its salt.

3.Reaction with acy chlorides. The details can be found here.
⇓  Primary amines react with an acy chloride to form a secondary amide and HCl gas ⇓
              CH3COCl  +  CH3CH2NH2  →  CH3CONHCH2CH3  +  HCl
                                              N-ethylethanamide
⇓ Secondary amines react with an acy chloride to a form a tertiary amide amide and HCl ⇓
             CH3COCl  +  (CH3CH2)2NH  →  CH3CON(CH2CH3)2  +  HCl
                                              N,N-diethylethanamide

IDENTIFICATION OF AN AMINE (using the above reaction with ethanoyl chloride).
This is considered on a separate webpage – here.

4.Reaction with acid anhydrides.
The details can be found here.
⇓  Primary amines react with an acid anhydride to form a secondary amide and CH3COOH ⇓
              CH3COOCOCH3  +  CH3CH2NH2  →  CH3CONHCH2CH3  + CH3COOH
                                                     N-ethylethanamide
⇓ Secondary amines react with an acid anhydride to form a tertiary amide and CH3COOH ⇓
            CH3COOCOCH3  +  (CH3CH2)2NH  →  CH3CON(CH2CH3)2  + CH3COOH

                                                     N,N-diethylethanamide

5.Reaction with halogenoalkanes. This was covered earlier here.

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