Nitration of Methyl Benzoate Experiment

Introduction

Background

 The purpose of this reaction it’s to perform a nitration reaction on methyl benzoate to create a product of 3-nitro methyl benzoate. Within a nitration reaction it is typical to see electrophilic aromatic substitution reactions occur.¹ It is important to note the characteristics of an aromatic structure. for a compound to be aromatic the molecule must be cyclic, planar, an aromatic ring may only contain sp² hybridized atoms, and the number of π electrons in the delocalized π system must equal 4n + 2. This is also known as the Huckel rule. This is commonly used in organic chemistry.² With this criteria Benzene fits the description perfectly for aromaticity.

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With carrying out the reaction stated above, the electrophile within the methyl benzoate is the nitronium ion generated from the interaction of concentrated nitric and sulfuric acid. This nitronium ion reacts with the protonated intermediate of the meta position. The meta position is where the electron density is at its highest point. This means that there is no positively charged resonance form and will yield the intermediate arenium ion, which has four resonance forms. A proton is transferred from this ion to the basic bisulfate ion to give methyl 3-nitrobenzoate.¹To understand the meta position that this reaction favors one must understand the difference of ortho, para in comparison to meta. These directors correlate with activating and deactivation groups. Both corresponding to hydrogen, activating groups increase the rate of electrophilic aromatic substitutions in comparison to deactivating groups where they decrease the rate of electrophilic aromatic substitution. To further ones understanding of ortho, para, and meta directors, it is important to understand the stability of the carbocation intermediate.³ This also explains why an ester group is a meta director instead of an ortho or para product.

Mechanism

Figure 1: Reaction Mechanism – Nitration of Methyl Benzoate

Side Reaction(s)

Figure 2: Possible Side Reaction

Experimental Section

Medium Size Test Tube

0.6mL Conc. H2SO4

0.3g Methyl Benzoate

Swirl Mixture

Cool to 0°C

Prep mixture (0.2mL Conc. H2SO4 and 0.2mL Conc. HNO3)

Dropwise while stirring – Keep reaction at 0°C

Stir mixture for 25 minutes

Reaction Mixture at Room Temperature

Remove mixture from ice and warm to room temp for 15 minutes

Add 3g of cracked ice to 50mL beaker (pour reaction mixture over ice)

Product should solidify

Vacuum filtration, wash with cold H2O and 0.5mL ice cold MeOH

Crude Product Recrystallization

Weigh product transfer to clean test tube

Recrystallization with equal weight of MeOH

 Large quaintly of MeOH [sol.] and add H2O [insol.] dropwise

Mix solution with pipet to become clear

Remove sample from test tube and filter product

Analysis

Obtain Mass

Calculate Percent Yield

Determine Melting Point

Obtain H NMR

Table of Chemicals

Methyl Benzoate (C₈H₈O₂)

Physical Properties: Colorless oily liquid

Chemical Properties: Boiling Point 199°C, Melting Point -12°C, Molecular Weight 136.15g/mol

Hazards and Toxicity: Potential Acute Health Effects and Chronic Health Effects including, but not limited to, irritant in case of skin contact, eye contact and inhalation.⁴

Nitric Acid (HNO₃)

Physical Properties: Liquid, Colorless, Yellow

Chemical Properties: Boiling Point 121°C, Melting Point -44°C, Molecular Weight 63.0g/mol

Hazards and Toxicity: Potential Acute Health Effects and Chronic Health Effects including, but not limited to, irritant in case of skin contact, eye contact and inhalation. Compound is an oxidizer.⁵

Sulfuric Acid (H₂SO₄)

Physical Properties: Colorless, Oily Liquid

Chemical Properties: Boiling Point 337°C, Melting Point 10°C, Molecular Weight 98.0g/mol

Hazards and Toxicity: Potential Acute Health Effects and Chronic Health Effects including, but not limited to, irritant in case of skin contact, eye contact and inhalation. Compound is corrosive.⁶

Nitrogen Dioxide (NO₂)

Physical Properties: Reddish-brown gas or liquid

Chemical Properties: Boiling Point 21.1°C, Melting Point -11.2°C, Molecular Weight 46.0g/mol

