Author Topic: The quest for alkali cyanide  (Read 3742 times)

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Polverone

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The quest for alkali cyanide
« on: July 19, 2002, 01:09:00 AM »
I have tried many a method for the production of alkali cyanides under less-than-ideal circumstances. As failure has piled atop failure I have merely become more obsessed with the issue. I've already read Rhodium's site, all the old Hive threads, and several old chem journal articles as part of my quest.

I know about distilling HCN from H2SO4 and ferri/ferrocyanides. I don't want to do it. I could probably do it without incident - I'm not a slob and I've worked with the almost-as-toxic H2S before, and I'm one of the lucky people who can smell HCN - but I really don't want to.

Speaking of ferrocyanides, I am rather skeptical of the sodium ferrocyanide synth written by Catastrophe on Rhodium's site. It sounds very much like the Kurt Saxon preparation of potassium ferrocyanide but it substitutes sodium for potassium carbonate and uses a gas burner instead of a charcoal furnace. I have tried this method and I have never even been able to get the mix to properly fuse, much less react as described, and I have a large, hot lab burner with good air/fuel mixing. I would be very skeptical that this can realistically be done with a bunsen burner or portable propane torch as Catastrophe suggests, but maybe I'm just doing something wrong. I am especially suspicious that he never tried his own method because he describes purple flames coming from the mix (as you might expect from potassium compounds), not yellow as you would expect from a sodium compound. Back in the 19th century they used considerably higher temperatures than you'll get from a lab burner, performed the reaction in airtight containers, ran the reaction for several hours, and introduced nitrogen to the mixture from animal byproducts (as you can see if you read that section of the Muspratt book). I'd be very interested in anybody who *has* experienced success with the Catastrophe ferrocyanide preparation (I'm not skeptical of the ferrocyanide to cyanide conversion). Also, for what it's worth, I found an ACS article that said that cyanides prepared using the old 19th century methods were extremely impure, rarely exceeding 40% KCN by weight. Another old journal article mentioned that the old methods worked considerably better starting with potassium carbonate than with sodium carbonate.

My own independent attempt at producing sodium ferrocyanide involved dissolving dried blood (blood meal organic fertilizer) in molten NaOH. The blood should have provided all the carbon, nitrogen, and iron I'd ever need. I never purified the product but I definitely had some success. When I added H2SO4 to the reaction products in water I got Prussian blue precipitate as the pH dropped (I'm guessing from the excess iron from the blood forming sulfate that could react with the ferrocyanide) and then HCN (detected, cautiously, by nose). Unfortunately, this method made unpleasant odors and went quite slowly because I got a lot of frothing whenever I stirred more blood meal into the molten NaOH. Besides, I am really interested in cyanides, not ferrocyanides; this was just a detour.

I read with great interest the patent involving production of alkali cyanide from alkali nitrite or nitrate (thread "Cyanides from Nitrates/Nitrites".) Unwilling and unable to build an arc furnace, I tried the pyrotechnical approach: igniting KNO3 with finely powdered charcoal in the proper proportions. The first time I did a very small batch and used very finely powdered (ballmilled) reactants. Most of the reactants went up in smoke but the small amount of residue on the bottom of the dish did give a whiff of HCN with water and citric acid. I tried again more recently, using a larger batch and coarser powders to lower the vigor of the reaction (and hence amount of reactants disappearing in a white cloud). I obtained more residue this time but it did not give HCN scent on addition of acid.

I found an old ACS article that said some authorities believed that barium carbonate would easily form barium cyanide at a cherry red heat in a reducing atmosphere containing nitrogen. This would be ideal since barium carbonate is essentially insoluble and barium cyanide is very soluble - easy separation. I rigged a little setup that would maintain a reducing atmosphere (propane burned with too little air) around a small stainless steel dish filled with barium carbonate and charcoal powder and simultaneously heat that dish. I maintained heat (ranging from dull red to medium orange by the radiance of the dish) for about 30 minutes. When I dumped the powder into water afterward and filtered it, there had been no change. I didn't get any fizzing in the filtrate on citric acid addition.

