Post Lab #6 - I earned an A in this lab class. PDF

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I earned an A in this lab class....

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Experiment #6: Nitration of Methyl Benzoate Name :Danielle Curtis Lab Partners: Virginia Van Grod and Yefrain Munoz TA: Katrinah Tirado

Introduction/Background Aromatic compounds are cyclic compounds derived from benzene.1 However, in order for a compound to be considered aromatic it must meet specific requirements. For example, it must contain a total of 4n+2 electrons, where n represents any integer.1 The electrons must be in a conjugated ∏ system, helping to promote resonance stabilization, and planar.1 Aromatic compounds are very important in organic chemistry because they have the ability to undergo an electrophilic aromatic substitution reaction. An aromatic compound is similar to an alkene in the sense that both compounds contain double bonds, or ∏ bonds.2 However, because of the delocalization of electrons in the conjugated ∏ system, aromatic compounds are extremely stable and will prefer to undergo substitution as opposed to addition reaction typical of alkenes.2 The reagents and conditions used during this reaction are electrophilic in nature.2 Therefore, the electrons in one ∏ bond of the aromatic system attack the electrophile, forming a ∂ bond between the aromatic compound and the electrophile.2 This rate-determining step will form a positively charged arenium intermediate.2 The aromaticity of the compound is temporarily lost at this step. The intermediate is then deprotonated, a fast step, that rearomatizes the compound and produces a substituted aromatic compound.2 For example, in this experiment, the electrons in one of the ∏ bonds of methyl benzoate attack the nitronium ion, formed from nitric and sulfuric acid, to produce an arenium intermediate.3 The intermediate is deprotonated by H2O, producing nitro methyl benzoate.3

The position where the proton is substituted for a group depends on substitutents that are already on the aromatic compound. These substitutents are referred to as directors.4 Activating substiuents will donate electrons to the aromatic compound, thus making them more reactive.4 Activating substiuents often have lone pairs that are readily available to donate.4 For example, alkyls, -NH2, -NR2, -OH, -OCH3, -OR, -SR are activating functional groups.4 Aromatic compounds with these substitutents will favor the ortho (1,2) or para (1,4) substitution because of an extra, more stable, resonance contributor.4 In contrast, deactivating substituents will withdraw electrons from the aromatic compound, thus making them less reactive.4 Many deactivating substituents contain a carbonyl or atoms that have high electronegativities and inductive effects.4 For example, -NO2, -CF3, -CN and any group containing C=O are deactivating functional groups.4 Aromatic compounds with these substitutents will favor the meta (1,3) substitution position.4 The purpose of this experiment was to perform an electrophilic aromatic substitution reaction, specifically a nitration, on methyl benzoate to produce 3-nitro methyl benzoate.3 The starting compound, methyl benzoate contained an ester group, -COOCH3.3 An ester group is a meta director because of the electron withdrawing effects of the carbonyl that is adjacent to the aromatic compound.4 Substitutions to the ortho or para positions of methyl benzoate are unstable, and therefore unfavorable, because the carbocation in the intermediate is adjacent to the electron withdrawing substituent.4 Therefore, since the meta substitution is the most stable, it is the major product of the reaction in this experiment and is favored.

Nitric Acid

Methyl Benzoate

Sulfuric Acid

Intermediate

Nitronium Ion

Deprotonation Step

Nitronium Ion

Water

3-Nitro Methyl Benzoate

Figure 1: Mechanism for Nitration of Methyl Benzoate Nitration Resulting in Ortho Product

Methyl Benzoate

Nitronium Ion

Deprotonation Step

2-Nitro Methyl Benzoate

Nitration Resulting in Para Product

Methyl Benzoate

Nitronium Ion

Deprotonation Step

4-Nitro Methyl Benzoate

Dinitration of Methyl Benzoate Methyl Benzoate

Nitronium Ion

3-Nitro Methyl Benzoate

Nitronium Ion

Deprotonation Step

Deprotonation Step

3-Nitro Methyl Benzoate

3,5-Dinitro Methyl Benzoate

Figure 2: Mechanism for the 3 Possible Side Reactions

Experimental Section: Two medium sized test tubes and one 50 mL beaker were washed with acetone and dried in the oven for 10 minutes. 0.3 mL of methyl benzoate and 0.6 mL of conc. H2SO4 was added to a medium sized test tube. A mixture of 0.2 mL conc. H2SO4 and 0.2 mL HNO3 was prepared in the 50 mL beaker.

The beaker contents were poured into a Hirsh funnel and the solid product was collected via vacuum filtration. The product was washed with coled H2O and 0.5 mL of cold methanol. The product was purified via recrystallization. Combining an equal weight of methanol with the product recrystallized the product.

The mixture in the beaker was added to the medium test tube dropwise. While adding the mixture, the test tube was kept on ice and stirred occasionally. After all of the remaining mixture had been added to the test tube, the test tube remained in the ice bath for an additional 2 minutes while being continuously stirred. The test tube was removed from the ice bath and allowed to cool to room temperature for 15 minutes.

