Diels-Alder Reaction Discussion PDF

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The TA's name was Kayla Bates....

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Dana Woods CHEM 243b 2 February 2016 Diels-Alder Reaction For this experiment, the goal was to synthesize 4,5-dimethyl-4-cyclohexene-1,2dicarboxylic acid. This was accomplished by utilizing a Diels-Alder reaction followed by a hydrolysis reaction. After the reaction was complete, IR spectroscopy and melting point were used for identification and purity of both the intermediate and the product.

In a Diels-Alder reaction, a diene reacts with a dienophile in a pericyclic reaction (rearrangement of bonding electrons to form a ring). In the reaction mechanism above, the substance on the left (2,3-dimethyl-1,3-butadiene) is the diene and the substance on the right (maleic anhydride) is the dienophile. They react in a polyethylene glycol solvent to form 4,5-dimethylcyclohexene-1,2-dicarboxylic acid anhydride. It is an anhydride

because it is missing hydrogen anions. The hydrolysis step takes care of this problem so we can end up with our desired product. For the Diels-Alder reaction, it was heated to about 65°C. This is because the boiling point of the 2,3-dimethyl-1,3-butadiene is only 69°C, and we did not want it to boil away before we could obtain our product. For the hydrolysis reaction, the mixture could be heated to 70°C or 75°C because the intermediate anhydride had a boiling point of 78°C-79°C. The same reasoning applies to this reaction, as the anhydride needs to remain in the reaction in order for us to get the best yield possible. After each reaction, a work-up procedure was performed in order to purify the intermediate and the product. For the Diels-Alder reaction (intermediate), the reaction mixture was added to a beaker with water. Since it is an anhydride, it will crystallize, and then the water can be eliminated by suction filtering the mixture. For the hydrolysis reaction (product), the reaction mixture was immediately cooled in an ice bath, which allowed it to crystalize because the dicarboxylic acid is very insoluble, especially at cold temperatures. The quantity and quality of the reaction was measured by calculating percent yields, recording IR spectras, and determining the melting points. The yield for the overall reaction was 43.15%. This could be due to some of the substances in the reaction mixture boiling away, not retrieving all of the crystals after they dried, or not allowing the reaction to complete. By looking at the IR spectra of both the intermediate and the product, an important difference was that the product had a peak for a carboxylic acid and a peak for a hydroxyl group. Since these were not present in the intermediate spectra, it confirmed that our desired product was received from the intermediate. As for melting

point, the intermediate was recorded at 61°C-66°C and its literature value was 78°C79°C, so this had some impurities. The melting point for the product was 198°C-205°C, indicating that this product was purely the dicarboxylic acid. Even though our yield was low, the reaction was still successful because the correct peaks were found in the IR and the melting points showed that our product had very little impurities.

Diels-Alder Reaction

Dana Woods CHEM 243B Section 43 TA: Kayla...