Experiment VIII: Preparation of Isopentyl Acetate:
Reaction.
CH3
O
H3C C CH2CH2OH +
H2SO4
H3 C C
O
O CH2CH2 C CH3
OH
H
Isopentyl alcohol
CH3
H3C C
+ H2O
H
Acetic acid
Isopentyl acetate
Purpose
Esters are found in many fruits and are their main odor component. In this lab we will be making an
ester; what is the odor of this ester? (Write down this observation in your notebook).
Experimental Procedure.
Estimated time to complete the experiment: 3.0 h. Unless otherwise noted, all manipulations should be
done in the chemical fume hood.
Physical Properties of
Reactants
Compound
Isopentyl alcohol
Acetic acid
Sulfuric acid, concentrated
MW
88.15
60.1
Amount
800 µL
1.5 mL
4 drops
mmol
7.4
26.2
bp (oC)
132
116
d
0.81
1.05
CONICAL VIAL W/ SPIN VANE, REFLUX CONDENSER
nD
1.3720
Place 800 µL (7.4 mmol) of isopentyl alcohol (use your 1mL syringe; use care not to poke yourself!), 1.5
mL (26.2 mmol) of glacial acetic acid (graduated cylinder), 4 drops (Pasteur pipet) of concentrated
sulfuric acid, and apporoximately 100 mg of silica gel beads (approximately 3 beads) into a 5.0-mL
conical vial containing a magnetic spin vane and equipped with a reflux condenser with an attached
calcium chloride drying tube. Cap the vial immediately after the addition of each reagent. Dispense the
reagents in the hood using automatic delivery pipets and cap the vial immediately after the additions are
complete. Concentrated acetic and sulfuric acids are corrosive.
Heat and stir the reaction mixture using a sand bath temperature of 160-180 oC for 1 h. Cool to room
temperature and remove the spin vane.
Remove the liquids from the silica gel beads and place them in a small test tube. Wash the liquids with 2mL of 5% sodium bicarbonate solution. (Shake gently and vent carefully). Remove and place the
aqueous layer in a beaker labeled ‘aqueous wash exp. 8’. Repeat this “washing” two more times, placing
the aqueous phase into the beaker each time. Finally wash the crude organic product with 2 mL of water.
Dry the remaining organic liquids by adding anhydrous sodium sulfate to the test tube until it “snows”.
Carefully pipet the liquid into a tared disposable vial.
Characterization.
Obtain the weight of your product and calculate the % yield. Check the purity of your sample by taking:
RI of the starting material and product
IR (neat) of the starting isopentyl alcohol and of the product
Questions (to be answered in your laboratory notebook):
1.
What purpose does the anhydrous sodium sulfate serve?
2.
What are the main impurities in the product and how will the IR spectrum tell you if they are
present?
3.
Use the Aldrich catalog to find the index of refraction of the product and compare it to your
experimental value.
Figure IR spectrum: isopentyl acetate
IR spectrum: isopentyl alcohol