Fa23 Enantiomers Formal Lab Report

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Jan 9, 2024

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The Resolution of Enantiomers: Isolation of (+)-Phenylsuccinic Acid with (-)-Proline Suzanne Varughese CHEM 301, L16 12/8/2023 Abstract In this experiment, (+)-phenylsuccinic acid was isolated from a racemic phenylsuccinic acid mixture. The resolution of enantiomers was achieved by reacting phenylsuccinic acid with (-)-proline. This mixture was then refluxed, resulting in the formation of a pair of diastereomeric bis-salts. These salts were subsequently separated based on their solubility in 2-propanol (isopropyl alcohol). The (+)-bis salt was neutralized and collected with vacuum filtration. The optical activity of the final solid was measured using a polarimeter. In this report, the overall percent recovery of (+)-phenylsuccinic acid, the enantiomer excess (EE), and the percent composition of the final phenylsuccinic acid were calculated and discussed. Reactions The reactions are related before the reaction as both react with (-)-proline to create products that are diastereomers of each other. These products after the reaction are enantiomers because the pair of products formed are mirror images that cannot superimpose one upon another.

Varughese 1 Procedure The procedure used the chemicals: acetone, hydrochloric acid, phenylsuccinic acid, (+)- phenylsuccinic acid, (-)- proline, and 2-propanol. The table below displays the chemical hazard of each chemical. Table 1: Chemical Hazards Chemical Name Hazard Acetone Highly flammable Irritant for skin, eyes, and respiratory tract Hydrochloric Acid Corrosive Phenylsuccinic Acid Irritant for skin, eyes, and respiratory tract (+)- Phenylsuccinic Acid Irritant for skin, eyes, and respiratory tract (-)- Proline Irritant for skin, eyes, and respiratory tract 2-propanol Highly flammable Irritant for skin, eyes, and respiratory tract 1.009 g of racemic phenylsuccinic acid was measured and was then added to a 50 mL round bottom flask. Additionally, a stir bar and 25 mL of isopropyl alcohol were added to the flask. The mixture was swirled to facilitate the dissolution of most of the solid. Once most of the solid had been dissolved, 0.6012 g of (-)-proline was added to the flask. The mixture was swirled, and then the mixture was heated at reflux for 30 minutes. After this duration, the flask was allowed to cool to nearly room temperature. During the cooling process, the solid was broken using a spatula. Once the flask was almost at room temperature, the solid was collected through vacuum filtration. By pulling air through, the solid was nearly dried in the Buchner funnel. Then, the solid was rinsed with 8 mL of acetone, and the drying process was continued. When the solid was almost dry, it was rinsed again with 8 mL of acetone. The drying process was continued for a few more minutes until the solid reached a state resembling powdered sugar. The large pieces that were present once the solid dried were broken up. Once the solid reached complete dryness, it was placed into a 1000 mL flask containing 5 mL of 6 M HCl. The mixture was stirred and swirled for 5 minutes, after which the solid was collected through vacuum filtration until it reached dryness. This solid was saved to be measured by the polarimeter. The reading of the polarimeter was +9.99 degrees with a pathlength cell of 1 dm.

Varughese 2 Calculations Observed Specific Rotation Calculation: [α] D t = α / cl If α = +9.99 o c = 0.787/10 mL l = 1.0 dm Then, [α] D t = +9.99 / (0.0787 g/mL * 1.0 dm) = + 126.9 o The EE calculation: EE = (observed specific rotation / specific rotation of pure) * 100 EE = (126.9) / (173 1 ) * 100 = 73.35 ee The (total) %+/- of the isomer in excess: % in excess = all the excess + ½ of the remaining molecules = EE + ½(100 – EE) = 73.35 + 0.5*(100-73.35) = 86.675% in enantiomer excess Therefore [(+)-phenylsuccinic acid % = 86.675] and [(-)-phenylsuccinic acid % = 13.325] Discussion : The separation of a racemic mixture into their enantiomers plays an important role in the development of drugs and medications. Specifically, our reaction of “ phenylsuccinic acid with (-)-proline to form a pair of diastereomeric bis-salts gives us a resolution of enantiomers.” This reaction introduces students to the techniques of reflux and recrystallization. The product was purified by the detailed procedure above. In short, 1.009g of racemic phenylsuccinic acid was dissolved in a 50 mL round-bottom flask with a stir bar and 25 mL of isopropyl alcohol. After adding 0.6012 g of (-)-proline, the mixture was refluxed for 30 minutes, cooled, and the solid collected via vacuum filtration. The nearly dried solid underwent acetone rinses and further drying until it resembled powdered sugar. The dried solid was then placed in a 1000 mL flask with 5 mL of 6 M HCl, stirred for 5 minutes, and collected through vacuum 11 Merck. IR Spectrum Table & Chart. Merck 2021 , 1 (1).

