Protium
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Oxymercuration co-solvent ???
I had performed an oxymercuration/demercuration of 1-hexene.
The Hg(OAc)2 was dissolved in H2O. I had used THF as the co-solvent which with strong stirring brought the 1-hexene, THF, and H20 into a single phase.
Is it possible to use another co-solvent such as an alcohol or DMSO?
Does THF - being an ether - play a part in the reaction mechanism OR does it merely act to bring such insoluble alkenes into solution with aqueous
phase?
It just depends on how you look at it...
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Sergei_Eisenstein
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Oxymercuration
Oxymercuration proceeds with the formation of an intermediary mercurinium ion. To obtain an alcohol, water is used as a nucleophile and an hydroxy
will be inserted at the carbon that forms the most stable carbocation (follows Markovnikov so to say). Addition of sodium borohydride will complete
the demercuration.
When choosing a solvent, you have to make sure it cannot interact with the mercurinium ion (unless that is what you want). Alcohols, for instance,
will also act as nucleophiles and will yield esters. THF is inert (it does not add to the intermediary carbocation) and a good choice as solvent.
Just to tell you: you can obtain the same end products without the use of mercury salts.
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Protium
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Is it possible to use HgCl2 for oxymercuration?
Is it possible to use aluminum amalgum or some other OTC reagent to effect the demercuration?
P.S. Sergei_Eisenstein,
What type of reaction would yield the markovnikov alcohol product without mercury salts?
It just depends on how you look at it...
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Sergei_Eisenstein
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| Quote: | | What type of reaction would yield the markovnikov alcohol product without mercury salts? |
Dilute sulfuric acid.
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bennator
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Problem is though, if you do the reaction acid-catalyzed, the carbon chain may re-arrange giving you something you don't want. So, if you know it
won't happen, go acid (a lot better/safer), but if it will, go mercury.
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Protium
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Ok. I found a reference which besides THF, describes the use of ethyl ether or even acetone as the co-solvent for the oxymercuration. Acetone is soooo
cheaper than THF.
The paper also mentions using perchloric acid to speed up the oxymercuration as Hg(ClO4)2 is of higher reactivity than Hg(OAc)2.
Organic Syntheses, Coll. Vol. 6, p.766; Vol. 53, p.94
OXYMERCURATION-REDUCTION: ALCOHOLS FROM OLEFINS: 1-METHYLCYCLOHEXANOL
I STILL WONDER IF THERE IS ANY WAY TO COMPLETE THE FINAL DEMERCURATION YIELDING THE MARKOVNIKOV ADDUCT...
It just depends on how you look at it...
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