2. I. INTRODUCTION
Esters, were a type of organic compound that were responsible for the fragrance and flavor of
flowers and fruits. For example, were the isopentyl acetate in bananas,methyl salicylate in wintergreen,
and ethyl butyrate in pineapples. Thus, esters were also commonly used in the production of synthetic
flavors, perfumes, and cosmetics. Moreover, other volatile esters were also used as solvents for
lacquers, paints, and varnishes. It is commonly prepared by a simple reaction of carboxylic acids and
alcohol in the presence of a catalyst usually hydrochloric acid or sulfuric acid in a process called Fisher
Esterification.
Figure 1. General reaction of esterification
The general reaction esterification involved the substitution reaction of the –OH substituent in
the carboxylic acid and of the Alkyl group in the alcohol to form ester and water as shown in figure 1.
The presence of sulfuric acid allowed the reaction to go faster since the Fisher-Esterification reaction
had a slow rate of reaction at room temperature. In addition to this, it was also refluxed to increase the
rate of reaction in a short span of time. This allowed the formation of ester faster without the loss of its
volatile reactants and prouct. An example of the Fisher Esterification reaction was shown below.
Figure 2. An example reaction of an alcohol and a carboxylic acid to form an ester.
However, the esterification reaction is reversible thus one of the reactants should in excess to
ensure the reaction favors the product formation. On the other hand, the formation of water in this
reaction allowed the reaction of the formed ester back to carboxylic acid. This could resulted to low
percentage yield of the desired ester. Thus, it was noted that the reaction should as much as possible
favor the production of the ester. It is then distilled to remove the ester from the unwanted by-products
which would resulted to a more pure ester.
3. II. MATERIAL
NOTE: The organic liquids used are very flammable. Do not use an open flame
to heat samples. Hot plates will be provided.
III.PROCEDURE
The assigned alcohol was methyl alcohol and the assigned carboxylic acid was butyric acid. Based on
the general reaction of esterification the ester product was Methyl butyrate with a given reaction below.
Figure 3. Reaction of butyric acid and methyl alcohol to form methyl butyrate
First was that the amount of butyric acid and methanol based on their respective moles, 0.50
for the butyric acid and 0.65 moles of the methyl alcohol, and their densities. The densities of methanol
and butyric acid were 0.791 g/mL and 0.964 g/mL respectively. Their volume was then measured using
two different graduated cylinder to minimize error. The same was also done to measure the amount of
concentrated sulfuric acid needed in the experiment. Second, the theoretical yield of methyl butyrate
was calculated based on the limiting reactant present which was the carboxylic acid and later the %
yield of the ester was calculated.
Next, in a 125-mL flat bottom flask, 0.65 moles (26.33 mL) of methyl alcohol was mixed with
0.50 moles (45.70 mL) of butyric acid and 8 g (4.35 mL) of concentrated sulfuric acid. The addition of
concentrated sulfuric acid was done inside the fume hood for safety purposes. Meanwhile, the reflux
set-up was prepared carefully. The general simple setup of the reflux system was shown below. It was
4. securely fastened at the iron stand with the iron ring, Bunsen burner, and the wire gauze secured at the
bottom of the flask.
Figure 4. Reflux Set-up
After mixing the reactants and the acid catalyst, the flat bottom flask was placed in the fully
prepared reflux set-up. After the go signal was given by the instructor, the reflux was done for 30
minutes. Next, after 30 minutes the reflux set-up was rearranged for distillation set-up.
Figure 5. The simple distillation set-up
The thermometer’s bulb was placed near the pathway towards the condenser. The distillation
started when the approval of the instructor was given. The temperature reading in the thermometer was
noted and critically monitored in order to avoid the distillation of alcohol in the solution. Once 10 drops
5. of the distillate was produced it was tested with 1 mL of water to correctly identify if it is ester if a layer
in the waterwasobserved to form. Once the distillate is validated to be anester,the temperature reading
of the thermometer was manually controlled in order for the temperature to remain in the approved
temperature. This allowed the distillation of the desired ester. During this time, the color of the ester
was observed alongside with its odor. After all of the available ester was distilled, it was checked for
its pH using litmus paper and was neutralized with 6M of NaOH. Once neutralized the formed ester
was checked for purity. The purity was checked using 5 drops of ester and mixed with 5 drops of
potassium dichromate and 2 drops of concentrated sulfuric acid in a warm bath. Once the color of the
sample changed after sometime the formed ester contains impurities otherwise if not.
