Sciencemadness Discussion Board - Preparation of cyanides

Quote: Originally posted by Hawkguy

Its probably easiest (If you're looking for convenience) to add cooled Hydrochloric Acid to Potassium Ferricyanide, and distill the Hydrogen Cyanide directly into aqueous Potassium Hydroxide.... .

I answered this on p.24. I use H2SO4 to stabilize any HCN which is collected as such (now that I fully appreciate the danger).

There is polymerization going on, I'm just not sure it's the HCN itself that causes it because it only happens...well, let me summarize:

1) HCN is generated, condensed in a distillation head, then allowed to drip into cold, stirred aq. NaOH directly. Result: Black solution.

2) HCN is generated, condensed in a distillation head, collected in a flask containing H2SO4 stabilizer. This liquid is then allowed to drip into cold, stirred aq. NaOH. Result: Colorless to slightly yellow solution.

3) HCN is generated, condensed in a distillation head, collected in a flask with no stabilizer. This liquid is then allowed to drip into cold, stirred aq. NaOH. Result: Colorless to slightly yellow solution. It IS NOT suggested that you try this, I did it only out of ignorance.

Interesting observation: The material in the discharge end of the distillation head (which hasn't touched base yet) also turns black in the "direct addition to base" scenario described in (1). It doesn't do it in (2) or (3).

I know this sounds crazy. But I have done it several times (both ways) with the same results always. The collected HCN was typically (but not always) stored overnight in a freezer before addition to base.

A note about stabilization: This is done to prevent explosion (uncontrolled polymerization) of HCN which is catalyzed, especially strongly, by the CN anion. It is said that glassware needs to be very clean before condensing liquid HCN into it. Since many labs use base bathes to clean glassware, it should be rinsed off very thoroughly. Stabilization with 1 - 2 % H2SO4 can be seen to be very appropriate to staying safe.

[Edited on 22-10-2014 by Dan Vizine]

careysub - 22-10-2014 at 10:29

...
I am hoping he clarifies whether he uses acid to stabilize the product while being collected, or afterwards, which may help to explain the the difference between the two apparently similar scenarios he described.[/rquote]

I answered this on p.24. I use H2SO4 to stabilize any HCN which is collected as such (now that I fully appreciate the danger).

There is polymerization going on, I'm just not sure it's the HCN itself that causes it because it only happens...well, let me summarize:

1) HCN is generated, condensed in a distillation head, then allowed to drip into cold, stirred aq. NaOH directly. Result: Black solution.

2) HCN is generated, condensed in a distillation head, collected in a flask containing H2SO4 stabilizer. This liquid is then allowed to drip into cold, stirred aq. NaOH. Result: Colorless to slightly yellow solution.

3) HCN is generated, condensed in a distillation head, collected in a flask with no stabilizer. This liquid is then allowed to drip into cold, stirred aq. NaOH. Result: Colorless to slightly yellow solution. It IS NOT suggested that you try this, I did it only out of ignorance.

Interesting observation: The material in the discharge end of the distillation head (which hasn't touched base yet) also turns black in the "direct addition to base" scenario described in (1). It doesn't do it in (2) or (3).

I know this sounds crazy. But I have done it several times (both ways) with the same results always. The collected HCN was typically (but not always) stored overnight in a freezer before addition to base.
...
[Edited on 22-10-2014 by Dan Vizine]

Having the case by case comparisons is very helpful in pondering what may be going on here.

The difference between 1 and 3 is what is puzzling - no polymerization with the acidic stabilizer (2) is what we would expect.

A few useful facts there - the pH of HCN itself is about 4.5, but to prevent polymerization the pH should be 4 or below.

Polymerization is autocatalytic so unnoticeable amounts of polymer, once formed, can drive polymerization.

Initiation of polymerization of HCN during distillation is a known problem, there are patents that seek to address this.

The blackening of the discharge end in 1) suggests that perhaps the dripping process itself is causing the transport of base up to the distillation tube end. Perhaps microdroplets are being created that then contaminate the tube end with hydroxide? This then sets a troublesome degree of polymerization in motion.

But why would this not also happen in 3) when not adding an acid-stabilized product? Perhaps the freshly distilled material (recently warm) is more "active" in some way and more sensitive to trace quantities of base? Dissolved traces of newly formed HCNx that settle on surfaces later? Effects of trace oxidation of the HCN?

Dan Vizine - 22-10-2014 at 18:45

Yeah, it's a difficult nut to crack. So many maybe's...

About the blackening in the condenser in (1)...the idea of splashes is very unlikely. The drip tube of the 14/35 distillation head was fitted with a Teflon tube about a foot long and 1/8 "dia. to lead the liquid HCN into the base flask.

The HCN is never allowed to warm above 0 C except for the brief residence time in the dropping funnel. Even then, it doesn't warm very high at all since it starts out colder than 0 C and is poured into a pre-chilled dropping funnel.

I'm one of the sub-group that easily smells HCN. Suitably diluted, I really like the smell...delicious almond pastries!

As poisons go, I prefer working with this type. If you walk away at the end of the day, it's behind you. Not like working with MeI or Me2SO4, where you can only hope you didn't just methylate any of your essential DNA. I even prefer working with HCN over HMPA.

Funny story, a former boss worked at DuPont in Niagara Falls. During an ill-advised pipeting incident (it was a different time....you know) he got a mouth full of LHCN. I asked him what he did...his answer...I spit it out. Probably with a lot of mouth rinsing.

The most interesting HCN experience I've ever had was maybe 25 years ago when I opened an autoclave in which a Ba salt of some arcane mercapto S,N-heterocycle was being reacted. Apparently the reaction could produce HCN as a side-product. This wasn't mentioned in the patent I was following (I know..big surprise) and I got a pretty good whiff. I had that little rush up the spine you get when you realize something bad just happened but it hasn't hit yet. Then it hit and I got tunnel vision. It was getting a bit dark in the room and I turned to walk toward a labmate and was preparing to say "cyanide". Before another 2 steps the lights were coming on, and just about as quickly as it hit, it was subsiding.

[Edited on 23-10-2014 by Dan Vizine]

Dan Vizine - 24-10-2014 at 08:26

I wonder what possible role that the other tautomer, hydrogen isocyanide, may play (if any)? It is supposed to quite base stable, so maybe no role at all.

It's clear that either HCH or HNC are both able to produce polymers that are black.

Hawkguy - 24-10-2014 at 09:41

I apologise if this sounds stupid, but what about reacting the Potassium Ferricyanide and Hydrochloric Acid stoichiometrically, then adding aqueous Potassium Hydroxide and recrystallizing? I wouldn't happen to know of a suitable solvent unfortunately, but hopefully the idea comes across.

careysub - 24-10-2014 at 09:49

...
The most interesting HCN experience I've ever had was maybe 25 years ago when I opened an autoclave in which a Ba salt of some arcane mercapto S,N-heterocycle was being reacted. Apparently the reaction could produce HCN as a side-product. This wasn't mentioned in the patent I was following (I know..big surprise) and I got a pretty good whiff. I had that little rush up the spine you get when you realize something bad just happened but it hasn't hit yet. Then it hit and I got tunnel vision. It was getting a bit dark in the room and I turned to walk toward a labmate and was preparing to say "cyanide". Before another 2 steps the lights were coming on, and just about as quickly as it hit, it was subsiding.

That is so scary.

It is a good thing that not only is cyanide detoxified by the body, but that cytochrome oxidase complex inhibition is highly reversible.

You got enough in one breath so that the initial CN surge substantially inhibited brain cytochrome oxidase, causing the visual blackout (which can simulate by holding your breath long enough), but with CN-free blood circulating immediately afterward the CN released from the co, reactivating it.

careysub - 24-10-2014 at 10:01

Quote: Originally posted by Hawkguy

I apologise if this sounds stupid, but what about reacting the Potassium Ferricyanide and Hydrochloric Acid stoichiometrically, then adding aqueous Potassium Hydroxide and recrystallizing? I wouldn't happen to know of a suitable solvent unfortunately, but hopefully the idea comes across.

You would at least end up with a mixture of FeCl3 and KCl with your KCN, not a desirable product mixture I expect.

After forming aqueous HCN perhaps you could extract it into ether, then extract the ether-HCN solution with aqueous NaOH or KOH.

Dan Vizine - 24-10-2014 at 12:05

The deep blue ferric ferricyanide which results from the acid reaction (not all of the CN comes off the iron) is very bulky. I believe that this is called Prussian Blue. It would be an isolation nightmare. Catalysis by Cu salts and/or Cu helps push the reaction further according to one source.

Anyway, a way around the problem has been found. I have just always wondered why it happens, though.

[Edited on 24-10-2014 by Dan Vizine]

Dan Vizine - 24-10-2014 at 12:27

That is so scary.

....

The really scary part is if you've ever seen a cyanide antidote kit. It relies on totally untrained people to get large needles into your veins quickly. Good luck.

careysub - 24-10-2014 at 15:14

The deep blue ferric ferricyanide which results from the acid reaction (not all of the CN comes off the iron) is very bulky. I believe that this is called Prussian Blue.

Making Prussian Blue was my favorite "chemical magic" reaction with my ChemCraft chemistry set.

It has the distinction of being the wholly first synthetic dye ever.

Dan Vizine - 24-10-2014 at 15:19

Oh, back in good old days when chemistry sets actually contained chemicals!

