Nitration Of Methyl 3-Metazoate

Recrystallization of Methyl 3-nitrobenzoate
Santiago Horta, Daniella I
School of Chemistry and Biochemistry, Georgia Institute of Technology
Atlanta, GA 30332
Submitted: 18 February 2015

In this experiment, the product of a nitration will be purified by recrystallization using a selected solvent. Methyl benzoate is treated with nitric acid and sulfuric acid to obtain methyl 3-benzoate, which will be mixed with a solvent that will dissolve the product at its boiling temperature but not at room temperature. Comparing the melting point of both the crude and recrystallized product with that known for methyl 3-benzoate will check its purity. This process is important to learn how to use a compound’s properties for picking a solvent for a process as well as identifying a substance. A purified product will show a melting point close to that of methyl 3-benzoate, 78 ºC.

Introduction:

The objective of this experiment was to complete a nitration of methyl benzoate with nitric acid and sulfuric acid. Its product would then be recrystallized with a picked solvent and melting point of both crude and pure products were tested to check for
purity. This is significant because it will practice skills of recrystallization and purity check using melting point. The melting point expected is that around 78ºC for the purified product and lower than that for the crude.

The nitration is performed in an ice bath to keep it stable during the addition of each compound.
After everything is added, the mixture is removed from the cold temperature and mixed intermittently to ensure proper interaction between substances. Then it is cooled again to precipitate the product and separate it from some of the impurities. For further purification the product is recrystallized. A solubility test was performed on water, acetone, and methanol to pick a solvent for this process. For a substance to be optimal for recrystallization, the product has to be insoluble at room temperature and soluble at the solvent’s boiling point1. The selected solvent will allow everything to dissolve at its boiling point but the product to precipitate at room temperature, thus separating it even more from
impurities.

Result:

Table1 Reagents:
Compound
Melting Point (C)
Molecular Weight (g/mol)
Density (g/mL)
Amount (mL)
Amount (mol)
Sulfuric Acid
10.0
98.08
1.84
0.81
0.015
Methyl benzoate
-12.5
136.15
1.08
0.30
0.002
Nitric acid
-42.0
63.01
1.52
0.20
0.005

Table 2 Product:
Name
MW (g/mol)
Yield (g)
Percent Yield (%)
Color
Consistency
Percent Recovery (%)
Crude
181.15
0.357 (0.317)
99
White
Grainy
-
Crystallized
181.15
0.221
69
White clear
Grainy
70

Table 3 Solvent Data:
Solvent
Dissolve at Room T?
Dissolve at Boiling T?
Acetone
Yes
Yes
Water
No
No
Methanol
Yes
No

Table 4 Melting point rages:
Sample
Start to Melt ºC
Melts Completely ºC
1 (ramp rate 5ºC/min)
Crude
63.9
72.1

Crystallized
70.1
78.3
2 (ramp rate 2ºC/min)
Crude
60.1
72

Crystallized
71.3
78.1

Calculation Percent Yield:

Calculation Percent Recovery:

Discussion:

In this experiment an electrophilic aromatic substitution reaction was performed, purified, and checked for impurities. Methyl benzoate was treated with nitric acid and sulfuric acid to form methyl 3-benzoate. To help keep the reaction stable, it was kept inside an iced reaction tube while each component was added. As soon as the addition was completed, it was removed from the cold and stirred intermittently at room temperature to ensure proper mixing. Since these interactions caused the solution to heat up, to precipitate the product, the mixture was carefully poured over ice remembering that this was an exothermic reaction. The melting point of methyl 3-benzoate is higher than that of water, 78ºC vs 0 ºC, causing the product to form a solid when poured over ice and lowered to this temperature. The mass of this crude precipitate was taken and as observed in table 2 above was 0.357g. Comparing this to the expected amount, 0.362g, this shows a good percent yield of 99%. But, keeping in mind, this is not a pure product so its apparent recovery is probably a cause of the impurities in the product. A small of the crude product was taken out for the melting point test and the remaining was reweighted, 0.317g as seen in table 2. This was done to be able to calculate the fraction used in crystallization and the percent recovery according to the amount that was used specifically for recrystallization, as seen in the calculations above.

