Isopentyl Acetate

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Experiment 12: Isopentyl Acetate
19 October 2012

The purpose of this experiment is to prepare isopentyl acetate by direct esterification of acetic acid with isopentyl alcohol. After refluxing there is an isolation procedure where excess acetic acid and remaining isopentyl alcohol are easily removed by extraction with sodium bicarbonate and water. The ester is then purified by simple distillation and the IR is then obtained.

Techniques and equipment used throughout the experiment include a reflux apparatus, separatory funnel for isolation, vacuum filtration, and simple distillation. The reflux condenser is used to allow thorough distillation of the product with the use of heat to accelerate and stir while vapors fall back into the round bottom flask. Isolation of product is used with the help of the separatory funnel and vacuum filtration. Simple distillation is used to purify product and IR spectroscopy helps compare and test validity of our final product.

The experiment is started by assembling a reflux apparatus with a 50 ml round bottom flask containing 5 ml of isopentyl alcohol, 7 ml of acetic acid, and 1 ml of sulfuric acid. It is essential to make sure that the solution is swirled immediately once the sulfuric acid is added. The mixture is then refluxed for 60 – 75 minutes. Once this is done, it is cooled to room temperature.

The mixture is then transferred to a separatory funnel. It is first washed with 10 ml of water and when the layers separate, the bottom layer is disposed of. The mixture remaining in the separatory funnel is then washed with 5 ml portions of 5% sodium bicarbonate until the pH of the aqueous layer is basic. It is then mixed with 5 ml of saturated NaCl solution and the layers should once again separate.

The product is then dried for 10 – 15 minutes with ~1 g. of anhydrous sodium sulfate and then vacuum filtrated. A simple distillation apparatus is then assembled and the mixture is heated and distilled at boiling temperatures of 134 – 143 degrees Celsius. Afterwards, the IR spectrum is obtained and the percent yield is calculated.

Results and Discussions:

Reaction equation

Reaction mechanism:

Side reactions:
Ester hydrolysis can occur when there is water present causing a reverse reaction to occur:

Elimination can occur with the aid of sulfuric acid:

The limiting and excess reagent:
Isopentyl alcohol:
5 mL = Vd = m m = (d)(v) m = (0.809)(5) = 4.045 g
4.045 g C5H12O x 1 mol C5H12O = 0.04589 mol C5H12O
88.15 g C5H12O
Acetic acid:
7.0 ml = Vd = m m = (d)(v) m = (1.06)(7ml) = 7.42 g
7.42 g C2H4O x 1 mol C2H4O = 0.1234 mol C5H12O
60.1 g C2H4O

Limiting reagent: Isopentyl alcohol
Excess reagent: Acetic acid

Theoretic yield:
0.04589 mol C5H12O x 130.19 g C7H14O2 = 5.97 g C7H14O2
1 mol C7H14O2

Percent and experimental yield:

Actual and experimental yield: 8.152 g
Percent yield: Actual x 100 = 8.152 g x 100 = 136.5%
Theoretical 5.97 g

Analytical Data:

Weight of final Product| 8.152 g|

IR reading:
Frequency| Type of vibration|
3444.54| 0-H|
1740.41 cm-1| C=O (ester)|
1056.81 – 1367.70| Signifies presence of an ester|

When mixing the isopentyl alcohol, acetic acid, and sulfuric acid it was important to swirl immediately to avoid a side reaction. I believe I was able to prevent this from occurring by immediately swirling the solution when all components were added. Then, when refluxing this mixture I did not use a boiling stone and this may have interfered with my product. There was a possibility that the mixture had already started to boil without my knowledge and this might have caused the mixture to be refluxed longer than 60 – 75 minutes, which probably caused the hydrolysis side reaction to occur. This match with the IR spectrum of my...
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