My first chemistry set, back in the early 60's, set the course of my life. That can't happen today unless the child has very low standards. Growing crystals, investigate pH....just kill me now. I preferred to set fire to steel wool in an atmosphere of Cl2 just as "The Golden Book of Chemistry Experiments"showed me how to do.

[Edited on 25-10-2014 by Dan Vizine]

careysub - 27-10-2014 at 07:14

Have you ever used HCN in the Gatterman synthesis?

I have done some looking for a procedure description. Gatterman's two texts on-line here don't have it, and I haven't found any elsewhere despite substantial Googling.

Accounts mentioning Gatterman do so only in passing (describing some other aldehyde production procedure) or describe an 'improved' version (most often with zinc cyanide).

In a world where alkali cyanide salts are essentially unavailable the supposed superior safety of zinc cyanide is illusory - obtaining it requires making HCN anyway.

And oddly, there is apparently no such taboo about using dimethyl sulfate. OrgSyn.org has DMS procedures, but no HCN. Shulgin declines to give an HCN procedure (which gives much better results than the one he does describe), but has no problem with describing a procedure using 126 g of DMS. [Dimethyl sulfate was actually used as a war gas in WWI - it is similar to mustard gas, but is 1/5 as potent - would you do a synthesis calling for 25 g of mustard gas instead?]

I would much rather run a reaction with HCN than DMS. If you check the NIOSH safety limits for the two compounds, DMS has a much lower permissible level (this is good rule-of-thumb way of estimating low level exposure hazards). HCN skin exposure risks are zero, but are severe with DMS. HCN has no cumulative or delayed effects - not so DMS. HCN has a useful warning odor, again nada DMS. I could go on.

[Edited on 27-10-2014 by careysub]

Dan Vizine - 27-10-2014 at 10:47

No, I've never done the reaction. We probably would have been much more likely to go the BuLi followed by DMF route. The place where I spent nearly my whole synthesis career wasn't the type of place that would've had a convenient source of HCN available, but we had gallons of butyl lithium.

Personally, I couldn't agree with you more. I'm not very impressed by the dangers of the chemicals that get you in the here and now. I've never found that the available safety options for using these things made me feel unsafe. They seemed adequate or at least it was a chance I was willing to take. Over the course of a career spanning decades, it's not too uncommon to realize that the difference between you and dead you is about an eighth of an inch of glass. I'm sorry, but sometimes it was just convenient to do reactions with potassium cyanide in DMF or potassium fluoride in DMSO at the 22 L scale. It doesn't take much imagination to realize that a splash with the fluoride isn't something you'd come back from. Common sense precautions were always enough. I never witnessed or experienced a life-threatening situation.

The scary things were exactly the types of things you mentioned. The scariest things were the reactions that had HCl and a potential formaldehyde source like an N-hydroxymethyl group together in one pot. You can leave work that day smiling like a fool, and then 20 or 30 years later the molecular machinery goes awry.

careysub - 27-10-2014 at 11:48

...
The detoxification rate is about 0.07 mg per minute per kilogram of body weight. if you weight 70 kg you can absorb 5 mg a minute continuously without suffering any ill effect (don't test this - it is a safety feature, not a challenge). The 25 mg LD given above requires breathing a high vapor concentration so that the entire dose is absorbed in a minute or less (e.g. 2.5 grams evaporated in a cubic meter of air).

I apparently cannot edit my original post about safety/hazard data. The source I pulled up for the detoxification rate had a misprint, the rate is actually 0.017 mg/min/kg NOT 0.07 mg/min/kg, so it is 1/4 as fast. This means you only metabolize 1.25 mg/min.

Oxirane - 27-10-2014 at 12:18

In a world where alkali cyanide salts are essentially unavailable

What happened to the classic carbothermic reduction that contains maybe three of the most available chemicals there are?

careysub - 27-10-2014 at 14:21

Quote: Originally posted by Oxirane

In a world where alkali cyanide salts are essentially unavailable

What happened to the classic carbothermic reduction that contains maybe three of the most available chemicals there are?

And if that is what you have to do to get KCN then "unavailable" it is!

There is a significant difference between being able to buy KCN, and needing to first buy an electric (or other) furnace so that potassium ferricyanide, carbon, and potassium carbonate can be heated at 650 C for three hours first, then extracted and purified to get the same KCN. (Also it vents carbon monoxide from the crucible, much less dangerous than HCN, but not harmless).

This is a method to redress unavailability, it does not change the fact that you cannot buy it.

Dan Vizine - 27-10-2014 at 18:46

The carbothermic process is one of those industrial processes that doesn't translate well to the home. I welded a steel crucible, built a forced-air coal furnace, tried the reaction several times, I even had a spin evaporator to quickly evaporate the ultimate product and still the best I got was a cyanide odor. The performance of the reaction is very subjective, the amount the crucible can be open to the air needs to be just right (with no criteria for "correct" except, apparently, success or failure at the end), it's a reproducibility nightmare. There's a lot of luck involved.

I guess some members have gotten it to work, I haven't pursued it. But, if you can get potassium ferricyanide and H2SO4 you'd be crazy to go the other route.

edit: I noticed people mentioned using HCL. This is a poor idea. You need to heat the mixture to get the HCN out. You don't want HCl carry over. H2SO4 is the answer.

[Edited on 28-10-2014 by Dan Vizine]

Oxirane - 28-10-2014 at 06:53

Versuchschemie presented a method that uses urea, charcoal and sodium carbonate to first generate sodium cyanate and then reduce it to cyanide. I have performed this test and although I did not have test to determine if it was cyanide or cyanate, it corroded aluminium and the synthesis gave all clear indicators same as the VC describes.

I think this is viable method to make even kilos of cyanide salts when needed, because electric furnace is quite easy to make once you get the specs and materials, since you will need only some nichrome and a dimmer to control the power. I made quite a few different designs before I got it all right but then I had a furnace that could bring anything that fits inside to 1000C. This oven is not to be run inside your living room for sure so it's not otc for people living in cities but for just about everyone else, if the syntesis works as it stands, even a little bit too easy method to make large amounts of it.

[Edited on 28-10-2014 by Oxirane]

Dan Vizine - 28-10-2014 at 07:31

Yes, mine also gave the "indicators" and I also used the urea method, but the product wasn't cyanide.

Corroding aluminum is fairly meaningless as an indicator of having isolated a salt of HCN, IMHO. After all, if you decompose the cyanide to NaOH during isolation you'll also see the same thing.

I'll believe in this method as a viable home prep. when somebody either does a further reaction with it [the product] and gets the expected product in the expected yield, or they perform a chemical assay. After extensive testing over many, many runs and careful analyses of the various products, you just may hit upon it. Or maybe not.

There isn't any question about the ferricyanide and acid product.

[Edited on 28-10-2014 by Dan Vizine]

Oxirane - 28-10-2014 at 12:15

So in where do it goes wrong? I understand that many have performed this synthesis succesfully. I still have got what's left on that synthesis in a vial, so I can test it out if you give me a method for it.

I also note that NaOCN reduction is very temperature sensitive. I made a test with insulated propane burner with calcium carbonate and I never got any basicity with litmus paper, while my electric furnace did that easily. The flames from supposedly carbon monoxide were generated at the high end of heating and the whole furnace interior glowed bright cherry red. The clunker left in the stainless steel crucible was broken down with chisel and hammer and dissolved easily into hot water, filtered and precipitated with ethanol.

The aluminium was wrapped around the SS container that held the clunker for the time for it to cool down. It stood there overnight and aluminium was eaten away. It was never in direct contact but there was about 100mm minimum distance from the clunker to the foil. So gases evolved from the clunker released something that had disastrous effect on the foil. It was just simply gone, like vaporized.

[Edited on 28-10-2014 by Oxirane]

Dan Vizine - 28-10-2014 at 12:49

http://www.cyanidecode.org/cyanide-facts/sample-analysis

Pick your poison, no pun intended.

OR...

Put some in a test tube, outdoors. Add a little sulfuric acid and warm the bottom while you cool the upper part with a wet, cool paper towel. Do you see a band of condensation (liquid HCN)?

Oxirane - 28-10-2014 at 13:08

I'm ashamed to admit, but after all the other equipment I possess, I do not have test tubes!

Hawkguy - 15-1-2015 at 16:59

I think someone might have already mentioned this because I haven't read through all the pages, but its worth noting that apparently Sodium Cyanide is (harder?) to store than its Potassium Counterpart as it hydrolyses more easily. Ive only seen this from one source, but its worth something I guess.

bolbol - 29-3-2015 at 16:30

Quote: Originally posted by Polverone

YIKES! I found the following information on another site:

a patent on making metal cyanides from nitrates or nitrites and
carbon; US patent 579988.
KNO3 + 4C -> KCN + 3CO
KNO2 + 3C -> KCN + 2CO

I was unable to access the patent since I'm temporarily banned from the database for running too many queries (oops).

So I decided to try just forming a pyrotechnic mixture with the right ratios. 10 grams KNO3, 4.8 of charcoal, place in stainless steel vessel and ignite with gas heating from below...

As expected, the mass of what remained was much reduced, from loss of gas, solid particulates, things flung from the vessel by the reaction, etc. There was little material left in the bottom. I figured there had to be more to the method than this; after all, nobody talks about pyrotechnic formulas leaving cyanide lying around, and this is pretty much the same thing.

