Separating Acids and Neutral Compounds by Solvent Extraction

Separating Acids and Neutral Compounds by Solvent Extraction

Aim:

The purpose of this experiment was to use solvent extraction techniques and chemicals such as tert-butyl methyl ether, sodium bicarbonate, and sodium hydroxide to separate a mixture.

Introduction and Theory:

Extraction is a process utilized in labs to separate an organic compound from a mixture of compounds by specifically dissolving selective compounds into a solvent. In other words, this process transfers compounds from one liquid solvent into another liquid solvent. In this process, the solvents are immiscible meaning that they are not soluble in one another and produce separate layers based on their relative densities, after they are mixed. It is important to mix vigorously to allow the organic layer and the aqueous layer to react with each other. In doing so, the ionic form in the organic layer, is soluble in the aqueous layer and can therefore be extracted into it. The identities of these layers are confirmed with one or two drops of water. If the water falls through the top layer to the bottom layer, then the aqueous layer is on the bottom. This process takes advantage of the fact that “like dissolves like.” In other words, nonpolar compounds are soluble in nonpolar solvents and polar compounds are soluble in polar solvents. Solvent extraction is also frame worked from acid base reactions where stronger acids tend to react with the conjugate bases of the weaker acids. In this experiment, we will extract p-toluic acid into a NaHCO3 solution and p-tert-butylphenol into a NaOH solution. With the addition of HCl, each of the extracts with precipitate and using vacuum filtration, we will isolate the precipitates. The mass of each compound and it’s percent yield was calculated.

Table of Physical Properties and Hazards:

Compound

Physical Properties

Hazards

Sodium bicarbonate

(NaHCO3)

Molar mass: 84.007 g/mol

Melting point: 50 °C

Boiling Point: 851°C

Physical state: Liquid

Exposure to large amounts of sodium bicarbonate may result in coughing, sneezing, and gastrointestinal irritation. Reactions between this chemical and acids produces CO2, which can result in foaming. 

Sodium hydroxide

(NaOH)

Molar mass: 39.997 g/mol

Melting point: 318 °C

Boiling Point: 1,388 °C

Physical state: Liquid

Sodium hydroxide is toxic and corrosive. It can cause severe irritation to the nose and throat if inhaled. If met with the skin, this chemical can cause pain, redness, burns, and blistering.

tert-butyl methyl ether

(C5H12O)

Molar mass: 88.15 g/mol

Melting point: -109 °C

Boiling Point: 55.2 °C

Physical state: Liquid

tert-butyl methyl ether is a flammable chemical and should be handled within the fume hood. It reacts violently with strong oxidants and is irritating to eyes and skin.  

Sodium sulfate

(Na2SO4)

Molar mass: 142.04 g/mol

Melting point: 884 °C

Boiling Point: 1,429 °C

Physical state: Liquid

Sodium sulfate can cause irritation to the eye and skin but is non-toxic. If contact is made, rinse and then wash with water and soap. In a fire, this chemical gives off toxic fumes but is not combustible.

Procedures and Observations:

In this experiment, 25mL of tert-butyl methyl ether was placed within a separatory funnel and attached to a support ring within the fume hood. 10mL of 0.5M aqueous NaHCO3 was then added to the separatory funnel. A glass stopper was placed on top of the separatory funnel and the funnel was inverted several times while holding the stopper in place. This step allowed the layers to mix, but my lab partner and I did not shake as vigorously which may have impacted our results. The funnel was then placed back onto the support ring to allow the layers to separate – with the organic layer settling on top and the denser aqueous layer settling at the bottom of the funnel. To confirm the identities of the layers, a drop of water was introduced to the layers and because the drop of water fell through the top layer to the layer below, it was confirmed that the bottom layer was in fact the aqueous layer.

After the layers were confirmed, the glass stopper was removed, and the bottom aqueous layer was drained into a clean flask labeled A (NaHCO3 extracts). The organic layer was then drained into a flask labeled B. The organic layer was poured back into the separatory flask and the above steps were repeated with the addition of 10mL of 0.5M aqueous NaHCO3. The organic layer was then poured back into the separatory funnel for a second time. However, instead of adding NaHCO3, 10mL of 0.5M NaOH was added instead. The layers were then mixed to allow for the interaction between p-tert-butylphenol and NaOH. The layers were separated with the aqueous layer (NaOH extracts) drained into a flask labeled C and the organic layer drained into a flask labeled D. This was repeated again.

After, 5mL of 3M HCl was poured into Flask A containing the NaHCO3 extracts which allowed for the p-toluic acid to precipitate. The crystals that were formed from this precipitation were then separated from the solution using vacuum filtration with a Büchner funnel and a pre-weighed filter paper. 5mL of 3M HCl was also poured into Flask C containing the NaOH extracts which allowed for the p-tert-butyl phenol to precipitate. Again, the crystals that were formed from this precipitation were then separated from the solution using vacuum filtration with a Büchner funnel and a pre-weighed filter paper. The masses of each compound were measured (0.144g and 0.535g respectively). Next, the organic layer in Flask D was transferred into a clean flask and approximately 1g of Sodium sulfate (Na2SO4) was added to the solution in order to remove any traces of water. Gravity filtration was then carried out. A Rotoevaporator was also used to spin the organic layer. The mass was then measured to be 0.648g.

To clarify, it was important to ensure that NaHCO3 was introduced to the organic layer first because it is a weaker base than the p-tert-butyl phenoxide ion, so HCO3will not take the H+ from p-tert-butyl phenol. As a result, p-tert-butyl phenol does not become water soluble. This is significant because when NaOH is added to the organic layer, it can then react and extract p-tert-butyl phenol. If it was the other way around, because OH is a strong base, it would have reacted with p-toluic acid, removing the H+ ion and causing the acid to form a salt that is aqueous in the solution. This would have hindered the reaction that would have taken place with NaHCO3.

Results:

Initially, the amount of p-toluic acid and p-tert-butylphenol added to the ter-butyl methyl ether was 0.6g. The percent yield of the p-toluic acid was 24%. There is a possibility that this low percent yield is a result of not mixing the solutions vigorously which hindered the transfer of the dissolved compound from one layer to another. The percent yield of the p-tert-butyl phenol was 89%. Both compounds were white in color and crystallized in nature.

Conclusion:

In the final analysis, this experiment utilized the method of solvent extract to extract p-toluic acid into a NaHCO3 solution and p-tert-butylphenol into a NaOH solution. Extraction is an extremely important method in labs as it is often utilized as a separation technique. This was clearly demonstrated in this lab with the separation of several compounds from one solvent to the next. At the end of this experiment, the masses of each compound were observed, and the present yield was calculated. Although the percent yield for one of the compounds was low, the problem was identified and was clearly corrected for the next compound, which generated a relatively high percent yield. All in all, the extraction process was successfully used to transfer compounds from one liquid solvent to another liquid solvent.

References:

National Center for Biotechnology Information. PubChem Compound Database; CID=516892,

https://pubchem.ncbi.nlm.nih.gov/compound/516892  (accessed Mar. 3, 2019).

National Center for Biotechnology Information. PubChem Compound Database; CID=14798,

https://pubchem.ncbi.nlm.nih.gov/compound/14798  (accessed Mar. 3, 2019).

National Center for Biotechnology Information. PubChem Compound Database; CID=15413,

https://pubchem.ncbi.nlm.nih.gov/compound/15413  (accessed Mar. 3, 2019).

National Center for Biotechnology Information. PubChem Compound Database; CID=24436,

https://pubchem.ncbi.nlm.nih.gov/compound/24436  (accessed Mar. 3, 2019).

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