Extraction Lab Report - Sai Kottapalli PDF

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Separation and purification extraction of an organic base (4-ethyl aminobenzoate) using an acid (HCl)

Abstract: The purpose of this experiment is to extract an organic base, 4-ethyl aminobenzoate, using an acid (HCl) and naphthalene from a starting 1:1 mixture of naphthalene and 4-ethyl aminobenzoate. The objective of the base extraction experiment was primarily achieved through acid base reactions allowing for changes in solubility to extract the 4-ethyl aminobenzoate. The addition of HCl protonated the base, therefore ionizing it and allowing it to be water soluble. Consequently, the addition of NaOH deprotonates the base and returns it to its neutral form allowing it to precipitate out and be extracted. This process led to a 113.94% recovery of 4-ethyl aminobenzoate (the greater than 100% percent recovery could have come from excess water weight from the base crystals being dried insufficiently) and an experimental melting point range of 87.2-89.1 ℃. In addition, naphthalene was extracted with the aid of sodium sulfate and its strong ion dipole interactions with water. This process led to a 89.7% recovery of naphthalene with an experimental melting point range of 78.4-80 ℃. Introduction: Extraction is an important analytical chemistry technique based on separation and purification of substances/chemicals in a mixture. It has many applications which outlines its importance because it is used to separate and increase the purity of the chemicals based on different solubilities of the parts of the mixture in the context of different solvents. It has larger

applications in medicine and research as it can also be used to extract DNA and analyze genetic markers, etc. The separation is made possible by the variable solubilities of the solute particles in the two different immiscible solvents. Therefore, the overall objective of the experiment is to separate naphthalene and 4-ethyl aminobenzoate using extraction, separation, and purification which are all contingent on the different solubilities of the solutes in the specified solvents. In this lab specifically, the two immiscible solvents are water in the aqueous layer and diethyl ether in the organic layer. To extract the organic base 4-ethyl aminobenzoate, acid is added first followed by a base which is the premise for the general acid-base reactions that take place in the extraction. The 2 reactions are depicted below.

Figure 1: Chemical Equations for the 2 Acid Base Reactions Involved in the Organic Base Extraction of 4-ethyl aminobenzoate There is a change in solubility due to the aforementioned acid-base reactions which allows for the extraction of 4-ethyl aminobenzoate. The 4-ethyl aminobenzoate is initially soluble in the water solution and also ionizes upon the addition of HCl, making it dissolvable in water. The organic base is then brought back to its neutral nonpolar water insoluble form so that it can precipitate out making it insoluble in the 6M NaOH. Therefore, the solubility changes due to the ionization and ultimately protonation and deprotonation of the base caused by the acid-base reactions. Similar principles can be applied for the extraction of naphthalene as the sodium sulfate in water is a strong ionic compound which will absorb the water and leave behind the naphthalene because of the strong ion dipole IMFs between the sodium sulfate and water.

In order for the extraction to be effective, the two solvents have to be immiscible. Two liquids are immiscible when they have very low solubility when mixed within each other. They simply do not dissolve each other. This is evidently seen in the scenario of water and diethyl ether (the aqueous and organic layer) because water is polar protic with hydrogen bonding as its strongest IMF while diethyl ether is polar aprotic with dipole dipole interactions which are weaker than the hydrogen bonding IMFs of water. Therefore, it costs more energy to break the H-bonds of water compared to the energy released to make the diethyl ether and water IMFs making the two liquids immiscible. Another factor that ties in with the miscibility of two liquids is density. Water is more dense than diethyl ether because water has a density of approximately 1 g/cm^3 while diethyl ether has a density of approximately 0.73 g/cm^3. Since water has a higher density, it will be at the bottom and makes up the aqueous layer solvent while diethyl ether, the lower density solvent, will be in the top/organic layer. The expected results of the extraction are 100% recovery along with an expected melting point of 88.4 degrees Celsius for 4-ethyl aminobenzoate and 80.26 degrees Celsius for naphthalene. These expected results can be used to determine the efficiency and success of the extraction while the melting point can be used to determine the purity of the extracted chemicals. Experimental Procedure: The mixture that needed to be separated was 4-ethyl aminobenzoate and naphthalene. 5 mL of diethyl ether was added to an approximate 150 mg of the aforementioned mixture and shaken until dissolved. 2 mL of HCl was added to the centrifuge tube containing the mixture and diethyl ether and shaken vigorously. Each time the tube was shaken vigorously, the cap was slightly unscrewed to release pressure build up. The shaking was continued until there were two

