Preparation of Isoamyl Acetate

Preparation of Isoamyl Acetate

REYES, Ronz Austin A.

*RIMANDO, Denise Anne A.

RONQUILLO, Viarra Janae D.

Department of Biological Sciences

College of Science, University of Santo Tomas

España, Manila, Philippines

ABSTRACT

An ester, isoamyl acetate or isopentyl acetate (3-methylbutyl acetate), often called as banana oil, was synthesized by a direct esterification reaction between acetic acid and isoamyl alcohol (3-methylbutanol). In this experiment, acetic anhydride was used in excess because it is less expensive than the isoamyl alcohol and is easier to remove from the reaction mixture. During the isolation procedure, much of the excess acetic anhydride and the remaining isoamyl alcohol were removed by extraction with sodium bicarbonate(NaHCO3) and water (H2O). After drying this with anhydrous sodium sulfate(Na2SO4), the ester was purified by distillation.

INTRODUCTION

Ester is an organic compound formed in a reaction between an acid and an alcohol (and some phenols) with the elimination of water. This class of organic compounds known to be widely distributed in nature. They are recognized by their very characteristic flavors and odors. This functional group is often used as fragrant. Table 1 are some ester with its flavor and fragrances.

Table 1. Ester Flavors and Fragrances

Esters can be synthesized by many methods. One of the simplest approach is the Fischer esterification. By this method, esters are produced by refluxing an acetic anhydride and alcohol in the presence of a concentrated acid catalyst. To exploit Le Chatelier’s principle and to shift the position of the equilibrium to the right, we add an excessive of one of the reactants to the reaction mixture. Normally, we choose the least expensive reactant, which, in this case, is the acetic anhydride. The process is thermodynamically controlled yielding the most stable ester product. Typically, only primary and secondary alcohols are used in the Fischer method since tertiary alcohols are prone to elimination.

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Figure 1. Fischer Esterification of Isoamyl Acetate

This experiment aims to: (1) prepare the assigned ester which is the banana flavor via Fischer reaction, (2) construct and use a reflux setup, (3) perform a liquid-liquid extraction, and (4) to calculate the percent yield.

METHODOLOGY

10 mL graduated cylinder was used to measure 2.5 mL of isoamyl alcohol and 2.6 mL of acetic anhydride which are to be placed in pear-shaped flask. After this, 5 drops of concentrated sulfuric acid were added in the same flask. The resulting mixture was then placed in a reflux set-up with 1 boiling chip and heated in a water bath at 80°C ± 5°C for 30 minutes.

Afterwards, the hot bath was removed and cooled for a minute. The content was poured in a small beaker with a cube of crushed ice included. Also, a 5mL of water was added in the mixture. It was then transferred to a separatory funnel containing 15ml saturated sodium bicarbonate(NaHCO3) solution and was swirled gently. The aqueous layer of the mixture is to be discarded while in the organic layer, a 15 mL of sodium chloride(NaCl) was added and swirled. This was done twice until the mixture becomes basic. The organic layer of the mixture was transferred into a small clean 50 mL beaker with half spatula of anhydrous sulfate(Na2SO4). After the process of decantation to a pre-weighed vial, the weight of the final product was measured and the percent yield was also calculated.

RESULTS AND DISCUSSION

Table 2. Data Table of the Organic Compounds

Table 2 illustrates that the molecular weight and density of the compounds for this experiment is directly proportional to each other: knowing that, as the molecular weight increases, the density also increases. Since density is defined as mass per volume (g/ml), the more mass you have for a given volume, the greater its density.