ALDOL CONDENSATION

Condensation between two molecules of an Aldehyde or a ketone to form a β-hydroxyaldehyde or a β-hydroxy ketone is known as a ALDOL CONDENSATION.

ALDOL CONDENSATION is possible only when the carbonyl compound contains atleast one

α-hydrogen atom.

Thus the following Aldehydes or ketones having no α-hydrogen atom do not undergo Aldol Condensation.

Some conditions regarding the

Aldol ReactionA reversible equilibrium

OH is the base typically used in an aldol reaction.

Aldol reactions can be carried out with either

aldehydes or ketones.

With aldehydes, the equilibrium favors products

With ketones the equilibrium favors the starting

materials.

MECHANISM OF ALDOL

CONDENSATION

Step 1: First, an acid-base reaction. Hydroxide functions as a base and removes the acidic a-hydrogen giving the reactive enolate. Step 2:  The nucleophilic enolate attacks the aldehyde at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide. Step 3: An acid-base reaction. The alkoxide deprotonates a water molecule creating hydroxide and the β-hydroxyaldehydes or aldol product.

Step:1

An enolate ion is the anion formed when an alpha hydrogen in the molecule of an aldehyde or a ketone is removed as a hydrogen ion.

enolate ion

Step:2

The alkoxide ion is the conjugate base of alcohols.

 Alkoxide ion  is protonated by water.

Step:3

aldol product

GENERAL FEATURES OF

ALDOL CONDENSATION

The aldol condensation is facilitated by-I groups on the carbonyl component and retarted by +I groups as described in CHзCHO and CHзCOCHз condensations.

The condensation is readily reversible and the position of equilibrium is not always favorable to the product.

Eg:

LIMITATIONS: Aldol products,as such, are not always

isolated from the reaction mixture.eg:acetaldol readily forms a cyclic hemi-acetol.

EXTENSIONS: Aldol condensation can occur between Two identical or different aldehydes Two identical or different ketones An aldehyde and a ketone

The R groups may be H, alkyl, or aryl. When the R

groups in one molecule are different than those in the

other, the reaction is called a crossed-aldol

reaction. The ability to join different aldehydes and

ketones together is what give this process its synthetic

value.

The name aldol condensation is also commonly

used,especially in biochemistry,to refer to just the first

stage of the process the aldol reaction itself as

catalysed by aldolases.

In its usual form ,it involves the nucleophilic

addition of a ketone enolate to an aldehyde

to form a β-hydroxy ketone or

aldol(aldehyde+alchohol), a structural unit

found in many naturally occuring molecules

and pharmaceuticals.

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Presented by -Akili Karuna