[cvengo]

Has anyone came across a publication dealing with issues related to the sensitivity of THF?
Or what is your general experience, for how long would you store dry THF (distilled from benzophenone/Na) in Schlenk tube with septum under argon?

[Markov]

It depends very much on the chemistry you want to use it for. What sort of stuff are you having in mind?

If it is for normal, "stoichiometrically moisture sensitive" reagents, e.g most hydride reagents or simple grignard chemistry, it may probably stay dry enough for weeks and weeks, particularly if you use proper schlenck-techniques when handling it. For this type of chemistry, many people don't even bother to dry the THF, just make sure your bottle is reasonably fresh (weeks to months). Of course, it depends also A LOT on the air humitity where you live.   

On the other hand, If you are doing something that is on the very extreme, like eg something with a minute amount of a highly sensitive catalyst, you might not want to store it even overnight. Maybe store over molecular sieves?

If you don't have access to a continous dry distilling apparatus, I would not reccomend putting up one for occasional batchwise drying. Maybe you can get by with using molecular sieves, or buying dried THF when you need?

[cvengo]

thanks for the response, it is pretty much what I think, I would just need some data to convince a sceptic colleague of mine (just a simple experiment of determining the water content in THF being stored in  Schlenk under argon over a period of time). So I thought that maybe someone saw something like that published.

[movies]

We tested the water content of THF distilled from benzophenone/Na in a standard solvent distillation setup connected to a nitrogen line (not as rigorous as a Schlenk setup) and we found that the water content increased quite noticeably just in the course of a few hours sitting in the collection bulb under N₂.  I don't recall the exact numbers but it was definitely from <10 ppm H₂O to >15 ppm.  I hesitate to do any sort of serious organometallic chemistry without freshly dried THF.

[macman104]

Does that have to do with the nitrogen at all?  I know that our house nitrogen line is pretty wet

[rajan]

concerning storage of peroxide forming chemicals -- be careful when you distill your inhibitor away and then keep your THF for a while. i've never personally heard of a problem with THF forming peroxides, but you probably don't want to be the guy that everyone knows only by reputation.

[Arctic-Nation]

We tested the water content of THF distilled from benzophenone/Na in a standard solvent distillation setup connected to a nitrogen line (not as rigorous as a Schlenk setup) and we found that the water content increased quite noticeably just in the course of a few hours sitting in the collection bulb under N₂.  I don't recall the exact numbers but it was definitely from <10 ppm H₂O to >15 ppm.  I hesitate to do any sort of serious organometallic chemistry without freshly dried THF.

In my previous lab distilling solvents was all but banned after a few explosions, one of which released a cloud of asbestos as it cracked the walls and ceiling. After that distillation was to be done by a technical staff member, who distilled solvents once week, or maybe if you asked him nicely and he didn't have anything else to do. Like surfing on the internet. Just great.

[movies]

The nitrogen was passed over Drierite before it got to the still, so it should have been reasonably dry.

Good point from rajan about the peroxides thing.  THF isn't as bad as some other ethers, but it will definitely form peroxides over time.  Could be a concern if you reactions are sensitive to oxidants.

There are a lot of things that can go wrong with a solvent still, but if it is well-maintained then it shouldn't be an issue.  There are a number of precautions that need to be taken, but these are well documented in lab manuals, etc.  We usually had a solvent purification system that used activated alumina to dry the solvents (much safer!) but it was acting up and so we set up the THF still in the meantime while we got it fixed.

[cvengo]

We tested the water content of THF distilled from benzophenone/Na in a standard solvent distillation setup connected to a nitrogen line (not as rigorous as a Schlenk setup) and we found that the water content increased quite noticeably just in the course of a few hours sitting in the collection bulb under N₂.  I don't recall the exact numbers but it was definitely from <10 ppm H₂O to >15 ppm.  I hesitate to do any sort of serious organometallic chemistry without freshly dried THF.

what do you think how does the water get in against the stream of nitrogen? (taking into consideration that your nitrogen was dry)

[movies]

Well, we are talking about very small amounts of water accruing in a solvent that is miscible with water, so it doesn't take too much to cause a detectable change in the water level.  My guess is that water was coming in through one of the joints or through the nitrogen.  Drierite drying tubes work well, but they are certainly not perfect.  A ppm level of water in the atmosphere will be absorbed pretty quickly by the THF and the water level would rise steadily over time if the bulb were not emptied & redistilled.

[P]

Cant the THF be stored over sodium wire? Would that keep it dry?

[movies]

That can be very dangerous because the water may not distribute evenly throughout the THF and then once the flask is moved a lot of water may react with the sodium at once.

[P]

Once the THF has been distilled then there won't be alot of water left in it anyway.  We used to store our toluene over Na wire all the time.

[movies]

Toluene is a different story because it isn't miscible with water.