Sciencemadness Discussion Board

purification of a lot of NACN

spankyetal - 21-8-2017 at 08:06

have accidentally acquired over 1 lb of NaCN. Long story. Looking to purify it through re-crystallization. Any thoughts. Have experience with this stuff so am aware of haz mat handling.

Melgar - 21-8-2017 at 22:37

It's super hygroscopic, and drying it out could be dangerous due to the metathesis with CO2 when water is present. Probably better to titrate it to determine purity and assume the remainder is sodium carbonate.

unionised - 22-8-2017 at 13:15

Quote: Originally posted by spankyetal  
... Any thoughts. ...

Don't.
If you got it accidentally then you have no use for it. Why take the risk for something that's not useful to you?

XeonTheMGPony - 22-8-2017 at 14:33

with cyanide you only screw up once!

Velzee - 22-8-2017 at 17:52

Quote: Originally posted by spankyetal  
have accidentally acquired over 1 lb of NaCN. Long story. Looking to purify it through re-crystallization. Any thoughts. Have experience with this stuff so am aware of haz mat handling.

I can take it off your hands :)

symboom - 23-8-2017 at 02:18

Put some to good use
Sodium cyanoborohydride
A medium reducing agent no one has made it here yet be the first
And you got the cyanide
it can be prepared easily. One method involves combining sodium cyanide and borane

Borane
Magnesium powder and boric acid in excess
Magnesium boride
MgB2 and hydrochloric acid forms borane gas

[Edited on 23-8-2017 by symboom]

PirateDocBrown - 23-8-2017 at 19:39

Making NaBH3CN is an excellent idea!

But if you wanna purify NaCN, turn it into HCN gas by heating with a nonvolatile acid, then condense into NaOH. Crash out with EtOH. Use really good ventilation.

Melgar - 23-8-2017 at 22:00

Quote: Originally posted by symboom  
Put some to good use
Sodium cyanoborohydride
A medium reducing agent no one has made it here yet be the first
And you got the cyanide
it can be prepared easily. One method involves combining sodium cyanide and borane

Borane
Magnesium powder and boric acid in excess
Magnesium boride
MgB2 and hydrochloric acid forms borane gas

[Edited on 23-8-2017 by symboom]

The only preparation I saw that ever made any sense was getting HCN in THF, then combining with NaBH4. I'd imagine it could be more easily made in situ by reacting stoichiometric potassium bisulfate and potassium cyanide in ethanol, in a tightly-sealed flask. (Sulfuric acid would react much, MUCH too quickly) When you need a solution of sodium cyanoborohydride, the cold HCN solution in ethanol could be added to sodium borohydride in ethanol
Quote: Originally posted by PirateDocBrown  
Making NaBH3CN is an excellent idea!

But if you wanna purify NaCN, turn it into HCN gas by heating with a nonvolatile acid, then condense into NaOH. Crash out with EtOH. Use really good ventilation.

Good lord, that is one terrible idea after another! If you'd done a few minutes of research, you would have realized that sodium cyanide is soluble in ethanol! Actually, the fact that you're wrong is a good thing, because it means he can just use methanol or ethanol to dissolve the cyanide and recrystallize it, rather than potentially turn his entire block into a gas chamber. Those fume hoods have to send their exhaust somewhere, you know. Since the main impurity in old alkali cyanides is their carbonate salts, everything would be quite straightforward, as long as water is very strictly excluded from recrystallization.

[Edited on 8/24/17 by Melgar]

Dan Vizine - 24-8-2017 at 05:17

Melgar has it EXACTLY right....."It's super hygroscopic, and drying it out could be dangerous due to the metathesis with CO2 when water is present. Probably better to titrate it to determine purity and assume the remainder is sodium carbonate."

In synthesis work, if possible, NaCN or KCN are used in 5 to 10% excess to account for cyanide's facile transformation into junk.

XeonTheMGPony - 24-8-2017 at 06:31

What about drying in a Vacuum desiccator system? Mind you I control the humidity in my lab (Dehumidifiers help a ton !!!)

Is it bad as Copper Nitrate or Ammonium Nitrate?

PirateDocBrown - 24-8-2017 at 06:41

Quote: Originally posted by Melgar  

Quote: Originally posted by PirateDocBrown  
Making NaBH3CN is an excellent idea!

