Isopentyl acetate, banana oil, is a naturally occurring compound that has a very distinct and recognizable odor. It is most commonly found in bananas but also can be found in other organisms. The purpose of this lab was to synthesize the ester isopentyl acetate via an acid catalyzed esterification (Fischer Esterification) of acetic acid with isopentyl alcohol. Emil Fischer and Arthur Speier were the pioneers of this reaction referred to as Fischer Esterification. The reaction is characterized by the combining of an alcohol and an acid (with an acid catalyst) to yield and ester plus water. In order to accomplish the reaction, the reactants were refluxed for an hour to yield the product. The advantages of using this particular esterification process is that is fairly simple to set up and recreate, as long as the proper acidic conditions are present.
Experimental Section: The first step in this experiment was to set up a ring stand which will hold the glassware while the reflux process is occurring. After the ring stand was set up, a heating mantle was placed underneath the round-bottom flask and two rubber hoses were attached to the condensing tube. Now that the instruments were set up, the reagents were ready to be weighed and then added. Approximately 5 ml of isopentyl alcohol was added to a 10 ml graduated cylinder. Next, a 25 ml round bottom flask was placed on a cork ring and then tared on the balance.
The alcohol was then added to the flask and the mass was recorded in a notebook. 7 ml of acetic acid was then added to the 10 ml graduated cylinder and then transferred to the 25 ml round bottom flask which already contained the alcohol. Approximately 1 ml of concentrated H2SO4 was added to the 25 ml round bottom flask and the mixture was swirled. Finally, a boiling chip was added to the round bottom flask and the reflux procedure was ready to commence. Water was then circulated through the condenser and the reaction was refluxed for an hour. After an hour went by, the reaction was removed from the mantel, while the condenser still circulated with water, and the mixture was allowed to cool to room temperature.
Once cooled, the mixture was then transferred to a separatory funnel using the funnel while avoiding adding the boiling chip. 10 ml of water was then added to the mixture. The mixture was gently shaken and the phases were allowed to separate. The funnel was then unstopped and the lower aqueous phase was drained into a beaker. 5 ml of 5% aqueous NaHCO3 was added and then shaken gently. A great deal of caution was taken into consideration because of the production of carbon dioxide gas which caused pressure to develop inside the funnel. The pressure needed to be released so the funnel was vented frequently.
The phases were allowed to separate and the lower aqueous phases was drained into the beaker. After draining, 5 ml of saturated NaCl was added to the funnel and then shaken gently. Once again, the phases were allowed to separate and the lower aqueous phase was drained into a beaker. An ester product was produced and was transferred into a 25 ml Erlenmeyer flask. This organic product was then dried over anhydrous Na2SO4 to trap small amounts of water in its crystal lattices thus removing it from the product. Finally the ester was decanted, so that the drying agent was excluded from the final product.
Results and Discussion: Fischer esterification is the primary way of synthesizing this ester. The reactants involved in this reaction are isopentyl alcohol and acetic acid. Fischer esterification is the nucleophilic addition of isopentyl alcohol to the carbonyl group of the protonated acetic acid. Nucleophilic addition is followed by elimination of a proton. An unstable tetrahedral intermediate forms. This intermediate undergoes dehydration and reforms the carbonyl group. Reformation of the carbonyl group forms the isopentyl acetate. The driving force behind the mechanism of this reaction is the acidic environment.
Conclusion: Fischer esterification is a very simple and useful method that anyone with a slight knowledge of chemistry could accomplish. It is widely utilized throughout the world of chemistry and can be used to produce many products, including isopentyl acetate.
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