What is the principle of aldol condensation reaction?

The aldol reaction is one of the important reactions in organic chemistry to form carbon-carbon bonds. It refers to: having a hydrogen atom.

aldehydes or ketones form enol anion under certain conditions.

It is then added with another molecule of carbonyl compounds to form a class of organic chemical reactions of -hydroxycarbonyl compounds. This reaction, independently discovered by Charles Adolf Wuz and Alexander in 1872, respectively linked two carbonyl compounds (aldehydes were used in the initial reaction) to synthesize new -hydroxyketone compounds. This type of product is called "aldol", which is a name formed from the word "hydroxy" (ol) for hydroxyl alcohols and the word "aldehyde" (ald) for aldehyde compounds.

A typical modern aldol addition reaction is the nucleophilic addition of aldehydes by the nedon anion of ketones. Once the reaction takes place, the aldol product can sometimes lose a molecule of water to form an unsaturated carbonyl compound, which is called the aldol condensation reaction.

A variety of affinity reagents can be used in aldol reactions, including enols, enol aniones, ketone enol ethers, aldehydes, and other carbonyl compounds. Electrophiles that react with it.

Usually aldehydes or ketones (there are many variations like the Mannich reaction here.

If nucleophile.

Unlike electrophiles, the reaction is called: cross-aldol reaction; If the nucleophile and electrophile are the same, it is called: aldol dimerization reaction. If the catalyst is a mild base, such as hydroxide ions.

or alcohol anions, the aldol reaction can attack another molecule of carbonyl compounds by forming resonant-stable enol anion and nucleophilic. Its product is an alkoxide of the aldol product, and then it dehydrates itself to obtain unsaturated carbonyl compounds. The mechanism of aldehyde reaction under alkali-catalysis is demonstrated.

Carbonyl compounds such as aldehydes or ketones can be converted to enols or enol ethers. Both of them are nucleophilic on the -carbon atom and can attack some reactive protonated carbonyl compounds, such as protonated aldehydes, known as the "enol mechanism". Carbonyl compounds or organic matter containing active hydrogen on carbon atoms can be deprotonated at the carbonyl site to form enol anions, and the ion form is more nucleophilic than enols and enol ethers, and can directly attack electrophiles.

The common electrophiles are aldehyde compounds, while the activity of ketones is relatively low, and this kind of reaction mechanism is called "enol anion mechanism". If the reaction conditions are particularly violent, a condensation reaction will occur; This can be avoided by low temperature conditions and with a mild base, and the aldol adduct product is treated with a strong base, which can lead to reverse-aldol cleavage to obtain the starting material. Aldol condensation is generally considered to be an irreversible reaction, but cross-aldol reaction kinetics studies have shown that it is actually a reversible reaction.

In essence, it is a heterocleavage reaction, or an ionic reaction, which is a condensation reaction in terms of Bi Shengqing's mechanism.

Aldehydes with -h are catalyzed by dilute alkali to form carboanions.

The carboanion then acts as a nucleophile.

The nucleophilic addition of aldehydes and ketones is carried out to form -hydroxyaldehydes, which are dehydrated by heating to unsaturated aldehydes.

Under the action of dilute alkali or dilute acid, two molecules of aldehydes or ketones can interact with each other, and the -hydrogen in one aldehyde (or ketone) molecule is added to the carbonyl oxygen atom of the other aldehyde (or ketone) molecule, and the rest is added to the carbonyl carbon atom.

, a molecule of -hydroxyaldehyde or a molecule of -hydroxy ketone is generated.

This reaction is called aldol condensation.

or aldol condensation. Through alkaldehyde condensation, new carbon-carbon bonds can be formed in the molecule and carbon chains can be grown.

Aldol condensation reaction process to:AcetaldehydeThe following is an example:

In the first step, the base combines with the -hydrogen in acetaldehyde to form an enol anion or negative carbon ion.

The second step is that this negative ion, acting as a nucleophile, immediately attacks the carbonyl carbon atom in another acetaldehyde molecule, and an addition reaction occurs.

An intermediate anion (alkoxy hand pre-anion) is generated.

In the third step, alkanox anion reacts with water to obtain aldol and OH.

The aldol condensation reaction is a reaction in which carbonyl compounds such as aldehydes, ketones or carboxylic acid derivatives form new carbon-carbon bonds next to the carbonyl group, thus combining two molecules, and these reactions are usually catalyzed by acids or bases. One carbonyl compound forms an enol or enol anion in the reaction and then attacks the carbon atom of another carbonyl group, resulting in a new carbon-carbon bond.

The simplest example is the aldol condensation reaction of acetaldehyde, the product 3-hydroxybutyraldehyde has the potential to further lose water to form 2-butenal, and acid catalysis is conducive to the progress of the water loss reaction. The reaction of acetaldehyde to 2-butenal is an example of the condensation of carbonyl groups with methylene, which starts in the form of aldol condensation and then loses water to obtain the product of carbon-carbon double bond.

You can take it off, but look at the hydrogen activity, and it is determined by the group next to it.

The reaction conditions for aldol condensation are as follows:The aldol condensation reaction refers to the reaction of aldehydes and ketones under alkaline conditions to obtain enols and another carbonyl compound to condense to obtain -hydroxyaldehyde ketone. Sometimes -hydroxyaldehydes and ketones are dehydrated to obtain unsaturated carbonyl compounds.

Enols are added to aldehyde to obtain alcohol, so this reaction is called aldol condensation reaction. <>

The original Aldol reaction is catalyzed by the BR nsted acid-base, but this method will have a series of side reactions, such as self-condensation, polycondensation, and Michael addition of the dehydrated product. The preparation of enols before further condensation is a major breakthrough in the Aldol reaction. Various metalenols such as Li, Na, Mg, Zn, B, Al, Ti and so on can be prepared by migration metallization, among which only the enols of silicon and tin can be separated and refined.

In particular, the aldol addition reaction of silenols under Lewis acidic conditions is often referred to as the mukaiyama aldol condensation reaction.