Hilski
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Olefin epoxidation
I recently read a paper on an Olefin epoxidation procedure which used only sodium hypochlorite and KBr in either tert-Butanol or acetonitrile and pH
buffered water. I plan on trying this mostly out of curiosity to see if it really works, because it seems so easy. I was just wondering if anyone
else here may have tried this particular procedure with any success, and whether any other solvents might work other than acetonitrile or
tert-butanol.
Here is the paper I am referring to:
http://www.sciencemadness.org/talk/viewthread.php?action=att...
Thanks
\"They that can give up essential liberty
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deserve neither liberty nor safety. \"
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chemrox
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I haven't found an application for the resultant epoxide so it's in storage but it looks promising- I might try it after I get my IR up and running.
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smuv
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this article may interest you.
If you plan on using the epoxide as an intermediate to form a carbonyl compound, it may behoove you to consider hydrolyzing the chlorohydrin to form
the corresponding diol.
"The styrene glycol was prepared by hydrolyzing styrene chlorohydrin with boiling aqueous sodium bicarbonate. After distillation, the crude product
was crystallized from benzene."
--Journal of the American Chemical Society, 67, 518-20; 1945
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Hilski
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Quote: | Originally posted by smuv
this article may interest you.
If you plan on using the epoxide as an intermediate to form a carbonyl compound, it may behoove you to consider hydrolyzing the chlorohydrin to form
the corresponding diol.
"The styrene glycol was prepared by hydrolyzing styrene chlorohydrin with boiling aqueous sodium bicarbonate. After distillation, the crude product
was crystallized from benzene."
--Journal of the American Chemical Society, 67, 518-20; 1945 |
Thanks for the link. I'm not after carbonyl compounds at this point, but I appreciate the tip anyway.
Your article lists aqueous acetone as the solvent of choice as opposed to acetonitrile for chlorohydrin production when using TCCA, But when using
TCCA instead of NaOCl and KBr, the procedure becomes a two step process requiring a later reaction with KOH in EtO2 and pentane to produce the
epoxide.
The other article I linked to in my earlier posts is a one pot procedure, going from the alkene to the epoxide in one step. I wonder if the
difference is mostly because the authors were using TCCA instead of NaOCl/KBr, or because of the different solvents that were used.
It would be nice if the aqueous acetone (1:5) would also work for the one pot procedure.
Thanks again.
[Edited on 18-9-2007 by Hilski]
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smuv
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Aqueous acetone would not work for the procedure you cited, as acetone would eat up all of the hypobromite (produced in situ from KBr and NaOCl)
forming predominantly bromoform.
In the procedure I outlined, the likely reason why the chlorohydrin was extracted before being converted to the epoxide was because under basic
conditions the acetone would react with any remaining hypochlorite.
P.S. I think there are easier ways to obtain an epoxide from a chlorohydrin than the weird 3 solvent biphasic system outlined in the Brazilian journal
article. It may be worthwhile to look up the (older) industrial processes of synthesizing ethylene oxide, from ethylene chlorohydrin (produced of
course from ethylene) as i suspect that most chlorohydrins will react as ethylene chlorohydrin does (in terms of forming an epoxide). For a good
overview of chlorohydrin and epoxide chemistry "Ethylene and its industrial derivatives" by Miller is a good source (although it deals with ethylene
oxide/chlorohydrin I think its worth a look)
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Ozone
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I thought this was *really* cool:
http://pubs.acs.org/cen/news/85/i36/8536notw1.html
Perhaps this is something you could try with your epoxides (I'd try maybe, omega 3's).
I have not tried your procedure, but hav ealways had good results with perbenzoic acid.
Cheers,
O3
[Edited on 16-10-2007 by Ozone]
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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Hilski
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Quote: | It may be worthwhile to look up the (older) industrial processes of synthesizing ethylene oxide, from ethylene chlorohydrin (produced of course from
ethylene) as i suspect that most chlorohydrins will react as ethylene chlorohydrin does (in terms of forming an epoxide). |
From all the patents and papers I have read regarding ethylene and propylene chlorohydrins it seems that an aqueous base (usually Ca(OH)2 or NaOH) and
an inert, water-immiscible organic solvent is all that is required for saponification of the chlorohydrin to the epoxide.
So basically, CaO in water (not sure what %) and Hexane with stirring and a little heat should do the trick, should it not?
