Nitration of Bromobenzene Lab Report

Abstract

The objective of this experiment was to synthesize p-bromonitrobenzene from bromobenzene through nitration. Electrophilic aromatic substitution was used to add a nitro group to the aromatic ring. The experiment involved weighing crystals before and after adding ethanol and calculating the actual yield and percent yield. Bromobenzene was determined to be the limiting reagent in the reaction. The results of this experiment demonstrated the electrophilic aromatic nitration of a monosubstituted aromatic ring.

Introduction

Nitration is a chemical reaction in which a nitro group (-NO2) is added to or substituted in a molecule.

It is typically carried out using a mixture of concentrated nitric acid and sulfuric acid, which generates the active nitronium ion necessary for the reaction. Electrophilic aromatic substitution is a common method used to introduce functional groups onto an aromatic compound. In nitration, the nitronium ion acts as the electrophile and attacks the electron-rich benzene ring.

Aromatic substitution reactions are electrophilic due to the high electron density in the benzene ring.

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Benzene rings are found in many important natural and synthetic compounds. Nitration is a fundamental example of electrophilic substitution, with the nitronium ion as the electrophile, generated from nitric acid through protonation and dehydration using sulfuric acid as a dehydrating agent.

Data

This table illustrates the weight of the crystals that were formed before the addition of ethanol. 2.8 grams x 5 = 14 mL - This is the amount of ethanol that is needed to just dissolve the bromonitrobenzenes at 78.

2°C.

This table illustrates the weight of the crystals that were formed as the final product. The wet sample and dry sample both have different values.

Observations

When bromobenzene was added, the solution turned yellow. The final product obtained was yellow crystals.

Calculations

a. Bromobenzene

0.0142 moles of bromobenzene

b. Nitric Acid

0.090 moles of nitric acid

Therefore, it can be said that bromobenzene is the limiting reagent.

c. Actual Yield and Percent Yield

Percent Yield: 33%

The percent yield is 33%.

Conclusion

In conclusion, this experiment aimed to synthesize p-bromonitrobenzene from bromobenzene through electrophilic aromatic nitration. The reaction involved the addition of a nitro group to an aromatic ring using a mixture of concentrated nitric acid and sulfuric acid. The crystals formed during the reaction were weighed both before and after the addition of ethanol to calculate the actual yield and percent yield.

Electrophilic aromatic substitution allowed the introduction of a nitro group onto the benzene ring, which can occur at different positions—ortho, meta, or para—depending on the substituents already present on the ring. In this experiment, the starting material, bromobenzene, was expected to yield two possible products: 1-bromo-2-nitrobenzene and 1-bromo-4-nitrobenzene, due to bromine's ortho and para directing nature.

The weight of the crystals formed prior to the addition of ethanol was found to be 2.8 grams, which was used to determine the amount of ethanol needed (14 mL) to dissolve the bromonitrobenzenes at 78.2°C. The wet and dry weights of the final crystals were also recorded, with a difference of 0.45 grams.

Calculations revealed that bromobenzene was the limiting reagent in the reaction. The percent yield was calculated to be 33%.

Recommendations

Further experiments could explore the effects of different reaction conditions, such as temperature and reaction time, on the selectivity of product formation in electrophilic aromatic substitution reactions. Additionally, conducting similar experiments with different aromatic compounds could provide valuable insights into the regioselectivity of nitration reactions.

Questions

1. What products did you expect this reaction to form? Explain the effect that the group(s) present in the starting material have on reactivity and orientation in this reaction and why.

There were two possible products that could have been formed in this experiment: 1-bromo-2-nitrobenzene and 1-bromo-4-nitrobenzene. The reactivity and orientation of the reaction are influenced by the substituents already present on the aromatic ring. In this case, bromobenzene is a monosubstituted aromatic compound, and bromine is an ortho-para directing group. This means that bromine directs the incoming nitro group to either the ortho or para position relative to itself, resulting in the possibility of both products. The orientation is determined by the electron density distribution on the ring, and bromine's electron-withdrawing nature makes the ortho and para positions more favorable for electrophilic substitution.