GUIDE QUESTION:
1. How does Schotten-Baumann reaction differ from Fisher reaction? Write a
mechanism for the former.
ANSWER: The Schotten-Baumann reaction is an organic reaction used to convert an
acyl halide or anhydride to an amide if reacted with an amine and base, or an ester if reacted
with an alcohol and base. The reaction with the amine begins with the nitrogen attacking the
carbonyl carbon of the acyl halide which rearranges to kick out the halide. Deprotonation
with the base then provides the final amide product. The reaction with the alcohol would
happen in a similar fashion.
6. While the Fischer esterification is an organic reaction used to convert a carboxylic acid and
an alcohol to an ester using an acid catalyst. The mechanism begins with protonation of the
carbonyl group of the carboxylic acid, which is then attacked by the alcohol. Proton transfer
and the subsequent release of water result in an oxonium ion intermediate. A final
deprotonation step provides the ester product.
2) What is the function of the sulfuric acid in this reaction? Is it consumed in the reaction?
ANSWER: Sulfuric acid is used as a catalyst for this reaction in order to accelerate the rate at
which the product is formed. Since a catalyst is not consumed during the course of a reaction, you
need to use only a small amount of sulphuric acid in order for it to be effective.
7. 3. What is the purpose of adding 5% sodium bicarbonate to the oil?
ANSWER: Sodium bicarbonate removes the remaining acid from the catalyst which helps in
the removal of esters (Tremble, 2014)
4) Why was 5% sodium bicarbonate used in the extraction? What would have happened if 5% sodium
hydroxide had been used? What do you call this undesirable reaction?
ANSWER:5% sodium bicarbonate is used in the extraction to neutralise the acid present.
When adding sodium bicarbonate, the carbon dioxide will form and will cause a pressure build up.
(Williams.2017)
5) Give the purpose of washing the organic layer with saturated sodium chloride.
ANSWER: Washing the organic layer with sodium carbonate helps to decrease the solubility
of the organic layer into the aqueous layer. This allows the organic layer to be separated more easily.
If the organic and aqueous layer are in a homogenous mixture (one in which the solvents are
uniformly dispersed), then sodium carbonate can be effective in separating the two layers.
(Williams.2017)
6) Enumerate some of the common drying agents and identify how each can be advantageous to the
others.
ANSWERS:
Calcium chloride is a very good drying agent for a broad variety of solvents but is
generally not compatible with hydroxy (alcohol, phenol), amino (amine, amide) and
carbonyl (acid, ketone, ester) functions due to basic impurities such as Ca(OH)2 and
CaCl(OH). In addition, it tends to form adducts with some of those compounds as
well. It is often used in drying tubes because it also is available in granular form.
Calcium sulfate is a neutral and good drying agent. However,it does not have a high
capacity, which makes it useless for very wet solutions. The commercially available
Drierite® contains about 2 % cobalt chloride as indicator, which can be leached out
into various solvents i.e. ethanol, DMSO, DMF, ethers, etc. Drierite is often used in
desiccators. If the compound is pink, the water can be removed by heating the
compound to 210 oC for an hour.
Magnesium sulfate is a slightly acidic drying agent. It works well in solvents like
diethyl ether, but not as well for ethyl acetate. It is a fast drying agent, in part because
it comes as a fine powder with a large surface area.
8. Sodium sulfate has a very high capacity and is mainly used for very wet solutions. It
is very efficient in etherealsolutions, but it also absorbs other polar compounds like
alcohols, etc. In addition, it is slower compared to magnesium sulfate, etc.
Potassium hydroxide and Potassium carbonate are both of basic nature and often
used to dry basic solutions containing amines. They cannot be used to dry acidic
compounds since they react with them.
