Sciencemadness Discussion Board

Anyone ever worked with concentrated 11M n-butyllithium solution? Is a cloudy suspension normal?

Sidmadra - 18-4-2018 at 09:45

I've only ever worked with ~1M solutions in the past and they've been clear. I have a 1 year old, 11M bottle (in hexanes) from Sigma that has never been punctured/used. When left to sit for extended periods, there is significant precipitation at the bottom, that is easily resuspended by swirling or shaking. The suspension appears to be micronized enough to fit through an 18g syringe, but I haven't tried.

I called Sigma and the tech support I spoke with seemed to be giving me mixed answers. First he said when it was prepared it was clear (not suspended), but then he said mild haziness was normal. He also said since the product has never been used and doesn't have an expiration date that it should be fine. He also stated that even though I purchased it a year ago, the batch number I gave him was prepared in 2015. He stated it should be fine to use, but I was getting the impression that he was just guessing.

I asked another chemist and they told me that 11M concentration would certainly be highly suspended, whereas a 1M concentration wouldn't be, which I felt like this somewhat contracted what the Sigma rep said.

I just wanted to get some additional opinions before I use this since it is highly pyrophoric, and don't want my syringe to get clogged, or potentially waste my time with a totally inactive product. Any advice is welcome

[Edited on 18-4-2018 by Sidmadra]

Tsjerk - 18-4-2018 at 13:07

I found this;

http://www.organ.su.se/bo/Gruppfiler/BuLi%20titration.pdf

I'm afraid though that what you are seeing as a suspension is LiOH, as apparently BuLi is a liquid.

I'm not too sure about the liquid claim, but it seems hard to get a solid BuLi according to this reference;

https://sci-hub.tw/10.1021/ja00057a050

Sidmadra - 18-4-2018 at 13:14

I'm not sure how water could get in there in the first place. The bottle has been perfectly sealed, stored, and undisturbed since it's purchase, shipped directly from Sigma. Rubber seal never pierced, and the additional top-cap that goes over that remaining on.

I found this on wikipedia:
Quote:
n-BuLi exists as a cluster both in the solid state and in a solution. The tendency to aggregate is common for organolithium compounds


The solid that's in the solution is not at all crystalline, and it does seem somewhat like an aggregate, though I've never dealt with this before. Very tiny nanoparticles that stay suspended for a short while when agitated. If it were all (or at all) LiOH I would be surprised, given the sheer amount of it.

Edit:

I found this:
http://orgsyn.org/demo.aspx?prep=cv7p0121

It references a 90% butyllithium solution as a "A suspension of 90% butyllithium in hexane".

Additionally, on Sigma's datasheet, they state the appearance of this 11M solution is "Clear to Hazy"


Maybe I'm worrying over nothing. There's no reason the product should be degraded given it hasn't been used, and there does seem to be indication it is a suspension, though I would hope to hear from someone who has worked with it before.

[Edited on 18-4-2018 by Sidmadra]

Tsjerk - 18-4-2018 at 13:28

That is good to hear, and quite easy to test wouldn't it? I hope it is a reversible aggregate as much as you do.

Can't you take a bit and dilute it in hexane? If it is as fine as you describe it, there should be the least risk of clogging the syringe.

BromicAcid - 18-4-2018 at 17:13

Yes, BuLi is a liquid at room temperature, what you are seeing is LiH, BuLi undergoes a elimination reaction. The more concentrated it is, the faster the reaction. That is why it is always stored in a refrigerator or freezer. 11M being cloudy is nothing abnormal though, stuff is nasty to work with though. Unlike the lower concentrations is usually crusts over but disturb that crust and it will burn merrily. I had some oxide plug the needle during a pressure transfer at one point, what a pain.

Look at the chart on page 10 of the following link to see how fast the decomp takes place:

http://www.fmclithium.com/portals/fmclithium/content/docs/do...

Dr.Bob - 18-4-2018 at 17:30

I have not used it that concentrated, but I have used higher than 1M and even it becomes cloudy over time. If you really are doing something critical, you can titrate it, but I would likely just let the solids settle, syringe off the liquid, carefully, and use it as is, perhaps assuming it is only 10M, run a test reaction, and see if it goes to completion. It is pretty common in some reactions to use an excess anyway, but some chemistry does not like excess base, so testing it is always a good idea.

