Preparation of Acetaminophen

PREPARATION of ACETAMINOPHEN

OBJECT

To synthesize the common pain reliever: acetaminophen (paracetamol)

To determine the purity of acetaminophen.

THEORY

Acetaminophen is an amide, a compound that is a derivative of ammonia that has been reacted with an acidic

substance, in this case, acetic acid. Acetaminophen acts as a fever reducer and pain reliever. It can be found in

several analgesic preparations, such as Tylenol, some of which may contain other ingredients such as caffeine and

buffers.

Qualitatively, the purity of an acetaminophen sample can be determined from its melting point. The

melting point of a substance is essentially independent of atmospheric pressure, but it is always lowered by the

presence of impurities (a colligative property of pure substances). The degree of lowering of the melting point

depends on the nature and the concentration of the impurities.

SAFETY PRECAUTIONS

Wear safety glasses or goggles at all times in the laboratory.

Acetic anhydride is corrosive and its vapor is irritating to the respiratory system. Avoid skin contact and inhalation

of the vapors. In the event of skin contact, rinse well with cold water. If the vapors are inhaled, move to an area

where fresh air is available.

Sulfuric acid is corrosive. Avoid skin contact. In the event of skin contact, rinse well with cold water.

p-aminophenol is harmful by inhalation and by contact with the skin. In the event of skin contact, rinse well with

cold water. If the vapors are inhaled, move to an area where fresh air is available.

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, H3PO4 , 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