Anyway, not having an analytical method for detecting cyanides at hand and being too stupid to look one up (and also expecting failure), I added a bit of vinegar to the residue left in the bottom. It fizzed vigorously and I caught the distinct odor of almonds... At which point I backed the heck away from there. I now intend to find a method for assaying KCN that is not so suicidal, and also to try making some more and purifying it (I have no idea what purity I obtained with this first test.) This method seems to be a vastly superior route to cyanides for the home experimenter, compared to the laborious steps given in the PMJB and the 19th century texts from which they were derived. I hope to view that patent soon and see if it contains any additional refinements (compared to crude ignition).

KNO3 + 4C -> KCN + 3CO

Does that actually work?????
If so would NaNO3 + 4C -> NaCN + 3CO work as well?

morganbw - 30-3-2015 at 00:25

This may have already been linked.
Here is the patent.
US patent 579988

woelen - 30-3-2015 at 02:20

I have severe doubts on this. I know that KNO3 + C can be used to make KNO2 (by oxidizing the C). Maybe with further heating you get reaction beyond the nitrite, but I have never seen a description of this reaction in any practical synth.

bolbol - 30-3-2015 at 10:30

The same mixture is also used in gunpowder and I have never seen a gunpowder decomposition equation state any cyanides.

I will try this later with NaNO3 and charcoal to see if any cyanides are made at all.

Blunotte - 2-4-2015 at 22:24

Hello, I'm new on this forum, and I don't speak usually in the Shakespeare language, so please forgive my mistakes

A simple way to obtain cyanides can be this?

Put in a heat resistant test tube potassium ferricyanide and sodium, and melt together until the reaction will be done in absence of air:
K3[Fe(CN)6] + 3 Na -> 3KCN + 3NaCN + Fe

In a second time, purify the cyanides first using water, and in a second time using alchool.

I apologize if the reaction has already been published
Thank you very much

Blunotte - 2-4-2015 at 22:36

Or, more simple, why don't decompose the potassium ferrocyanide at 400°?

K4[Fe(CN)6] -Heat-> 4 KCN + FeC2 + N2?

PS: In my previous post, I had used sodium metal instead potassium metal because is more available and less expensive, and obviously you can use ferrocyanide instead ferricyanide changing the quantities

bolbol - 3-4-2015 at 19:58

How would you go on to purify the Cyanide?
I've read that it is turned into HCN under the pH of 7?

Blunotte - 3-4-2015 at 20:36

Mmm ...
This can be difficult.

in my previous post I think I made a mistake.

Since there may be residues of sodium or potassium, we can not use water to purify the reagents.
Potassium or sodium and water = boom!!!

One solution may be to use the ethyl alcohol to separate the compounds.
Potassium and sodium that can possibly be left, will melt in alcohol forming the ethoxides:

So, we will have a solution that contains Potassium ethoxide and Potassium cyanide.

From here, we can work togheter

Edit & PS: PH under 7 in a mix with alkali metals? Impossible :cool:

[Edited on 4-4-2015 by Blunotte]

bolbol - 4-4-2015 at 11:56

If the following equation is accurate
K4[Fe(CN)6] -Heat-> 4 KCN + FeC2 + N2
Then I don't think you need to worry about K/Na in water. I think by using a solution of a dilute NaOH or KOH will be sufficient enough to raise the pH efficiently enough to perform a re crystallization

Blunotte - 4-4-2015 at 13:18

You can found the reaction
K4[Fe(CN)6] → 4 KCN + FeC2 + N2
for example in Wikipedia (LINK)

But I found it in other publications.

Blunotte - 4-4-2015 at 13:25

Here you can find a better explication:

Quote:

Abstract Potassium hexacyanoferrate(II) trihydrate, K4Fe(CN)6·3H2O, was heated under controlled conditions of mass and rate in a derivatograph in the presence of oxygen. The heating was stopped at different temperatures and Mössbauer spectra and X-ray diffractograms were taken on the quenched material at room temperature. The reaction pathway was studied in this way and the advantages and drawbacks of each of the techniques are described. At different stages of the thermal process we were able to show the presence of K4Fe(CN)6,α-Fe2O3, Fe3O4, Fe3C, Fe, FeO, KFeO2,Β-FeOOH, KOCN, K2CO3 and KCN.

(LINK)

Blunotte - 8-4-2015 at 20:39

From the book in your library (Industrial Nitrogen Compounds, Geoffrey Martin & William Barbour), pag 72:

Quote:

manufacture of cyanide by Erlenmeyer's process of
fusing with metallic sodium, when the following changes take place :

K4Fe(CN)6 + 2Na = 4KCN + 2NaCN + Fe.

In this process, first worked between 1890-1900, all the cyanogen is recovered in the form of sodium or potassium cyanide, the sodium cyanide being technically of the same vahie as the potassium cyanide, provided the CN content is the same.
The process is carried out as follows:
In covered iron crucibles, some 30-40 cm. in height dehydrated potassium ferrocyanide, K4Fe(CN)6, is mixed with the proper amount of metallic sodium in the form of short bars, and the crucible is then heated over a free fire until the contents are completely fused. The molten contents of a number of these crucibles are next poured into an
iron crucible, heated by direct fire as before, but provided with a filtering arrangement made of spongy iron (obtained in the above-mentioned melting process), below which are outlet tubes. The cyanide is forced_through this filter by means of compressed air and a compressing piston, as it flows away from the filtering crucible solidifies to a white crystalline mass. It contains some cyanate, KCNO or NaCNO, along with a little alkali carbonate. Nevertheless, in practice the cyanide is always valued on the basis of the parts of NaCN are technically equivalent to ioo g. KCN, the cyanide can be placed on the market as " 100 per cent. KCN" in spite of the presence of these impurities. It is only the CN which counts, technically ; whether the CN is united with K or Na...

Mixed cyanide salt from heating ferrocyanide and sodium metal

ChemPlayer_ - 22-6-2015 at 03:51

It just so happens that this process of reacting sodium metal and ferrocyanide is my 'go to' method for making cyanide salts (the 'Erlenmeyer modification of the Rodgers process' according to the text book).

I can justify the use of expensive sodium metal for this because stoichiometrically it only takes a few grams of sodium metal to do a reasonable sized reaction run.

This also seems to be a much faster and cleaner process than heating ferrocyanide either on its own or by heating with an alkali carbonate, and doesn't require a very silly high temperature. There's no carbonate residue in the product.

I'm sure the atmospheric exposure does generate a small amount of cyanate as well, but it doesn't seem to be a large amount in practise.

Stating the obvious, make sure the ferrocyanide is completely anhydrous and finely powdered, and use good ventilation because I'd imagine there's bound to be at least a small amount of CO generated from side-reactions.

Details here: https://www.youtube.com/watch?v=kwGf4LVIb3g

Boffis - 22-6-2015 at 06:12

This is my "go to" method for cyanide production too. I have posted some details before on this site and I have discovered that flushing the stainless steel pot with methane or propane while packing alternate layers of hammered-out sodium metal and thoroughly dried sodium ferrocyanide 2-4 hr at 125 C is used. The gas is introduced through a piece of rubber tube to the bottom of the pot and when loading is complete it is simply withdrawn and the mix pressed down with a rammer. The pot is 3/4 filled and loosely covered with a heavy piece of iron plate with a small hole in it and heated until molten and then swirled or stirred through the little hole in the lid. I conduct this reaction on a larger scale so the liquid can be swirled around in the pot. I Keep it hot for a while and them pour onto a thin flexible stainless steel sheet, this chills it rapidly and simply flexing the sheet dislodges the solid cyanide. I break it into small lumps and then select the white lumps with little iron to store for later use or where solid NaCN is required, the more contaminated lumps I dissolve and use immediately along with the residue in the pot. The methane gas help reduce the amount of oxidation and reduces cyanate and CO generation though it does take fire sometimes above the hole in the cover.

Sodium ferrocyanide is easily available or can be prepared by numerous methods but most conveniently from commercial prussian blue pigment, I have posted detail of this too. I have never tried the recovery of solid NaCN from the aqueous leachate with alcohol though it sound easy enough.

The product is analysed prior to use using a silver nitrate titration in a slightly modified procedure from Vogel's Textbook of Quantitative Inorganic Analysis.

Magpie - 22-6-2015 at 07:20

Nice work, both of you. I have made KCN by reducing potassium ferrocyanide with carbon at high heat using an electric furnace. Your methods seem superior.

lysander - 12-7-2015 at 10:34

Quote: Originally posted by ChemPlayer_

Stating the obvious, make sure the ferrocyanide is completely anhydrous and finely powdered, and use good ventilation because I'd imagine there's bound to be at least a small amount of CO generated from side-reactions.

Details here: https://www.youtube.com/watch?v=kwGf4LVIb3g

Great video -- thank you for sharing that!

How does one fully dehydrate ferrocyanides? My understanding is they are not hygroscopic so is it sufficient to just mill and air-dry?

ChemPlayer_ - 12-7-2015 at 17:03

I just put the yellow trihydrate crystals into an oven at about 150C for a couple of hours, occasionally shuffling the powder around.

