Explain the aldol condensation mechanism - Chemistry - Organic Chemistry Some Basic Principles and Techniques

Question

Explain the aldol condensation mechanism

Tripti · Accepted Answer

Solution
The aldol condensation is a reaction between a ketone and an aldehyde and an enol or enolate, leading to the formation of a new C-C double bond, along with the release of a water molecule. The condensation happens if the aldol addition product is heated for prolonged a prolonged period. Because of the release of a water molecule, this reaction is called a "condensation" reaction.

In this reaction, a β−hydroxyaldehyde or a β−hydroxyketone is formed,β-hydroxyaldehyde or a β-hydroxyketone is formed,which gets dehydrated to form an enone.

$m e c h a n i s m o f a l d o l c o n d e n s a t i o n s t e p 1 : g e n e r a t i o n o f c a r b a n i o n O H^{-} + C H_{3} C H O \frac{⇀}{↼} \bar{C} H_{2} C H O + H_{2} O \bar{C} H_{2} C H O \leftrightarrow C H_{2} = \underset{\underline{O}}{C} - H$

formation of an enolate ion takes place.

STEP 2 : ENOLATE ADDITION

$C H_{3} C H O + C H_{2} = \underset{\underline{O}}{C} - H \overset{k_{2}}{\to} C H_{3} \underset{\underline{O}}{C} H C H_{2} C H O$

This is β Alkoxide

Step 3 : Protonation

$C H_{3} \underset{\underline{O}}{C} H C H_{2} C H O + H_{2} O \to C H_{3} \underset{O H}{C H} C H_{2} C H O$

An alkoxide are strong bases so step 3 is fast and cannot be rate determining step and the second step is also fast because its nucleophilic addition and thus the first step is the slow step and rate determining step.

Explain the aldol condensation mechanism.