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Varughese 3 filtration. The resulting solid, saved for polarimetry, showed a reading of +9.99 degrees with a 1 dm pathlength cell. A factor that may have impacted our recovery yield is the critical drying process of the solid after filtration. The overall recovery can be affected by insufficient or excessive drying, underscoring the importance of ensuring that the solid is fully dried before proceeding to subsequent stages to prevent potential moisture-related complications. Also, solid washing with acetone is a key factor in influencing both purity and recovery. Impurities may persist in the final product if filtration is incomplete, or washing is insufficient. Lastly, the temperature of the solution and solid when cooled is critical in influencing the yield. The temperature of the wash with HCl and H 2 O needed to be a certain temperature of cold, to yield high results. The enantiomer excess was determined to be 86.675%. Based on this enantiomer excess value, the purity of the product can be inferred as high. A larger enantiomer excess suggests that the product contains a higher proportion of the desired enantiomer, signifying a purer sample. In this case, the substantial enantiomer excess of 86.675% suggests a high level of purity, signifying a good presence of the desired enantiomer in the final product. Based on these results, the procedure could be scaled up to further improve the yield/purity in the future. The amount of material used could be increased to boost the yield, potentially indicating a stronger purity of the solid. For reference in the paper, "Optical Resolution of (+)-Phenylsuccinic Acid by Using (-)-Proline as a Resolving Agent," 100 mL of isopropyl alcohol and 2.296 g of (-)-proline were employed. Another factor influenced the temperature, as discussed in the paper. Any temperature above 40°C, excluding the ice bath to cool the solid, would produce +(-)1-2 salt that approached racemate. This significantly impacted the purity of the solid. Instead, decreasing the temperature as much as possible was recommended, as it was linearly aligned with the purity of (+)-1-2 salt 2 . In relation to the first source, the success behind the resolution of enantiomers using (+)-phenylsuccinic acid-bis proline salt from 2-propanol is detailed in the paper "Resolution of Racemic Phenylsuccinic Acid Using (-)-Proline as a Resolving Agent" by Ralph Stephani and Victor Cesare. It is explained that this experiment offers advantages compared to other resolution procedures, such as the use of toxic alkaloids that are not unpleasant in smell, utilizing (-)-proline as the resolving agent, and the usage of (+)-phenylsuccinic acid, a nontoxic solid that is easy to work with 3 . The procedure detailed in the paper closely resembles the one performed in the lab. Although not an exact replication, it is believed that this procedure allows 2 Shiraiwa, T.; Sado, Y.; Fujii, S.; Nakamura, M.; Kurokawo, H. Bull. Chem. Soc. Jpn. 1987, 60, 824–827. 3 Cesare, V.; Stephani, R. Resolution of Racemic Phenylsuccinic Acid Using (-)-Proline as a Resolving Agent: An Introductory Organic Chemistry Experiment. Journal of Chemical Education 1997 , 74 (10), 1226. https://doi.org/10.1021/ed074p1226.

Varughese 4 for a high yield and optical rotation value. In relation to our experiment and the prior paper, it presents an adaptation that is similar in techniques and materials. It also encourages the idea that the way our lab procedure was performed is the best approach to the resolution of enantiomers.