posted 10-10-1999 08:02 PM         

KOH, BaO, CaO, NaOH, and K2CO3 are all good for drying alcohols (I don't think the hydroxides can be used for lower alcohols).

I'm pretty sure that the sulfate salts (Mg, Cu, Na & Ca) can be used to dry alcohols too.

You might want to use CaO, followed by CaSO4 to get the last bit of H20 out.

posted 10-11-1999 07:06 PM         

Drying Agents

• Acidic
  H2SO4, P2O5 - especially good for hydrocarbons or their halogenated derivatives. Cannot be used for bases, for unsaturated compounds, or for most N- or O- containing compounds. P2O5 reacts irreveribly to give H3PO4.

• Basic
  K2CO3, KOH, BaO, CaO, NaOH - Good for drying alcohols and amines. Last four cannot be used with ester (hydrolysis) or aldehydes (condensation) (NOTE: I'm assuming that the last four cannot be used with some ketones either)

  CaH2 - Good for ethers and hydrocarbons. Will react with alcohols and amines or any compound with a reasonably acidic proton.

• Neutral
  MgSO4, CuSO4 - high intensity, high capacity. CuSO4 cannot be used with amines. These are often fine powders which may make removal from solution difficult

  Na2SO4 - low intensity, high capacity. Granular form makes for easy removal.

  CaSO4 - high intensity, low capacity. Often used after drying agent of higher capacity has been used.

  CaCl2 - Moderate intensity, moderate capacity. Forms complexes with O- and N- containing compounds, especially amines and alcohols, but also many aldehydes, esters, etc...
  

If the substance to be dried is a non-viscous liquid and there is a relatively large amount of it, it may be dried directly. If there is only a small amount of the liquid, or the liquid is viscous, it should be dissolved in an anhydrous solutions and then the solution dried. This process minimizes loss of compound by absorption/adsorption onto the drying agent.

Ok, this is getting to long, I will summarize:

• make sure that the container you use has a wide, flat bottom (such as an erlenmeyer flask) to permit the greatest surface exposure of the drying agent. (NOTE: this obviosuly doesn't apply if you will eb doing tons of shaking)
  
• keep together for minimum of 20-30 mins.
  
• make sure container is closed/stoppered
  
• drying is most intense and efficient at lower temperatures. In most cases absorption of water is reversible, and higher temps shift the equilibrium in the wrong direction
  
• cotton is a suitablt filter when granular drying agents are used.
  

Hope this helps someone. Actually, it better fucking help someone, cause that was a lot of typing.

PS

posted 10-11-1999 07:08 PM         

Sorry for the typos.