The water of crystallisation is lost fairly quickly and you end up with a fine sandy coloured powder which can be ground up very finely so it has the consistency of flour for the reaction.

lysander - 13-7-2015 at 07:25

Do you know what temperature range is adequate for melting and reacting the reagents?

Or is the reaction complete as soon as the mixture is molten?

Boffis - 13-7-2015 at 10:18

The "mixed" cyanide from sodium metal and anhydrous potassium ferrocyanide melts at a lower temperature than the "pure" sodium cyanide made using sodium metal and anhydrous sodium ferrocyanide. I don't have precise figures but I would estimate that the mixed cyanides melt at about the melting point of lead, say 300-350 C. With the sodium-only melt you need stronger heat and the bottom of the crucible needs to be just glowing red so I would say about 500 C. which is why I cover my sodium cyanide with a steel plate to exclude air and quench it quickly on a SSteel plate because oxidation is fairly rapid at this temperature.

The reaction is complete as soon as you have a homogenous melt. At dull red heat the sodium cyanide is mobile enough to allow much of the spongy iron to settle quickly making it possible to pour off about half the melt with only a little included iron.

ChemPlayer_ - 17-7-2015 at 05:16

Boffis is right and that's my experience too.

The mixed salt has a surprisingly low melting point and it's pretty easy to separate the iron (which sort of sticks together in clumps) from the freely liquid cyanide salt. Once you've got a nice free flowing liquid in the pot then you're done.

Given that 99% of the time I want to use alkali cyanide in aqueous solution I usually just store the solidified chunks for later dissolution in water (and filtering to remove the iron).

lysander - 19-7-2015 at 00:24

It appears that using ethanol to precipitate solids is less than 50% efficient. Is there any reason not to put the residual solution in a rotavap to recover the remaining solids? E.g., is the remainder already too hydrolized?

[Edited on 19-7-2015 by lysander]

Boffis - 19-7-2015 at 07:37

@lysander. I don't know but I think you could under vacuum. Alkali cyanide solution hydrolyse very quickly so you need to work fast and at low temperatures to minimise loss. I've never tried it I just pick out the cleanest bits of my fused cyanide and then extract to rest and use immediately for what ever process I have in mind.

skip - 19-7-2015 at 08:26

Anyone ever tried ice cold hydrocyanic acid added to chilled methanol/anhydrous sodium hydroxide. ?

Boffis - 19-7-2015 at 15:30

The problem is:- where do you get ice cold HCN or hydrocyanic acid (aqueous HCN?) from? I haven't checked it but I don't think HCN is that soluble in water at room temperature.

You could certainly make the alkali salts by passing HCN gas or adding liquid HCN to a saturated solution of NaOH or KOH in methanol or ethanol. I think this has been discussed before on this thread but again we come back to the OTC source of HCN.

skip - 19-7-2015 at 16:08

I meant ice cold hcn. Don't you know how to get that? I've made at least 8 moles of NaCN in my life maybe more. Every time I used HCN liquid that was ice cold slowly added to sat. sol. of the hydroxide in as little methanol as possible. It will precipitate right away in ice bath. The methanol was poured off and evaped off and the solid was dried. Hcn will dissolve in water, just so you know. All I made was sold to a gold refining friend.

SimpleChemist-238 - 19-7-2015 at 17:39

Quote: Originally posted by madscientist

Alternative method of production, by madscientist PREPARATION OF HYDROGEN CYANIDE FROM POTASSIUM PERMANGANATE, METHANOL, SULFURIC ACID, AQUEOUS AMMONIA, AND POTASSIUM HYDROXIDE

Notes:
-all potassium chemicals can be substituted with their sodium parallel, if mass ratios have been properly adjusted
-it is highly recommended that nbk2000 dismiss all described and inferred safety precautions

PREPARATION OF POTASSIUM FORMATE (HCOOK) AND MANGANESE FORMATE (Mn(HCOO)2):
126.4 grams of potassium permanganate (KMnO4) is added to 32 grams (approximately 40.2mL) of concentrated methanol (CH3OH):

10(CH3OH) + 8(KMnO4) --} 10(HCOOH) + 10(H2O) + 8(MnO) + 4(K2O)
10(HCOOH) + 10(H2O) + 8(MnO) + 4(K2O) --} 10(HCOOH) + 8(KOH) + 8(MnO) + 6(H2O)
10(HCOOH) + 8(KOH) + 8(MnO) + 6(H2O) --} 8(HCOOK) + 2(HCOOH) + 8(MnO) + 14(H2O)
8(HCOOK) + 2(HCOOH) + 8(MnO) + 14(H2O) --} 8(HCOOK) + Mn(HCOO)2 + 7(MnO) + 15(H2O)

Mixture is then filtered to remove the manganese oxide (MnO), and the filtered solution is then allowed to evaporate. What is left is a ratio of eight : one of potassium formate : manganese formate. The remaining crystals should weight approximately 81.77 grams if you acheived a 100% yield.

PREPARATION OF FORMIC ACID (HCOOH):
The mixture of potassium formate and manganese formate is added to concentrated sulfuric acid. That is, all 81.77 grams of the potassium formate and manganese formate crystals are added to 49 grams (26.5mL) of concentrated sulfuric acid. The remaining mixture is heated, and the vapors, which are composed of formic acid, are condensed. WARNING! FORMIC ACID IS TOXIC. PURE FORMIC ACID IS A COLORLESS FUMING LIQUID WITH A PUNGENT ODOUR; IT IRRITATES THE MUCOUS MEMBRANES AND BLISTERS THE SKIN.

8(HCOOK) + Mn(HCOO)2 + 5(H2SO4) --} 10(HCOOH) + 4(K2SO4) + MnSO4]

I thought that this over oxidized the potassium formate to potassium carbonate and water?

lysander - 7-8-2015 at 20:23

Quote: Originally posted by ChemPlayer_

This also seems to be a much faster and cleaner process than heating ferrocyanide either on its own or by heating with an alkali carbonate, and doesn't require a very silly high temperature. There's no carbonate residue in the product.

I thought I'd try the potassium ferrocyanide : sodium carbonate mix (8:2). I had to get it above 450C to melt, and even then the iron didn't clump but pretty much stayed suspended so it required extra filtration after dissolving. What is the carbonate residue left in this reaction?

Also above 500C I was getting bubbling in the crucible's hot points. Does some gas need to be cooked off?

Boffis - 8-8-2015 at 07:04

@lysander; What did you heat together? Did you use hydrated K ferrocyanide (trihydrate) and anhydrous sodium carbonate?

Then consider the likely reactions:

K4(CN)6Fe + Na2CO3 → 4KCN + NaCN + NaCNO + CO2 + Fe

K4(CN)6Fe → 4KCN + 2C + Fe + 2N

so it seem likely that carbon dioxide will be evolved when sodium carbonate is used. These equations are modifications of the ones given by Williams in his book (from the forum library). All of these equations are rather theoretical since I can also tell you from my own experience that carbon monoxide is also produced and that the yield of cyanide is only about 70% of that present in the original ferrocyanide. Using less than the theoretical amount of sodium carbonate results in much, difficult to filter, carbon being formed.

lysander - 8-8-2015 at 07:30

Was using anhydrous K-ferrocyanide. Just realized I didn't dehydrate the Na-carbonate, so indeed it must be the carbon that was suspended!

I couldn't find equations for this reaction; thanks for the reference!

I assume the excess O will almost always bind to create cyanates before it binds to the Fe?

I was trying this because I recall this being a preferred industrial method of producing cyan-salt. It's supposed to produce iron carbide as the precipitate, but now I'm wondering how this could possibly work with all that excess oxygen creating cyanates.

lysander - 8-8-2015 at 15:10

Well I ran it twice more today with anhydrous reagents. The second time I added a slight excess of Na-carbonate. Both times it came out with a lot of suspended carbon. I'm suspecting that temperature has to be more tightly controlled, perhaps along with heating and mixing rates. Also I'm probably not cooking it long enough: Half an hour after melting it still bubbles, but I ended it both times at that point.

Even so it appears reasonably practical: One pass of the solution through a cellulose filter removes the carbon. The solution also passes the acid test.

What other assays are easy to run to determine proportion of cyanides to cyanates, and K to Na, in the product?

[Edited on 8-8-2015 by lysander]

Stoichiometry

lysander - 9-8-2015 at 22:21

Quote: Originally posted by Boffis

These equations are modifications of the ones given by Williams in his book (from the forum library). All of these equations are rather theoretical since I can also tell you from my own experience that carbon monoxide is also produced and that the yield of cyanide is only about 70% of that present in the original ferrocyanide. Using less than the theoretical amount of sodium carbonate results in much, difficult to filter, carbon being formed.

I still haven't been given access to the library. What's the Williams book that details these?

And now I'm second-guessing the stoichiometry: is it supposed to be equal mols K-ferrocyanide and Na-carbonate, or 4:1 mass? Because I was using the mass ratio, but that gives 15% more mols of the K-ferrocyanide. To get equal mols the mass ratio should be 7:2 not 8:2! Unless there reaction is more complicated?

Oscilllator - 9-8-2015 at 23:09

lysander the library can be accessed at http://library.sciencemadness.org/library/index.html. It is available to everybody. The references section of the forum where articles are requested and shared is restricted access, however.