But if you wanna purify NaCN, turn it into HCN gas by heating with a nonvolatile acid, then condense into NaOH. Crash out with EtOH. Use really good ventilation.

Good lord, that is one terrible idea after another! If you'd done a few minutes of research, you would have realized that sodium cyanide is soluble in ethanol! Actually, the fact that you're wrong is a good thing, because it means he can just use methanol or ethanol to dissolve the cyanide and recrystallize it, rather than potentially turn his entire block into a gas chamber. Those fume hoods have to send their exhaust somewhere, you know. Since the main impurity in old alkali cyanides is their carbonate salts, everything would be quite straightforward, as long as water is very strictly excluded from recrystallization.

[Edited on 8/24/17 by Melgar]


Actually, if you condense the HCN to liquid, then drip that into saturated aqueous NaOH, you will capture nearly all of the cyanide. The vent would go to a trap, obviously. The only escape would be through apparatus leaks, if any. Good design would eliminate this problem in advance.

Solubility changes dramatically in an H2O - NaCN - NaOH system when EtOH is added, and the NaCN would preferentially crash out.

Take a look at how NurdRage purified his NaCN. He converted it into ferrocyanide, then back again. A chemical change means a far purer product in the end, though with some yield loss.

Now it's true, on the pound scale, some serious precautions must be taken, I myself have never much handled HCN in more than 10g quantities or so. But recapture of the liquid can be made such that I estimate no more than 100mg or so ever escaped, and that would be rapidly oxidized to OCN- in the atmosphere.

PirateDocBrown - 24-8-2017 at 06:42

Quite frankly, the B2H6 scares me more than the HCN.

Melgar - 24-8-2017 at 08:06

Quote: Originally posted by PirateDocBrown  
Solubility changes dramatically in an H2O - NaCN - NaOH system when EtOH is added, and the NaCN would preferentially crash out.

Take a look at how NurdRage purified his NaCN. He converted it into ferrocyanide, then back again. A chemical change means a far purer product in the end, though with some yield loss.

Do you realize that you're recommending an isolation method that will necessarily be contaminated with NaOH, and simultaneously claiming that it would mean "a far purer product"? If he has old NaCN, it's not contaminated with dirt and bugs and random other alcohol-soluble salts, it probably just has sodium carbonate and water as impurities. Dissolving in methanol, filtering, then vacuum evaporation of the solvent would give a purer product than the "NurdRage" method*, which incidentally is mainly useful because everything is very OTC.

I'd like to think I'd be secure enough to admit I was wrong if I inadvertently told someone to do something that's a really bad idea, for the sake of their safety. Are you?

* This reaction actually dates back to the middle ages. Did you say that just because I'd mentioned in a different thread how much it pisses me off when people attribute ancient reactions to yootoobers, and tell me to watch a video rather than explain the process briefly? In any case, it didn't work, because I understand this reaction well enough that I don't need to read or watch anything.

edit: one more thing: I don't know if sodium cyanide is soluble in isopropanol, but if it is, that might be better for recrystallizing, since it forms an azeotrope with water.

[Edited on 8/24/17 by Melgar]

PirateDocBrown - 24-8-2017 at 10:44

Well, sure, I'd be happy to say I was wrong. And I'm not thinking there's bugs in his compound. But NaCN is also likely to have NaOCN as an impurity, more likely, I would think, than Na2CO3. Water-ethanol (or isopropanol) would have a much greater affinity for NaOCN than it would for NaCN.

As for safety, I sketched out how risk might be avoided.

And, no, I've never seen your post about YouTubers. Further, I am familiar with the early methods of cyanide production. I don't mean to antagonize you at all, actually.

I myself have made HCN via heating ferrocyanide with H3PO4, condensing it, and then using it with NaOH to make NaCN. To be fair, I don't exactly recall the specific alcohol used to crash out the product, as it was many years ago.

I'd like to do a bit of amateur chemistry similarly, only starting with Fe7(CN)18, to see if I can get any yield at all.

spankyetal - 24-8-2017 at 17:59

Quote: Originally posted by unionised  
Quote: Originally posted by spankyetal  
... Any thoughts. ...

Don't.

If you got it accidentally then you have no use for it. Why take the risk for something that's not useful to you?


