The "symbolic equation"

The proper chemical equation

Expected student background

Time required

Safety concerns

General Safety Guidelines

1. Both the acetic anhydride and the sulfuric acid are potentially dangerous materials for students to handle. Thus, the directions state that you will dispense these materials – and in a fume hood, for added safety. Dispense the two liquids from small LDPE dropping bottles (not wash bottles) to minimize your exposure, too.

2. Even so, care must be taken to ensure that students do not spill these materials as they walk back to their lab stations. You need to be ever-vigilant.

3. One student should remain with the hot plate at all times.

4. The small amount of ASA produced in the experiment may be dumped down the drain if in solution, or thrown in the trash if still in crystal form.

Acetic anhydride
Iron (III) chloride hexahydrate
Salicylic acid
Sulfuric acid

For Day 1

1. Prepare the acetic anhydride and concentrated sulfuric acid dropping bottles.

2. Set out the small container of salicylic acid.

3. Purchase commercial aspirin tablets for the iron(III) chloride test. (Or obtain them from the school nurse.)

4. If you have access to a vacuum filtration system, its use will speed up the filtration process.

For Day 2

1. Prepare the 1% iron(III) chloride solution (1 g iron(III) chloride in 100 mL of solution).

2. Be aware that students may not have enough product to do a melting point determination. You might want to take a few aspirins and mix them with some SA to make a mixture, and then ask students to use this (as representative of their product sample) to determine melting point ranges.

3. Set up the mineral oil baths for the melting point determinations, if you plan to do this step. See page 9 of the "Chemistry in Medicine" module of the SourceBook for the materials and description of the apparatus and procedure.

Pre-lab discussion

1. Briefly explain the goal (synthesis) and the type of reaction (esterification). Make sure that the students grasp the connection between the macroscopic materials with which they are working, the symbols written in the chemical equation, and the unseen molecules being torn apart and rebuilt at the microscopic level. While this seems simple, the connections are not always apparent to students.

2. Stress material hazards as listed in the student version and in teacher notes above.

3. Remind students to measure masses precisely.

4. Review theoretical and percent yield calculations. (These could wait until day 2.)

5. Explain the iron(III) chloride test. Many phenols (R-OH) produce colored coordination compounds with iron(III) ions. These complex anions are composed of 6 molecules of the phenol combined with one iron(III) atom. Since salicylic acid has a phenolic –OH group, it produces the positive (purple) test with iron(III) chloride.When SA reacts completely to produce ASA, the phenolic group is replaced with an acetate (acetyl) group, so the iron test would be negative. Of course, students will not get 100% yield, so some SA remains to make their sample purple in the iron test.

6. Describe the method of determining the melting point range (from the temperature at which solid first begins to melt to the temperature at which the solid is completely melted), if you do this part of the experiment.

Anticipated student results

1. The SA should turn dark purple; the prepared sample should be dark purple (due to SA contamination), and the commercial aspirin sample will probably be a pale orange color (indicating no SA contamination).

2. This microscale experiment may not provide enough product sample to test melting point. While capillary tubes don't require much sample, students don't have much sample, either. If you want to pursue this experiment, refer to the SourceBook's "Chemistry in Medicine" experiment's Lab Activity: Teacher Notes, p. 9, which accompanies this module, for directions. These are photocopyable for student use. Values for melting point ranges will be broad, typically between 128 and 137°C, again indicating relative impurity.

3. See p. 10 of the Teacher Notes from SourceBook's "Chemistry in Medicine" for a description of the experiment using a Spectronic 20 visible wavelength spectrophotometer to determine the amount of SA in the lab product versus that in an actual aspirin tablet.

Relevant National Science Education Standards

Unifying Concepts and Processes — The students will learn the workings of a system which is the chemical reaction that produces aspirin.

Science as Inquiry — The readings familiarize the students with the steps of scientific inquiry as they investigate the results of their reactions.

Physical Science — Understanding of the structure of molecules and chemical reactions are central to the activity.

Science and Technology — The activity demonstrates the science that has been applied to pain-relief technology.

Science in Personal and Social Perspectives — Personal health is central to this activity of aspirin synthesis.

History and Nature of Science — The activity connects the students with the research of Felix Hoffmann and Arthur Eichengrün.

Relevant New Jersey State Science Curriculum Standards

5.1	The students will learn the workings of a system which is the chemical reaction that produces aspirin.
5.2	The readings familiarize the students with the steps of scientific inquiry as they investigatethe results of their reactions.
5.3	Aspirin is a major discovery whose story nicely meets this standard. Here the students re-create that discovery.
5.4	Many scientific principles must be applied to re-create the invention of aspirin.
5.5	Mathematical calculations are central to this activtiy.
5.8	This activity involves the students directly with changes taking place at the molecular level during the synthesis of aspirin.