Ether

         Ethers are anhydride of alcohols, they can be  obtained by elimination of a water molecule from two alcohol molecules.

         General formula is C_nH_2n+2O

         General processes of preparation of ethers

         (1) From alkyl halides

         (i) Williamson's synthesis

         It is a nucleophilic replacement reaction and proceeds through S _N² mechanism.

         (a) Order of reactivity of primary halide is CH₃X > CH₃CH₂X > CH₃CH₂CH₂X.

         (b) Tendency of alkyl halide to undergo replacement is 3^o > 2^o > 1^o.

         (c) For better yield alkyl halide could be primary and alkoxide should be secondary or tertiary.

         (d) Tertiary and Secondary alkyl halides voluntarily undergo E₂ elimination in the presence of a strong base to form alkenes.

•           Sodium alkoxide and aryl halide cannot be used for preparing phenolic ethers because aryl halide are less reactive toward nucleophilic substitution reaction than alkyl halides.

         (ii) On high temperature alkyl halide with dry silver oxide

         (2) From alcohols

         (i) By dehydration of alcohols

         (a) With conc. H₂SO₄ at 140° C

           .

•        In this reaction alcohol has to be present in excess.
•         This reaction is mainly applicable for the dehydration of primary alcohols, Secondary and tertiary alcohols form alkenes mainly.
•         When this reaction is taken out between different alcohols then there is a mixture of different ethers is obtained.

         (b) With Al₂O₃ at 250° C :

         (ii) By the reaction of diazomethane on alcohols: This reaction is in presence of catalyst, boron trifluoride or HBF₄.

         (a) This process is very useful for creating mixed ethers.

         (b) In higher cases, there may be 1, 2-hydride or 1, 2-methyl shift to form more stable carbonium ion.

         (3) Alkoxy mercuration-demercuration

•  This is the best process for the generation of t-ethers.

         (4) Reaction of lower halogenated ether with grignard reagent

         (i) Higher members may be generated by the action of grignard reagent on lower halogenated ethers.

         (ii) Ether form soluble synchronized complexes with grignard reagent.

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