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Orgo Lab - Midterm Lab Report...

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Extraction of Phenanthrene and Methyl 4-Aminobenzoate by Vacuum Filtration and Crystallization, Identification of Unknown Mixture by Determining Melting Points

DaHea (Lauren) Ham 10 November 2017

Ham 2 Abstract To extract phenanthrene and methyl 4-aminobenzoate from an unknown mixture containing 50% phenanthrene, 40% methyl 4-aminobenzoate, 10% 1,4-dibromobenzene, extraction, vacuum filtration, and crystallization were the techniques used in this experiment. By determining the melting point for each compound collected, the compounds were identified and checked if it contained any impurities. From aqueous phase, methyl 4-aminobenzoate was extracted by using acid-base reaction. From organic phase, phenanthrene was extracted by using crystallization. The percent recovery of phenanthrene was 25.735 % and that of methyl 4aminobenzoate was 36.170. The experimental melting point range determined of phenanthrene was 97.6 – 99.4 °C, and that of methyl 4-aminobenzoate was 106.3 – 108.2 °C. Separation Scheme Separation scheme should be turned and made bigger (landscape)

Procedure 1. Added about 0.987 g of unknown mixture contained 50% phenanthrene, 40% methyl 4aminobenzoate, 10% 1,4-dibromobenzene to a screw-cap centrifuge tube. Added 15.00 mL of diethyl ether to the tube and capped it. Shook the tube until the mixture dissolved completely. Then, transferred this solution into a 125-mL separatory funnel. 2. Added 5.00-mL of 1.0 M HCl to the separatory funnel and shook for 1 minute in a rocking motion. Held the stopper in place firmly and inverted the separatory funnel. While the funnel was

Ham 3 inverted, released the pressure by slowly opening the stopcock. Continued inverting and venting until the “whoosh” is no longer audible. Placed the separatory funnel in the iron ring and let it stand until the layers separate completely. Placed a 50-mL Erlenmeyer flask under the separatory funnel. Removed the bottom (aqueous) layer and placed this in an Erlenmeyer flask labeled “1st HCl extract.” 3. Added another 5.00-mL portion of 1.0 M HCl to the funnel and shook for 1 minute. When the layers had separated, removed the aqueous layer and put it in an Erlenmeyer flask labeled “2nd HCl extract.” 4. While stirring, added 6.0 M NaOH dropwise to “1st HCl extract” and “2nd HCl extract” flasks containing the HCl extract until the mixtures turned basic when tested by litmus paper. Observed the amount of precipitate. 5. Installed Buchner funnel. Moistened the filter paper with a few drops of distilled water, and turned on the vacuum (or aspirator) to the fullest extent. Swirled the mixture in both flasks and poured the mixture into the funnel, attempting to transfer both precipitate and solvent. When the liquid had passed through the filter, repeated this procedure until you had transferred all the liquid to the Buchner funnel. Continuing drawing air through the HCl extract on the Buchner funnel by suction for about 5 minutes. Transferred the HCl extract onto a pre-weighed watch glass for air-drying. You could usually determine if the HCl extract was still wet by observing whether or not they stuck to a spatula or stayed together in a clump. After completely drying it, weighed the weight of watch glass and methyl 4-aminobenzoate and calculated percent recovery. Determined the melting point by putting precipitate-filled capillary into digimelt machine. The literature melting point for methyl 4-aminobenzoate was 109 – 111 °C.

Ham 4 6. Added 5.00-mL of saturated aqueous sodium chloride to the ether layer in the separatory funnel. Shook for 1 minute and let the layers separate. Removed and discarded the aqueous layer. Poured the ether layer (without any water) from the top of the separatory funnel into a clean, dry Erlenmeyer flask. 7. Then, added granular anhydrous sodium sulfate to the ether layer over until no more clumps were made. Transferred the dried ether solution with a clean, dry Pasteur pipet to a dry roundbottom flask, leaving the drying agent behind. In a clean, dry Erlenmeyer flask, added about 15.00-mL 95% ethyl alcohol and a boiling stone. Heated the solvent on a warm hot plate until the solvent was boiling. Because 95% ethyl alcohol boiled as a relatively low temperature (78 °C), it evaporated quite rapidly. Setting the temperature of the hot plate too high would result in too much loss of solvent through evaporation. 8. Using rotary evaporator, the organic solution (dried ether solution) in a round-bottom flask was evaporated. 9. Before heating the flask containing the phenanthrene, added enough hot solvent into the round-bottom flask with a Pasteur pipet to barely cover the crystals. When the dried ether solution was completely dissolve in the hot solvent, transferred the mixture into a dry, clean Erlenmeyer flask. Then heated the flask containing the phenanthrene until the solvent was boiling. Added another small portion of solvent, continued to heat the flask, and swirled the flask frequently. If the solid had not dissolved after swirling the flask for 10-15 seconds, then added another portion of solvent. Continued repeating the process of adding solvent, heating, and swirling until the entire solid had dissolved completely. The time from the first addition of solvent until the solid dissolved completely should have not been longer than 10 – 15 minutes.

