Aldol Addition and Condensation
CHEM 0345, Mondays 6:00-10:00 PM, Sam Kavoosi
Michael Hensler*
Kevin Dou
Date Performed: November 7, 2016
1
1.0 Experimental Goal
The goal of this lab was to experimentally demonstrate how reaction conditions influence
the outcome of aldol addition and aldol condensation reactions. The base-catalyzed addition of 2acetylpyridine to 4-nitrobenzaldehyde performed at room temperature and at 50°C showed the
kinetic (aldol addition) and thermodynamic (aldol condensation) control of this reaction using
identical substrates. The techniques used to achieve this goal were vacuum filtration, TLC plate
analysis, and IR spectroscopy.
2.0 Experimental Outline
Figure 1: Aldol Addition Reaction
Table 1: Reactant and Product Values and Properties1
Compound
MW
Density
Amount
Moles (mol)
MP/BP (°C)
(g/mol)
(g/mL)
2-acetylpyridine
121.139
1.08
0.58 g
0.00479
8-10/188-189
4-nitrobenzaldehyde
151.12
1.546
0.59 g
0.00390
103-106/300
Methanol
32.042
0.810
10.0 mL
0.253
-97.8/64.7
Na2CO3
105.989
2.54
20.0 mL
0.479
856/decomposes
H2O
18.02
1.00
40.0 mL
2.22
0/100
Aldol Addition
Product
272
N/A
4.96 g
0.0182
N/A
Figure 2: Aldol Condensation Reaction
2
Table 2: Reactant and Product Values and Properties1
Compound
MW
Density
Amount
Moles (mol)
MP/BP (°C)
(g/mol)
(g/mL)
2-acetylpyridine
Table 1
Table 1
0.51 g
0.00421
Table 1
4-nitrobenzaldehyde
Table 1
Table 1
0.59 g
0.00390
Table 1
Methanol
Table 1
Table 1
10.0 mL
0.253
Table 1
Na2CO3
Table 1
Table 1
20.0 mL
0.479
Table 1
H2O
Table 1
Table 1
40.0 mL
2.22
Table 1
Aldol Condensation
Product
254
N/A
2.71 g
0.0107
N/A
Figure 3: Aldol Reaction Mechanism
3.0 Experimental
Aldol Addition
0.58 g of 2-acetylpyridine was stirred with 40.0 mL of H2O in a round-bottom flask. Over
a steam bath was dissolved 0.59 g of 4-nitrobenzaldehyde in 10.0 mL of MeOH. The resulting
mixture and 20.0 mL of 0.54 % (w/v) Na2CO3 were added to the stirring 2-acetylpyridine and
H2O solution. After 60 minutes of stirring, the reaction was stopped. The solid was collected via
vacuum filtration and washed twice using 20 mL of water. After the product air-dried for 30
minutes, the addition product was measured to be 4.96 g.
3
Aldol Condensation
0.51 g of 2-acetylpyridine was stirred with 40.0 mL of H2O in a round-bottom flask. Over
a steam bath was dissolved 0.59 g of 4-nitrobenzaldehyde in 10.0 mL of MeOH. The resulting
mixture and 20.0 mL of 0.54 % (w/v) Na2CO3 were added to the stirring 2-acetylpyridine and
H2O solution. The reactor flask was heated to approximately 50°C in a heating mantle filled with
sand. After 60 minutes of stirring at 50°C, the reaction was stopped. The solid was collected via
vacuum filtration and washed twice using 20 mL of water. After the product air-dried for 30
minutes, the condensation product was measured to be 2.71g.
Product Characterization
After both products were weighed, TLC analysis was performed using both of the
products, as well as authentic samples of 2-acetylpyridine and 4-nitrobenzaldehyde. IR
spectroscopy was also performed on each of the products. Both analyses are shown in the Results
section and discussed in the Discussion section.
4.0 Results
Both the addition and condensation reactions had a milky-white appearance in the reactor
flask. The solid condensation product was yellow while the solid addition product was white.
Figure 4: TLC Plate
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Table 3: Rf Values
Component
Distance A (cm)
Distance B (cm)
Rf Calculation
Rf
2
0.4
6.7
= 0.4/6.7
0.06
2
3.1
6.7
= 3.1/6.7
0.46
4
2.8
6.7
= 2.8/6.7
0.42
CP
0.4
6.7
= 0.4/6.7
0.06
CP
1.5
6.7
= 1.5/6.7
0.22
CP
2.9
6.7
= 2.9/6.7
0.43
AP
0.4
6.7
= 0.4/6.7
0.06
Table 4: IR Spectroscopy Values for Addition Product
Wavenumber (cm-1)
Functional Group
Intensity
3322.36
O-H
broad, strong
Table 5: IR Spectroscopy Values for Condensation Product
Wavenumber (cm-1)
Functional Group
Intensity
1673.34
C=C
sharp, medium
Table 6: Yield of Aldol Reactions
Compound
Addition Product
Amount of
limiting reagent*
(mol 4-NBA)
0.00390
Theoretical Yield
(mol product)
Actual Yield
(mol product)
Percent Yield
0.00390
0.0182
467%
Condensation
0.00390
0.00390
0.0107
274%
Proudct
*In both the addition and condensation reactions, the 4-nitrobenzaldehyde is the limiting
reagent.
