Author Topic: Easy KCN from ferrocyanides w/out HCN  (Read 7746 times)

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  • Guest
Easy KCN from ferrocyanides w/out HCN
« on: November 09, 2002, 12:31:00 PM »
As the cyanide synth on Rhodium's page sounds slightly hazardous, and the other one is not too well scalable, SWIM has found you an alternative way of preparing KCN. This is based on SWIM's own idea, no refs this time; of course only for informational purposes. Cyanides are very poisonous, anyone attempting this illicit reaction should wear gloves and perform it in a fume hood (or outside), even if no HCN is needed to be generated.    

K4[Fe(CN)6]* 2H2O (121.2 g, 0.3 mol) are dissolved in dH2O, FeCl3 soln (35.5 g FeCl3, 0.2 mol) is added in small portions with stirring. Doing this while hot will speed up filtration considerably.

(FeCl3 can be prepared the following way:  iron turnings and HCl, the Cl2 bubbled through it after dissolution is complete, or alternately, calculated amt of HCl and H2O2 can be added to the green FeCl2 solution. If this procedure is used, make sure the soln contains no excess acid or HCN gas will evolve.)

The precipitated Blue of Berlin is washed with water, some of it is colloidal and will come through the filter paper. The solids are added to a solution of 66.3 g of KOH (1.2 mol) pellets in 300 mL of water (cautiously, with good stirring), again with a higher temperature particle size will be larger. The resulting brown mess is vacuum filtered (Gravity filtration will be unsuccessful), the filtrate evaporated to dryness and the KCN recrystallized from dH2O then dried over CaCl2, do NOT use H2SO4 or P2O5.  Yield, ~110 g.

Blue of Berlin can also be prepared from K3[Fe(CN)6] and FeSO4.

3 K4[Fe(CN)6] + 2 Fe3+ -> Fe2[Fe(CN)6]3 + 3 K+
Fe2[Fe(CN)6]3 + 12 OH- -> 2 Fe(OH)3 + 3 Fe(OH)2 + 18 CN-



  • Guest
simillar procedure
« Reply #1 on: November 09, 2002, 02:21:00 PM »


  • Guest
« Reply #2 on: November 10, 2002, 12:57:00 PM »
It is very interesting!

Are you made this synthesis?
Are you use this KCN for synthesis?
I also  work above synthesis KCN:

Post 368479 (missing)

(fallen_Angel: "Öèàíèñòûé êàëèé", Russian HyperLab)


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I can top that
« Reply #3 on: November 12, 2002, 06:40:00 AM »
If you are able to work at relatively high temperatures, i.e. you have at least a balcony where you can use a charcoal barbecue, then it is trivially easy to prepare sodium cyanide from OTC materials. I will reproduce here a writeup that I did for another forum:

I get the feeling that other people don't care even half as much as I do about cyanides ;-) but I've got to share my latest experiment anyway.

I was treading the path of cyanate reduction again - see my earlier posts. This time I started with about 50 grams each of NaHCO3 (subsequently converted to Na2CO3 by heat) and cyanuric acid. The NaHCO3 was obtained as baking soda; I used it (as before) to obtain finely powdered Na2CO3 without a lot of manual labor.

This time I did a few things differently: I used charcoal instead of gas for my heat source - which allowed me to maintain a high temperature for a long time - and I mostly excluded air from the reaction vessel. I'm not sure if that mattered very much, though.

In any case, I built a fire in a little charcoal barbeque, using a mixture of briquettes and large lumps of mesquite charcoal (since I had both on hand). Once the fire had taken to the charcoal a little bit, I put the NaHCO3 in an empty soup can and heated it over the fire until it appeared that it had turned to carbonate. I then added the powdered cyanuric acid and 10 grams of powdered grapevine charcoal (this is well in excess of the amount theoretically needed for the reduction; I'd use less next time).

I placed the can back on the fire and loosely sealed the top by setting a tapering stainless steel dish weighted with sand in the mouth of the can; gases could escape, but little carbon dioxide from the fire would be making its way to the interior of the can.

I then invigorated my fire and heated the can up with the aid of an electric hairdryer directed at the burning charcoal. When all the charcoal was burning well and heaped up around the can, this was no longer necessary. The can maintained a healthy red-orange glow even without the extra air.

When I removed the air-blocking dish at the top of the can, I was greeted with a small spontaneous yellow fireball as the hot flammable gases inside finally met sufficient oxygen for combustion. I left the dish off for a bit just to watch. There were places in the pasty mass of chemicals where a continuous stream of flammable gas issued forth. I assume that the gas was carbon monoxide, but it burned with a vivid yellow, probably due to picking up sodium compound vapor from the hot melt.

I replaced the air-blocking dish and waited. At periodic intervals I removed it to check on the progress of the mixture. It wasn't long before the continuous streams of burning gas disappeared, but I continued to see bursts of flame when I removed the dish for about an hour. After that time, there was no sign of further reduction when I exposed the hot interior gases to the air. Nevertheless, I continued to let it heat for another 2 hours since my charcoal fire was proving so long-lived.

