Sciencemadness Discussion Board

KCN synthesis. Care to share your thoughts?

Benignium - 10-7-2020 at 23:57

I'm hoping to get opinions on this first draft of a potential apparatus for generating potassium cyanide. I was originally planning to start with cyanuric acid but arrived at the conclusion that the superior route for me is to bubble HCN into a solution of KOH in absolute ethanol. I have an excellent outdoor location at my disposal where the activity cannot endanger others. I also have a full face respirator with ABEK1 cartridges as a precaution.

The reason I want to do this is to have gold cyanide for electroplating.

The proposed setup is pretty simple. Battery electrolyte is added to potassium ferricyanide with mild heating. Generated HCN travels through the liebig where the bulk of the water vapor gets condensed. HCN is then passed through concentrated sulfuric acid in order to dry it further before bubbling it into KOH in 100% ethanol that is being stirred strongly. Potassium cyanide should start precipitating fairly quickly. Ethanol is then decanted or filtered off and the product is quickly dried on a hotplate.

That's pretty much it. I'd love to hear constructive criticism.
Please, if you can, be nice. I'm not out to kill anyone.

[Edited on 11-7-2020 by Benignium]

B(a)P - 11-7-2020 at 01:53

A full face respirator does not give you adequate protection. When working with HCN it is recommended to use supplied air. You will also need the appropriate coveralls with tapped gloves and booties to avoid skin contact.
Be very careful with this. I work with a lot of nasty stuff in my profession and HCN is definitely up there as one of the most challenging compounds to get appropriate safety controls in place to reduce the risk to acceptable levels.

brubei - 11-7-2020 at 02:06

Consider worst case scenario (glassware failure) and get enough material ready for quick neutralization from start to end.

Outdoor experimentation means wind distribution is random or null. I think you still need some ventilation to have a well dispersion of local atmosphere.

You can try arduino cuircuit with gaz probe (NDIR sensor cyanide max absorption is about 3.287┬Ám)

[Edited on 11-7-2020 by brubei]

Benignium - 11-7-2020 at 08:33

Thanks guys!

You're right B(a)P, 3M too lists supplied air as the only viable form of respiratory protection. The plan is to completely eliminate the need for the respirator but I still feel silly when I think about not using one even though I have one. I'm unable to justify it any better than that.

brubei, these are valid points and I wholly agree with the ventilation. Notably I have experience working outdoors with ammonia, chlorine, nitrogen dioxide, sulfur dioxide and even some hydrazine from when I tried my hand at making a small amount of hydrazine sulfate for making a copper mirror. I know how unpredictable the weather can be and how important it is to promote the dispersion of gases because of this.

I truly appreciate the concern and I do hope I don't come across as lax when it comes to discussing safety. I would, however, like to focus on the apparatus itself and what could be done to improve it.

RedDwarf - 11-7-2020 at 09:36

I wouldn't do it as I'm a wuss, but if I was going to I'd make the following changes:

1) You've got your HCN bubbling into an open vessel, which is a big No-No as it assumes all the gas will be absorbed. You should have this as a closed vessel with an offtake going to a sodium thiosulfate bubbler (or even two in series) so that any HCN not absorbed in your KOH solution is converted into less harmful thiocyanate.

2) I'd want the ability to be able to gas flush the whole apparatus after finishing adding acid, but without taking the apparatus apart (again flushing everything through a thiosulfate trap). With the addition funnel above the condenser, your're making this flushing difficult, so I'd use a two necked flask below the condenser and have the addition funnel adding directly into this. You could then flush the whole apparatus from the top of the addition funnel.

unionised - 11-7-2020 at 10:04

How fast is the thiosulphate/ cyanide reaction?
Is it fast enough to be useful?

Why bother with the 98% H2SO4 trap?
Commercial KOH has quite a lot of water etc in it.
If the container is open then the KOH/ EtOH will pick up water from the air.
Might be easier to work in two stages.
Trap the HCn into aqueous KOH.
then dry that down and leach out KOH with EtOH.

Belowzero - 11-7-2020 at 10:13

Quote: Originally posted by unionised  
How fast is the

Why bother with the 98% H2SO4 trap?

This and this setup might be prone to suckback which could create a big mess, or at best just ruin your experiment.

[Edited on 11-7-2020 by Belowzero]

Benignium - 11-7-2020 at 12:14

Beautiful points!

A closed receiving vessel sounds like a significantly more sensible solution for the protection of the solution as well as myself. The thiosulfate gas scrubber is a fine idea, too. I could also go with a very long exhaust tube with the closed receiving vessel. Flushing the system afterwards is a great call, as is the use of a two-necked reaction flask. I will definitely be doing both.

