[dimidola]

Hi!

I used sodium cyanoborohydride for the reduction of an aldehyde in the presence of NH3 and NH4OAc.
I am very worried for the side products, as NaCNBH3 can produce HCN.
The paper I followed states you can vac off the solvent (ethanol) and add water to the solid residue to retrieve product.
If I already have produced HCN, it will go into my vac trap, right? How do I get rid of it then? Sodium hypochlorite is the only solution I can use? Is it safe to keep it in a sealed container until waste pickup?
Is it safe to add water in the residue? If there is still unreacted NaCNBH3 there, will it produce HCN?
I do not understand the mechanism of this reaction, but I hope that the 100mg of NaCNBH3 won't cause issues.
Thanks.

[discodermolide]

Hi!

I used sodium cyanoborohydride for the reduction of an aldehyde in the presence of NH3 and NH4OAc.
I am very worried for the side products, as NaCNBH3 can produce HCN.
The paper I followed states you can vac off the solvent (ethanol) and add water to the solid residue to retrieve product.
If I already have produced HCN, it will go into my vac trap, right? How do I get rid of it then? Sodium hypochlorite is the only solution I can use? Is it safe to keep it in a sealed container until waste pickup?
Is it safe to add water in the residue? If there is still unreacted NaCNBH3 there, will it produce HCN?
I do not understand the mechanism of this reaction, but I hope that the 100mg of NaCNBH3 won't cause issues.
Thanks.

I doubt that 100mg will be a problem, even if it's all converted to HCN, Wikipedia gives a value for the toxic dose for inhalation of 2000 parts per million hydrogen cyanide causing death within one minute.

[Honclbrif]

I don't want to bust on you or make you feel bad, but you should have thought of this before performing your reaction so you wouldn't be left holding a flask of potentially hazardous material. This goes for everyone: for your own safety and the safety of others, please consider and research potential hazards before performing reactions.

Getting back on topic: if you add a healthy amount of  1N KOH to your waste you'll make it basically impossible for HCN to form. Furthermore, as Disco said, 100 mg of this material probably won't cause any huge problems. Be sure to mark all waste as containing cyanide before disposal and if you are still worried, talk to your environmental health and safety people.

Finally, as long as you don't have any other functional groups in your molecule which react with it, regular sodium borohydride should do the same reaction just as well without any cyanide hazard. The only reason cyanoborohydride gets used is that it is selective for immines over carbonyls.

[dimidola]

I don't want to bust on you or make you feel bad, but you should have thought of this before performing your reaction so you wouldn't be left holding a flask of potentially hazardous material.

Well, reading the MSDS where it says 'toxic' and 'irritant', you are not thinking 'deadly'.

If you add a healthy amount of  1N KOH to your waste you'll make it basically impossible for HCN to form.

Thanks, that was my guess too.

[DrCMS]

I don't want to bust on you or make you feel bad, but you should have thought of this before performing your reaction so you wouldn't be left holding a flask of potentially hazardous material.

Well, reading the MSDS where it says 'toxic' and 'irritant', you are not thinking 'deadly'.

So what did you think TOXIC meant?!? 

No MSDS uses words like 'deadly' they use 'toxic' and an LD50 etc. deadly only depends on the dose.  NaCl or water can kill you if you injest enough of them.

I think you need to spend some more time learning about things and how to carry out reactions and work ups safely before you do anything else in the lab.

[Dan]

Well, reading the MSDS where it says 'toxic' and 'irritant', you are not thinking 'deadly'.

Sodium cyanoborohyride is an R26/27/28 and R32 (among others).

These COSHH phrases translate as very toxic by inhalation, contact or ingestion, and contact with acid liberates very toxic gas. If you had undertaken an adequate risk assessment, you would have been thinking "deadly". R26/27/28 is pretty much the most severe risk statement a reagent can have.

This is exactly the kind of attitude that causes accidents.

OK, 100 mg of cycanoborohydride is not going to kill anyone, but if you don't assess the risks on small scale the habit will extent to larger, dangerous scales.

[Mobius1988]

Im assuming this is a reductive amination and you are actually trying to reduce the imine formed from the amine reagent.

Therefore, would it not be possible to use Sodium TriacetoxyBorohydride instead of the cyano version? I believe this has the same selectivity for imines over carbonyls and avoids this issue completely.

Someone please correct me if I am wrong.