Introduction
In this lab the synthesis, purification, and characterization of isoamyl acetate, or banana oil, was determined. The synthesis was completed by a reversible esterification reaction which required the heating of glacial acetic acid and isoamyl alcohol, combined with a sulfuric acid catalyst in hexane. In order to increase the efficiency of the reaction, Le Chatelier’s Principle is utilized by removing water from the products. As a result, the reaction as a whole shifts the left producing more isoamyl acetate to try and balance the reaction once again.
Once the product was collected, it was purified through means of fractional distillation. Finally to characterize the product, and assess its purity, IR and NMR spectroscopy were taken.
Experimental Procedure
In a 50 mL round bottom flask, 7. 5mL of Isoamyl Alcohol, 4. 0 mL of 17. 4M Glacial Acetic Acid, 1 mL of concentrated Sulfuric Acid, and 6. 9 mL of Hexane were combined along with two boiling chips. A Dean-Stark trap was then assembled, and 1. 25 mL of hexane was added to the trap and marked with a pen. The value used was predetermined in the pre-lab by stoichiometric calculations. The Dean-Star trap was attached to the flask and condenser, and was heated on an aluminum block until the flask started to reflux.
As the contents were heated, the solution turned from a peach color to purplish red. In order to prevent loss of any vapor, the aluminum foil was wrapped around the tube between the flask and condenser. Reflux was done for one hour, when the water level in the trap reached the previously made mark of 1. 25 mL. Flask was then cooled to room temperature before extraction. In order to separate the organic layer, the contents of the flask were placed into a 125 mL separatory funnel and washed first with two portions of 10 mL of water and then with ~10 mL of 5% NaHCO3.
After each addition of solution, the contents of the funnel were shaken and vented to release pressure build up and the white, cloudy aqueous layer was set aside. Before the first extraction, the organic layer remained a purple cloudy layer, but then changed to yellowish cloudy solution after the addition of NaHCO3. Finally the last extraction was done with ~10 mL of brine, after which the organic layer was transferred to a new flask and combined with 6. 457 g of anhydrous MgSO4. The solution was mixed until no longer cloudy and was then gravity filtered into a 25 mL round bottom flask.
During the second week of lab a fractional distillation apparatus was set up and wrapped with aluminum foil, to maintain higher temperatures, and the flask contents from the previous week were heated. The final fraction was tared and weighed in a flask, to determine weight and yield. In order to characterize the contents, a small portion of the sample was taken for IR analysis, and a sample for NMR was prepared for submission.
Discussion
In this lab, Isoamyl Acetate was synthesized though an esterification reaction involving Glacial Acetic Acid and Isoamyl Alcohol.
The reaction flask was set in a Dean-Stark Trap to maximize the amount of product produced, by taking advantage of Le Chatelier’s Principles. Once the product was obtained it was purified through means of fractional distillation and its purity then characterized by IR and NMR spectroscopy. In the esterification reaction, along with the Isoamyl Acetate being formed, there is also a byproduct of water. As is common in esterification reactions, the synthesis of a carboxylic acid and an alcohol produces an ester and water.
Le Chatelier’s Principle states that if a reaction in dynamic equilibrium is disturbed by changing conditions, then the equilibrium will move to counter this change to once again reach that dynamic equilibrium. In the esterification reaction of Isoamyl Acetate, the reaction flask is placed in a Dean-Stark Trap while it is being refluxed. The purpose of this is to utilize the trap to continuously remove water which is produced in the reaction. In doing so, according to Le Chatelier’s Principle, the reaction shifts to the products side to compensate for this lack of water.
As a result more Isoamyl Acetate is also produced. Although in theory this process may work well, experimentally everything will not react ideally. The experimental yield of the Isoamyl Acetate recovered was much lower than the expected theoretical mass. As shown in the calculations, there was only a 24. 84% yield. This poor percentage can be contributed to many factors. One main cause can be due to not refluxing the esterification reaction long enough; as a result less Isoamyl Acetate was produced. Another potential problem could have arisen in the fractional distillation.
Although the hexane began to boil out at about 68°C, and the alcohol began to boil out at 130°C, there could still be some alcohol which could have remained in the solution as the temperature only went to 136. 2°C. As the boiling point of Isoamyl Acetate is around 142°C, it can be said that some impurities remained in our solution, mainly some alcohol. Due to our solution temperature being slightly lower than that of pure Isoamyl Acetate, there could easily have been some impurities which were not completely boiled out; also contributing to the low yield.
In order to characterize the purity of the compound, the Infrared Spectra (IR) was utilized. Looking at the IR spectra we can see that there are many jagged peaks at and below 1400cm-1. These can be seen as C-O bonds, and a little farther up the graph, a distinct peak at around 1740cm-1 is the C=O, as its wavenumber resides in the ester functional group range. Following the ester peak, there is a large gap until the next distinct peaks are reached at 2870cm-1 and 2960cm-1, which falls into the methyl alkane functional group.
Finally the next prominent peak can be clearly distinguished as an alcohol since it resides well within 3200-3650cm-1 range. However, when compared to a pure alcohol IR spectrum, the experimental peak is much smaller and narrower. This difference between spectra can also be contributed to impurities which have altered the shape and size of the peak when measurements were taken. This piece of data further justifies some residual alcohol remaining, even after fractional distillation, within the Isoamyl Acetate liquid.
