explain the mechanism of aldol condensation using ethanol
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Answer:
Mechanism of Aldol Condensation
Step-1:
In reverse order, The hydroxide ion deprotonates the aldehyde.
Mechanism of Aldol Condensation
Step-2:
Here Enolate ion 1 adds to the unreacted aldehyde.
Enolate ion 1 adds to the unreacted aldehyde
Step-3:
Alkoxide ion 2 is protonated by water.
Alkoxide ion 2 is protonated by water
Step-4:
A small amount of aldol is converted into enolate ion (4) by hydroxide ion.
aldol converted into enolate ion (4) by hydroxide ion
Step-5:
Here Enolate Ion(4) loses a hydroxide ion.
Enolate Ion(4) loses a hydroxide ion
Step 1 to step 3 illustrates the aldol reaction.
Crossed Aldol Condensation
The condensation reaction between two different molecules of an aldehyde or ketone in a protic solvent such as water or alcohol constitutes the crossed aldol reaction. When condensation is between two different carbonyl compounds, it is called crossed aldol condensation. When both aldehydes have alpha hydrogens, both can form carbanions and can also act as carbanion acceptors. Hence a mixture of four products is formed which has little synthetic value.
If one of the aldehydes has no alpha hydrogen then it can act only as a carbanion acceptor. In such a case, only two products are formed. A common substrate for the crossed aldol reaction is an aromatic aldehyde, which has no alpha position. Furthermore, dehydration of the initial condensation product is rapid which leads to the formation of the α, β – unsaturated ketone and prevents the retro-aldol reaction from taking place.
Crossed Aldol Condensation
Types of Condensation
It is important to differentiate aldol condensation from various reactions of carbonyl compounds.
In a case of Perkin reaction, enolate generated by anhydride is aromatic.
A Claisen condensation contains two ester compounds.
A Henry reaction contains an aliphatic nitro compound and an aldehyde.
Dieckmann condensation contains 2 ester groups present in the same molecule, which produces cyclic molecule.
In Japp–Maitland condensation, water is removed by nucleophilic displacement
Aldol condensation is an organic reaction in which an enolate ion reacts with carboxyl compound in order to form a β– hydroxyaldehyde or β– hydroxyketone. ... This reaction can be seen as an acid-base reaction. The aldehyde is attacked at the electrophilic carbonyl carbon by the nucleophilic enolate ion.