Question

Show how you would use the Williamson ether synthesis to prepare the following ethers. You may use any alcohols or phenols as your organic starting materials.

1. Cyclohexyl propyl ether
2. Isopropyl methyl ether
3. 1-methoxy-4-nitrobenzene
4. Ethyl n-propyl ether (two ways)
5. Benzyl tert-butyl ether (benzyl =$\mathit{P}\mathit{h}\mathbf{-}{\mathbf{CH}}_{\mathbf{2}}\mathbf{-}$)

Short answer

Williamson ether synthesis is a ${\mathit{S}}_{\mathbf{N}}^{}\mathbf{2}$reaction in which an alkoxide ion acts as a nucleophile and displaces or substitutes halide ion from alkyl halide to produce ether as the product. In part (a), starting material is cyclohexanol and on reaction with sodium and 1-bromopropane it gets converted to cyclohexyl propyl ether. Sodium forms alkoxide ion and attacks at 1-bromopropane and forms the required product. Similarly, in part (b), propan-2-ol is the starting material and on reaction with sodium and methyl iodide forms isopropyl methyl ether.

In part (c), 4-nitrophenol is the starting material and reacts with sodium hydroxide which is a base and abstracts proton from phenol and forms phenoxide ion. Further, phenoxide ion acts as nucleophile and attacks at methyl iodide and forms 1-methoxy-4-nitrobenzene.

Formation of products via Williamson ether synthesis

Step-by-step solution

Step-1. Explanation of part (a), (b) and (c):

Williamson ether synthesis is a ${\mathit{S}}_{\mathbf{N}}^{}\mathbf{2}$reaction in which an alkoxide ion acts as a nucleophile and displaces or substitutes halide ion from alkyl halide to produce ether as the product. In part (a), starting material is cyclohexanol and on reaction with sodium and 1-bromopropane it gets converted to cyclohexyl propyl ether. Sodium forms alkoxide ion and attacks at 1-bromopropane and forms the required product. Similarly, in part (b), propan-2-ol is the starting material and on reaction with sodium and methyl iodide forms isopropyl methyl ether.

In part (c), 4-nitrophenol is the starting material and reacts with sodium hydroxide which is a base and abstracts proton from phenol and forms phenoxide ion. Further, phenoxide ion acts as nucleophile and attacks at methyl iodide and forms 1-methoxy-4-nitrobenzene.

Formation of products via Williamson ether synthesis

Step-2. Explanation of part (d), (e):

In part (d), propan-1-ol on reaction with sodium and ethyl bromide forms ethyl n-propyl ether and, ethyl n-propyl ether can also be formed from the reaction of ethanol with sodium and 1-bromopropane. In part (e), tert-butyl alcohol when reacts with sodium and benzyl bromide forms benzyl tert-butyl ether as the product. Carbocation is formed from benzyl bromide as benzyl carbocation is stable. Tert-butoxide ion acts as a nucleophile and attacks at benzyl carbocation and forms the product.

Formation of ethers via Williamson ether synthesis