Last week, I received an email from “the Man” saying that our funding was about to run out. His remedy was to rack it up and buy whatever we needed (bottom dollar wherever possible) to survive the next year. The total bill came out to ~$3K (reagents, synthons, silica, etc.). The best part was that it was all approved. Well, I’ll make this logical leap of faith because the reagents have started rolling in, and I haven’t received any warning messages from the purchasing office.
Anywho, I needed a bottle of nBuLi because all 6 of ours (buried at the back of our freezer) are crap. This is evidenced by the fact that when I get into the 5th step of my synthesis (LDA, TMS-Cl), the rather volatile starting material dies on workup (please don’t ask me to elaborate on “dies.” It just does). I suspected poor lab practices the first time this happened, but the 2nd and 3rd times, I started becoming skeptical of the nBuLi (which has a healthy, pale yellow sediment at the bottom and a ginormous hole in the septum). In my defense, “the Man” said it was okay to use nBuLi if there was sediment in the bottle as long as it was titrated before use.
Since “the checkbook was open” I figured I’d buy 2 bottles of nBuLi. Alfa-Aesar offered the best prices around, so I bought 2 one-mole bottles (I kid you not) of 2.2 M nBuLi in hexanes.
DHL arrived today with the nBuLi, and the bottles do not have septa! Has anyone else had this experience? I asked our departmental organometallic guru about how to tame this beast. His suggestion was to blanket the headspace with argon before resealing the bottle. Apparently, he knew someone in grad school that had to do the same thing with a bottle of tBuLi using nitrogen instead (goodness that sounds dangerous).
I’ll let you know how it turns out.
Update: This reaction normally gets ~85% yield using the Sigma-Aldrich nBuLi (with a new bottle); switching to Alfa-Aesar gave me a 7% yield increase! The nBuLi was a beautiful, golden yellow compared to the cloudy pale yellow crap I’d been using before; let’s assume that Alfa-Aesar’s product is a bit better than the alternative.
It turns out that when you peel away the sticker, (TADA!) there is no septum. I ended up blanketing the headspace with argon and cramming a 24/40 septum in the neck of the bottle, flipped the septum down (to make a seal) then went around the rim of the septum with Teflon tape. Finally, I tightened the seal with a braid of copper wire. After 18 h in the freezer, there is no sediment formation (definitely a good sign). I wish I could upload a picture of my “modern marvel,” but you’ll just have to visualize it mentally.
Thanks for all of your feedback!
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8 comments:
Haha. Yep. That is a pretty standard rookie move.
They expect you to acquire a makeshift septum. You could possibly also empty out one of your spent BuLi bottles and press on a sure-seal cap*, provided you can find someone that stocks those devices for sealing them on.
Word of warning - if you do go this route, try practicing on some empty bottles first, the untrained hand can find itself snapping off the lip of a bottle.
http://orgprepdaily.wordpress.com/2007/05/21/on-air-sensitive-reagents-and-anhydrous-solvent-storage/
See comment 33!!
Thanks for the heads up! I'll be sure to do that.
Do you have schlenk-ware. I've stored such compounds in a Schlenk vial under Ar. It worked pretty good.
Come on this is simple. Aldrich Sure-leaks have to be replaced after a couple penetrations with large canulas so did routinely (harder because not screw cap). As suggested establish a good blanket of Ar (N2 OK but Ar better) take off cap and replace with Septum (presume can find correct size) either for immediate or longer term use (can use two septa with 2nd larger upside down over the first). Change Septa about once a month because can degrade if used extensively. Yes can do with tBuLi just have to be quick.
On larger scales these reagents come in cylinders (like propane tanks) that connect up and use pressure to push out. Scary at first because so much material but is actually much safer that syringe/canula transfer.
CMC guy
The cloudy precipitate in the Aldrich nBuLi is actually LiH.
Also, never trust the purity or anhydrousness of any reagen purchased from Aldrich.
Doing chemistry in Australia all our lithium reagents come by ship so it's a pain waiting for them. Hence we buy in bulk, and it's cheaper to get big bottles. But if you keep changing the septum eventually the BuLi goes off. Solution? We take the fresh stocks and immediately divide the large volume stuff into smaller containers (like these storage bottles from Aldrich: http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALDRICH/Z148008). That way you're always working from a small bottle of fresh BuLi.
That's a really good idea! Perhaps I'll do that with the next batch
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