Chem 201 Nitration of Methyl Benzoate and Recrystallization TLC Lab Report completed

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Feb 20, 2024

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Nitration of Methyl Benzoate and Recrystallization/TLC Lab Report Introduction The purpose of this reaction was to perform a nitration reaction on methyl benzoate creating a product of either Methyl 2-nitrobenzoate, Methyl 3-nitrobenzoate, or Methyl 4- nitrobenzoate. By combining nitric acid and sulfuric acid, the nitronium ion NO 2 + ¿ was generated. This reagent was used for the nitration and acted as a strong electrophile for the electrophilic aromatic substation reaction. The substitution of the nitro group ( − NO 2 ) for a hydrogen atom on the methyl benzoate ring that was made by this reaction. Electrophilic aromatic substitution occurs when a C-H bond is broken, and a carbon bonded to an electrophilic atom is formed by substitution. The position the nitro group was placed in, depended on the functional group attached to the ring. Methyl benzoate has the functional group ester attached to it. Ester causes deactivation due to the substituent − CO 2 CH 3 electron-withdrawing effect. Due to the deactivation and the partial positive charges on positions 2, 4, and 6, I hypothesized the position of the nitro group to be at position 3. Position 3 is a deactivating meta group. This experimental process was simple and analyzing the data that I got after completing the experiment was simple. The data that was collected from the experiment supported the hypothesis I came up with well. The melting point of my product was close to the melting point of methyl 3 nitro. Recrystallization is a technique used to purify solids. During this process, it is possible for impurities to form. Impurities make the compound less stable, therefore affecting the melting point. Impurities tends to lower the melting point, and the more impurities you have, the lower the melting point will be. A successful process of recrystallization starts with choosing the best solvent. To do so, we had to find the solvent that didn’t dissolve the solid when cold, but when the solvent was heated, it dissolved the solid. After purifying the solvent in the experiment, we recorded the melting points of the crude and pure methyl m-nitrobenzoate. We then used a technique called Thin-Layer Chromatography (TLC) to determine the purity of the compound. The TLC plate will confirm a pure solid by showing one spot that traveled up the plate and confirm an impure solid by showing two spots that traveled up the plate. The experimental

process was simple and reflected by hypothesis well by getting a product of methyl 3- nitrobenzoate. Table 1 Name Methyl Benzoate Nitric Acid/ Sulfuric Acids Methyl Nitrobenzoate Formula C 8 H 8 O 2 HNO /H ₃ 2 SO 4 C 8 H 7 NO 4 Structure FW(s) 136.15g/mol 63.01g/mol ; 98.08g/mol 181.04 g/mol mL used 1.5 1.0mL / 1.0mL Theoretical grams 1.62g 2.0g / 2.0g 2.17g Theoretical moles 0.012 moles 0.032 moles/ 0.020 moles 0.012moles Density 1.08g/mL 1 / 1 Actual Grams 1.62g 2.17g Actual Moles 0.012 moles 0.012moles % Yield Procedure The materials used in this experiment was 4.0 mL of conc. sulfuric acid , 1.5 mL of methyl benzoate , 1.0 mL of conc. nitric acid , and 10 g of ice. In an ice-water bath we cooled 3.0 mL of sulfuric acid and 1.5 mL of methyl benzoate in a clean, dry 25 mL Erlenmeyer flask to below 10 o C. In a small test tube 1.0 mL of sulfuric acid and 1.0 mL of nitric acid was also cooled in the ice-water bath. The cold sulfuric acid/nitric acid mixture was then added dropwise, using a plastic dropper, to the cold methyl benzoate. We then swirled the flask vigorously to mix the reagents, and allowed it to warm to room temperature, standing for 15 minutes. To precipitate the product, we then poured the mixture onto 10 g of ice in a 50 mL beaker. The flask was then rinsed, and the water was poured in the beaker with the mixture. We allowed the ice to melt and collected the product of our reaction by suction filtration. After suction filtration, we disposed the filtrate, and collected the melting point of the crude and pure methyl m-nitrobenzoate. For the crude methyl m-nitrobenzoate the melting point recorded was 58.8-71.9  C, and the melting point of the pure methyl m-nitrobenzoate recorded was 68.8-76.6º C. Lastly, the theoretical yield, actual yield, and percent yield was calculated. The materials used for the Recrystallization and TLC was 0.4g of the impure compound, 1mL of water, 1mL of ethanol, and 1mL of toluene. First, we gathered 3 small test tubes and placed 0.1g of the compound in each test tube and then approximately 1mL of each of the solvents (water, ethanol, and toluene) to each of test tubes. We stirred them well and observed the solubility. The test tubes of solvent which still contained some of the solid compounds were

then heated in a warm water bath and observed to see which one dissolved the compound at a higher temperature. This solvent, ethanol, was confirmed to be the best for recrystallization. Then, 0.1g of the solid was placed in round bottom flask with a small amount of solvent to wet it. The mixture was then heated, using a hot plate to dissolve the solid. Once dissolved, we then removed the flask from the heat source and allowed it to cool. Once cooled, recrystallization is complete and the solid is collected by suction filtration. While the process of filtration is going on, we rinsed the remaining solid from the flask to remove any impurities left. Once the solid was dry, we scraped it onto filter paper to dry completely. We then found the melting point of the solid and discarded it properly. Results Table 2 Observed melting point Literature melting point Yield, grams Yield, % Appearance Product 68.8-76.6  C 78-80  C 0.71g 32.72% White, flakey, solid crystal-like Product structure : TLC To determine the relative purity of methyl 3 nitrobenzoate before and after recrystallization we use a technique called Thin Layer Chromatography (TLC). To elute the methyl m-nitrobenzoate, we used ethyl acetate as the solvent. Before and after recrystallization, there were two spots. The position of the spots for the crude and pure compound were different which gave different retention factors. B Distance traveled by solid Discussion C P

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Methyl 3 nitrobenzoate was the product of this nitration. Methyl benzoate is a electron withdrawing structure and a meta director on the benzene ring. The ester group deactivates the benzene ring by withdrawing electron density from the ring. The electron density at the meta position is higher than ortho and the para positions. The meta position is less deactivated toward the nitration, resulting in the electrophilic substitution occurring at the meta position. There is a difference in melting points between the crude and pure compound due to impurities. The crude compound has impurities that lowers the melting point, making pure compounds have wider and higher melting points. The difference in the spots is the based on the solubility in the solvent. The distance traveled by the spots also depends on the size of the compound. References : 1. “Methyl 2-Nitrobenzoate.” National Center for Biotechnology Information. PubChem Compound Database , U.S. National Library of Medicine, https://pubchem.ncbi.nlm.nih.gov/compound/Methyl-2-nitrobenzoate. 2. Nitration of methyl benzoate . (2021). RSC Education. https://edu.rsc.org/resources/nitration-of-methyl-benzoate/2323.article 3. Ashenhurst, J. (2021, February 4). Electrophilic Aromatic Substitution: Introduction . Master Organic Chemistry. https://www.masterorganicchemistry.com/2017/07/11/electrophilic-aromatic- substitution-introduction/