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Author: Subject: Preparation of cyanides
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[*] posted on 31-5-2005 at 16:09


Well Polverone, that is just plain delicious!:D Buy the way, after you solvate your raw product do you filter it before adding to alcohol? I know it may seem to be a smartass question but I remeber the cyanurate process involved filtering through a little diatamaceous earth. Did I even spell that right?:o



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[*] posted on 31-5-2005 at 17:21


Yes, the liquid should of course be filtered. Coffee filters will do okay but a layer of diatomaceous earth will filter out even the finest charcoal particles. Denatured alcohol definitely works for the precipitation, and since I'm in the US my denatured alcohol is more than half MeOH. I think ethanol should work too. I've also tried isopropanol and acetone to force the precipitation, but they are immiscible with the cyanide solution and no precipitation takes place.

Also, as I mentioned in another thread, I discovered more recently from <A HREF="http://www.sciencemadness.org/library/books/industrial_nitrogen_compounds_and_explosives.pdf"><i>Industrial Nitrogen Compounds and Explosives</i></A> that the high-temperature reduction of cyanates was at one time used as a patented industrial source of cyanides:

Quote:
<b>Siepermann's Process</b> (see English Patents 13,697 of 1889, 9,350 and 9,351 of 1900).

One part of sodium carbonate and two parts of charcoal (that is, sufficient charcoal to keep the mass from fusing during the process) is heated to dark redness in the upper part of a vertical iron tube while a current of ammonia gas is sent through the mixture. Potassium cyanate, KCNO, is formed thus :

K2CO3 + NH3 = KCNO + KOH + H2O.

The mixture is then allowed to fall to the bottom of the tube, where it is heated to bright redness. The cyanate is decomposed with formation of cyanide:

KCNO + C = KCN + CO.

The final product is thrown into air-tight vessels, cooled, lixiviated with water, the solution being evaporated in vacuo until the KCN crystallises out. <b>KCN is soluble with difficulty in the presence of much KOH or K2CO3, and crystallises out before these salts in the form of anhydrous crystals.</b> As first made the KCN was a damp deliquescent mass, which had to be fused with the product of the ferrocyanide process. The working of the process is difficult. It has been worked at Stassfurt since 1892.

<b>Bielby Process</b> (see English Patent, 4,820 of 1891). The principle is much the same as the Siepermann Process, but differs in important details. Much less carbon is used, so that at the end only slight excess remains. The charcoal is added gradually during the operation, so that the material is always present as a molten liquid through which the ammonia gas is forced under a slight pressure, when the following action takes place:

K2CO3 + 4C + 2NH3 = 2KCN + 3CO + 3H2.

The final molten product is filtered from the small excess of unchanged charcoal, and thus a white saleable product is directly obtained without the difficulties of lixiviation. However, since the melting point of the pure potassium carbonate is inconveniently high (about 890 C), ready-made cyanide is added to it in order to reduce the temperature of fusion.

The Beilby process has been worked since 1892 by the Cassel Gold Extracting Co. at Glasgow, has achieved remarkable success. In 1899 Beilby's process was estimated to supply fully 50 per cent of the world's output of high-strength cyanide.


Despite the mix-up with sodium and potassium carbonates near the beginning of the text, the description offers an interesting method of forming pure cyanide without the danger of working with HCN: evaporating KCN solutions containing excess K2CO3 or KOH <i>in vacuo</i> will cause the KCN to precipitate out as pure crystals before the contaminants. Since home experimenters are concerned more with convenience than with cost and throughput, it is of course more convenient for us to form the cyanate from urea or cyanuric acid than gaseous NH3, but the final reduction should work the same either way.

Edit: these tidbits of information nicely illustrate some of the WWW's limitations. The above text says that the Beilby cyanide process once provided half of the world's cyanide demand, yet there are only two unique references to it on the whole web, one from the Sciencemadness Library and another from the Digital Library of India.

[Edited on 6-1-2005 by Polverone]




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[*] posted on 14-6-2005 at 08:18


I just got two nice small crucibles (30ml capacity, easily heated to red glow with a bunsen burner), one made of iron, the other one made of nickel.
I purchased them primarily for small- scale cyanide production (and also for molten salt electrolytic processes).
Which one would be better for cyanide production? I'd use the iron one since everyone here uses iron.

Your method for analyzing the cyanide product (test for cyanate) is interesting, Polverone. An easy test for cyanate was something I've been looking for.
The precipitation of crystalline cyanide with alcohol is also an enormous improvement.

