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bolbol
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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?
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morganbw
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This may have already been linked.
Here is the patent.
US patent 579988
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woelen
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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.
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bolbol
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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.
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Blunotte
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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
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Blunotte
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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 
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bolbol
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How would you go on to purify the Cyanide?
I've read that it is turned into HCN under the pH of 7?
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Blunotte
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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 
[Edited on 4-4-2015 by Blunotte]
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bolbol
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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
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Blunotte
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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.
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Blunotte
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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)
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Blunotte
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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... |
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ChemPlayer_
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Mixed cyanide salt from heating ferrocyanide and sodium metal
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
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Boffis
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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.
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Magpie
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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lysander
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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?
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ChemPlayer_
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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.
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lysander
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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?
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Boffis
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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.
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ChemPlayer_
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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).
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lysander
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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]
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Boffis
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@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.
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skip
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Anyone ever tried ice cold hydrocyanic acid added to chilled methanol/anhydrous sodium hydroxide. ?
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Boffis
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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.
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skip
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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.
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