Hmm, sorry for this long, rambling setup. I just wanted to establish that this isn't something I just started thinking of this afternoon.

I now have a new idea in my head but I don't know if it's crazy or worthwhile, and I don't have time to test it before I go traveling. Potassium cyanate is the salt of cyanic acid. It can be converted to cyanide with heat and carbon (carbon mainly to disturb the equilibrium between cyanate and cyanide when it's being heated in an oxidizing atmosphere like air). Cyanuric acid is the trimer of cyanic acid. It's inexpensive and readily available as a pool/spa chemical. Can potassium cyanurate be reduced at reasonable temperatures to potassium cyanide, like potassium cyanate can? The molecule has enough carbons and nitrogens to make it look feasible to me, but I'm just a hobbyist and don't know if I'm way off base here.

Oh, and finally, this isn't really a sources question (though if the thread gets moved there I'll understand). Like I said, I already know I should bubble HCN through NaOH solution. And I could just buy it from one of my suppliers, but I wouldn't like to given the current political climate. I seem to recall an article a few months back about some guy who had been hiding cyanides in subway tunnels getting arrested, with the implication that you'd better have a good reason to possess cyanides or you're guilty until proven innocent.

19th century digital boy

Chemikaze

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Cyanate
« Reply #1 on: July 19, 2002, 02:56:00 AM »
Then why not preparing cyanate from Na2CO3 and urea?

When I die bury me upside down so the world can kiss my ass.

Polverone

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My face is red!
« Reply #2 on: July 19, 2002, 11:57:00 AM »
Here I have 50 pounds of urea sitting in my bedroom and it didn't even cross my mind to get the cyanate from it! Well, this will certainly be something to try the next time I can do a little lab work...

19th century digital boy

alchemy_bee

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Just a suggestion, if your urea was sourced from ...
« Reply #3 on: July 19, 2002, 02:29:00 PM »
Just a suggestion, if your urea was sourced from ag applicaiton you may need to purifie it before using it in any reaction.

A nut for a jar of tuna.
-The drive by palindromer

Dr_Heckyll

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Urea in the bedroom
« Reply #4 on: July 19, 2002, 06:19:00 PM »
The 50 pounds of urea sitting in your bedroom wouldn't happen to have accumulated in your jerry which you forgot to empty the last couple years?  ;D

Sorry, but I couldn't help it when I read about the 50 pounds of urea sitting in your bedroom. Peace!


Dr. Heckyll & Mr. Jive by Men at Work
...tells my tale.

Polverone

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Encouraging results
« Reply #5 on: August 01, 2002, 08:55:00 PM »
I have recently been able to experiment further, with encouraging results. First, I found a British patent, (710143), that relates a method of preparing cyanates from cyanuric acid. In the patent they are concerned about avoiding cyanide, but I am obviously NOT.

Quick summary of the patent: powdered alkali carbonates are mixed with powdered cyanuric acid and heated to about 520 C. If this is done in a carbon dioxide atmosphere, there is no detectable amount of cyanide formed. The reaction is carried out in a closed steel vessel at atmospheric pressure. Only about 2/3 of the stoichiometric amount of alkali carbonate should be used. If more carbonate is used, some remains unconverted to cyanate. If less is used, some ammonium carbonate and other products form.  I didn't end up using my urea at all because another patent mentioned in passing that it was difficult to directly obtain better than 50% purity of cyanate starting from alkali carbonate and urea, and I didn't want to deal with another purification step.

I was using an open vessel so I used a slightly larger excess of cyanuric acid than the patent recommends, especially since I was planning on heating the mixture strongly enough to drive off any ammonium carbonate.

