Separating Acids and Neutral Compounds
The purpose of this experiment was to use solvent extraction techniques in order to separate a mixture consisting of a carboxylic acid (p-toulic acid), a phenol (p-tert-butylphenol), and a neutral compound (acetanilide). Extraction is the process of selectively dissolving one or more of the compounds of a mixture into an appropriate solvent, the solution that contains these dissolved compounds is called an extract (Manion, 2004). Impurities that are present in the solution can be removed by extracting them from the original solvent into another solvent.
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This is done by mixing two immiscible (insoluble to one another) solvents (Manion, 2004). By mixing the solvents together rapidly the exchange of the desired product from one solvent will be transferred to the other and the impurities remain in the original solvent. The two solvent layers then completely separate from each other as they are immiscible. The process washing is the reverse process, it leaves the desired compound in the original solvent and the impurities are transferred to the second solvent (Manion, 2004).
The solvent selection generally is determined by polarity, on will be polar typically wathe while the other a non-polar solution (hydrocarbon). The solvent choices that are used will always separate as they are unlike molecules and will not be able to be dissolved into each other. The result is a layering effect of the solvents within the container they are held, the denser layer of the mixture will always appear at the bottom of the container. This phenomenon allows for quick identification of the layers within the experiment with a water drop test indicating which of the solvent take on the water is the aqueous layer.
If one of the compounds in the mixture can be converted into its ionic form it can be more easily extracted into an aqueous layer as it becomes soluble within the solvent (Manion, 2004). By use of acid-base reactions the ionic components that have been broken down due to the reaction become soluble with in the aqueous solutions. The techniques also need to facilitate this experiment were the use of pH paper to 2 determine acidity; determine melting points of experimentally derived substances, separate solids from solution with vacuum filtration, and to speed evaporation by use of air.
Materials and Methods The extraction mixture was prepared by weighing out 0. 25-. 35 g of acetanilide, 0. 4-0. 6 g of p-toluic acid, and 0. 4-0. 6 g of p-tert-butylphenol. The exact masses weighed for the experiment were recorded in a lab notbook. Then in a 100-mL beaker 25 mL of tert-butyl methyl ether was added and the three solid compounds listed above were added and mix until dissolved. The solution was then poured into a 125-mL separatory funnel and place in a support ring attached to a stand.
The extraction of the p-toulic acid was carried out by the addition of 10 mL of 0. 5M aqueous NaHCO3 being added to the separatory funnel. Then a glass stopper was placed into the funnel the funnel was inverted while keeping pressure on the stopper not allowing any of the mixture to spill out while the funnel was rocked back and forth in order to gently mix the two layers. The gas was released from the funnel periodically as the mixture was shaken until there was no longer any gas escaping from the open stopper in the funnel.
The separatory funnel was then placed back on the supporting ring stand and the layers were allowed to again separate. The identity of the two layers was then determined by introducing several drops water of just below the surface of the top layer of solution with a pasture pipette in the funnel. Observation of the aqueous layer’s change was noted. The glass stopper was removed from the funnel and the stopcock on the funnel was opened to drain the aqueous layer from the funnel into a clean and labeled 100-ml beaker.
The ether layer remained in the funnel as the stopcock was closed just as the bottom of the aqueous layer reached the top of the stopcock. This process was then repeated two more times with subsequent additions of 10 mL of the 0. 5M aqueous NaHCO3 and the aqueous layers drained off into the above mention labeled 100-mL beaker. Finally 5 mL of deionized water was placed into the funnel and mixed. The water was then drained off into the beaker containing the aqueous solution extracts. The solution was then saved until need later in the experiment.
The extraction of the p-tert-butylphenol was then carried out in the exact same fashion as the p-toulic acid, with the exception that the aqueous solution added to the remaining ether solution was 10 mL of 0. 5M NaOH. The solution was mixed and the gas was in the funnel, along with the extraction of the aqueous layer three times into a clean and labeled 100-mL beaker. As in the previous step an addition of 5 mL of deionized water was used in the final extraction step. The extracted solution was also saved for later in the experiment as was the ether layer remaining in the separatory funnel.
The retained solution from the NaHCO3 extraction was used to precipitate the P-toulic acid. Drop wise 3M HCl was added to the extracted solution carefully until no more precipitate was formed and the solution tested acidic, with a pH reading less than 3 as indicated by pH paper testing. A piece of clean filter paper was then weighed and the mass recorded in a lab notebook. A vacuum filtration system was constructed with a Buchner funnel the filter paper was used to retain the precipitate crystals that were formed in the previous process.
Then the crystals were set to air dry completely atop the filter paper on a watch glass. The dried compound was then weighed to obtain the sample mass and a small amount of the compound was placed into a capillary tube to be used to obtain a melting point measurement. The isolation of the p-tert-butylphenol was done by first heating the NaOH extracts to 60° C obtain previously in the experiment to remove any remaining tert-butyl methyl ether that could inhibit the crystallization of precipitate.
The solution was heated on a hot plate in a fume hood to the desired temperature and then allowed to cool. Next, 3M HCl was added until the mixture was acid having a pH less than 3. The mixture was then placed in an ice bath to further facilitate crystallization. A piece of new filter paper was weighed and the mass recorded in a lab notebook. The filter paper was then used in a Buchner funnel filtration system to separate the p-tert-butylphenol crystals from the solution. The crystals were than placed on a watch glass along with the filter paper to air dry completely.
The dried compound was then weighed to obtain the sample mass and a small amount of the compound was placed into a capillary tube to be used to obtain a melting point measurement. In order to isolate the acetanilide the reserved ether layer in the separatory funnel was transferred to a clean 125-mL Erlenmeyer flask. Then approximately 1 gram of anhydrous sodium sulfate was added to remove any traces of water from the solution. The flask was then stoppered to allow the solution to dry for five minutes as it was swirled occasionally.
A clean 100-mL beaker was weighed and the mass recorded and the cleared dried ether-acetanilide layer was transferred to it. The ether was then evaporated from the solution by being heated on a hotplate as a stream of air was passed over it. The remaining oily residue, the acetanilide, was crystallized by placing it in an ice bath. The acetanilide crystals were then allowed to dry, after they dried they were weighed and the mass recorded. The dried compound was then weighed to obtain the sample mass and a small amount of the compound was placed into a capillary tube to be used to obtain a melting point measurement.