And while working with BuLi, make sure to wear non-synthetic clothing, unless it is nomex, and wear a cotton lab coat. If your syringe leaks or something catches fire, you don't want to have your clothes melt onto your skin. I have seen a few lab fires (not started by myself), and plastic melts and burns in a horrible manner. 1M is not too bad, but the concentrated stuff is vicious, much like tBuLi, LAH, and KH. Good luck.

Sidmadra - 18-4-2018 at 17:35

Quote: Originally posted by BromicAcid  
Yes, BuLi is a liquid at room temperature, what you are seeing is LiH, BuLi undergoes a elimination reaction. The more concentrated it is, the faster the reaction. That is why it is always stored in a refrigerator or freezer. 11M being cloudy is nothing abnormal though, stuff is nasty to work with though. Unlike the lower concentrations is usually crusts over but disturb that crust and it will burn merrily. I had some oxide plug the needle during a pressure transfer at one point, what a pain.

Look at the chart on page 10 of the following link to see how fast the decomp takes place:

http://www.fmclithium.com/portals/fmclithium/content/docs/do...


Interesting. Lithium Hydride would interfere with my reaction, and I'm not trying to deal with that anyways, so I should probably let the bottle settle before using it.

I had this bottle stored at room temperature, so if I'm reading that chart accurately, the potency would drop about 2% every 60 days, or 1% a month.

So if I had it unused for 12 months, I wonder if it would be safe to assume it's at 88% of it's original potency. So instead of an 11M solution, I could treat it like 9.66 M (11*0.88)? Roughly estimating of course.

zed - 24-4-2018 at 15:47

Just read about it. Scary stuff. You probably already know the horror story. But, for the sake of those that underestimate lab dangers, I'll attach it.

In the real world, a fancy chemistry degree, doesn't mean much. It is kind of like a driver's learners permit. Only experience and the wise advice of other chemists, can help to protect you from mishap. In this case, probably uninformed supervisors were instructing uninformed employees, and the result was disaster.

https://www.youtube.com/watch?v=MS6XaKhzV3Q


This second entry is a little off topic, but an extension of the former. Practical boots on the ground people, are sometimes being supervised by "Academics", that may be unfamiliar with real life perils.

https://www.youtube.com/watch?v=sjDdl_d8br8
https://www.youtube.com/watch?v=OzG6xNzyj8k

Side note: A quick talk with the guys in Energetic Materials, might have saved some fingers.

Who uses a Mortise and Pestle, on explosive materials? That's not clever.




[Edited on 25-4-2018 by zed]

Rogueasset - 30-4-2018 at 15:15

I have used 10M for a scale up, best to titrate with the diphenylacetic acid prep or the menthol prep first to calculate your true Molarity or your reaction will be at risk of failure. Make sure your titration vessel is vacuumed and purged with inert gas before titration and titrate it a second time to be sure.

This stuff is dangerous, the seal caught fire just taking the needle out when I used it, so make sure there are no solvent fumes or a fire risks or oxidising agents nearby and make sure the needle tip is not flaming or sparking when it enters the reaction solvent.

Do you really need to use this? there are easier molarities to use. I don't know you but I am concerned this will be an expensive failure with risk to human health, make sure you have appropriate fire extinguishers handy and they are in date.

zed - 2-5-2018 at 14:12

Aww. This stuff is probably pretty safe to use. Provided you use only special syringes and needles, and all of the procedures are conducted in a specially constructed enclosure/glove box, under an atmosphere of Argon gas.

It's just that, well.... Pretty much, nobody has that kind of safety equipment. It isn't standard.

The young woman that was burned to a crisp, was using an ordinary disposable plastic syringe, in an ordinary hood, without the benefit of an inert atmosphere, and she wore no useful protective clothing.

JJay - 2-5-2018 at 14:27

Eh, I think the glove box is overkill for something like that, but I could handle that with my setup, and I know my setup is not as advanced as Magpie's, Texium's, Chem Player's, Dan Vizine's, ....