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Slow addition of the acetaldehyde to a benzaldehyde solution containing the base will often result in less self-condensation. Explain. Identify one other method that can be used to combat this competitive reaction.
Accepted Answer
Slow addition of acetaldehyde to a benzaldehyde solution containing base minimizes self-condensation of benzaldehyde because it allows the acetaldehyde to react with the base and form the enolate faster than benzaldehyde. This enolate is then more reactive with benzaldehyde than benzaldehyde's own enolate. This method essentially favors the cross-aldol condensation over the self-condensation of benzaldehyde.
Another method to combat this is to use a different base. For example, using LDA (lithium diisopropylamide) instead of a strong base like hydroxide or alkoxide will result in selective deprotonation of the acetaldehyde, promoting the desired cross-aldol reaction.
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