Dan Vizine - 11-8-2015 at 08:30

IMHO, You are making this unnecessarily complicated. Add H2SO4 to a concentrated soln of potassium ferricayanide containing a few grams of copper shavings*. Stir mechanically with heat in a larger than usual flask. At times the suspension foams badly. A few drops of silicone anti-foaming reagent helps. Circulate 0 C degree H20 through condenser. Put a few drops of H2SO4 in the receiver flask to lessen the explosive decomposition potential of the endothermic HCN product. Can be stored weeks in a flask with greased stopper in freezer (probably much longer). All ingredients are strictly OTC.

*Supposed to catalytically release more of the HCN according to an old patent that I have.

Exact experimental details are found in the much longer HCN thread located elsewhere in this forum under my user name.

lysander - 11-8-2015 at 11:43

Dan: I assume you mean this thread. (Which, BTW, contains this helpful link to assays I had been looking for.)

I'm trying to create cyan-salts, not HCN.

[Edited on 11-8-2015 by lysander]

jokovi4 - 11-8-2015 at 14:24

Greetings, mad scientists!
I want to share with you my experience with the preparation of KCN. First of all, I have visited this forum for some time(a couple of years maybe), but never actually posted anything. It's a very good place for sharing exotic information which a fellow home or even professional chemist sometime needs to fulfil his needs. Thank you all for keeping the forum alive.
So, let's begin with some background first. I'm last year bachelor student, currently working in a copper metal refining company. I've been using cyanides(esp KCN) in my home lab for refining gold metal from computer chips' pins, so I am aware of the potential uses and hazards of the chemical. I usually get KCN from trusted chemical companies, but if you’re not certified chemist, you can try make it yourself. The driven force of my synthesis was just pure interest and exploring the science of it. I suggest anyone who tries to synthesize any sort of cyanide to be thorough careful and to understand what is needed, why is needed, how it has to be done and what are the precautions to be taken in advance.

My experiment is done under custom made fume hood. If you are unsure of yours, do the experiment outside.
Used chemicals:
K4[Fe(CN)6].3H2O - technical grade
85% H3PO4 - technical grade
KOH - technical grade
Absolute ethanol(99.8%) - analytical grade
Bidistilled water(custom distilled)
Used apparatus:
Distillation flask with a thermometer
Non-mechanical magnetic stirrer with a teflon stir bar
Liebig's condenser
Wash bottle with a cut tail to collect the distillate

15 g of K4[Fe(CN)6].3H2O is partly dissolved in 30 ml of bistilled water. I'm using the water to cut away potential foaming during distillation(a part of the salt remains undissolved, don't mind it). A teflon magnetic stir bar and 3-4 crystals of pumice are added and the solution is heated up to 60 C. Then 28 ml of 85% H3PO4 is added and the distillation flask is connected to a Liebig's condenser and a wash bottle with a cut tail to collect the distillate(I'll talk about the tail later). The wash bottle contains 100 ml saturated solution of KOH in absolute methanol. To do this you just simply crush KOH in a pestle and mortar, add it to the ethanol, stir, add more KOH until undissolved KOH appears on the bottom(I added around 25-30 g of KOH). Then you filter the solution. The filtrate is the saturated solution which is then added to the wash bottle.
When the apparatus is all properly assembled, a green to blue change to the color(from yellowish) is almost instantly visible. That's due to the formation of Fe3(PO4)2 and K2Fe(CN)6. K3PO4 is also a product but it's dissolved in the water, so it's not visible. When the temperature of the gas phase reach 78-85 C, first drops of distillate is obtained. When they get in contact with the alcoholic solution of the KOH, the distilled HCN react with the KOH and KCN is instantly crystalized. The instant crystallisation is possible because KCN has very low solubility in ethanol. So you get a product with lowest possible losses. When the temperature of the gas phase in the distillation flask start to go up, you are finished. It took 35-40 mins in my experiment. Mind that my stirrer is somewhat powerful, it can take more.
The slurry in the wash bottle is then filtered through a Buhner and the product is collected in petri. The product is transferred to a vacuum exicator with KOH used for a drying agent. Yield is weighted after a couple of days. In my case I got 10.48 g KCN. After calculation that means that 77.39% of the CN- ions are obtained as KCN. Possible losses are from evaporated HCN through the distillation of by polymerization and what not.
The product is tested qualitative with AgNO3 solution.Wwhite sediment appears. The sediment is compared with the sediment from KCN(that I got from Aldrich) solution. It is the same. I tested the pH from the exact amouth of salts and got similar results(difference only in 0.0x). I am not insisting on the purity of the product, titration was not made, that was not my goal. This is just raw data.
I promised that I'll talk about the wash bottle. I have one with a cut tail and I prefer using it when I make distillations. With a tail that is immersed in the solution reflux can occur and some of the solution used as a receiver can be sucked in the condencer. And you DO NOT want that to happen. The increased internal pressure can damage your apparatus, break it and cause leaks. So I recommend receiving the distillate through freely falling drops. Bubbling can be dangerous and since the nature of the HCN(even if you distillate other gases it's the same) you don't want anything bad to happen. So better safety than higher yield. Trust me on this one.
You’ll get residuum after the whole process. The distillation flask’s residuum can be neutralized with H2O2 or NaClO(preferred and easily to get). The alcoholic solution can contain HCN/KCN too so it’s better to neutralize it too. Flushing after that is possible. Read your country’s procedures for disposing chemical waste. Still if you don’t care about this stuff, please at least burry the residuum in a glass jar with a good cap.
Please, read some information about the used chemicals in advance before jumping to the synthesis. HCN is highly toxic. Take all the precautions needed. Use the above synthesis method at your own risk.

PS: Sorry for my bad Englando.

[Edited on 11-8-2015 by jokovi4]

lysander - 11-8-2015 at 17:50

Interesting: There are plenty of ways to generate HCN. You get KCN by condensing it into a solution of KOH and ethanol. But isn't water the other product of that reaction, so don't you end up with water hydrating the KCN as it's formed? Or does deliquescent KCN still precipitate out of the saturated ethanol?

Dan Vizine - 11-8-2015 at 19:18

Yes, freshly precipitated alkali salts contain water and alcohol. Careful drying procedures are very important to avoid hydrolysis. And, yes, I don't belong in this thread....

Sorry.

lysander - 11-8-2015 at 20:23

Yeah, I've learned the hard way a lot of methods to not use in drying cyan-salts:

Heating above 100C. Not only do they splatter, but I also imagine they oxidize if the atmosphere is not kept inert.
Heating at less than 100C. Not sure what the reaction is, but I got tons of ammonia and the salts started turning yellow. (There was some aluminum involved though )
Drying on pretty much any metal. (Why is it that we can cook them in steel but not glass, but we can store them on glass but not most metals?)
Putting in an ambient dessicater (circulating dry air): This will remove excess moisture but can't seem to get them past deliquescense.

The old literature seems to suggest that one should first press out excess water using absorbent cellulose paper, and then vacuum dry them.

I'm also wondering if freeze-drying (i.e., freezing in combination with the vacuum) would be efficient, since AFAIK vacuum alone can supposedly take days.

It would be convenient to have a dry supply, which I assume in a sealed container has a good shelf-life, so one doesn't have to make the salts every time one needs them.

[Edited on 12-8-2015 by lysander]

Dan Vizine - 11-8-2015 at 20:33

Freeze drying ought to be ideal if you have aqueous salts. I remember being dubious about the process at first, but if you have a really good vacuum at a high throughput, it amazes me. It's a viable process! It was very facile as long as you kept the LN2 traps topped off.

I would precede this by collecting the salt in a funnel with a good rubber dam or by the classical pressing method.

jokovi4 - 11-8-2015 at 23:36

lysander, yes it still precipites. Mind that the water is really in low quantity, so it does not dilute the alchoholic solution to the point that all the KCN get hydrolized. Yes, it still do it though. That's why I mentioned in the end that the alcholohic solution still can contain HCN exactly due to the hydrolisis. You get good yield and solid phase nonetheless.
And yes, as you all mentioned, drying is very crucial. It seems that my method is working. I didn't point out that I use cellulose paper at the bottom of the petri and then put it in the exicator. It is just a habit and I've been doing this since I started to do chemistry, so I forgot to mention it- I thought everyone is doing it the same way

.
You could try good ol' fashioned furnace pressing drying at room temperature. But I don't feel the need to make my life hard and I just use vacuum drying in exicator instead.
The product is stored in custom designed dish with a very tiny whole in it, where I suck up all the air possible after closing it. Then I use parafilm to pack up the thing and store it somewhere where people doesn't get access to.

PS: One more thing: after drying the water with KOH, you can use CaO, anhydrous K2CO3 or anhydrous CaSO4 to dry the ethanol remained due to filtration. On a teoritical stand of view it is a good way to get really dry KCN.

[Edited on 12-8-2015 by jokovi4]

lysander - 12-8-2015 at 05:31

It was very facile as long as you kept the LN2 traps topped off.

You're freeze drying with LN2?! I assumed just putting the vacuum vessel in an ice bath, maybe -20C, would be adequate for deliquescent salts. Maybe stepping down to dry ice at the limit? (I don't have LN2 but I guess dousing the salts with that before closing and turning on the vacuum would be faster and easier!)

lysander - 13-8-2015 at 18:15

Add H2SO4 to a concentrated soln of potassium ferricayanide containing a few grams of copper shavings*. Stir mechanically with heat in a larger than usual flask. At times the suspension foams badly. A few drops of silicone anti-foaming reagent helps. Circulate 0 C degree H20 through condenser. Put a few drops of H2SO4 in the receiver flask to lessen the explosive decomposition potential of the endothermic HCN product.

