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