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Preparation of ethers

  1. Intermolecular dehydration of alcohols
     
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  2. Williamson’s etherification method: When an alkoxide is treated with an alkyl halide, ether is produced. The method was developed by Williamson and is useful for the preparation of symmetrical as well as unsymmetrical ethers.
     
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    where R′ can be same as or different from R.
     
    RO – H + K ROK+ + ½ H2
     
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    For ether to be obtained as major product, the reaction should follow substitution and minimize elimination reaction. This can be achieved by taking only methyl halides or 1° halides with lesser branching near the reaction site.
     
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  3. Alkoxymercurationdemercuration:
     
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Chemical reactions of ethers

  1. Cleavage by heating with acids: Ethers on reaction with acids (HX) in the presence of heat undergoes cleavage to form an alkyl halide and an alcohol. Alcohol on further reaction with HX gives second molecule of alkyl halide.
     
    R – O – R′ + H – X R – X + R′ – OH
     
    R′ – OH + H – X R′ – X + H2O
     
    HI is more reactive towards ether than HBr, and HBr is more reactive than HCl.
     
    The cleavage of ethers takes place in vigorous conditions, i.e., in concentrated acids (HI and HBr) and at elevated temperatures.
     
    Mechanism
     
    Step I:
     
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    Step II:
     
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  2. Oxidation of ether by air or ozone
     
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Preparation of epoxides

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Reactions of epoxides

  1. Acid-catalyzed cleavage of epoxides
     
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  2. Base-catalyzed cleavage of epoxides
     
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