distinct layers, the aqueous layer and the organic layer. The aqueous layer was extracted using a pipette and transferred to a beaker. This process was repeated with another 2 mL of HCl. 1 mL of deionized water was used to give a final rinse to the diethyl ether solution and the aqueous layer was extracted for the final time. The organic base was then returned to its neutral form using 6M NaOH. NaOH was added drop by drop until the pH of the water solution reached 10.0. The pH was tested using pH strips. As NaOH was added, the organic base 4-ethyl aminobenzoate started to precipitate out of the solution. This water solution with the base in it was ran through a Hirsch funnel for filtration to filter out the 4-ethyl aminobenzoate crystals. The crystals were dried and weighed. Naphthalene was recovered by adding sodium sulfate, a drying agent. Sodium sulfate was added until it no longer formed clumps in solution. The physically separate the naphthalene, the supernatant was poured out and the diethyl ether was dried through evaporation in a fume hood. The naphthalene crystals were dried and weighed. The extracted naphthalene and 4-ethyl aminobenzoate were placed into capillary tubes to take a melting point range using the DigiMelt machine.

Results: Table 1 below will depict the experimental results of the solubility of the organic acid and organic base in 3 different solvents. Table 1: Solubility Characteristics of Different Solids in Different Solvents Solid/solvent

HCl 6M pH ~ 0

H2O

NaOH 6M pH ~ 14

Benzoic acid

insoluble

insoluble

soluble

4-ethyl aminobenzoate

soluble

insoluble

insoluble

Table 2 below will outline the experimental outcomes of masses along with expected literature values and experimental melting point range. Table 2: Experimental Results of Masses, Expected and Experimental Melting Point Ranges for Extraction of Organic Base Chemical/Mixture

Mass(g)

Melting Point Range ( )

Literature Melting Point Range ( ) Source: HMDB

Initial 4-ethyl aminobenzoate + naphthalene mixture

0.165

N/A

N/A

Extracted Naphthalene

0.074

78.4-80.3

79.0-81.0

Extracted 4-ethyl aminobenzoate

0.094

87.2-89.1

88.0-90.0

Experimental Sum of Extracted Naphthalene + 4-ethyl aminobenzoate

0.168

N/A

N/A

Calculations: Since initial mixture of 4-ethyl aminobenzoate and naphthalene is in a 1:1 ratio, 0.165g / 2 = 0.0825 g of naphthalene and 4-ethyl aminobenzoate % recovery formula: extracted weight / initial weight * 100%

(1)

4-ethyl aminobenzoate % recovery using equation (1): 0.094 g / 0.0825 g * 100% = 113.94% recovery Naphthalene % recovery using equation (1): 0.074 g / 0.0825 g * 100% = 89.70% recovery Total % recovery using equation (1): 0.168 g / 0.165 g * 100% = 101.82% recovery Discussion: The purpose of the experiment is to extract 4-ethyl aminobenzoate and naphthalene from an initial 1:1 mixture of the two. This was accomplished because of the varying solubility of the two solutes in the solvents water and diethyl ether.According to table 2, 4-ethyl aminobenzoate is soluble in 6M HCl (a strong acid with a pH of ~ 1.0). This is possible because the protonation of the base induced by the HCl leads to the formation of a conjugate acid that is water soluble because the conjugate acid is now ionic and the solvent is insoluble while the conjugate acid that is formed can now dissolve in the solvent because of ionization. Likewise, benzoic acid s only soluble in the 6M NaOH (a strong base with a pH of ~14.0). This is because the acid becomes ionic upon the addition of NaOH because the NaOH deprotonates the benzoic acid which becomes water soluble and is able to dissolve because of similar IMFs between the conjugate

base and the organic solvent. In the experimental mixture, 4-ethyl aminobenzoate is polar protic because of the -NH2 (amine group) while naphthalene is nonpolar because it only consists of C and H bonds. The 4-ethyl aminobenzoate changes in solubility because it is initially polar protic and water soluble because of its H-bonding IMFs. Upon the addition of the 6M HCl, the organic base 4-ethyl aminobenzoate becomes ionic (ionic conjugate acid) because the HCl protonated the base making it water soluble in the insoluble organic solvent. There is strong ionic IMFs in the ionized conjugate acid and strong H-bonding IMFs in the solvent, making very strong ion-dipole IMFs in the solution. This is why the organic base is water soluble after adding the 6M HCl and becoming ionized as the energy and entropy gain is large enough to offset the cost of breaking the IMFs. The 2 immiscible liquids used in the extraction are water and diethyl ether. The immiscibility can be determined in two different ways: one by looking at the IMFs and two by comparing densities. From the IMFs perspective, water is polar protic and diethyl ether is polar aprotic. The two liquids are miscible because the energy cost of breaking the H-bonding IMFs is too large to compensate for the weak dipole-induced dipole IMFs formed in solution which has a small energy gain compared to the energy needed to break bonds in water. This phenomena is defined by the hydrophobic effect which explains the lack of solubility of diethyl ether and water which also explains their immiscibility. From the densities perspective, the density of diethyl ether (0.73 g/cm^3) is lower than that of water (1 g/cm^3) which is why out of the two immiscible liquids, diethyl ether will be on top in the organic layer because it has a lower density compared to water.