Dan: I was thinking of giving this a try, but there's confusion from both this and the other mention of this recipe. Here you say ferricyanide, there you say ferrocyanide. What molarity sulfuric acid (on both ends)? What temperature does the reaction run at? Some reaction equations would be a nice bonus! Thanks!

Big Boss - 14-8-2015 at 11:00

<iframe sandbox width="560" height="315" src="https://www.youtube.com/embed/VUeooyhD5Xk" frameborder="0" allowfullscreen></iframe>

Dan Vizine - 14-8-2015 at 12:10

It was very facile as long as you kept the LN2 traps topped off.

I wasn't freeze-drying a sample at LN2 temps. LN2 trapped the water vapor.
This was a simple setup. A flask with a frozen aqueous solution was connected to a trap cooled in LN2 which led to the vacuum pump. Dry ice and acetone would also be fine. As I recall, the ice stayed frozen at room temp or just slightly below because of the evaporative cooling.

[Edited on 15-8-2015 by Dan Vizine]

fluorescence - 14-8-2015 at 13:37

I see there is quite much discussion on that topic. I don't want to read through all 27 pages,
at least not tonight.

So I need quite a bit of cyanide for my research. Too much I guess to really make it. At least
I don't want to destill that amounts of gaseous HCN. So for my work on d-metal cyanides I
simply purchased a bottle so I never really made it myself.

However a close friend of mine who works in a small laboratory once needed some KCN for
an experiment. And they didn't have any in the lab. So he and his team decided to test
a simple method and made some. He once told me but I'm not really sure if I remember that
correctely. I could ask him however.

So they set up a simple destillation setup and filled their flask with some Ferricyanide.
They then added sulphuric acid which does not automatically start the reaction as he says.
But if you start to heat it you can controll the amount of HCN coming off quite well.
The destilled it into a beaker with KOH solution, quite saturated I guess. You have to calculate how
much you need so there is as little KOH left as possible in the end. And then they simply added
a large amount of Ethanol. Cyanides are really poorely soluble in Ethanol. Methanol works quite
good, I use that to stabilize stuff like Cu(II)Cyanide at low temperatures but Ethanol just works
perfectely. He said the second they added Ethanol it was all full with white precipitate.
And then they filtered it and washed it with ethanol. It was pure enough to work with it.

So I guess this method is the esiest and you can do this with OTC chemicals.
I really don't recommend that. And just warn you to not do it.
That is just what I have been told. I never tried it. It should work quite well
but it's still extremely dangerous to destill large amounts of Cyanides.

lysander - 14-8-2015 at 15:12

So I need quite a bit of cyanide for my research. Too much I guess to really make it. At least
I don't want to destill that amounts of gaseous HCN. So for my work on d-metal cyanides I
simply purchased a bottle so I never really made it myself.

You can buy HCN? Where? I can't imagine any common carrier, or anybody sane, would transport that!

Dan Vizine - 14-8-2015 at 16:41

The equations are more complicated than you might imagine.

Notice my earlier comment "Exact experimental details are found in the much longer HCN thread located elsewhere in this forum under my user name."

EVERY time I led gaseous or condensed HCN directly into base soln, it turned brown-black. Conversely, every time I collected the liquid and then dripped it into base solution, it only acquired a faint color.

I didn't isolate any KCN solid. The aqueous solution was used as is.

All H2SO4, unless otherwise noted, is always assumed to be conc. H2SO4.

Never underestimate the danger of strongly endothermic cmpds. Several drops of H2SO4 in the receiver is essential.

So are greased joints, Keck clamps and most importantly, substantial tubing connecting your reactor to the great outdoors.
If you aren't a professional chemist, I'd suggest doing it outside.

BTW, ferrocyanide, wherever I said it, is wrong. Ferricyanide is usually used.

[Edited on 15-8-2015 by Dan Vizine]

fluorescence - 14-8-2015 at 23:34

Oh no I didn't buy HCN I bought KCN. I try to keep the amount of HCN liberated from experiments as low as possible. HCN is the last thing I want in the lab.

And for the ferro/ferricyanide thing, one person once told me "red = dead" so I guess that's easier to remember.

lysander - 15-8-2015 at 18:58

The equations are more complicated than you might imagine.

Here's a balanced equation with the ferricyanide:

2 K3Fe(CN)6 + 6 H2SO4 = 12 HCN + 3 K2SO4 + Fe2(SO4)3

However, researching this further it seems much more common to find the ferrocyanide mentioned in the H2SO4 distillation for HCN, in which case the primary reaction is one of the following:

3 K4[Fe(CN)6] + 6 H2SO4 = 12 HCN + Fe2[Fe(CN)6] + 6 K2SO4
2 K4[Fe(CN)6] + 3 H2SO4 = 6 HCN + K2Fe[Fe(CN)6] + 3 K2SO4

(The distinctions between the two make reference to iron ion characteristics with which I am not familiar.)

But like Dan said, it's probably not that simple. For one thing, there's a bunch of water (ideally, from what I've read, 2 parts water to 1 part sulfuric acid) on the left-hand side that I wouldn't expect to stay out of the reactions. Also note that this does not produce pure HCN, because of course some of the water ends up in the distillate. (For practically anhydrous HCN I saw one reference suggest dropping 50% H2SO4 onto KCN.)

Any more accurate descriptions of either reaction would be appreciated.

I'd like to try one of these since HCN is such a useful precursor, but not before I understand it!

[Edited on 16-8-2015 by lysander]

fluorescence - 16-8-2015 at 03:00

I'm not sure, I've heard that you get less HCN gas than expected. Maybe it need further heating or there are
byproducts but they didn't really get that much out of quite some ferricyanide. That's something one has
to try under precise measurement and than calculate how much yield he got. But I think this is still the best way
to do it. It's safe to handle since the reaction only starts when it's heated and you can destill it directely into
the KOH with some washing bottles afterwards. So you won't get into contact with the HCN if you do everything
right. The other stuff I read here seems difficult like getting Permanganates and so on.
You need three easily accessable chemicals for that reaction.

The question is, can you smell cyanide ? I've tested it quite often and there is always a bit of cyanide smell in my lab
when I'm working on cyanides but if you don't have any KCN or NaCN laying around where you could smell that characteristic odour, I wouldn't start a destillation where I'm not sure if I could even sense any leaking gas.

[Edited on 16-8-2015 by fluorescence]

lysander - 16-8-2015 at 08:00

The question is, can you smell cyanide ? I've tested it quite often and there is always a bit of cyanide smell in my lab
when I'm working on cyanides but if you don't have any KCN or NaCN laying around where you could smell that characteristic odour, I wouldn't start a destillation where I'm not sure if I could even sense any leaking gas.

Yeah, that sounds like a good safety measure. I've never had HCN outside of a strong vapor hood while wearing a face mask, so I don't know if I can smell it. I do note a pungent, almost nauseating odor from wet cyan salts. Do those smell the same as HCN?

[Edited on 16-8-2015 by lysander]

fluorescence - 16-8-2015 at 08:12

We had that discussion on Versuchschemie some time ago. Back then when I worked with Cyanides for the first time
at the university. I asked whether there was a safe way to test if you can smell it and we came up with the idea
to smell on an open bottle of KCN or NaCN. So don't put your nose on the bottle but rather fan a bit with your hand.
Cyanide Salts react with moisture in the air to form HCN. If you have a bottle where there isn't that much cyanide left there is quite an amount of air and if you keep that bottle closed for some time and then open it up you can clearely smell
a strong odour of HCN. I've tested this with a small sample of very dry KCN and was able smell it.

The KCN that I have is quite wet since the bottle is very old. It's quite useful since the crystals are a bit bigger and you don't have any dusts it's like handling any other hygroscopic potassium salt. But due to the water there is always a strong smell of HCN when you open that bottle.

So if you have any cyanide salt you could smell the air that comes from the bottle if you do this very carefully.
I think it's the safest way to really test it and better than just making HCN gas.

For people who say it smells like almonds I can't really relate that. What is ment by almonds is rather green almonds not the ones you can buy. The smell is very characteristic and I don't remember anything that would smell like HCN.
But I've heard that you can even smell small quantities of cyanide in air. Like with H2S. So smelling it doesn't mean that you'll drop dead in like a second.

But be careful !

lysander - 16-8-2015 at 10:04

Notice my earlier comment "Exact experimental details are found in the much longer HCN thread located elsewhere in this forum under my user name."

EVERY time I led gaseous or condensed HCN directly into base soln, it turned brown-black. Conversely, every time I collected the liquid and then dripped it into base solution, it only acquired a faint color.

I think I have failed to find that thread, even after attempting to review all posts with your username! Could you provide a link?

FYI, here is one possible explanation for your HCN turning black:

Quote:

A polymer of hydrogen cyanide is slowly produced when an aqueous solution of the latter is kept in presence of alkali carbonate or cyanide. Under these conditions the liquid turns brown, and a black mass separates after some days.... [P]robably the dinitrile of aminomalonic acid, NH2CH(CN)2.

fluorescence - 16-8-2015 at 23:57

I just tried that Ferricyanide method on a very small scale.
I've added a bit of conc. sulphuric acid in a test tube to
the red ferricyanide and left it over night. As you can see nothing
changed, so those two don't react if they aren't heated.

