Hi Robert, it's the stabilizer that troubles you! You will have to distill the solvent in order to remove it.

Hi Roland, thanks. We're actually using non-stabilized THF, but I will investigate whether has been some contamination nonetheless.

Cheers,

Robert

Storage of these two chemicals in dry form is, in general problematic. The problems are (a) moisture and (b) peroxide formation. In my opinion these solvents should be used in freshly dried form. 

As a quick drying method, these solvents could be dried by passing through a short column using a suitable adsorbent. This is to remove moisture as well as peroxides.

When storing fully degassed solvents peroixdes cannot form. Over a prelonged period of time you could try to re-degas. I used to redegass my solvents after every usage.

THF and ether are very hygroscopic. Just open a bottle to the air and they are wet. As suggested before, use dry gases N2 to store. A bottle of Diethyl-ether can have up to 10% HOH and CH3CH2OH accounting t o 30%. Molecular sieve may be OK but takes a long time to dry them. Dry molecular sieves under vacuum at 120°C, and please cool them before adding. The best is to distill them in air free glassware with Na-benzofenone.

Hi Robert,

We have had similar problems with random batches of THF when used in n-BuLi reactions. Although we did not thoroughly investigate what was the problem? swirling the solvent from SPS over vacuum dried MS (overnight @120 C) did solve the problem! Of course handling after removing MS from the oven should be done under inert atmosphere (Schlenk line and cannulas with filter paper) 

It would be interesting to know what is the root cause of this problem. Please let us know if you find out.

Good luck

Hazem  

Hello, we did have exactly the same problems with those two solvents with the SPS. The other solvents are ok. Although we never investigated the reasons for that, we just decided to set up stills for Et2O and THF. Maybe SPS is not good enough for ethereals!

A couple'o days earlier I posted this "Dry molecular sieves under vacuum at 120°C, and please cool them before adding to ether".

Well, I forgot to mention that Molecular sieves must be dried above100°C  under vacuum, BUT, in order to cool and use them you must flush the vacuum flask with N2, so HOH doesn't reenter the MSieves, OBVIOUS .

Check out "Vogel's PRACTICAL ORGANIC CHEMISTRY, chapter 2" Drying of solvents... Standard techniques in organic chemistry.

There is only one method that simultaneously removes all water and eliminates all peroxides, and prevents their reformation even if explosed to air.  I have used it successfully for years for all the organic liquids I could find- but it does not work with alcohols.  The compound?  Calcium hydride.  A lump left on a bench almost before your eyes turns from grey hydride into white calcium hydroxide.  A lump added to an orgainic liquid (except alcohols) reacts with the water present and the calcium hydoxide formed is insoluble in organic solvents.  The dry peroxide-free liquid can either be decanted off or distilled off.  To prove that it is peroxide-free take a sample and add an iodide soluble in the solvent, prefeably a quaternary ammonium one, with a large cation to ensure its solubility, such as tetra-N-hexyl ammonium iodide,  If the solution turns yellow it still contains peroxide but this is unlikely since the reaction with peroxides is complete after a few minutes - stirring and shaking is advised. No colour change - no peroxide.  The tri-iodide formed has a high molar extinction coefficient and spectroscopic measurements made at 360 nm will show if there was peroxide present.  Peroxidescan be detected this way down to 10(-8) molar - how's that for sensitivity!

I'm currently having this same issue with THF. We use Co(PMe3)4, very moisture/air sensitive. Our THF comes off our SPS at about 3 ppm (KF determination) which has always been a fine water content for this chemistry. Now this is the second time we've dealt with this Co catalyst reacting upon THF dissolution. Previously, we thought it was the butyrolactone (BL) (THF peroxide byproduct). But some of the BL ppm was 80 ppm which is within spec for the HPLC grade THF that we buy and put in our columns. Obviously, we buy stabilizer free THF as all HPLC grade is. If anyone has any other ideas why this problem keeps arising let me know. We changed from Omnisolv THF to Fisher THF and got rid of the problem but it recently came back.

I have used adding CaH2 successfully to remove peroxides and water traces from THF plus over 40 organic solvents, without the need to reflux or distil, only shaking or stirring, as the Ca oxides, hydroxides and excess CaH2 settle to the bottom of the flask/container and peroxide and moisture free THF can be pipetted or removed and is best stored, depending on your intended use, under an oxygen-free atmosphere and in the dark as much as possible. To check that it is peroxide-free to a sample add a quaternary ammonium iodide (e.g., tetrahexylammonium iodide) which will dissolve (KI will not) in THF and turn the solutiion yellow if any peroxide is present. A faint yellow colur indicates that the concentration of peroxide is less than 10(-6) Molar.

Trevor, a faint yellow color indicates low levels of peroxides (good) or is greater than 10^-6 M which is bad? Your wording of less than 10^-6 M is confusing me.