The conc. sulfuric acid trap is there mainly because I have no idea how much water would make it past the condenser alone. I agree that it could be unnecessary. The suckback isn't something I had considered yet.

These are all valuable observations. Thank you!

[Edited on 11-7-2020 by Benignium]

Whathappensif - 11-7-2020 at 12:31

HCN apparently smells like almonds. In spite of the precautions you take, consider this the last line of defense. If you smell such a smell, run for it!

Benignium - 11-7-2020 at 14:19

Yes, let us not forget to have a pair of good running shoes. :)

SWIM - 11-7-2020 at 19:43

A bubbler with a glass frit, like in gas washing bottles, would help maximize absorption.

In fact, a gas washing bottle would be a natural in that setup

Refinery - 12-7-2020 at 00:12

If you have the space, you can vent the system outside, preferably through a chimney so all HCN traces will be exhausted into the atmosphere. As long as the system is gas tight and you take proper measures not to break any of it, it should be viable. ABEK gas masks are decent for protecting minor exposure to HCN.

You can use cold finger with CaCl2 solution cooled to as low as you can get it in a thermos flask to vent the gases, so you can easily monitor any leaks of HCN. It has BP of 26C so it easily condenses in such environment. Make sure the tubing is compatible with HCN and other gaseous products you are handling. Suckback is mandatory because injecting strong base into strong acid is a recipe for disaster on it's own, but adding a volume of HCN into the equation takes it a few magnitudes more serious.

After reaction is done, you could neutralize the remaining liquid with base, and you could also flush the system with vacuum ejector, as long as you discard the water either outdoors or directly below water lock.

B.D.E - 12-7-2020 at 01:15

Using a cold diluted NaOCl+NaOH solution for the bubbler is probably good enough choice. Keep in mind that HCN is pretty soluble in cold water, so I wouldn't be worrying too much if you have good ventilation.

I actually worked with cyanides all week long. Although I preferred using the sodium metal reduction intead, just because I hate bubbling gases into liquids(I always screw it up somehow).

This is not a suggestion, just me sharing my experience: I did felt as if I was exposed to the cyanide as I experienced slight headache and nausea. However, before even starting working with cyanides, I prepared n-butyl nitrite just in case. I took a few sniffes and gradually felt much better.

Again, this is not a suggestion, just something I've read: apperantly vitamin B12 is also a common choice for an antidote, and it is from my understanding that it's practically impossible to overdose on it. As an antidote it usually administered IV, but it's a very bad idea to crush vitamin pills and inject whatever additives in them. It might also be effective taken under the toungh or maybe up the butt. But keep in mind that in every medical reference I've read, the administrations was exclusiveley intraveious(most likely due to the short onset, but who knows).

Sodium nitrite is toxic and possibly carcinogenic. However, it is also a well known antidote for cyanide poisoning in 100-300mg IV dosages. It too might also work taken up the butt, but who knows.

I also read that cobalt(II) compounds found to have risen the LD50 in rats by quite a lot(I don't remember exactly by how much, but if I recall correctly it was more than x100 with cobalt acetate). Cobalt compounds are toxic and probably carcinogenic.

All in all, I preferred going with an alkyl nitirite just because I already familiar with its effects + these have a long history of recreational use in humans and are found to be quite safe + nothing gets inside my butt/veins + no risk to overdose on it(there's not even 1 documented death from the use of "poppers"). I also had a syringe(no needle) full with 200mg of NaNO2 in 3 mL of dH2O ready to enter my butt, but thankfully I never got to use it.

Please don't play Russian roulette with your life based only on some random guy's message online. Keep in mind that you can just as well poison yourself to death while trying to treat a poisoning that never actually occurred. If you experience symptoms of cyanide poisoning - SEEK MEDICAL HELP IMMEDIATELY.

I just wanted to share my experience and also some cool antidotes I've read about recently. That is it.

[Edited on 12-7-2020 by B.D.E]

Benignium - 12-7-2020 at 13:29

More awesome advice! Thanks guys!

I will replace the single receiving vessel with two gas washing bottles in line, the first one being set up as a safety bottle in case of suck back. I'll have to look for one with a glass frit!

Refinery, my plan is to indeed dump whatever escapes into the atmosphere. The idea of condensing any such HCN is intriguing to say the least but I think I'll be better off immediately disposing of it in the gaseous state.

I'm thinking of flushing the system using an air pump, that is attached to the addition funnel using a vacuum adapter with a valve.

