Synthesis of Isopentyl Acetate (Banana Oil) Using a Fischer Esterification Reaction

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Synthesis of Isopentyl Acetate (Banana Oil) Using a Fischer Esterification Reaction Zhenshu Wang (Stan)
TA: Aaron League
September 23, 2012

Purpose: The purpose of the experiment was to perform the acid-catalyzed Fischer Esterification of acetic acid and isopentyl alcohol to form isopentyl acetate, or banana oil, which is used in flavor industries. The equilibrium of the reaction was changed by adding an excess amount of acetic acid. The reaction was refluxed and product was purified by extraction and distillation. Isopentyl acetate was analyzed by infrared spectroscopy and 1H NMR spectroscopy.

Reaction Scheme:

Mechanism: Key features of the Fischer Esterification mechanism are: a. protonation of the carbonyl group, b. the formation of the tetrahedral intermediate, and c. regeneration of acid to show its role of catalyst in the reaction.

Procedure: The procedure followed was as described in the Wissinger Manual.1 Modifications of the procedure included: The drying agent took 25 minutes, as opposed to the suggested 10-15 minutes. The voltage for the heating mantle was changed from 70 volts, in the manual, to 80 volts.

Reagent/Product Table
| Acetic Acid| Isopentyl Alcohol| Con H2SO4(95-98%)| Isopentyl Acetate| H2O| Mol Wt.| 60.05| 88.15| 98.079| 130.19| 18.02|
Grams| 8.9| 5.0| 2.2| X| X|
moles| 0.148| 0.0567| 0.0225| X| X|
mL| 8.5| 6.2| 1.2| X| X|
Density 2g/mL| 1.049| 0.813| 1.84| 0.876| 1.00|
bpt/mpt, oC 2| 118| 130.5| 337| 142| 100|
Solubility 2| Miscible with water| Slightly sol in water| Miscible with water| Slightly sol in water| N/A| Hazards 3| irritant| Avoid breathing vapors| corrosive, irritant| Flammable, avoid skin contact| No hazards|

Results and Observations:
Observations: When concentrated sulfuric acid was added to the acetic acid and isopentyl alcohol, an exotherm was observed. The reflux was performed as described in the manual; however, the mixture was not boiling after 30 minutes, therefore voltage for the heating mantle was changed from 70 volts to 80 volts. The mixture turned from colorless to dark purple and the odor of banana was observed. After cooling down, a set of extractions were performed. The upper layer was the product layer and it was colorless; the lower layer was aqueous layer and it was cloudy and dark brown. A few drops were lost while transferring product from the separatory funnel to a 50-mL Erlenmeyer flask. Following drying with anhydrous MgSO4, the liquid was transferred for distillation. The boiling temperature for the final product was 129 oC, and a small amount of residue was left in the distilling flask.

Yield and Property Data for Isopentyl Acetate
Theoretical Yield| ActualYield| % Yield| Bpt| LiteratureBpt| Appearance| 7.44g| 4.45g| 59.8%| 129 oC| 142 oC| Clear, colorless liquid with banana odor|

Yield Calculations:
Limiting Reagent—
Weight for acetic acid: 8.5 mL x 1.049= 8.92g
Moles for acetic acid: 8.92g/ 60.05g mol-1=0.148 mole
Weight for Isopentyl alcohol: 6.2mL x 0.813g/mL= 5.04g
Moles for Isopentyl alcohol: 5.04g/ 88.15g mol-1=0.0572 mole < 0.148 mole Since the H2SO4 is a catalyst, the isopentyl alcohol is the limiting reagent. Because the reaction is 1:1 ratio, therefore

Moles for Isopentyl acetate: 0.0572 mole
Weight for Isopentyl acetate: 0.0572mole x 130.19 g mol-1= 7.44g Theoretical Yield is 7.44g
Actual Yield is 4.45g
Percentage: 4.45g/7.44g x 100%= 59.8% yield

1H NMR (200MHz, CDCl3): See attached spectrum for peak assignments with structures. (ZW page 9) Compound| Protons Hx| Chmical Shift, δ| Splitting| Integration Area| Number of H| J value Hz| Isopentyl acetate| Ha| 4.053-4.121| Triplet | 3.75cm| 3.75/1.88= ~2| 6.8| | Hb| 2.040| Singlet | 5.35cm| 5.35/1.88=~3| N/A|

| Hc| 1.459-1.753| Multiplet | 6.20cm| 6.20/1.88=~3| 6.6| | Hd| | | | | |
| He| 0.899-0.932| Doublet | 11.00cm|...
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