Lab 5 Base Extraction of Benzoic Acid from Acetanilide PDF

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Lab 5: Base Extraction of Benzoic Acid from Acetanilide Recrystallization of Products Katja Gonzalez with partner Kyle Leonida March 6, 2018 Methods and Background

Figure 1. Chemicals used for lab 5

The first goal of this lab was to utilize the technique of base extraction. This was done by taking NaOH to split our 1:1 mixture into its separate parts of acetanilide and benzoic acid. The next goal was to take the each solid that had been isolated and purify it by using the method of recrystallization. This was accomplished using boiling water. To determine if our purified compounds were truly isolated melting point was used. This a way to distinguish each compound in the substance and to ensure separation of each. After characterization of each compound is solved by using melting point the next step is to identify what key functional groups are present. This is accomplished by using infrared or IR spectroscopy. To finish off the lab the mass of each sample that has been separated is used to identify their respective percent yields. The first step of this lab is to complete a liquid-liquid extraction. This commonly used method needs to be used with substances that will not react to each other, the extracting solvent needs to be immiscible with the original solution, the extracting solvent must be able to remove the desired components and the extracting solvent should be easily separable in order to ensure this is properly performed. To be able to do this you must know the differences between benzoic acid and acetanilide. Benzoic acid has a molecular formula of C7 H6O2, a molecular weight of 122g/mol and a melting point in the range of 121-123°C.  Acetanilide has a molecular formula of C8H9NO, a molecular weight of 135g/mol and a melting point in the range of 111-115°C.  By knowing this it can be concluded that when liquid-liquid extraction takes place the organic layer will contain the acetanilide while the aqueous layer will contain the benzoic acid.

This technique is used to transfer a solute from a solvent. The solution that is known as less dense and more aqueous will be the solution on top(benzoic acid) while the organic layer will be on the bottom (acetanilide). When comparing both chemical benzoic is seen as more acidic in comparison to acetanilide which would be neutral. The NaOH (hydroxide) that is used in this lab is a base that will deprotonate a carboxylic acid and lead to the form of a benzoate. Due to benzoate being soluble in water you will be left the neutral acetanilide in the organic layer. Acetanilide is incapable of containing itself in the aqueous layer and this is why we result in the separation of the two chemicals. At the end of this process benzoate is protonated by using a strong acid (HCl or hydrochloric acid) and reverts back to the original form of benzoic acid. The last process of this lab was recrystallization. This process is when a solid is combined with a solvent and dissolved at extremely high temperatures which will result in the re-formation of crystals. This process is based on how solids are the most soluble at constantly high temperatures in comparison to cold temperatures. The precipitation ability of the solid is dependent upon the solubility of the solvent. This is used with the extremes of the temperature, the boiling point is used as the upper extreme while the lower extreme in the case of this lab is the 0°C of the water. Experimental Procedure The lab is started by obtaining a 1:1 mixture of acetanilide and benzoic acid. In two seperate graduated cylinders, a 3 mL sample of NaOH was collected and a 10 mL sample of methylene chloride (CH2 Cl2) was collected. All three liquids were combined into the same separatory funnel. Once the funnel was sealed it was inverted ten times stopping every two to three times to release the gas pressure that was forming. After this was completed there should be two layers that are notable to the human eye. The bottom layer of this is too be removed and placed into a separate flask. The top layer should remain in the funnel in order to perform the inverting process again using 10 mL CH2Cl2 for this extractions. The bottom layer again will placed into the flask you have put aside. The next step is to add roughly 1g of Na2SO4 to the organic layer that you have obtained in order to rid the solution of any residual water. The pure sample that had remained in the funnel was poured into a 50 mL beaker. At this time the organic solution was also placed on a hot plate in order to boil off the remaining excess of methylene chloride. After you are done boiling the organic solution let it sit out so it may cool completely to room temperature. At this time a 500 mL beaker was filled with ice and the smaller 50 mL beaker with the other solution was place inside. After the organic sample has reached room temperature the vacuum suction apparatus was able to be utilized in order remove any remaining liquid from the organic layer. The remaining liquid is placed on to the heat in order remove remaining methylene chloride. This is then left to cool down down to room temperature. As it reaches the correct temperature it is then placed into an ice bath. Another vacuum filtration was then set-up in order to separate any present liquid. The solid is then scrapped off of the filter paper onto a watch glass and this is known as the acetanilide. The remaining aqueous layer is to combined with 3mL of HCl and placed into an ice bath. It should be notable that you should see crystals forming at this