The contents of the test tube were poured over ice in a 50 mL beaker. The product was allowed to solidify. ** Note: The product formed was oily, not solid. Therefore, the rest of the steps could not be completed for this groups experiment**

The solid product was collected by vacuum filtration again. The mass of the product was recorded and percent yield was obtained. The melting point, 1H NMR, 13C NMR and IR spectra were obtained.

Chemicals Used: Name of Chemical IUPAC Name Formula Molar Mass Melting Point Boiling Point Density Safety

Methyl Benzoate Methyl benzoate C8H8O2 136.15 g/mol -12.5C 199.6C 1.08 g/cm3 > Skin/eye irritant > Hazardous if ingested > Skin permeator > Combustible

Nitric Acid Nitric oxide HNO3 63.012 g/mol -42C 83C 1.51 g/cm3 > Corrosive to skin/eyes > Skin/eye irritant > Skin permeator

Chemical Structure

Table 1: Table of Chemicals – Starting Material and Reagent Name of Chemical IUPAC Name Formula Molar Mass Melting Point Boiling Point Density Safety

Sulfuric Acid Sulfuric acid H2SO4 98.079 g/mol 10C 337C 1.84 g/cm3 > Corrosive to skin/eyes > Skin/eye irritant > Skin permeator

3-Nitromethyl Benzoate 2methyl-3-nitrobenzoate C8H7NO4 181.147 g/mol 76-80C 279C 1.30 g/cm3 > Skin/eye irritant > Hazardous if ingested/inhaled

Chemical Structure

Table 2: Table of Chemicals – Catalyst and Product Results: ** NOTE: These results were obtained from another group in the lab, this groups experiment was inconclusive and no results could be collected Appearance of Product Crystals appeared white, fine and flakey Color of Product White crystals Melting Point 80˚C Mass of Crystals 0.4 g Percentage Yield 92.8% Unsure because the reaction did not proceed correctly. An Overall Reaction Rate oil was produced instead of a solid. (Easiness) Table 3: Data Collected from the Product Synthesized

Figure 3: 1 H NMR Spectra of Final Product of this Group’s Product

Figure 4: 1 H NMR Spectra of Final Product Obtained by Group #6

Figure 5: 13 C NMR of Synthesized 3-Nitro Methyl Benzoate

CALCULATIONS: 0.3 mL C8H8O2 x 1.08 g/mL C8H8O2 x 1 mol C8H8O2 x 1 mol C8H7NO4 = 0.002238 mol C8H7NO4 1 mL C8H8O2 136.15 g/mol C8H8O2 1 mol C8H8O2

0.2 mL HNO3 x 1 mol HNO 3 x 63.12 g/mol HNO3

1 mol C8H7NO4 = 0.00479 mol C8H7NO4 1 mol HNO3

*Therefore, C8H8O2 is the limiting reagent Calculation 1: Determining the Limiting Reagent

0.00479 mol C8H7NO4 x 181.147 g/mol C8H7NO4 = 0.431 g C8H7NO4 1 mol C8H7NO4

Calculation 2: Determining Theoretical Yield

% Yield = Actual Yield x 100% = 0.4 g C8H7NO4 x 100% = 92.8% Theoretical Yield 0.431 g C8H7NO4 Calculation 3: Determining % Yield

Discussion: It is important to note that the data values mentioned in this lab report were obtained from group #6 because an incorrect product, an oil-based substance, was produced for this experiment. As a result, mass and melting point were not able to be determined for this experiment’s product. However, a 1H NMR spectra was obtained from the oil-based product and will be compared to the 1H NMR from the product of group 6, as well as the 1H NMR spectra obtained from the laboratory manual, later on in the discussion. To confirm that the correct product was obtained, the percent yield and melting point was determined, and a 1H NMR spectra for the final product was obtained. At the end of the experiment, the product was weighed and found to be 0.4g. The limiting reagent of this reaction, methyl benzoate, was used to calculate the theoretical yield of the nitration reaction. It was calculated that the theoretical yield should have been 0.431 g. Based on this information, the percent yield for this product was found to be 92.8%,

