ESTERIFICATION: ISOPROPYL ACETATE

Juan Luis Timaná Lanfranco (20152627K), Gustavo Javier Pérez Contreras (20152646E)
Organic Chemistry Laboratory II, PQ-322, FIPP
juanluistblull@gmail.com, gperezc152@gmail.com

Completed: May 14, 2018

Presented: May 21, 2018

SUMMARY

In the present laboratory report, the knowledge obtained in class is successfully put into practice.
of organic chemistry, both in the procedural aspect of conducting the experiment and in the theoretical part.
upon drawing a conclusion with the obtained results. In this experiment, the synthesis of
isoamyl acetate, known as banana oil, from the reaction of a carboxylic acid and
an alcohol. The experience mainly consists of the dehydration between an alcohol and an acid
carboxylic, this process is called Fischer esterification when heating the reactants to obtain the
corresponding ester achieving an acceptable performance and the subsequent identification of the ester.

Fischer esterification; Isoamyl acetate; Banana oil.

1. INTRODUCTION

Given the importance of esters, many processes have been developed to obtain esters. The most
It is common to heat a mixture of alcohol and the corresponding acid in the presence of
catalytic amounts of sulfuric acid, using the most economical reagent in excess to
increase the yield of the reaction (Fischer-Speier esterification). Sulfuric acid serves in
this case both as a catalyst and as a hygroscopic substance that absorbs the water formed in the
reaction (sometimes replaced by concentrated phosphoric acid). In general, this procedure
requires high temperatures and long reaction times, thus presenting
disadvantages; Alcohol can undergo elimination reactions forming olefins, esterification

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with sulfuric acid itself or the formation of the corresponding symmetric ether. Likewise, the
The organic acid intended for esterification may undergo decarboxylation.
The esterification reaction involves a nucleophilic attack by the oxygen of an alcohol molecule.
to the carbon of the carboxylic group. The proton migrates to the hydroxyl group of the acid, which is then eliminated.
like water. The role of the catalyst is to increase the carbon activity (the partial positive charge
about the carbon atom) by protonation of one of the oxygens of the acid.

Scheme 1. Synthesis of isoamyl acetate.

The mechanism of Fischer esterification is a nucleophilic substitution at the acyl group.

catalyzed by acid. The carbonyl group of a carboxylic acid is not electrophilic enough.
to be attacked by an alcohol. The acid catalyst protonates the carbonyl group and activates it towards the
nucleophilic attack. The attack by the alcohol, followed by the loss of a proton, produces the hydrate
from an ester. The loss of water from the hydrate of the ester occurs by the same mechanism as the loss
from the water of a ketone hydrate. The protonation of any of the hydroxyl groups allows for
It exits like water, forming a cation stabilized by resonance. The loss of a proton from the second
hydroxyl group forms the ester.

Scheme 2. Mechanism of the Synthesis of Isoamyl Acetate.

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Esterification can shift to the right by using an excess of one of the reactants or by removing
one of the products. For example, in the formation of ethyl esters, ethanol is often used in
excess to shift the equilibrium as far as possible towards the ester. Alternatively, water can
eliminate by distillation or by adding a dehydrating agent such as magnesium sulfate or sieves
molecular (dehydrated zeolite crystals that adsorb water).
The shift of Fischer esterification towards a favorable equilibrium is not very difficult, so
that this is a common method for the preparation of esters, both in the laboratory and in
industry.

The working hypothesis is:

The synthesis of isoamyl acetate will allow for the evaluation of the competencies acquired in the subject of
Organic Chemistry

General objective: Evaluate the procedural competencies theoretically acquired by students.

in the subject of Organic Chemistry.

Specific Objectives:
Experimentally achieving the synthesis of isoamyl acetate, that is, performing the esterification.
of the Fischer.
Determine the identification of the ester through simple tests.

