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3.3 Washes


3.3.1 Procedure

1. Dilute the crude reaction mixture with your solvent of choice and transfer to your chosen sep. funnel:
Large amounts of material require large amounts of solvent. Normal reactions (50-500 mg) can be diluted with between 25-100 mL of solvent. Put a funnel with a little peace of cotton to contain the residues when transfering the solution.

In this procedure we used DCM (red bottle) as the solvent of choice for this wash.



2. Washing the organic layer to remove impurities:
The volume of a wash phase is typically one tenth to one half the volume of the organic phase. It is sometimes best to repeat a wash two or three times. An acid wash (usually 10% HCl) is used to remove amines, while a basic wash (usually usually sat. NaHC or 10% NaOH) is used to remove unwanted acids. In most cases, when neither acidic nor basic impurities are an issue, the solution is washed with distilled water to remove any non-organic compounds. Also, when shaking mixtures in a sep. funnel be sure to vent it regularly by holding it upside-down, pointing it up and to the back of your hood, then opening the stopcock. This will release any pressure that has built up during mixing.

In this procedure, we washed with 1 M aqueous NaHSO4 (and the final wash should always be with brine).

Additionally, when draining liquids out of the sep. funnel, be sure to first remove the stopper. Here we removed firstly the organic layer (bigger density so was on the bottom) and then the aqueous layer.



3. If your compound is somewhat water soluble:
It has several polar functional groups ­you may need to back-extract the water layers with ether or ethyl acetate to avoid a significant loss to the aqueous phase. TLC can be used to determine when all of your compound has been removed from the water (see TLC for details).

4. Finish with a brine (saturated NaCl solution) wash:
This helps disrupt any emulsions and will "dry" the organic layer by extracting water that may have dissolved in the organic phase.

 

Next - 3.4 Drying