[bstanley]

Hi all,

Part of my project is to synthesize an aldehyde from a nitrile. This requires the use of DIBAL-H. However, upon reading the MSDS, it says that it is ignites upon contact with air and moisture. Anhydrous solvents apparently needs to be dried further. My questions are:

1) How do I dry anhydrous solvents further? By bubbling nitrogen when I extract the solvent?
2) I'm supposed to add the DIBAL-H dropwise to my starting reagent. How do I safely transfer the DIBAL-H to the dropping funnel? Is it safe to simply close the opening on the dropping funnel (the part where I pour the DIBAL-H to) or should I bubble nitrogen to it while it is being added to my starting reagent?
3) I assume I may need to work under nitrogen. What is the common method to work under nitrogen? I heard some organic chemist used balloon of some sort. Can someone describe this "device" to me? Perhaps you know a better trick?

Thank you for all the responses. I'm an analytical chemist and not a trained synthetic chemist so, please pardon all the stupid questions. I have yet to know the tricks when dealing with dangerous synthetic chemicals.

Bob

[KritikalMass]

Personally, I think it would be safer to ask someone in charge of safety at your school, or ask someone in person rather than on an Internet forum. I am sure there are people here who can help, but still think it would be safer to get some face to face advice on this question.

[Dan]

Agreed, you should not perform this experiment unsupervised.

For DIBAL reductions I normally use the 25% in toluene solution (~1.5 M) supplied my Sigma-Aldrich. Solid DIBAL is far more dangerous in terms of spontaneous flammability, but the solutions are not too bad - that said you need to be careful.

My usual procedure is to take a properly dried flask (hot oven, or flame dried) and add the starting material and a stirrer bar. Now seal the flask with a "suba seal" (a common rubber seal for round bottom flasks).

Now I evacuate the flask by connecting it to a vacuum line fitted with a hypodermic needle (which will easily penetrate the rubber seal), and then fill the evacuated flask with an inert gas (argon or nitrogen) using a balloon filled with argon fitted with a hypodermic needle. This balloon is left in place for the duration of the reaction.

Next, I add the dry solvent using a syringe with a hypodermic needle. In my experience the solvents do not have to be incredibly dry, although THF can get quite wet, so I normally use HPLC grade dichloromethane with no additional drying. I usually use 0.2-0.5 molar excess of DIBAL to mop up any water in the system. The solution is then cooled to -78 degrees C and the DIBAL solution is added dropwise, again using a syringe with a hypodermic needle.

Always wear gloves, specs and a lab coat.

[nj_bartel]

My experience isn't with DIBAL, but with nBuLi, but I think the SOP is pretty similar.

Agree with what Dan said.  If you havea access to a schlenk line, you can make your flask somewhat more inert, and more easily.  Just insert a syringe connecting the schlenk line to your flask (or use a connector if you're using a schlenk flask), then vacuum until empty, fill with inert gas from line, repeat x3.  Follow there from what Dan said.

One thing he didn't cover was transfer of the DIBAL to the reaction flask.  If the container you have has a septum (safer), evacuate some of the air inside with vacuum (by syringe connection to schlenk), fill with inert, repeat x3.  Leaving inert gas on, insert another syringe, and draw out your solution.  Then insert to your reaction container (my experience is that dropwise addition isn't really necessary at dry ice temps, but I've also been doing deprotonations that aren't THAT energetically favorable (deprotonation of carbon connecting to only one nitrogen on imidazoles).)

If your reactant container isn't connected to a septum, you need to connect a rubber line to an inert gas source and a funnel.  Turn the inert gas on pretty high.  Position the funnel covering the reactant container as best as possible as you open it and draw out your solution.

[bstanley]

Hi Dan and Bartel,

Thank you for your replies. It makes more sense now. When I designed the set up, the thing that was missing was to suck the air inside the flask using vacuum and refill it with inert gas. Now I think I am ready to to the synthesis. I am still going to run my design by the safety officer in my school to make sure everything is good. Thank's again for all the advices.

[Juliegeng97]

Hi Dan

Does DIBAL-H have to be handled in a glove box? When you syringe it out from a bottle, what if it catches moisture and ignite?

Thank you!

Julie <3

[zsinger]

From what I have found, no hydride sources are fun to play with, and all have complications (but they are usually very effective).  Be very careful, and there are several good youtube videos regarding the lab use of hydrides with examples. .
       -Z

[Dan]

Does DIBAL-H have to be handled in a glove box? When you syringe it out from a bottle, what if it catches moisture and ignite?

No it doesn't need a glove box, but you should follow the usual inert atmosphere bench protocols. I have never had a problem with DIBAL-H solutions - occasionally I have spilled a drop while transferring the syringe from the bottle to the reaction vessel, but it is not so reactive that it spontaneously ignites.

To give you an idea, it is less aggressive than Grignard reagents.

[Juliegeng97]

Hi Zsinger

Could you provide me with some links or key words to the videos?

Thank you so much!

Julie <3

[clarkstill]

In my experience DIBAL-H and nBuLi aren't too bad to handle, and small-scale spillages are generally uneventful.  However, if you're worried about handling pyrophoric liquids I think this advice from UCLA is pretty good:

http://www.chemistry.ucla.edu/sites/default/files/safety/sop/SOP_Pyrophoric_Liquid_Reagents.pdf

It's pretty rigorous, unsurprisingly in the wake of the fatal t-BuLi fire a few years ago.