Intermolecular forces are important to discuss the change in solubility that allows for the extraction of the 4-ethyl aminobenzoate and naphthalene. For the extraction of naphthalene, naphthalene is a nonpolar compound with induced dipole IMFs. Diethyl ether is a polar aprotic solvent with dipole dipole interactions. Sodium sulfate forms ion-dipole IMFs with the water that the diethyl ether was exposed to and the water is attracted to the very strong ionic solid sodium sulfate due to the strong ion-dipole IMFs as mentioned before. As a result, the naphthalene crystals are extracted from the diethyl ether solution because the diethyl ether simply evaporates. IMFs are also involved in the extraction of the organic base because they are responsible for the changes in solubility. 4-ethyl aminobenzoate is initially soluble in the water solvent because both are polar protic with H-bonding IMFs making 4-ethyl aminobenzoate water soluble. When the 6M HCl is added, it ionizes the organic base making the conjugate acid water soluble because a chemical reaction that changes the structure from the neutral base (4-ethyl aminobenzoate) to its ionic conjugate acid changes the solubility in water. The addition of NaOH (a strong base) deprotonates the base and returns it to its neutral form which will allow the solid organic base to precipitate out of the solid. In the specific 4-ethyl aminobenzoate extraction (organic base extraction) and naphthalene, 4-ethyl aminobenzoate is polar protic while naphthalene is nonpolar. Naphthalene is in the organic layer with diethyl ether (a polar aprotic solvent) which physically separates it from the 4-ethyl aminobenzoate (a polar protic solute) in water (polar protic solvent) in the aqueous layer. When the HCl is added to the aqueous layer, the base is protonated and therefore ionized. In order to extract the organic base, it has to be returned to its deprotonated neutral form.

The addition NaOH deprotonates the organic base and returns it to its neutral form which allows it to precipitate out and therefore allowing for its extraction. Overall, the experiment was moderately successful. The percent recovery was calculated to be 113.94% for 4-ethyl aminobenzoate, 89.70% for naphthalene, and 101.82% overall. The experimental percent recovery is greater than 100% which could have been caused by an experimental error especially in the extraction of the 4-ethyl aminobenzoate. The crystals were probably not dried sufficiently before weighing which could have introduced excess water weight. Also, when transferring the crystals from the Hirsch funnel to weighing paper, the weighing paper came in contact with some water drops already present on the lab bench which moistened the crystals slightly which could have increased the experimental weight of the crystals. The melting point range for 4-ethyl aminobenzoate was experimentally determined to be 87.2-89.1 ℃ which is not largely removed from the literature range of 88.0-90.0 ℃(HMDB). Since the two are not largely removed from each other and the experimental range is narrow like the literature value, the purity of the experimentally extracted 4-ethyl aminobenzoate is fairly high. Similarly, the melting point range for naphthalene was experimentally determined to be 78.4-80.3℃ which is not largely removed from the literature range of 79.0-81.0 ℃. Since the difference is approximately 0.6℃ and the experimental range is narrow instead of broad, it can be said that the purity of the extracted naphthalene is fairly high as well. Conclusion: The extraction of an organic base (4-ethyl aminobenzoate) through using an acid (HCl acid) from an initial 1:1 mixture of 4-ethyl aminobenzoate and naphthalene was completed through a couple of acid base reactions as well as separation and purification techniques. The

base was protonated through the addition of HCl and deprotonated and returned to its neutral form upon addition of NaOH which allowed for its physical precipitation out of the solution and consequently, its extraction. Naphthalene was extracted with the aid of sodium sulfate which is a strong ionic solid that water (polar protic) is attracted to due to strong ion-dipole IMFs. The overall percent recovery was calculated to be 101.82% which allows for the discussion of error that the crystals still had some water weight when weighed. Although the percent recovery was higher than 100%, the experimental melting point ranges for both naphthalene (78.4-80.3℃) and 4-ethyl aminobenzoate (87.2-89.1 ℃) were not extremely different from the literature values attained from HMDB of 79.0-81.0 ℃ and 88.0-90.0 ℃ respectively. Both ranges are narrow as opposed to broad and have less than one degree Celsius difference which indicates high purity of the experimentally extracted 4-ethyl aminobenzoate and naphthalene. Therefore, the extraction of 4-ethyl aminobenzoate (an organic base) using HCl (a strong acid) and naphthalene from an initial 1:1 mixture of 4-ethyl aminobenzoate was largely successful. References: 1. Arizona State University (2018, September 17). Extraction Lab Packet. Retrieved from http://myasucouses.asu.edu 2. HMDB (2018, September 30). Naphthalene. Retrieved from http://www.hmdb.ca/metabolites/HMDB0029751 3. HMDB (2018, September 30). Benzocaine. Retrieved from http://www.hmdb.ca/metabolites/HMDB0004992...