Drying Methods

• Aqueous Wash with Brine: The final brine wash during workup is extremely effective for removing most of the water from the organic layer. The rest of the water can be removed using one of the drying agents listed below.
• Magnesium sulfate: Fast, always works, but kind of messy.
• Sodium Sulfate: convenient for small scale drying- it is very easy to filter. You should start with a clear organic layer (washed with brine, and not poured into a wet flask). Drying takes longer than for magnesium sulfate. Sit it over the drying agent ~15 minutes for dichloromethane, ~30 minutes for ethyl acetate. It does not work well for ether.
• Celite: Sometimes it is useful to filter small scale reactions through Celite to remove trace water.
• High vacuum: Placing a sample on the high vacuum line for a hour, or overnight (depending on the compound) sometimes removed residual water.
• Azeotroping: Often traces of a high boiling solvent or other impurity can be removed from a product or reaction mixture by concentration of a solution of the compounds from an appropriate solvent. This works because higher boiling solvents often azeotrope with lower boiling solvents, forming an easy to remove binary distillate. For an extensive table of azeotropic mixtures, see The Chemists Companion.
  1. Pyridine: repeated (2-3 times) concentration of a reaction mixture containing pyridine from heptane, cyclohexane, or toluene.
  2. Water: For highly water sensitive reactions, the organic substrate can be conveniently dried by adding benzene or (especially) toluene to the organic residue, and concentrating by rotoevaporation. This process is typically repeated three times. This technique is also useful for removal of water from organic hydrates (eg. NMO) by concentrating the compound from toluene 1-3 times followed by drying in a vacuum dessicator.