BRANDEIS UNIVERSITY
CHEMISTRY 29A
PRELAB WRITEUP AND EXPERIMENTAL REPORT SHEET
NAME Richard Fan______________ T.A.'S NAME
David Gay
__
___
___________
DATE 7/13/06 _____EXPERIMENT# __1___TITLE _NMR Spectroscopy / Nitration of Methyl Benzoate
PURPOSE _To obtain methyl-3-nitrobenzoate from a reaction of methyl benzoate with HNO3 / H2SO4______
PRELIMINARY WRITEUP:
Materials:
reaction tubes
Pipettes, beaker
0.2mL, 0.6mL H2SO4
0.3g methyl benzoate
0.2mL HNO3
0.2mL methanol
ice
Hirsch funnel, flash
Stirring rod
% yield = (experimental/theoretical) × 100%
Expected weightx = # of moles used × MWx
Methyl benzoate
MW 136.16
BP 199.6ºC
MP -12ºC
HNO3 (nitric acid)
MW 63.0
MP -42ºC
BP83ºC
Methyl-3-nitrobenzoate
MW 181.15
MP 78ºC
H2SO4 (sulfuric acid)
MW 98.18
MP 10ºC
BP337ºC
EXPERIMENTAL PROCEDURES*
(Include in preliminary writeup.)
-Add 0.6mL H2SO4 to reaction tube.
-Weigh 0.30g methyl benzoate, add to tube, keep on ice.
-Prepare mix of 0.2mL H2SO4 and 0.2mL HNO3 on ice.
-Add dropwise to reaction tube, on ice.
-Let mixture warm in room temperature water for 20-25
minutes. (Will become yellow viscous liquid)
-Weigh 2.5g of ice, pour mixture onto ice.
-Use vacuum filtration to isolate crude product.
-Wash with a few drops of ice cold methanol.
-Get crude weight, melting point.
-Recrystallize in minimal methanol.
-Vacuum filtration to isolate final product.
-Wash again with a few drops of water, and a few drops
of ice cold methanol.
-Get final weight, melting point, and infrared
spectroscopy.
MODIFICATIONS AND OBSERVATIONS*
(Obtained from the lab experience)
For this experiment, only 0.2966g of methyl benzoate could be
effectively weighed out due to the size of the drops added. After all
of the initial reactants had been added to the reaction tube, the
mixture had two layers which were evenly mixed together with a
stirring rod before the tube was placed in a water bath. The mixture
was removed from the room temperature water bath after carrying
out the reaction for 25 minutes. The reaction tube had no
noticeable increase in temperature upon removal from the water
bath. When this mixture was poured into a small beaker of ice, a
yellowish clumped precipitate formed. This was then poured onto a
filtered Hirsch funnel for vacuum filtration. The beaker was
washed with a small amount of cold methanol to ensure most of
the precipitate had been transferred. The crude product on the
Hirsch funnel appeared slightly yellow, but turned white as the last
of the beaker contents (with methanol) was transferred, and as it
was washed again with a few drops of methanol. The weight of the
crude product was 0.3764g, and the melting point was 64º-73ºC.
After dissolving in minimal methanol over heat and recrystallizing,
the final product weight was 0.3547, and the melting point was
76º-78ºC. There was no noticeable change in color of the product
after recrystallization, as the crude product was already very white
in appearance. See attached for IR spectroscopy.
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RESULTS, DISCUSSION AND CONCLUSIONS*
Before the reaction takes place in this experiment, two separate reagent mixtures are prepared: sulfuric acid / methyl benzoate,
and sulfuric acid / nitric acid. This is done to create the necessary reactive intermediates. As the sulfuric acid and methyl benzoate
mixture is prepared and set aside, a hydrogen ion bonds to the double bonded oxygen to create a protonated intermediate. The
sulfuric acid and nitric acid mixture creates the nitronium ion that then bonds to the protonated methyl benzoate intermediate at a
meta position to then form the final product. Since a total of 0.2966g, or about 2.2mmol, of methyl benzoate was used for the
reaction (0.2966g / 136.16g = 0.00218mol), about 2.2mmol (0.3946g) of methyl-3-nitrobenzoate is expected as the product
(0.00218mol × 181.15g). After the first vacuum filtration, the crude product weighed 0.3764, about a 95.4% yield. This crude
product also appeared very white in color, suggesting that it had relatively few impurities. Melting point analysis of this crude
product did indicate the presence of impurities however, due to the wide and depressed melting point (64º-73ºC) as compared to
the expected (78ºC). After recrystallizing in methanol and drying, the final product weighed 0.3547g, which was an expected but
reasonable decrease from the crude weight. This final product was a 89.9% yield of the expected amount. This decrease in weight
and percentage yield can probably be attributed to the loss of impurities and some product during the transfer, dissolving, and
final filtration processes of the product. The melting point of the final product was observed to be 76º-78º, which is a much
smaller range than that of the crude product and is much closer to the expected melting point. This showed that the final product
was indeed more purified than the crude product, even though the appearance (crystal color) of the final product was about the
same as that of the crude product. Infrared spectroscopy analysis of the final product shows the bonds of the product as well as the
bonds of the solvent methylene chloride (see labeled on attached IR spec). Accompanying peaks may be those of remaining
impurities in the final product. There was already a relatively high yield for this experiment, but it may be increased further by
careful transfer of the mixtures in the experiment, as well as careful addition of methanol. While methanol acts to remove
impurities, using large amounts to wash the product (especially if the methanol is not ice cold) may dissolve some of the product
and carry it away in solution.
ANSWERS TO END-OF-CHAPTER QUESTIONS*
1.
Methyl benzoate is able to dissolve in sulfuric acid due to their similar polar characteristics. Sulfuric acid is
very polar and has highly mobile protons, which help it as a solvent. Esters are normally not very polar, but
methyl benzoate has a very high boiling point (199.6ºC) suggesting that it is very polar as well. Together,
methyl benzoate is able to dissolve in sulfuric acid and produce the intermediate ions that can be used in the
nitration step of the experiment reaction.
2.
The dinitro structure may have the second nitro group on the number 5
position opposite to the first nitro group. This is due to the locations of
positive charge on the resonance forms of the aromatic ring. As the methyl
benzoate becomes protonated, electrons shift and change the locations of
double bonds, leaving resonance forms that have positions of positive
charge. The nitro group, having a positive charge, will only bond to the
meta positions on the ring, which are 3 and 5.
3. Unreacted methyl benzoate is removed from the product during the first vacuum filtration and again
during recrystallization and the second vacuum filtration. As the mixture was poured onto ice, the product
became a solid (melting point of 78ºC) but the unreacted methyl benzoate remained in solution (melting
point of -12ºC). The product is then removed from the solution by filtration. If any methyl benzoate
remained with the product, it was removed again in solution in methanol as the purified product
recrystallized and separated with filtration.
4. When examining the 1H NMR spectrum of methyl-3-nitrobenzoate, there are five main peaks. The peak
with 0 shift is most likely the solvent. The next lowest shift is around 3.9ppm and is the hydrogens attached
to the ester group. The three peaks with the highest shifts (from lowest to highest shift) are the hydrogen in
the para position, the ortho position opposite the nitro group, and finally the ortho position between the ester
and nitro groups.
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