Sciencemadness Discussion Board

NaBH4/H4BK

Dimitri - 4-4-2008 at 04:55

Looking at the two they seem to have the same uses, the only trouble I have is whether the potassium borohydride is able to be converted into Potassium Triacetoxyborohydride following the same procedure used for the NaBH4?

I am basically after NaBH4 to convert into triacetoxyborohydride but am unable to get it, but am able to get Potassium Borohydride.

Any info on this would be much appreciated..

Klute - 4-4-2008 at 09:18

You would need to check the respective solubilities. IIRC, triacetoxyborohydride forms a thick suspenion/gel when made from NaBH4, as described by Grind in the recent triacetoxyborohydride thread. So if the k salt is even less soluble, you might need to take appropriate precautions to avoid excessive precipitation.
Otherwise, i think the reactivity of the two are rather similar, more so than the Li salt.

jon - 4-4-2008 at 12:47

kbh4 is easier to explain too it's used in water treatment.

grind - 4-4-2008 at 16:25

Quote:
Originally posted by Klute
You would need to check the respective solubilities. IIRC, triacetoxyborohydride forms a thick suspenion/gel when made from NaBH4, as described by Grind in the recent triacetoxyborohydride thread. So if the k salt is even less soluble, you might need to take appropriate precautions to avoid excessive precipitation.

I think NaBH(AcO)3 is nearly insoluble in toluene. KBH4 is generally less soluble in organic solvents than NaBH4. So I guess KBH(AcO)3 is completely insoluble in toluene.
An excessive precipitation is not avoidable, at least in toluene. But that is no problem cause the reaction occurs even heterogeneously with high yields.
KBH(AcO)3 is probably slightly less reactive compared with NaBH(AcO)3 and longer reaction times may be necessary.

Dimitri - 7-4-2008 at 00:59

Anyone heard of K borohydride being used in reductive amination? The other option is for me to make Sodium Borohydride as sodium hydride is availble to me. Its just making the Trimethyl borate to react with it.

[Edited on 7-4-2008 by Dimitri]

grind - 7-4-2008 at 16:49

Quote:
Originally posted by Dimitri
Anyone heard of K borohydride being used in reductive amination?

Never heard but it should be possible. You can reduce a preformed imine with KBH4.
For reductive amination KBH(AcO)3 will be better. One can expect that all potassium borohydride compounds (KBH4, KBH3CN, KBH(AcO)3) are less soluble in organic solvents than the comparable NaBH4 compounds.

Klute - 7-4-2008 at 21:27

Couldn't you possibly form TBA.BH4 (tetrabutylammonium borohydride) or even LiBH4 by metathesis? The TBA.BH4 is very soluble in DCM and other chlorinated solvants IIRC, you would need to find a solvant in which KBH4 is soluble enough to be able to perform the metathesis though. I'm not sure if the LiBH4 could done as easily though...

grind - 19-4-2008 at 15:07

http://www.rohmhaas.com/assets/attachments/business/process_...

Good review concerning sodium borohydride. The table (site 4) gives a comparison with KBH4 (and AcOH).

Klute - 20-4-2008 at 10:48

Apparently, LiBH4, very soluble in ethers, can easily be made from KBH4 and LiCl by metathesis according to this article.

solo - 10-1-2009 at 09:23

Direct and indirect reductive amination of aldehydes and ketones with solid acid-activated sodium borohydride under solvent-free conditions
Byung Tae Cho, Sang Kyu Kang
Tetrahedron Volume 61, Issue 24, 13 June 2005, Pages 5725-5734






Abstract
A simple and convenient procedure for reductive amination of aldehydes and ketones using sodium borohydride activated by boric acid, p-toluenesulfonic acid monohydrate or benzoic acid as reducing agent under solvent-free conditions is described.



[Edited on 10-1-2009 by solo]

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