Melgar
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Proposed sodium cyanoborohydride synthesis
First of all, I'm proposing to produce it in an ethanol solution, which would presumably be used immediately. This could probably also work in THF or
ether with modifications.
1) Put ethanol in the freezer. My roommate would normally freak out if he saw chemicals in the freezer, but practically everyone keeps vodka there.
2) Prepare stoichiometric amounts of NaBH4 and NaCN. (Probably a slight excess of NaBH4) Also prepare 50/50 mixture of ethanol and 85% phosphoric
acid.
3) Get cold ethanol out of the freezer, and add it to a flask that can be quickly sealed if needed. Dissolve the NaCN in the ethanol.
4) Carefully, with good ventilation, add the phosphoric acid to the NaCN solution dropwise. Do not let the ethanol get warm, and use an ice bath if
needed. Watch for precipitate formation, as sodium phosphate salts form, which are insoluble in ethanol. Phenolphthalein indicator might also be
helpful, since NaCN is a strong base.
5) When solution pH begins to approach neutral, remove the precipitate somehow, exposing it to air as little as possible. Once this is done, it
should then be possible to add the NaBH4 to the HCN solution.
My main concern is if there would be a problem with using ethanol, and how well the reaction would occur in this solvent. I'd imagine methanol could
be used if ethanol could, but I had an easier time finding the appropriate data for ethanol.
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unionised
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I'm fairly adventurous as a home chemist, but I draw the line at (or somewhere before ) HCN in the home.
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symboom
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There must be a way to avoid HCN production
There is a procedure using borane gas and sodium cyanide
The reagent is invariably purchased, although it can be prepared easily. One method involves combining sodium cyanide and borane.
https://en.m.wikipedia.org/wiki/Sodium_cyanoborohydride
The HCN requires high pressure.
https://erowid.org/archive/rhodium/chemistry/index.html
I know its a drug synth site but it have the pdf of synthesis of
Sodium cyanoborohydride a useful reducing agent
Looks like THF is the solvent used
You already have sodium borohydride
https://m.youtube.com/watch?v=-rJRFXI4R70
Sulfuric acid and sodium borohydride forms borane
It interesting you just add acid to the sodium borohydride instead of the sodium cyanide to form the product and work with borane gas instead
Side note borane reacts with sodium amalgam to form sodium borohydride
[Edited on 27-8-2017 by symboom]
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Melgar
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HCN in a cold ethanol solution would have a low vapor pressure, which could be eliminated just by using a tight-sealing flask. In any case, this
reaction would ideally be done outside, since HCN is lighter than air, and most people can smell it at levels far below lethal. Every HCN poisoning
I've heard of has been indoors, too, and I agree that unless quantities are extremely small, HCN should NOT be in the home. Outside, though, the
risks are greatly reduced.
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