Question

Question: Draw a stepwise mechanism for the following reaction.

Short answer

Answer

Mechanism for the conversion of acetal to lactone

Step-by-step solution

Step-by-Step Solution Step 1: Hydrolysis of acetals

Germinal diether derivatives of carbonyl compounds are called acetals. They are formed when carbonyls react with alcohol.

Hydrolysis of acetals is the reverse reaction of its formation. Therefore, acetals on hydrolysis give carbonyl and alcohols.

The hydrolysis reaction is catalyzed by acids that protonate the acetal oxygen and activate the compound.

Fischer esterification

An esterification reaction taking place in the presence of a mineral acid catalyst is called a Fischer esterification.

It involves refluxing the alcohol and the ester with the catalyst.

The reaction is an equilibrium reaction, and the yield of the reaction depends on the concentration of acid and alcohol used in the reaction.

The acid catalyst activates the carboxylic acid by protonating the carbonyl group.

Mechanism of the given reaction

The given reaction consists of two-step hydrolysis of acetal and Fischer esterification.

The reaction is initiated by the protonation of acetal oxygen followed by the attack of a water molecule on the electrophilic carbon center.

A series of stabilizing reactions cause the removal of oxonium ions from the compound, which removes a proton to form acetone.

Fischer esterification on the compound followed by a series of stabilization reactions forms the final product.

Stepwise mechanism for the conversion of acetal to lactone