2. RESEARCH DESIGN

For the development of the experimental synthesis of isoamyl acetate, it was proceeded to heat the
Reagents: glacial acetic acid, isoamyl alcohol, and sulfuric acid in a flask, adding pieces of
glass with the aim of better boiling of the previously mixed and stirred reagents, and it
connected the capacitor in reflux position.

The mixture was heated in an air bath, which means it should not come into contact with the balloon of
Bake for 45 minutes controlling the temperature and then let cool to room temperature.
Next, the mixture was transferred to a separating funnel and a dose of water was added with the purpose of
to separate the organic phase. For better separation of this phase, a drying agent was added,
in this case, sodium bicarbonate. The aqueous phase is removed and the organic layer is washed with a mixture
of saturated sodium chloride and water, finally, the organic phase was dried with anhydrous sodium sulfate.
Finally, the identification of the obtained ester was carried out with the Angelo-Rimini test, with the
presence of intense violet coloration.

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3. EXPERIMENTAL PART

In a round-bottom flask of 50 mL, place 4.0 mL of isoamyl alcohol and 6 mL of acetic acid.
glacial and add, carefully shaking, 1 mL of concentrated sulfuric acid, add cores
porous to regulate the boiling and connect the condenser in reflux position. Heat the mixture.
of reaction in an air bath maintaining reflux for 45 minutes. After this time, suspend
the heating, remove the air bath and cool the reaction mixture to room temperature. Pass the
reaction mixture into a separatory funnel. Rinse the reaction flask with 14 mL of cold water and
pour the water into the separation funnel. Shake several times, separate the aqueous phase and dispose of it. The phase
organic contains the ester and a little acetic acid, which can be removed by two washes
successively with 7.5 mL of a 5% sodium bicarbonate solution. Wash the organic layer with 6 mL
of water mixed with 1.5 mL of a saturated sodium chloride solution. Discard the aqueous layer,
Pour the organic phase into a beaker and dry with anhydrous sodium sulfate. Finally
we use the Angelo-Rimini test for the identification of the ester with the presence of violet coloration
intense.

Figure 2. Isoamyl alcohol and glacial acetic acid.

Figure 3. Equipment for heating with reflux.

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 Figure 4. Decantation equipment for the aqueous phase.

Figure 5. Obtaining banana oil.

Flow Diagram of the experiment

Below, Diagram 1 shows the main operations carried out during the
experimental procedure.

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 Diagram 1. Diagram showing the synthesis of isoamyl acetate.

4. RESULTS

Let it be the reaction:

Scheme 3. Synthesis of isoamyl acetate.

V = 6mL 4mL V= 1.3 mL

p = 1.049 g/mL p = 0.809 g/mL p = 0.876 g/mL

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m = 6.294 g m = 3.236 g m = 1.1388 g
PM= 60 g/mol 88.15 g/mol 130.19 g/mol

n = 0.1048 mol n = 0.037 mol n = 0.00875 mol

.
% = × = . %
.

5. DISCUSSION OF RESULTS

After synthesizing isoamyl acetate from isoamyl alcohol and acid

acetic in the presence of an acid catalyst, a rather low yield was obtained of
23.65%.

The reaction between a carboxylic acid and an alcohol (Fischer reaction) was carried out with
a nucleophilic substitution in the acyl group catalyzed by an acid, that is, a
esterification where the hydroxyl group of the carboxylic function was replaced by the group
–OR' from alcohol thus giving the ester more water and the function of H2SO4as a catalyst was of
protonate the carbonyl group and activate it towards nucleophilic attack; the loss of the proton gave
place to an ester hydrate.

Later, the dehydration of the hydrate took place, again catalyzed by the acid,
transforming it into a good leaving group, the water, then a carbocation is formed
stabilized by resonance, the loss of the proton resulted in isoamyl acetate, a liquid
amber yellow in color with a smell between banana and pear, with a slightly oily consistency.