Here's how my latest experiment went:

I strongly heated sodium bicarbonate (obtained as baking soda) to produce sodium carbonate. I have sodium carbonate on hand but it is in the form of sand-like granules containing some moisture, and I wanted a fine, anhydrous powder. I measured out 20 grams of the freshly prepared sodium carbonate and 27 grams of cyanuric acid granules. The granules were obtained as a swimming pool supply - "chlorine stabilizer, 100% cyanuric acid." I reduced the cyanuric acid to powder in a mortar and thoroughly mixed it with the carbonate. I also powdered 5 grams of charcoal and set it aside.

I poured the powder mix into a stainless steel dish, put the dish in a ring stand, and took the stand outside. I heated the dish with a large laboratory burner using propane as a fuel. Considerable "smoke" was given off as the mixture was heated. I don't know if this was volatilized cyanuric acid, ammonium carbonate, or a mixture of substances. It took about 10-15 minutes for the powder to completely melt down to a fluid. This occurred at a temperature so low that the reaction vessel was not glowing at all, so I am sure that the sodium carbonate (or at least a large proportion) was converted to cyanate. I then added the 5 grams of charcoal (somewhat in excess of what is theoretically needed to reduce cyanate to cyanide) and increased the heat by placing the burner closer to the vessel.

The charcoal powder does not readily mix with the molten salt, but it gradually absorbs and is wetted by the fluid to form a sort of paste. Gas evolution was fairly rapid at first, with lots of large bubbles forming and popping. As time went on the bubbles became fewer but the gases leaving the mix must have changed because the gas jets would ignite and burn with a sodium-yellow flame. I am unsure about this 2-phase gas evolution. What is the first gas that doesn't burn, and what is the second gas that does? I expected the reaction NaCNO + C = NaCN + CO, which could be the source of my flammable gas, but I'm not sure about the first part of the reaction.

The whole time this was going on, the liquid was slowly creeping up the sides of the vessel, forming interesting patterns. It was bubbling a bit on the metal. Near the top of the dish it was forming patterns that resembled snake skin. It was also turning white and infusible at the top - converted, I fear, back to sodium carbonate from my burner's carbon dioxide.

I continued the heating for 20-30 minutes after I added the charcoal. I wanted to heat it until all gas evolution ceased, but I wasn't sure how long that would take and didn't want to run out of propane. Plus, I feared that I would eventually be working counterproductively as CO2 converted my cyanide back to carbonate. Perhaps in future runs I should cover the dish with something to minimize CO2 intrusion.

I then withdrew heat and scraped the paste in the bottom into a lump while it was still hot (previous experience showed that it was very hard to remove if left as a uniform layer until cold). The lump, once it had cooled somewhat, was added to water. Stirring and heat, over the course of 1-2 hours, broke up the glassy lump and allowed me to filter the liquid to remove the charcoal.

The liquid was evaporated in a shallow dish over the course of a night. There is a faint cyanide odor to the granular masses I have that has persisted through drying and storage, but I have no idea as to purity. This morning, again consulting the concise Kirk-Othmer, I learned that sodium cyanide can considerably hydrolyze to formate and ammonia above 50 C. Whoops! In the future I will use cooler water. That could definitely explain the strong ammonia scent over the dish in the later phases of evaporation. I thought it was just leftover cyanate hydrolizing and releasing that NH4.

These results seem fairly encouraging. I seem to have made sodium cyanide (of unknown purity, unfortunately) without a furnace, any special chemicals, or handling HCN gas. I don't know if I have enough propane left to do another run before refilling. I would really like to discover if the flammable-gas-evolution ever ceases, and if that also marks the complete conversion of cyanate to cyanide. I would like to try running the reaction at a higher temperature to see if the conversion is appreciably faster. I would also like - good lord would I like - to be able to perform a more sophisticated analysis to see what I really have, and in what proportions. But if I could afford to do sophisticated analysis I wouldn't be interested in this method in the first place.  :)

19th century digital boy