Noshtuba
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Mercury (II) cyanide with sodium borohydride
I'm trying to make sodium cyanoborohydride since it is so expensive commercially. Found this paper proposing a synthesis from mercury (II) cyanide and
borohydride (attached), instead of using chemicals like HCN which is way deadlier. However there is no detailed procedure or the amounts being used.
Also the solvent being used is THF, which only dissolves NaBH4 very slightly. Don't know if a suspension can work. Anybody knows anything about this?
Attachment: A new method for the synthesis of cyanoborane complexes.pdf (153kB)
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Justin Blaise
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THF heated to reflux probably dissolves a good amount of NaBH4. Even as a suspension, the reaction is driven by forming Hg, so it likely still will
proceed by drawing more NaBH4 into solution as the dissolved NaBH4 is consumed.
Depending on the reactions you had in mind for this reducing agent, you may consider sodium triacetoxyborohydride as a substitute. For reductive
aminations, I find it works equally well and there is no CN- waste to deal with after the reaction. It is prepared very simply by adding acetic acid
to NaBH4. Additionally, if it is too weak of a reductant for your reaction, you can add a small amount of acetic acid to crank up the reactivity.
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careysub
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This PhD thesis, "Chemistry of B1- and B10- boranes containing halogen or pseudohalogen groups", offers a useful explanation:
https://cora.ucc.ie/bitstream/handle/10468/1656/MyersM_PhD19...
"Due to the much greater solubility of Na[BH3 CN] over Na[BH4 ] in THF, the product is easily isolated from the reaction solution."
So this is a key feature, not a problem.
Also note that the classic sodium cyanoborohydride synthesis paper by Wade et al 1970 using exactly this technique: rapid stirring of a NaBH4 slurry
in THF, adding HCN in THF, then filtering the solution to remove unreacted NaBH4.
[Edited on 21-8-2016 by careysub]
Attachment: wade1970.pdf (638kB)
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