Download Microscale Synthesis of Acetylsalicylic Acid

Microscale Synthesis of Acetylsalicylic Acid
OH
+
C
OH
O
O C O
CH
OH 3
C
O
H C C
3
O
H C C
3
O
O
+
C
H C
3
OH
O
Introduction:
Acetylsalicylic acid is a wonder drug par excellence. It is widely used as an
analgesic (pain reliever) and fever depressant. It also reduces inflammation and may even
prevent heart attacks. It has a few side effects for some people, yet it is safe enough to be
sold without a prescription. Because it is easy to prepare, aspirin is one of the most
inexpensive drugs available. It is produced in vast amounts. In fact, industry makes
43,000,000 pounds of the drug every year.
This microscale experiment will permit you to make an amount of aspirin equivalent
to about 1/2 of that found in an aspirin tablet.
Purpose:
To synthesize acetylsalicylic acid on a microscale basis.
Equipment / Materials:
salicylic acid
acetic anhydride
conc. phosphoric acid
boiling chips
microscale kit
thermometer
filter paper
hot water
ice
eyedropper
2 beakers
Safety:


Wear goggles at all times in the lab.
The product is aspirin, but do not ingest it. It contains a lot of other dangerous
chemicals, too.

Phosphoric acid is very dangerous, handle it with care.
Procedure:
1. Accurately weigh out 135 - 140 mg. of salicylic acid and place it in a test tube from
the microscale kit. Add a boiling chip.
2 Add to the test tube one drop of 85% phosphoric acid and 0.3 mL of acetic anhydride
with the syringe in the microscale kit. The acetic anhydride should wash all other
ingredients to the bottom of the test tube.
3. Mix the reactants thoroughly and heat the mixture gently by placing it in a beaker of
hot (but not boiling) water. The temperature must be between 70 and 90C.
4. After several minutes of heating, cautiously add 0.2 mL of water to decompose the
excess acetic anhydride. When you observe no more evidence of reaction, add 0.3
mL more water; remove the tube from the hot water bath and allow it to cool slowly
to room temperature. If crystallization does not occur spontaneously, add a seed
crystal or scratch the inside of the tube with a stirring rod.
5. Cool the tube in a cup of ice water for several minutes until crystallization is complete.
Do not let the tube tip over and spill into the ice water.
6. Collect the crystals of acetylsalicylic acid by vacuum filtration with a Hirsch funnel
and wash the product with only tiny amounts of ice water.
7. Dry the crystals on a piece of filter paper and then allow to dry thoroughly in air before
weighing. It is a common practice among synthetic organic chemists to calculate the
percent yield of a product. You may also wish to check its purity by measuring the
melting point and comparing it with the accepted value.
Data:
Mass of :
salicylic acid used:
___________g
filter paper:
___________g
filter paper and product:
___________g
dry product:
___________g