Experiment 6 Extraction - Separation of Benzoic Acid and Phenanthrene PDF

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Lab Report Organic Chemistry...

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Experiment 6: Extraction -- Separation of Benzoic Acid and Phenanthrene INTRODUCTION The purpose of this experiment is to extract benzoic acid and phenanthrene from solution. The compounds will be separated using the methods of liquid-liquid extraction, drying agents, and vacuum filtration. This experiment as well introduces complex extraction techniques such as acid-base extractions for solutions with compounds of similar solubility. The initial solution contains dichloromethane as a solvent in which benzoic acid and phenanthrene are dissolved in.

FIGURE 1. PERTINENT MOLECULES.

Acid-base reaction for extraction Both benzoic acid and phenanthrene are soluble in dichloromethane, however only the benzoic acid will react with NaOH to form sodium benzoate, an aqueous solution. This acid-base reaction allows the two compounds to be separated into solutions of distinct densities, isolating one into an aqueous layer and the other in an organic layer in the separatory funnel.

FIGURE 2. BENZOIC ACID AND SODIUM HYDROXIDE REACTION.

Precipitation of benzoic acid reaction To isolate the benzoic acid, the aqueous sodium benzoate (created in the above reaction) must react with hydrochloric acid. This reaction produces the precipitate benzoic acid and aqueous sodium chloride.

FIGURE 3. SODIUM BENZOATE AND HYDROCHLORIC ACID PRECIPITATE REACTION.

PHYSICAL DATA Compound

Molecular Weight (g/mol)

Melting Point (°C)

Boiling Point (°C)

Density (g/mL )

Solubility

Hazards

Benzoic acid

122

121-123

249-250

1.26

s OH, eth, bz, chl, ace, c, dis; ss pet.eth, hex

mild irritation if inhaled, in contact with skin, or eyes; moderately toxic; slight fire hazard

Chloroform-d

120

-64- -63

60-62

1.49

msc organic solvents, ethyl acetate, and acetone

severe irritation if in contact with eyes and skin; toxic if ingested or inhaled; corrosive; carcinogenic

Dichloromethane

84.9

-97- -94

39-40

1.32

msc OH, eth, EtOH; s CCl4; imsc H2O

irritation if in contact with eyes and skin; irritation of digestive tract if ingested; hazardous and irritant if inhaled

Hydrochloric acid

36.5

-116-114

-87- -85

1.18

s H2O, EtOH, Met, OH, eth, bz

severe irritation and burns if in contact with skin and eyes; severe hazard if ingested or inhaled; toxic

Phenanthrene

178

99.2-101

338340

1.18

s toluene, CCl4, bz, CS2, EtOH, ace, diethyl ether; i H2O

poisonous if ingested; eye and skin irritant; irritant if inhaled

Sodium benzoate

144

>300

450~475

1.44

s H2O; sl EtOH

severe irritant when in contact with eyes and skin; hazardous in case of ingestion and inhalation

Sodium hydroxide

39.9

318-323

13871389

2.13

vs H2O; s EtOH, OH, Met, glycerol

burns if in contact with skin or eyes; hazardous if ingested or inhaled

Sodium sulfate

142

884-886

16991701

2.7

s H2O, glycerin, HI; i OH

irritant if in contact with skin, eyes, or inhaled; hazardous if ingested

Percent Recovery To find the percentage of benzoic acid or phenanthrene able to be extracted from the initial solution.

percent recovery=( 100)

amount isolated initial amount

PROCEDURE 1. Collect and clean with acetone two NMR tubes and set aside to dry.