Edit***Changed Xylene to hexane, which I intended to write to begin with. I'm not sure why I wrote Xylene anyway, because I never use it for
anything. Oh well.
[Edited on 20-9-2007 by Hilski]
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roamingnome
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@smuv im not saying your pointers arent valid...
but as i try to isolate the chlorohydrins from the TCCA acetone procedure i ponder confusion.
hypochlous acid results from lowering the pH of bleach or OCL- ion
in water/acetone 1:5, hypochlorous acid(HCLO) from TCCA breakdown is the agent that reacts with the double bond
so im not sure if hilski was getting at this, but if using bleach and KBr then lowering the pH to 4ish to form HCLO in acetone one could isolate
bromohydrin?
i dont know of adding KBr to TCCA would form bromohydrin
what im getting out is that isolating bromohydrins from these procedures could be more useful to someone then following threw to the epoxides.
bromohydrins might react better in radical promoted substitutions with a nucleophile then chlorohydrins or epoxides
either way i cant find any information about halohydrin radical reactions
it would seem that the halogen would pop right off under the proper wavelength making way for additions of your suiting.
[Edited on 16-10-2007 by roamingnome]
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smuv
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Quote: | so im not sure if hilski was getting at this, but if using bleach and KBr then lowering the pH to 4ish to form HCLO in acetone one could isolate
bromohydrin?
i dont know of adding KBr to TCCA would form bromohydrin |
This is actually a dangerous game. In the procedure you described, there would likely be quite a bit of Br2 in solution, which would of course
readily react with the alkene substrate.
Assuming you overcome this hurdle (I beleive in industry with chlorine it was overcome by blowing air through the solution) next you have the problem
of hydrogen halides in solution as: Br2 + H2O --> HBr + HOBr. In this case HBr in solution could add to the alkene, which would be undesirable.
This hurdle can be overcome by adding a weak base to neutralize the HBr but be sufficiently weak to allow its salts with hypobromous to be mostly
hydrolyzed.
If this is overcome the dichloroalkane is still produced even in the absence of free halogen, because the carbonium intermediate of the reaction may
react with some x- (x = halogen) in solution instead of the OH- from the hypohalous acid.
Even greater problems arise if an organic phase separates from the aqueous, but I will stop here as I think my point has been made: The procedures
with TCCA are very efficient. Industrially for even a simple Chlorohydrin such as ethylene chlorohydrin (produced by the methods described) yields
are usually bellow 85%.
Also I think it is not a big deal, although in reality I have done no experimenting with chlorohydrins (I eagerly want to in the future, I think they
are a very versatile intermediate) from literature they seem reactive enough.
Note: A lot of this information was gleaned from Ethylene and its industrial Derivs. by miller
[Edit] About attempting this procedure with tcca and KBr in the water/acetone system, I think you would get some bromohydrin but I think mostly
chlorohydrins would be produced. I think allowing everything to come to equilibrium before adding the substrate in attempt to produce more HOBr would
reintroduce many of the problems outlined above. But then again its not like I'm a chemist.
[Edited on 15-10-2007 by smuv]
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roamingnome
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its looking like there is a gazillion different ways to form an epoxide these days...
but the more elegant of the bunch is
United States Patent 4560451
http://www.google.com/patents?id=rKEvAAAAEBAJ&printsec=a...
Abstract: Alkene oxide can be made in a simple, closed process that uses electrolysis to make bromine and hydroxide from bromide and water. The alkene
reacts with bromine and then water to form an alkene bromohydrin, which is dehydrobrominated by hydroxide, regenerating bromide, to give alkene oxide
if a clay pot was put around hydroxide forming electrode one could feasbily gather bromohydrin
%%%%%%%%%%%%%%%%%%%%%%%%%%%%
first run using 10 mls of styrene in 500mls water and 10% acetone. 41.2 grams NaBr, 7 grams NaHCO3, pH 8.4 small clay pot to divide electrodes. oh
and 5volts and probably quite a few amps....
A dark forest-green precipitate forms
possible polystyrene gel forming on anode as well..
check calculations, numbers and wiring for wrongness
another run with just water and NaBr. a small amount of NaHCO3
undivided electrodes of stainless steal mesh
the same green precipitate
bromohydrins are maybye desirable for storage issues
better then alkenes or epoxides i would think,
but i must skip directly to the dibromide after seeing it is a filterable solid
[Edited on 22-10-2007 by roamingnome]
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