point. Vacuum filtration was again set-up to remove the liquid from the crystals that had formed. The crystals atop this filtration were known as the benzoic acid and were scrapped off on to a seperate watch glass. Both crystals were weighed on scales and then take to the melting point station. A capillary tube was then obtained and used to gather the crystals of one watch glass. It was then dropped down a larger tube in order to use gravity to push it to the bottom of the capillary. This was then placed into a heat reader. The substance was closely monitored in the machine as it begins to reach its supposed melting point and it is the temperature is then recorded. This is then repeated with the substance that you have not used yet. In order to perform IR and NMR a tube was filled with enough of your crystals and filled at least half way with chloroform. This was done for each crystal. At the NMR machine the tube you created was placed directly into the machine and the computer was run. This is repeated for each tube you have created and the chart was printed each time. As for the IR machine the plate was sterilized with alcohol and then the hole was filled with the liquid from one of the tubes and the computer is started. The graph is then printed out. This is again repeated with the second liquid. Data Acquisition Chemical

Molecular Formula

Benzoic Acid

Acetanilide

Molecular Structure

Molecular Weight

Melting Point

C7H6O2

122.12g/mol

122 °C

C8H9NO

135.17g/mol

114.3 °C

Chemical

Mass of crystals (g)

Temperature of Melting Point (°C)

Benzoic Acid

0.22

99.9

Acetanilide

0.15

117.9

Relevant Equations Percent yield = Percent error =

actual theoretical x 100 |theoretical−actual| x theoretical

Calculations Benzoic Acid Percent yield =

0.22 g 0.50 g

100

x 100 = 44% |122−99.9|

Percent Error melting point = 122 Acetanilide 0.15 g Percent yield = = 0.50 x 100 = 30% g Percent error melting point = =

x 100 = 18.1%

|117.9−114.3| 114.3

x 100 = 3.15%

IR Spectroscopy Data Benzoic Acid Bond

Wavenumbers (cm-1)

C-H stretch

3000

C=O stretch

1700-1600

C-H bending

~1500

Monosubstituted benzene ring

700-800 Acetanilide

Bond

 ) Wavenumbers (cm-1

N-H stretch

3250.60 - 3081.72

C=O stretch

1660.23

Aromatic C-C

1597.39, 1553.35

C-H stretch

1499.96

Monosubstituted benzene ring

753.97

NMR Spectroscopy Data Benzoic Acid Group

ppm

NH

7.87

Arene

7.86-7.07

Methyl Group

1.90-1.55 Acetanilide

Group

ppm

Arene

8.33-7.25

Conclusion The first objective of this lab was to use liquid-liquid base extraction to separate a 1:1 mixture containing benzoic acid and acetanilide. Once this was completed the second objective of recrystallization took place. After this process took place the crystals were weighed and taken to the machine to determine melting point. Lastly, the sample was taken to IR and NMR machine to determine the possible functional groups and purity of the crystals. The samples were weighed and crystallized in order to determine the percent yield of each of your compounds. The percent yield of each compound is the amount of extracted compound that was taken from the mixture. This compound is then looked at against the ideal amount that should have been extracted. This is used to determine how successful the experiment was. For this lab we were supposed to achieve 0.50 g of benzoic acid and 0.50 g of acetanilide as we started with 1g of the mixture. The data we actually collected was 0.22 g of benzoic acid and 0.15 g of acetanilide. There percent yields were 44% and 30% in there respective order. These percentages show that an error must have occurred as they are lower than the ideal. When looking at the melting points we obtained very different data in comparison to the ideal. For benzoic acid the range is from 121-123° C  while our experimental melting point was 99.9° C.  As for the acetanilide the melting point should have been between 111-115°C  however our melting point was 117.9° C.  Theses melting points are both similar as well as irregular. This can

most likely be concluded from the separation process not being being done correctly and the samples contained impurities. The final steps of this lab were IR and NMR. This was accomplished by using their respective machines and graphs were printed. The functional groups that were identified into there respectful groups were true to each compound. However, there were some peaks that did not correlate which would suggest the presence of some impurities. Overall this lab has many potentials for errors to occur. Some of these errors include human, initial solution impurity, error in measurement, and just unclean equipment. Due to this error it can induce the possible impurities that were seen in our results that made them less than ideal. ReferencesGilbert, J.C., and Martin, S.M., Experimental Organic Chemistry , 5th Edition, Cengage Learning, Boston, MA, 2011. Landrie, C.L., and McQuade, L.E., Organic Chemistry: Lab Manual and Course Materials , 3rd Edition, Hayden-McNeil, LLC, Plymouth, MI, 2013....