Synthesis of Isoamyl Acetate Using the Fischer Esterification Method

Synthesis of Isoamyl Acetate Using the Fischer Esterification Method

Mark Jason Santos, Grace Sharmine Sotto, Chrio Sta. Ana, Lorenzo Terania*

Department of Biological Sciences, College of Science

University of Santo Tomas, España, Manila 1008

Abstract

The objective of this experiment is to produce isoamyl acetate and to determine the yield and also percent yield to measure the effectiveness of the synthetic procedure. Isoamyl acetate is used to confer banana flavor in food. Isoamyl alcohol and acetic anhydride were used to make isoamyl acetate. Fischer esterification was the method used. Using the formula to compute the percent yield, it was determined to be 81.49%.

Introduction

Isoamyl acetate (C7H14O2), also known as isopentyl acetate, is a clear, colorless liquid with pleasant fruity odor indicative of bananas and sometimes pears. It is often known as banana oil when industrially produced and used for substituting banana as flavoring in some food.

Banana oil can be synthesized by the reaction of isoamyl alcohol and acetic anhydride. This type of reaction is called esterification reaction, the reaction of an organic alcohol and an organic acid. The reaction of a carboxylic acid and an alcohol produces ester and water. This reaction is considered as a Fischer reaction because a carboxylic acid and an alcohol with the presence of a catalyst are involved.

Several techniques are employed in this experiment. One of this is the reflux setup (Fig. 1).

In most cases, organic reactions are done by mixing the reactants in an inert solvent and allowing the reaction to proceed at elevated solvent at reflux temperature, i.e., the boiling point of the solvent, and at the same time preventing it from evaporating. The reflux setup which contains a condensing system at a 90-degree angle with the reaction flasks allows condensed solvent to go back to the reaction pot. [1]

Although esters find great applications in foods and beverages, they are not used in perfumes that are applied to the body. Esters, generally, are not stable to perspiration and tend to break down forming carboxylic acids which have unpleasant odors. Only the very inexpensive toilet waters use esters while the more expensive perfumes use essential oils that are usually extracted from natural sources. [2]

Experimental

Preparation of Crude Banana Flavor. Isoamyl alcohol (2.5 mL) and acetic acetic anhydride (2.6 mL) were mixed in a test tube. The test tube was labelled as A. In another clean test tube, same reagents were mixed but sulfuric acid (H2SO4) was added this time. The test tube was labelled as B. Both test tubes were placed in an ice bath. While in an ice bath, contents of tube B was slowly added to tube A. The tube was swirled constantly.

Reflux Method. A reflux setup was assembled. The resulting mixture was transferred in the reflux setup. Boiling chips were added and heated the mixture in a water bath at 80oC for 15 minutes. After 15 minutes, the hot bath was removed and the mixture was cooled down for a minute. The mixture was transferred to a beaker and crushed ice were added.

Separation of Organic Layer from Aqueous Layer. The mixture was again tranferred in a separatory funnel. 15 mL saturated sodium bicarbonate (NaHCO3) were added. The funnel were secured with cap and waited for the bubble to cease. The funnel was swirled gently to avoid emulsion. Two layers were allowed to separate (shown in Fig. 2). The cap was removed and the lower layer was discarded. The extraction was repeated with another 15 mL of NaHCO3. The mixture was then washed with 15 mL saturated sodium chloride (NaCl) solution.

Drying of "wet" Banana Flavor. The organic layer was transferred into a clean beaker and then dried with half spatula of anhydrous sodium sulfate (Na2SO4). The beaker was swirled very gently until the power became free-flowing.

Measuring of Final Product. The dried mixture was decanted and transferred to a preweighed vial. The vial containing the mixture was weighed in the balance room.

Results and Discussion

Isoamyl acetate was synthesized by esterification of isoamyl alcohol and acetic