I then placed the test tube for about 5 minutes into a beaker
with about 85°C hot water. As you can see the color changed
from orange-brown to a pink-purple.

I then took it out and heated it very gently and carefully with
a heat gun that was set to be somewhere between 200 and 300°C
The mixture became nearly colorless so the ferricyanide must have
reacted. As I heated the test tube filled with a gas, you can see that
marked with a red arrow.

Since sulphuric acid and water form an azeotrope and I wasn't heating it for the boiling point of the Acid it should be HCN gas, I guess.
At least this method seems to work and does not produce toxic gases
the second you add the acid. So the destillation setup can be prepared with all the time it needd and you don't have to rush there.

Note: The gas can be some water, too. I'm not sure about that.

[Edited on 17-8-2015 by fluorescence]

nux vomica - 18-8-2015 at 15:53

We had that discussion on Versuchschemie some time ago. Back then when I worked with Cyanides for the first time
at the university. I asked whether there was a safe way to test if you can smell it and we came up with the idea
to smell on an open bottle of KCN or NaCN. So don't put your nose on the bottle but rather fan a bit with your hand.
Cyanide Salts react with moisture in the air to form HCN. If you have a bottle where there isn't that much cyanide left there is quite an amount of air and if you keep that bottle closed for some time and then open it up you can clearely smell
a strong odour of HCN. I've tested this with a small sample of very dry KCN and was able smell it.

The KCN that I have is quite wet since the bottle is very old. It's quite useful since the crystals are a bit bigger and you don't have any dusts it's like handling any other hygroscopic potassium salt. But due to the water there is always a strong smell of HCN when you open that bottle.

So if you have any cyanide salt you could smell the air that comes from the bottle if you do this very carefully.
I think it's the safest way to really test it and better than just making HCN gas.

For people who say it smells like almonds I can't really relate that. What is ment by almonds is rather green almonds not the ones you can buy. The smell is very characteristic and I don't remember anything that would smell like HCN.
But I've heard that you can even smell small quantities of cyanide in air. Like with H2S. So smelling it doesn't mean that you'll drop dead in like a second.

But be careful !

You could just stand outside a electroplating shop they always smell strongly of the zinc cyanide solutions they use.

careysub - 18-8-2015 at 16:23

I just tried that Ferricyanide method on a very small scale.
...
I then took it out and heated it very gently and carefully with
a heat gun that was set to be somewhere between 200 and 300°C
The mixture became nearly colorless so the ferricyanide must have
reacted. As I heated the test tube filled with a gas, you can see that
marked with a red arrow.

Since sulphuric acid and water form an azeotrope and I wasn't heating it for the boiling point of the Acid it should be HCN gas, I guess.
At least this method seems to work and does not produce toxic gases
the second you add the acid. So the destillation setup can be prepared with all the time it needd and you don't have to rush there.

Note: The gas can be some water, too. I'm not sure about that.

How much is a "very small scale"? The lethal dose of HCN, inhaled all at once, is 25 mg and will kill you immediately. If you can see the HCN as a gas you are making too much.

HCN is detectable at about 1 mg/M^3 (but individuals vary, the minimum level is usually given as 0.7 mg/M^3).

It takes 10 minutes of breathing for 200 mg/M^3 to become deadly. Even at 1000 mg/M^3 exactly one normal resting breath (~0.5 L) is harmless (actually ten times this concentration is still harmless for one single breath, but I would rather have a safety factor of 50 than 5). So you have a large safety margin to see what it smells like if you approach cautiously from below.

If you can't place a firm upper bound on how much HCN you have, you shouldn't be trying this.

careysub - 18-8-2015 at 16:28

...I asked whether there was a safe way to test if you can smell it and we came up with the idea
to smell on an open bottle of KCN or NaCN. So don't put your nose on the bottle but rather fan a bit with your hand.
Cyanide Salts react with moisture in the air to form HCN. If you have a bottle where there isn't that much cyanide left there is quite an amount of air and if you keep that bottle closed for some time and then open it up you can clearely smell
a strong odour of HCN. I've tested this with a small sample of very dry KCN and was able smell it.

The KCN that I have is quite wet since the bottle is very old. It's quite useful since the crystals are a bit bigger and you don't have any dusts it's like handling any other hygroscopic potassium salt. But due to the water there is always a strong smell of HCN when you open that bottle.

So if you have any cyanide salt you could smell the air that comes from the bottle if you do this very carefully.
I think it's the safest way to really test it and better than just making HCN gas.

For people who say it smells like almonds I can't really relate that. What is ment by almonds is rather green almonds not the ones you can buy. The smell is very characteristic and I don't remember anything that would smell like HCN.
But I've heard that you can even smell small quantities of cyanide in air. Like with H2S. So smelling it doesn't mean that you'll drop dead in like a second.

But be careful !

Indeed, be careful!

The general procedure, slowly approaching a detectable concentration from a situation of high dilution, is sound - but I do not buy that the bottle of cyanide salts is in any way safer than making a small, known amount of HCN. You have no idea how much HCN vapor might be in the bottle.

Right - no one knows what "bitter almonds" smells like, really. It is not a item most people ever come in contact with.

HCN via acidification & heating of aq. K3Fe(CN)6

lysander - 28-8-2015 at 16:52

Following Dan Vizine's notes, backed up by mentions I've since found in texts, I've tried this reaction twice, and it's not working:

1. Saturate 2 parts distilled water with K3Fe(CN)6, and leave stirrer running
2. Add 1 part H2SO4
3. Connect to condenser

At the instant of adding the H2SO4 some HCN vapor forms (detectable by smell before connecting to condensation apparatus).

However, after that it appears that nothing happens. Each run I increased heat slowly over half an hour until the mixture was just below 100C, but all I have gotten is a tiny amount of water condensate with a hint of HCN.

Dan suggested including a gram of copper shavings as a catalyst. I tried that on the second attempt but they ultimately reacted (leaving me with green acidic sludge instead of blue acidic sludge).

What could I be missing?

The only questionable part is the use of ferricyanide: more of the published mentions of this reaction cite ferrocyanide. But Dan insists ferricyanide is typically used, and the two are so easily confused/typo'd I'm inclined to believe him. Also since it's a dissolved salt I'm not expecting it to make a big difference since the anion is the same. Balanced equations suggest one of the following:

2 K3Fe(CN)6 + 6 H2SO4 = 12 HCN + 3 K2SO4 + Fe2(SO4)3
or
3 K4Fe(CN)6 + 6 H2SO4 = 12 HCN + 6 K2SO4 + Fe2[Fe(CN)6]
4 K4Fe(CN)6 + 6 H2SO4 = 12 HCN + 6 K2SO4 + 2 K2Fe[Fe(CN)6]

[Edited on 29-8-2015 by lysander]

cyanureeves - 28-8-2015 at 17:24

i have used ferrocyanide and sulfuric acid but just bubbled the gas expelled straight into cold potassium hydroxide solution.not much condensate was made but hydrogen cyanide sure as hell went into my solution.i used the solution to gold plate and it all turned into ammonia eventually.you are producing HCN gas i'm sure but i'm guessing you want to liquify the gas?

lysander - 28-8-2015 at 18:14

Yes, I'm trying to condense (and store in freezer) as feedstock for later reactions.

What are the specifics of the reaction you used to generate the gas? Did you add heat? Did you add water, or just mix H2SO4 with K4Fe(CN)6 trihydrate?

cyanureeves - 28-8-2015 at 18:31

i did add heat and probably too much and also used water on both flasks except i had ice on the receiving flask and hydroxide.i used the yellow crystal ferrocyanide not my ferricyanide because it cost more.i think you will produce HCN with or without heat. i think this method of making cyanide is way more inferior to the method shown in that youtube video shared in the cyanide thread here.potassium/ sodium cyanide is made and can be turned aqueous as needed just like you are trying to make.i think you have already succeeded in making something dangerous so be safer now and take advantage of this wonderful video while it lasts.i did not use stoichiometric amounts as the folk here at first but did on all other runs.the cyanide thread here has all that and is where i got it from.i will never ever do this method again.oh! i remember why i stopped using this method.it is so similar to making ammonia gas and if you let up on the heat it can create suck back pressure.as i said,i bubbled the gas into a liquid but i know you are not.my reaction flask exploded when i was making ammonium hydroxide.

[Edited on 8-29-2015 by cyanureeves]

lysander - 28-8-2015 at 20:04

I don't want this for cyan salts, although I agree that for that purpose heating sodium with ferrocyanide as shown in that video is tough to beat! I can certainly go that route, and then hit the cyan salts with H2SO4 to get (bonus!) anhydrous HCN.

But given the apparent popularity of the approach I'm attempting here I'm intent on figuring out what's going wrong, because half of this is about proving/verifying/maintaining my proficiency.

The addition of H2SO4 to the solution in this reaction generates plenty of heat -- I measured the mix hitting 70C. And right there is a reasonable amount of HCN. But something is stopping HCN production pretty quickly thereafter. I'm wondering if I have some polymerization going on, perhaps due to contaminants. Certainly by the time I let the mix cool it has a sludge-like consistency. (Fingers crossed than an orgo expert will weigh in!)

