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3.2 Extractions

3.2.1 Procedure

• Remove any solids by filtration
• Partition reaction mixture between an organic solvent and water (or other aqueous solutions)

3.2.2 Removal of solids

It’s important to remove any solids before partitioning the reaction mixture, as the presence of fine particles can lead to the formation of an emulsion, making separation difficult. 

To remove fine particles:

• Dilute the quenched reaction mixture with the reaction solvent
• Make a Celite pad by packing Celite onto a sintered glass funnel
• Wash the pad with water and solvent to remove any impurities in the Celite
• Filter your mixture through the Celite pad, washing thoroughly with water and solvent

3.2.3 Partitioning

Partition the product between an organic solvent and water or another aqueous solution such as brine.

Procedure:

• Extract the desired layer a minimum of 3 times
• If product in organic layer, make final wash brine
• Most dense solvent is the bottom layer (as a general rule of thumb, halogenated solvents such as DCM sit on the bottom, however, this is not always the case)
• Densities can be found in Alrich catalogue
• If densities of the two solvents are similar, a third layer may form. In this case, add salt to the mixture, as this will increase the density of the aqueous layer, giving a better partition.

Do not dispose of either layer until you are sure that your product has been recovered.

3.2.4 Pick an extraction solvent

Specific gravity is often quoted in place of density:            SG < 1.0 = Float on H₂O

SG = Density of solvent / Density of water                         SG > 1.0 = Sink under H₂O

Ether is the most popular because it can be removed easily on the rotary evaporator, ethyl acetate also works well but is harder to remove.

3.2.5 Pick the size of your separatory (sep.) funnel

Usually 125 or 250 mL, large scale reactions (1-10g) require 500 mL or 1 L sizes. Remember that your sep. funnel will contain the solvent and wash liquid which must be thoroughly mixed.

Next - 3.3 Washes