Question

Write out your separation scheme for this experiment.

1. Heat 75 mL of water to 90 °C in a 250-mL beaker.

2. While the water is being heated, place 250 mg of salicylic acid, 1 drop of 85% phosphoric acid and 0.5 mL of acetic anhydride in a test tube. Add a boiling chip to the mixture and gently shake it in order to mix the reactants.

3. Heat the tube in the beaker of water at 85 - 90 °C for about 5-6 minutes.

4. Remove the tube from the hot water bath and carefully add 4 drops of water to decompose the unreacted acetic anhydride (the acetic anhydride is converted into two molecules of acetic acid). The test tube will feel warm to the touch due to the heat generated by the reaction of the anhydride with water. Allow it to cool and then add another 0.5 mL of water.

5. Next, place the tube in an ice bath and allow the solid product to crystallize out of solution. If the solid does not crystallize, scratch the side of the test tube in order to aid in crystal formation. The mixture should be cooled on ice for at least 10 minutes in order to ensure that all of the product has come out of solution.

6. Collect the product crystals by vacuum filtration on a Hirsch funnel. A minimal amount of ice-cold water can be used in order to transfer the product from the test tube to the filter funnel. Allow air to pass through the crystals for 7-10 minutes to promote drying.

7. Weigh the crude product.

8. Recrystallize from a hot ethanol:water solvent system (ask your TA for help with this system). Add a minimum amount of HOT ethanol to the solid in a small beaker (not an Erlenmeyer flask). This requires that you keep the entire solution HOT as you add the solvent slowly with swirling. Once the solid has completely dissolved, slowly add hot water dropwise to the ethanolic solution until the solution becomes slightly cloudy. Allow the tube to cool to room temperature. If after 7-10 minutes the solid has not recrystallized, immerse the beaker in an ice/water bath. Still no crystals? Concentrate the solution on a hotplate and cool to room temperature.

9. Isolate the product by vacuum filtration and dry for approximately 10 minutes. 10. Weigh your final product and calculate a percent recovery (final mass/crude mass x 100) and a percent yield. Measure the melting point range of your product and the acetylsalicylic acid standard (recall that two melting points can be measured at a time), and collect an IR spectrum.

Answer 1

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