B.D.E, this (antidotes) is an interesting subject. Somewhat inconveniently alkyl nitrites have largely been pulled off the store shelves in my country, but seem like a good idea nonetheless. Since I lack medical education and/or a drug habit I wouldn't really trust myself to self-administer injections, even if I wasn't choking on a cellular level and had ample time to aim. Therefore I agree that rectal administration would probably be the fastest available route to the bloodstream. No one can really know if it would be fast enough, though.
I'd think that B12 could in theory be taken in advance orally, since it has quite a long half-life. I seem to recall reading that the peak plasma concentration also lasts a good few hours. Grains of salt.

Refinery - 12-7-2020 at 13:52

Alkyl nitrites, being the active ingredient in poppers, are banned in certain countries, but can be ordered online from various countries that are within different trade zones (like EU). They are also available under the counter in certain type of shops, if you know people or know what to ask.

Hydroxycobalamin is indeed administered IV, and it has very rapid onset. The main issue with cyanide poisoning is it's rapidity. Anything taken orally, rectally, topically etc. will generally be insufficient, unless taken beforehand, but the body can metabolize the active ingredients. Cyanide will incapacitate very quickly if exposure is major. In minor exposure, the poisoning symptoms could serve as pre-warning.

Proper way to do injections is either auto-injector or learning to do it. I have done it, and one gets used to it quickly. And for the record, I have never done any non-prescription drugs.

Unless cob is available in IV form in some extent, best way for amateur is to use multiple layers of protection. First is the enclosure of the process, second would be the enclosure of the process environment(a fume hood with strong enough duct fan and chimney exhaust), third PPE, including full-face mask with ABEK and splash protection(either PP suit or long sleeve gloves), and fourth a planned exit maneuver in case of catastrophic event (process equipment failure). Fifth layer would be careful planning of all steps of the process, especially dismantling the system and processing the end product for storage. The antidote step would be placed between these steps according to preference, if available. It would also be mandatory to perform the process in a location where collateral exposure in case of anomaly is either nil or minimal.

woelen - 13-7-2020 at 04:58

I would not bubble HCN in an aqueous solution of KOH. In alkaline water solution, the cyanide fairly quickly degrades to a brown polymeric species. That is the reason why it is prepared in ethanol. The presence of water at high pH greatly speeds up the polymerization reaction.

unionised - 13-7-2020 at 05:24

Quote: Originally posted by Whathappensif  
HCN apparently smells like almonds. In spite of the precautions you take, consider this the last line of defense. If you smell such a smell, run for it!

Some people can't smell it.
And you don't run, you walk.
You don't want to risk tripping over.

SWIM - 13-7-2020 at 10:48

Have you checked over other threads on cyanide manufacture?
There are a number, and some fine points of conditions and technique are discussed in some of them.

Woelen's mention of polymerization reminded me of this because that is something they discuss as a problem.

@B.D.E. I just realized that your post was the first time I've ever heard of anybody using butyl nitrite because they DON'T want something up their butt.

[Edited on 13-7-2020 by SWIM]

[Edited on 13-7-2020 by SWIM]

Bedlasky - 13-7-2020 at 13:40

I think, that conc. sulfuric acid will oxidize HCN.

B.D.E - 14-7-2020 at 12:35

Quote: Originally posted by SWIM  

@B.D.E. I just realized that your post was the first time I've ever heard of anybody using butyl nitrite because they DON'T want something up their
[Edited on 13-7-2020 by SWIM]

haha I laughed my ass off man :D
Quote: Originally posted by Bedlasky  
I think, that conc. sulfuric acid will oxidize HCN.

Check this:
The Interaction of Sulphuric Acid and Potassium Ferrucyanide

Benignium - 6-1-2021 at 12:37

As it currently is, and will for several months continue to be, cold as balls outside, I decided to try out one of the easier methods of producing cyanide and to see what I would get.

To a stainless steel mug, 40 grams of anhydrous potassium ferrocyanide was added along with 15 grams of anhydrous potassium carbonate. The mixture had been mixed thoroughly in a mortar, with a pestle, and had the consistency of a fine flour. The mug was covered with aluminium foil and heated until red hot and the mixture inside had melted. Heating was continued for 20 minutes and the mixture was set to cool in a cold water bath. After cooling, the concrete-resembling cake of solidified material was broken up and extracted with sufficient methanol to dissolve a quantitative yield of potassium cyanide. The methanol was filtered and the clear filtrate distilled off until 80 milliliters of the solution remained in the flask. The contents were gravity filtered and the solid dried, yielding 18 grams of KCN of unknown purity.

500 milligrams of the crude KCN with the addition of 10 milligrams or so of potassium iodide was titrated using a 0.01M silver nitrate solution. The purity was determined to be 28.4%.

