Organic Chemistry: Purification and Separation Flashcards
Extraction
The separation of a compound dissolved in solution by mixing an aqueous and organic phase. Successive extractions will provide more product and the product could be obtained from solvent evaporation. Use a separatory funnel.
How do intermolecular forces affect solubility?
Molecules that can hydrogen bond move into the aqueous layer easily. Molecules with only dipole-dipole interactions and/ or van der Waals forces will be more likely to move into the organic layer.
Wash
Extractions that remove impurities rather than isolate a pure product.
Filtration
Separating a liquid/ solid mixture by using a filter and either gravity or a vacuum.
Recrystallization
Could be used to prepare high-purity chemicals with either a good/ bad solvent system (where the good solvent dissolves the desired product while the bad solvent dissolves the impurities, like in extraction) or a minimal amount of a carefully chosen hot solvent. The solubility of the desired product should depend on the temperature of the solvent.
Sublimation
Using a cold finger under a vacuum, a heated solid turns into the gas, allowing for the separation of a subliming product.
Centrifugation
Sedimentation depends on mass, density and shape, where compounds of greater mass and density settle toward the bottom.
Distillation
The separation of one liquid from another through vaporization and condensation. Simple distillation can be used to separate liquids that boil below 150 degrees C that are at least 25 degrees Celsius apart, involving a distilling flask, distillation column, thermometer, condenser, and a receiving flask. Vacuum distillation can be used for liquids that boil above 150 degrees Celsius and are at least 25 degrees Celsius apart, where the reduced pressure of the system lowers the boiling points of the liquids. Fractional distillation separates liquids that boil less than 25 degrees Celsius apart, where a fractionating column (filled with inert objects that increase the surface area) connects the distilling flask to the distillation column.
Chromatography
The separation, identification, and isolation of individual compounds from a complex mixture based on how strongly they adhere to the stationary, or solid, phase. The speed of migration also differs between compounds, depending on how easily they elute into the mobile phase. Thin-layer chromatography uses a piece of paper or thin layer of silica/ alumina gel and a solvent to separate compounds by polarity (Rf = distance traveled/ solvent front) and it can be used for qualitative identification and isolation. Column chromatography involves an adsorbant in the form of a column where the solvent and compounds move through the column by gravity or with a gas [there exists ion exchange chromatography where the column attracts negative substances, size-exclusion chromatography that involves tiny beads that slow small molecules, and affinity chromatography]. Gas chromatography uses gas as the solvent and a vaporized mixture. High-pressure liquid chromatography is similar to a gas chromatography column, but under pressure.
Eletrophoresis
Anion attracted to anode and cation attracted to the cathode, in electrophoresis, which can separate macromolecules (v = Ez/f), where small molecules and highly charged molecules will move most rapidly. SDS-PAGE and agarose gel electrophoresis separate based on size. Isoelectric focusing separates based on pH, where a protein stops moving when it reaches its isoelectric point.
