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Author: Subject: Preparation of cyanides
Dan Vizine
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[*] posted on 20-2-2017 at 09:32


I'm a chemist by trade. Thus, if a starting material is available for purchase, I'll almost never make it. Why waste time on starting materials or reagents unless you have to. And that is a good price.

Yields have been around 50-55 %. You can never say for sure. Some water vapor is carried over with the HCN just by entrainment.





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clearly_not_atara
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[*] posted on 1-9-2017 at 14:58


Could you trans-ligate ferricyanide to ferrioxalate? I.e.:

K3Fe(CN)6 + 3 K2C2O4 >> K3Fe(C2O4)3 + 6 KCN

If not, are there some other ligands that might accomplish this? Wikipedia claims that the anion FeF5H2O(2-) is very stable, so that would be:

K3Fe(CN)6 + 5 KF + H2O >> K2FeF5H2O + 6 KCN

These methods may avoid producing any HCN if you're careful, although you then need to precipitate cyanide, unless you want to convert it to thiocyanate in situ, which might be possible somehow.

[Edited on 1-9-2017 by clearly_not_atara]
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clearly_not_atara
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[*] posted on 1-11-2017 at 17:14


A-ha!

"Formaldoxime readily decomposes into its nitrile (hydrogen cyanide) and water when it is heated with aqueous alkalis"

Dunstan & Bossi, Proceedings of the Chemical Society Vol 10 no 136, "Formaldoxime", attached.

This method is nearly perfect. There are no side products, the precursor formaldoxime is easily prepared from formaldehyde and hydroxylamine, and the cyanide is produced in alkali.

Attachment: dunstan1894.pdf (1.5MB)
This file has been downloaded 288 times





[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 9-11-2017 at 01:45


Found this in an 1897 text, titled "Manual of Chemical Technology":

kcn-nacn.png - 608kB

Apparently, a mixture of KCN and NaCN can be easily prepared by melting 8 parts anhydrous potassium ferrocyanide with 2 parts sodium carbonate. Iron carbide precipitates from the melt.

[Edited on 11/9/17 by Melgar]




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[*] posted on 9-11-2017 at 21:42


I think I saw the above method in a Cody's Lab video. I've wanted to try it before, and might soon. Also, Iron carbide, hmm...



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[*] posted on 18-6-2018 at 19:14


Sorry for bringing the thread back up, but I did a rough test of the burning carbon/KNO3 method, and it seems promising. Has anybody else done this, or know the best ratios?
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[*] posted on 25-6-2018 at 16:18


I made a test solution to test for any cyanide produced, and it showed positive, strangely it also was positive for sugar and potassium nitrate burned. Anybody know why?
The gunk left over from the reaction was dissolved in water and filtered to get the cyanide, it may leave some kno3 in solution, but for the moment its good enough.
The test solution was made by putting and iron nail in sulfuric acid and adding some h2o2. Dripped into the cyanide solution, it creates a definite prussian blue.
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[*] posted on 26-6-2018 at 17:14


Quote: Originally posted by Hunterman2244  
I made a test solution to test for any cyanide produced, and it showed positive, strangely it also was positive for sugar and potassium nitrate burned. Anybody know why?


There is a lesser known reaction between KNO3 and C that indeed forms KCN;

\[KNO_3 + 4C \rightarrow KCN + 3CO\]

This probably occurs to a small extent as some of the sugar is reduced to carbon, and further reacts with KNO3.




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[*] posted on 27-6-2018 at 04:42


Quote: Originally posted by Velzee  

This probably occurs to a small extent as some of the sugar is reduced to carbon, and further reacts with KNO3.

It seemed a lot stronger a reaction in the test. The blue showed up faster. The amount of sugar and kno3 I burned was also less.
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[*] posted on 27-6-2018 at 05:59


Has anyone had any luck with reducing cyanate to cyanide by aluminum, magnesium or zinc?
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[*] posted on 27-6-2018 at 23:00


Yes I tried it using Magnesium, it does work, but you get a lot of smoke, which is probably containing lots of cyanide.
I dissolved the cyanide using water, which left the Magnesium oxide and unreacted Magnesium. The filtered solution was able to dissolve Gold, so I would call it a success.
But I thought, the reaction between Sodium cyanate and Magnesium would be much less vigorous and you would need to constantly heat it, but it does burn quite fast and vigorous:o
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[*] posted on 28-6-2018 at 06:44


I did some quick calculations,

3NaCNO + 2Al ---> 3NaCN+ Al2O3 = -780 kj

NaCNO+Mg ---> NaCN+MgO = -287 kj

NaCNO+Zn ---> NaCN+ZnO = -39 kj

I might try and see how the zinc and aluminium reductions compare.
Sodium cyanate can be made from store bought cyanuric acid very cheaply so it could be a very practical method.

