Q36E - Organic Chemistry (Mcmurry)

Question

It is not uncommon for organic chemists to prepare acetals by an exchange-type process known as transacetalization. Predict the product(s) and show the mechanism for the transacetalization reactions below.

a. 

b. 

Step-by-Step Solution

Answer

a. 

b. 

(a) The mechanism for the transacetalization of the hydroxyl group in catechol

The nucleophilic attack of one of the hydroxyl groups in catechol on the acetal of acetone displaces a methoxy group which is removed as methanol. A proton exchange takes place in the next step to produce a protonated hydroxy ether. The internal nucleophilic attack of another hydroxyl group displaces another methanol molecule to yield the cyclic acetal required.

The mechanism of the reaction is:

(b) The mechanism for the transacetalization of the hydroxyl group in ethylene glycol

The nucleophilic attack of one of the hydroxyl groups in ethylene glycol on the acetal of diethyl ketone displaces a methoxy group which is removed as methanol. A proton exchange takes place in the next step to produce a protonated hydroxy ether. The internal nucleophilic attack of another hydroxyl group in ethylene glycol displaces another methanol molecule to yield the cyclic acetal required.

The mechanism of the reaction is: