Aspirin Synthesis (Long Version)
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.
salicylic acid
acid
+ acetic anhydride
acetylsalicylic acid
+
acetic
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
Syringe
Filtering flasks
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. Place a container on the balance, tare it; add between 135 and 140 mg of salicylic acid to the
container. Record the mass (all four decimal places!) in the data table.
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. Using the syringe from your microscale kit, add 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. Be sure to rinse the syringe well with water to clean it after use.
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 from a central source.
7. To heat its contents, place the test tube in the water bath between 70 and 90° C. 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, heat the solution in the reaction tube for 2 minutes more then
cautiously add 0.5 mL of distilled water.
10. Remove the test tube from the water bath and allow it to cool to room temperature.
11. [If crystallization has not occurred at room temperature, use a spatula to scratch the inside of
the test tube.] Check with your teacher before doing this step.
12. 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.
13. Transfer all of the contents of the test tube to the Hirsch funnel. You may use your spatula
and rinse the test tube with ice water to be sure you transfer all of your product to the funnel.
14. Filter your product using the vacuum pump provided.
15. Scrape your acetylsalicylic acid product onto the filter paper; and leave it to dry overnight.
16. [Write your name on a plastic bag with a Sharpie. Weigh 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).]
17. 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.
18. Once your product is dry, weigh the filter paper and product in the bag. Record its mass in
the table below then calculate the mass of the dry product. [You may need to save your
product on the filter paper in the bag until you can weigh the filter paper and product in the
bag.]
Name _________________________
Partner’s Name(s) _________________________
Period ______Date_______________
Data:
Mass of salicylic acid used
Mass of filter paper
[Mass of plastic bag]
[Mass of bag, filter paper and product]
Mass of 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. (HINT: Write a unit path to outline how
you will calculate the quantities needed to decide which is 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 productformed (experimental)
theoretical amount of productformed
percent yield =
x 100
Name _________________________
Partner’s 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?