Acetaminophen = Paracetamol.
OPTION 2: THE PREPARATION OF ACETAMINOPHEN
Materials Needed
p-aminophenol
Acetic anhydride
Phosphoric acid, concentrated
Ethanol
Dropper
Erlenmeyer flask, 125-mL
Beakers, 2 400-mL, 100-mL, 10 or 20-mL
Graduated cylinders, 10-mL, 25-mL
Watch glass
Stirring rod
Vial to hold aspirin sample
Ring stand
Clamp (to hold 125-mL Erlenmeyer flask)
Buchner funnel
Filter paper to fit Buchner funnel
Vacuum filtration flask
Rubber tubing for vacuum flask
Ice
Melting point capillary tube
Melting point apparatus
dropper
Disposable IR card
Optional: rubber gloves
Procedure
Fill a 400-mL beaker about half full with water. Place the beaker and water on a hot plate and bring to a boil.
Weigh out 1.5 g of p-aminophenol and transfer it into a 125-mL Erlenmeyer flask. (Avoid contact with skin. You
may wish to wear gloves.)
Add 25 mL of water. Add 20 drops of concentrated phosphoric acid, H
3
PO
4
, and swirl the flask until all of the
amine dissolves. If not, add a few more drops of phosphoric acid.
Turn off the hot plate. Place the flask in the hot water. Carefully add 2 mL of acetic anhydride to the flask. Leave
the flask in the warm water for 10 minutes.
Remove the flask and place it an ice-water bath. Stir the mixture to crystallize the acetaminophen. You may need
to scratch the walls of the flask to start the crystallization. If no crystals appear, add a small seed of acetaminophen
to start the crystal formation. Allow the flask to stay in the ice-water bath for 30 minutes.
Collect the crystals in a Buchner funnel using vacuum filtration.
Wash the crystals with 10 mL of cold water. Allow the crystals to dry.
Determine the mass of the crude acetaminophen.
Recrystallization of the Acetaminophen
Place the crude acetaminophen in a 100-mL beaker. Add 20 mL of water and heat on a hot plate until the crystals
dissolve. If the solution boils and crystals remain, add another 10 mL of water.
Remove the beaker and allow the solution to cool. When crystals begin to appear, place the beaker in an ice bath
for 20 minutes. If no crystals appear, scratch the inside walls of the beaker.
Collect the crystals using the Buchner filtration apparatus. Wash with 10 mL of cold water.
Transfer the filter paper and crystals to a watch glass and let dry.
Determine the mass of the purified acetaminophen.
Determine the Melting Point of the Acetaminophen Sample
Fill a capillary melting point tube to a depth of 0.2 cm with the recrystallized acetaminophen.
Place the capillary tube in the melting point apparatus. Determine its melting point. (Your instructor will
demonstrate the use of this apparatus.)
The melting point of acetaminophen is 169-171°C. p-aminophenol melts at 189-190°C.
The acetaminophen sample should be labeled with your name, the mass of the acetaminophen, the percent yield, and
its melting point.
NOTE: Don't use your acetaminophen for a headache! Its purity is not assured.
Verification of Acetaminophen
Place a small amount of your acetaminophen sample (about 0.10 g) in a 10-mL or 20-mL beaker. Add
approximately 2 mL of ethanol. Stir or swirl to dissolve. If necessary, warm the mixture slightly on a hot plate to
assist in solution. CAUTION: Ethanol is flammable. Do not allow it to boil.
Place one or two drops of the acetaminophen solution on a disposable IR card. Allow the ethanol to evaporate.
Run an IR of your acetaminophen.
Compare your IR spectrogram with the standard IR spectra of p-aminophenol and acetaminophen. How do they agree?
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