Ham 5 10. Removed the flask from the heat and allowed the solution to cool slowly. Covered the flask with a small watch glass, or stopper the flask. Crystallization should have begun by the time the flask had cooled to room temperature. If it had not, scratched the inside surface of the flask with a glass rode to induce crystallization. When it appeared that no further crystallization was occurring at room temperature, placed the flask in a beaker containing ice water. When crystallization was complete, vacuum filtered the crystals using a small Buchner funnel like Step 5. Moistened the filter paper with a few drops of 95% ethyl alcohol. To transfer the remaining crystals to the funnel, added about 2.00-mL of ice-cold 95% ethyl alcohol to the flask. When vacuum filtration was over, transferred the crystals onto a pre-weighed watch glass for airdrying. Weighed the weight of dry crystals and pre-weighed watch glass and calculated the percentage recovery. Determined the melting point of phenanthrene by putting crystals-filled capillary into digimelt machine. The literature melting point for phenanthrene was 98 – 100 °C. Rationale 1. Through extraction, acid or base compound was dissociated into aqueous layer because of their similarities in polarity. Extraction was a technique used for the recovery of an organic compound from an aqueous solution by using an organic solvent (usually nonpolar or slightly polar). Due to the acid or base compound being more soluble in the second solvent (NaOH or HCl) than in the first solvent (ether); the acid or base compound transferred from the first solvent eventually to the second solvent. Diethyl ether was chosen as organic (first) solvent, as it was a nonpolar solvent because of no O-H bonds and therefore could fully dissolve the unknown mixture containing 50% phenanthrene, 40% methyl 4-aminobenzoate, 10% 1,4-dibromobenzene, which were all nonpolar compounds. The 15.00 mL of diethyl ether was added to completely dissolve the unknown mixtures at room temperature.

Ham 6 2. The 1.0 M HCl was selected as best aqueous (second) solvent. As HCl was a polar solvent while diethyl ether was a nonpolar solvent, they were immiscible and created two layers. Also, the density of HCl (1.19 g/cm3 ) was greater than the density of diethyl ether (0.7 g/cm3 ). So, HCl layer (aqueous phase) was placed bottom of diethyl ether layer (organic phase) in the separatory funnel. Methyl 4-aminobenzoate was a basic compound because of the amino group, so an acidic solvent was required for the acid-base reaction. Acid and base reaction caused ionization and made methyl 4-aminobenzoate soluble in HCl. So, base was dissociated into HCl extraction, and only phenanthrene and 1,4-dibromobenzene were left in the organic phase. Due to methyl 4-aminobenzoate not being a strong base, 1.0 M was enough concentration for acid and base reaction to be happened. The 5.00-mL of 1.0 M HCl was a proper amount for base compound to be soluble and extracted from aqueous solvent. 3. To decrease chances of methyl 4-aminobenzoate left in the organic layer (ether), another 5.00mL portion of 1.0 M HCl was added. 4. The 6.0 M NaOH was added for each of the 1st and 2nd HCl extract to turn those acidic solutions back to basic solutions. The concentration of NaOH was 6.0 M because methyl 4aminobenzoate had to be oversaturated due to the strong concentration of NaOH in the solvent. When 6.0 M NaOH turned the extract to basic, methyl 4-aminobenzoate was insoluble in HCl as it reconverted back to its insoluble base because of the lack of ionization. So, methyl 4aminobenzoate was observed as some precipitates. Testing by litmus paper proved that the mixtures turned basic when the litmus paper turned blue. 5. As methyl 4-aminobenzoate was in water due to the formation of water through acid and base reaction, the filter paper used was moistened with distilled water. To dry HCl extract on the Buchner funnel, the vacuum was turned to the fullest extent for drawing air.

