Module code: NCHE 322

Experiment One: Aldol Reaction-

Condensation Reactions, aldol reaction

Abstract
The aim of the aldol condensation experiment was to introduce the concept of the
carbon-carbon bond formation reaction and to understand the basic mechanism of the
aldol condensation reaction. The aldol Condensation is an organic reaction in which
enolate ion reacts with a carbonyl compound to form β-hydroxy ketone or β-hydroxy
aldehyde followed by dehydration to give a conjugated enone. Aldol condensation plays
an important role in organic synthesis by creating a path to form carbon-carbon bonds.
In this experiment we performed a base catalyzed, condensation reaction using
benzaldehyde and acetone. An alpha, beta and unsaturated ketone are synthesized
using solvent-free conditions and the product is then purified through re-crystallization
we then characterize the product formed using NMR and FTIR, we also measure the
melting point range. From our experiment we obtained a mass of 0.8759 g and a
percentage yield for the synthesized products of 76.03 %. The melting range of the
substance was from 104- 107 ⁰C, this is lower than the melting point of pure
dibenzlacetone observed in literature indicating that the product had impurities. From
this information we can conclude that the experiment was performed successfully.
Introduction
The aldol condensation is an important synthetic method widely used in organic
chemistry, it is an organic reaction that was discovered independently by Russian
chemist Alexander Borodin in 1869 and by the French chemist in 1872 (Mestres.,2004).
Aldol condensation is a type of coupling reaction where an enol or enolate reacts with a
carbonyl compound to form a conjugated enone. The process occurs in two parts: an
aldol reaction, which forms an aldol product, and a dehydration reaction, which removes
water to form the final product. This reaction can be catalyzed by either a strong acid or
a strong base (Wagay et al.,2023:317-349).

All aldol condensation reaction involves the formation of new carbon-carbon bond
through the nucleophilic attack of a ketone enolate to an aldehyde to form a B-hydroxy
ketone, known as an aldol (aldehyde + alcohol). Claisen-Schmidt condensation reaction
is one type of many aldol condensation reactions that results in the formation of a
Carbon-Carbon bond between a single ester and one carbonyl compound or between
two esters. The reaction proceeds when a strong base such as sodium hydroxide NaOH
is present and the product of the reaction is a beta-keto ester or a beta-diketone (Carey
et al., 1977:33-71).
This reaction is named after Rainer Ludwig Claisen and J. Gustav Schmidt, who
independently published on this topic in 1880 and 1881 (Wagay et al.,2023:317-349).
The mechanism of the Claisen-Schmidt condensation reaction starts with the removal of
an alpha proton through the action of a strong base to result in the formation of an
enolate ion, this enolate anion is relatively stable due to the delocalization of the
negative charge (electrons). The carbonyl carbon belonging to the second ester
reactant is now the target of a nucleophilic attack from the enolate anion. This leads to
the elimination of the alkoxy group and the regeneration of the conjugate base of the
alcohol. This alkoxide ion removes the doubly alpha proton which is formed, giving rise
to a new enolate anion which is now resonance stabilized. An aqueous acid (phosphoric
acid or sulphuric acid, for example) is now added to neutralize the negative charge on
the enolate anion as well as any base which is still present. This leads to the formation
of a beta-diketone or a beta-keto ester, which is immediately isolated. The leaving group
is removed and therefore the ester (or carbonyl compound and ester) reactants are
converted into beta-keto esters or beta-diketones (Ouellette and Rawn., 2018:711-762).
For our experiment we conducted a Claisen-Schmidt condensation reaction for
preparation of dibenzalacetone to observe how aldol condensation reaction happens
and how every step of the reaction illustrates the mechanism of formation stated above.
Dibenzalacetone is used in sunscreens and sunblock preparations because of its
spectral properties (Lynch et al., 2021). Benzaldehyde, a non-a-hydrogen aromatic
compound, and acetone (ketone compound) are used as reactants. Sodium hydroxide
is used as strong base to catalyze the reaction. Ethanol is used as organic solvent to
dissolve the starting materials. Heat is required to speed up the processes of the
reaction.
Due to acetone having three hydrogens of its alpha-hydrogen carbon and benzaldehyde
does not, it's easier to be attacked by the base. Once acetone is deprotonated by the
base, it forms water molecule and an enolate which readily nucleophilic attack one
molecule of very reactive aldehyde carbonyl to form an alkoxide, then is protonated to
form a ᵦ-hydroxyketone followed by the dehydration/elimination (E2 reaction) by the
base catalyst to give an ester called enone and known as benzalacetone. E2 reaction is
multiple steps exothermic reaction (heat will be produced). The Claisen-Schmidt
reaction can also occur between two esters depending on the quantities of the reactants
in the presence of the strong base such as NaOH, as a result two moles of
benzaldehyde are required to form ẞ-diketone known as dibenzalacetone, because one
molecule of benzalacetone readily react with the other molecule of benzaldehyde. The
final product may exist in many conformation trans, trans, trans,cis, or cis,cis but the
major product is trans, this is because trans is the most stable conformation which
forms readily, two moles of water and sodium hydroxide are regenerated at the end of
the reactions as a result of protonation and deprotonation (Nielsen and
Houlihan.,2004:1-438).
We will use crystallization followed by vacuum filtration as a purification technique to
remove impurities or any basic filtrate crude from the product. Heating and cooling our
impure solid compound with solvent will initially create saturated solution that allow
crystals to form by decreasing its solubility (Shigehisa et al.,2005:5057-5065).