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clearly_not_atara
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[*] posted on 9-7-2018 at 14:43


It seems likely that in basic solutions isonitrosoacetone would decompose to acetyl cyanide, which is typical of aldoximes in alkali, and thereafter to cyanide anion and acetate:

https://pubchem.ncbi.nlm.nih.gov/compound/Isonitrosoacetone#...

As is typical for other ketones this compound should be produced by nitrosation of acetone.




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 10-7-2018 at 04:31


Many paths involving exotic compounds (at least for the humble home chemists) and high temperatures have been presented.

How about the room temperature photolysis of NH3 and C2H2?

Here is the reference: 'Formation of hydrogen cyanide and acetylene oligomers by photolysis of ammonia in the presence of acetylene: applications to the atmospheric chemistry of Jupiter' by James P. Ferris, and Yoji. Ishikawa in J. Am. Chem. Soc., 1988, 110 (13), pp 4306–4312, DOI: 10.1021/ja00221a033, a link to the extract only available at https://pubs.acs.org/doi/abs/10.1021/ja00221a033?journalCode... , note suggested Equations (1) to (4). Interestingly, it is mentioned that the photolysis of CH4 can apparently lead to the formation of some C2H2 (more details on this path to C2H2 is available in the ebook 'Jupiter: The Planet, Satellites and Magnetosphere', edited by Fran Bagenal, p. 139 at https://books.google.com/books?id=aMERHqj9ivcC&pg=PA139&... ).

Also, 'cyano-containing hydrocarbons may act as photolytic sources for HCN and HNC in astrophysical environments' per http://iopscience.iop.org/article/10.3847/1538-4357/aa8ea7/m... .

Excuse me for not diving into details on just how just about 'anyone', not skilled in the art, could possibly photo cook a batch of a highly toxic gas. Somehow, I sleep better especially, if per chance, my windows are open!

Anyone performing photolysis experiments involving ammonia and hydrocarbons (like CH4) should, however, be advised to avoid smell tests, just in case ;) .

[Edited on 10-7-2018 by AJKOER]
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[*] posted on 20-1-2019 at 07:32


My latest attempts at making KCN by reducing KCNO made from urea and KOH were terrible.
For the first batch I tried using Mg powder, which worked, but I think it worked too well, since I only got a few grams of Prussian blue from the mixture, when the theoretical yield should have been like 40 g or so. I'm pretty sure what happened there is that the magnesium metal stripped away not only the O from the KCNO, but also the N from the molecule, leaving behind a very hot potassium carbide, which oxidized in air producing a very nice purple flame, to form lots of potassium carbonate (which crashed out beautifully from the methanol I used to extract the cyanide from the mixture).
A second attempt, using Al powder failed miserably, and even when I used a torch to directly ignite the mixture, all that happened is that the mixture melted, and nothing else. Adding a small amount of magnesium powder to act as a starter failed to do that, and it would appear that Al powder just doesn't work.

I also tried a different approach, to make Prussian blue directly, I heated together a mixture of KOH, urea and some steel wool, mainly because last time I cleaned the SS cup from the KCNO leftover, I noticed a small amount of Prussian blue forming on the center of the bottom of the cup, where the temperature would be the highest, so figured that maybe making Prussian blue might work better. After the solid cooled, I took it apart, but didn't see any blue formations, figured I'd either have to use a different form of iron or simply the temperature wasn't high enough. Upon addition of acid however, I noticed that the solution has turned black, but it also has a weak dark blueish hue, and it's not the soluble part, but rather from the suspensions. I think I might have got some Prussian blue, but it's very little, although I'll only know more after I've purified the whole solution. If this works, I might try using iron powder or turnings next time, and also use higher temperatures.




