Nitrating Methyl Benzoate: Electrophilic Aromatic ... - Franklin College

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Nitrating Methyl Benzoate: Electrophilic Aromatic Substitution Part 5 – Melting Points and Infrared Spectrum Prepare a melting point capillary of the recrystallized product and take its melting point. Also, perform an infrared spectrum on the recrystallized product. Do this by adding 100 mg KBR to approximately 1mg of the recrystallized product. Mix the two using a mortar and pestle, being sure to grind the two compounds into a fine powder. Place some of this mixture in a microcup, making sure the surface is smooth. Then place the pellet in the infrared spectrometer and obtain an infrared spectrum of the product. Part 5 – Clean Up Place all waste materials in their appropriate waste containers. Data and Calculations: Mass methyl benzoate used: 0.554 g Mass recrystallized crystals: 0.413 g Percent Yield: 56.42% Melting Point recrystallized product: 77.5 - 80°C Literature Value: 78 - 80°C Finding Limiting Reagent HNO3 (0.5 mL HNO3) (1.5027 g HNO3) (1 mol HNO3) (1 mol methyl nitrobenzoate) (181.3 g methyl nitrobenzoate) (1 mL HNO3) (63.01 g HNO3) (1 mol HNO3) (1 mol methyl nitrobenzoate) = 2.159 g methyl nitrobenzoate H2SO4 (0.6 mL H2SO4) (1.841 g H2SO4) (1 mol H2SO4) (1 mol methyl nitrobenzoate) (181.3 g methyl nitrobenzoate) (1 mL H2SO4) (98.08 g H2SO4) (1 mol H2SO4) (1 mol methyl nitrobenzoate) = 2.039 g methyl nitrobenzoate Methyl Benzoate (0.554 g methyl benzoate) (1 mol methyl benzoate) (1 mol methyl nitrobenzoate) (181.13 g methyl nitrobenzoate) (136.15 g methyl benzoate) (1 mol methyl benzoate) (1 mol methyl nitrobenzoate) = 0.732 g methyl nitrobenzoate The limiting reagent for this electrophilic aromatic substitution reaction is methyl benzoate. It yields the least amount of methyl nitrobenzoate in this reaction, and therefore is the limiting reagent. Theoretical Yield (0.554 g methyl benzoate) (1 mol methyl benzoate) (1 mol methyl nitrobenzoate) (181.13 g methyl nitrobenzoate) (136.15 g methyl benzoate) (1 mol methyl benzoate) (1 mol methyl nitrobenzoate) = 0.732 g methyl nitrobenzoate Percent Yield For recrystallized product (mass of recrystallized methyl nitrobenzoate) (0.413 g methyl nitrobenzoate) x (100) = (theoretical yield) (0.732 g methyl nitrobenzoate) =56.42% yield
Nitrating Methyl Benzoate: Electrophilic Aromatic Substitution Observed Properties and IR Data and Interpretation: An infrared spectrum of the recrystallized product revealed that it was methyl m-nitrobenzoate. The peak located at 1534.48 cm -1 indicates the presence of an –NO2 group. The peak located at 1734.33 cm -1 is the result of a carbonyl group and the peak at 1584.9 cm -1 indicates the presence of a benzene ring. Also, the peak at 1076.30 cm -1 indicates a C—O bond, which is present in methyl m-nitrobenzoate. Regarding the regiochemistry of the obtained product, the peak at 823.14 cm -1 indicated that the product was a meta-substituted benzene, as was predicted. All these peaks together indicate that the product was methyl m-nitrobenzoate. Results and Conclusions: The electrophilic aromatic substitution reaction between methyl benzoate and a nitrating solution of sulfuric and nitric acids was successful and yielded methyl m-nitrobenzoate. The percent yield of the recrystallized product was 56.42%. Percent yield of the crude product was not calculated because the experiment did not include this step and consequently, percent recovery for the recrystallized product cannot be calculated either. The melting point of the recrystallized product was 77.5 - 80°C. This was then compared with a data table given in the experiment in order to determine the regiochemistry of the obtained product. The observed melting point was extremely close to the literature value of 78 - 80°C for the meta-substituted product. Therefore, analysis of the melting point determined that the product was methyl meta-nitrobenzoate, as could be predicted. Since –CO2H3 is a strongly deactivating group, it is meta-directing. Thus, we expected the –NO2 group to be added to the methyl benzoate at the meta position. The melting point analysis proved that this is what happened and the product obtained was methyl mnitrobenzoate. An infrared spectrum of the product also confirmed its identity as methyl m-nitrobenzoate. A peak located at 1534.48 cm -1 indicated the presence of an –NO2 group. The peak located at 1734.33 cm -1 was the result of a carbonyl group and the peak at 1584.9 cm -1 indicated the presence of a benzene ring. Another peak at 1076.30 cm -1 indicated a C—O bond, which is present in methyl m-nitrobenzoate. Regarding the regiochemistry of the obtained product, the peak at 823.14 cm -1 indicated that the product was a meta-substituted benzene, as was predicted. All these peaks together indicated that the product was methyl m-nitrobenzoate. Reference: Chemistry Lab Experiments CHEM 224 REAC 716 pgs. 61 – 71 By Wigal/Manion/LeFevre/Wade, Jr./Rapp/Lee/Wikholm Weast, Robert C., ed. CRC Handbook of Chemistry and Physics. 70 th ed. Boca Raton, FL: CRC Press, Inc., 1990. Post-Lab Questions: 1. (a) The percent yield of my product was 56.42%. See Data section for calculation. (b) The melting point of my product was 77.5 - 80°C. (c) The observed melting point of 77.5 - 80°C was most closely related to the literature melting point of 78 – 80°C for a meta substitututed product. Therefore, my product has a meta- regiochemistry. The meta- product forms because the ortho- and para- products both have very unstable resonance forms with 2 positive charges next to each other. The two positive charges right next to one another cause the resonance forms to be unstable, so ortho- and para- substituted products do not form in this reaction. The meta- position is electron-rich, and thus reacts best with the –NO2 group to form methyl m-nitrobenzoate. Also, we knew the meta- product was going to form because –CO2H3 is a strongly deactivating group and is meta-directing. Thus, we expected the –NO2 group to be added to the methyl benzoate at the meta position. This was confirmed by analyzing the melting point.
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Nitrating Methyl Benzoate: Electrophilic Aromatic ... - Franklin College

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