6. CONCLUSIONS AND RECOMMENDATIONS

The synthesis of isoamyl acetate was experimentally achieved, demonstrating the ability to
analysis and synthesis acquired theoretically, as well as the procedural techniques, resulting
poor performance due to various conditions such as the quality of the reagents, the formation of
other compounds, and in turn to the negligent maneuvers of the laboratory students.
The synthesis of the ester depended heavily on the amount of reactants used since being a
reversible reaction was necessary to control or separate the products that were intended to be obtained with
the aim of achieving better performance, and this was achieved with excess reagents and to the
difference in boiling points of these same ones.
Different laboratory techniques such as distillation and decantation were used, and at the same time,
a simple chemical test for the identification of ester.

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 On the recommendations side, it is important to work with reagents of the best quality.
which was not the case in the experiment developed. Similarly, carry out a correct
use of laboratory instruments at the time of handling them and performing techniques in
each of the processes involved such as the mixing and stirring of the reactants, the
correct assembly of the distillation equipment and a good separation of the obtained products
Especially at the moment of heating the mixture, it is important that the ball does not make contact.
with the boiling equipment.
In the same way, control the temperature when heating the mixture and carry out a
Correct separation of the product are factors that greatly influence its performance.
obtained ester.

7. QUESTIONNAIRE

1. Write a reasonable mechanism for the formation of isoamyl acetate.

Figure 4. Mechanism of the studied reaction.

2. Determine the percentage yield of the reaction.

A yield of 23.65% was obtained.

3. Why is an excess of acetic acid added instead of isoamyl alcohol? In

In what cases would it be advisable to use alcohol excess instead of acid excess?

Firstly, the addition of either acetic acid or isoamyl alcohol is to promote the
obtaining products due to the principle of Le Chatelier. Therefore, we must decide
which of the two will we add.

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In the case of isoamyl alcohol, it tends to form ternary azeotropes with water and ester,
For that reason, in a possible warming we will be losing product, which is not the case.
desired, deciding on an excess of acetic acid.

In an extreme case, an excess of alcohol will be preferred over acid.

It accounts for a factor of availability and cost.

4. Explain why CO is produced.2during the experience. What is the equation of the

reaction that generates CO2.

CO2 is produced during the experiment, due to the reaction between acetic acid and the
5% sodium bicarbonate.

3 + 3→ 3 + 2+ 2

5. Explain what the uses of esters are.

Manufacture of semisynthetic polymers such as cellulose acetate

(called "rayón" if processed as fiber and "cellophane" if processed as film)
and synthetic polymers such as polyesters, with the most common being PET or
polyethylene terephthalate
and increasingly used as plastic in films and especially in molded bottles
by blowing.

Among the esters of alcohols and low molecular weight acids that are produced in large
the scales are ethyl acetates, isopropyl, butyl, and amyl which
they are important solvents, especially for lacquers (including nail varnishes and
(varnish removers). n-butyl acetate is the most important solvent for
the lacquers formulated based on nitrocellulose and are manufactured through batch processes or
continuo.

Many simple esters, derived from the different combinations of alcohols and
Acids (linear or branched, generally with 5 carbons or less) have a use
very important in the food industry and in perfumery as flavorings and
artificial flavorings, whether alone or in mixtures with other natural compounds or
synthetic. This application is due to the pleasant smell of many esters,
frequently of a fruity type, coupled with its relatively low toxicity.

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 Table 1. Esters and the flavors for which they are responsible.

Ester Flavor Ester Flavor

Isoamyl acetate Banana Isopentyl salicylate strawberry
Benzyl acetate Peach Amyl valerate Apple
Octyl acetate Orange Isobutyl propionate Ron
Ethyl butyrate pineapple Amyl acetate plum

8. BIBLIOGRAPHIC REFERENCES

R. T. Morrison, R. N. Boyd, Organic Chemistry Fifth Edition, Mexico: Addison Wesley

C. Timaná de La Flor, Organic Chemistry II - Laboratory Guide

L. Wade, Organic Chemistry Volume 2, seventh edition, Mexico: Pearson Education, 2011

H. Beyer and W. Walter, Organic Chemistry Manual, Barcelona: Editorial Reverté, 1987

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