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Author: Subject: Synthesis Sodium Ferrocyanide?
CharlesWood
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[*] posted on 1-7-2022 at 19:25
Synthesis Sodium Ferrocyanide?


I'm having difficulty sourcing Sodium Ferrocyanide in my locality so I'd like suggestions on synthesis using the reagents I have available and seem like they might contribute.

I have urea, potassium nitrate, sodium carbonate, sodium hydroxide, iron (steel wool), calcium chloride, sodium chloride. I can also get cyanuric acid.

There is a 'recipe' on this board using molten sodium carbonate, iron, and charcoal, but it obviously won't work as there is no nitrogen source.

Any suggestions for an alternative that doesn't involve making cyanide as an intermediate?

[Edited on 2-7-2022 by CharlesWood]
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woelen
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[*] posted on 3-7-2022 at 02:12


Must it really be the sodium salt? The sodium salt is very uncommon. The potassium salt, on the other hand, can easily be obtained and is available, even on eBay. It is a fairly innocuous salt, and you need quite extreme conditions to release the cyanide as free acid or as free ion.

The same is true for the ferricyanide. The potassium salt can be purchased easily, while the sodium salt is very hard to find (I never saw a place where you an buy it).




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Bedlasky
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[*] posted on 3-7-2022 at 06:32


Quote: Originally posted by CharlesWood  
There is a 'recipe' on this board using molten sodium carbonate, iron, and charcoal, but it obviously won't work as there is no nitrogen source.

[Edited on 2-7-2022 by CharlesWood]


This method was used in the past for synthesis of NaCN. Nitrogen is from the air, iron is catalyst for reaction between mixture and N2. Apparently conditions can be changed for formation of sodium ferrocyanide (but it is possible that ferrocyanide will be contaminated with cyanide).

https://smartech.gatech.edu/bitstream/handle/1853/11874/lati...
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CharlesWood
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[*] posted on 3-7-2022 at 18:29


I have found one possible synthesis using urea

2CNa2O3 + Fe + 3C + 3CH4N2O → CO2 + 6H2O + CO + C6FeN6Na4

I got the clue from an old source showing how ferrocyanide was made a century ago where they used animal hoofs and horns as the nitrogen source.
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[*] posted on 4-7-2022 at 06:31


When they were making ferrocyanide from nitrogenous animal matter, they purified the product by boiling it with the milk of lime and treated the calcium ferrocyanide with KCl. This way the sparingly soluble K2Ca[Fe(CN)6] was separated out. This was boiled with K2CO3 to get more or less pure K4[Fe(CN)6]*3H2O.

I think cyanuric acid is a more readily available source of CN- groups than urea (which depending on the temperature decomposes with the formation of cyanuric or isocyanic acid and something not containing any CN).

But forming CN groups in a hot process is something I am not ready to perform in my home lab, especially if I don't understand the process well.
How I will get my Fe oxidized (even in a form of really fine powder)? How I will balance the ferrocyanide formation and decomposition? Do I need the temperature of molten Na2CO3 here (it is really TOO high)? Could Na2CO3 be replaced with NaOH to perform the reaction at ~350C in the molten NaOH (which is very dangerous but still much safer)?

I would prefer to buy ferrocyanide on eBay. For other complex cyanides, I would use NaCN or KCN salt - I think it is much safer than trying to produce HCN/CO in a hot process.


[Edited on 4-7-2022 by teodor]
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CharlesWood
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[*] posted on 4-7-2022 at 15:41


I have a second possible synthesis using cyanuric acid.

2(CNOH)3 + 3C + Fe +2CNa2O3 → 4CO2 + 3H2O + CO + C6FeN6Na4

This has an advantage over Urea in that it does not decompose with heat.
Urea decomposes to Ammonia and isocyanic acid on heating so losing some nitrogen

CO(NH2)2 → NH3 + HNCO

I have no problems with the carbon monoxide produced as the synthesis is done at red heat in a gas or charcoal furnace in an iron crucible.
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CharlesWood
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[*] posted on 4-7-2022 at 16:31


I have looked at a synthesis using sodium hydroxide and cyanuric acid. They both melt around 320C, but I'm not sure if that is hot enough to generate the Sodium Ferrocyanide.
I guess experiments will tell.

2(CNOH)3 + 3C + Fe +2NaOH → 2CO2 + 3H2O + CO + C6FeN6Na4
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[*] posted on 5-7-2022 at 01:11


CharlesWood,

Usually, we write the formula as Na4[Fe(CN)6] to designate the compound structure. Your way of writing the formula could be used when you are talking about possible isomers, but it will be not necessary ferrocyanide but any compound containing the elements in a given proportion. Because the way how the elements are bound with each other also matters (it changes chemical properties), to designate the particular compound we write the elements in some particular order. I think only Na4[Fe(CN)6] or [Fe(CN)6]Na4 are acceptable for ferrocyanide.

I don't see how you will get Fe oxidized. Heating Na4[Fe(CN)6] with Na2CO3 leads to the decomposition of ferrocyanide with Fe deposit. There is a lot of documented experimental evidence for that. I am not aware of any real experiment when things go in the opposite direction except those "old method" which lacks any useful details to repeat the process in a home lab.

