Materials and Methods s3

INTRODUCTION

Isopentyl acetate (with the formula C7H14O2) is a naturally occurring ester found in bananas and bee pheromones. This compound is commonly used as a food additive and as a flavoring agent. The objective of the study was to prepare isopentyl acetate using esterification process. The compound was prepared by reacting acetic acid and isopentyl alcohol together with sulfuric acid and heat to form isopentyl acetate and water, respectively. The mixture was then purified by removing the excess acetic acid using diethyl ether and water as solvents. It was then washed with 5% aqueous NaHCO3 and saturated NaCl. The mixture was then “dried” using anhydrous MgSO4 and was evaporated using water bath. The residue was weighed to obtain the percent yield of the product.

MATERIALS AND METHODS

Esterification. Crude isopentyl acetate was obtained after mixing 2.5mL of isopentyl alcohol, 6mL glacial acetic acid and 2mL sulfuric acid. The mixture was then refluxed for 1.5 hours and was set to cool to room temperature.

Acid extraction. Crushed ice and 30mL of diethyl ether were added to separate the unreacted acetic acid from isopentyl acetate. The mixture was placed in a separatory funnel and was swirled. The presence of two layers was observed. Figure 1: A reflux set-up used in esterification

The lower layer was discarded. The mixture was further purified by adding NaHCO3. Again, the presence of two layers were observed. The lower layer was discarded. The same procedure was repeated, only this time, using saturated NaCl was added.

Drying. The upper layer (ether layer) was mixed with one-half teaspoon of anhydrous Magnesium sulfate (MgSO4). The liquid was decantated into a tared evaporating dish. The mixture was heated until only the residue remained.

Percent Yield Calculation. Theoretical yield was obtained by calculating for the mass of the limiting reagent. Actual yield was obtained by calculating the difference weight of the residue and the evaporating dish and the weight of the empty evaporating dish. Percent yield was obtained by dividing the actual yield over the theoretical yield, then multiplying it by 100.

RESULTS AND ANALYSIS

Crude isopentyl acetate was obtained using esterification process. In the process, refluxing was used. The reaction was endothermic. If the set-up was covered, it will result to the accumulation of pressure. On the other hand, if the set-up was not covered, it will result to the loss of components. A condenser (reflux unit) keeps the component from being lost by evaporation by transforming the steam into liquid through condensation.

Excess acetic acid that were unreacted were separated by adding diethyl ether and water. Isopentyl acetate was soluble only in diethyl ether, but acetic acid was soluble in both solvents. Therefore, the extraction procedure of acetic acid was not able to completely separate the two compounds.

Table 1: Solubility behavior of isopentyl acetate and acetic acid in water and diethyl ether

NaHCO3 was then added to react with what was left of the acetic acid to form carbon dioxide, carbonic acid and sodium acetate. Anhydrous MgSO4, a drying agent, was added to acquire the water from the isopentyl acetate mixture to form hydrated MgSO4. Simple distillation of the ether solvent was not used because ether is volatile and is flammable.

Isopentyl acetate was observed to possess a sweet-smelling aroma similar to bananaodor. The residue was observed to have a brown color.

The percent yield was observed to be low because of the improper handling of the separatory funnel.

CONCLUSION

This study evaluated the preparation of isopentyl acetate using esterification process as a possible food additive. Based on the results obtained, isopentyl acetate can be used as a food additive and as a flavoring agent.

In addition, results show that the esterification of isopentyl acetate is a reversible process guided by Le Chetelier’s principle. It was found out that adding more reactants (in this case, adding more acetic acid) would shift the reaction towards the product side, which is the production of ester.

REFRENCES

Atkins, R., Carey, F. Organic Chemistry – 3rd edition: A Brief Course. McGraw-Hill Companies, New York, 2002

Brown, W., Foote, C. Organic Chemistry 3rd edition. Harcourt College Publishers, Orlando, FL, 2002

Kritz, G., Engel, R., Lampman, G. et al. Introduction to Organic Laboratory Techniques: A Microscale Approach. Harcourt College Publishers, Orlando, FL, 2002

Loudon, G. Organic Chemistry. Oxford University Press, Oxford, NY, 2002

McMurry, J. Fundamentals of Organic Chemistry

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