[23SigmaTropic]

Hello,

So I have a literature prep for a propargyl mesylate. The mesylate is en route to a vinyl allene and the authors use the crude mesylate to make the allene. I  made the mesylate with the intention of storing it overnight and using it first thing the next day. There was no evidence of any polymerization when I stored it (under Argon in the fridge).  When I take it out the next day and concentrate the residue, immediately after taking it off the rotovap I see a color change and before I could get it under argon the whole sample turns black. I take NMR and its all polymerized. It didn't decompose on the rotovap but as soon as a good amount of air hit it it was toast.

So I'm thinking that maybe some trace peroxide from the ether in the workup reacted with my compound and upon hitting air it was done. The decomposition was exothermic and released fumes. Has anyone ever seen something like this? There is not a lot of literature for this type of mesylate and the prep itself mentions no warning as to the stability of the compound.

My gut says peroxides from the ether were to blame in some indirect way. I have never seen a perfectly good sample be destroyed by air so quickly.

[wildfyr]

Doesn't your ether have BHT or some other stabilizing agent in it? I thought all ether these days was sold with that, which should prevent any peroxide formation from occuring for years. Could there have been a metal containment that underwent some 1 electron redox that caused radical initiation?

[discodermolide]

I would expect such a compound to be unstable.
A couple of points: use it immediately, do not concentrate it but use it directly in the next step, keep it away from moisture. keep it cold.
The fumes were probably methane sulfonic acid which no doubt assisted in the decomposition process.

[Corribus]

Plus, iodine test can easily determine whether your ether has significant peroxide in it.

[23SigmaTropic]

Plus, iodine test can easily determine whether your ether has significant peroxide in it.

I have tested the bottle used with the commercial test strips and peroxides are below the threshold of detection. I do have access to a solvent purification system so maybe it would be best to use the good ether from the still for the workup.

[discodermolide]

If the peroxide is below the detection limit, check the water content (Karl-Fischer). If that's ok then just use it.
Your problems are the molecules stability not the solvent.

[phth]

use still ether refluxed overnight, and pump thaw 3x with liquid nitrogen, or switch to dioxane which freezes at 12 ºC. oxygen is shifting the equilibrium of triplet sensitization of the π system.  This is a photochemical trick to, for example, catalyze trans to cis double bond isomerization by leaving oxygen in the flask.  The less you have in your flask the better it will be because it is a catalyst.

[discodermolide]

I still maintain that the thermal stability of this compound is the problem. Putting it under thermal  stress on the rotavap in a water bath, at RT? This is obviously not the way to go. Just use the ether solution in the next step. With that in mind a vinyl allene may also be thermally unstable.

[23SigmaTropic]

In case anyone was wondering I was able to successfully use the crude mesylate and got the vinylallene in good yield. I kept the mesylate solution under argon during workup and was very quick with the solvent swap while keeping it under inert conditions. Interestingly the TLC profile for the mesylation looked horrible, but from talking to other people doing mesylations I was convinced it was quick and quantitative, and  he mesylate was simply unstable to silica gel. I am basically flying blind with this reaction. Not sure how else to monitor the reaction.

I'm looking into different conditions for the mesylate formation such that I don't need a workup/ solvent swap to use the mesylate. What about generating the alkoxide in THF and treating that solution with MsCl? This would be ideal as my next reaction is in THF. I know it's been done but I'm not seeing very much in the literature and it seems uncommon.  If anyone has done this, I'm not sure what base to use. Ideally something with a hard lewis acid as the counter ion? BuLi?

With regards to vinylallenes, yes they are usually heat sensitive but often stable at room temp. The substitution pattern obviously plays a large role in the stability. 

[23SigmaTropic]

I still maintain that the thermal stability of this compound is the problem. Putting it under thermal  stress on the rotavap in a water bath, at RT? This is obviously not the way to go. Just use the ether solution in the next step. With that in mind a vinyl allene may also be thermally unstable.

The yield for the vinylallene was higher after doing the workup/solvent swap at 0 C, so yes. Tried using the ether solution, vinylallene reaction is extremely slow in ether.

[kriggy]

And in what solvent you want to run the reaction? Maybe you could add the allene in ehter to the other solvent and then distill the ether away by rotovap at room temperature

[MOTOBALL]

This topic raised a flag in my brain, and I checked my Ph.D. thesis (1970).

I had reacted 1,5-hexadiene-3,4-diol with xs MsCl in pyridine and usual work-up with extraction into CHCl3.  Concentration on the rotovap gave a yellow oil.

"On attempted distillation under reduced pressure (7 mm) the product decomposed explosively at ca. 120 deg. C (oil-bath temp.)."

I well remember the distillation apparatus being shattered, but do not recall if a black mess was obtained.

It looks like unsaturated C-C bonds and O-mesyl groups can be bad news.