True. It can be rendered nontoxic by simply adding hydrogen peroxide solution. I came into possession of this compound via ebay. Seller flat out LIED about it being empty -twice. Shipped it without haz mat labels etc. Purchased it as an vintage chemical container with a Fischer label. Quite old as it dates back to Fischer's joint venture with another company- also on the label.
Never thought about the borohydride use. Problem in shipping it to someone else is all the haz mat requirements. If its even legal to posses. Didn't see it on the DOJ lists.. I drilled the seller for lying about the item. Shipped it USPS UNLABELED. Felony offense .
So much for a conversation piece.

ninhydric1 - 24-8-2017 at 19:04

@spankyetal

Honestly, purifying such a dangerous chemical when you have no use for it is pointless. I'd recommend giving it to someone on this forum that would have a use for it. They would have much more experience and would actually have a reason to purify/use sodium cyanide. If you can't (shipping costs X(), render it harmless and store it until you actually have a use for it and/or you plan to give it away.

[Edited on 8-25-2017 by ninhydric1]

j_sum1 - 24-8-2017 at 19:05

Well, I think it was a good idea to give the seller some stick for not being honest with you. Now, what to do in your predicament.

Two options:
One is to treat the NaCN as something unwanted that you never ordered and to neutralise it with hypochlorite or some such thing.
The second is to recognise its value as a resource and do something wise with it. I commend you for considering the second.

CN– is not something to be trifled with. One option might be to get some help. If you were to tell your location you might find someone able to help you with (a) recovery of a useful product from the material you have and (b) rendering the remains safe so that you actually have the item you purchased. NaCN is sufficiently useful in the right hands that you might find someone willing to help you in return for a portion of the product and/or help you with safe distribution with profit potential.

Melgar - 25-8-2017 at 10:37

Quote: Originally posted by spankyetal  
Never thought about the borohydride use. Problem in shipping it to someone else is all the haz mat requirements. If its even legal to posses. Didn't see it on the DOJ lists.. I drilled the seller for lying about the item. Shipped it USPS UNLABELED. Felony offense .
So much for a conversation piece.

I can actually buy sodium and potassium cyanide OTC from a jewelers' supply shop in the US, so it's not illegal to possess, it's just illegal to ship using any of the major carriers. It's needed for gold and silver plating. There are "cyanide free" methods for plating gold and silver, but the consensus is that they're inferior.

The largest use in the world for sodium cyanide is in gold mining, where it's used regularly without incident, by the ton.

It is a useful chemical to have though. It can be used in organic chemistry, in the Gabriel synthesis, Strecker amino acid synthesis, and such. It's even more useful in inorganic chemistry, because of its coordinating ability with so many different transition metal ions. HCN is lighter than air, so if you work with it outside, it's actually not super dangerous. And even though some people can't smell it, most people can, at levels much below the toxic level.

You can use it to make Prussian blue, too. You mix iron salts of different valences with an aqueous solution, and you'll eventually see a deep blue color.

@PirateDocBrown Sorry about being a jerk. Even though this stuff can be safely used, the problem is that it can kill you when it's unsafely used. The rule that's been drilled into me is, don't ever mix it with acid and you'll be good, mix it with acid and you'll be dead.

clearly_not_atara - 25-8-2017 at 10:48

Suggestion: don't. Instead of "purifying" sodium cyanide as such, convert it to CuCN by using CuSO4 and Na2S2O5 (copper sulfate and sodium bisulfite). This has three advantages: the product will precipitate right out of aqueous solution, cuprous cyanide is not hygoroscopic and does not hydrolyse in air to release toxic gas, and CuCN can still be used as a cyanidation reagent directly, unlike ferrocyanide. It's much safer to store and work with and CuCN is soluble in aqueous ammonia and IIRC also in acetonitrile and can be used to introduce the cyanide group from a Sandmeyer reaction. It can also convert aryl halides to nitriles.

http://en.wikipedia.org/wiki/Copper(I)_cyanide#Preparation
Quote:
On addition of sodium bisulfite the copper sulfate solution turns from blue to green, at which point the sodium cyanide is added.


Second best option is recrystallizing from methanol as Melgar suggested.

[Edited on 25-8-2017 by clearly_not_atara]

[Edited on 25-8-2017 by clearly_not_atara]

[Edited on 25-8-2017 by clearly_not_atara]

Melgar - 25-8-2017 at 17:29

I still think my first suggestion is the best way to go. Don't fuck with it, just titrate it to determine purity and assume that the main impurity is sodium carbonate.