174298384-Nitration-of-Methyl-Benzoate (2018 05 31 03 01 51 UTC) PDF

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Lab Report....

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Lab 43 Nitration of Methyl Benzoate

Abstract In this lab a 66.1 % yield of Methyl m-nitrobenzoate was synthesized by a electrophilic aromatic substitution reaction (EAS ) of methyl benzoate and an acidic solution containing

nitronium ions generated from the protonation of nitric acid with concentrated sulfuric acid. Techniques of vacuum filtration, ice baths, and recrystallization were used in order to isolate the crude product during synthesis. Measurements of purity were obtained via analysis of the melting point and Infrared Spectrum was performed on the final product along with a percent yield calculation. With a boiling point range of 71-74°C, physical analysis indicates a some impurities in the final product, the IR spectrum analysis also indicated that the final product was possibly still hydrated.

Purpose The objective of this lab was to synthesize a pure sample of methyl m-nitrobenzoate via an electrophilic aromatic substitution reaction. Techniques of vacuum filtration, recrystallization, and IR spec analysis were revisited as well. The electron withdrawing effects of the ester group act as a meta director for this reaction and the increased stability of the meta isomer is visible through by drawing out the resonance structures of each isomer and comparing the locations of the cations. Nitration is the addition of an NO2 + (nitronium ion) which acted as the electrophile in the reaction due to the electron deficit. The aromaticity of methyl benzoate is temporarily disturbed upon the initial bonding of the nitronium ion but restored upon the abstraction of additional sp2 hydrogen. Further nitration of the product is not observed due to the fact that the nitro group is significant deactivator.

Reactions O

O CH3 O

+

CH3 H2SO4

O

+

HONO2

H2O

+

-

O

N

O

Competing Side Reaction Although energetically unfavorable a small amount of the Ortho and Para isomers were likely obtained.

2

O O O

CH3

+

CH3

H2SO4

O

HONO2 O

+

H2O

+

N

-

H2SO4

O

O O +

O

CH3

+

H2O

N

-

O

Separation Scheme

3

Methyl Benzoate + HNO3 [H2SO4] + Crushed ICE (Vacuum Filtration) • Filtrate Discarded Crude Product + Methanol

(Vacuum Filtration)

• Filtrate Discarded

Recrystallized Product

Procedure The procedure was conducted in accordance with experimental procedure 43 in the textbook.1 Physical Constants1,3 Compound

Molecular Formula

Molecular Weight (g)

Density(g/m l)

Methyl Benzoate Methyl m-Nitrobenzoate

C8H8O2 C8H7NO4

136.15 181.15

1.0837 NA

Melting Point (°C) 113-115 78-80

Calculations A. Limiting Reagent  Methyl Benzoate: (3.05 g)(1 mole/136.15 g C8H8O2) = .0224 moles Excess Reagent 

Nitric Acid: (.002 L)(16 M) = .032 moles

B. Theoretical Yield 4

(Limiting moles)(Ratio)(Molecular Weight of Product) (.022 moles Methyl Benzoate)(1:1)(181.15 g/mole of Methyl m-Nitrobenzoate C8H7NO4) = 3.98 grams of C8H7NO4 C. Actual Yield and Percent Yield Crude Product Mass = #.## grams Percent Yield = (Actual/Theoretical) 100% (2.63/3.98)100% = 66.1 % yield D. Analytical Data The observed melting point of 71-74°C strongly indicates that there were some impurities in the final recrystallized product obtained. The literature values for the melting point of Methyl m-nitrobenzoate are 78-80°C which is significantly higher. This conclusion is also in line with the IR spectrum analysis that was obtained. A considerable amount of –OH functional group can be seen on the graph, this is most likely due to water contamination of the specimen. Spectra2 The attached printout was obtained from analysis of the recrystallized product. The large broad strong absorption from 3550-3200 cm-1 indicates that there is a –OH functional group present, and there is a multitude of undifferentiable aliphatic absorptions. These impurities seen in the graph could have possibly been due to the presence of water in the sample that could be due to an incomplete drying of the product or possible contamination of the specimen tested. The IR spectra of pure methyl m-nitrobenzoate would show a strong absorption just above 1700 cm-1 indicating the carboxyl (C=O) of the ester. At 3100 an apsorption typical of aromatics would be present along with the nitro group that absorbs around 1350 and 1550 cm-1.

Citations

5

1) D.L. Pavia, G. M. Lampman, G. S. Kriz, and R. G. Engel “Introduction to Organic Laboratory Techniques: A Small Scale Approach, 3rd Ed.”, (2011) Brooks/Cole, pp.38-342

2) D.L. Pavia, G. M. Lampman, G. S. Kriz, and R. G. Engel “Introduction to Organic Laboratory Techniques: A Small Scale Approach, 3rd Ed.”, (2011) Brooks/Cole, pp.865-885

3) "Methyl 3-nitrobenzoate." ChemicalBook---Chemical Search Engine. Chemica Book, n.d. Web. 03 Oct. 2012. .

Questions

6

1. The meta configuration is obtained do to its increased resonance stabilization. The ester is a withdrawing group and acts as a meta director. If the nitro group was placed on ortho or para then a cation would be placed on the alpha carbon of the ester which is highly unfavorable.

O

O CH3

O

+

CH

O

O

O

O

+

CH

HC

+

+

+

O

CH3

CH3

+

-

O

CH3

N

O

-

O

-

N

O

-

O

-

+

N

O

-

O

-

N

O

2. At elevated temperatures the dinitrification side product is produced. The excess heat allows for the higher EA activation energy to be overcome since dinitrification is energetically unfavorable due to the deactivating effects upon initial nitrification. 3. The acid is added slowly to aid in maintenance of the low temperature which aims to lower the dinitrification products from forming. Heat is produced when acid is added due to the exothermal reaction taking place. 4. The IR spec of methy m-nitrobenzoate would show a strong absorption just above 1700 cm-1 indicating the carboxyl (C=O) of the ester. At 3100 an absorption typical of aromatics would be present along with the nitro group that absorbs around 1350 and 1550 cm-1. 5. (Benzene) Nitrobenzene (Toluene) p-nitrotoluene and O-nitrotoluene *steric hindrance may prevent Ortho (Chlorobenzene) P-nitrochlorobenzene and O-nitrochlorobenzene *steric hindrance may prevent Ortho (Benzoic Acid) m- nitrobenzoic acid

7...