Would it be more convenient to produce NaCN or KCN? I'm thinking about the solubility in alcohol (Ethanol), which should be as low as possible.
Does anyone know which one has lower solubility in ethanol?

EDIT: I found out: KCN dissolves in ethanol only 4,5g per liter! Perfect for this application.
NaCN has "low solubility" in ethanol- it's no further specified what this means.
Maybe someone has got reliable data on NaCN solubility in ethanol?


[Edited on 14-6-2005 by garage chemist]
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[*] posted on 14-6-2005 at 23:25


The iron crucible should work fine. Remember to keep it covered from air while you are heating it, as much as possible. I always used old food cans rather than any proper crucibles, and by the end of the reaction the cans were always very embrittled and thinned near the bottom. It may be simply because this is where the heat is applied more strongly; I don't know if the vessel contents contribute to the deterioration of the metal.

I have produced mostly NaCN. The first time I did it, I didn't heat it long/strong enough and got considerable cyanate along with my cyanide, as evidenced by the ammonia smell of my warm aqueous extract. Keep in mind that aqueous cyanide solutions too can hydrolyze to form ammonia (and formate), but this is considerably slower than with the cyanate. So I would be suspicious of your cyanide extract if it immediately smells like ammonia, but not so suspicious if it smells like ammonia after being kept warm for an extended period of time. This degradation, as well as interaction with atmospheric CO2, makes me prefer the precipitation with alcohol over plain evaporation to dryness.

For many purposes, some residual cyanate and carbonate in your cyanide will not matter very much, but it does complicate measurements when you are unsure of purity.

Empty gas cylinders look like they would be almost perfect makeshift crucibles -- CO2 cartridges for the small scale, or disposable propane cylinders for the larger scale. Their narrow necks and larger bodies should easily exclude air.

In the future, I would like to try compressing the powder into the vessel before heating it. It's possible that I could get better heat transfer and a larger batch size that way. Another variation that I would like to try is using a hydroxide, instead of carbonate, in the initial mixture, since this too should lead to easier melting.




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[*] posted on 15-6-2005 at 01:20


I'm far from an expert in this reaction but my understanding is when formed in this way molten cyanides tend to dissolve iron metal from the container to produce ferrocyanides. Maybe a graphite or clay slurry bound with a little sodium silicate coating the inside of the container would help?

Cyanates tend to hydrolyse very easily, under the circumstances water produced by use of hydroxide might cause problems.
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[*] posted on 15-6-2005 at 02:04


Yesterday I tried it out with 6,9g K2CO3, 6,2g urea and 1,6g Charcoal.

I first dissolved both the urea and K2CO3 in water, boiled this down to dryness and heated it until no more ammonia was evolved (now I see that this was no good idea, and I likely have considerable formiate contamination in my product because of hydrolysis).

Reduction was carried out in the iron crucible. I first melted the cyanate and then stirred in the charcoal, this was very convenient.
CO evolution was evident at red glow, since when I lifted the lid to stir it a bit, there was a quick bluish flame and the mix was evolving gas streams.

After cooling and extraction with water, I saw that my charcoal was way too coarse and a lot was left behind.
However, the extract strongly smelled like almond and I didn't smell ammonia.

I'll do another batch and melt the urea + carbonate dry instead of first dissolving in water. I'll also use finer charcoal powder.
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[*] posted on 22-8-2005 at 02:40


I read this CN-Thread with interest. Some Years ago, I nearly killed myself by heating a very small amount of ferrocyanide with accumulator-acid (H2SO4, 37%) in a testtube on the balcony. So I made my first experience, how damned toxic this shit is...

But it's still fascinating. Things that are forbidden by law, are always fascinating.;)

The best method to get real pure CN ist to neutralize a solution of NaOH or KOH with the right amount of HCN, (as already described) there is no other way.

But there are different methods to produce HCN. The easiest way ist to heat some ferrocyanide in dilluted H2SO4, but I wonder if prussian blue will work for this too.

In a painter-shop you can order kg's of pigmented prussian blue (pure! also called as milori blue) = Fe4(FeCN6)3 which decomposes in contact with strong acids.
I'm not sure if HCN will be produced by mixing and heating it with dilluted H2SO4, cause i found no information on this on the web, but I believe so.

You also can produce Calciumcyanide (ca. 40% pure) by heating Calciumcyanamide with Calciumcarbide and NaCl. This will work without arc furnace too - lowers only the yield. This "black cyanide process" ist described on this page: http://pubs.nrc-cnrc.gc.ca/cmq/29941-3.html

It's easily possible to produce amounts of blackcyanide, that can be turned into pure cyanide by mixing with acid and bubbling the gas into an -OH solution. Unfortunately it's quite dangerous, but can be done safe if you know how.



