Nucleophilic Substitution of Alkyl Halides|
Dr. Ishrat Khan and Mr. KevinSuggs|
Alexandria L. Howard|
Monday, February 11, 2013|
Background & Theory
Aromatic compounds react with electrophiles to give products resulting in substitution of
a hydrogen atom by the electrophile. Nitration is one of the most important examples of electrophilic aromatic substitution. Aromatic nitro compounds are used in products ranging from explosives to pharmaceutical
synthetic intermediates. The electrophile in nitration is the nitronium ion (NO2+). The nitronium
ion is generated from nitric acid by protonation and loss of water, using sulfuric acid as the dehydrating agent. The purpose of this experiment is was to synthesize methyl 3-nitro benzoate from methyl benzoate through an electrophilic aromatic substitution reaction.
Table I.Physical Data
Reagent /Compound| Formula /Structure| Molecular weight| Density(g/mL)| BoilingPoint OC| Melting Point 0C| GramsUsed (g)| VolumeUsed (mL)| Moles(mols)| SafetyHazards| methyl benzoate| C6H5CO2CH3 | 136.14| 1.08| 199| -12.3| N/A| N/A| 3.18 mmol| Combustible, Toxic, irritant | nitric acid| HNO3| 63.01| 1.51| 83| -42| N/A| 20 | N/A| Flammable| sulfuric acid| H2SO4| 98.079| 1.84| 337| 10| N/A| N/A| N/A| toxic, infectious,corrosive, non-flammable| methanol| CH3OH | 32.04| 0.7918| 64.5| -97.8| N/A| N/A| N/A| Highly flammable, toxic|
Prepare the nitrating agent in a test tube by mixing 1.0 mL of conc. sulfuric acid and 1.0 mL of cold conc. nitric acid (chilled in an ice‐water bath). Weigh out 3.18 mmol of methyl benzoate and place into a Erlenmeyer flask. Procedure Outline
Prepare 0.5 mL of nitric acid and sulfuric acid0.5 mL in seperate test tubes and label them. Then immerse both tubes in an ice‐water bath and let stand for 15 minutes. After the 15 minutes is up it is time to prepare the nitrating solution. Using a Pasteur pipet, SLOWLY add the cold sulfuric acid dropwise into the cold nitric acid while swirling the reaction mixture. Lower the new nitrating solution back into the ice-water bath for 10 minutes. While waiting for 10 minutes gather the materials needed for the next part of the experiment, Nitration of Methyl Benzoate. Weigh out 3.18 mmol of methyl benzoate and place into an Erlenmeyer flask. Obtain 1.0 mL of concentrated sulfuric acid and a support stand. Add the 1.0 mL of concentrated sulfuric acid to the Erlenmeyer flask containing the methyl benzoate. Clamp the flask containing the mixture to a support stand. 6) Add about 10 g of crushed ice into the reaction mixture. Stir the mixture vigorously. 7) After the ice has melted, isolate the solid product by vacuum filtration. 8) Wash the filtrate with 20 mL cold water, 10 mL of 5% NaHCO3, and 20 mL of cold water again until the last drop of filtrate is neutral (tested with litmus paper). 9) Dry the product on a watch glass over a steam bath, weigh the product before crystallization.
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10) Crystallize the product using methanol.
11) Weigh the crystallized product. Calculate yield and recovery percentages. 12) Measure the melting point of the purified product and determine the structure of your product based on the information from the pre‐laboratory assignment.
2) Immerse the flask in an ice‐water bath. Slowly add 2 mL of concentrated sulfuric acid .
4) SLOWLY add, , the solution from step 3 into the mixture from step 2 while being chilled all the time. Stir the mixture regularly. The addition period should not be less than 15 minutes. If the mixture becomes cloudy, add a few drops of conc. sulfuric acid until the solution is clear.
5) Let the reaction stand in a water bath (no ice) at room temperature for 15 minutes. 6) Add about 10 g of crushed ice into the reaction mixture. Stir the mixture vigorously. 7) After the ice has melted, isolate the solid product by vacuum filtration. 8)...