If you are determined already to do a hot process I would recommend trying just to melt cyanuric acid with an excess NaOH but without any iron or carbon and try to get NaOCN. Then you probably can make Na4[Fe(CN)6] in a water solution using ferrous sulfate as a source of Fe ions and some reducer. It is still a lot of experimental work and everybody will be really interested if you will find some working process to make ferrocyanide this way - not everybody is willing to do it as a high temp reaction.

[Edited on 5-7-2022 by teodor]

[Edited on 5-7-2022 by teodor]
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[*] posted on 5-7-2022 at 03:33


@Charleswood; almost a decade ago I posted on this site a detailed preparation of specifically sodium ferrocyanide, the post was accompanied by photographs. The starting material was Prussian blue or "blue billy" from gasworks waste.

There are several old books available online that deal entirely with the preparation of cyanides and ferrocyanides, check out:
1) The cyanide industry Robine & Lenglen 1906

2) Chemistry of cyanogen & cyanide by H E Williams 1915

The original method of using low temperature animal waste char, iron fillings and Caustic soda is really a version of the charcoal-iron-caustic soda and urea or cyanuric acid methods described above. These methods do not require very high temperatures and sodium cyanide is the initial product mixed with some iron compound that when mixed with water and heated for a long time reacts with the cyanide to give the ferrocyanide.
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[*] posted on 5-7-2022 at 03:58


@teodor: NaOCN cannot be used easily to make cyanide. In aqueous solution, the OCN(-) ion is not oxidizing. It differs quite a lot from hypochlorite or hypobromite, which are strongly oxidizing. I once did an experiment with mixing CN(-) and OCN(-) in aqueous solution and then adding an acid. If that experiment is done, then the CN(-) simply leads to formation of HCN and the OCN(-) leads to formation of HOCN, which hydrolyses to ammonia, water and carbon dioxide. So, you just get bubbles of CO2, contaminated with HCN. With Cl(-) and OCl(-) you get Cl2 on acidification, but for CN(-) and OCN(-) there is no analogous reaction. The other way around, however, does occur, so (CN)2 gives OCN(-) and CN(-), when passed through an alkaline solution.

Making ferrocyanide from ferrous ions is easy when you have cyanide. Just adding the solution of cyanide to a solution of ferrous sulfate gives rise to formation of a precipitate, with empyrical formula "Fe(CN)2", and on addition of more cyanide, this redissolves to form the pale yellow [Fe(CN)6](4-).
So, the best way to make ferrocyanide most likely is some hot process to make NaCN and leach that from the melt and then reacting that with a ferrous salt. One should exclude access of air to the solutions, ferrous ions are easily oxidized to ferric ions at high pH.

Isolating the ferrocyanide is much easier when you make the potassium salt. The latter crystallizes very well and can easily be purified. The sodium salt is hygroscopic and not easily isolated. That's most likely the reason why the potassium salt is available online at many places, while the sodium salt is rare.

[Edited on 5-7-22 by woelen]




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BAV Chem
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[*] posted on 13-7-2022 at 22:56


@CharlesWood

As boffis already said you might want to check this out:
https://www.sciencemadness.org/whisper/viewthread.php?tid=18...

It seems there's no practical way of making ferrocyanide that doesn't involve NaCN in some way. However cyanide isn't quite as dangerous as it seems to be. Something like 2 months ago I made around 100g of NaCN as an intermediate in preparing NaSCN and I gotta say it's not that bad. As long as one doesn't try to acidify it or acidentally spill it all over the bench (oops:() it's relatively safe to work with.




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[*] posted on 14-7-2022 at 03:19


Quote: Originally posted by BAV Chem  
@CharlesWood

As boffis already said you might want to check this out:
https://www.sciencemadness.org/whisper/viewthread.php?tid=18...

It seems there's no practical way of making ferrocyanide that doesn't involve NaCN in some way. However cyanide isn't quite as dangerous as it seems to be. Something like 2 months ago I made around 100g of NaCN as an intermediate in preparing NaSCN and I gotta say it's not that bad. As long as one doesn't try to acidify it or acidentally spill it all over the bench (oops:() it's relatively safe to work with.


Sure, solid cyanide's not bad to work with at all. Gloves and mask. Keep it away from acid.




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[*] posted on 28-7-2022 at 13:07


Quote: Originally posted by woelen  
Must it really be the sodium salt? The sodium salt is very uncommon. The potassium salt, on the other hand, can easily be obtained and is available, even on eBay. It is a fairly innocuous salt, and you need quite extreme conditions to release the cyanide as free acid or as free ion.

The same is true for the ferricyanide. The potassium salt can be purchased easily, while the sodium salt is very hard to find (I never saw a place where you an buy it).


To reiterate Woelen's question:
Do you really need the sodium salt?

General question to everyone:
If the sodium salt really is needed, would ion exchange resin work?
Could one saturate a cation exchange resin with e.g. NaCl, then run
a solution of the readily available K4(Fe(CN)6) through it to replace
K with Na?
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