Advices For Studying Organic Chemistry

(^)

1. Attempts to synthesize ethers with 2° alkyl groups by intermolecular dehydration
   of 2° alcohols are usually unsuccessful because alkenes form too easily ⇒ This
   method of preparing ethers is of limited usefulness.


2. This method is not useful for the preparation of unsymmetrical ethers from 1°
   alcohols because the reaction leads to a mixture of products:
   1 o alcohol
   H 2 SO 4 R
   OH OH O H 2 O
   O
   R +R' R'
   R' R'
   ROR

11.15B THE WILLIAMSON SYNTHESIS OF ETHERS

1. Williamson Ether synthesis:

A Mechanism for the Reaction

The Williamson Ether Synthesis

R O −Na+ + R' R O R' + Na+

Sodium

(or potassium)

al

L − L

koxide

Alkyl hslide,

alkyl sulfonate, or

dialkyl sulfate

Ether

The alkoxide ion reacts with the substrate in an SN2 reaction, with the resulting

formation of the ether. The substrate must bear a good leaving group. Typical

substrates are alkyl halides, alkyl sulfonates, and dialk yl sulfates, i.e.

–L = −Br , −I , –OSO 2 R", or –OSO 2 OR"

2. The usual limitations of SN2 reactions apply:
   
   
   1. Best results are obtained when the alkyl halide, sulfonate, or sulfate is 1° (or
      methyl).