Sciencemadness Discussion Board

removing peroxides from thf with ferrous sulfate

soma - 9-6-2015 at 22:59

I've been trying to remove peroxides from thf using ferrous sulfate. I've found several different methods recommended. E.g.:
Quote:
method 1. Peroxides in 100.0 mL of water-insoluble solvent can usually be removed by shaking with 80.0 mL of acidified ferrous sulfate solution (6.0 grams of FeSO4•7H20 / 0.60 mL conc. H2SO4 / 11.0 mL H20) in a separatory funnel or stirred vigorously in a flask until the solvent no longer gives a positive test for peroxide; often a few minutes will suffice.

method 2. Decomposition of ether peroxides with ferrous sulfate is a commonly used method; 40g of 30% ferrous sulfate solution in water is added to each liter of solvent. Caution is indicated since the reaction may be vigorous if the solvent contains a high concentration of peroxide.


I tried shaking 30g of 30% ferrous sulfate in ~2L thf without success. (I'm using quantofix indicators.) Then I tried acidifying the solution to ~pH 4. This gave better results but still doesn't seem to remove them.

Also, the quantofix instructions said to add a drop of water to the strip after the solvent has evaporated. At first the strip turns very light blue. Then after maybe 2 minutes, it becomes dark blue. The instructions don't say how long to wait after adding the water. If I wait til the water has dried, I get a large white area with blue around the strip borders. Would this mean the peroxide is gone?

When I test freshly distilled thf, the strip becomes very slightly blue and doesn't change after sitting. If I add water after the solvent is gone, the strip becomes completely white.

I'm thinking of going to basic alumina.

Help appreciated.

[Edited on 10-6-2015 by soma]

[Edited on 10-6-2015 by soma]

TonyZ - 10-6-2015 at 13:42

Perhaps this may help..

Burfield et al . "Deperoxidation of Ethers. A Novel Application of Self-Indicating Molecular Sieves"



Attachment: J Organic Chemistry V47 iss20 1982 [doi_10.1021_jo00141a003] Burfield - Deperoxidation of ethers.pdf (513kB)
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[Edited on 10-6-2015 by TonyZ]

smaerd - 10-6-2015 at 14:07

Basic Alumina works well. I relied on it solely last semester for a research project after I was met with a flask full of peroxides (visible gram quantities). Basic alumina also drys the THF. Just use it as fast as possible, I think it removes the stabilizer.

Ferrous sulfate will work for quenching but how to recover the THF after I'm not sure. Bisulfite is similar.

TonyZ I think that only works with some molecular sieves. IE: 3A and 4A do not work.

soma - 10-6-2015 at 14:27

If I remember correctly, the self indicating sieve removes the peroxide because the cobalt decomposes it. But it also produces ethanol.

soma - 10-6-2015 at 14:31

Update:

I added more water to the THF/FeIISO4/H2SO4 mix. THF is fairly soluble in water.

The addition of more water seems to have caused the removal of the peroxides. I then distilled off the THF. I'm going to test the remaining water to see if there's any peroxides in it.

soma - 11-6-2015 at 21:54

Tested the remaining water after distilling.

No peroxides!

Couldn't get rid of them no matter how much shaking of the FeSO4/H2SO4/(small amount of)water mix.