Previous Chapter - 2.5 Quenching a reaction (REACTION)

 

3. WORK-UP

3.1 General approach

Definition: “A series of manipulations required to isolate and purify the product(s) of a chemical reaction.”

Importance:

General Comments:

General Work-up Procedure:

Step by Step:

Time-sensitive - Follow the instructions in your literature procedure. For an aqueous workup of most organic compounds this will involve:

  1. Diluting the reaction mixture with a solvent for workup (this is the organic layer).
  2. Washing the Organic Layer with various aqueous solutions. Some of the byproducts generated during the reaction will be neutralized or removed by dissolving in the aqueous layer. Ideally, the two layers will be clearly visible. If the result is one cloudy layer, you have an emulsion.
  3. Drying the Organic Layer with one of the drying agents.
  4. Filtering off the drying agent.
  5. Rotoevaporation to remove the solvent

The residue left is the crude product, ready for diagnosis. Certain types of compounds are more difficult to isolate than others, if your product might be volatile, soluble in water, charged at low or high pH (e.g. an amine or a carboxylic acid), unstable, or possesses stench.

Rules of thumb: The reaction mixture should be diluted to 3-4 times its original volume.

Tips:

 

Work-up Tricks:

Acetonitrile

Aluminum based Reductions

Benzene

Boron Compounds

Chromium Oxidations

Copper Salts

DCC

DMF or DMSO

m-CPBA

Metal Salts

Polar and water-soluble solvents

Reactions with Triphenylphosphine Oxide

Removing Alcohols

R3Sn-X Byproducts

THF/Dioxane

Titanium


Next - 3.2 Extractions