Sulfuric acid and Phosphorous pentoxide are both acidic drying agents that are
mainly used in desiccators and not in direct contact with the solution since they are very
aggressive reagents. Both have a very high capacity. Sulfuric acid forms hydrates while
phosphorous pentoxide is ultimately converted into phosphoric acid.
Molecular sieves are aluminosilicates with a three-dimensional network with different
pore sizes (3-5 Å). They have to be activated prior use and also can be regenerated at
higher temperatures (~180 oC - 260 oC, 1-2 hours).
7) Rank the following according to ease of esterification with methanol: acetic acid, carbolic acid,
benzoic acid, and salicylic acid.
ANSWER: ➔ Acetic acid – Carbolic acid – Salicylic acid – Benzoic acid
Presentation of Results
When 26.33 mL of methyl alcohol and 45.70 mL wasmixed with 4.35 mL concentratedsulfuric
acid, it produced a colorless and transparent solution. Moreover, upon the addition of the concentrated
sulfric acid, the reaction was observed to be exothermic. It was then boiled for 30 minutes in a round
bottom flask and reflux condenser. It was observed that the vapour that tied to escape was turned into
vapor once it reached the reflux condenser which returned to the solution below it. This allowed the
formation of ester without the loss of reactants and of the products. After 30 minutes of reflux the odor
of the methyl butyrate was examined. Initially, the odor of the ester was observed to be rubber-like in a
very concentrated solution. However, once analysed futher of its odor, it was clear that it has a strong
odor and very pungent. After reflux, the whole set-up was changed to distillation set-up. The set-up was
fitted loosely to avoid the build-up of pressure in the glassware which would result to explosion if fitted
tightly. The thermometer bulb was placed near the output that goes to the condenser which would help
the temperature of the vapor monitored. It was then distilled in a temperature of 90 degrees Celsius, the
distillate was then tested in water. Once a layer was observed to form, the distillation was then made
constant around the temperature range of 90 - 92 degrees Celsius. Once nearly all of the solution was
distilled leaving only a small liquid in the flask, its volume was then calculated to be around 25 mL.
9. Before the experiment started, the theoretical yield was calculated to be 56.87 mL. Upon
calculation, the yield was only 56.04%. However, the ester was not fully recovered because the liquid
present in the flask was small and the distillation was not safe if it will be continued. Moreover, the
reaction also failed to shift to the right, favoring the production of the ester,or the given reactants were
not pure, or it is due to the presence of water in the solution that reacted with the ester present that
transformed it back to carboxylic acid. Afterwards,it was then neutralized using 6M NaOH and its pH
wastestedin litmus paper.The solution is declared asneutralized if the blue and red limus paper refused
to change in color. Lastly, the purity of the ester was checked with 5 drops of the sample mixed with 5
drops of potassium dichromate and 2 drops of 6M sulfuric acid in a small vial and heated in a warm
bath. The color of the solution once the 5 drops of potassium dichromate was added was yellow and
after several minutes, the color of the solution was still yellow.
Reactant Volume used Moles Density
Alcohol (Methyl
Alcohol/ Methanol)
26.33 mL 0.65 moles 0.791 g/mL
Carboxylic Acid
(Butyric Acid)
45.70 mL 0.50 moles 0.946 g/mL
Theoretical Yield 56.87 mL
Volume of the distilled
ester
25.00 mL
% Yield of ester 56.04 %
Table 1. Summary of the calculations in the experiment
DISCUSSION OF RESULTS
The Fisher Esterification reaction is driven by shifts in equilibrium, therefore the yield of the
desired ester can never be 100%. Even though, concentrated sulfric acid was added to increase the rate
of the reaction and alcohol is in excess to favor the production of the methyl butyrate. Moreover, once
the solution was heated in reflux, no volatile reagents and products may escape the flask. It was heated
to increase the rate of reaction and to favor the production of the desired ester which is methyl butyrate.
