Experiment 6
Fischer Esterification
Rxn 1
O
H3C
H3C
OH
heptanoic acid
Rxn 2
O
cat. CH3COCl
O
ethanol
O
O
cat. CH3COCl
O
OH
ethanol
benzoic acid
For this week’s lab, you will perform either Rxn 1 or Rxn 2 shown above. Both are
Fischer Esterifications, in which you can use either supplied heptanoic acid (Rxn 1) or
the benzoic acid you synthesized in last week’s lab (Rxn 2).
Procedure:
Rxn 1:
To a 5 mL conical vial, add 0.1 mL heptanoic acid followed by 2.0 mL of absolute
ethanol (200 proof).
Rxn 2:
To a 5 mL conical vial, add 0.1 g benzoic acid followed by 2.5 mL of absolute ethanol
(200 proof).
Rxns 1 and 2:
Add a magnetic spin vane for stirring. Lastly, add 40 µL of acetyl chloride (which can be
measured out as 4 drops from a dry disposable Pasteur pipette). Then connect the waterjacketed reflux condenser and a CaCl2-charged drying tube. Be sure to tightly cap the
acetyl chloride bottle after use because acetyl chloride reacts rapidly with moisture in the
air.
With an aluminum block-equipped hot plate stirrer, heat the reaction mixture at a gentle
reflux for one hour (block plate temp ~120oC). Remove the reaction mixture from the
heat source and allow to cool.
Once the reaction vial is comfortable to the touch, replace the spin vane with a boiling
stone, and concentrate the reaction mixture to an approximate volume of 0.3 mL. This is
done to prevent emulsions during the following extractive isolation. Upon cooling of the
conical vial, add 1 mL of diethyl ether and 1 mL of 5% aqueous sodium bicarbonate to it.
Gently agitate the conical vial after having capped it. Make sure to vent the conical vial
periodically by slightly loosening the cap. Remove the lower aqueous layer with the
disposable pipette. Extract the ether layer with two more 1 mL portions of 5% sodium
bicarbonate. Combine the aqueous extracts, and discard. Keep the upper ether layer.
Drying and further purification of the ether solution of your ester is achieved by column
chromatography. To prepare a column for chromatography, plug a disposable pipette
with a small piece of cotton, and sequentially add 50 mg sand, 500 mg silica gel, and 500
mg anhydrous sodium sulfate. Wet this column with 0.5 mL of dichloromethane, and
then apply your ethereal product solution to the column. Use a tared 10 mL beaker to
collect the eluant. Rinse the conical rxn vial with 0.5 mL dichloromethane, and add to the
column to elute more product. Repeat this step with another 0.5 mL dichloromethane.
Complete product elution by the addition of 1.0 mL of dichloromethane directly to the
column. Concentration (boiling) of the eluant using hot plate affords the ester product.
Determine the amount of product and calculate percent yield. If the yield is low, the
further elution of the chromatography column with dichloromethane should be
considered. Collect the eluant in the same conical vial as above and concentrate.
Obtain an IR spectrum of the product.