Recap on HCN from ferrocyanide

lysander - 29-8-2015 at 10:08

I found this old thread: Distilling HCN from potassium ferrocyanide... which contains a copy of Potassium Ferrocyanide Decomposition Using Sulfuric Acid - HCN generation.pdf, which gives some great reaction equations and empirical analysis for ferrocyanide:

H4Fe(CN)6 = Fe(CN)2 + 4HCN and
Fe(CN)2 +H2SO4 = FeSO4 + 2HCN

It specifies the sulfuric acid be diluted with water to at least a 10:1 molar ratio. It is unclear about the reaction temperature (boiling?) but suggests full evolution of HCN takes about 2 hours, and gives the final equation:

K4Fe(CN)6 + 5(H2SO4,10H2O) = 4KHSO4 + FeSO4 + 6HCN + 50H20
... so there's a lot of work left to get the water out! For dehydration this patent provides useful information on distillation. (The alternative method of producing anhydrous HCN from cyan salts is covered in this patent.)

Brauer's Handbook of Preparative Inorganic Chemistry (p.659) prescribes the following preparation:

200g potassium ferrocyanide trihydrate
Cold mixture of 160g sulfuric acid and 250g water
"Gentle" heat applied
Gas passed through three CaCl2 drying tubes immersed in 40C water bath before hitting Liebig condenser
Buffer condensate with two drops of hydrochloric acid for storage

In both these cases ferrocyanide is the prescribed reagent, and sensitivity to the dilution of the sulfuric acid is noted.

And in both cases required heat is unclear. (And presumably one would want to keep it as low as possible to minimize water evaporation.)

[Edited on 29-8-2015 by lysander]

[Edited on 30-8-2015 by lysander]

papaya - 29-8-2015 at 15:02

I'm sorry if this was asked before, what will happen if you drop a nitrile glove into a molten sodium hydroxide(or even boiling water solution), what will happen with -CN groups? Is there any chance that some way NaCN forms ?

[Edited on 29-8-2015 by papaya]

Hawkguy - 29-8-2015 at 15:46

Quote: Originally posted by papaya

I'm sorry if this was asked before, what will happen if you drop a nitrile glove into a molten sodium hydroxide(or even boiling water solution), what will happen with -CN groups? Is there any chance that some way NaCN forms ?

[Edited on 29-8-2015 by papaya]

Tried it today smelled like shit. I tried adding Ferrous Sulfate to the dissolved product, and got a blue precipitate. Likely Ferrous Carbonate, and not the Ferrocyanide.

Also tried heating Potassium Nitrate/ Charcoal at about 900 degrees C and got the same result. Hmm.

papaya - 29-8-2015 at 15:56

You should have added gold into it. But seriously, anyone tried what I asked above? I mean to analyze the products..

[Edited on 29-8-2015 by papaya]

Hawkguy - 29-8-2015 at 17:43

Like add Acid and distil? I'll try that once the power comes back on. Once the distillate is collected, the Prussian blue test will be 100% accurate.

Not going to let this practical beat me!

lysander - 13-9-2015 at 18:36

My previous two attempts at evolving HCN from ferricyanide failed, I have concluded, because I diluted the cyanide in the full amount of water first and then (while that was mixing) added the full dose of concentrated H2SO4 all at once. That produced a puff of HCN, but, I surmise, then polymerized enough in the solution that most further evolved HCN bonded to the polymers instead of evaporating, so I only got a few mL of HCN out of the process..

After my third attempt today I think that for the first time in a decade I'm going to have nightmares about failing Orgo Lab:

This time I followed Ledgard's instructions precisely, with the sole exception of using a hotplate and Florence flask instead of a mantel. (However, given that I was running a strong stirrer the whole time I don't believe that difference was material. Just to be sure, I regularly measured and noted the exterior temperature of the lower half of the flask was always higher than that shown by the thermometer in the flask.)

54g K4Fe(CN)6 trihydrate (=47g anhydrous) put in flask
Added 50mL distilled water and began stirrer
Added 75g (41mL) H2SO4 to 100mL distilled water. Temperature measured 60C.
Slowly added dilute to flask. Solution gradually turned light blue
Added heat. Reaction is supposed to start and run at 60C. Somewhat beyond that temperature the solution gradually turned darker, but absolutely no gas evolved.
Allowed to run for 2 hours at up to 80C but no vapor made it through the Kjeldahl bulb.
Exasperated, allowed solution to run up past 90C at which point condensate formed at the mouth of the Liebig condenser.
1 hour later shut down.

The collection flask, sitting in the ice bath that's also feeding the condenser, and which I had prepped with a few mL of H2SO4, yielded a grand total of 15mL of two immiscible fluids in roughly equal portions. There was only a vague odor of HCN, and it was overpowered by a far more pungent rubber-like odor that almost induced gagging. The lighter fluid was mostly water, I assume, because it mostly froze at 0F. I have no idea what was mixed into it, or what the denser immiscible fluid is. Instead of a dark prussian blue the reagents had turned a more turquoise color you can see in the following photo. Any guesses as to what chemicals were actually produced? When I cut the mix with sodium hypochlorite it reacted vigorously, and when I dumped it from the flask the fumes almost knocked me over.

Could anyone please tell me what I might be missing here? Everything I've read suggests the majority of HCN should evolve out over a few hours at 60C.

This time I used almost all different glass from the first two attempts, and I switched from ferri to ferrocyanide. Given the heat generated by mixing the H2SO4 with the water I don't doubt its adequacy. I don't know what I could be doing to kill this reaction!

[Edited on 14-9-2015 by lysander]

HCN failure #4

lysander - 14-9-2015 at 18:49

For my fourth attempt I tried the Brauer/Vizine formula, which essentially doubles the amount of ferrocyanide but still uses a 25% dilution of H2SO4.

Combine 100mL distilled water with 100mL H2SO4. This reaction heats the dilute to 100C. Therefore wait for it to cool back to room temperature
Add 211g K4FE(CN)6 trihydrate to 1 liter boiling flask.
Add 200mL water and begin stirring. (This requires a more powerful stirrer).
Add the cooled 200mL H2SO4 dilute to boiling flask.
Heat solution to 60C.
Run for four hours. Nothing evolved!
Raised heat to 80C. Managed to get 15mL of condensate in cooled collection flask that smells of HCN, but also of something more strong and pungent.
Hang head in disappointment.

Here's a photo of the apparatus running after about an hour:

The color gets perhaps a little darker by the end, as seen in this video taken right before shutdown:

http://youtu.be/dTFK_o-D_JI

(Compare that color to the two runs where I dropped the concentrated H2SO4 into the ferricyanide solution:
http://youtu.be/SqLJU862yMQ

Questions:

A. Does the color indicate any failure? What is the expected progression of color over the course of the reaction?

B. Is HCN miscible with H2SO4? (If not that would explain the two layers I'm getting in what little I collect.)

[Edited on 15-9-2015 by lysander]

kmno4 - 16-9-2015 at 10:56

Heat solution to 60C.

The mixture should be heated untill it starts boiling.
The temperature is then increasing from ~60 C to ~100 C as reaction goes on.
At relatively high concentrations (total), reaction ends at FeK2[Fe(CN)6] step (larger amount of H2SO4 will not help). Further conversion (to FeSO4) is terribly slow. Great dilution and boiling expels all HCN but with large amounts of water. You can add some CuCl (or even CuSO4) to the reaction mixure: it is converted to CuCN.
It has so small solubility that FeK2[Fe(CN)6] is (slowly, on boiling) converted to CuCN (-> HCN). In this way all CN can be removed as HCN.

The purgent odour is possibly SO2 and/or HCOOH : it indicates too concentrated H2SO4. Better use 20-30 % solution (or H3PO4).
The paper you mentioned is disscused on previous pages - it turns out that it gives information that high concentration of H2SO4 is not good and nothing more. From preparative point of view t is useless.
There are a lot of missinformation and lies in this topic, I understand that is may be hard to filter them off.
I conducted this reaction many times, you may read my posts (starting from page 4) if you wish.
I decided not to write any posts here: everything has been said and written. But sometimes it is worth to hepl someone who is really interested. I think it is the case.

S.C. Wack - 16-9-2015 at 17:56

I followed Ledgard's instructions

There's something ugly about that phrase for some reason. Like this quote, considering that this member's last login came less than 2 weeks later:

Quote: Originally posted by mbrown3391

I am going to attempt this synthesis

BTW at the end of that article I posted an abstract of a while back, the 1912 Williams CuCl article, well there were comments from being a lecture I guess, and there was some agreement on ferricyanide giving 85% with the standard treatment.

lysander - 16-9-2015 at 19:21

Quote: Originally posted by S.C. Wack

I followed Ledgard's instructions

There's something ugly about that phrase for some reason.

Indeed; I should have been more clear: The structure of the process is well-documented across many references. What varies are the concentration of H2SO4 (from 20-26%, with theoretical maximum of 33%), the final dilution of ferrocyanide (from 25%-60%), rate of dilution (instantaneous to very gradual), the temperatures indicated (from 50-100C), the process duration (from 2 to 4 hours), and the catalyst (if any). For #3 I was trying Ledgard's exact values for each parameter, but they are within the ranges established by the other 5 references I made notes on.

lysander - 16-9-2015 at 19:35

Quote: Originally posted by kmno4