Hazards and Toxicity: Potential Acute Health Effects and Chronic Health Effects including, but not limited to, irritant in case of skin contact, eye contact and inhalation. Compound is corrosive, compressed gas, oxidizer, and acute toxicity.⁷

Results

Table1: Reaction Results

Limiting Reagent

$0.3\mathit{ml\; C}8H8O2\mathit{ x}\frac{1.08\frac{g}{\mathit{ml}}\mathit{ C}8H8O2}{1\mathit{ml \; C}8H8O2 }x\frac{1\mathit{mol \; C}8H8O2 }{136\frac{g}{\mathit{mol}}\mathit{ C}8H8O2\mathit{ }}x\frac{1\mathit{mol\; C}8H7\mathit{NO}4}{1\mathit{mol \; C}8H8O2 }=0.002238\mathit{ mol\; C}8H7\mathit{NO}4$

$0.2\mathit{ml\; HNO}3\mathit{ x}\frac{1\mathit{mol\; HNO}3}{63\frac{g}{\mathit{mol}}\mathit{ HNO}3}\mathit{ x}\frac{1\mathit{mol \; C}8H7\mathit{NO}4}{1\mathit{mol\; HNO}3}=0.00479\mathit{ mol\; C}8H7\mathit{NO}4$

The limiting reagent is C₈H₈O₂

Theoretical Yield and Percent Yield

$\frac{\mathit{Actual\; Yield}}{\mathit{Theorectial\; Yield}}\mathit{ x }100=\frac{0.248\mathit{g\; C}8H7\mathit{NO}4}{0.431\mathit{ g\; C}8H7\mathit{NO}4}\mathit{ x }100=57.54\%$

H NMR

Figure 3: H NMR Results

Discussion

 In comparison of the obtained results and the literature values of 3-nitromethyl benzoate one may be concerned that the final product was not obtained. The melting point of 3-nitromethyl benzoate is 78°C. The obtained melting point was 76°C. The percentage yield is relatively low at 57%. This is not a main concern due to it not falling below 50%. The main concern with the results is the H NMR results due to the obtained peaks in comparison to the literature. The spectra provided in the lab manual is slightly different. The peaks are in the proper ppm areas but there are more peaks than anticipated. this could be due to an unlikely side reaction with an additional Nitro group added on the benzene ring. It is possible that the product obtained was not the expected product. To confirm that the structure of the final product is not of 3-nitromethyl benzoate a C NMR should have been obtained. This was not completed due to the amount of time a C NMR takes, which is approximately 2 hours. overall, the product obtain may in fact be of 3-nitromethyl benzoate with a mixture of side part.

Conclusion

 The information revealed from the data can explain the process of a nitration of methyl benzoate in an electrophilic aromatic substitution reaction. This reaction is very common in organic chemistry labs due to the importance of understanding ortho, para, and meta positions. It is also important with understanding electron density an intermediate form within resonance forms. Overall, the lab accomplished what it was set out to do even if the side reaction occurred one can understand why it occurred. From this experiment I learned how a nitration reaction occurs and the importance of learning how ortho, para and meta positions occur in a reaction. In addition to learning the reaction practice with spectroscopy is very important moving forward an organic chemistry.

References

1. Weldegirma, S. Experimental Organic Chemistry, 8th ed.; ProCopy: Tampa, FL, 2018.
2. Aromatic Compound. https://www.sciencedirect.com/topics/chemistry/aromatic-compound (accessed Oct 12, 2019).
3. Matthew; James; Lima, P.; Laura; Ashenhurst, J.; Haroon; Veekshith; Shrestha, K.; Parth; Nicole; Bandara, A.; Parvati; Emmy. Ortho-, Para- and Meta- Directors in Electrophilic Aromatic Substitution. https://www.masterorganicchemistry.com/2018/01/29/ortho-para-and-meta-directors-in-electrophilic-aromatic-substitution/ (accessed Oct 12, 2019).
4. Methyl benzoate. https://pubchem.ncbi.nlm.nih.gov/compound/Methyl-benzoate (accessed Oct 12, 2019).
5. Nitric acid. https://pubchem.ncbi.nlm.nih.gov/compound/944 (accessed Oct 12, 2019).
6. Sulfuric acid. https://pubchem.ncbi.nlm.nih.gov/compound/1118 (accessed Oct 12, 2019).