Ham 7 6. Saturated aqueous sodium chloride was used to remove water in the ether layer using extraction. Two layers of solvents were made due to ether (organic phase) was a nonpolar solvent and saturated aqueous sodium chloride (aqueous phase) was a polar solvent. Because of the similarities in the polarity of saturated aqueous sodium chloride and water, water was more soluble in saturated aqueous sodium chloride than it was in ether. So, water moved to the aqueous phase from organic phase. The 5.00-mL of saturated aqueous sodium chloride was a proper amount for water to be soluble in it for extraction. 7. Granular anhydrous sodium sulfate was added to the ether layer to get rid of any water in it. Sodium sulfate was a salt, which wanted to dilute itself. Dilution required water; so granular anhydrous sodium sulfate took water in ether layer. When no more clumps were created in the ether layer, drying up was complete as sodium sulfate finished diluting itself. Crystallization was a technique used to purify solids. It happened because of the theory of solubility of the compounds, which was that they were less soluble in cold solvents compared to they were in hot solvents. Through crystallization, the pure solutes were collected, and the experimental melting point range and the percent recoveries of the solid compounds were obtained. As crystallization happened because of the change in solubilities at different temperatures, 95% ethyl alcohol was chosen as a proper solvent for crystallization of phenanthrene because of a great increase of its solubility at higher temperature. To maximize its solubility before crystallization, 95% ethyl alcohol was heated before added into dried ether layer. 8. To dry up the ether layer, rotary evaporator was used. 9. To dissolve the entire dried ether layer, heated 95% ethyl alcohol was added. Using more solvent caused higher solubility, so more solids were dissolved. Thus, another small portion of solvent was added when the solid was not completely dissolved in the solvent.

Ham 8 10. As the solubility of phenanthrene in 95% ethyl alcohol had to get decreased for crystallization, the flask was cooled at room temperature first. The flask was covered with a small watch glass to avoid any evaporation of 95% ethyl alcohol. When no more crystallization was happened at room temperature, the flask was placed in a ice-bath because the solubility of phenanthrene in 95% ethyl alcohol would have decreased even more at a lower temperature. Unlike vacuum filtration for methyl 4-aminobenzoate, the filter paper was moistened with 95% ethyl alcohol because phenanthrene was in 95% ethyl alcohol through crystallization. As some crystals were stuck at the flask, ice-cold 95% ethyl alcohol was added to transfer the remaining crystals. The 2.00-mL of ice-cold 95% ethyl alcohol was enough amounts for that. Results Table 1 below showed the data for the extraction of phenanthrene and methyl 4aminobezoate from unknown mixture. The initial mass of unknown mixture containing phenanthrene, methyl 4-aminobenzoate, and 1,4-dibromobenzene obtained was 0.987g. The final mass of phenanthrene collected was 0.254g and that of methyl 4-aminobenzoate was 0.357g. The percent recovery for phenanthrene was 25.735%, and that of methyl 4-aminobenzoate was 36.170%. For phenanthrene, the experimental melting point range was 97.6 – 99.4 °C, and the literature value was 98.0 – 100.0 °C. For methyl 4-aminobenzoate, the experimental melting point range was 106.3 – 108.2 °C, and the literature value was 109.0 – 111.0 °C. Table 1: Data for the Extraction of Phenanthrene and Methyl 4-Aminobenzoate

Initial Mass of unknown mixture (g) Final Mass of unknown compound (g) Percent recovery of unknown compound (%) Experimental melting point range (°C) Literature melting point range (°C)

Phenanthrene 0.987 0.254 25.735

Methyl 4-Aminobenzoate

97.6 – 99.4 98.0 – 100.0

106.3 – 108.2 109.0 – 111.0

0.357 36.170

Ham 9 Discussions The initial unknown mixture given was made of 50 % phenanthrene and 40 % methyl 4aminobenzoate. As the percent recovery of phenanthrene was 25.735 %, only about half of phenanthrene was extracted. To dry the ether layer, rotary evaporator was used. As the dried ether layer was stuck on the wall of round-bottom flask, heated 95% ethyl alcohol was poured into the round-bottom flask instead of added by drops. This caused more solvent to be used than expected. Using more solvent caused higher solubility, so more solids were dissolved. And, more solids remained dissolved in the mother liquor after crystallization, so less pure crystals were collected, which eventually caused the decrease in percent recovery. For phenanthrene, the experimental melting point range was 97.6 – 99.4 °C while the literature melting point range was 98.0 – 100.0 °C. Crystallization happened well when the experimental melting point range and the literature value were closer, so the crystallization happened well here. A little decrease in the experimental melting point range compared to the literature value was observed. It supported the melting point theory that containing impurities required a decrease in the melting point of the pure compounds. As the percent recovery of methyl 4-aminobenzoate was 36.170 %, most of methyl 4-aminobenzoate was extracted. For methyl 4-aminobenzoate, the experimental melting point range was 106.3 – 108.42 °C while the literature melting point range was 109.0 – 111.0 °C. Containing impurities were observed to cause the wider and decreased experimental melting point range than the literature value. As the experimental melting point range had the wider and decreased experimental melting point range, it proved that some impurities were contained in the methyl 4-aminobenzoate collected. To obtain as much as methyl 4-aminobenzoate, both “1st HCl extract” and “2nd HCl extract” were vacuum filtrated. This increased the percent recovery of

Ham 10 methyl 4-aminobenzoate, but also caused containing some impurities, which caused the wider and decreased experimental melting point....