Results
Product produced from the experiment: Dibenzalacetone which is a solid yellow crystal
with a melting point of 104-107 ⁰C.
Percentage yield:
Density of benzaldehyde: 1.044 g/ml
mass
Density=
volume
Mass= density × volume
= 1.044 g/ml × 1 ml
= 1.044 g
Density of Acetone: 0.79 g/ml
mass
Density=
volume
Mass= density × volume
= 0.79 g/ml × 0.33 ml
= 0.2607 g
Acetone:
Molar mass( M r =58.08 g/mol)
m
n=
Mr

0.2607 g
=
58.08 g /mol
= 0.0045 mol
Benzaldehyde:
Molar mass( M r =106.12 g/mol)
m
n=
Mr

1.044 g
=
106.12 g /mol
= 0.0098 mol
From the reactions balanced equation, 2 moles benzaldehyde react with 1 mole
acetone. Therefore 0.0098 mol benzaldehyde will react with 0.0098 mol/2= 0.0049
moles of acetone.
But the available amount of acetone is 0.0045 mole. Hence acetone is the limiting
reagent: n benzalacetone = 0.0045 mol
By using the limiting reagents moles and molar mass of product, yield can be
determined as:
Molar mass( M r ¿of dibenzalacetone: 234.29 g/mol

Mass= M r × n
Mass = 234.29 g/mol × 0.0049 mol
Mass = 1.152 g
Theoretical yield of dibenzalacetone = 1.152 g
Mass of filter paper= 1.5320 g
Mass of dibenzalacetone = (mass of filter paper + mass of crystal) - mass of filter paper
= 2.4079 g – 1.5320 g
= 0.8759 g

Actual yield
% yield = × 100
Theoretical yield
0.8759 g
= × 100
1.152 g
= 76.03 %
NMR and FTIR spectra for product:
Figure 1.1: ¹³C NMR spectrum of dibenzalacetone
Figure 1.2: ¹H-NMR structure of dibenzylacetone
 Figure 1.3: FTIR spectrum of dibenzalacetone

Discussion
From the FTIR spectra above, there is a peak at 3100 – 3000 cm−1 indicating the
presence of olefins, there is a peak at 1600 - 1575 cm−1 indicating the presence of an
aromatic ring, there is also a small peak at 1715 cm−1indicating the presence of a ketone
functional group. From the ¹H NMR diagram, peaks are observed in the aliphatic region
(8.0-7.0 ppm) belonging to the aromatic rings. From the ¹³C NMR spectra, there are
peaks at 140-120 ppm indicating the presence of an aromatic ring and olefins (C-C
double bond). From the NMR and FTIR spectra the information indicates that the
product synthesized could be dibenzalacetone.

A percentage yield of 76.03 % indicates that we obtained a good yield. The boiling point
of pure dibenzalacetone is 110 – 111 ⁰C, the one we obtained from the lab was 104-107
⁰C (377.15 – 380.15 K), this lowered melting point is due to the presence of impurities in
the synthesized product. The presence of even a small amount of impurity lowers the
compound’s melting point by a few degrees and broadens the melting point temperature
range, this is because the impurity causes defects in the crystalline lattice, in that way it
is easier to overcome the intermolecular interactions between the molecules
(Brittain.,2016).

Recrystallization is a technique used to purify solid compounds, it is useful in that it

reduces the amount of impurities in the synthesized product. But the impurities in
dibenzalacetone are difficult to remove (Halpani and Mishra.,2020:152-175). Some of
the errors that may have led to a lower yield being measured include, using too much
solvent (ethanol and water) to dissolve the sample during recrystallization and not
chilling the ethanol enough. Adding too much solvent ruins the crystallization of the
product.

