Q44E - Organic Chemistry (Mcmurry)

Question

Paraldehyde, a sedative, and hypnotic agent, is prepared by treatment of acetaldehyde with an acidic catalyst. Propose a mechanism for the reaction.

Step-by-Step Solution

Answer

Step-by-Step Solution Step 1: Protonation of acetaldehyde

Paraldehyde is a sedative that is prepared by using three moles of acetaldehyde in an acidic medium.

In the given reaction, acetaldehyde is reacted with the acidic hydrogen to give the protonated form of acetaldehyde.     

In the above step, the lone pair of the oxygen atom abstracts hydrogen ions.

Step 2: Reaction of protonated form with another molecule of acetaldehyde

In the second step carbonyl oxygen of the second aldehyde, molecule attacks the carbonyl carbon and we get the following intermediate.

Protonation of acetaldehyde

Reaction with Protonated acetaldehyde

Step 3: Reaction of intermediate with the third molecule of aldehyde

Aldehyde reacts with the intermediate by the following mechanism;

Formation of Paraldehyde