2. Make the solution of benzoic acid and phenanthrene by combining 0.5g of each compound with 10 mL of dichloromethane in a beaker, measure to the nearest 0.01g. 3. Once fully dissolved, place solution in separatory funnel with the stopcock completely closed. Use a stemmed funnel to reduce spillage of organic solution. 4. Add 5 mL of 1 M NaOH to the funnel with a slightly wet stemmed funnel. Do not let the volume exceed ¾ of the separatory funnel. 5. Place a hand on the stopcock and another on the stopper. Carefully shake the funnel back and forth a couple of times, releasing pressure by opening the stopper after every shake 6. For 30 seconds, forcibly shake the funnel, releasing pressure when necessary. This should bring the solvents to equilibrium. 7. Place the funnel back on the stand and wait until there are definite layers established. Check which layer is the organic or aqueous layer by dropping in a small amount of water: if it sinks, the top layer is the organic layer; if it mixes with the top, then the bottom layer is the organic layer. For this reaction the lower layer should be the organic layer. 8. With an Erlenmeyer flask below the funnel, open the stopcock and drain the denser solvent until the lighter layer is almost to the stopcock. Do not discard of any layers separated until the end of experiment. 9. Remove the aqueous, lighter layer from the top of the funnel and pour into a separate flask or beaker. 10. Repeat extraction steps (4-9) with the organic layer of the previous extraction. Again using 5 mL of NaOH as the aqueous extracting solution. 11. Mix the resultant aqueous layers from both extractions and add 1 M HCl until it reaches an acidity of approximately pH 3 or lower. Clean pH reader with a Kimwipe between each reading 12. Once acidified, the solution should precipitate out benzoate acid, a white appearing solid from the chemical interaction with sodium benzoate and hydrochloric acid. The reaction will also release heat, so it should be thoroughly cooled in an ice bath before proceeding to filtration. 13. With a side-arm flask, Buchner funnel, Hirsch funnel, and rubber adapter construct the filtration apparatus. Secure the side-arm flask to the ring stand and attach the rubber adapter and Buchner funnel to the opening of the flask. Lightly wet a piece of filter paper with solvent and place in Buchner funnel opening, make sure all openings are covered. Connect rubber vacuum hose to flask. 14. Check that the vacuum is pulling air from the filter. Then pour the aqueous solution into the filter. 15. Clean off the solids removed by the filter with cold water and let dry. 16. With the collected precipitate, measure the weight and melting point of the compound; using the prepared NMR tube, gather and analyze data on benzoic acid. 17. Use anhydrous sodium sulfate as a drying agent for dichloromethane (organic) solution by adding it to the solution until no clumps are observed. 18. Remove the sodium sulfate by pouring out the organic solution into a separate flask and leaving the wet salt behind, use a pipet to separate if the volume is too small. 19. Using a large round-bottom flask, record its weight and then pour the organic solution in 20. Look at the rotovap instrument and clear out old vapor in solvent trap and clean the bump trap and adapter. 21. If isolating a powder, use a kimwipe to block entrance into the adapter. The coils should feel cold if proper cooling fluid is circulating. 22. Turn on the water bath, heating should be ~60°C. Connect round-bottom flask to adapter and semi submerged in water.

23. Spin the flask and start closing the vacuum outlet to evaporate solvent. Once all solvent is evaporated completely close vacuum outlet and remove the flask from bath. 24. Measure the weight of the compound and melting point of the phenanthrene remaining and observe/analyze its NMR spectra. 25. Clean all funnels and save compounds for recrystallization.

DISCUSSION OF RESULTS The objective of this experiment was to isolate benzoic acid and phenanthrene from a provided solution. The sample contained 10 mL of dichloromethane and 0.51g of a benzoic acid and phenanthrene mixture. The two compounds were in a 1:1 ratio, thus it was expected that the solution contained 0.255g of both benzoic acid and phenanthrene. However, that assumed that the measurement was perfectly ideal and had an exact 1:1 ratio of the two. To verify the amount and purity of both compounds, extraction with the following methods observed in the flowchart were performed.