The product had to be recrystallized to remove any of the impurities that remained. To do this, either water, acetone, or methanol had to be picked as a solvent. The best solvent is that which is dissolves crude solid at boiling temperatures but not at room temperatures1. Small amounts of the crude product were placed on reaction tubes with 0.25 mL of each solvent. These were tested for solubility at boiling and room temperature; results can be seen in table 3. The appropriate solvent for this recrystallization turned out to be methanol since it met the conditions of solubility. Boiling methanol was added to the crude product until it was all dissolved. Then it was let cooled down until a sufficient amount of crystals were formed. As seen in the table 2 above the amount of crystal recovered was 0.221g giving a percent yield of 69% and a percent recovery of 70%. This shows that the original product contained impurities that were removed in this step. Apart from this, this could also show that not all product was recrystallized.

Both crude and crystalized products were then tested for their melting points using a mel-temp apparatus. For methyl 3-nitrobenzoate this was expected to be 76-80 ºC 2. As seen above, the melting point ranges when the ramp rate was 5 ºC/ min were 63.9-72.1ºC for the crude and 70.1-78.3ºC for the crystal. Since a melting range greater than 2ºC usually indicates an impure compound1, it can be seen that both of these samples contained impurities. When a substance is contains unwanted product, its melting point will go down since these impurities impede proper molecular interaction. As expected, the crude substance melted quicker than the recrystallized one thus had a lower melting point range temperature.

The melting point test was redone but this time with a ramp rate of 2ºC/min. Here the temperature changed slower so better results were expected. The melting point range for the crude product was 60.1-72 ºC and for the crystallized product was 71.3-78.1 ºC. These ranges do not differ much from the other ones but there are some slight changes. For the crude product, the range broadened around 3 degrees. This may have been either because there was more product in this sample or that the product actually started melting at 60.1 ºC but wasn’t seen at this temperature with a ramp rate of 5ºC/min. For the crystallized product, the range decreased approximately 1 degree. This probably was because since the ramp rate was slower the starting and ending temperature were better observed. In between then you can now see a difference in the broadness of their range. The crude product has a range of around 12ºC while the crystallized product now has a rage of around 7ºC. Even though both of these ranges are more that 2ºC, so the both contain impurities, it can be clearly seen that the recrystallized product is purer. Also the recrystallized product has a melting point range that is was closer to that expected for methyl 3-nitrobenzoate2.

Conclusion:

The nitration of ethyl benzoate with nitric acid and sulfuric acid produces the desired product of methyl 3-benzoate. This product is purified by recrystallization using a solvent that dissolves it when boiling but not at room temperature. This ensures that everything will mix at high temperatures but at the temperature goes down the product will precipitate separating it from the impurities. The melting point of both crude and purified products are tested and compared to that known for methyl 3-benzoate to check their purity. Learning how to perform each step of this experiment is important to practice laboratory techniques and data analyzing abilities.
References:

1 Zubrick, James W. The Organic Chem Lab Survival Manual: A Student 's Guide to Techniques. 6th ed. Hoboken, NJ: Wiley, 2003. 104-105.

2 "Methyl 3-nitrobenzoate - CAS # 618-95-1." CAS 618-95-1 : METHYL 3 NITROBENZOATE. ALS Environmental, 1 Jan. 2014. Web. 18 Feb. 2015. <http://www.caslab.com/Methyl_3-nitrobenzoate_CAS_618-95-1/>.
Supplemental Information:

Methyl 3-benzoate: a mixture of sulfuric acid (0.2 mL) and nitric acid (0.2 mL) was added to a mixture of sulfuric acid (0.6 mL) and methyl benzoate (0.3mL), and then was chilled, removed from ice and stirred. This mixture was transferred to a Hirsh Funnel and washed twice with cold water (1 mL) and once with chilled methanol (0.2mL). The dried product (0.3574g) was then tested for solubility by placing small amount (10mg) in reaction tubes containing water (0.25mL), acetone (0.25mL), and methanol (0.25mL). Crude product was re-weighted (0.3169g) and recrystallized with methanol. This mixture was transferred to a Hirsh Funnel and the crystals weighted (0.221g).: m.p. 78ºC. Melting Point Test: 1 Crude (63.9ºC, 72.1ºC), Cryst (69.9 ºC, 78.3ºC); 2 Crude (60.1ºC,72ºC), Cryst (68.2ºC, 78.1ºC).