To produce temperatures up to 1800°C you can use a burner like this:
http://caravaning-shop.ch/oscommerce-2.2ms2/catalog/images/3...

if the mixture is given in a quartz tube, it can be reacted by heating than without having contact with the surrounding air.

Calciumcyanide is cheap and available as an black prilled fertilizer (called Kalkstickstoff in GER)

A way to form Calciumcyanamide
If somebody has N2 in flasks, just let it flow over CaC2 in a tube and heat up to 1000°C. It will react: CaC2 + N2 --> CaCN2





[Edited on 22-8-2005 by Saugi]
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[*] posted on 22-8-2005 at 04:04


The Calciumcyanamide process is interesting, since this substance is available as "Kalkstickstoff" easily where I live.

It is made by reaction of calcium carbide with N2: CaC2 + N2 ---> CaCN2 + C (this doesn't produce cyanide, but cyanamide! Seems like a typo in your above post).
The C isn't removed from the commercial product, the black mass is just prilled and sold as fertilizer.

This fertilizer therefore already presents an intimate mixture of CaCN2 and C. We only need to add NaCl and heat it.
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[*] posted on 22-8-2005 at 15:25


You're right, sorry for my mistake! I corrected it.

And I forgot to write that "Kalkstickstoff" is industrial grade Calciumcyanamide. It's an important info, cause not everybody will know this.

If one of you crazy guys has tested the cyanide synthesis with CaCN2 + NaCl - please let me know the results!

I'm sure this will work, but it depends on the correct amounts. If I had the time, I would make the test for my own. But be aware, the product and even it's fine dust will be evil toxic!
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[*] posted on 7-9-2005 at 09:08


I think that the only way to obtain pure (>98%) cyjanides is introducing mixture HCN+H2O to akoholic solution KOH or NaOH. I have made many grams of KCN using this methode (more than 1kg :o)
Mixture HCN/H2O was obtained by heating K4[Fe(CN)6]+H2O+H2SO4 or H3PO4. Both acids work good and concentration(%) has no special meaning: 30%-60% is ok.
Reaction is:
2K4[Fe(CN)6]+3H2SO4 -> 6HCN + FeK2[Fe(CN)6]+3K2SO4
With a simple distilling aparaturus, during haeting, at about 50*C (temperature of vapors) the mixture HCN/H2O starts to evolute, and after condesation it is introduced into KOH/C2H5OH solution.
KCN starts to precipitate,the solution is getting warm, but there is no need to to cool it. This mixture MUST be continual stirrig by magnetic stirrer - in another case a "cake" is collecting at the surface and there is no full reaction between HCN and KOH - it is a little dangerous.
The distillation is interputted at about 95*C - just too many water is then evoluted.
KCN is filtered, washed 2-3 times and dried in stainless steal pot, at the gas burner.
Yield is about 80%, counting at given theoretical equation, very pure KCN. Do not dry it in the air, it is hygroscopic. I used about 100g K4[Fe(CN)6]*3H2O per one run.
In distillation flask there is a lot of green "shit" - it is FeK2[Fe(CN)6] and it is useless, not dissolvig in acids and easly oxidicing itself.
By reduction KOCN or NaOCN is very hard to obtain pure cyanides. In the best case you will have something what is a poison, being mixture of KOCN, KCN and K2CO3...
Read http://www.showa-pk.co.jp/information/cyanate.html
Also thermal decomposition of K4[Fe(CN)6] is not good, because KCN is very easily oxidate by atmospheric O2, yielding KOCN.
DO NOT TRY THIS If you are not sure of yourself or your lab equipment.
;)

[Edited on 7-9-2005 by kmno4]
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[*] posted on 29-1-2006 at 10:04


Hi I am a new User looking for preparation of NaCn. I find a very easy method at
http://www.hypatia-
lovers.com/footnotes/Section01.pdf.. There is written the formula:

Na2Co3+4C+N2+ Heat ( Fe Catalyst)------> 2NaCn+3Co

The Bucher Process for the Preparation of Sodium Cyanide:
To prepare sodium cyanide, simply heat 5.41 grams of sodium carbonate [Na
with
2.45 grams of powdered charcoal or lampblack [C] with 4 grams or so of iron filings
[Fe] in a stream of nitrogen [N] (air, being 78% nitrogen, will suffice).