AgNO3 being added to KCN solution

end point

Perhaps usable in some context, but the yield alone is unsatisfactory. I want to try adding some activated charcoal into the mix to see what kind of improvement the reduction of cyanate to cyanide will afford.

[Edited on 7-1-2021 by Benignium]

aromaticfanatic - 6-1-2021 at 15:08

I may be mistaken but couldn't you just use baking soda and less heat? You would get the sodium salt but it is usable and safer than HCN.

From the picture, your reaction vessel is glowing red and I believe alkali cyanide salts are prone to decomposition and I am sure heating it red hot will do the trick.

Perhaps try a smaller scale experiment and monitor which temperature works better.

When purifying the result try to use anhydrous methanol or ethanol as water will hydrolyze the cyanide to HCN resulting in loss of yield and less safe conditions.

teodor - 6-1-2021 at 16:38

Hydrogen cyanide is actually liquid under 26C and the liquid state is always much safer to work with than gaseous form for any compound and most dangerous ones are not exception here. I am wondering, is it possible to extract the product of reaction of X (something) with ferrocyanide to let say, organic layer in a good well ventilated ice bath without any HCN-driven pneumatic effects in a system with more than 7 joints?.

Benignium - 6-1-2021 at 17:00

aromaticfanatic, I don't think the use of sodium bicarbonate in place of potassium carbonate would be beneficial. My aim is to make either Na/K, and not a mixture of the two.
The point of heating so much is to melt the mixture which provides a more complete reaction. As far as I know, alkali cyanides are quite robust when heated but react more readily with oxygen.
The methanol I used was anhydrous. The fatal flaw here is that potassium carbonate and potassium cyanate are also soluble in it.

teodor, HCN is rather prone to polymerization, so while it might make sense to condense it and use it as a liquid, I feel like passing gaseous material into a stirred solution of KOH in EtOH is the safest bet.

Thank you both for taking the time!

teodor - 8-1-2021 at 01:50

Quote: Originally posted by Benignium  

teodor, HCN is rather prone to polymerization, so while it might make sense to condense it and use it as a liquid, I feel like passing gaseous material into a stirred solution of KOH in EtOH is the safest bet.

When everything is assembled and reaction is already going and well controlled it is one thing, but assembling the apparatus every time, disassembling, neutralising etc is a big work which adds risks like you finished reaction but didn't disassemble equipment, and after few days your H2SO4 wash bottle still have some HCN in liquid phase. So, my approach is the "simpler is the safer".

Thanks for the information, I was unaware about HCN polymerisation. It's very interesting. But it polymerises only in alkaline conditions. "Small amounts of acid, e.g. sulphuric acid can be added to HCN as a stabiliser. The acid reacts with any basic materials and keeps the HCN solution acidic. HCN is normally stabilised with 0.06-0.08 wt. % sulphuric acid, keeping the pH of the HCN < 4." - from here

By the other hand, this document says the polymerisation of HCN upon contact with base can be so exothermic than can lead to explosion. So, it is not safe to drop a base into HCN solution and your approach of bubbling HCN through a base solution is safer than that.

I think that adding aspirator at the end of the chain could be a good idea:
1) potentially it will eliminate the heating element, the reaction could be driven by a heat of H2SO4 dilution only;
2) it will prevent HCN from condensation along the way to the reaction bottle;
3) it will create negative pressure inside the apparatus, and controlling this pressure you control the absence of leaks; any problem with sealing will raise the pressure and stop the reaction.

Using excess of alcohol in the reaction bottle you will allow this to evaporate and constant vacuum will cool this bottle to the temperature of alcohol boiling under vacuum, this will depress HCN vapour pressure and make absorption more effective.

There are 3 problems with vacuum:
1) it is not possible to condense the water vapour;
2) you should maintain the reaction very carefully to limit the concentration of HCN in the water stream from the aspirator; but I think it is possible
3) all your wash/bubbling becomes 2 directional; actually it is not a new problem, it the original design suck-back is also possible, so this should be addressed in any case

As for water vapours condensation/drying with H2SO4 I didn't still get why it is necessary.

Update: I checked publications about the reaction of both ferro- and ferricyanides with H2SO4 and found it is not so straightforward to estimate any constant stream of HCN. Also oxygen participates in the reaction and its presence/absence can change the yield.
The lowest temperature at which HCN can be produced is likely to be 60C (decomposition of hydroferrocyanic acid by water).

I still think other possible routes are more practical. I think worth to study decomposition of Zn, Cd, Cu and Hg cyanide complexes because they are not so insanely strong.

[Edited on 8-1-2021 by teodor]

[Edited on 8-1-2021 by teodor]