How would you purify biphenyl contaminated with fluorene? What method and solvent would you use?
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To purify biphenyl contaminated with fluorene, you can use a technique called recrystallization. Here's how you can do it:
Materials needed:
1. Biphenyl contaminated with fluorene
2. Solvent for recrystallization (e.g., hexane, toluene, or ethyl acetate)
3. Hot plate/stirrer or a heating mantle
4. Glassware: beaker, filter funnel, filter paper
Procedure:
1. Start by selecting a suitable solvent for recrystallization. The choice of solvent should be based on the solubility of biphenyl and fluorene. Common solvents for recrystallization of biphenyl-like compounds include hexane, toluene, and ethyl acetate.
2. Weigh the contaminated biphenyl to determine the initial amount.
3. Take a clean, dry beaker and add the contaminated biphenyl into it.
4. Add a small amount of the chosen solvent to dissolve the mixture. Gently heat the beaker using a hot plate or heating mantle, while stirring the mixture until all the solid dissolves. Heating the mixture will help to increase the solubility of both biphenyl and fluorene in the solvent.
5. Once all the solid has dissolved, remove the heat source and let the solution cool down slowly. Slow cooling promotes the formation of large, well-formed crystals.
6. As the solution cools, crystals of biphenyl and fluorene will start to form. Allow the solution to cool to room temperature or, if necessary, place it in a refrigerator for further cooling.
7. Once the solution has reached a lower temperature, you can induce crystal formation by scratching the inside of the beaker with a glass rod. This provides a surface for the crystals to grow on.
8. After allowing sufficient time for crystal formation (several hours or overnight), filter the crystallized mixture using a filter funnel and filter paper. The crystals obtained will be a mixture of pure biphenyl and fluorene.
9. Wash the crystals on the filter paper with a small amount of cold solvent to remove any impurities. Take care not to use excessive solvent, as this can dissolve the desired product.
10. Once the crystals are dry, weigh them to determine the final amount and calculate the percentage yield based on the initial weight of the contaminated biphenyl.
Recrystallization is a common technique used to purify solid compounds by dissolving them in a suitable solvent and then allowing them to re-form as pure crystals. The choice of solvent is critical, as it should dissolve the compound of interest at elevated temperatures but have minimal solubility at room temperature, allowing the compound to crystallize out. By following these steps, you can obtain purified biphenyl, with the fluorene impurities removed.