Separation by Chemical Extraction

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0°C

Bp: 100°C

Density: 1.00g/mL

What’s in the water can be more hazardous than the water.

Table 3. All Products; Crude and Recrystallized

Compound

MW (g/mol)

Isolated

moles

% recovery

Crude Phenanthrene

C14H10

178.23

1.030 g

0.005779

51.5%

Recrystalized Phenanthrene

C14H10

178.23

0.730 g

0.004096

36.5%

p-Bromoaniline

BrC6H4NH2

172.02

0.315 g

0.001831

31.5%

Physical description of isolated compounds:

Crude Phenanthrene – white and shiny solid crystals

Recrystalized Phenanthrene - shiny white crystals.

p-Bromoaniline – white powder

Yield Calculation for p-Bromoaniline:

Percent recovery = mass of product isolated/mass of reagent used x 100%

Percent recovery = (0.315 g / 1.00g) x 100% = 31.5%

Yield Calculation for Crude Phenanthrene:

Percent recovery = (1.030 g / 2.00g) x 100% = 51.5%

Yield Calculation for Recrystallization of Phenanthrene:

Percent recovery = (0.730 g / 2.00g) x 100% = 36.5%

Melting Range Data

Table 4. Melting Range Data

Sample Determined

Observed Melting Range

Lit. Melting Range

Identification

Component from solution A

56-59°C

56-62°C

p-Bromoaniline

Component from solution B

92-96°C2

107-113°C

m-Toluic acid

Crude phenanthrene

87-89°C

98-100°C

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Recrystallized phenanthrene

86-89°C

98-100°C

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Discussion

Stock solution A was separated into p-bromoaniline and phenanthrene using liquid-liquid extraction, with respective weights of 0.315g and 1.030g, and respective percent yields of 31.5, and 51.5%. The crude phenanthrene was then recrystallized to obtain a mass of 0.730g and a percent yield of 36.5%. The low percent yields seen in this experiment were likely from improper methods and technique used to obtain them.

Thin layer chromatography was used to compare Rf values for the crude phenanthrene solution, recrystallized phenanthrene solution, and a stock solution. A 6.5 cm silica gel was run with a solvent of a 2:1 mixture of cyclohexanes and ethyl acetate and then a p-anisaldehyde stain was used to turn the p-bromoaniline spot yellow against the white plate background, but it did not immediately react with the phenanthrene or benzoic acid. The Rf values for the phenanthrene, both in the stock solution and in the crude and recrystallized solutions, had very close values, with the recrystallized and stock solutions having identical values of 0.556, and the crude having one of 0.533, which suggests that the recrystallized phenanthrene had a higher purity and therefore it is to be expected that it had a similar value to that of the stock. The crude phenanthrene, having lower purity, is expected to have a different value, reflecting its impurities present.

The p-anisaldehyde turned the p-bromoaniline spot yellow against the white background of the plate, and the data observed on the tlc plate stained with bromocresol green by Tia Dash2 was observed to turn the benzoic acid into a yellow spot against a blue background. p-Bromoaniline and m-Toluic were both present in the stock solution, with Rf values of 0.289 and 0.402, respectively. No p-bromoaniline or m-Toluic acid were present in the crude or recrystallized phenanthrene solutions. This suggests that the crude and the recrystallized phenanthrene obtained were relatively pure.

The melting ranges of crude phenanthrene, recrystallized phenanthrene, m-toluic and p-bromoaniline were 87-89°C, 86-89°C, 92-96°C2 and 56-59°C, respectively. These were relatively close to the actual theoretical melting ranges of respectively 98-100°C, 98-100°C, 107-113°C, and 56-62°C. This which indicates that the compounds were relatively pure.

The best solvent system for recrystallizing anthanilic acid, based on Table 5 solubilities, would be hexanes or toluene due to the fact that it is insoluble when they are cold, but slightly soluble for hot hexanes and very soluble for hot toluene. Based on this assumption that the best system will have a higher solubility in hot than cold, the best solvent system for recrystallizing m-Toluic acid would be hexanes because it is more soluble in the hot version than the cold. The best solvent system for recrystallizing p-bromoaniline would be hexanes and water.

Conclusion

Liquid-liquid extraction was used to separate 0.315 g of p-bromoaniline and 1.030 g of crude phenanthrene, with respective percent yields of 31.5% and 51.5%. The phenanthrene was then recrystallized to obtain 0.730g and a percent yield of 36.5%. The melting points of the compounds were used to confirm that they were in the range of the theoretical