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Eric Min 4/10/19 Chem 230-3 TA: Keegan Fitzpatrick, Wednesday 2pm Title of Experiment – Nitration of Ethyl Benzoate Objective – To synthesize ethyl 3-nitrobenzoate by a nitration reaction that proceeds via an electrophilic aromatic substitution mechanism, and to confirm the regiochemistry of the product by NMR spectroscopy. Reaction

Table of Reagents/Products Reagent 1

Reagent 2

Solvent/Catalyst

Byproduct

H2SO4

Predicted Product Ethyl 3Nitrobenzoate C9H9NO4

Name

Ethyl Benzoate

Sulfuric Acid

Formula

C9H10O2

Nitric Acid from 1:1 (by vol) H2SO4/HNO3 HNO3

Molecular Weight Quantity (g, mL) Millimoles Equivalents Physical properties

150.17 g/mol 0.42 mL 2.9 mmol 1 Clear liquid

63.01 g/mol 0.45 mL 6.75 mmol 2.33 Clear liquid

98.079 g/mol 0.9 mL 16.2 mmol 5.59 Clear liquid

195.174 g/mol 0.566 g 2.9 mmol 1 White sticky solid

18.015 g/mol 0.052 mL 2.9 mmol 1 Clear liquid

Water H2O

Experimental procedure A large magnetic spin bar and 420 microliters of ethyl benzoate were added to a 10-mL round-bottomed flask. Then, 900 microliters of concentrated sulfuric acid was added to the flask. The mixture was clear. An air condenser was then attached to the flask with a threaded connector to secure it. An ice bath was made in a Tupperware container and the flask was clamped so that the bottom of the flask was in the ice bath. As the mixture was stirred, 900 microliters of a 1:1 mixture of sulfuric acid and nitric acid was slowly added with a Pasteur pipet over 5 minutes. Then, the ice bath was removed, and the mixture was stirred and warmed to room temperature for 35 minutes. The mixture turned a light yellow color. Using a Pasteur pipet, the mixture was withdrawn and added to a small tared beaker with 9.327 g of ice. After processing and mixing the mixture with a spatula, a white sticky solid precipitated. The product was then collected through a vacuum filtration using a 125 mL side-arm flask, a plastic fritted funnel, and a stream of air. The product was transferred to a tared 20 mL vial and massed as 720 mg of crude product. Then, roughly 15 mL of hexanes were warmed and added to dissolve the product. Then, a small amount of sodium sulfate was added to absorb any remaining water. The mixture homogenous and clear and decanted to a separate tared 20 mL vial. This product was then recrystallized through nitrogen gas and then filtered again by vacuum filtration. The product was collected in a tared 20 mL vial and massed as 143 mg of recrystallized product. An IR sample was gathered, and a small fraction of the product was placed into a 4 mL vial with DMSO-d6. Then, this mixture was pipetted into an NMR tube and used as a sample for 1H NMR. Results Theoretical Yield (mass) Actual Crude Yield (mass, %) Actual Recrystallized Yield (mass, %) Description (state, color) MP (actual/reported)

Ethyl 3-Nitrobenzoate 0.566 g 0.720 g, 127% 0.143 g, 25.3% Solid, white 40-45 °C / not gathered

FT IR (diamond anvil, solid) 3111 (sp2 C-H stretch, aromatic), 3096 (sp2 C-H stretch, aromatic), 3000 (sp2 C-H stretch, aromatic), 2904 (sp3 C-H stretch), 2868 (sp3 C-H stretch), 1708 (C=O stretch, conjugated ester), 1615 (C=C stretch, aromatic), 1585 (C=C stretch, aromatic), 1527 (N-O stretch, nitro) cm-1

