Introduction: The chemical reaction of nitration consists of a nitro group being added to or substituted in a molecule. Nitration can basically be carried out by a mixture of concentrated nitric acid and sulfuric acid; this mixture is useful to obtain the active nitronium ion. Electrophilic aromatic substitution is a method used when a functional group is needed to be substituted on to an aromatic compound. In the nitration, nitronium ion acts as the electrophile that involves the attack of the electron-rich benzene ring.
Aromatic substitution is electrophilic, due to the high density in benzene ring. Benzene ring is one of the components in most important natural products and other useful products. The species reacting with the aromatic ring is usually a positive ion or the end of a dipole. Nitration is one of the most important examples of electrophilic substitution. The electrophile in nitration is the nitronium ion which is generated from nitric acid by protonation and loss of water, using sulfuric acid as the dehydrating agents. Data:
Beaker + Crystals
Weight of Crystals (Prior to Addition of Ethanol)
Figure 1: This table illustrates the weight of the crystals that were formed before the ethanol was added. 2.8 grams x 5= 14 mL
– This is the amount of ethanol that is needed to just dissolve the bromonitrobenzenes at 78.2oC.
Wet Sample of Crystals
Dry Sample of Crystals
Difference Between Wet and Dry Samples
Figure 2: This table illustrates the weight of the crystals that were formed as the final product. The wet sample and dry sample both have a different value.
Figure 3: This is the structure of bromobenzene; this was the liquid that was given for this laboratory experiment.
Figure 4: Mechanism for the formation of 4-bromonitrobenzene.
Observations: When the bromobenzene was added, the solution turned yellow. The final product was also yellow crystals.
0.0142 mol bromobenzene
b. Nitric Acid
0.090 mol nitric acid
THEREFORE, IT CAN BE SAID THAT BROMOBENZENE IS THE LIMITING REAGENT
c. Actual Yield and Percent Yield
THE PERCENT YIELD IS 33%.
Conclusion: It can be said that the objective of this experiment was to synthesize the p-bromonitrobenzene out of bromobenzene by nitration. This
experiment studied the electrophilic aromatic nitration of a monosubstituted aromatic cring under a standard set of conditions. Electrophilic aromatic substitution is the addition of a nitro ( NO2+) group to an aromatic ring. When the aromatic ring is monosubstituted (meaning it already has one substituent on it), the nitro group can be added to either the: ortho, meta, or para position. Figure 1 illustrates the weight of the crystals prior to the addition of ethanol. The weight of the crystals before the ethanol was added was 2.8 grams. These were the crystals that were formed when the nitric acid and sulfuric acid mixture was slowly added to the bromobenzene. The weights of the crystals were determined before the addition of ethanol; this was important to do in order to find the amount (mL) of ethanol to add. The weight of the crystals was 2.8 grams and was multiplied by 5 to get 14mL; this was the amount of ethanol that was added. The ethanol was added to the crystals to dissolve the bromonitrobenzenes at 78.2oC. Figure 2 illustrates the weight of the wet crystals and the dry crystals. The weight of the wet crystals was 1.40 grams and the weight of the dry crystals was 0.95 grams.
The difference between these two weights was 0.45 grams. The number for the dry crystal was then later used to determine the actual yield and the percent yield of the laboratory experiment.. The moles of bromobenzene were calculated to be 0.0142 moles. The moles of nitric acid were calculated to be 0.090 moles. Therefore, since the moles of bromobenzene were lower than the moles of nitric acid, it can be said that bromobenzene is the limiting reagent. After the limiting reagent is found, it is used to find the theoretical reagent.
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. The first product that could have formed was 1-bromo-2-nitrobenzene and the second product that could have formed was 1-bromo-4-nitrobenzene. These were the two products that could have been formed because bromine is in an ortho and para directing group.