Lab 8 Isopentyl acetate 1

Lab 8: Isopentyl Acetate
CHM 2211L
October 22, 2014
Abstract
Many esters are naturally occurring compounds that are responsible for the fragrance of fruits and flowers. Isopentyl Acetate is the compound responsible for the smell of bananas. However, when Isopentyl acetate is treated with H3O+ it will hydrolyze back into the carboxylic acid, which will change the fragrance. In this experiment 3.11g of Isopentyl Acetate were produced with a 51.92 percent yield.

Introduction
Esters are carboxylic acid derivatives in which the acyl carbon bears an ether group instead of the hydroxy group. Esters are synthesized by different methods such as an Sn2 process where a carboxylic acid is treated with a strong base followed by an alkyl halide. Fischer Esterification is a nucleophilic acyl substitution reaction that converts a carboxylic acid into an ester when the carboxyl group of an acid and the hydroxyl group of an alcohol are condensed with the expulsion of a water molecule. The by product is removed to exploit Le Chatelier’s principle in order to favor the formation of the ester over the starting material.

Fig. 1: Esterification of Isopentyl Acetate
Fig. 2: Mechanism for the esterification of Isopentyl Acetate.

Procedure
Assemble a reflux apparatus (Figure 4) with a 50 mL round bottom flask with a heating mantle. Add 5 mL of isopentyl alcohol and 7 mL of acetic acid to the round bottom flask. While stirring add 1 mL of acetic acid to the round bottom flask. The solution was gently heated until the solution was boiling and then refluxed for 60 minutes. The solution was then transferred to a separatory funnel. 10 mL of DI water was added to the funnel. Then the funnel was carefully shaken and vented to allow gasses to escape. The solution was then allowed to rest for two minutes. After resting the bottom aqueous layer was drained rom the funnel. The water wash process was repeated again. Then the organic layer was washed with 5 mL of 5% sodium bicarbonate solution. Following the wash the aqueous layer was drained. The organic layer was washed again by adding 5 mL of saturated sodium chloride solution. Then the ester was transferred to a dry 25 mL Erlenmeyer flask containing 1g of anhydrous sodium sulfate. The solution was allowed to dry for 15 minutes. The solution was transferred to a second 25 mL Erlenmeyer flask containing 0.5g of anhydrous sodium sulfate and allowed to dry for another 5 minutes. After the drying was complete an IR-spectrograph was generated.

Data
Calculations
Theoretical yield:
5.00mL x 0.810g/1mLx 1 mol/88.15g= 0.046 mol isopentyl acetate (limiting reagent)
7.00mLx1.05g/mLx 1mol/60.05g= 0.122 mol acetic acid (excess reagent)
0.046 mol x130.19g/1mol = 5.99g theoretical yield

Actual yield:
Actual yield: 3.11 g
%Yield= 3.11g/5.99g x 100%= 51.92% yield Isopentyl Acetate

IR spectrograph analysis (figure 3)
2900 cm-1: C-H stretch
1750 cm-1: C=0 stretch
1250 cm-1: C-O stretch.

Figure 3: Spectrograph of Isopentyl Acetate

Figure 4: reflux apparatus

Conclusion
The esterification of Isopentyl acetate and acetic acid in this lab produced a yield of 3.11g. When compared to the theoretical yield of 5.99 grams this gives a 51.92 percent yield of Isopentyl acetate. Sources of error arise from the multiple washing processes or from separating the organic layer from the aqueous layer. The organic layer would either be incomplete or it might contain excessive amounts of water. The IR spectrograph has three signals that are indicative of a pure ester: The moderate peak just below 3000 cm-1 indicates the presence of C-H stretching. The strongest peak at 1750 cm-1 is produced by the C=O bond from the carbonyl carbon. The Signal at 1250 cm-1 is produced by the C-O single bond on the acyl carbon. The strong fragrance of banana was further proof of a positive result.