The Diels-Alder Reaction of
Anthracene with Maleic Anhydride
The Diels-Alder reaction is a member of a class of reactions called cycloadditions. The reaction involves three π bonds, two from the diene and one from the dienophile in a concerted reaction to form a six-membered ring. Since the reaction involves four π electrons in the diene and two π electrons from the dienophile, it is sometimes referred to as a 4 + 2 cycloaddition.
Normal Diels-Alder reactions are favored by electron donating groups on the diene and electron withdrawing groups on the dienophile. The diene must be capable of achieving an s-cis conformation to generate the cis double bond in the cyclohexene product. ...view middle of the document...
Obtain and wear goggles. Protect your arms and hands by wearing a long-sleeve lab coat and gloves. Conduct this reaction in a fume hood.
2. Weigh out 0.80 g of anthracene and 0.40 g of maleic anhydride and transfer the reagents into a 50 mL round bottom flask containing a stir bar. Record both masses to the nearest 0.01 g.
3. Add 10 mL of xylene to the round bottom flask. CAUTION: Xylene is flammable. Keep away from open flames and hot plates.
4. Set up a reflux with the condenser and a drying tube, making sure to clamp the flask and condenser securely. Remember to grease the joints to prevent the glass from sticking.
Note: Maleic anhydride is water sensitive and the drying tube will help prevent water in the air from entering the flask.
5. Heat the reaction mixture using a heating mantle to reflux (~180°C) for approximately 30 minutes. Monitor the temperature using a Temperature Probe or thermometer.
6. While waiting, prepare two ice water baths using two 250 mL beakers.
7. Obtain approximately 5 mL of xylenes in the 100 mL beaker. Place the beaker in the ice water bath to cool.
8. After 30 minutes, let the reaction flask warm to room temperature. Wait at least 15 minutes for the flask to warm to room temperature. Then, place the flask in the second ice water bath for 10 minutes. You should observe crystallization at this point.
9. Collect the solid.
a. Weigh the filter paper and record the mass to the nearest 0.01 g.
b. Set up a vacuum filtration with the Büchner funnel.
c. Filter the solid and wash the solid with ~5 mL of cold xylene.
d. Place the filter paper containing the solid on a watch glass and gently direct a stream of air (low flow) to thoroughly dry the solid.
10. Weigh the filter paper and dried product. Record the mass to the nearest 0.01 g. The sample should be completely dried before taking a melting temperature.
Part II Test the Melting Temperature
11. Obtain a small amount of your product. The solid should be in a powdered form. If it is not, use a mortar and pestle to carefully grind the solid to a powder.
12. Prepare a sample for melting.
a. Pack a capillary tube 3–4 mm (~1/8 inch) deep with your sample by inserting the open end into a small pile of the solid. A small amount of the solid will be pushed up into the tube.
e. Tap the closed end of the capillary tube on the table top to compress the sample into the closed end.
f. Check the control knob on the Melt Station to confirm that it is in the Off position.
g. Carefully insert the capillary tube of solid into one of the sample holders of the Melt Station.
13. Connect the Melt Station power supply to a powered electrical outlet.
14. Connect the Melt Station sensor cable to LabQuest or to a computer interface.
15. Start the data-collection program, then choose New from the File menu. You are now set up to take melting temperature data for up to 20 minutes.
16. In the first trial, you will...