Upon observation the methyl butyrate had a strong pungent odor that is hard to remove in clothing and
from its storage area.The esterwasthen distilled which would allow the esterand the other by-products
to separated. However,not all of the available ester was successfully distilled because of the minimal
amount of liquid present in the flask. If the distillation process continued, the whole set-up could either
result in an explosion or any form of accident. It is also not advised to distil any liquid if the amount of
liquid present is less than 2/3 of its capacity. NaOH was used in neutralization to neutralize the present
10. concentrated sulfuric acid in the solution. By doing so, the final ester was separated from the inorganic
water layer. The purity of the ester formed was based on the given reaction below.
Figure 4. The reaction of the impurities present in the esterwith potassium dichromate and sulfuric acid
Based on the reaction shown in figure 4, the impurities reacted in the presence of potassium
dichromate and sulfric acid to form the given general by-products. These by-products were responsible
in the change of color of the vial that contained the sample ester.Basedon the experiment of the formed
methyl butyrate, the color of the vial that contained the sample with potassium dichromate and sulfric
acid did not changed in color. Therefore,the formed methyl butyrate is pure and contains no unwanted
impurities.
CONCLUSION
Therefore, an ester can be formed from the reaction of any alcohol and carboxylic acid. The
by-product of this reaction is an ester that can produce varied odors and water. The water by-product in
the reaction will reacted with the ester that would result to the formation of the carboxylic acid in the
reactant side. The reaction was manually manipulated to at least favor the formation of the ester and not
the other way around. It is manipulated by its reaction with the presence of concentrated sulfuric acid
and was refluxed to increase the rate of reaction and to increase the formation of the desired ester.
Furthermore, the formula of the percentage yield was equal to the actual amount divided by the
theoretical amount multiply by 100%. The result indicated the amount of completion in reaction
whether the reaction goes to completion or not. Other factors such as human error may also contribute
to the low result of the percentage yield. However, in organic chemistry reactions were difficult to
control because of the unpredictability of the organic compounds in study. To conclude, it should be
noted that the reaction of esterification processhad limitation which would contribute to the low percent
yield despite severalprecaution was made to increase its yield. These limitation primary came from the
fact the reaction is reversible and the reaction was in equilibrium.
REFERENCES
Carey, F.A. (2008). Carboxylic Acid Derivatives: Nucleophilic Acyl Substition (7th
Ed.) In Organic
Chemistry (pp. 842 - 844). New York, NY: McGraw-Hill
Drying Agents. (2016). Retrieved from
http://www.chem.ucla.edu/~bacher/Specialtopics/Drying%20Agents.html
11. Fischer Esterification (n.d) Retrieved from https://www.name-reaction.com/fischer-
esterification
Encylopaedia Britannica (2015, July 07). Ester. Retrieved October 11, 2019 from
https://www.britannica.com/science/ester-chemical-compound
Othmer, K. (n. d.). Esterification. Encyclopedia of chemical technology, 4(9). Retrieved on
February 4, 2019 from %20documents/ Esterfication.pdf
Preparation of Esters (2019, June 5). By Chemistry LibreTexts from chem.libretexts.org accessed on
October 11, 2019
https://chem.libretexts.org/Courses/Eastern_Mennonite_University/EMU%3A_Chemistry_for
_the_Life_Sciences_(Cessna)/15%3A_Organic_Acids_and_Bases_and_Some_of_Their_Derivatives/
15.08_Preparation_of_Esters
Schotten-Baumann reaction. (n.d.). Retrieved from https://www.name-reaction.com/schotten-
baumann-reaction
Synthesis of esters: natural and artificial flavourings (n.d) from
https://www.swisseduc.ch/immersion/chem/synth/docs/Synthesis_ofEsters.pdf
Tremble, J. (2014). Fischer Esterification. Retrieved from https://www.odinity.com/fischer-
esterification/
Williams, M. (2017). The Effects of Washing the Organic Layer With Sodium Carbonate.
Retrieved on February 4, 2019 from https://sciencing.com/the-effects-of-washing-the-
organic-layer-with-sodium-carbonate-12263030.html
https://youtu.be/R6UugHqpu2Y
