Diels Alder Lab Report
Be sure to address any questions posed in the lab procedure as well as any additional questions that your TA wants you to answer. You should also analyze any NMR spectra that you have from the reaction (if applicable). Spectra of starting materials are available on the Vista site. This reaction was carried out using standard reflux conditions. Both the anthracene and maleic anhydride dissolved immediately in xylene to give a slightly yellow solution. As the reflux was conducted, the reaction mixture appeared to darken a bit in color, and after 30 minutes, it was a distinct yellow color.
Crystal formation occurred almost immediately after removing the round-bottomed flask from the heating mantle, with even more crystals forming during the time the flask was in the ice bath. The crystals were a pale yellow color, with an irregular, powdery shape. The crude material was recrystallized from boiling xylene. Xylene is an excellent solvent for both anthracene and maleic anhydride, as evidenced by their complete solubility in the early part of the synthesis.
Due to this fact, any unreacted starting materials would remain soluble throughout the recrystallization process. Additionally, the Diels-Alder product is soluble in boiling xylene, but insoluble in cool xylene. This makes for an ideal recrystallization solvent. The purified crystals that were collected from the recrystallization were a faint off-white color, with a regular, shiny plate-like shape. The purity of the crystals was improved as seen in the melting point for the recrystallized product. This particular Diels-Alder reaction exploits an interesting phenomenon.
Although aromatic compounds do not normally participate in Diels-Alder reactions, the central ring in anthracene is reactive as a diene. Since all three rings of anthracene can not simultaneously have benzenoid character (Figure 1), the electrons in the pi system of the central ring react more like those of a standard diene.
The reaction of the central ring in anthracene allows for the formation of two, independent benzene rings, as seen in the mechanism outlined in Figure 2. (You can hand-draw structures in ink. ) Figure 1: Resonance structures of anthracene. All figures should have captions. ) xylene140 COOOOOO Figure 2: Mechanism of the Diels-Alder reaction. Conclusions Write a brief paragraph that summarizes your results. The Diels-Alder adduct, 9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboxylic anhydride, was successfully synthesized from anthracene and maleic anhydride.