What is an aldol reaction

Aldol reaction

Scheme:

In the case of aldol addition, two carbonyl compounds (aldehydes or ketones) react to form a β-hydroxycarbonyl compound. One of the components must have a hydrogen atom in the α position, i.e. enolizable be. The aldol addition is an important reaction for the C-C linkage. Sometimes this is followed by dehydration with formation of an α, β-unsaturated carbonyl compound; the entire process is then referred to as Aldol condensation.

Mechanism:

The aldol addition usually proceeds with base catalysis. First, one of the reactants is deprotonated to form a mesomeric-stabilized enolate anion. This carbanion acts as a nucleophile and attacks the C atom of the carbonyl group of the other reaction partner. Finally, the intermediate product takes up a proton. (In the acid-catalyzed variant, the enol form reacts with the protonated carbonyl group of the other reactant.)

Example 1:

The simplest example is the dimersization of acetaldehyde to "acetaldol" (3-hydroxybutanal). Note that this creates a new stereocenter.

Example 2:

A biologically very important reaction is the addition of dihydroxyacetone to D-glyceraldehyde. Four stereoisomers can be formed here, including D-fructose. Note that the carbonyl group of the aldehyde is more reactive than that of the ketone, which acts (enolizes) as a nucleophile.

literature

T. Laue, A. Plagens: Name and keyword reactions in organic chemistry. Teubner study books, Stuttgart 1994.

Coding

Reaction scheme: RRCHRCO + RRCO → RRCOHRRCRCO

Response code: -RRCHRCO-RRCO + RRCOHRRCRCO


Author: BKi