Nitration of Methyl Benzoate Full ReportFull description
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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.
(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 l ikely due to water contamination of the specimen. 2
Spectra
The attached printout was obtained from analysis of the recrystallized product. The -1
large broad strong absorption from 3550-3200 cm 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 -1
absorption just above 1700 cm 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 -1
around 1350 and 1550 cm .
Citations
5
1) D.L. Pavia, G. M. Lampman, G. S. Kriz, and R. G. Engel “Introduction to Organic Laboratory rd
Techniques: A Small Scale Approach, 3 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, 3 rd Ed.”, (2011) Brooks/Cole, pp.865-885
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.
CH3
+
+
CH
N
-
O
-
N
O
+
+
+
+
2.
O
O
O
HC
-
CH3
CH3
CH3
+
CH
O
O
O
O
O
O
O
-
-
O
N
-
O
-
O
N
O
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. -1
4. The IR spec of methy m-nitrobenzoate would show a strong absorption just above 1700 cm
indicating the carboxyl (C=O) of the ester. At 3100 an absorption typical of aromatics would be -1
present along with the nitro group that absorbs around 1350 and 1550 cm . 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
