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Topic: Allylic oxidation using selenium dioxide  (Read 6367 times)

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Offline digchick21

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Allylic oxidation using selenium dioxide
« on: September 12, 2012, 04:40:25 AM »
Hi, i was hoping i could get some assistance on a reaction that i am doing at the moment. I would upload a schematic of it, but i'm having  trouble attaching documents.

Anyway, i am using selenium dioxide in catalytic amounts, along with salicylic acid, tBuOOH(TBHP) 70% Water, Dichloromethane for an allylic oxidation of a C-H bond to a C-OH.

When i perform this reaction i get a messy mixture of products, mainly with a mixture of C-OH and C=O amongst others, which results in a low yield. Ideally, i would like to have as much of C=O as possible, so i've come up with a few ideas and i was wondering what your thoughts were on this.

After doing some reading, i found that it is the amount of selenium dioxide and the reaction time that determines the ratio of alcohol to aldehyde, with shorter reaction  times resulting in alcohol and longer reaction times resulting in the aldehyde.

Most of the reactions i see, usually use 0.5 eq of selenium dioxide but varying equivalents of TBHP ranging from 1-2.5 eq in either water or decane. Another question is also what is the benefit to using more equivalents of TBHP and in different media?

So i was thinking if i am going to go for mostly C=O then i would require a more forceful reaction, with greater equivalents of Selenium dioxide and TBHP than i am already using. If i was going to go for mainly C-OH then i could go for similar conditions but shorter reaction times, or stick with the catalytic amounts and go for shorter reaction times.

Also why do you need an acid present when working with catalytic amounts of salicylic acid??

I realise that there is a lot here, and i would appreciate any help available.

Offline Doc Oc

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Re: Allylic oxidation using selenium dioxide
« Reply #1 on: September 12, 2012, 09:35:58 AM »
I don't like this oxidation at all, as I've had similar experience with it as you.  Very messy, very finicky, and the selenium is very toxic.  It's a trifecta of bad.  Sorry I don't have any advice on how to improve it.

Offline digchick21

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Re: Allylic oxidation using selenium dioxide
« Reply #2 on: September 13, 2012, 11:04:09 AM »
When you did you reaction, what was your work-up. Did you quench the reaction or go straight to extraction, or do something else?

Offline digchick21

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Re: Allylic oxidation using selenium dioxide
« Reply #3 on: September 14, 2012, 07:13:16 AM »
Well next week, i will try again, and let you know how it goes. Got to show this reaction who's boss LOL

Offline Doc Oc

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Re: Allylic oxidation using selenium dioxide
« Reply #4 on: September 14, 2012, 07:49:59 AM »
I don't know that I ever worked it up.  The NMRs were such a mess that I think I just tossed everything.

Offline digchick21

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Re: Allylic oxidation using selenium dioxide
« Reply #5 on: September 20, 2012, 06:33:02 AM »
Ok, so its not going as well as i hoped. What reaction did you use instead?

Offline OC pro

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Re: Allylic oxidation using selenium dioxide
« Reply #6 on: September 20, 2012, 07:12:47 AM »
For allylic oxidations I typically had good results (50-70% yield) using this procedure: J. Org. Chem. 1987, p. 5048.
It is important to use the tert-butylhydroperoxide in decane solution!

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