RU_KLO
Hazard to Others
Posts: 313
Registered: 12-10-2022
Location: Argentina
Member Is Offline
|
|
Potassium Ferrocyanide from Cyanate
Objective: to optain Potassium hexacyanidoferrate(II) K4[Fe(CN)6]·3H2O - without using cyanides (directly) - cyanides are made in situ from cyanate.
INTRO:
How its made:
(Ullmanns Cyano Compounds, Inorganic)
Historically, the preparation of hexacyanoferrates (II) was based on the fusion of potash with iron compounds and animal residues such as hide, horns,
or dried blood, which led to the German name gelbes Blutlaugensalz (yellow salt of blood lye).
Later, the absorption of hydrogen cyanide from coal gas on iron hydroxide was used to produce hexacyanoferrates.
Today, synthetic hydrogen cyanide, iron(II) chloride, and alkali metal or calcium hydroxide are the raw materials for the large-scale production of
hexacyanoferrates(II) on a large scale.
3 Ca(OH)2 + FeCl2 + 6 HCN -> Ca2[Fe(CN)6] + CaCl2 + 6 H2O
Liquid hydrogen cyanide and an aqueous solution of iron (II) chloride are mixed with calcium hydroxide solution in stoichiometric amounts in a stirred
reactor.
After filtration, the solution is concentrated by evaporation of water under reduced pressure, and the calcium hexacyanoferrate(II) crystallizes with
eleven molecules of water of crystallization.
The relatively coarse-grained salt is then separated by filtration and generally used without drying. For the conversion of calcium
hexacyanoferrate(II) to the potassium or sodium salt, two methods are used.
In the first, a stoichiometric amount of potassium chloride is added to the filtered calcium hexacyanoferrate(II) solution and the
hexacyanoferrate(II) precipitates as a sparingly soluble potassium calcium double salt.
Ca2[Fe(CN)6] + KCl -> K2Ca[Fe(CN)6] + CaCl2
The double salt is separated by filtration, redispersed in water, and then converted to the soluble potassium hexacyanoferrate(II) by the addition of
potassium carbonate:
K2Ca[Fe(CN)6] + K2CO3 -> K4[Fe(CN)6 + CaCO3
After separation of the insoluble calcium carbonate, the potassium hexacyanoferrate (II) solution is concentrated by evaporation, and the potassium
salt crystallizes with three molecules of water of crystallization. After filtration, the salt is carefully dried and packaged.
After some research:
1) "Cyanate, may be reduced to cyanide in reducing environments"
The reduction rate of cyanate to cyanide increases with decreasing solution redox potential. A solution with a lower redox potential presents a more
reducing environment and, hence, is more favorable for the reduction of cyanate to cyanide. This phenomenon is also depicted in the cyanide system
Eh-pH diagram (attached); at lower solution redox potentials, the system favors HCN or CN-. ref. Reduction of cyanate to cyanide in cyanidation
tailings under reducing environments (H.K. Lin and D.E. Walsh Professors, University of Alaska Fairbanks, Fairbanks, Alaska)
2) Hydrogen cyanide can be produced when sufficient energy is supplied to any system containing the elements hydrogen, nitrogen, and carbon.
3) All hexacyanoferrates decompose above 400°C to form alkali metal or cyanides, elemental iron, carbon, and nitrogen.
4) From experience (hypothesys) : carbon monoxide/dioxide is detrimental for the production of Alkaly - ferrocyanide, because a lot of alkaly
carbonates are made.
I think that the potassium ion likes carbonate more than cyanide, so the production of CO / CO2 removes the potassium ions, thus reducing the
production of ferrocyanides.
this was tested with my FeC2O4 test. https://www.sciencemadness.org/whisper/viewthread.php?tid=16...
Currently trying to get some K-ferrocyanide by cristallization. (a lot of K2CO3 is dissolved in the pale yellow solution)
So with this in mind, current idea (s):
1) 6 KOCN + 3 Fe -> K4[Fe(CN)6] + 2Fe2O3 + K2O (basic media)
(no water added, done in molten KOCN (aprox 330°C)
pro:
No other element is added (maybe oxigen/CO2 from atmosphere)
Fe is a reductor - > Fe (-0.44)
cons:
High temperature 330C
Will Iron reduce -OCN to -CN?
How easily is Iron reduced Fe -> Fe(3+) + 3e?
As there are (maybe) more than a reduction step Fe -> Fe(2+) + 2e; Fe(2+) -> Fe(3+) + 1e; then (maybe) -OCN is reduced completey to C and N.
(I think O will produce the corresponding Iron Oxide)
Procedure (my own devised):
24 grs of KOCN is melted at 330°C.
to this molten solution, 9 grs of Iron (fillings or wool) is added with stirring.
If there is a reaction, the "transparent" KOCN solution should turn oxide orange from the Iron oxide forming.
Keep in the heat at least 30 minutes (1 to 2 hours better). From what I read, Cyanides/Cyanates needs a lot of time.