Can tell me someone if it will work??????




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[*] posted on 31-7-2006 at 02:24


I asked myself if polyethylene could not be used for reducing the cyanate to the cyanide. PE is known to reduce many metal oxides to the metal and if it works for reducing cyanates it might be a cleaner alternative to charcoal.

/ORG




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[*] posted on 31-7-2006 at 18:40


That would be interesting to try as a variation. The greatest problems I've had are with frothing/bubble formation, which limits the amount that can be produced in a given volume and also impedes heat transfer. I fear that using PE would make the gas production even more of a problem, and I wonder how well the molten PE or its vapor would mix with molten cyanate/cyanide. The charcoal-reduced cyanide does seem to have traces of sulfur in it (faint smell of H2S), which PE would avoid.



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[*] posted on 1-8-2006 at 00:03


Hmm...
Frothing, bubbling, heat transfer? Coarse steelwool?
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[*] posted on 1-8-2006 at 01:12


Wouldn't polyethylene start "cracking" at the temperature required? Most of it might escape in form of vapors of higher olefins.

If using pre-prepared tripotassium cyanurate the powder is fine enough (and chemicaly homogenous = as much as it can be) to form KOCN at lower temperatures (250-350°C).* This yields a highly homogenous and very fine product. Perhaps such product would be more ready to react with something like polyethylene at somewhat lower temperatures.
Perhaps the reduction would work even better with thoroughly homogenized crude KOCN with sugar:D, which then carbonizes to some fine carbon that should do the job. However, at the begining there would be a lot of annoying froating due to evolved H2O and CO2 from such a "caramel candy". Starch does not melt, so perhaps it would be more apropriate even though it would be less homogenous.

* This is how I once supposedly prepared some KOCN: I prepared "tripotassium cyanurate" (due to pKa3, I doubt one can prepare it stoichiometricaly pure from KOH) from cyanuric acid and 3 eq of KOH in IPA solution, vacuum filtered the white voluminous paste and while still wet (to avoid CO2 absorption) heated it on a hotplate well covered with alu-foil until up to some 250-350°C and left there for about 2h. There was some cracking of the powder at the beginning and later no more notable change. I haven't analyzed the product but given that no cyanuric acid precipitated after acidification with HCl of an aqueous solution of the product, I assume only KOCN could have formed. This was a modification based on GB710143 where Na2CO3 with cyanuric acid is used to produce NaOCN. If someone is terribly curious if this was truly KOCN, I might bother to check with IR (if someone is so kind to provide a reference spectra:P).




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[*] posted on 8-11-2006 at 20:47
Analytical methods


Hello,

Polverone, on page one you indicated an interest in some analytical tests for cyanide (besides the nose...). I have attached EPA 9014 which includes the usual protocol for both titrimetric (more likely to find use here) and spectrophotmetric (better) methods.

This assay methodology is quite general, and so long as the matrix is not really nasty, there should be no distillation required (which is commonplace in more elaborate methods).
These methods are designed for trace levels though, so large dilution factors will be required, viz. 30,000 or more, for a relatively pure product.

Hope this helps,

O3




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[*] posted on 8-11-2006 at 20:49


Oops,

My apologies, I forgot to attach the file; here it is.

O3

[Edited on 9-11-2006 by Ozone]

Attachment: EPA 9014.pdf (73kB)
This file has been downloaded 1217 times





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[*] posted on 11-11-2006 at 18:25


BTW:

KOCN can be obtained just by simply heating urea and K2CO3. Heating mixture easy melts (CO2+H2O goes out). Molten substance is KOCN. NaOCN (from Na2CO3) melts in much higher temp. and is harder to obtain as pure substance.
KOCN does not react even with Mg or Al at about 700 C.
[I wrote it all somewhere in this forum, but it was a long time ago :P]



[Edited on 12-11-2006 by kmno4]
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[*] posted on 11-5-2007 at 16:26
"Murder Most Foul"


I watched this Agatha Christie film today on TCM, the film classics channel. One person was murdered by what I think Jane Marple said was "Prussic acid," which she deduced by the "smell of almonds." Apparently some sodium cyanide mixed with candle wax was placed in a pot on a stove. A timer was set for the burner to go on and off when the victim was in the kitchen. This generated the HCN thereby killing said victim. The victim, btw, was unintentional, Miss Marple being the intended victim.



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[*] posted on 11-5-2007 at 21:14


Not that I want to work with cyanides (still not as scary to me as HF, but scary enough), but I have some use for the [much safer] cyanate. I'm working on some experiments with chemical microscopy of iron compounds. So I was looking at the old urea / K2CO3 method of making KOCN, mentioned above.

