The synthesis and analysis of aspirin

The Synthesis And Analysis Of Aspirin
Aspirin, the ubiquitous pain reliever, goes by the chemical name acetylsalicylic acid. One of the compounds used in the synthesis of aspirin is salicylic acid, which is itself a pain reliever that was known to many ancient cultures, including the Native Americans who extracted it from willow tree bark. Salicylic acid is extremely bitter tasting, and frequent use can cause severe stomach irritation. The search for a milder form of this pain reliever led to the successful synthesis of acetylsalicylic acid by the German chemist Felix Hoffmann in 1893.
Your two primary objectives in this experiment will be to synthesize and analyze aspirin. There is more than one way to synthesize aspirin; in this experiment, you will react acetic anhydride with salicylic acid in the presence of phosphoric acid (which acts as a catalyst). A drawing of the You will conduct two tests of your synthesis to verify that you did indeed make aspirin, and to determine its relative purity. First, you will measure the melting point of a sample of your product. Second, you will use a Colorimeter to test the absorbance of your aspirin after it has been “prepped” with an iron solution to give it color.
• Synthesize a sample of acetylsalicylic acid (aspirin).
• Calculate the percent yield of your synthesis.
filter funnel, filter flask, and filter paper 0.025 M iron(III) nitrate solution, Fe(NO3)3 Procedure
Part I Synthesize Aspirin
1. Obtain and wear goggles and lab aprons. Note: conduct this reaction in a fume hood or a
2. Measure out 2.0 grams of salicylic acid into a 50 mL Erlenmeyer flask.
3. Add 5.0 mL of acetic anhydride and 5 drops of 85% phosphoric acid. Swirl the mixture. If necessary, use a sparingly small amount of distilled water to rinse down any bits of solid that may be on the inner walls of the flask. CAUTION: handle the phosphoric acid and acetic
anhydride with care. Both substances can cause painful burns if they come in contact with 4. Heat the mixture on a hot plate, at 75°C, for 15 minutes, or when the mixture ceases releasing vapors. Stir the mixture occasionally during heating. After about 10 minutes, add 2 mL of distilled water to the flask. Set up a Büchner funnel and filter flask so that you are ready to filter the reaction mixture after it has cooled.
5. When you are confident that the reaction has reached completion (no vapors appearing), carefully remove the flask from the hot plate and add 20 mL of distilled water. Allow the mixture to cool to near room temperature. Transfer the flask to an ice bath for about five minutes. As the mixture cools, crystals of aspirin should form in the flask.
6. Transfer the contents of the cooled flask to a Büchner funnel assembly. Filter the mixture with vacuum suction. When most of the liquid has been drawn through the funnel, turn off the suction and wash the crystals with 5 mL of cold, distilled water. After about 15 seconds, turn the suction back on. Wash the crystals with cold, distilled water twice more in this 7. Store the aspirin crystals in a safe place and prepare to test their purity.
Part II Test the Colorimetric Absorbance of an Aspirin Sample
Your synthesis converted most, but not all, of the salicylic acid into acetylsalicylic acid. You will mix iron(III) nitrate with salicylic acid and your aspirin sample to complex the salicylic acid, which is a bluish-purple color. You will analyze several samples to determine the amount of salicylic acid in your synthesized aspirin. You can use this information to calculate the purity of your aspirin sample. Follow Steps 8-10 to prepare a set of salicylic acid standard solutions and conduct testing to develop your own Beer’s law plot of the standards. If your instructor supplies you with the Beer’s law standard data, start at Step 9.
8. Quantitatively prepare the stock salicylic acid solution.
a. Measure out about 0.20 g of salicylic acid. Record the precise mass that you use.
b. Transfer the salicylic acid to a 250 mL beaker and add 10 mL of 95% ethanol. Swirl the c. Add 150 mL of distilled water to the beaker. Mix the solution.
d. Transfer the solution from the beaker to a 250 mL volumetric flask. Thoroughly rinse the beaker with several portions of distilled water, and transfer the rinse water to the volumetric flask. Add distilled water to fill the flask to the 250 mL mark. Mix the solution. Calculate the precise molar concentration of your stock solution and record it in 9. Prepare four standard solutions of varying concentrations of salicylic acid.
a. To prepare 100 mL of your standard solution (the solution you will use for Trial 1), quantitatively transfer 10 mL of the stock salicylic acid solution you prepared in Step 15 b. Add 0.025 M Fe(NO3)3 solution to the flask to make precisely 100 mL.