Let is cool and add water to disolve. (if any K2O , will hydrolize to KOH. If any Prussian blue (iron(III) ferrocyanide), then :In 1752, the French
chemist Pierre Joseph Macquer (1718–1784) first reported the preparation of Potassium hexacyanidoferrate(II), which he achieved by reacting Prussian
blue (iron(III) ferrocyanide) with potassium hydroxide).
other idea:
hypothesis:
Instead of Fe, use FeCl2.
6KOCN + 3FeCl2 -> K4[Fe(CN)6] + 2Fe2O3 + 2KCl + 2Cl2?
As KOCN is soluble in water 75g/100ml and FeCl2 is also soluble 68.5 g/100 mL (20 °C), could this reaction be done in water?
If yes, at what temperature?
Will KOCN dissociate completely into K and OCN ions?
The same as FeCl2?
The important question is: Can oxidation of FeCl2 -> FeCl3 reduce -OCN to -CN?
pro:
maybe it could be done in water.
Chlorine help in some form to the Cyanides/cyanates interaction. (modern production uses FeCl2) - also read somewhere - could not find and recall-
that containing chlorine compound is used as catalisys for reduction of cyanate to cyanide. It was organic chem.)
Probably FeCl2 is acidic and will lower the ph of the solution, thus "Solutions with lower pH favor the reduction rate"
ref. Reduction of cyanate to cyanide in cyanidation tailings under reducing environments (H.K. Lin and D.E. Walsh Professors, University of Alaska
Fairbanks, Fairbanks, Alaska)
cons:
Cl- will remove K+ ions -> KCl
last idea: to bubble H2 gas in the upper experiments.
H2 gas is a reductor, and maybe it could remove the O ion from -OCN by making H2O....
So the main idea is: What is needed to reduce -OCN to -CN, or under what condition will the Oxigen change partners from Cyanate -leaving cyanide - to
marry Iron..... (maybe only heat....)
Thoughs?
Go SAFE, because stupidity and bad Luck exist.
|
|
|
Aqua-regia
Hazard to Others
Posts: 136
Registered: 18-12-2006
Member Is Offline
Mood: No Mood
|
|
I spent lot of time studying cyanate. Alkali cyanate cannot reducing in solution phase. Not working. KOCN/NaOCN are unstable in water The solution
fast hidrolyzed: 2KCNO +H2O —> K2CO3 +(NH4)2CO3. Not exist such solvent to dissove it intactly. You can it only in solid phase reduce with H2 or
CO but the suitable temperature is 700-800 celsius, and the reduction rate max 60%, cause the K- or NaOCN in the maintime decomposed in the
following ways:
5KOCN -> 3 KCN + K2CO3 + CO2 + N2
4NaOCN -> Na2CO3 + CO + N2
The contaminated alkali cianide purification is again big sucks and a lot of material loss. But don't give up.
|
|
|
Boffis
International Hazard
Posts: 1910
Registered: 1-5-2011
Member Is Offline
Mood: No Mood
|
|
Besides alkali cyanates are not easy to get, they are not very stable they absorb atmospheric water and hydrolyse. In several older chemistry books
where alkali cyanates are used they recommend preparing then immediately prior to use from things like ethyl carbamate etc.
Have you read the various old books on the cyanide industry? I would recommend "The cyanide industry" by Robine & Lenglen, 1906. I think I
downloaded my copy from Archive.org.
In the past I have tried the old "blood" route using partly calcined "hoof and horn" which is sold in garden centres as a slow release source of
nitrogen. The process was horrible, the charring of the horn chips gives off an awful smell and the whole process is pretty shitty and the yield very
small and impure. if I ever try this again I might try using left over cyanuric acid from making chlorine or calcium cyanamide-cyanoguanidine as they
part way to cyanide already.
|
|
|
kmno4
International Hazard
Posts: 1523
Registered: 1-6-2005
Location: Silly, stupid country
Member Is Offline
Mood: No Mood
|
|
Not easy to get ? Possiby, but very easy to prepare.
Absorbing water ? No problem - tightly closed container.
It is the same problem like with NaOH ... etc.
Long time ago I prepared both Na and K cyanates. KOCN is easier to prepre, becuse of lower melting point. Besides this and the rubbish from the top of
the topic, an issue of reduction of cyanates is risen (too) many times at SM.
The reduction is possible, but it goes in temperatures around 1000 C, becuse it is almost fully entropy driven. As far I remember, Polverone reported
some success performing the reaction (KOCN+C).
However, there were two similar industrial processes (Bielby and Siepermann), where this reaction is exploited.
Just you may read slightly newer, or rather less old book than mentioned by Boffis, namely "Industrial Nitrogen Compounds And Explosives" (Martin
& Barbour, 1915).
One must remember, that cheap commercial urea, from which cyanates are easily prepared, appeared after 1940 year (or so).
Слава Україні !
