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Solubility and Extraction

Solubility and Extraction. Summer 2012. Separatory Funnel. Separation of immiscible liquids. Extraction. To pull out a compound from one layer into another A compound partitions more toward where it is more soluble (equilibrium) Partition coefficient

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Solubility and Extraction

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  1. Solubility and Extraction Summer 2012

  2. Separatory Funnel Separation of immiscible liquids

  3. Extraction • To pull out a compound from one layer into another • A compound partitions more toward where it is more soluble (equilibrium) • Partition coefficient • Multiple extractions may be needed to completely extract a substance

  4. Separation Using Extraction • What if our solid sample contains two substances? • When the solids dissolve and partition, there are three possibilities—which would be effective for a purification technique?

  5. Flowchart Extract  Separate  Dry  Evaporate

  6. Solubility • To plan for an extraction, must be able to choose proper solvents to separate impurities from target • Partitioning is based on relative solubility • Is the compound more organic soluble or more aqueous soluble?

  7. Solubility Rules of Thumb • Water soluble • Ionic • Organic ions of < 7-8 carbons • Small polar molecules • Organic compounds with one H-bond donor per 3-4 carbons

  8. Water Insolubility Spectrum • Somewhat soluble • Insoluble • Detergents

  9. Organic Solvent Solubility • Organic Soluble • Other organic molecules unless extremely different polarity • Organic insoluble • Ionic These are not organic soluble:

  10. Planning an Extraction • You want to separate the following two impurities from your target with extraction. You dissolve the mixture in water/ether in a separatory funnel. • Will the purification work? • In which layer is your target (top or bottom)?

  11. Acid/Base Extractions • Rather than neutral water, extract with aqueous acid or aqueous base • Acid/base reaction MIGHT occur with your target and/or impurity • Solubility changes due to ionization • Allows for better separations

  12. Extraction Revisited • You want to separate the following two impurities from your target with extraction. You dissolve the mixture in aqueous base/ether in a separatory funnel. • Will the purification work? • In which layer is your target (top or bottom)?

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