5.0 Discussion
The TLC analysis of both the aldol addition and condensation reactions suggest that
starting materials were not completely consumed. For the addition and condensation products, Rf
values of 0.06 aligned with the 2-acetylpyridine starting material, which thus suggests that 25
acetylpyridine may have been present in the final products. Additionally, for the condensation
product, the Rf value at 0.43 shows that 2-acetylpyridine and 4-nitrobenzaldehyde may have
been present in the final condensation product. The relative Rf values between the addition and
condensation products make sense. That is, the condensation product is expected to move up the
TLC plate more than the addition product. This is due to the fact that the addition product
possesses an -OH group that the condensation product does not possess, which makes the
addition product more polar. This higher polarity of the addition product therefore has more of
an attraction with the highly polar silica than does the condensation product, which allows it to
resist the mobile phase more than the condensation product.
There are two distinguishing factors between the IR spectra of the addition and
condensation products. The first defining characteristic is given by the strong, broad peak at
3322.36 cm-1 on the addition product spectrum, which denotes the formation of the secondary
alcohol. This peak is not present on the condensation product IR spectrum. Additionally, the
condensation product IR spectrum contains a peak at 1673.34 cm-1, which signals the formation
of the C=C double bond via the E1 elimination reaction.
As for the 1H NMR spectrums, there are 5 unique hydrogens in 2-acetylpyridine
(Spectrum A). Each of these unique hydrogens are summarized in Table 7 (Appendix A-1: 1H
NMR Spectra Peak Data) and labeled in the attached NMR spectrum. As shown in Table 7, Ha is
the most downfield hydrogen in 2-acetylpyridine and thus is the most deshielded. The reason this
hydrogen is the most downfield is because of the nearby N atom in the aromatic ring. Nitrogen is
an electronegative element and it thus draws electron density away from the nearby C-Ha bond.
As a result of this, the Ha hydrogen is highly deshielded. The Hd hydrogen, on the other hand,
does not have the strong, inductive withdrawing of electrons that Ha has and is thus more upfield
than Ha. It is important to note, though, that Hd is somewhat deshielded as a result of the
neighboring carbonyl group, which is weakly electron withdrawing. This puts a partial positive
charge on the C-Hd bond and allows for a slight deshielding of the Hd atom.
There are 3 unique hydrogens in p-nitrobenzaldehyde (Spectrum B). Each of these unique
hydrogens are summarized in Table 8 and labeled in the attached NMR spectrum. Hb is the more
downfield hydrogen relative to Ha. This is due to the two functional groups attached to the
aromatic ring. The nitro group is strongly electron withdrawing, which puts a strong negative
charge in the positions meta to the nitro group. Thus, the Ha atom is more upfield as a result of
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the shielding from the negative charge. The carbonyl group, on the other hand, is weakly electron
withdrawing. Thus, there is a weak negative charge in the positions meta to the carbonyl group.
The Hb atom is therefore more downfield since it is not as shielded by a negative charge as Ha.
The signal at 2.713 ppm of the 2-acetylpyridine compound can be used to determine if
there is any starting material in spectrums C and D. In both spectra, there is no peak at 2.713
ppm, which indicates that no methyl group is present. As a result of the methyl group not being
present, it can be concluded that there is not any unreacted 2-acetylpyridine in the two spectra.
As for the 4-nitrobenzaldehyde starting material, the signal at 10.163 ppm can be used to
determine if it is present in spectrums C and D. In both spectra, there is not peak at 10.163 ppm,
which indicates that the aldehydic hydrogen of the 4-nitrobenzaldehyde is not present. Thus, it
can be concluded that there is not any unreacted 4-nitrobenzaldehyde in the two spectra.
Each of the unique hydrogens for spectrums E and F are given by Tables 9 and 10,
respectively, and labeled in the attached NMR spectrum.
6.0 References
1. National Library of Medicine. PubChem Compound.
https://www.ncbi.nlm.nih.gov/pccompound (accessed Nov 14, 2016).
Appendix A-1: 1H NMR Spectra Peak Data
Table 7: 1H NMR Shifts of Spectrum A
Chemical Shift (ppm)
2.713
~7.450
~7.814
~8.020
~8.670
Corresponding H
He
Hb or Hc
Hb or Hc
Hd
Ha
Table 8: 1H NMR Shifts of Spectrum B
Chemical Shift (ppm)
~8.077
~8.399
10.163
Corresponding H
Ha and Hd
Hb and Hc
He
7
Table 9: 1H NMR Shifts of Spectrum E
Chemical Shift (ppm)
3.518-3.688
~4.709
~5.384
~7.545
~7.634
~7.903
~8.086
~8.237
~8.692
Corresponding H
Hc and Hd (overlapping)
Ha
Hb
Hg or Hj
He
Hg or Hj
Hi
Hf
Hh
Fragment
N/A
N/A
N/A
A
B
A
A
B
A
Table 10: 1H NMR Shifts of Spectrum F
Chemical Shift (ppm)
~7.532
7.853-7.953
~8.194
~8.269
~8.435
~8.762
Corresponding H
He or Hj
He or Hj, Hd, and Hf (overlapping)
Ha
Hg
Hb
Hc
8
Fragment
A
A and B
N/A
B
N/A
A