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Explain why a slow addition of acetaldehyde to a benzaldehyde solution containing the base will result in less self condensation and give another method that can combat this competitive reaction
Accepted Answer
The slow addition of acetaldehyde to a benzaldehyde solution containing a base minimizes self-condensation due to kinetic control. Adding acetaldehyde slowly favors the formation of the mixed aldol product because the concentration of benzaldehyde is always higher than that of acetaldehyde. This reduces the chance of acetaldehyde molecules reacting with each other.
Another method to combat self-condensation is to use a different base, such as LDA (lithium diisopropylamide), which is a very strong, non-nucleophilic base. LDA will selectively deprotonate the more acidic α-hydrogen of benzaldehyde, leading to a more reactive enolate. This enolate can then react with acetaldehyde to form the desired mixed aldol product. The use of LDA minimizes self-condensation as it does not react with the carbonyl group of acetaldehyde, unlike other bases.
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