Aspirin Synthesis
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 in one of the most inexpensive drugs available and 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 acetylsalicylic acid, or aspirin, by reacting
salicylic acid with acetic anhydride. You will make an amount of acetylsalicylic acid equivalent to about
half of an aspirin tablet, but your aspirin will not be in a form that can be ingested because it will still be
contaminated with harsh chemicals from the reaction.
The reaction is given below; remember that each corner of the hexagon represents one carbon
atom with enough hydrogen atoms to provide four bonds to each carbon atom.
O
O
HO
C
O
OH
H3 C
C
O
O
C
OH
H3 C-C
OH
O
+
+
H3 C-C
H3 C-C
O
O
salicylic acid
+ acetic anhydride
acetylsalicylic acid
+ acetic acid
Purpose:
To synthesize acetylsalicylic acid on a microscale basis.
Materials/Equipment:
analytical balance
filter paper
stirring rod
Hot plate
microscale kit:
test tube
Hirsch funnel
Filtering flasks
Syringe (optional)
salicylic acid
acetic anhydride
boiling chips
conc. phosphoric acid
Pure water
100 mL beaker
thermometer
vacuum pump
ice/styrofoam cup
Safety Considerations:
 Wear goggles and an apron at all times in the lab.
 Several of these chemicals will irritate your skin and eyes. If you spill anything on you, wash the
area thoroughly with soap and water.
 Do not rub your face or eyes because you may get chemicals in your eyes. If your eyes start to
burn, rinse them at the eye wash station.
Do not ingest the aspirin you produce. It still contains harmful chemicals and is not fit to be taken.
Procedure:
1. Accurately mass 135-140 mg of salicylic acid to the container. Record the mass (all four decimal
places!) in the data table. Remember that the balances read “grams,” not “milligrams.”
2. Transfer all of the acid to a reaction tube (test tube) from the microscale kit.
3. Add one boiling chip and one drop of conc. phosphoric acid to the test tube.
4. Add 7 drops (approx. 0.3 mL) of acetic anhydride to the test tube. Try to rinse all the other ingredients
to the bottom of the test tube when adding the acetic anhydride.
5. Shake the reaction tube vigorously side to side to mix the reactants thoroughly.
6. Fill a styrofoam cup about one-third full with hot water (between 70 and 90° C) from a central source.
7. Place the test tube in the water bath. You are trying to dissolve the salicylic acid and may need to
agitate the test tube while it is in the water bath.
8. While waiting write your name in pencil on a piece of filter paper. Determine its mass using an
analytical balance, and record it in the data table (all of the digits).
9. Once the acid is dissolved (contents will be completely clear), heat the solution in the reaction tube for
2 minutes longer. Cautiously add 12 drops (0.2 mL) of water to decompose excess acetic anhydride.
10. Remove the test tube from the water bath and allow it to cool to room temperature. If crystallization
does not occur spontaneously at room temperature, use a spatula to scratch the inside of the test tube.
Check with your teacher before doing this step.
11. Once crystallization has started, cool the test tube in a cup of ice water for several minutes until
crystallization is complete. Be careful not to let the tube tip over and spill into the ice water.
12. Press the piece of filter paper in the Hirsch funnel. Transfer all of the contents of the test tube to the
Hirsch funnel. You may use your spatula, rinsing it and the test tube with ice water, to be sure you
transfer all of your product to the funnel.
13. Filter your product using the vacuum pump provided.
14. If a drying oven is available, dry the crystals on the filter paper thoroughly in the oven and let cool to
room temperature before massing. Do not let the paper heat so long that it burns. If a drying oven is
not available, see step 15.
15. If a drying oven is not available, it will be necessary to dry the crystals overnight. Write your name
on a plastic bag with a Sharpie. Mass it using an analytical balance. Make sure that the bag does not
touch the sides or bottom of the balance case. Record the mass in the data table (all of the digits).
Place filter paper with product in the bag and allow to dry overnight.
16. To clean your lab station, rinse all glassware and the funnel and return them to the microscale kit.
You may need to roll a paper towel carefully to wipe clean the inside of the reaction tube.
17. Once your product is dry, mass the filter paper with product. [If you dried the product in a plastic bag
overnight, be sure to mass the filter paper with product in the plastic bag.] Record its mass in the
table below. Then calculate the mass of the dry product.
18. It is 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 with a Mel-Temp and
comparing it to the accepted value. You may also wish to measure the melting point of the reactant in
order to see that a chemical change actually occurred.
Name(s) ____________________________________________Period ______Date_______________
Data:
Mass of salicylic acid used
Mass of filter paper
[Mass of plastic bag, if bag was used]
[Mass of bag, filter paper and product, if bag was used]
Mass of filter paper and product
Melting Points (optional)
Salicylic acid (reactant)
Acetylsalicylic acid (product)
Calculations: (limiting reactant version)
1. You reacted salicylic acid and acetic anhydride to form aspirin, or acetylsalicylic acid. The reagent
that runs out is called the limiting reagent because it limits the amount of product that can be formed.
Determine which reactant, acetic anhydride or salicylic acid, will be used up first. The density of
acetic anhydride is 1.08 g/mL. You used 7 drops of acetic anhydride (approximately 0.3 mL). HINT:
Write a unit path to outline how you will calculate the quantities needed to determine the limiting
reactant.
2. Calculate the theoretical yield, that is, the mass of aspirin that should be formed if all of the limiting
reactant is used to form acetylsalicylic acid.
3. Calculate the percent yield for your reaction given
actual amount of product formed (experimen tal)
percent yield =
x 100
theoretica l amount of product formed
Name(s) ____________________________________________Period ______Date_______________
Data:
Mass of salicylic acid used
Mass of filter paper
[Mass of plastic bag, if bag was used]
[Mass of bag, filter paper and product, if bag was used]
Mass of filter paper and product
Melting Points (optional)
Salicylic acid (reactant)
Acetylsalicylic acid (product)
Calculations (non-limiting reactant version):
You reacted salicylic acid and acetic anhydride to form aspirin, or acetylsalicylic acid. You were
directed to use an excess amount of the acetic anhydride so that the amount of aspirin produced would be
determined by the amount of salicylic acid reacted.
1. Calculate the molar mass of salicylic acid, C7H6O3.
2. From the mass of salicylic acid measured out, calculate the moles of salicylic acid reacted.
3. From the equation in the introduction, determine the number of moles of acetylsalicylic acid produced
by the moles of salicylic acid calculated above.
4. Calculate the mass of aspirin that should have been produced, the theoretical yield. (HINT: First
calculate the molar mass of the acetylsalicylic acid.)
5. Calculate the percent yield for your reaction.
actual amount of product formed (experimen tal)
percent yield =
x 100
theoretica l amount of product formed
Name(s) ____________________________________________Period ______Date_______________
Questions:
1.
What is aspirin?
2.
How does aspirin work?
3.
What are some of the side effects of aspirin?
4.
What are the natural and synthetic sources of aspirin?
5.
Who first made aspirin naturally and synthetically?
6.
What is the chemical formula for aspirin?
7.
If you got less than 100% yield, pose an explanation or two about how you might have lost some of
your aspirin.
8.
What chemicals may still be present that would contaminate your aspirin product?
9.
How could you use a Mel-temp (a melting point apparatus) to check the purity of the aspirin you
produced?