Героям слава !
|
|
|
Aqua-regia
Hazard to Others
Posts: 136
Registered: 18-12-2006
Member Is Offline
Mood: No Mood
|
|
It is really easy to produce KOCN in a pure form and the yield is good. I agree with this. I wrote that reducing KOCN to cyanide is a big sucks,
because it is difficult to clean it from the large amount of contaminating carbonates that are present due to the self-decomposition of KOCN (it
decomposes at the reduction temperature) and the overall yield is also poor. The cited literature is very old, but if you look at the patents and
descriptions of cyanide production from the past 50 years, you will not come across KOCN reduction. I described why not. Of course, this route may be
good for hobby chemists, but in return they have to make do with the crappy yield and boring purification procedure.
|
|
|
kmno4
International Hazard
Posts: 1523
Registered: 1-6-2005
Location: Silly, stupid country
Member Is Offline
Mood: No Mood
|
|
Of course, I agree with Aqua-regia. Just because of troublesome purification, the only use of such products was gold extraction.
Nowdays, HCN (-> cyanides) is produced industrially in completely different ways and reduction of cyanates methot was abandoned before 1900.
However, recently I have read not very old ('80) patent (chinese ?) about "production of cyanides" from some mixture of carbonates+urea+some
carbonaceous crap. Just bad translation, or simply bullshit - under the conditions given there, nothing more may be obtained but cyanates.
Слава Україні !
Героям слава !
|
|
|
RU_KLO
Hazard to Others
Posts: 313
Registered: 12-10-2022
Location: Argentina
Member Is Offline
|
|
Thanks for the information.
So,to my understanding, my "major problem" is:
The reduction is possible, but it goes in temperatures around 1000 C, becuse it is almost fully entropy driven.
Ferrocyanates start decomposing at 400C+.
Getting this high temperature is not possible to me (for long times)
(I read the book Boffis indicated, they state max 800C to decompose ferrocyanates)
Although not the same, (probably) Sulfur is less strongly bonded that Oxigen, but these reductions exist:
Hydrogen: 4 KSCN + 6H -> K2S + 2 KCN + 3H2S + 2C +2N
KSCN + R -> RS + KCN
(R any reducting metal. Zn, Fe, Cu - At least these where stated in the book)
(from The Cyanide Industry - 1906 -)
ok, How do I change: it is almost fully entropy driven
(no pressure, please)
Go SAFE, because stupidity and bad Luck exist.
|
|
|
Aqua-regia
Hazard to Others
Posts: 136
Registered: 18-12-2006
Member Is Offline
Mood: No Mood
|
|
buy prussian blue pigment on ebay. (OTC product)
Iron(III)-[hexacyanoferrate(II)], commonly known as Prussian blue, does not react with dilute acids, but decomposes when boiled with
potassiumhydroxide. to form potassium-[hexacyanoferrate(II)] and iron(III) oxide:
Fe4(Fe(CN)6)3 + 12KOH ——> 3K4(Fe(CN)6) + 4Fe(OH)3
If potassium hydroxide is reacted in a smaller amount than the stoichiometric amount, the resulting cyanoferrate be separated by filtration from the
water-insoluble and unreacted mixture of Prussian blue and iron(III) hydroxide.
|
|
|
Aqua-regia
Hazard to Others
Posts: 136
Registered: 18-12-2006
Member Is Offline
Mood: No Mood
|
|
You can now make pure KCN from this product. (you can find a lot of literature about it) if you already have KCN in hand, then your original plan can
come to you, to prepare Potassium hexacyanidoferrate(II) I will give a description for this:
|
|
|
Aqua-regia
Hazard to Others
Posts: 136
Registered: 18-12-2006
Member Is Offline
Mood: No Mood
|
|
This is my own recipe because I worked a lot with cyanide compounds at one time: Weigh out 13.90 g (0.05 molar) of crystalline, pure iron(II) sulfate
and dissolve it in freshly boiled, oxygen-free distilled water, then add 6.50 g (0.1 molar) of an aqueous solution of potassium cyanide. Stir the
resulting precipitated solution thoroughly, boil it in a water bath, concentrate it and filter it. Wash it with cold water until it is sulfate-free.
Transfer the wet precipitate to a beaker and stir it with 12.35 g of an aqueous solution of KCN (5% less than the calculated amount (0.19 molar) while
heating it so that the precipitate goes into solution. Bring the mixture to a boil, add 1 spoonful of charcoal and, after boiling for a few minutes,
filter it while hot. Evaporate the yellow solution to dryness, initially with a gas burner and then on a water bath. yield 95%
FeSO4 +2KCN ——> Fe(CN)2 +K2SO4
Fe(CN)2 ++ 4KCN ——> K4Fe(CN)6
|
|
|
RU_KLO
Hazard to Others
Posts: 313
Registered: 12-10-2022
Location: Argentina
Member Is Offline
|
|
Aqua Regia, thanks,
probably I can buy potassium ferrocyanide.
Also read the KCN, HCN route.
But the idea is not to buy and not use cyanides (highly toxic), but cyanate (less toxic).
Go SAFE, because stupidity and bad Luck exist.
|
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