The use of toxic and expensive reagents, low yields, long reaction times and formation
of a mixture of products are among the drawbacks of the Claisen-Schmidt reaction. A
study was conducted on Zr(HSO4)4/SiO2as an Efficient Alternative Catalyst for the
Claisen-Schmidt Condensation (Mirjalilia et al., 2008:1421-1424). In this study it was
shown that Zr(HSO4)4/SiO2 promotes the regio-, stereo- and chemoselective Claisen-
Schmidt condensation of aromatic aldehydes with ketones under solvent-free conditions
with improved yields. The work-up of the reaction mixture is simple, and the catalyst is
easily removed from the products by simple filtration.
Researchers also found an efficient and selective microwave-assisted Claisen-Schmidt
reaction for the synthesis of functionalized benzalacetones (Rayar et al, 2015:1-5). It is a
simple and direct method for the Claisen-Schmidt reaction to prepare functionalized α,
β-unsaturated ketones have been developed. Microwave irradiation of aldehydes with
acetone produces benzalacetones selectively without self-condensation product in very
short reaction times and good yields.
Experimental
An ice water bath for recrystallization was prepared. 1.0mL of benzaldehyde (PhCOH)
was combined with 0.33mL of acetone (CH3COCH3), 2.0mL of 5M aqueous sodium
hydroxide solution and 10mL of ethanol (CH3CH2OH) into a reaction tube and that tube
was capped. The amount of all starting materials was recorded. Every few minutes the
tube was shook for a total of 30 minutes.
After that time period, the liquid was removed from the crystals using a pipette. 10mL of
water was added and tube was shaken. Water was removed with a pipette and the tube
was washed two more times. The crystals were collected using vacuum filtration. The
crystals were recrystallized using ethanol. The solution was cooled down to room
temperature. The reaction tube was placed in ice water bath. The crystals were vacuum
filtered and washed with cold solution of ethanol/water (70:30). The crystals were then
dried and weighed and the melting point was taken and the percentage yield was
reported.
Conclusion
In this experiment, a solid yellow crystal was obtained that was found to be
dibenzalacetone when using ftir spectrum and literature of aldol condensation reaction.
The melting point of the synthesized dibenzalacetone was lowered by the presence of
impurities. The aim of this experiment was to prepare the organic compound
dibenzalacetone from benzaldehyde and acetone in the presence of sodium hydroxide.
We were able to obtain a mass of 0.8759 g and a percentage yield of 76.03 %. From
the results obtained the aim of the experiment was achieved in a manner that agrees
with literature from other researchers. To this end the experiment was successful.
References
Brittain, C.G., 2016. Using melting point to determine purity of crystalline solids.
Carey, F.A., Sundberg, R.J., Carey, F.A. and Sundberg, R.J., 1977. Reactions of
Nucleophilic Carbon Species with Carbonyl Groups. Advanced Organic Chemistry: Part
B: Reactions and Synthesis, pp.33-71.
Halpani, C.G. and Mishra, S., 2020. Lewis acid catalyst system for Claisen-Schmidt
reaction under solvent free condition. Tetrahedron Letters, 61(31), p.152-175.
Lynch, H.N., Harnage, A.H. and Liyana Pathiranage, A., 2021. Gas Chromatography–
Mass Spectrometric Analysis of Derivatives of Dibenzalacetone Aldol Products. Journal
of Chemical Education, 98(11), pp.3572-3579.
Mestres, R., 2004. A green look at the aldol reaction. Green Chemistry, 6(12), pp.583-
603.
Mirjalilia, B.B.F., Bamoniri, A., Alipour, M. and Zarchia, M.A.K., 2008. Zr (HSO4) 4/SiO2
as an efficient alternative catalyst for the Claisen-Schmidt condensation. Zeitschrift für
Naturforschung B, 63(12), pp.1421-1424.

Nielsen, A.T. and Houlihan, W.J., 2004. The aldol condensation. Organic reactions, 16,
pp.1-438.

Nolen, S.A., Liotta, C.L., Eckert, C.A. and Gläser, R., 2003. The catalytic opportunities
of near-critical water: a benign medium for conventionally acid and base catalyzed
condensations for organic synthesis. Green Chemistry, 5(5), pp.663-669.

Ouellette, R.J. and Rawn, J.D., 2018. Condensation reactions of carbonyl

compounds. Organic Chemistry. Elsevier, pp.711-762.
Rayar, A., Veitía, M.S.I. and Ferroud, C., 2015. An efficient and selective microwave-
assisted Claisen-Schmidt reaction for the synthesis of functionalized
benzalacetones. SpringerPlus, 4(1), pp.1-5.
Shigehisa, H., Mizutani, T., Tosaki, S.Y., Ohshima, T. and Shibasaki, M., 2005. Formal
total synthesis of (+)-wortmannin using catalytic asymmetric intramolecular aldol
condensation reaction. Tetrahedron, 61(21), pp.5057-5065.
Wagay, Shafieq Ahmad, Ishfaq Ahmad Rather, and Rashid Ali. "Unraveling the potential
role of green chemistry in carrying out typical condensation reactions of organic
chemistry." In Nanoparticles in Green Organic Synthesis, pp. 317-349. Elsevier, 2023.