Benzoic Acid, Phenanthrene, and Addition of Dichloromethane NaOH for Solution acid-base extraction Sodium Phenanthrene Benzoate and Addition of Vacuum AqueousHCl to Rotary Dichloromethan filtration of evaporatio Solution precipitate benzoic e Solutionn of Benzoic Aqueoacid Phenant benzoic precipitate dichlorom Acid us FIGURE 4. ISOLATION PROCESS. hrene Precipitat Soluti Due to the solubility properties of both benzoic acid and phenanthrene, the two were Isolate ethane indistinguishable in the dichloromethane. Thus to begin the extraction process, the solution was treated e on with 1 M NaOH in a separatory funnel to separate the compounds in an aqueous and organic solution. As illustrated by the chemical structures in figure 1, benzoic acid has a reactive hydroxyl functional group while phenanthrene is solely structured with alkenes. This difference caused only benzoic acid to react with sodium hydroxide and form an aqueous solution of sodium benzoate, while phenanthrene remained in the organic solvent. Once the base was added to the funnel, the solutions were intermittently shaken in order for the reaction to reach equilibrium. The immiscibility and differing densities between dichloromethane and water produced two distinct layers, a top aqueous and bottom organic layer. The bottom, more dense layer was drained out and the top was placed into a separate beaker. The process was repeated with the organic layer to provide maximum separation and eliminate any contamination of sodium benzoate. Although effective, this process lead to a loss of product as the solutions spilled while transferring containers and the aqueous layer had the chance of leaking into the organic layer. Through acidification of the combined aqueous solutions of the separations, benzoic acid was precipitated out. As shown in figure 3, when 1 M HCl was added, the benzoate protonated and formed a solid, white compound. The solution took 15 mL of hydrochloric acid to fully precipitate out benzoic acid and reach a pH of 2. To isolate the precipitate, the mixture was filtered with a vacuum, dried, and weighed. The final amount of isolated benzoic acid was 0.224g, and the percent recovery was 87.84 %. The main sources of benzoic acid loss occurred in the acid-base reactions and filtration. Both reactions

percent recovery benzoic acid=(100)

0.224 g = 87.84 % 0.255 g

with sodium hydroxide and hydrochloric acid most likely were not ideal and did not react all the benzoic acid. With the filtration method, some of the precipitate could have leaked into the aqueous solution and not been isolated on the paper, leading to a smaller end weight. Volume of HCl

pH

Precipitate?

2

10

no

4

10

no

8

9

no

10

9

no

15

2

yes

FIGURE 5. VOLUME OF HCl REQUIRED FOR PRECIPITATION.

To isolate the phenanthrene, the organic layer was first mixed with anhydrous sodium sulfate to remove any aqueous or water contaminants that could have remained from the separation. When added the sodium sulfate bound to the water or ionic molecules to ensure that only phenanthrene would be a solute. Using a rotary evaporation instrument, the solution was spun and heated in a water bath until all the dichloromethane solvent evaporated. This left the phenanthrene in solid form on the walls of the round-bottomed flask. The final amount of extracted phenanthrene was 0.300g, giving a percent recovery of 117.64 %. The calculation suggests a product gain instead of a product loss; the additional mass

percent recovery p h enant h rene=(100)

0.300 g = 117.64 % 0.255 g

could be attributed to contaminants of the compound. Possible contamination could have occurred due to a dirtied separatory funnel, incorporation of sodium sulfate, or incomplete evaporation of solvent. To analyze the purity of both isolates, NMR spectra and melting point temperatures were taken. The melting point of the benzoic acid sample was observed to be 121.1°C suggesting no impurities because the melting point range is 121.5-123.5°C. The NMR spectra supported this claim because chloroform-d and acetone emerged as impurities, which are both negligible as chloroform is the solvent for the NMR solution and acetone was used to clean the glassware. Neither chemicals would have attributed to the weight as both were used after the extraction.

FIGURE 6. ISOLATED CRUDE BENZOIC ACID NMR SPECTRA.

Compound

Initial Amount (g)

Isolated amount (g)

Percent Recovery (%)

Melting Point (°C)

Benzoic Acid

0.255

0.224

87.84

121.1

CDCl3 Acetone

Phenanthrene

0.255

0.300

117.64

100.3

CDCl3 Acetone Dichloromethane

FIGURE 7. ISOLATE WEIGHT AND PURITY DATA.

NMR Impurities

The melting point of phenanthrene was observed to be 100.3°C, which did not support contamination because it was in the range of the actual melting point data. If contamination did occur then it would be assumed that the melting temperature would be lower; however, the NMR spectra showed a clear contamination of dichloromethane around 5.30 ppm. This peak in the spectra suggests that not all the solvent in the organic solution evaporated and would have remained with the phenanthrene solid. This would have led to the high product recovery because the dichloromethane added additional mass not in the initial solid mixture. The NMR spectra as well showed chloroform-d and acetone peaks, but as in the case of the benzoic acid those were negligible.

FIGURE 9. ISOLATED CRUDE PHENANTHRENE NMR SPECTRA.

To avoid future contamination, all glassware will be thoroughly cleaned and dried before the experiment begins. If possible contamination occurs then the extraction process should be restarted. To improve percent recovery, precautionary measures to preserve solutions when transferring from vial to vial should be taken and all solvents should be fully evaporated or filtered out....