[thenuttyprofessor]

Why is it necessary to dry an organic phase before distilling a solvent?  And are you drying it with liquid??? 

[mir]

Dear Mr. Nutty

I assume you meen using the rotavapor, when you say distilling.

You should remove water from the org phase while it is easy, so you don't need to do it later under vacuum (you save time). You might dry it by making an azeotropic mxture of water and maybe toluene. Then both the solvent and the water disappears while using the rotavapor.

[beheada]

The drying agent is employed to remove water so that the 100C fraction is removed for distillation, but also to absorb the water and the impurities carried in the aqueous phase. If you're concerned about the purity of your product, drying it greatly increases the chances of removing possible impurities.

[Ψ×Ψ]

Dear Mr. Nutty

I assume you meen using the rotavapor, when you say distilling.

You should remove water from the org phase while it is easy, so you don't need to do it later under vacuum (you save time). You might dry it by making an azeotropic mxture of water and maybe toluene. Then both the solvent and the water disappears while using the rotavapor.

Toluene itself isn't exactly easy to remove in a rotavap...unless you throw in some pentane. 

[mir]

Well, I have learned to be patient, and do something else in stead. Our vacuum pump is also really good too, when all the rubber is soften up and becomes really tight

[Mitch]

Dear Mr. Nutty

I assume you meen using the rotavapor, when you say distilling.

You should remove water from the org phase while it is easy, so you don't need to do it later under vacuum (you save time). You might dry it by making an azeotropic mxture of water and maybe toluene. Then both the solvent and the water disappears while using the rotavapor.

Toluene itself isn't exactly easy to remove in a rotavap...unless you throw in some pentane. 

Woh...woh...woh can you explain that trick?

[hypha]

dichloromathane could be use to dry a product and is very easy to remove. (bp 40°C). 5% water in the azeotrop..

[hypha]

An obvious fact is that at lower pressure the azeotropic composition changed.

[Ψ×Ψ]

Mitch: If you have toluene you're trying to get rid of, add some pentane and put it on the rotavap.  Do NOT heat the water bath.  (I kinda started a fire that way once...)

[Yggdrasil]

Why is it necessary to dry an organic phase before distilling a solvent?  And are you drying it with liquid??? 

A lot of the time you will want to remove water from your product before you heat it for any procedure if the compound is sensitive to hydrolysis (e.g. an ester).  At high temperatures, water can destroy many of the products that you have tried to synthesize.

[Bronwen Dekker]

I was reading through the posts and wanted to raise a related question.

I have mostly dried organic phases with something like sodum sulfate.

Under what circumstances would it be better to azeotrope off the water?

Is it mostly a matter of personal preference? Is it that sodium sulfate is significantly soluble in some solvents?

[movies]

Azeotropes are better when you have very polar compounds that might stick to Lewis acidic drying agents (MgSO₄ is notoriously bad in that respect).  Azeotropes are also good for removing organic solvents that aren't removed by the hygroscopic drying agents.  Things like pyridine are often a pain to get rid of, but can be azeotroped away with heptane.

[Ψ×Ψ]

No kidding!  I didn't know that!  Would you expect alcohols to be particularly bad for this?  If so, it might explain a few things about a reaction I'm using...

[Yggdrasil]

Here's a fairly good reference page on some commonly used drying agents:

http://www.chem.ucla.edu/~bacher/Specialtopics/Drying%20Agents.html

[movies]

I always use sodium sulfate for anything that's really polar (alcohols, beta-ketoesters), except for amines, where potassium carbonate tends to be a little better.