Preparing Isopentyl Acetate by the Fischer Esterification

Preparing Isopentyl Acetate by the Fischer Esterification

Leah Monroe

May 8, 2003

Organic Chemistry Lab II

Experiment performed on April 29 and May 1, 2003

Abstract:

The purpose of this experiment was to synthesize isopentyl acetate via an esterification reaction between acetic
acid and isopentyl alcohol, using concentrated sulfuric acid as a catalyst. The product was washed with sodium
hydrogen carbonate, as well as with water, then dried with anhydrous sodium sulfate. The product was then
distilled using a Hickman still and characterized using infrared spectroscopy. The percent yield of isopentyl
acetate was 61.52%. This may have been low due to not all of the condensed product being removed from the
Hickman still, some product being lost during transfer of the product from the reaction tube into the Hickman
still, or the loss of some product due to evaporation during distillation. Infrared spectrum analysis of the product
indicated that the product was isopentyl acetate, as expected, and thus that the reaction was successful.
 Preparing Isopentyl Acetate by the Fischer Esterification

Introduction: The purpose of this experiment is to synthesize isopentyl acetate via an esterification reaction
between acetic acid and isopentyl alcohol, using concentrated sulfuric acid as a catalyst. The
product will be washed, distilled, then characterized using infrared spectroscopy.

Materials Used:
Paraffin sand bath
test tube clamp
50-mL Erlenmeyer flask Hickman still
cork Pasteur pipettes with bent ends
microspatula Kim-wipes
sand bath vial
Pasteur pipettes
Rubber bulbs

Reagents and Properties:

Substances Formula Weight Quantity Moles Used Mole Ratio Melting Point Boiling Point Density
g/mol °C °C g/mL
Acetic Acid 60.05 2 mL 0.0349 1 to 1 118 N/A 1.049
Isopentyl acetate 130.19 product N/A 1 to 1 N/A 142 0.876

Isopentyl alcohol 88.15 0.820 g 9.3 x 10-3 1 to 1 N/A 130 0.809

Conc. sulfuric acid 98.08 0.15 mL 2.82 x 10-3 N/A N/A N/A 1.841 g/mL
Sodium hydrogen 84.01 3 mL 0.036 N/A N/A N/A 1.0018
carbonate, 5%
Sodium sulfate, 142.04 0.3 g 2.11 x 10-3 N/A N/A N/A N/A
anhydrous
Reaction and its Mechanism:

Overall Reaction:
O O CH3
CH3 H2SO4
CH3 C OH + CH CH2 CH2 OH CH3 C O CH2 CH2 CH
Acetic Acid CH3
Isopentyl Alcohol Isopentylacetate CH3

Mechanism:

H+ + +
OH OH OH O H O
O H+
CH3 C OH CH3 C OH CH3 C OH2
+ CH3 C OR CH3 C OR
CH3 C OH
R O H R O
+ H R O + H2O

Where R is CH3

CH2 CH2 CH

CH3
 Preparing Isopentyl Acetate by the Fischer Esterification

Procedure:
Part 1 – Refluxing Reaction Mixture
Weigh a reaction tube while it is in a 50-mL beaker. Record the mass of the beaker and the tube. Place 0.809 g
isopentyl alcohol in a test tube using a Pasteur pipette. Then, add 2 mL acetic acid and 3 drops concentrated
sulfuric acid to the tube. Add a boiling chip, then wrap a wet Kim-wipe around the top of the test tube. Place the
tube in a sand bath on a setting of 2-3. Heat to boiling, then reflux solution for 1 hour.
Part 2 – Separating and Washing Product Layer
Remove the test tube from the sand bath and allow to cool to room temperature. Remove the boiling chip from
the tube using a microspatula. Slowly add 1 mL of 5% NaHCO3 to the reaction mixture in the tube. Swirl tube
gently to mix. Then put a cork in the tube, and shake gently with venting until bubbles are no longer produced.
Label a test tube “Aqueous Layers”. Use a Pasteur pipette to remove the lower aqueous layer from the vial.
Place this aqueous layer into the labeled test tube. Repeat the extraction twice using new 1 mL portions of 5%
NaHCO3 each time. Then, wash the organic layer with 1 mL of distilled water. Again, remove the lower
aqueous layer and place in the labeled test tube. Finally, add 0.3 g anhydrous sodium sulfate to the test tube to
dry the product. Wrap a film of paraffin around the top of the tube, cork the tube, and place in the refrigerator
for a couple days.
Part 3 – Distilling the Product
Transfer liquid from test tube into the bottom of a Hickman still using a Pasteur pipette. Add a boiling chip to
the still, and wrap a wet Kim-wipe around the top of the still. Using a clamp to hold the still in place, put the
still into a sand bath and clamp into place. Set the sand bath on a setting of 2 – 3. Heat to boiling. As the liquid
evaporates and condenses, use a Pasteur pipette with a bent tip to remove the condensed liquid from the upper
ring of the Hickman still. Transfer the condensed liquid into a clean, dry, vial. Make sure you weigh and record
the mass of the vial before transferring any liquid into it. Continue until all of the liquid from the bottom of the
still has evaporated and all the distilled product collected. Measure and record the mass of the product.
Part 4 – Characterizing the Product
Place one drop of the distilled product on an infrared spectrum card. Place card in spectrometer and run an
infrared spectrum on the product.
Part 5 – Cleaning Up
The aqueous layers from the washings performed in Part 2 may be put down the sink with a lot of water. Place all
other materials in their appropriate waste containers.

