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Topic: Sharpless Epoxidation tips?  (Read 4751 times)

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Offline zzzisoo1

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Sharpless Epoxidation tips?
« on: March 11, 2013, 06:19:22 PM »
Hi guys, I have been running SAE on methallyl alcohols and have been getting no product.
I have tried using up to 20/24 % Ti(OiPr)4 and tartrate. I tried to follow sharpless paper as closely as possible other than distillating tartrate and catalyst prior to use. I dried everything else very closely.

Ultimately, I am trying to do in situ ring opening with phenols but I would want to make sure that epoxides formed before I had phenols.

Can anyone comment on the importance of distillating tartrate and the catalyst? or any tricks in general?
 Also it's very hard to monitor the reaction. I mainly followed it by looking at the disapperance of the alkene under KMnO4 staining.

Offline Doc Oc

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Re: Sharpless Epoxidation tips?
« Reply #1 on: March 12, 2013, 08:53:12 AM »
Can you give a quick rundown of your procedure?  If I remember correctly, the temperature during the epoxidation is very important.  I had to setup an obnoxiously large chilling apparatus to keep it at -50 for several hours, then aged the solution in the freezer overnight.  I didn't distill the tartrate or the catalyst, and neither of them were particularly new.

Offline zzzisoo1

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Re: Sharpless Epoxidation tips?
« Reply #2 on: March 12, 2013, 10:46:01 AM »
Can you give a quick rundown of your procedure?  If I remember correctly, the temperature during the epoxidation is very important.  I had to setup an obnoxiously large chilling apparatus to keep it at -50 for several hours, then aged the solution in the freezer overnight.  I didn't distill the tartrate or the catalyst, and neither of them were particularly new.

Sure, thanks for the response.
I found a literature and a patent, both of which ran the reaction with this particular substrate at -20C. I used brine/dry ice batch. So I oven dried the RBF, flushed with argon. I added Toluene (dried over molecular sieves), and tartrate, catalyst, and cumene peroxide (dried over M.S. for 30 min) in that order and cooled it down to -20C. I aged the catalyst for 30 minutes and added my alcohol slowly. I kept the reaction at -20C for about 5 hours as the paper suggested. I couldn't really check my reaction progress other than staining it with KMnO4 to see the disappearance of the alkene of the alcohol.
It's good to hear that you didn't distill tartrate or catalyst but it still worked fine. So I think it comes down to temperature and dryness problem.. How dry was your reaction? did you take extra attention to it? what kind of substrate did you use?

Offline zzzisoo1

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Re: Sharpless Epoxidation tips?
« Reply #3 on: March 12, 2013, 11:18:07 AM »
Also it was noted in the literature that the addition order of peroxide and alcohol doesn't matter.
I could add alcohol or peroxide at the last step. I added alcohol later in order to keep the reaction temperature as stagnant as possible at -20C

Offline Doc Oc

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Re: Sharpless Epoxidation tips?
« Reply #4 on: March 13, 2013, 09:41:58 AM »
Couple things:

1) Like I said, I did my reaction at -50.  I don't know whether this is substrate specific or not, but I was following one of Sharpless' procedures (a JOC article or something similar, it was a long paper).  After that, I left it overnight in the freezer.
2) I used tert-butyl hydroperoxide.  I don't have experience with cumene hydroperoxide so I don't know the relative reactivities, but you may consider using that instead as well.
3) We did have a solvent drying system, and if I'm not mistaken I was using DCM, not toluene (but it's been a while so I may be off on this).

Let me go back through my notes and see if I can dig up that Sharpless paper, that will clear a lot of this up I think.

Offline Doc Oc

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Re: Sharpless Epoxidation tips?
« Reply #5 on: April 03, 2013, 09:50:37 AM »
Sorry it took me so long to get back to this.  Maybe not useful anymore, but check out this paper:

http://pubs.acs.org/doi/abs/10.1021/ja00253a032

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