Description: In which explain about Aldol condensation, Cross aldol condensation reaction, Mechanism and Faq
Aldol Condensation
An addition reaction between two aldehydes, two ketones or one aldehyde and one ketone in which they have at least one alpha-hydrogen undergoes a reaction in the presence of dilute alkali ( alkali means:- any of the soluble hydroxides(–OH) of alkali metals like lithium, sodium, potassium, rubidium and caesium.Alkali are strong base like NaOH ) as catalyst ( catalyst mean it make a fast reaction or fast process of reaction by reagents like NaOH, etc.) to form beta-hydroxy aldehydes (aldol) or beta-hydroxy ketones (ketol), respectively. This is known as the Aldol reaction.
%20.webp "Example of Aldol condensation reaction with two ethanal (Aldehydes)") |
Example of Aldol condensation reaction with two ethanal (Aldehydes) |
%20.webp "Example of Aldol condensation reaction with two propanone (Ketones)") |
Example of Aldol condensation reaction with two propanone (Ketones) |
The names Aldol is derived from the names of two functional groups aldehyde and alcohol, this group is present in the product side of the reaction.
The Aldol and ketol readily lose water to give alpha or beta-unsaturated carbonyl compounds [Carbonyl compounds are those compounds in which carbon double bonds with oxygen ( C=O) ] which are aldol condensation products and the reaction is called Aldol Condensation.
Though ketones give ketol (compounds containing keto and alcohol groups) the general name Aldol Condensation still or also applies to the reaction of ketones due to their similarity with aldehydes.
Table Of Content
3 Steps Mechanism of Aldol Condensation reaction
- Enolate ion formed (or Aldol and Ketol reaction formed).
- Nucleophilic attack by the enolate ion (or Aldol and Ketol readily to lose of water to give alpha or beta-unsaturated carbonyl compound).
- Protonation ( Adding of (H+) to an atom, molecule, or ion )
Alpha hydrogen
[Carbon which is attached or bonded with functional groups ( —C-C-functional group(like OH ).
In which first carbon is made a bond with functional groups in the left or right side that carbon is known as alpha carbon and 2nd carbon make a bond with Alpha carbon this is called beta carbon and it continues after this is called gamma carbon ), double and triple bond (-C-C-C-≡C-C-C- or -C-C-C=C-C-C- in this carbon bond with double or triple bond left or right side has alpha carbon) and bond or attach with a methyl group is called alpha carbon and hydrogen of alpha carbon is called Alpha hydrogen]
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Alpha hydrogen |
Cross Aldol Condensation
When the use two different aldehydes or ketones reactions then we get Aldol Condensation this is called Cross Aldol Condensation.
If both of them (two different aldehydes Or ketones) contain alpha hydrogen atoms, it gives a mixture of four products. This is illustrated below by the aldol reaction of a mixture of ethanal and propanal.
Cross aldol condensation reaction
Cross aldol condensation reaction
Mechanism of Cross aldol-condensation reaction
Reaction |
It explains cross aldol condensation reaction mechanism step by step
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1st product of cross aldol condensation reaction |
1st product makes from two molecules of ethanal.
In which remove of oxygen from the first ethanal and remove of 2 alpha- hydrogen (or hydrogen atoms) from alpha carbon of another ethanal and reaction occurs in the presence of NaOH (Catalyst) and then heat provide to release or remove water (H2O) from the product side of Cross aldol condensation reaction and then we get 1st product (But-2-enal)
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2nd product of Cross aldol condensation reaction |
2nd product makes from two molecules of propanal.
In which remove of oxygen from the first propanal and remove of 2 hydrogen atoms (alpha hydrogen) from alpha carbon of another propanal and reaction occurs in the presence of NaOH ( Catalyst) and then heat provide to release or remove water (H2O) from the product side of Cross aldol condensation reaction and then we get 2nd product (2-Methylpent-2-enal)
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3rd product of Cross aldol condensation reaction |
When ethanal and propanal react they get 3rd product of the reaction.
In which remove of oxygen from ethanal and remove of 2 hydrogen atoms (alpha hydrogen) from alpha carbon of propanal and reaction occurs in the presence of NaOH (Catalyst) and then heat provide to release or remove of water (H2O) from the product side of Cross aldol condensation reaction and then we get 3rd product (2-Methylbut-2-enal)
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4th product of Cross aldol condensation reaction |
When propanal and ethanal react then get the 4th product of Cross aldol condensation reaction.
In which remove of oxygen from propanal and remove of 2 hydrogen atoms (alpha hydrogen) from alpha carbon of ethanal and reaction occurs in the presence of NaOH (Catalyst) and then heat provide to release or remove of water (H2O) from the product side of Cross aldol condensation reaction and then we get 4th product (Pent-2-enal)
This Cross aldol condensation reaction mechanism helps him to know how these four products are formed. It helps to more understanding about Mechanism of Cross aldol condensation reaction
Yes, we can use one component of ketones and one component of aldehydes in the Cross aldol condensation reaction.
