The Synthesis of 9,10-dihydro-9,10-ethanoanthracene 11,12-dicarboxylic Anhydride

The synthesis of 9,10-dihydro-9,10-ethanoanthracene 11,12-dicarboxylic anhydride by the Diels-Alder Reaction Introduction The objective of this experiment is to synthesize 9,10-dihydro-9,10-ethanoanthracene11,12-dicarboxylic anhydride by Diels-Alder reaction1. The Diels-Alder reaction was discovered by Otto Diels and Kurt Alder in 1928. Diels-Alder reactions are one of the most widely used reactions in organic chemistry that go under a class of reactions called cycloadditions2. They form cyclohexane rings in one step by reacting conjugated dienes (four pi electrons in a cis conformation) and dienophiles (two pi electrons)1. The following figure 1 shows the synthesis of a cyclohexane by diene and dienophile. Figure 11. The synthesis of a cyclohexane by diene and dienophile In Diels-Alder reactions, dienes contain the electron donating groups and dienophiles have the electron withdrawing groups. The electron withdrawing groups, C=O groups, present in each side of the maleic anhydride molecule makes it a very reactive dienophile. However, anthracene is a stable and aromatic molecule that has less reactivity than maleic anhydride1. The following figure 2 shows anthracene and maleic anhydride molecules. Figure 21. Anthracene and Maleic Anhydride Molecules For this experiment, anthracene acts as the diene and maleic anhydride acts as the dienophile. Xylene is added to the anthracene and maleic anhydride to function as the solvent. xylene has a high boiling point with 139 ℃ that helps the reaction to proceed quickly. The product of this reaction is 9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic anhydride1. The following figure 3 shows the synthesis of 9,10-dihydro-9,10-ethanoanthracene 11,12dicarboxylic anhydride by anthracene and maleic anhydride. Figure 31. The Synthesis of 9,10-dihydro-9,10-ethanoanthracene 11,12-dicarboxylic anhydride Table 15. Table of Reagents Reagents Molecular Weight g/mol Melting Point ℃ Boiling Point ℃ Density g/mL Anthracene 178.23 216-218 340 1.25 Maleic Anhydride 98.06 54-56 202 1.48 Xylene 106.16 139 139 0.87 9,10-dihydro- 276.29 261-262 1.47 9,10ethanoanthracen e-11,12dicarboxylic anhydride Experimental: In a 5 mL round bottom flask, 0.3 g of anthracene, 0.15 g of maleic anhydride, and 3 mL of xylene were mixed. A stir bar was placed in the round bottom flask with the mixture, then fitted with a condenser tube. The round bottom flask was placed in the sand bath and wrapped the tub with a piece of wet paper towel. Then, the sand bath was plugged into a Variac and the voltage was increased to no higher than 40. The mixture was allowed to reflux for 30 minutes at high temperature. After the mixture was brought to reflux, the contents were poured into a beaker and allowed to cool to room temperature. After cooling to room temperature, the beaker was placed in an ice bath for 10 minutes. Using a Hirsch funnel, the solid that was formed through suction filtration was filtered. After filtration, the solid was washed with 1.5 mL of ice-cold xylene and allowed to dry. Once the solid was dried, the product was weighted and percent yield was calculated. The melting point of the product was observed. Results The observed weight of the product was 0.245 g with a melting point ranging between 236-234℃ . Equation 1 shows the calculations of anthracene and maleic anhydride and the percent yield. 0.303ganthracene 0.156gmaleic anhydride 0.0016molmaleicanhydride× 1 molanthracene =0.0017molanthracene 178.23ganthracene 1 molmaleicanhydride =0.0016molmaleicanhydride 98.06gmaleicanhydride 1 mol9,10−dihydro −9,10− ethanoanthracene−11,12−dicarboxylicanhydride 1 molmaleicanhydride 276.29g 9,10−dihydro−9,10−ethanoanthracene11,12−dicarboxylicanhydride =¿ 1 mol9,10−dihydro−9,10−ethanoanthracene11,12−dicarboxylicanhydride 0.4421g 9,10-dihydro-9,10-ethanoanthracene 11,12-dicarboxylic anhydride Percent yield of the product ¿ 0.2450g ×100=55% 0.4421g Equation 1. Anthracene, Maleic Anhydride, and 9,10-dihydro-9,10-ethanoanthracene 11,12-dicarboxylic anhydride Calculations The following Table 2 shows the known and the experimental melting points of 9,10dihydro-9,10-ethanoanthracene 11,12-dicarboxylic anhydride. Table 21. The known and the experimental 9,10-dihydro-9,10-ethanoanthracene 11,12dicarboxylic anhydride melting points Product Melting point ℃ Known 9,10-dihydro-9,10-ethanoanthracene 11,12-dicarboxylic anhydride 261-262 Experimental 9,10-dihydro-9,10ethanoanthracene 11,12-dicarboxylic anhydride Calculations 236-234 Discussion In order to synthesize 9,10-dihydro-9,10-ethanoanthracene 11,12-dicarboxylic anhydride by the Diels-Alder reaction, anthracene and maleic anhydride reacted together. Anthracene acted as the diene and maleic anhydride functioned as the dienophile. In addition, xylene was used as a high boiling temperature solvent that helps the reaction to go under high heat1. Xylene is a benzene ring with two methyl groups attached that make it aromatic, stable and unreactive4. Due to the aromaticity of xylene, it will not react with maleic anhydride which makes it a good solvent for the Diels-Alder reaction3. The poor percent yield calculated of the final product was 55%. Some of the final product was lost during the transferring of the mixture and filtering it. Some of the mixture was stuck and hard to observe in the used beakers. This loss of the final product made the observed percent yield low. By comparing the known and the experimental melting points of the final product, 9,10dihydro-9,10-ethanoanthracene 11,12-dicarboxylic anhydride, the calculated melting point 236234 is almost close to the known melting point 261-262. The observed melting point concludes that the final product is 9,10-dihydro-9,10-ethanoanthracene 11,12-dicarboxylic anhydride since the other reactants have less melting points than 9,10-dihydro-9,10ethanoanthracene-11,12-dicarboxylic anhydride. Conclusion The cyclohexane ring was produced by the Diels-Alder reaction is 9,10-dihydro-9,10ethanoanthracene 11,12-dicarboxylic anhydride. The cyclohexane ring was formed in a one step by reacting anthracene as diene and maleic anhydride as dienophile. Xylene was used as a heat catalyst to bring the reaction to reflux as needed. In order to obtain a higher percent yield in this experiment, the mixture should be observed by special tools like spatula to avoid any loss of the final product.