Dehydration in a Base-Catalyzed Aldol Condensation

Dehydration in a Base-Catalyzed Aldol Condensation THE OVERALL REACTION  

Step 1 Hydroxide ion abstracts a proton from the a-carbon atom of the (B-hydroxy aldehyde to form the corresponding enolate. 

Step 2 Hydroxide ion is expelled from the negatively charged enolate to give a double bond between the a and (3 carbons. 

As with other reversible nucleophilic addition reactions, the equilibria for aldol additions are less favorable for ketones than for aldehydes. For example, only 2% of the aldol addition product of acetone is present at equilibrium. 

The situation is similar for other ketones. Special procedures for aldol addition and selfcondensation of ketones have been developed, but are rarely used. 

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