I came up with a balanced equation (OK I'm tired so it might not be all balanced):

2H2NCONH2 + K2CO3 -----> 2KOCN + CO2 + 2NH3 +H2O

Now, it's late and I'm getting sleepy, so I'm not sure if this is the correct equation of what happens, but it seemed to fit. Urea and potass. carbonate going into just KOCN, CO2 and water was unable to be balanced.

I have some old refs. for qualitative tests for both CN- and OCN-, some of which are pretty interesting. It's a pity CN- is so toxic, because it is used in a lot of qualitative tests I'd like to try. Not to mention it's still hard to beat for gold & silver recovery. But cyanate itself is interesting for a few reasons, I might edit this post later for a couple uses of it.

I may still have a jar of old crabgrass killer that's kicking around somewhere, I recall it was mostly KOCN. From the looks of it, I think the jar was from the 1960's or even the 50's. I should dig that out and test its purity.

EDIT: strange, but last night I checked and there was one copy of this post. Today I came back and there was a double, a quote of this post from myself. I deleted the double. Still not sure what happened.

[Edited on 12-5-2007 by Pyridinium]
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[*] posted on 12-5-2007 at 05:59


I'm not sure if this holds any value:

"Carbonyl cyanide has been obtained[2] from <a href="http://www.sciencemadness.org/talk/viewthread.php?tid=2969&page=1#pid94304">diisonitrosoacetone</a>. It is a colourless liquid with a boiling point of 65-5° C. at 740 mm. Density, 1.124 at 2O°C. By hydrolysis it decomposes forming carbon dioxide and hydrocyanic acid." M. satori, <a href="http://www.sciencemadness.org/library/books/the_war_gases.pdf">The war Gases</a>, pg. 58.

2] MALACHOVSKY and coll., Ber., 1937, 70, 1012.

[Edited on 13-5-2007 by Axt]
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[*] posted on 15-5-2007 at 01:42


Thermodynamic says that reaction:

KSCN + Pb -> KCN + PbS

is possible, dG is about -20kJ.
I am not able to check it, because my KSCN turned out to be NH4SCN ....

[Edited on 15-5-2007 by kmno4]
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[*] posted on 15-5-2007 at 14:08


How do you seperate the lead from the sulfide? In solution is not going to work, it will passivate. A fusion akin to the nitrite/lead process might work.

Tim




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[*] posted on 15-5-2007 at 16:27


Hmm, I will soon need a sizeable quantity of a crude cyanide in order to prepare the liquid anhydrous HCN that I need for the TCT synthesis.
I originally planned on purchasing 1 kg of potassium ferrocyanide and melting this with K2CO3 (liberates 5 of the 6 bound cyanide ions as KCN, one is turned into KOCN). But this would be quite expensive, and I also would have to buy more K2CO3 which isnt cheap either.
K4(Fe(CN)6) also comes as the tetrahydrate, adding dead weight.
Heating ferrocyanide with acid is out of the question, that is very wasteful of material due to hydrolysis of HCN and because only half of the cyanide is liberated as HCN in the first place.

I now decided upon melting soda with urea to make NaOCN and reducing this with charcoal powder in a soup can. The heating will be done with burning charcoal, I'm simply going to place it in a pile of lit charcoal in the grill and blow air at it.
I know that this makes some NaCN since I did this in a steel crucible in small scale.
The problem is that an awful lot of side reactions are going on, cyanates produce cyanides while melting even without any reducing agent by disproportionation into things like cyanamide, carbonate and also with nitrogen loss which is highly undesirable.
I will probably not be able to exceed a few ten percent of NaCN content in the resulting material. Not that this would be a big problem, I can simply make more, but I cant really dose the HCN for the synthesis.
I will probably react a weighed amount of raw cyanide with acid, condense the evolved HCN and weigh it to determine the HCN yield of my raw product.
Cyanate will liberate HOCN which immediately hydrolyses into carbonate, carbamate and ammonium, giving no rise to impurities in the liquid HCN.

Can you suggest better methods for determining the NaCN content of a solid crude material, in the presence of cyanate, cyanamide, carbonate and other gunk?




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[*] posted on 15-5-2007 at 16:37


Why not colorimetrically with Fe(II) / Fe(III) solution? Redox titration perhaps?

Raw gravimetric or whatever methods are probably the only way to go for the impoverished chemist, unfortunately.




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