Extraction Theory and General Procedure
(Adapted from Mohrig, pp. 57-64, 72-77.)

Extraction is a very common laboratory procedure used when isolating or purifying a product. Organic chemistry employs solid-liquid, liquid-liquid, and acid-base extractions. The following applies to liquid-liquid extractions, which will be used in this course.

It is very common for organic products synthesized in a reaction to be purified by liquid-liquid extraction. A separatory funnel (see picture) is used for this process. In this procedure, the organic product is isolated from inorganic substances. The organic product will be soluble in an organic solvent (organic layer) while the inorganic substances will be soluble in water (aqueous layer). The organic solvent used for extraction must meet a few criteria:

1. Should readily dissolve substance to be extracted.
2. Should not react with the substance to be extracted.
3. Should not react with or be miscible with water (the usual second solvent).
4. Should have a low boiling point so it can be easily removed from the product.

Common extraction solvents are diethyl ether and methylene chloride.

Removal of water: (Mohrig, pp. 72-75)
Although the criteria states that the organic solvent chosen should not be miscible with water, some solvents dissolve a small amount. Thus, water must be removed before separating the organic product from the organic solvent or else the product will be contaminated with water. A drying agent must be used. There are a number of drying agents available to the organic chemist: we will be using sodium sulfate and magnesium sulfate in this course. Placing the organic solvent containing the dissolved product in contact with the chosen drying agent will allow the agent to absorb any dissolved water. The agent can then be removed from the solvent and then the product can be isolated.

General Extraction Procedure:

Here's everything you will need to perform an extraction!

Ensure that the stopcock to the separatory funnel is closed. As a safety measure, place a beaker underneath the funnel in case it leaks.

Here is a separatory funnel with a beaker under it before pouring a mixture into the separatory funnel. (This is done just in case there is a leak in the sep. funnel OR as in this picture, the stopcock is accidentally left open.)

Place the solution to be extracted in the separatory funnel. As the organic solvent and water are not miscible with each other, you should be able to see the two layers (organic and aqueous layers) clearly. You should also have two beakers ready, one labeled "organic layer" and the other labeled "aqueous layer". To remove all inorganic substances from the organic layer, shake the separatory funnel to increase the contact between these substances and the water. The proper way to hold a separatory funnel is to grasp the funnel so that the stopper is in the palm of one hand the stopcock is held with the other. This way leaks are prevented and any pressure built up inside the funnel will not pop the stopper off.

It is imperative to VENT the separatory funnel of any gas pressure. After a few shakes, hold the funnel upside down with the funnel stem pointed away from nearby people, and open the stopcock to release any pressure. Close the funnel and shake the funnel a little more vigorously and vent again as necessary. This "shake and vent" method can be repeated two or three times as needed. When finished, the funnel can be returned to the ring stand and the layers allowed to separate. To determine which layer is which, one can simply add distilled water to the funnel. Whichever layer increases in size must be the aqueous layer and the other is the organic layer. At this point the two layers can be separated into their respective beakers. To be safe, never throw out any removed layers until the desired product has been isolated! Once the extraction process is completed, drying agents can now be used and the product can be isolated from the organic solvent. Your instructor will give you specific instructions on drying your organic layer.