LRMS (ESI) m/z = 196 (calcd for C9H9NO4+H+ [M+1]+: 196) 1 H NMR (400 MHz, DMSO-d6)  8.63 (dd, J = 2.0, 2.0 Hz, 1H, A),  8.51 (ddd, J = 6.6, 2.4, 1.1 Hz, 1H, B),  8.38 (ddd, J = 8.0, 2.7, 1.2 Hz, 1H, C),  7.86 (dd, J = 8.0, 7.1 Hz, 1H, D),  4.39 (q, J = 7.1 Hz, 2H, E),  1.37 (t, J = 7.1 Hz, 3H, F) ppm 13 C NMR (125 MHz, DMSO-d6)  164.4, 148.3, 135.6, 131.8, 131.1, 128.1, 123.9, 62.1, 14.5 ppm Discussion The reaction attempted was a nitration of ethyl benzoate to form ethyl m-nitrobenzoate. The sulfuric acid catalyst helped nitric acid form the nitronium ion and water, where the aromatic ring of the ethyl benzoate attacked the nitronium ion to form the sigma complex1. Then, a proton on the sigma complex was removed by the deprotonated sulfuric acid to give the desired ethyl m-nitrobenzoate product. The nitro group was added at the meta position due to the destabilizing characteristic of the ester; forming an ortho or para product would result in two adjacent positive charges, which is energetically unfavorable. The reaction occurred initially on ice and was slowly done while increasing the temperature to room temperature. The crude yield of ethyl m-nitrobenzoate was 127% due to the presence of impurities like water and other byproducts. The recrystallized yield was 25.3%, where product was lost through transferring the product between the plastic fritted funnel and Scintillation vial and from transfer between Scintillation vials many times. Also, not all of the product was recrystallized since having a heterogeneous mixture aids vacuum filtering the final product. Considering the purity of the product, this was determined through spectroscopic techniques. For IR spectroscopy, there were sp 2 C-H stretches from the aromatic ring at 3111, 3096, and 3000 cm -1 as well as the C=C stretch of the aromatic ring at 1585 cm -1. There were also sp3 C-H stretches at 2904 and 2868 cm-1. Furthermore, the nitro group had N-O stretch peak at 1527 cm 1 . Lastly, the conjugated ester had a peak at 1708 cm -1 for its C=O stretch, which is at a lower frequency (red shift) than normal esters due to conjugation with the aromatic ring; all of this IR data gave information regarding the purity of the final product. For mass spectrometry of the product, there was the typical [M+1]+ peak for electrospray ionization at m/z 196; however, the [M]+ peak at 195 m/z was not present, which is not unusual in electrospray ionization, particularly of esters. Additionally, the other two standard ESI peaks of [M+23]+ and [2M+23]+ were not present, though these peaks will not always be present with ESI. Thus, only the [M+1]+ peak at 196 m/z was helpful for determining the product purity. For 1H NMR, the aromatic ring proved the regiochemistry of the product. The product is not para-substituted since there would only be two resonances based on symmetry for a para-substituted aromatic ring, and there were four distinct resonances. Using the coupling constants and first-order splitting patterns of the peaks on the ring ruled out orthosubstitution as a possibly. For instance, there was 4J coupling for both coupled hydrogens to H A at 8.63 ppm as the frequencies were typical of 4J coupling (around 2.0 Hz). A meta substitution would provide this splitting pattern while an ortho substitution would have a 3J4J splitting pattern for H A, where the 3J frequency would be higher than 2.0 Hz (likely around 7-8 Hz). Moving upfield to H B at 8.51 ppm, the peak was a doublet of doublet of doublets with a 3J4J4J splitting pattern. This matches the meta splitting pattern while an ortho substitution would actually have a doublet of doublets at H B, which was not observed. For H C at 8.38 ppm, there was a doublet of doublet of doublets with a 3J4J4J splitting pattern, matching the meta substitution and not the ortho substitution that would have a 3J3J4J splitting pattern. Again, this was determine by the frequencies of the coupling constants. Lastly, for H D at 7.86 ppm there was a doublet of doublets with a 3 3 J J splitting pattern, again matching the meta substitution and not the ortho substitution that would be a doublet of doublet of doublets splitting pattern. Therefore, using this analysis showed that the ethyl m-nitrobenzoate product was observed rather than the ethyl o-nitrobenzoate product. There were two final peaks observed in 1H NMR; one at 4.39 ppm corresponding to the methylene group (H E) and one at 1.37 ppm corresponding to the methyl group (H F). For 13C NMR, there were nine distinct peaks corresponding to nine distinct carbons as the molecule has no symmetrical carbons. The peaks, starting downfield and going upfield, started at 164.4 ppm corresponding to the carbonyl carbon, 148.3 ppm corresponding to the carbon attached to the nitro group, 135.6 ppm corresponding to the carbon of H C, 131.8 ppm corresponding to the carbon attached to the carbonyl carbon, 131.1, 128.1, and 123.9 ppm corresponding with carbons attached to hydrogen D, B, and A respectively, and 62.1 and 14.5 ppm corresponding to the methylene and methyl carbon respectively. The peak heights were also informative as the taller peaks had hydrogens attached to the carbons. Thus, both NMR spectra gave critical information about the structure of the final product. For other properties of the product, the melting point of the lactone product based on literature is between 40-45°C, though a melting point was not collected in the experiment. Overall, considering all of the data from spectroscopic techniques the product was synthesized in its pure and correct regiochemical form. Citation 1. “The Entropies of Activation in the Nitration of Ethyl Benzoate” LeNoble W. J.; Wheland G. W. Journal of American Chemical Society. 1958, 80, 20.

1. NMR SPECTRA

2. IR SPECTRA

3. MS DATA...