Hiram College, Chem. 320: Spring 2010

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Student Notes: Diels-Alder Reaction with Maleic Anhydride and Anthracene

In this experiment you will: synthesize a product using a Diels-Alder reaction via two different methods of heating

characterize and compare the products using both IR and melting points

Techniques: refluxing, suction filtration, recrystallization, and microwave

Characterization: melting point and IR Spectroscopy

Chemicals Used: anthracene, maleic anhydride, toluene, and ethyl acetate (All of these should be in table of reagents including the overall product)

Pre-Lab Assignments Notebook After table of reagents include: overall reaction (draw the structures) convert all amounts to moles label the limiting reagent calculate the theoretical yield product info: 9,10-dihydroanthracene-9,10-alpha,beta-succinic anhydride (MW=276.29, MP= 262-264 °C) Questions (on a separate sheet of paper, turn in at the beginning of lab) 1. Draw the mechanisms and products of the following Diels-Alder reactions:

Waste Disposal: dispose of all solid and liquid waste in the appropriate labeled container

Hiram College, Chem. 320: Spring 2010

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Introduction The Diels-alder reaction is named for Otto Diels and Kurt Alder, who discovered and developed the reaction in the late 1920’s. The importance of this reaction in understanding pericyclic reactions and as a tool in synthetic organic chemistry led to their award of a Nobel Prize in 1950. The Diels-Alder reaction is a concerted (one step) reaction between a diene and a ‘dienophile’ to form a cyclohexene ring. Because the reaction involves 4π electrons in the diene and 2π electrons from the dienophile, it is often called a 4 + 2 cycloaddition. Scheme 1: Example of a 4 + 2 Diels-Alder reaction

Low molecular weight dienes typically are volatile, unpleasant smelling substances. This laboratory exercise uses anthracene as the diene to avoid this problem. Anthracene has a relatively high molecular weight, and therefore a low vapor pressure and odor. However, it is classified as an aromatic compound, and is stabilized by resonance. It is relatively unreactive as a diene in the Diels-Alder reaction. To compensate for the low reactivity of the diene, a highly reative dienophile, maleic anhydride is used. It has two EWG’s attached to the double bond. The reaction will also be run at high temperature to increase the rate. The mechanism of the reaction is: Scheme 2: Diels-alder Reaction of Anthracene and Maleic Anhydride

Hiram College, Chem. 320: Spring 2010

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Procedure Part A: Traditional Method 1. Add 1.78g anthracene, 0.979 g maleic anhydride, 10 ml toluene, and a stir bar in a 50 ml rbf with a reflux condenser. 2. Place the flask and reflux set-up on a hot plate. Using a thermometer determine the setting needed to reach 125°C, and be sure to check often to ensure that the temperature is somewhat constant. 3. Reflux the mixture for 3 hours at 125°C 4. After 3 hours allow the mixture to cool to room temperature, and then place it in an ice bath for crystallization. 5. Collect the product by suction filtration (wash with ethyl acetate) and recrystallize it with hot ethyl acetate. Allow the purified product to dry. 6. Characterize the product using IR spectroscopy and melting points. Part B: Microwave Method 1. Add 0.879 g anthracene, 0.4895 g maleic anhydride, and 10 ml toluene in a large microwave process vial along with a stir-bar and passive heating element (PHE). 2. Seal the vial and program the microwave. The first setting should start at room temperature (20 °C) and should be ramped up to 50 °C over 6 minutes at 50 W until the microwave reaches 160°C and 250W. Then set the microwave to remain at 160 °C with a power of 250 W for 10 minutes. 3. Place the microwave vial with the reaction mixture in the microwave and start the program. After the microwave has cooled down the vial should be allowed to cool for 30 minutes. Filter and recrystallize the product the same as before. 4. Characterize the product using IR spectroscopy and melting points.

LAB REPORTS (20 points) -You must have in order: 1) Title (in bold and centered) 2) Objectives-1 pt 3) Procedure -a few sentences, reference where the entire procedure can be found -1 pt 4) Results -must include overall reaction, equation for percent yield, one sample calculation for percent yield, a table with all obtained percent yields, a table for melting points with both experimental and literature values and reference where it was found, a table with important stretching frequencies from IR-labeling each frequency with it’s characteristic bond- 6 pt 5) Discussion-discuss the results from the percent yields, melting points, and IR spectra, (comparing the products for Parts A and B, as well as an IR spectrum of maleic anhydride). Also discuss the two different methods and their efficiency-9 pt 6) Conclusion- be brief, restate results, include error, and provide enhancements for future experiments-3 pt