c. Prepare the remaining three salicylic acid standard solutions according to the table below, diluting the standard solution in the 100 mL flask with distilled water. Mix thoroughly.
Calculate the precise molar concentrations of the four standard solutions in the table above and record them in your data table.
a. Start the EasyData application, if it is not already running.
from the Main screen, and then select New to reset the application.
from the Main screen, and then select Events with Entry
d. Prepare a blank by filling an empty cuvette ¾ full with distilled water. Place the blank in the cuvette slot of the Colorimeter and close the lid.
e. Set the wavelength on the Colorimeter to 565 nm. Then calibrate by pressing the AUTO 11. You are now ready to test the four standard solutions.
b. Remove the cuvette from your Colorimeter and pour out the water. Using the solution in the first 100 mL volumetric flask of salicylic acid, rinse the cuvette twice with ~1 mL amounts and then fill it ¾ full. Wipe the outside with a tissue, place it in the Colorimeter, c. When the value displayed on the calculator screen has stabilized, select . The absorbance and concentration values have now been saved for the first solution.
d. Discard the cuvette contents as directed by your instructor. Using the solution in the second 100 mL volumetric flask, rinse the cuvette twice with ~1 mL amounts, and then fill it ¾ full. After closing the lid, wait for the value displayed on the calculator screen to . Enter the concentration in mol/L and select e. Repeat the procedure for the remaining salicylic acid solutions that you prepared.
to stop data collection. A graph of absorbance vs. concentration will be g. Examine the data points along the curve. As you move the cursor right or left, the concentration (X) and absorbance (Y) values of each data point are displayed above the graph. Record the absorbance and concentration values in your data table.
12. Calculate the best-fit line (linear regression) equation for the standard solutions.
, and then select Linear Fit. The linear-regression statistics for these two lists
are displayed for the equation in the form where y is absorbance, x is concentration, a is the slope, and b is the y-intercept. b. Record the linear regression equation in Part III of your data table.
c. To display the linear-regression curve on the graph of absorbance vs. concentration, 13. Prepare the aspirin sample for testing. Complete this step quickly.
a. Measure out about 0.20 gram of aspirin and transfer it to the 250 mL beaker. Record the precise mass of aspirin that you use.
b. Add 10 mL of 95% ethanol to the beaker of aspirin sample. Swirl the mixture to dissolve c. Add 150 mL of distilled water to the beaker. Mix the solution.
d. Quantitatively transfer the solution from the beaker to a 250 mL volumetric flask. Thoroughly rinse the beaker with several portions of distilled water, and transfer the rinse water to the volumetric flask. Add distilled water, as needed, to fill the flask to the 250 mL mark. Mix the solution thoroughly.
e. Transfer 5 mL of the aspirin solution from the 250 mL volumetric flask to a clean and dry 100 mL volumetric flask. Add 0.025 M Fe(NO3)3 solution to the flask to make precisely 100 mL. Mix the solution thoroughly.
14. Measure and record the absorbance of the treated aspirin sample. This must be done within 5 a. Transfer about 1 mL of the treated aspirin sample to a clean and dry plastic cuvette.
b. Rinse and fill the cuvette ¾ full with the sample. Cap the cuvette and place it in the Colorimeter. Monitor the absorbance on the Main screen. Record this value in Part III of c. If the absorbance value falls within the range of the salicylic acid standard solutions, record it in your data table. If it does not, repeat Step 20d with a more dilute, or more d. Repeat Parts a–c of this step two times with new aliquots of the treated aspirin sample.
15. Discard all solutions as directed.
Synthesis of Aspirin
Mass of acetic anhydride used (vol. × 1.08 g/mL) Salicylic Acid Standard Stock Solution
Beer’s Law Data for Salicylic Acid Standard Solutions
Best- fit line equation for the salicylic acid standards Purity of the Synthesized Aspirin
Moles of salicylic acid in aspirin sample (mol) Mass of salicylic acid in aspirin sample (g)


These questions were originally published in the AA Grapevine in conjunction with a series on the Twelve Traditions that began in November 1969 and ran through September 1971. While they were originally intended primarily for individual use, many AA groups have since used them as a basis for wider discussion. Tradition One: Our common welfare should come first; personal recovery depends upon

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