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MHT-CET : Chemistry Entrance Exam

MHT - CET : Chemistry - Amines Page 1

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1.

Amines

 

The organic derivatives of ammonia, in which one or more hydrogen atoms of ammonia are replaced by alkyl or aryl groups, are called amines.
Example: CH3
- NH2 (methylamine)
     (CH3)2
- NH (dimethylamine)

 

 

2.

Classification of Amines

 

  1. Primary Amines -
    The derivatives of ammonia formed by replacing only one hydrogen atom of ammonia by an alkyl group are primary amines.
    General formula: R
    - NH2
    Examples: CH3
    - NH2 (methylamine)
                    C2H5
    - NH2 (ethylamine)
  2. Secondary Amines -
    The derivatives of ammonia formed by replacing two hydrogen atoms of ammonia by two alkyl groups are secondary amines.
    General formula: R1
    - NH - R2
    Examples: (CH3)2
    - NH (dimethylamine)
                    (C2H5)2
    - NH (diethylamine)
  3. Tertiary Amines -
    The derivatives of ammonia formed by replacing all the three hydrogen atoms of ammonia by three alkyl groups are tertiary amines.

General formula:  

R1 - N - R2

R3

  1. Examples: (CH3)3N (trimethylamine)
                    (C2H5)N (triethylamine)

 

 

3.

Preparation of Amines

 

  1. By the Action of Ammonia on Alkyl Halides:

R - X + NH3  

  R - NH2 + HX

  1.         excess (alc.)
  2. Reduction Methods:
    1. Reduction of Oximes:

C2H5OH + Na  

  C2H5 - ONa + [H]




    1. Reduction of Alkyl Cyanides (Nitriles):

R C N + 4[H]  

Na/C2H5OH

  R CH2NH2

 

    1.  
    2. Reduction of Nitroalkanes:

3 Sn + 6HCl  

 3 SnCl2 + 6 [H]

 

(conc.)

 

 


 

 

4.

Physical Properties of Amines

 

  1. Lower amines are liquids.
  2. They have a typical fishy odour.
  3. Lower amines are miscible with water.
  4. Lower amines are inflammable.
  5. They are weakly basic in nature.

 

 

 

 

 

5.

Chemical Properties of Amines

 

  1. Basic Nature of Amines:
    1. According to Lewis theory, a substance which donates a lone pair of electrons is called a base.
    2. In all the three types of amines, the nitrogen atom possesses a lone pair of electrons. It can be donated to a suitable electron acceptor (a Lewis acid). Hence, amines are basic in nature.
    3. Amines react with acids to form salts.

iv.

R - NH2 + HCl  

  R - NH3+ Cl-

  1.  
  2. Acetylation (acylation) of Amines:
    1. With Primary Amines -


                                                 monoacetyl alkylamine
                                                                or
                                                    N
      - Alkyl acetamide

    2. With Secondary Amines -


                                                 monoacetyl alkylamine
                                                                 or
                                                  N, N
      - Dialkyl acetamide

    3. With Tertiary Amines -
      As tertiary amines do not contain any hydrogen atom attached to nitrogen
      atom, they do not undergo acetylation or acylation reactions.
  3. Action of Nitrous Acid :

NaNO2 + HCl 

 NaCl + HNO2

  1.                                         Nitrous acid
    1. With Primary Amines -

    2. With Secondary Amines -



                                                    N - nitroso amine
    3. With Tertiary Amines -
      Tertiary amines do not react with nitrous acid.
  2. Methylation of Amines :
    The reaction in which hydrogen atoms of an amine are replaced by methyl (- CH3)
    group is called as methylation of amines.
    It is carried out by reacting an amine with methyl iodide.
    Example: methylation of methylamine.

CH3 - NH2 + CH3 -

 (CH3)2 NH + HI

 

 

dimethylamine

  1.  

(CH3)2NH + CH3 -

 (CH3)3 N + HI

  1.                                                 trimethylamine

(CH3)3N + CH3 -

 (CH3)4 N+ I -

 

 

 tetramethyl ammonium iodide

  1.                     

 

 

 

 

 

6.

Quaternary Ammonium Salt

 

The salt in which there is a positively charged nitrogen atom attached to four alkyl groups is called a quaternary ammonium salt.
Its general structure is R4N+ X
-
A quaternary salt is obtained by reacting a tertiary amine with any alkyl halide.
Example:

(CH3)3N + CH3 -

 (CH3)4 N+ I -

 

 

 

 




 

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