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 |filter paper | | |acetic anhydride |hot water | | |conc. phosphoric acid |ice | | |boiling chips |eyedropper | | |microscale kit |2 beakers | | |thermometer | | | 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 90C.
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.