Answer:

When an aldehyde (or a ketone) having alpha hydrogen atom is treated with dilute BASE NaOH, KOH or sodium carbonate, two molecules of aldehyde ( or ketone) ADD together to form β hydroxy aldehyde (aldol) or β hydroxy ketone (ketol). New C−C BOND is formed in this reaction.

When aldol or ketol is heated in presence of an acid, a molecule of water is lost and α−β unsaturated aldehyde or α−β unsaturated ketone is formed.

Aldol condensation of ETHANAL:

2CH

3

−CHO

dil NaOH

CH

3

−CHOH−CH

2

−CHO

H

+

Δ

CH

3

−CH=CH−CHO+H

2

O

Aldol condensation of propanone:

2(CH

3

)

2

CO

dil NaOH

(CH

3

)

2

C−OH−CH

2

−CO−CH

3

H

+

Δ

(CH

3

)

2

C=CH−CO−CH

3

+H

2

O

Explanation:

When an aldehyde (or a ketone) having alpha hydrogen atom is treated with dilute base NaOH, KOH or sodium carbonate, two molecules of aldehyde ( or ketone) add together to form β hydroxy aldehyde (aldol) or β hydroxy ketone (ketol). New C−C bond is formed in this reaction.

When aldol or ketol is heated in presence of an acid, a molecule of water is lost and α−β unsaturated aldehyde or α−β unsaturated ketone is formed.

Aldol condensation of ethanal:

2CH

3

−CHO

dil NaOH

CH

3

−CHOH−CH

2

−CHO

H

+

Δ

CH

3

−CH=CH−CHO+H

2

O

Aldol condensation of propanone:

2(CH

3

)

2

CO

dil NaOH

(CH

3

)

2

C−OH−CH

2

−CO−CH

3

H

+

Δ

(CH

3

)

2

C=CH−CO−CH

3

+H

2

O