[discodermolide]

You weigh your LiAlH₄ in the RBF with the other attachments already on the flask. You can do this under nitrogen or argon. Then you add the THF. Then you can add the proline with a spatula still maintaining a positive nitrogen pressure.

Personally I would use a mechanical stirrer, it is more efficient, especially for the work-up.
How much THF are you going to use?

[Messi]

You weigh your LiAlH₄ in the RBF with the other attachments already on the flask. You can do this under nitrogen or argon. Then you add the THF. Then you can add the proline with a spatula still maintaining a positive nitrogen pressure.

Just realized this, thanks!

How much THF are you going to use?

Probably ~60mL


If I do use a three-necked, round-bottomed flask fitted with a reflux condenser (CaCl2 drying tube), addition funnel, and a mechanical stirrer, would I simply add a septa and needle feeding in nitrogen from the schlenk line at the top of the reflux condenser?

[discodermolide]

Once your apparatus is under nitrogen or argon you can put a bubbler on the top of the condenser with a slight positive pressure of the inert gas going through it. Too much and you will evaporate the solvent.
Or you can use septa and needles if you wish. I personally don't like them especially for reflux. But it's up to you.
You will have around a 1.0molar solution of hydride, would it not be better to use the solution from Aldrich which I seem to remember is about 1.0molar in THF?
Can you be sure of your quality of LiAlH₄? Try and get an unopened tin.

[Messi]

Can you be sure of your quality of LiAlH₄? Try and get an unopened tin.

Yup, I had checked earlier today, I have an unopened tin!

In the procedure I was following on http://www.orgsyn.org/orgsyn/prep.asp?prep=cv7p0530, how come there is no mention of adding ethyl acetate to destroy excess LiAlH₄ when I am about to isolate/purify my product?

[discodermolide]

You don't need that. I think they use water? That's OK, just keep the addition slow and watch for foaming, that is keep the gas evolution as low as possible. This is why I would use a mechanical stirrer, it's more efficient. As you quench the reaction you get lots of aluminium salts and the mixture can become quite hard to stir and the magnet may not be able to cope with it.

[Messi]

Super! By the way, when it says reflux my reaction mixture... what temperature is that?

[discodermolide]

The reflux temperature of THF, the BPt. about 65°C I think.

You do have some supervision for this reaction? Read up about the properties of LiAlH₄ especially the hazards.

[Messi]

I have a tiny bit of supervision. I am running the reaction as we speak! Hope it works well! Picture of my reation below!

[orgopete]

You need to have you argon inlet on top of your condenser.

[discodermolide]

Looks OK. Still prefer a mechanical stirrer!
Good luck.

[Messi]

You need to have you argon inlet on top of your condenser.

Any reason why?

Still prefer a mechanical stirrer!

Couldn't find one

[discodermolide]

Couldn't find one
[/quote]


LOL, just make sure the magnet is always stirring.

[Messi]

LOL, just make sure the magnet is always stirring.

Yup, I put two big magnets in my RBF, and put the stirrer on a super high setting

I see what you're trying to do, and it seems feasable. However, it can be done more efficiently:

You can "protect" the amine by forming the hydrobromide salt:



Then heat it with PBr₃ to get the alkyl bromide.

Regarding this Dan, would the easiest way to do this be just to react my amine with HBr, in let's say either ether or THF as a solvent, and then without any purification just to add PBr₃ to my solution and reflux? After these reactions, I purify my amine? Won't my amine be in salt form? Having it in free-base form is a better idea if I plan on doing another reaction with this amine, no?

[orgopete]

You need to have you argon inlet on top of your condenser.

Any reason why?

I prefer to use a condenser to reflux the solvent and not the argon inlet. The set up is virtually like having a big stopper on the side of the flask. If the reaction began refluxing, the vapors will push out the argon inlet.

[Dan]

Regarding this Dan, would the easiest way to do this be just to react my amine with HBr, in let's say either ether or THF as a solvent, and then without any purification just to add PBr₃ to my solution and reflux? After these reactions, I purify my amine? Won't my amine be in salt form? Having it in free-base form is a better idea if I plan on doing another reaction with this amine, no?

Essentially yes. These procedures are published, just check the literature.

The free-base form of this compound is probably fairly unstable so I would isolate it as a salt and generate the free base for in situ in the next step.