BRANDEIS UNIVERSITY
CHEMISTRY 29A
PRELAB WRITEUP AND EXPERIMENTAL REPORT SHEET
NAME Richard Fan______________ T.A.'S NAME
David Gay_______________________________
DATE 8/1/06________EXPERIMENT# ___7___TITLE ___Fischer Esterification_____________________
PURPOSE Synthesizing an ester using Fischer esterification with a carboxylic acid and an alcohol__________
PRELIMINARY WRITEUP:
Materials:
0.6g acetic acid
1.3g 1-octanol
0.2g Dowex
Apparatus
Sandbath, reaction tubes, pipettes
syringe
%yield = experimental/theoretical × 100%
theoretical yield = weight9-anthraldehyde/MW9-anthraldehyde ×
MWfinal product
Acetic acid
MW 60
1-octanol
MW 130
Octyl acetate
MW 172
BP 210ºC
O
O
R C OH
+
R'
R C O R' + H2O
OH
EXPERIMENTAL PROCEDURES*
(Include in preliminary writeup.)
-Place sandbath on jackstand, set to 3-4.
-Set up apparatus as shown.
-Fill long neck flask with 0.2g Dowex.
-Add 0.01mol of carboxylic acid and 0.01mol of alcohol of
chosen ester into flask.
-Tilt apparatus to allow water to collect in sidearm.
-Use syringe to remove water from sidearm as mixture
refluxes.
-Run the reaction for 45-60 minutes.
-Pour any organic layer from sidearm back into pot.
-Obtain boiling point and infrared spectrum for final
product.
-Obtain weight of final product.
MODIFICATIONS AND OBSERVATIONS*
(Obtained from the lab experience)
This experiment was restarted partway through the reaction process.
Condensation and collection of water in the sidearm was originally
very slow, so the heat was slowly increased to try to speed up the
reaction. As this was done, the mixture began “popping” more, as in
the case of becoming superheated. As this popping occurred, the
mixture and Dowex were pushed into the sidearm, and eventually
completely out of the apparatus. Further observations are from the
second trial of the experiment. The chosen ester was octyl acetate,
with the fragrance of orange. The reagents used for this ester were
acetic acid and 1-octanol, which originally had a strong metallic
smell. The procedure asks for the use of 0.01mol of each of these
reagents, which were 0.6g acetic and 1.3g 1-octanol. These were
calculated from multiplying the moles needed by their molecular
weights, 60g and 130g, respectively. The mixture of acetic acid, 1octanol, and Dowex (catalyst) were refluxed over heat with boiling
chips. Care was taken in this second trial to heat the mixture lightly,
as heavy heating would cause the liquid to “pop.” The vapor of the
boiling mixture moved upward along the apparatus very slowly, and
eventually stayed around the sidearm section. This contributed to the
difficulty of obtaining the condensed water. After approximately 50
minutes, no more water was appearing in the sidearm, and the reaction
was stopped. The mixture in the pot was removed and an IR spectrum
was obtained (see attached), as well as a boiling point for the solution.
The weight of this final solution was 0.9657g, and the boiling point
was 193ºC.
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RESULTS, DISCUSSION AND CONCLUSIONS*
This experiment demonstrated the Fischer esterification reaction of an acid with an alcohol to produce an ester. The ester chosen
for this was octyl acetate, which has the fragrance of orange. The reagents used for this esterification reaction were equal amounts
(0.01mol of each) acetic acid and 1-octanol. The actual weights of the reagents used were calculated from multiplying 0.01mol by
their respective molecular weights to obtain the weight that should be used. These amounts were added to the reaction mixture
along with 0.2g of Dowex, which acts as the acid catalyst in place of sulfuric acid. This makes it simpler to separate the final
aqueous product from the acid at the end of the reaction. The initial trial of the reaction was ruined because attempted rapid
heating of the mixture resulted in superheating that pushed a portion of the mixture out of the apparatus. Slower and steady
heating was used in the second trial to ensure stable movement of the vapor inside of the apparatus. While this vapor region
should have been kept in the middle of the top section of tubing in the apparatus, it mostly did not move any higher than the
sidearm section of the apparatus. This may have been due to the large size of the octyl acetate molecule, which hinders its
vaporization and movement up the apparatus. During the reaction, the hydroxyl group on acetic acid attacks a proton from the
acid catalyst, resulting in the removal of a molecule of water. The resulting positive 2º carbon is attacked by the hydroxyl group
of 1-octanol, and the final octyl acetate results after a proton is pushed out of the hydroxyl group of 1-octanol. Since 0.01 moles
of each reagent were used, 0.01 moles of final product should be expected. The molecular weight of the product, octyl acetate, is
172, so the expected final weight should be about 1.72g. The experimental yield of this product however was only 0.9657g, which
was a 56% yield. This relatively low yield may be due to an incomplete reaction as much of the Dowex stuck to the roof of the
flask during reflux. It is not likely that product was lost to the sidearm because not organic layer was seen in the water removed,
and it was likely too heavy to move high up the apparatus. The experimental boiling point of the final product was 193ºC, which
was lower than the expected value of 210ºC for octyl acetate, which indicates the impurity of the product. The IR spectrum
supports this by showing the expected bonds of the product (C-H, C-O, and C=O), but shows other peaks as well, including a
large O-H stretch that may be from water or starting material (OH from acetic acid and 1-octanol).
ANSWERS TO END-OF-CHAPTER QUESTIONS*
Chp40, #2 – The three shifts at 8.0ppm, 7.5ppm, and 7.4ppm represent the three different CH groups
attached to the benzene ring of methyl benzoate. The two larger shifts are those of the two groups each
containing two CH. The smaller shift at 7.5ppm is that of the group containing only one CH on the ring. The
large shift at 3.8ppm is the CH3 group on the end of the COOCH3 substituent.
- The advantage of using Dowex over sulfuric acid is primarily that the former can be removed much
more easily after the completion of the reaction. Dowex contains sulfonic acid groups attached to some
of the phenyl groups, which would react similarly to sulfuric acid. Due to its bead shape however, it can
simply be filtered from the solution after it has been used.
- The NMR may be that of a propane with an ester group.
Predicted NMR (1H) for octyl acetate:
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