Sciencemadness Discussion Board

How fast is drying with Magnesium Sulfate?

Lillica - 27-1-2017 at 17:30

There's a dozens of articles and posts on drying with Magnesium Sulfate, but I can't find any that specify how long it takes.

I want to dry some Ethyl Acetate I distilled, how long would I stir the MgSO4 for, and would I just use a quantitative amount, based on how much water is in the Ethyl Acetate? Or would I use excess?

JJay - 27-1-2017 at 18:06

You would use an excess but not so much that you suffer significant mechanical losses. Stirring overnight is ordinarily considered more than sufficient.

Praxichys - 27-1-2017 at 18:51

I would suggest not using MgSO4 for that. Ethyl acetate is not nearly as polar as water and can easily be salted out.

Add some crushed K2CO3, CaCl2, or NaCl and shake. In about 5 minutes you'll end up with two layers of liquid. A water/salt solution will be on the bottom and ethyl acetate on top. Add enough desiccant to saturate the water layer, shake, let the layers settle again. Decant off the ethyl acetate and you're done. You can evaporate the water layer to recover the salt.

This will easily get it to <1% water. If you're looking to go lower than that, you can then stir overnight with MgSO4 or mol. sieves and redistill.

[Edited on 28-1-2017 by Praxichys]

Lillica - 27-1-2017 at 21:52

Quote: Originally posted by Praxichys  
I would suggest not using MgSO4 for that. Ethyl acetate is not nearly as polar as water and can easily be salted out.

Add some crushed K2CO3, CaCl2, or NaCl and shake. In about 5 minutes you'll end up with two layers of liquid. A water/salt solution will be on the bottom and ethyl acetate on top. Add enough desiccant to saturate the water layer, shake, let the layers settle again. Decant off the ethyl acetate and you're done. You can evaporate the water layer to recover the salt.

This will easily get it to <1% water. If you're looking to go lower than that, you can then stir overnight with MgSO4 or mol. sieves and redistill.

[Edited on 28-1-2017 by Praxichys]


Can I use Sodium Carbonate as a substitute for Potassium Carbonate? Also, you're saying just add the dry solid, not in a solution, correct?

So I add the Carbonate to the Ethyl Acetate, and just shake, filter off any excess, and the water layer will separate out?

veganalchemist - 28-1-2017 at 05:37

I've just got (this morning) the new edition of Purification of Laboratory Chemicals.

For ethyl acetate, is says to wash with 5% Na2CO3 (aq) then with brine.

Dry with K2CO3, CaSO4 or MgSO4.

Fractionally distilled. bp 77.1'C.

Quick method, Distill, dry with K2CO3, re-distill and store over 4A molecular sieves.

Praxichys - 28-1-2017 at 08:31

@ Lillica - Yes, sodium carbonate should also work although I have not personally tried it on ethyl acetate myself.

Also note that carbonates should not be used in long-term contact with esters since their basicity will cause the ester to slowly hydrolyze. They work fine for drying but the two should not be stored together, i.e. storing ethyl acetate over Na2CO3. In your case, the sodium carbonate would slowly react with the ethyl acetate and traces of water to make ethanol and sodium acetate, leading to ethanol-contaminated ethyl acetate.

Sulaiman - 28-1-2017 at 09:40

I believe that EtOH distillers add sodium carbonate (or bicarbonate) to convert ethyl acetate to ethanol and acetic acid
so maybe not a good combination ?

Lillica - 8-2-2017 at 18:46

So I had stirred my Ethyl Acetate with freshly dried Magnesium Sulfate the other day, for about 30 minutes, and when I filtered it the Ethyl Acetate was visibly yellow. Does anyone know why this is?

Today I am going to dry some before I distill it so I don't run into that problem, but I was wondering what that yellow color could be. Neither Ethanol or Acetic Acid are yellow.

Melgar - 9-2-2017 at 11:55

Quote: Originally posted by Lillica  
So I had stirred my Ethyl Acetate with freshly dried Magnesium Sulfate the other day, for about 30 minutes, and when I filtered it the Ethyl Acetate was visibly yellow. Does anyone know why this is?

Today I am going to dry some before I distill it so I don't run into that problem, but I was wondering what that yellow color could be. Neither Ethanol or Acetic Acid are yellow.

You didn't dry it on a steel baking sheet, did you? I made that mistake once and got yellow iron (iii) contamination.

I don't think that sodium carbonate would substitute well for potassium carbonate in this instance. Potassium carbonate has a much higher solubility in water than its sodium counterpart, but is virtually insoluble in everything else, much like the sodium salt. This means that it would take a very long time, and a large amount of sodium carbonate to work. Sodium sulfate, on the other hand, would make for a very good desiccant, which you could probably make from sodium carbonate and magnesium sulfate via salt metathesis.