After that time I removed the can from the fire and let it cool. I then cut the can up with tin snips - the metal was extremely brittle and was heavily oxidized - until I retrieved the bottom portion with the hardened mass of charcoal and salts. I smashed the mass free with a small hammer, crushed it into small chunks, and covered it with room temperature water in a small jar. I swirled the jar periodically and 2 hours later filtered the liquid to remove the charcoal. The bulk of the filtrate is now drying at room temperature in a large glass pan covered with a grocery bag (to prevent dust/other junk from falling in).

I would love to dry this material more rapidly but hot water will accelerate the hydrolysis of the cyanide. If I used forced air to dry it, I would be exposing the liquid to increased carbon dioxide from the atmosphere, again decreasing yields (and presenting a possible hazard as well). I suppose what I really need is a vacuum distillation setup so I can remove the bulk of the water rapidly at low temperatures. Alternatively, a solvent that dissolves NaCN without decomposition and evaporates more rapidly than water would be used, if I knew of one. Or a solvent that is miscible with water but unreactive with and a poor solvent of NaCN could be used to force crystals out of solution so they could be collected by filtration.

Anyway, how do I know I have NaCN of reasonable purity? The solution has the slipperiness of a base, more intense than Na2CO3. It has the characteristic odor of HCN (don't rely on this alone - many can't smell HCN). Small amounts that I have evaporated have yielded cubical crystals resembling table salt - a crystal structure that NaCN has and Na2CO3 and NaCNO don't. I have obtained a lovely prussian blue on adding drops of the filtrate to a slightly acidified mixture of Fe(II)/Fe(III) salts. Anyway, that's my tale. I hope you enjoyed it.

A subsequent message indicated that at least one other person managed to duplicate my success using urea instead of cyanuric acid for making the cyanate:

16g of urea, 16g of NaHCO3 and 5g of charcoal were ball milled for half an hour, to form an intimately mixed dark grey powder.
The mixture was heated on an oil bath at around 150*C with stirring until the reaction had stopped (lots of ammonia is given off, so do it outside!), as indicated by the effervescence susbsiding. The pasty mixture was stirred as it cooled to break it up.
The black, gravel-like substance remaining was put into an iron crucible with a narrow neck (used to be a CO2 canister), and placed in a very hot (bright yellow) fire. I used a coal fire, fed with air at about 400*C from a paint stripping gun. After a short amount of time a flammable gas was produced (CO), and heating was stopped 10 minutes after this gas was no longer produced. Charcoal was poured into the crucible, which was then left to cool, with the charcoal hopefully excluding most air.

The residue was extracted with cold water and filtered, leaving a clear, colourless, strongly alkaline solution. A drop put into citric acid solution produces HCN smell. I'll do the prussian blue test soon.

After I wrote the large message above, I actually tried relatively rapid drying of the NaCN solution on a hotplate. Although I don't doubt the Kirk-Othmer encyclopedia when it says that above 50 degrees C, NaCN solutions undergo some irreversible conversion to formate and ammonia, I didn't smell any ammonia, and I smelled a *lot* of ammonia when I had tried this previously with a batch that still had a lot of unreacted NaCNO in it.

Oh, and while I have the floor, I'd like to say that Catastrophe's "easy cyanide synth" writeup is worthless. It's a mishmash of extrapolation and wishful thinking. I'm sure he never actually did it himself. Just notice what color of flames he claims come from the SODIUM carbonate mixture: purple! He was just adding a new twist to Kurt Saxon's already-lousy KCN synth and he never even tried it himself. Or if he did try it himself, he's such a poor experimentalist that it's a wonder he didn't burn himself to death lighting the bunsen burner.

19th century digital boy


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Just an alternative
« Reply #4 on: November 12, 2002, 08:51:00 PM »
I decided to post this because the largest crucible SWIM is in possession of is maybee capable of holding 50 cm3 of material. Of course nacn.txt is similar, but charcoal generally contains lots of impurities and the procedure is not all that convenient for kitchen chemistry. Surely enough, this is not an entirely new procedure but some may find it useful if they wanted larger amounts of pure KCN. Just do not poison yourself.

If one would want to reduce NaCNO with charcoal, it can be made by melting CO(NH2)2 and adding Na2CO3, watching out for the effervescence of CO2 then recrystallizing.


  • Guest
« Reply #5 on: November 14, 2002, 12:05:00 AM »
hey Wraith, have you actually performed the cyanate synthesis?  what about its conversion to cyanide?


  • Guest
First-hand experience
« Reply #6 on: November 14, 2002, 01:50:00 AM »
The urea+carbonate -> cyanate releases CO2 and NH3. Because of the NH3 in particular it's not a kitchen-chemistry activity. I think recrystallization is more trouble than it's worth. Cyanates hydrolyzes easily. I'd just use a considerable excess of urea to ensure conversion.

I may be stating the obvious, but don't use charcoal briquettes for the charcoal powder that you mix with the cyanate; briquettes are full of clay, grit, binders, and other crap. They're only good for burning. I used homemade grapevine charcoal. It's clean, low-density, and easy to powder. If you don't want to make your own charcoal I'd suggest using powdered activated charcoal. It's expensive compared to baking soda, cyanuric acid, and urea, but you don't need very much carbon anyway.

As mentioned in my previous post, you don't need any real equipment. A small BBQ-scale charcoal fire works well as the heat source and a soup can with the top loosely sealed makes a very acceptable disposable crucible.

19th century digital boy