Short Notes On Aldol Condensation
Aldol condensation reaction is a Carbon-Carbon bond forming reaction in which an enolate ion reacts with a carbonyl compound in presence of suitable acid or a base to form a β-hydroxy aldehyde or β-hydroxy ketone. This further undergoes dehydration to give conjugated enone. Dehydration may be accompanied by decarboxylation when an activated carboxyl group is present.
It involves the nucleophilic addition of a ketone enolate to an aldehyde to form a β-hydroxy ketone, or β-hydroxy aldehyde (aldol).
An aldol is a structural unit that is a union of an aldehyde and alcohol, i.e., Aldol = aldehyde + alcohol.
The fundamental steps of the aldol condensation reaction are:
- Aldol (aldehyde + alcohol) reaction
- Dehydration/Elimination reaction
Reaction Mechanism-
We can summarize acid and base-catalyzed reaction in this manner-
The aldol addition product can be dehydrated through any of these two mechanisms-
- In presence of a strong base like- potassium t-butoxide, potassium hydroxide, or sodium hydride; it deprotonates the product to an enolate.
Here, elimination occurs via the E1cB mechanism.
- In presence of acid, dehydration proceeds via the E1 mechanism.
Depending on the nature of the desired product, the aldol condensation may be carried out under two types of conditions: kinetic control or thermodynamic control.
The reaction mechanism of Aldol condensation can also be explained step by step as follows-
Step 01: The hydroxide ion deprotonates the aldehyde.
Note:
- The addition products formed from the Aldol Addition reaction can easily be converted (in situ) to α,β-unsaturated carbonyl compounds, either thermally or under acidic or basic catalysis. For spontaneous dehydration, the driving force is the formation of the conjugated system.
- In an aldol condensation between an aldehyde and a ketone, the ketone acts as the nucleophile as its carbonyl carbon does not possess high electrophilic character due to the +I effect and steric hindrance.
Note: The products of aldol condensation when heated with dilute acids undergo dehydration which further yields α, β-unsaturated aldehydes or ketones. Example-
Intramolecular Aldol Condensation:
If a compound contains two aldehydes/ketones or one aldehyde and one ketone group at 1,6 or 1,7-positions with respect to to each other, intramolecular aldol condensation occurs to yield α, β-unsaturated aldehyde/ketone.
Download Study Notes On Aldol condensation - CLICK HERE←
Enrol for CSIR NET 2022 Crash Courses - Join Online Classroom Program
Get Access to Unlimited Test Series for CSIR NET 2022 Exam
Check Out:
- Complete Study Notes on Chemical Science - Download PDF
- Most Expected Questions for the Upcoming CSIR NET Chemical Science 2022
- Topic Wise Formula Sheets for Chemical Science
BYJU'S Exam Prep
Download the BYJU’S Exam Prep App Now.
The Most Comprehensive Exam Prep App.
#DreamStriveSucceed
App Link: https://bit.ly/3sxBCsm
Comments
write a comment