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Topic: Removing Oxalyl Chloride  (Read 19169 times)

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Offline Wisemanleo

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Removing Oxalyl Chloride
« on: July 26, 2007, 08:49:57 PM »
I have on several occasions used oxalyl chloride to halogenate a hydroxy-amino species, but I have never been able to properly remove excess oxalyl chloride. I have tried using a vacuum pump, only to leave residue in my manifold. I have tried using a base trap, but it's not very effective at neutralizing the vapor evolved. I have tried using the pump on the rotary evaporator, only to damage the pump completely. Finally, I've tried using the water aspirator on the rotary evaporator, only to find a large amount of smokey-vapors collecting in the collecting bulb.

Does anyone know the proper and sure-fire way of removing excess oxalyl chloride?

Any help would be much appreciated!!
Scientia est potentia.

Offline kiwi

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Re: Removing Oxalyl Chloride
« Reply #1 on: July 27, 2007, 08:20:33 AM »
besides some sort of quench?

Offline Wisemanleo

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Re: Removing Oxalyl Chloride
« Reply #2 on: July 27, 2007, 11:40:16 AM »
I can't use any aqueous quenching methods in my reaction or I'll just be reverting my compound back to its starting material. I've used a stirring base trap, but it's not very effective as I still see vapours coming out the other end.
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Offline movies

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Re: Removing Oxalyl Chloride
« Reply #3 on: July 27, 2007, 12:30:34 PM »
I've never had trouble rotovaping off excess oxalyl chloride.  If you are sure to have an efficient, dry ice cooled condenser, it should be fine.

Other than that, you might be able to set up a trap between you reaction and your vacuum pump that would draw the vapors over some high molecular weight primary amine before it they get to the pump.

Offline Wisemanleo

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Re: Removing Oxalyl Chloride
« Reply #4 on: July 27, 2007, 02:21:26 PM »
Our condenser is just water cooled, so maybe that's the problem...

The compound that I'm trying to form is N-p-Toluenesulfonylchloroglycine ethyl ester (J. Am. Chem. Soc. 2001, 123, 10853-10859). I'm starting to have doubts over the prep, because I have done the reaction several times with newly-purchased reagents. I do end up with the expected yellowish compound, but when I run a H-NMR, all I observe is starting materials. It's frustrating  >:(
Scientia est potentia.

Offline kiwi

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Re: Removing Oxalyl Chloride
« Reply #5 on: July 27, 2007, 08:11:31 PM »
from casting an eye over the prep, i'd blame the ethyl glyoxylate. It goes off relatively readily, forming oligomers. i would have thought the reaction conditions would crack the oligomers open, but that might not be the case. It is very easy to prepare fresh stuff in ~2hrs, by sodium periodate cleavage of dirt cheap diethyl tartarate.

Offline Wisemanleo

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Re: Removing Oxalyl Chloride
« Reply #6 on: July 27, 2007, 08:56:46 PM »
Can't you also just heat up the solution of ethyl glyxolate to depolymerise?
Scientia est potentia.

Offline kiwi

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Re: Removing Oxalyl Chloride
« Reply #7 on: July 28, 2007, 01:32:02 AM »
yeah apparently - thats why i thought it should depolymerise under the reaction conditions (PhMe, reflux o/n). But when ever i've needed it (admittedly only 2-3 times) i've made it. not sure whether thats the problem in your situation, but it does look like the weakest link. I assume by "starting material" you mean you recover tosyl amide? have you checked the intermediate hydroxyglycine compound is in fact forming? this might help narrow down where the problem is, and you might be able to check out alternative chlorination conditions if they're to blame

Offline Wisemanleo

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Re: Removing Oxalyl Chloride
« Reply #8 on: July 28, 2007, 07:44:47 AM »
Oh yeah, the hydroxygleucine forms beautifully. Easily isolable too, and bench stable. There's characteristic a peak at about 5.5 ppm, which corresponds to proton alpha to the amine group. When you replace the hydroxy group with a chlorine, it is supposed to shift down to about 6ppm (as Hafez reports).

I have just made it again last night, and man does the reaction stink. I suspect I made the product, because the fumes the solid product release is very acidic, so it must be releasing HCl gas. I wonder if the chlorine is really eliminating to give the imine...?

Otherwise I really don't know, I wish I could say its my technique, but I have done this so many times, and used oxalyl chloride in different levels of excess, that I can't understand the reason it's not going (or maybe it is going, but quickly reverts back, even under N2 venting).
Scientia est potentia.

Offline kiwi

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Re: Removing Oxalyl Chloride
« Reply #9 on: July 28, 2007, 07:38:37 PM »
have you tried thionyl chloride instead? that paper seems to use it for some examples

Offline Wisemanleo

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Re: Removing Oxalyl Chloride
« Reply #10 on: July 29, 2007, 12:02:26 AM »
Haha, I have used thionyl chloride for chlorination of diphenyl acetic acid, and did I ever hated that prep! Thionyl's stinkier, more work to quench, and eats through a supply of septa faster than a French retreat. However, it does do the job...so might be worth the try. I have an extra-old bottle, so perhaps the HCl that's floating about can help to better stabilize my final compound?
Scientia est potentia.

Offline kiwi

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Re: Removing Oxalyl Chloride
« Reply #11 on: July 29, 2007, 04:56:02 AM »
yeah i'm an oxalyl chloride/DMF man myself (for forming acyl chlorides), but you gotta do what you gotta do.

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