Chapter 14: Q13P (page 721)

Which of the following ethers can be formed in good yield by condensation of the corresponding alcohols? For those that cannot be formed by condensation, suggest an alternative method that will work.
(a) $dibutyl ether$
(b) $ethyl n-propyl ether$
(c) $di-sec-butyl ether$

Short Answer

Expert verified

(a) $dibutyl ether$ is a symmetrical ether and hence good yield can be produced by condensation method.

(b) $ethyl n-propyl ether$ is an unsymmetrical ether and hence good yield cannot be produced by condensation method. In such case, Williamson ether synthesis can eb used for good yields.

Step by step solution

Bimolecular condensation

The cheapest method for synthesizing simple symmetrical ethers is the acid catalyzed bimolecular condensation where two molecules of alcohols are joined with the loss of a small molecule like water. The alcohol must have an unhindered primary alkyl group to form an ether and also the temperature of the reaction should not be too high. Bimolecular condensation of alcohols is considered to be a poor synthetic method.

$\begin{array}{l} 2R - OH \overset{H^{+}}{⇄} R - O - R + H_{2} O \\ alcohol ether water \end{array}$

Williamson ether synthesis

The most reliable and versatile method for synthesis of ethers is given by Williamson method. In this method, ${S_{N}}^{2}$ attack of an alkoxide ion takes place on an unhindered primary alkyl halide or tosylate. The yield is poor if secondary alkyl halide is used. The alkoxide is generally made by adding $Na, K or NaH$ to the alcohol.

Explanation

(a) $dibutyl ether$ is a symmetrical ether and hence good yield can be produced by condensation method.

(b) $ethyl n-propyl ether$ is an unsymmetrical ether and hence good yield cannot be produced by condensation method. In such case, Williamson ether synthesis can eb used for good yields.