ALDOL CONDENSATION

OBJECTIVE

• To synthesize α,β-unsaturated ketone from an aldehyde and ketone

• To purify product through recrystallization.• To identify and analyze purity through tlc and

melting point analysis• To analyze the product using IR spectrum

Dibenzalacetone

• It consist of two aromatic rings with unsaturated chain

• Many biological activities have been attributed to this group.

• such as,1. Anticancer2. Antioxidant3. Antifungal4. Anti-inflammatory5. Antibacterial6. Antimicrobial

O

Techniques

• TLC analysis• Recrystallization• Melting point analysis

Introduction

• Aldol condensations are nucleophilic additions of an enolate ion,which are strong nucleophiles, to another C=O group under basic conditions

• Protonation gives the aldol product• Abstration of a proton gives an

enolate that can expel an -OH ion to give a conjugate product

• Dehydration is usually exothermic because it leads to a very stable conjugated product.

R

HC

CH

CH3

O

CHEMICAL EQUATIONO

H

+ H3C CH3

O

CH3

O

NaOH

Benzaldehyde Acetone Aldol Product

O

H

+H3C

O

CH3

O

2

Benzaldehydeacetone

Dibenzalacetone

NaOH

Mechanism

• H3C CH2

O

H

H3C CH2

O

H3C

O

CH2+ H2O

C

H

O

+ H2C CH2

OC

CH2

O

H O

CH3

H OH

OH

HC

H

H O

CH3

NaOH

+

H2O+

+H2O

C

OH

CH

H O

CH3

+ H2O

AcetoneFormation of enolate

Addition of enolate protonation of alkoxide

deprotonation of a-carbon Elimination of hydroxide

C

OH

CH

HO

H3C

Elimination of hydroxide

C

H O

CH3

a,b-unsaturated ketone

C

H O

CH3

a,b-unsaturated ketone

+

O

HNaOH

O

Dibenzalacetone

General Aldol Condensation

• Aldol condensation reaction is carried out in an organic solvent,such as ethanol

• Isolation of the product requires a much more involved workup

• Another challenge is that solution phase reaction is reversible,so low product yield may result.

Experimental Procedure

• Place aldehyde and ethanol in Erlenmeyer flask

• Stir the mixture • Slowly add 6M NaOH• Add acetone in the

last.• Continue to react for

15 minutes at room temperature

Purification and product isolation• Filter the precipitate

through suction filtration.

• Wash precipitate with mixture of 4% acetic acid and 95% ethanol.

• Recrystallize crude product in hot ethanol.

• Collect the purified solid and allow it to dry.

• determine the melting point.

• Obtain final product mass and calculate % yield

TABLE 1

theoretical yield (g)

4-(4-nitrophenyl)-3-buten-2-one

1,5-bis(phenyl)-1,4-pentadien-3-one

1,5-bis(4-nitrophenyl)-1,4-pentadien-3-one

1,5-bis(2-hydroxyphenyl)-1,4-pentadien-3-one

1,5-bis(4-methoxyphenyl)-1,4-pentadien-3-one

Actual yield(g)

1.7 1.7 5 4.5 2.5

% yield 89 30 92 81 49.5

Melting range( C) ͦͦͦͦͦͦ

110-112 110-111 128

Product appearance

black solid light yellow solid

brownish-black solid

blackish green solid yellow solid

Table 2

CompoundTLC Rf value

refernce

TLC Rf value

product

4-(4-nitrophenyl)-3-buten-2-one

0.88 0.69

1,5-bis(phenyl)-1,4-pentadien-3-one

0.38 0.5

1,5-bis(4-nitrophenyl)-1,4-pentadien-3-one

0.44 0.26

1,5-bis(2-hydroxyphenyl)-1,4-pentadien-3-one

0.6 0.19

1,5-bis(4-methoxyphenyl)-1,4-pentadien-3-one

0.5 0.4

IR SPECTRUMFunctional Group

Base Values(cm-1)

4-(4-nitrophenyl)-3-buten-2-one

1,5-bis(phenyl)-1,4-pentadien-3-one

1,5-bis(4-nitrophenyl)-1,4-pentadien-3-one

1,5-bis(2-hydroxyphenyl)-1,4pentadien-3-one

1,5-bis(4-methoxyphenyl)-1,4-pentadien-3-one

sp3 CH Stretch

2800-3000

sp2CH stretch

3000-3100

C=O Stretch

1680-1740

Aromatic C=C Stretch

1500-1600

C-O Stretch

1000-1200

Aldehyde CH stretch

2700-2800