Example of cross aldol condensation reaction:- reaction between Benzaldehyde and Acetophenone
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Benzaldehyde and Acetophenone reaction |
When the reaction between Benzaldehyde and Acetophenone reaction undergoes cross aldol condensation in the presence of dilute NaOH.
In which remove of oxygen from Benzaldehyde and the removal of 2 hydrogen atoms (alpha hydrogen) from alpha carbon from Acetophenone and the reaction occurs in the presence of Hydroxide (OH− )at 293k (kelvin) and we get 1,3-Diphenylprop-2-en-1-one (Benzalacetophenone) ( Major product).
Difference between Aldol Condensation reaction and Cross Aldol Condensation reaction
(1) An addition reaction between two aldehydes, two ketones or one aldehyde and one ketone in which they have at least one alpha-hydrogen undergoes a reaction in the presence of dilute alkali
as catalyst to form beta-hydroxy aldehydes (aldol) or beta-hydroxy ketones (ketol).
The Aldol and ketol readily lose water to give alpha or beta-unsaturated carbonyl compounds which are aldol condensation products and the reaction is called Aldol Condensation
(2) Beta hydroxy aldehyde or beta hydroxy ketone is the product of Aldol Condensation
Example of Aldol condensation reaction with two propanone (Ketones) and two ethanal (Aldehydes). |
(2)Cross Aldol Condensation
(1) When the use two different aldehydes or ketones reactions then we get Aldol Condensation this is called Cross Aldol Condensation.
(2) We get four products of the Cross Aldol Condensation
- But-2-enal
- 2-Methylpent-2-enal
- 2-Methylbut-2-enal
- Pent-2-enal
Example of cross aldol condensation reaction:- reaction between Benzaldehyde and Acetophenone
( FREQUENTLY ASK QUESTIONS) FAQ
On Aldol condensation and Cross Aldol condensation reaction with a mechanism
Question
What is Cross Aldol Condensation reaction?
Answer
When the use two different aldehydes or ketones reactions then we get Aldol Condensation this is called Cross Aldol Condensation.
Question
What is the ALDOL CONDENSATION reaction?
Answer
An addition reaction between two aldehydes, two ketones or one aldehyde and one ketone in which they have at least one alpha-hydrogen undergoes a reaction in the presence of dilute alkali ( alkali means:- any of the soluble hydroxides(–OH) of alkali metals like lithium, sodium, potassium, rubidium and caesium. Alkali are strong base like NaOH ) as catalyst ( catalyst mean it make a fast reaction or fast process of reaction by reagents like NaOH, etc.) to form beta-hydroxy aldehydes (aldol) or beta-hydroxy ketones (ketol), respectively. This is known as the Aldol reaction
The names Aldol is derived from the names of two functional groups aldehyde and alcohol, this group is present in the product side of the reaction.
The Aldol and ketol readily lose water to give alpha or beta-unsaturated carbonyl compounds [Carbonyl compounds are those compounds in which carbon double bonds with oxygen ( C=O) ] which are aldol condensation products and the reaction is called Aldol Condensation.
Question
Why do ketones apply in Aldol Condensation reaction?
Answer
Aldol Condensation also applies to the reaction of ketones due to ketones has similarity with Aldehyde
Question
What are Alpha Hydrogen and Alpha Carbon?
Answer
Carbon is attached or bonded with functional groups ( -C-C-functional group.
In which first carbon is made a bond with functional groups in the left or right side that carbon is known as Alpha carbon and 2nd carbon make a bond with Alpha carbon this is called beta carbon and it continues after this is called gamma carbon ), double and triple bond (-C-C-C-≡C-C-C- or -C-C-C=C-C-C- in this carbon bond with double or triple bond left or right side has alpha carbon) and bond or attach with a methyl group is called alpha carbon and hydrogen of alpha carbon is called Alpha hydrogen
Question
What is Cross Aldol Condensation? How many products form by this Cross Aldol condensation reaction?
Answer
When the use two different aldehydes or ketones reactions then we get Aldol Condensation this is called Cross Aldol Condensation.
If both of them (two different aldehydes Or ketones) contain alpha hydrogen atoms, it gives a mixture of four products.
Question
Explain Aldol condensation by mechanism.
Answer
Remove alpha hydrogen from the first component (like aldehyde or ketone) and breakdown of pi Bond of carbon double bond with oxygen (C=O) of the second component (like aldehyde or ketone) react in the presence of dilution NaOH to form beta hydroxy aldehydes (Aldol) or beta hydroxy ketones (ketol), respectively with water (H2O) and then heat provide to remove or release of water(H2O) from product side where Aldol or ketol present and then we get alpha or beta-unsaturated carbonyl compound (C=O) which are Aldol condensation products and this reaction is called Aldol Condensation
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