Data and Calculations:

Mass isopentyl alcohol: 0.820 g
Mass product (isopentyl acetate): 0.745 g
Theoretical Yield: 1.211 g
Percent Yield: 61.52%
Finding Limiting Reagent
Acetic Acid (2 mL AA) ( 1.049 g AA) (1 mol AA) (1 mol product) (130.19 g product)
(1 mL AA) (60.05 g AA) (1 mol AA) (1 mol product)

= 4.549 g isopentyl acetate

Isopentyl Alcohol (0.820 g IA) (1 mol IA) (1 mol product) (130.19 g product)
(88.15 g IA) (1 mol IA) (1 mol product)

= 1.211 g isopentyl acetate

The limiting reagent for this esterification reaction is isopentyl alcohol. It yields the least amount of isopentyl
acetate in this reaction, and therefore is the limiting reagent.
 Preparing Isopentyl Acetate by the Fischer Esterification

Theoretical Yield
Isopentyl Alcohol (0.820 g IA) (1 mol IA) (1 mol product) (130.19 g product)
(88.15 g IA) (1 mol IA) (1 mol product)

= 1.211 g isopentyl acetate

Percent Yield
(mass of isopentyl acetate) (0.745 g isopentyl acetate) x (100) = 61.52% yield
(theoretical yield) (1.211 g isopentyl acetate)

Observed Properties and IR Data and Interpretation:

An infrared spectrum of the product revealed that it was isopentyl acetate. A peak at 1743.55 cm-1 indicated the
presence of a carbonyl group. The peak at 1056.08 cm-1 indicated a C-O-C bond, and the peak at 2960.55 cm-1 was
indicative of alkane –CH2- groups. Also, the peak at 1387.85 cm-1 indicated alkane bonds which include an isopropyl
split. As can be seen in the structure of the product, isopentyl acetate contains an isopropyl group at one end. It also
contains a carbonyl group, a C-O-C bond, and alkane –CH2- groups.

Results and Conclusions:

The esterification reaction between acetic acid and isopentyl alcohol, using concentrated sulfuric acid as a catalyst,
was successful and yielded isopentyl acetate. The percent yield of this reaction was 61.52%. This may have been low
due to the fact that not all of the condensed product was able to be removed from the Hickman still. Although most of
it was able to be removed using the bent Pasteur pipette, some may still have been stuck inside the still. Also, some
product was lost when the liquid was transferred from the test tube into the Hickman still. Some of the product may
have also evaporated during the distillation.

The product was proven to be isopentyl acetate via infrared spectroscopy. A peak at 1743.55 cm-1 represented a
carbonyl group. The peak at 1056.08 cm-1 indicated a C-O-C bond, and the peak at 2960.55 cm-1 represented alkane –
CH2- groups. Also, the peak at 1387.85 cm-1 indicated alkane bonds which include an isopropyl split. As can be seen
in the structure of the product, isopentyl acetate contains an isopropyl group at one end. It also contains a carbonyl
group, a C-O-C bond, and alkane –CH2- groups. Together, all these peaks indicated that the product was indeed
isopentyl acetate and that the esterification reaction was successful.

Reference:

Chemistry Lab Experiments CHEM 224 SYNT 713 pgs. 29– 44

By Wigal/Manion/LeFevre/Wade, Jr./Rapp/Lee/Wikholm

Weast, Robert C., ed. CRC Handbook of Chemistry and Physics. 70th ed. Boca Raton, FL: CRC Press, Inc., 1990.
 Preparing Isopentyl Acetate by the Fischer Esterification

Post-Lab Questions

1. The percent yield of isopentyl acetate was 61.52%. Please see calculations section for actual calculation.

2. Please see Observed Properties and IR Data and Interpretation section for a detailed list of the distinctive peaks
found in the IR spectrum of isopentyl acetate. Distinctive features of the IR spectra of acetic acid and isopentyl
alcohol are as follows:

Acetic Acid:
-COOH carboxylic acid group strong, broad peak 2500 – 3100 cm-1

Isopentyl Alcohol
-OH alcohol group strong, broad peak 3400 – 3640 cm-1
-C-O group 1050 – 1150 cm-1

3. A gas chromatogram was not obtained in this experiment.

4. An NMR spectrum was not performed in this experiment.

5. Write the equation for the reaction of 5% NaHCO3 with acetic acid.

NaHCO3 + C2H4O2 Æ NaC2H3O2 + H2CO3

Sodium bicarbonate + acetic acid Æ sodium acetate + carbonic acid

The carbonic acid breaks down into water and carbon dioxide. H2CO3 Æ H2O + CO2

6. What is the IUPAC name for isopentyl acetate?

The IUPAC name for isopentyl acetate is 3-methylbutyl acetate.