Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: curiouscat on October 23, 2012, 04:35:45 AM
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Does one get a hydroperoxide if an aliphatic alkene is reacted with H2O2 (under some suitable conditions)? If so, can that hydroperoxide then be decomposed to give an alcohol?
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It should give an epoxide. see this paper;
http://www.erowid.org/archive/rhodium/pdf/epoxidation.bicarbonate-activated.h2o2.pdf (http://www.erowid.org/archive/rhodium/pdf/epoxidation.bicarbonate-activated.h2o2.pdf)
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It should give an epoxide. see this paper;
http://www.erowid.org/archive/rhodium/pdf/epoxidation.bicarbonate-activated.h2o2.pdf (http://www.erowid.org/archive/rhodium/pdf/epoxidation.bicarbonate-activated.h2o2.pdf)
Thanks!
Bummer because I was hoping for a cleaner alternative to alkene-to-alcohol hydration. (conventionally done by mineral acids. )
Any "easy" ways to get to the alcohol from the epoxide? Lithium aluminium hydride does it but that doesn't sound any better than using an acid in the first place. :-\
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Which alcohol do you want?
You can hydroborate then oxidise with peroxide. It gives the anti-Markovnikov addition (terminal alcohol).
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Which alcohol do you want?
You can hydroborate then oxidise with peroxide. It gives the anti-Markovnikov addition (terminal alcohol).
Won't work because I need the Markovnikov product. Wanted to make 2,4-Dimethyl-2-hexanol starting from 2,4-dimethyl-2-hexene. Needs to be something scalable beyond the lab..
PS. How much BH3 is typically used in hydroboration? Catalytic amounts or more?
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Just hydrate the double bond then.
Typically one equivalent of diborane is used
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Just hydrate the double bond then.
You mean maintain the status quo using H2SO4? It isn't the greatest option: We need large quantities of acid, slow reaction, not-too-good selectivity (including forming some cyclic products apparently; I've no clue how... ??? ). And lots of dil. acid effluent to get rid of.
Your lead was good though: I remembered Oxymercuration-Demercuration gives the Markovnikov product. Plus I avoid the Carbocation intermediate and the attendant rearrangement products.
The only hitch is handling the toxic Hg-Acetate.
Are there any "cleaner" Markovnokov addition alternatives to Oxymercuration-Demercuration? Any sugesstions?
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It should give an epoxide.
Found more stuff; apparantly in some cases it does form an hydroperoxide:
Early work on the electrophilic addition of hydrogen peroxide to alkenes was performed in the
presence of an acid catalyst, usually sulfuric acid or p-toluenesulfonic acid. The reaction proceeds
via Markovnikov-directed protonation of the double bond. Subsequent nucleophilic attack of
hydrogen peroxide on the carbocation, followed by loss of a proton, furnishes the alkyl hydroperoxide.
Since the reaction involves a carbocation, it is subject to the normal substituent effects. Hence, the addition
of hydrogen peroxide to a mixture of 3-methyl-2-hexene and 3-methyl-3-hexene yields the tertiary
alkyl hydroperoxide as the only product
Even more interesting was this bit:
Recently, it has been proposed that alkyl hydroperoxides are formed from the Co catalyzed Markovnikov
addition of hydrogen peroxide to alkenes. The alkyl hydroperoxides thus formed are immediately
decomposed into ketones and alcohols under the reaction condition
I'll dig up the primary Refs. now, maybe it is indeed possible to get the Alcohol from Alkene in one clean step: H2O2 addition.
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It should give an epoxide. see this paper;
http://www.erowid.org/archive/rhodium/pdf/epoxidation.bicarbonate-activated.h2o2.pdf (http://www.erowid.org/archive/rhodium/pdf/epoxidation.bicarbonate-activated.h2o2.pdf)
That is a different mechanism. That doesn't occur with an aliphatic alkene.
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If you want the acid catalyzed addition, but not use acid, do an oxymercuration/reduction. There is an Org Syn prep for this reaction. The alternative is acid catalyzed addition of acetic acid. Because the acetate is less basic, I believe this can be a more productive route. Obviously, you have to saponify the ester to get the alcohol.
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It should give an epoxide. see this paper;
http://www.erowid.org/archive/rhodium/pdf/epoxidation.bicarbonate-activated.h2o2.pdf (http://www.erowid.org/archive/rhodium/pdf/epoxidation.bicarbonate-activated.h2o2.pdf)
That is a different mechanism. That doesn't occur with an aliphatic alkene.
According to table 2 in the paper (J. Am. Chem. Soc. 2000, 122, 3220-3221) aliphatic alkenes react to give the epoxides in good yields but rather long conversion times.
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I did miss looking at Table 2. None the less, I don't see how the editors let this paper into JACS. This looks like a standard (buffered) Payne epoxidation reaction. What am I missing?
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According to table 2 in the paper (J. Am. Chem. Soc. 2000, 122, 3220-3221) aliphatic alkenes react to give the epoxides in good yields but rather long conversion times.
I was a bit suspicious of those "good yields": Is it typical to work at such low concentrations? e.g. 0.05 M alkene makes for a 0.6 % (w/w) solution of alkene.
Those concentrations are almost meaningless for any scale of process development. And no wonder they can get such good selectivity.
Maybe that's a generic rant against experimenters using "artificial" reaction conditions to make their yields look good.
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I did miss looking at Table 2. None the less, I don't see how the editors let this paper into JACS. This looks like a standard (buffered) Payne epoxidation reaction. What am I missing?
I don't know why the editors let this through. Maybe we should look at the supp. mat.?
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I did miss looking at Table 2. None the less, I don't see how the editors let this paper into JACS. This looks like a standard (buffered) Payne epoxidation reaction. What am I missing?
Footnote#20: "In contrast to the simplicity of the homogeneous BAP procedure, the Payne procedure requires stirring and continuous addition of peroxide and base."
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I don't know why the editors let this through. Maybe we should look at the supp. mat.?
I didn't find any.
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Just a recap, why would anyone use a peracid to make an epoxide if you could just use hydrogen peroxide? To my knowledge, that reaction doesn't work. You can use hydrogen peroxide and a carboxylic acid to make a peracid or just start with a peracid to make an epoxide. There is also a Payne epoxidation in which hydrogen peroxide is used with a nitrile to make an iminoperacid. So, my comment was, the JACS paper did not look like a new and novel way to make an epoxide. Furthermore, since JACS is noted to be very particular about the merit of their papers, I just thought at first blush, how did this make it into JACS? I didn't bother to read the paper, I should wondered how one could make an epoxide with hydrogen peroxide.
By the way, why this paper got published in JACS does nothing to answering the posters question.