Db33
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NaBH4 to Na triacetoxyborohydride
i DO have a source for sodium triacetoxyborohydride, but im interested in making it myself from the much more readily available sodium borohydride.
The only info i could find on this site is the following.
NaBH4 (0.1 mol.) was added portionwise to a solution of acetic acid (0.33 mol.) in dry benzene (1 l.), the temperature being kept at 20C. After
hydrogen evolution, the precipitate was rapidly collected by suction, washed with diethyl ether, and dried under vacuum.
First im wondering if Benzene could be substituted, if not thats fine, just curious maybe Ethyl Acetate or even Toluene. But Is it simply a matter of
adding powder NaBH4 to the acetic acid solution and then vacuum filtering and washing?
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Tsjerk
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Add the acetic acid to the borohydride, slowly. Otherwise you will get a mixture of tetra and di-acetoxyborohydrides. Usually this compound is made in
situ to avoid the whole solvent question.
Also adding 0.33 mol of acetic acid to 0.1 mol borohydride doesn't add up... Maybe they had a compound to reduce which is sensitive to over-reduction
by di-acetoxyborohydride and they used the tri/tetra mix in excess?
[Edited on 1-12-2016 by Tsjerk]
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CuReUS
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See this -http://www.sciencemadness.org/talk/viewthread.php?tid=7744&a...
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careysub
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Some references on this.
I note that these sources discuss adding NaBH4 solution to the GAA, but that thermal runaway problems exist that must be managed. They do not discuss
the reverse procedure, which sounds like it may be superior.
Attachment: lam2005.pdf (204kB)
This file has been downloaded 387 times
Attachment: SodiumTriacetoxyborohydride.pdf (184kB)
This file has been downloaded 423 times
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Dr.Bob
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I would not use ethyl acetate, but toluene would work likely. As said above, I would just make it as needed, the stuff is hydroscopic and clumps
badly. And use 3 eq, not 3.3, I agree with that as well. Just put the NaBH4 in the solvent of the final reaction, then add the acetic acid slowly,
let that stir a while, then add your substrate to reduce or add it to the substrate.
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