Question

Propose a mechanism for the acid-catalyzed reaction of benzaldehyde with methanol to give benzaldehyde dimethyl acetal.

Short answer

The mechanism for the acid-catalyzed reaction of benzaldehyde with methanol to produce benzaldehyde dimethyl acetal is shown below.

Step-by-step solution

Formation of Acetal

When aldehydes and ketones react with alchols in the presence of acid, they form acetal as the major product. The formation of acetal can be divided into two simpler process namely (i) acid catalyzed addition of alcohol to the carbonyl group and (ii) ${\mathrm{S}}_{\mathrm{N}}1$substitution of the hemiacetal that is protonated.

Mechanism for the Acid-catalyzed Reaction of Benzaldehyde with Methanol

Benzaldehyde reacts with methanol in the presence of acid to form benzaldehyde dimethyl aacetal. The corresponding reaction is shown below.

The meachanism for the acid-catalyzed reaction of benzaldehyde with methanol to produce benzaldehyde dimethyl acetal is shown below.

Step (a) Protonation of benzaldehyde

Step (b) Addition of an alcohol ( methanol)

Step (c) Deprotonation

Step (d) Protonation

Step (e) Loss of water

Step (f) Addition of second alcohol

Step (g) Deprotonation