Q18-5P - Organic Chemistry (Mcmurry)

Question

How would you prepare the following ethers? Use whichever method you think is more appropriate, Williamson synthesis or the alkoxymercuration reaction.

1. Butyl cyclohexyl ether
2. Benzyl ethyl ether ( ${\mathbf{C}}_6{\mathbf{H}}_5{\mathbf{CH}}_2{\mathbf{OCH}}_2{\mathbf{CH}}_3$)
3. sec-Butyl tert-butyl ether
4. Tetrahydrofuran

Step-by-Step Solution

Answer

a. Both Williamson synthesis and alkoxymercuration methods are appropriate for preparing Butyl cyclohexyl ether.

 

Williamson:

Alkoxymercuration:

b.  Both methods are appropriate, but the Williamson synthesis is more straightforward for preparing Benzyl ethyl ether.

c.  In sec-Butyl tert-butyl ether, both parts of the ether are branched. So, the method used here is alkoxymercuration.

d.  The method used for preparing Tetrahydrofuran is Williamson synthesis.

Step 1: Methods for ether preparation

The methods for the ether preparation are the Williamson ether synthesis and alkoxymercuration method. For Williamson synthesis, the ether components comprise primary or benzylic halide and alkoxymercuration, when one or both ether components are branched.

Step 2: Preparation of Butyl cyclohexyl ether by Williamson synthesis

a. In Butyl cyclohexyl ether, bromobutane is a primary halide. Thus, the method used here is Williamson synthesis. Here, cyclohexanol is treated with NaH and forms an alkoxide ion. This ion further reacted with bromobutane and resulted in Butyl cyclohexyl ether formation.

Preparation of Butyl cyclohexyl ether by Williamson synthesis

Step 3: Preparation of Butyl cyclohexyl ether by alkoxymercuration

Here, the compound used is cyclohexene. In the first step, cyclohexene undergoes alkoxymercuration with ${\left({\text{CF}}_{\text{3}}{\text{CO}}_{\text{2}}\right)}_{\text{2}}\text{Hg}$  and butanol. In the second step, by using  data-custom-editor="chemistry" ${\text{NaBH}}_{\text{4}}$ , Butyl cyclohexyl ether is formed.

Preparation of Butyl cyclohexyl ether by alkoxymercuration

Step 4: Preparation of Benzyl ethyl ether by Williamson synthesis

b.

In Benzyl ethyl ether, the primary halide used is bromoethane. Both methods can be used, but the simple one here is Williamson synthesis. Here, benzyl alcohol is treated with NaH and forms an alkoxide ion. This ion further reacted with bromoethane and resulted in Benzyl ethyl ether formation.

Preparation of Benzyl ethyl ether by Williamson synthesis

Step 5: Preparation of sec -Butyl tert -butyl ether by alkoxymercuration

c.

In sec-Butyl tert-butyl ether, both the ether components are branched. Thus, the method used here is alkoxymercuration. Here, alkene undergoes alkoxymercuration with ${\left({\text{CF}}_{\text{3}}{\text{CO}}_{\text{2}}\right)}_{\text{2}}\text{Hg}$  and alcohol. In the second step, by using ${\text{NaBH}}_{\text{4}}$ , sec-Butyl tert-butyl ether is formed.

Preparation of sec-Butyl tert-butyl ether by alkoxymercuration

Step 6: Preparation of Tetrahydrofuran by Williamson synthesis

d. For preparing Tetrahydrofuran, Williamson synthesis must be used. 

Here, ${\text{Br-CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$  is treated with NaH, and an alkoxide ion is formed. In the second step, NaBr, along with Tetrahydrofuran, is formed.

Preparation of Tetrahydrofuran by Williamson synthesis