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[*] posted on 20-1-2019 at 10:17


Why not zinc.



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Mabus
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[*] posted on 20-1-2019 at 12:27


Quote: Originally posted by S.C. Wack  
Why not zinc.

Don't have Zn powder yet.

Also, an update on my iron adventure. I managed to dissolve most of the rust from the mixture with acid, and there is some blue precipitate there. Not much, but still significant, especially since the wool barely reacted.
I guess the classical recipe works better.




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[*] posted on 11-2-2019 at 08:51


You can just buy Prussian Blue. Laundry bluing is just a suspension of it, get some, dry it in an oven. 3 bucks a pint, at my local Wal-Mart.



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[*] posted on 12-2-2019 at 12:25


Quote: Originally posted by Mabus  
Quote: Originally posted by S.C. Wack  
Why not zinc.

Don't have Zn powder yet.

Also, an update on my iron adventure. I managed to dissolve most of the rust from the mixture with acid, and there is some blue precipitate there. Not much, but still significant, especially since the wool barely reacted.
I guess the classical recipe works better.


You can make zinc powder by electrolising sodium zincate, which is where I get mine. NurdRage has a great video on this: https://www.youtube.com/watch?v=3X9c6epL7HQ
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[*] posted on 12-2-2019 at 16:24


Quote: Originally posted by PirateDocBrown  
You can just buy Prussian Blue. Laundry bluing is just a suspension of it, get some, dry it in an oven. 3 bucks a pint, at my local Wal-Mart.


I will state that I did not know this and that I will be looking into it as well.
Thank you.
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[*] posted on 12-2-2019 at 17:08


Zinc is everywhere. You can get it for pennies if you have a ball mill or iron mortar. I had no problems with the powder in fresh alkaline batteries as long as it was well washed free of alkali; dilute acid might help. Expensive when compared to the preferable fine powder sold by pyro suppliers for Zn/S rockets.



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[*] posted on 15-2-2019 at 08:09


For Zn, look for pyrotechnic suppliers. Last I got some, it was $8 a pound, powdered.

And you can get it FROM pennies, if you wanna go that way. Just melt some in a crucible, and pour into water, to make mossy zinc. It'll have some Cu contamination, but it'll be good for most purposes.


[Edited on 2/15/19 by PirateDocBrown]




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[*] posted on 15-2-2019 at 10:29


If you make CuCN from Prussian Blue as described in this old thread, could you then use a solution of CuCN in MeCN as a source of nucleophilic CN-? I.e. something like this:

CuCN + 4 MeCN (solv.) >> Cu(MeCN)4+ + CN-

CuCN + EtBr + excess MeCN >> EtCN + Cu(MeCN)4+ + CN-

Or, possibly, perhaps you could even precipitate KCN from this solution by adding KI?

[Edited on 15-2-2019 by clearly_not_atara]




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 15-2-2019 at 12:59


Unfortunately, CuCN (much easier to prepare than ionic cyanides) is not replacemet for K(Na)CN and it gives mainly isonitriles :(



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[*] posted on 10-10-2019 at 13:27


Could this process work:

urea + sodium hydroxide + carbon in a furnace heated to reaction temp to produce cyanate and via carbothermic reduction to sodium cyanide + residual of sodium hydroxide?

Then followed by purification with hot water, filtering, and crashing the sodium cyanide by adding ethanol which should reduce the solubility of NaCN to a significant degree, but still allow the remaining sodium hydroxide to stay dissolved?

I prepared a batch of this by blending the three ingredients with blender and heating up. The solution was filtered, and adding significant amount of ethanol caused white crystals to precipitate in a very good amount.

Should the product be mostly sodium cyanide that was produced? Unfortunately this process was done years ago and I had to get rid of my chemistry items due to changes in other life matters, hence no more info is available. The process described is from a german chemistry board.

To obtain high purity an acid distillation for HCN to base could do the job, but if possible avoidable mostly due to the process being too laborous.

(necessary safety disclaimer: im using A2B2E2K2 filter with the infamous breaking-bad yellow chemical suit and my workspace was located outdoors and I actually went so far as to build a 20-foot high chimney to my portable fume hood from 8" pvc tube to suck all nasties up to the sky.)

[Edited on 10-10-2019 by Refinery]
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