Aldol Condensation

Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl compound. A base-promoted condensation between ester molecules to produce a ꞵ-ketoester is known as the Claisen condensation. In the presence of a base, both reactions involve deprotonation of the acidic α hydrogen to produce the corresponding enolates. The nucleophilic enolates attack their respective nonenolized carbonyl compound forming a tetrahedral intermediate.

The Knoevenagel condensation is an aldol-type reaction involving the condensation of aldehydes or ketones with active methylene compounds such as β-diesters to produce substituted olefins. The reaction is catalyzed by amine base, which abstracts the acidic α hydrogen of the activated methylene to generate a resonance stabilized enolate ion. The basic strength of the amine is insufficient to form the enolate of aldehydes or ketones. However, it acts as a nucleophile that attacks the carbonyl...

As shown in Figure 1, under acidic conditions, the β-hydroxy ketone undergoes dehydration via an E1 elimination reaction to form an enone. Figure 1. The dehydration reaction of a β-hydroxy ketone. Figure 2 depicts the sequential processes involved in the mechanism of the reaction. Here, the acid protonates the hydroxyl group in the β-hydroxy ketone to form a hydrated hydroxyl group, which then departs to form a tertiary carbocation intermediate. Subsequently, the loss of the hydrogen atom from...

This lesson delves into the aldol condensation catalyzed by bases, where aldols undergo dehydration to enals. As shown in Figure 1, the β-hydroxy aldehyde formed in a base-catalyzed aldol addition reaction dehydrates on heating to yield an unsaturated carbonyl product, which is commonly referred to as an enal. Figure 1. The dehydration of a β-hydroxy aldehyde to an enal. This process follows a two-step mechanism, as depicted in Figure 2. Here, the base first deprotonates the mildly acidic...

Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. The aldol condensation reaction presented in Figure 1 constitutes an aldol addition reaction followed by the dehydration process. Figure 1. The general aldol addition reaction of aldehydes. Aldol addition reactions are reversible and are of two types: self-addition and crossed-addition. Combining two identical carbonyl compounds is called...