Introduction
Benzoin condensation is a reaction where aromatic aldehydes (that do not contain any α-hydrogen) combine with each other in the presence of cyanide ions acting as a catalyst. This reaction produces an important compound called benzoin, which belongs to a class of compounds known as acyloins.
This reaction is mainly observed with aromatic aldehydes and does not normally work with aliphatic aldehydes.
Mechanism of Benzoin Condensation
- Nucleophilic attack by cyanide (CN⁻): The cyanide ion attacks the carbonyl carbon of the aromatic aldehyde, forming an intermediate (1).
- Formation of a stabilized anion:
The CN group increases the acidity of the aldehydic hydrogen. This helps convert intermediate (1) into another more stable anion (2), because the benzene ring and cyanide group both stabilize the negative charge. - Nucleophilic attack on a second aldehyde molecule:
The anion (2) attacks the carbonyl group of a second aldehyde molecule. This step joins the two aldehyde molecules together. - Formation of the alkoxide ion (3):
A series of proton gain and loss steps lead to the formation of the alkoxide intermediate. - Departure of cyanide:
Finally, CN⁻ ion leaves the intermediate (3), resulting in the formation of benzoin.
Applications
Aromatic aldehydes such as anisaldehyde and p-tolualdehyde successfully undergo benzoin condensation to form the corresponding α-hydroxy ketones.
Other heterocyclic aldehydes like furfural also participate in the reaction to form furoin.
This reaction is an important method for forming new carbon-carbon bonds in organic synthesis.
Detailed Notes:
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PATH: PHARMD/PHARMD NOTES/ PHARMD FIRST YEAR NOTES/ ORGANIC CHEMISTRY/ PHARMACEUTICAL ORGANIC CHEMISTRY/ BENZOIN CONDENSATION.