Substitution and Elimination Reactions in Synthesis

When substitution or elimination reactions are used in synthesis, care must be taken to choose reactants and reaction conditions that will maximize the yield of the desired product. Thus, Sn2 and E2 reactions are preferred. 

In Section 9.2, you saw that nucleophilic substitution reactions of alkyl halides can lead to a wide variety of organic compounds. For example, ethers are synthesized by the reaction of an alkyl halide with an alkoxide ion. This reaction, called the Williamson ether synthesis (after Alexander Williamson, who discovered it in 1850) is still considered one of the best ways to synthesize an ether. 

The alkoxide ion (RO ) for a Williamson ether synthesis can be prepared by using sodium hydride (NaH) to remove a proton from an alcohol. 

The Williamson ether synthesis is a nucleophilic substitution reaction. It requires a high concentration of a good nucleophile, which indicates that it is an Sn2 reaction. 

If you want to synthesize an ether such as the one shown next, you have a choice of starting materials you can use either a propyl halide and butoxide ion or a butyl halide and propoxide ion. 

---