which is an ideal percent yield. There are many reasons for why the percent yield was not higher. For example, some of the product may have been lost due to human error; such as when transferring the product from the flask to the Hirsh funnel, some of the product could have been left behind in the flask. Another reason for a percent yield that was below 100% is because of the possibility of side reactions. For this nitration reaction, there are three possible side reactions. The final product could have been an o-nitro methyl benzoate, a p-nitro methyl benzoate or a 3,5-dinitro methyl benzoate. As a result, when the product was purified via recrystalization the pure product 3-nitro methyl benzoate product yield would have been lower than the crude yield, thus resulting in a lower percent yield. The melting point of the final product was found to be 80˚C. The literature states that the melting point range for 3-nitro methyl benzoate is 76-80˚C. It is evident that the determined data falls within the range established by the literature. This indicates that the product obtained at the end of the experiment was relatively pure 3-nitro methyl benzoate. At the end of the experiment, a 1H NMR spectra of the product was obtained and analyzed in order to determine if the correct product was produced. According to figure 6, if the 3-nitro methyl benzoate had been produced, there would be four distinct 1H NMR peaks. The first peak would be a singlet at about 3.9 ppm, indicative of proton #1. The second peak would be a triplet at about 7.7 ppm, indicative of proton #4. The third peak would be would be a doublet at about 8.4 ppm, indicative of both protons #3 and #5. The fourth would be a singlet at about 8.6 ppm, indicative of proton #2. Figure 5, the spectra for the product obtained from group #6, indicates that 3-nitro methyl benzoate was the

product formed because the appropriate peaks are present in the spectra. There is a singlet at around 3.9 ppm, a triplet at around 7.7 ppm, a doublet at around 8.4 ppm and a singlet at around 8.6 ppm. However, there is also an additional peak at around 1.5 ppm. This peak is indicative of the protons in water, which could mean that the product was not dried thoroughly enough. Moreover, when analyzing the 1H NMR of the incorrect final product (figure 3) it is evident that the product produced was not pure 3-nitro methyl benzoate. Although the peaks are located at the desired ppm ranges for the protons in pure 3-nitro methyl benzoate, it is evident that there are more than four unique peaks. Therefore, it can be concluded that this final product did not form the correct product because it was likely contaminated with another substance. 1

H NMR helps to determine whether the desired product was obtained or not

because protons exhibit different signals based on not only their unique locations within the molecule, but also their splitting patterns. It is because of this, that the data obtained from a 1H NMR spectra can be typically be used to elucidate the structure of the final product. Therefore, the initial reactant, methyl benzoate will display a different spectra than the final product, 3-nitro methyl benzoate will display. In the spectra for the initial reactant, only three unique peaks would be displayed. A singlet at about 4 ppm, indicative of the -CH3 protons, a peak at about 7.2-7.6 ppm indicative of three of the protons on benzene, and a peak at about 8 ppm indicative of the protons closest to the ester group. Therefore, the main difference between the final products 1H NMR and the initial reactants 1H NMR is the presence of an additional peak at about 8.8 ppm, which is indicative of the proton closest in proximity to the –NO2 group.

5 1 4 3

2

Figure 6: 1 H NMR Spectra of 3-Nitro Methyl Benzoate Obtained from the Lab Manual

Conclusion: The goal of this experiment was to prepare 3-nitro methyl benzoate from methyl benzoate and nitric acid, in the presence of phosphoric acid, via a nitration reaction. The data collected throughout this experiment indicates that the product produced was in fact 3-nitro methyl benzoate. It can be seen that the appropriate peaks are visible in the 1H NMR spectra. However, there is one additional peak in the 1.5 ppm range that is not accounted for in the structure of 3-nitro methyl benzoate. This peak is indicative of the protons in water Therefore, this suggests that the final product was not dried thoroughly.

The melting point can be used to confirm the theory that pure 3-nitro methyl benzoate was produced. The determined melting point, 80˚C, fell within the melting point range established by the literature, 76-80˚C, thus allowing the conclusion to be made that the final product formed was relatively pure 3-nitro methyl benzoate. Finally, the percent yield of the product, 92.8%, indicates that the experiment was successful because a large amount of the desired product could be produced. Therefore, proving the effectiveness of a nitration reaction. The skills learned throughout this experiment are important because nitration reactions have many real world applications. For example, nitration reactions play a vital role in the preparation of explosives, such as TNT, RDX, nitroglycerine and ETN.5 More specifically, the conversion of guanidine to nitroguanidine is a nitration reaction that produces an explosive propellant.5 Nitroguanidine reduces the propellant’s flame temperature and flash without sacrificing its chamber pressure, which is integral in explosives.5 For this reason, nitroguanidine is typically used in large bore guns because it is important to avoid barrel erosion and flash.5 Overall, this experiment was successful because the correct product, 3-nitro methyl benzoate was produced at a high percent yield and in a relatively pure composition. Moreover, the skills learned throughout this experiment are important because they have many real world applications that are important outside of the laboratory setting.

References: [1] Solomons, T. W. G., and Fryhle, C. B. (2010) Organic Chemistry 12th ed. WileyHoboken, NJ. [2] Wildegirma, S. Experimental Organic Chemistry Lab Manual; University of South Florida: Tampa, FL, 2016; P. 92-95 [3] Substitution Reactions of Benzene and Other Aromatic Compounds. Aromatic Reactivity. Accessed March 1, 2018. [4] Activating and Deactivating. Master Organic Chemistry RSS. Accessed March 1, 2018. [5] Akhavan, J. Chapter 7: Manufacture of Explosives. Chapter 7: Manufacture of Explosives | Engineering360. IEEE GlobalSpec. Accessed March 1, 2018....