Liquid-liquid extractions using a separatory funnel are essentially the only kind of extraction performed in the organic teaching labs. The "liquid-liquid" phrase means that two liquids are mixed in the extraction procedure. The liquids must be immiscible: this means that they will form two layers when mixed together, like oil and vinegar do in dressing. Some compounds are more soluble in the organic layer (the "oil") and
some compounds are more soluble in the aqueous layer (the "vinegar").
The photo at the right illustrates how two liquid layers separate. The red layer is simply red food coloring in water. Water is immiscible with the other liquid, which is methylene chloride. Methylene chloride is heavier (denser) than water, therefore, the clear methylene chloride layer is under the red, aqueous food coloring layer.
Quiz: Red food coloring is soluble in water and not in methylene chloride or diethyl ether. The photo at the right illustrates what you see if you mix methylene chloride, water, and red food coloring and allow the layers to separate. What would you expect to see if you mixed diethyl ether, water, and red food coloring? Click on the photo at the right for the answer.
In a particular experiment in simple extraction or in chemically active extraction, you will be able to figure out which layer, aqueous or organic, will contain the compound you want to isolate. (Please read the theory section in the Handbook for Organic Chemistry Lab.) You will also need to know which layer will be on top in the separatory funnel. This is determined by the density of the two solvents. Densities are listed in various sources of scientific data, as referenced on the Chem Info page on this orgchem site:
Details of how to carry out an extraction:
