a. CHM146L student, School of CHE-CHM-BE-MSE, Mapua Institute of Technology
b. CHM146L professor, School of CHE-CHM-BE-MSE, Mapua Institute of Technology
Colleen Samantha Dioquinoa, Christopher Jay Robidillob
Abstract
Esters are prepared in many ways and one of which is through fischer esterification. This reaction
involves carboxylic under acidic condition with alcohol. This experiment aimed to synthesize isoamyl
acetate and understand preparing ester’s mechanism. The test compounds underwent reflux, distillation,
extraction and vacuum filtration. Through an acid, acetic acid could serve as a substrate. This could
easily be attacked by isoamyl alcohol, thus producing isoamyl acetate. Work up was done through the
conjugate base. Assumed by-products of this reaction was water and sulfuric acid which was removed
after simple distillation. This experiment had produced a considerable yield of isoamyl acetate.
Keywords: ester, fischer esterification, isoamyl acetate, mechanism, substrate
Esters are prepared through SN2 reaction, acid
chloride or fischer esterification. Carboxylic
acids and its derivatives are usually the source
of ester. When these are treated with strong
base and alkyl halide, these will produce esters.
Acid chlorides reacted with alcohol would readily
yield ester since chlorines are good leaving
group. Moreover, carboxylic acid, if treated with
another acid and an alcohol, this would undergo
fischer esterification process.
This experiment aims to:
Synthesize isoamyl acetate
Understand the mechanism of preparing
ester
The test compounds used and produced in this
experiment are in Table 1.
Table 1-test compounds
Test Compounds
Name
Structure
Isoamyl alcohol
Sodium
Bicarbonate
NaHCO3
Glacial acetic
acid
NaCl
Sulfuric acid
Magnesium
sulfate
Isoamyl acetate
The reagents were prepared by the laboratory
assistant before the experiment was performed.
When isoamyl alcohol was mixed with acetone
and sulfuric acid, isoamyl acetate had been
formed after refluxing the mixture. The carbonyl
oxygen was first protonated using the acid.
Isoamyl alcohol would function as a nucleophile
and attacks the carbonyl carbon. To remove the
positive charge on oxygen, the conjugate base
would deprotonate oxygen.
Figure 1
Figure 2
The hydroxyl group is converted into water to a
better leaving group. The oxygen at another
hydroxyl group would give its lone pair to form a
π bond to expel water as a leaving group. The
positive charge on oxygen would be
deprotonated by the conjugate base.
Figure 3
When the product was distilled, there were some
liquid that were collected at 105ºC. This was
assumed to be water from the last extraction of
the isoamyl acetate.
Table 2-Data
Data
Weight of crude product
8.41 g
Weight of pure product
7.28 g
Percent yield
86.56%
From table 2, the weight of the crude product is
8.41g but after crystallization, the weight
decreased to 7.28 g. This is a considerable
percent yield due to the presence of excess
sulfuric acid that wasn’t neutralized by 5%
aqueous sodium bicarbonate since the acid was
concentrated.
The acetic acid was made less stable
through sulfuric acid which had protonated the
carbonyl group. Since the carbonyl group is
weak, it could be attacked by isoamyl alcohol to
produce ester. The positive charge on oxygen
was relieved through hydrogen sulfate,
conjugate base. The hydroxyl group was made
water to become a stable leaving group.
The experiment had produced a high
yield of isoamyl acetate. The remaining percent
might have been caused by the error brought by
distillation and the excess sulfuric acid that
wasn’t neutralized by the aqueous sodium
bicarbonate.
I would strongly recommend that the
base must be much stronger than 10% sodium
bicarbonate to reduce wasted chemicals since
the extraction was done nine times.
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