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MHT-CET : Chemistry Entrance Exam

MHT - CET : Chemistry - Ethers Page 1

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I

Ethers

 

The organic compounds containing two alkyl (or aryl) groups attached to an oxygen atom are called ethers. They are the alkyl derivatives of alcohols. They have the general formula R-O-R1.
Example: CH3
- O - CH3, dimethyl ether.

 

 

 

II

Classification

 

 

 

III

Isomerism shown by Ethers

 

  1. Chain Isomerism: Chain isomers have the same type of alkyl groups on either side of the oxygen atom but the arrangement of the carbon chain within the alkyl group or groups is different.
    1-Methoxybutane and 1-Methyl-2-methyl propane are chain isomers.

CH3 - O - CH2CH2CH2CH3

1-Methoxybutane

2-Methoxybutane

  1. Metamerism: Ethers having same molecular formula but different alkyl groups on either side of the oxygen atoms show metamerism. Ethoxy ethane and methoxypropane, phenetole and benzyl methyl ether show metamerism.

CH3CH2 - O - CH2CH3

CH3 - O - CH2CH2CH3

Ethoxy ethane

Methoxy propane

  1.  

Phenetole

Benzyl methyl ether

  1.  
  2. Functional Isomerism: Ethers containing two or more carbon atoms show functional isomerism with alcohols. Methoxy methane and ethanol are functional isomers. Aromatic ethers, like anisole and benzyl alcohol also show functional isomerism.

CH3 - O - CH3

CH3CH2OH

Methoxy methane

Ethanol

  1.  

Anisole

Benzyl alcohol

 

 

IV

Preparation:

 

1.

By Williamson's Synthesis

 

When sodium (or potassium) alkoxide is heated with an alkyl halide, a corresponding ether is formed.

 



This reaction involves nucleophilic substitution of the halogen atom of alkyl halide by the alkoxide group.

Williamson's synthesis is useful for the preparation of symmetrical and unsymmetrical ethers. For the preparation of unsymmetrical ethers, a primary alkyl halide is preferred. This is because, secondary and tertiary alkyl halides on reacting with a sodium alkoxide form alkenes as a major product instead of an ether.



 

2.

By continuous Etherification Process

 

When an alcohol is heated with a small quantity of concentrated H2SO4 at a high temperature, a corresponding ether is obtained.

 


This method is mainly used for dehydration of primary alcohols. As secondary and tertiary alcohols give alkenes as their major product.

Dehydration of alcohols in the presence of a heated catalyst like alumina (Al2O3) at about 525 K, also produce a corresponding ether.

 

3.

By using Diazomethane

 

This method is useful for preparing methyl ethers.
Alcohols react with diazomethane in the presence of fluoboric acid to form alkyl
methyl ethers.

 

 

4.

By using Dry Silver Oxide:

 

When an alkyl halide is heated with dry silver oxide, a corresponding ether
is formed.

 

V

Physical Properties

 

  1. Lower ethers are, generally, low boiling liquids and are volatile.
  2. They are inflammable.
  3. They are immiscible in water.
  4. They are inert towards most of the reagents.

 

VI.

Chemical Properties

 

1.

Action of Hydriodic Acid (HI)

 

a.

In Cold Conditions:

 

(i) With Simple Ethers:

(ii) With Mixed Ether:

 

b.

In Hot Conditions:

 

(i) With Simple Ethers:

(ii) With Mixed Ethers:

 

2.

Action of Dilute H2SO4:

 

VII

Uses of Diethyl Ether

 

  1. It is used as an industrial solvent for products like oils, fats, gums and resins, etc.
  2. It is used as an extracting solvent.
  3. It is used as a anaesthetic in surgery.
  4. It is a solvent for the preparation of Grignard's reagent and Wurtz reaction.
  5. It is used as a refrigerant.

 

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