Diels-Alder Reaction

Diels-Alder Reaction of Anthracene-9-Methanol with N-Methylmaleimide Results In this experiment, anthracene-9-methanol and N-methylmaleimide were reacted in solution to produce a single organic product, anthracene-maleic anhydride Diels-Alder adduct, in crystal form. During this experiment, green chemistry was demonstrated through the use of water as the solvent. After the collection of the crystalline products through filtration, the mass of the product was determined to calculate the percent yield of the product and the melting point was determined to analyze the purity of the final product. Since Diels-Alder reactions have 100% atom economy, the product was assumed to have the molar mass of both products combined, 319.36 g/mol. Therefore, when the theoretical yield was calculated with the anthracene as the limiting reagent, it came out to be 0.1009 g. However, the actual yield of the crystals collected at the end of the filtration was 0.061 g of product. Therefore, there was ultimately 60.46% yield of the final product. While the literature value of the product was 232-235 °C, the melting point range of the product collected at the end of the experiment ranged from 231.1 to 234.3 °C. Table 1:Percent Recovery and Melting Point Range of Product Theoretical Yield (g) 0.1009 Literature Value of Product (°C) 232 - 235 Product Actual Yield (g) 0.061 Percent Yield (%) 60.46 Melting Point Range (°C) 231.1-234.3 Discussion Diels-Alder reaction is a highly efficient way to synthesize cyclohexene rings through the conjugate addition reaction of a conjugated diene to an alkene—the dienophile. In this experiment, Diels-Alder reaction was carried out between anthracene-9-methanol, the diene, and N-methylmaleimide, the dienophile, to form the anthracene-maleic anhydride Diels-Alder adduct, as shown in Figure 1. The reaction forms a cyclic product through a pericyclic mechanism. Due to the concerted mechanism of the reaction, the products of the Diels-Alder reactions are often highly stereo- and regioselective. The high degree of selectivity in its stereo and regiochemistry makes Diels-Alder reaction a powerful and widely used reaction in synthetic organic chemistry. The reaction is often thermodynamically favorable due to the conversion of two pi bonds into two strong sigma bonds. Generally, Diels-Alder reactions favor electron donating groups on the nucleophilic diene and electron withdrawing groups on the electrophilic dienophile. Cyclic dienes, as used specifically in this experiment, can give stereoisomeric products depending on the position of the dienophile during the cyclic transition state. However, the endo product is usually the major product because the endo product is favored kinetically. Endo products are formed when the diene and the dienophile are directly aligned with one another. In this experiment, the Diels-Alder reaction took place at a high temperature and there were strong electron withdrawing groups, the double-bonded oxygen atoms, on the dienophile which helped to expedite the reaction. Figure 1: Diels-Alder Reaction The percent yield of the product was lower than 100% most likely due to the loss of product during the transfer of reaction solution and the precipitate that formed during the experiment through the vacuum filter. Loss through this cause may be reduced in the future by devising a method of transferring the filtered and dried crystal products from the filtration funnel or the beaker in a manner that conserves the product because it is an issue that requires more practice in the technique in which product is transferred and experimenting the most efficient way to do so. Additionally, the loss of product may have been simply due to the nature of the reaction. The reaction of anthracene-9-methanol with another diene via Diels-Alder mechanism removes the reactant fro the desired reaction from the solution; this issue can be resolved in the future by mixing the reaction solution well and maintaining the reaction at a relatively low temperature to prevent dimerization. The purity of the product was tested by melting point determination and analysis. The product was found to have a melting point range of 231.1-234.3 °C. The literatrue value for the adduct was 232-235 °C. The comparison of the two melting point ranges showed that the reaction have gone successfully to completiong because the melting point range of the observed product did not deviate too much from the literature value. If the reaction had not gone to completion, the melting process would have begun much earlier than expected due to the melting of N-methylmaleimide. However, the observed melting point range was lower than that of the literature value, most likely due to the presence of impurities. Any impurities that are left over in the solution of the product can cause a depression in the melting point range.